1
Universidade Federal do Rio Grande do Norte
Centro de Biociências
Programa de Pós-Graduação em Ecologia
Dissertação de Mestrado
O aquecimento dos oceanos pode ajudar zoantídeos a superar
competitivamente hidrocorais ramificados?
Bruno Charnaux Lonzetti
2
O aquecimento dos oceanos pode ajudar zoantídeos a superar
competitivamente hidrocorais ramificados?
Natal,
março de 2020
Dissertação de Mestrado apresentada ao Programa de Pós-Graduação em Ecologia, do Centro de Biociências da Universidade Federal do Rio Grande do Norte, como parte dos requisitos para obtenção do título de Mestre em Ecologia.
Orientador: Dr. Guilherme Ortigara Longo Coorientador: Dr. Edson Vieira Aparecido
3 Universidade Federal do Rio Grande do Norte - UFRN
Sistema de Bibliotecas - SISBI
Catalogação de Publicação na Fonte. UFRN - Biblioteca Setorial Prof. Leopoldo Nelson - -Centro de Biociências - CB Lonzetti, Bruno Charnaux.
O aquecimento dos oceanos pode ajudar zoantídeos a superar competitivamente hidrocorais ramificados? / Bruno Charnaux Lonzetti. - Natal, 2020.
57 f.: il.
Dissertação (Mestrado) - Universidade Federal do Rio Grande do Norte. Centro de Biociências. Programa de Pós-graduação em
Ecologia.
Orientador: Prof. Dr. Guilherme Ortigara Longo. Coorientador: Prof. Dr. Edson Aparecido Vieira.
1. Mudanças globais - Dissertação. 2. Coral - Dissertação. 3. Interação - Dissertação. 4. Competição - Dissertação. 5. Química - Dissertação. I. Longo, Guilherme Ortigara. II. Vieira, Edson Aparecido. III. Universidade Federal do Rio Grande do Norte. IV. Título.
RN/UF/BSCB CDU 504.7 Elaborado por KATIA REJANE DA SILVA - CRB-15/351
4 AGRADECIMENTOS
Agradeço à minha família por me ajudar a abraçar a oportunidade de morar do
outro lado do Brasil e descobrir um novo mundo profissional. Especificamente,
agradeço à minha mãe pelo amor incondicional que não deixa ser esquecido, ao meu pai
pelo jeito bobo-alegre e pela confiança depositada em qualquer ideia que venha a surgir,
e à minha irmã, mulher que admiro e tenho como referência para as grandes decisões da
vida. Vocês são especiais, são minha família. Um beijo!
Agradeço aos amigos da minha cidade natal, que me apoiaram durante a jornada
de mudança e se mantiveram presentes mesmo com a distância. A amizade de vocês é
uma joia que guardo com carinho. Vocês são meus irmãos, minha segunda família!
Agradeço aos amigos do Natal por me mostrarem quantas pessoas incríveis
existem no mundo. A entrega e o companheirismo de vocês é algo que faz aquecer o
coração e permite ver o mundo com olhos de mais amor. Conhecer pessoas tão
apaixonadas pelo que fazem me ajudou a entender um pouco mais sobre mim e a aceitar
que o mais belo da vida mora naquilo que te move.
Agradeço especificamente aos meus orientadores, Gui e Ed. O parágrafo anterior
é sobre vocês também. A paciência, a ajuda e a credibilidade que me deram são de valor
inestimável. Trabalhar ao lado de vocês faz eu me sentir gigante. Acho que nunca vi
pessoas mais dedicadas àquilo que amam e esse é um dos maiores ensinamentos que me
deram: ache aquilo que ama e seja bom e feliz pra demais fazendo o que faz! Obrigado!!
Agradeço à Helô por toda a parceria e leveza cultivadas. Estar do seu lado é
sinônimo de diversão e carinho. Obrigado por toda essa energia e bom humor! A
5 flores. É um presente maravilho conhecer e dividir momentos com as pessoas, gatas e
cachorra que te cercam. Obrigado!!
Agradeço à galera do LECOM, laboratório/casa que une pessoas de uma forma
que só vendo. Vocês são exemplo, simples assim. Obrigado por toda a ajuda!
Agradeço ao Dido, pessoa que nos recebe de braços e porta de casa abertos pra
trabalharmos num dos lugares mais bonitos que já vi. Obrigado por toda a ajuda em
campo e por todas as conversas. Você é uma daquelas pessoas que torna os dias de
trabalho mais felizes!
Agradeço à gestão da APARC por confiarem nas propostas de pesquisa. É um
prazer enorme ter a oportunidade de conhecer o excelente trabalho que desempenham.
Vocês fazem parte daquele aprendizado sobre ser foda! Parabéns!!
Agradeço a todos do Programa de Pós-Graduação em Ecologia da UFRN,
especialmente ao corpo docente. Vocês são professores e pessoas incríveis! Nunca
imaginei me sentir tão em casa em tão pouco tempo. Obrigado por todo o conhecimento
passado e por toda a horizontalidade na relação que criam com a gente. Vocês agregam
aquele sentimento essencial de pertencimento. Parabéns!!
Agradeço ao CNPq pela bolsa de mestrado, que viabilizou todo esse projeto de
pesquisa e de vida. Obrigado também pelo financiamento especificamente direcionado a
essa pesquisa. Obrigado!
Agradeço ao Serrapilheira pelo financiamento do projeto carro-chefe do
LECOM. Vocês contribuem pra magia acontecer e são símbolos de resistência e de
6 Por fim, agradeço a tod@s @s cientistas brasileir@s. Vocês têm uma raça
inexplicável. Obrigado pela resistência e pelo trabalho incansável por um futuro melhor.
O presente trabalho foi realizado com apoio da Coordenação de
Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Código de
7 RESUMO
Interações competitivas entre organismos sésseis em ambientes recifais geralmente ocorrem através do contato físico, dada a limitação espacial nesses ambientes. O aquecimento dos oceanos é um dos fatores que podem afetar os resultados dessas interações, alterando a habilidade competitiva e o potencial de recuperação dos organismos. O Painel Intergovernamental sobre Mudanças Climáticas prevê em sua projeção com as maiores emissões de gases do efeito estufa um aumento médio na temperatura do Oceano Atlântico de 3 °C para o ano 2100. Millepora alcicornis é uma das únicas espécies de coral ramificado no Brasil, contribuindo para a complexidade estrutural no ambiente recifal. O zoantídeo Palythoa caribaeorum é um dos competidores de corais mais importantes do Atlântico Oeste. Ambas as espécies competem entre si desde a costa da Flórida até o Sudeste brasileiro. Se M. alcicornis suportar os 3 °C de aumento na temperatura, seguirá competindo com P. caribaeorum, pois esta, apesar de ter sua distribuição afetada, ainda ocorrerá em áreas recifais como o Caribe e o Nordeste brasileiro. Não se sabe como o aumento de temperatura afetará essa interação. Indo além de previsões da distribuição de espécies e levando em conta que interações também podem ser moduladas pelo aquecimento dos oceanos, estudamos a interação competitiva entre P. caribaeorum e M. alcicornis através de experimentos em campo e laboratório, abordando particularmente: o efeito do contato físico na saúde de
M. alcicornis (campo e laboratório); o potencial de recuperação de M. alcicornis após o
fim do contato (campo e laboratório); se essa interação é mediada por compostos químicos presentes na superfície de P. caribaeorum (campo e laboratório); e como o aquecimento do oceano pode afetar esses processos (laboratório; 27 °C vs. 30 °C). Descobrimos que o contato físico com P. caribaeorum causa mais danos do que com o seu controle em campo e em laboratório a 27 °C. A recuperação de M. alcicornis em laboratório a 27 °C e em campo ocorreu dentro de 10 dias. Algas filamentosas colonizaram a área de M. alcicornis que teve contato com P. caribaeorum em laboratório a 30 °C, dificultando sua capacidade de recuperação. O contato com o extrato químico de P. caribaeorum em laboratório a 27 °C e em campo causou mais danos a M. alcicornis do que o contato com seu controle. O contato com o extrato e seu controle causaram danos iguais a M. alcicornis em laboratório a 30 °C. Nossos resultados indicam que P. caribaeorum supera competitivamente M. alcicornis através de mecanismos físicos e químicos, e que um aumento de 3 °C na temperatura do oceano prejudica a recuperação de M. alcicornis e torna o aspecto físico do contato mais importante do que o aspecto químico. A taxa de sobrecrescimento de P. caribaeorum em M. alcicornis tende a subir com a intensificação dessa interação à medida que o oceano aquece, podendo levar à perda de complexidade estrutural e, consequentemente, de diversidade em recifes do Caribe e Brasil. Entender como o aquecimento dos oceanos pode afetar as interações competitivas é fundamental para projetarmos o futuro dos recifes.
8 ABSTRACT
Competitive interactions between sessile organisms in reef environments generally occur through physical contact, given the spatial limitation in these environments. Ocean warming is one of the factors that can affect the outcomes of these interactions, changing the competitive ability and recovery capacity of the organisms. The Intergovernmental Panel on Climate Change predicts and average increase of 3 °C in the temperature of the Atlantic Ocean for the year 2100, under highest greenhouse gas emission projection. The hydrocoral Millepora alcicornis is one of the only branching coral species in Brazil, contributing to structural complexity in reef environments. The zoanthid Palythoa caribaeorum is one of the most important coral competitors in the Western Atlantic. Both species compete with each other from the coast of Florida to southeastern Brazil. If M. alcicornis withstands the 3 °C increase in temperature, it will continue to compete with P. caribaeorum, which will still occur in reef areas in the Caribbean and northeastern Brazil, despite minor distribution shifts. Going beyond predictions of species distribution, the effect of ocean warming on species interactions is poorly known. Because interactions can be modulated by ocean warming, we studied the competitive interaction between P. caribaeorum and M. alcicornis through field and laboratory experiments, addressing in particular: the effect of physical contact on the health of M. alcicornis (field and laboratory); the recovery potential of M. alcicornis after the end of contact (field and laboratory); whether this interaction is mediated by chemical compounds present on the surface of P. caribaeorum (field and laboratory); and how ocean warming can affect these processes (laboratory: 27 °C vs. 30 °C). We found that physical contact with P. caribaeorum causes more damage than with its control in the field and in the laboratory at 27 °C. The recovery of M. alcicornis in the laboratory at 27 °C and in the field occurred within 10 days. Filamentous algae colonized the area of M. alcicornis that had contact with P. caribaeorum in the laboratory at 30 °C, jeopardizing its recovery. Contact with chemical extract of P.
caribaeorum in the laboratory at 27 °C and in the field caused more damage to M. alcicornis than contact with its control. Contact with the extract and its control caused
equal damage to M. alcicornis in the laboratory at 30 °C. Our results indicate that P.
caribaeorum outcompete M. alcicornis through physical and chemical mechanisms, and
that an increase of 3 °C in the ocean temperature impairs the recovery of M. alcicornis and makes the physical aspect of contact more important than the chemical. The rate of
P. caribaeorum overgrowth in M. alcicornis tends to increase with the intensification of
this interaction as the ocean warms, which can lead to a loss of structural complexity and, consequently, of diversity in reefs in the Caribbean and Brazil. Understanding how ocean warming can affect competitive interactions in reef environments is essential to project the future of these ecosystems.
9 LISTA DE FIGURAS
Figure 1 - A) Red dot indicating the Parrachos of Rio do Fogo in Rio Grande do Norte, Brazil (5°24’S, 35°36’W). B) Parrachos de Rio do Fogo viewed from the boat._____ 25 Figure 2 – Millepora alcicornis colony on the Parrachos of Rio do Fogo. ________ 26 Figure 3 – Millepora alcicornis fragments deployed on the reef flat. A) Fragment attached to a nail by a cable tie. B) Replicate group of fragments with treatments (from right to left): control fragment with no contact treatment; fragment in contact with Palythoa caribaeorum chunk; fragment in contact with the inert mimic dishwasher; and a chunk of P. caribaeorum that was followed up to evaluate survival and damage related to the experimental manipulation. __________________________________ 27 Figure 4 - Laboratory experiment setup. A) Millepora alcicornis fragment glued to squared plastic base deployed to aquarium bottom with Velcro®. B) The two aquaria setup with running seawater in a closed system and with proper lighting conditions. 29 Figure 5 – A) Palythoa caribaeorum on the Parrachos of Rio do Fogo. B) Competitive interaction between P. caribaeorum and Millepora alcicornis on the Parrachos of Rio do Fogo. ____________________________________________________________ 34 Figure 6 - Damage area (bleached or dead; cm2 mean ± SE) over time on Millepora alcicornis fragments in contact with Palythoa caribaeorum and inert mimic. Controls without any contact never experienced damage and so are not shown. Post hoc Tukey’s Test determined differences between days. Day 1 (A), day 3 (A), day 13 (B). _______ 35 Figure 7 - Damage area (bleached or dead; cm2 mean ± SE) over time on Millepora alcicornis fragments in 27°C and 30°C in contact with Palythoa caribaeorum and inert mimic. Controls without any contact never experienced damage and so are not shown. Post hoc Tukey’s Test determined the temperature treatments trajectory over time. 27 °C: day 1 (AB), day 3 (C), day 5 (BC), day 13 (AB), day 23 (A). 30°C: day 1 (A), day 3 (B), day 5 (B), day 13 (AB), day 23 (AB). ___________________________________ 37 Figure 8 – Bar plots of the color parameters L, a and b (graphs A, B and C, respectively) observed on Millepora alcicornis branches in the field after 24h of contact with control and treated gels. The y-axis on graphs A and C is cut for better data visualization. _________________________________________________________ 39 Figure 9 – Bar plots of the color parameters L, a and b (graphs A, B and C, respectively) observed on Millepora alcicornis fragments in the laboratory after 24h of contact with control and treated gels under 27 °C (blue background; ncontrol = 19; ntreated
10
= 19) and 30 °C temperatures (orange background; ncontrol = 20; ntreated = 20). The y-axis on graphs A and C is cut for better data visualization. ____________________ 40
11 SUMÁRIO APRESENTAÇÃO ____________________________________________________ 12 REFERÊNCIAS _____________________________________________________ 15 CAPÍTULO ÚNICO __________________________________________________ 19 ABSTRACT _________________________________________________________ 21 INTRODUCTION ____________________________________________________ 22 METHODS _________________________________________________________ 24 Competitive interactions survey _____________________________________________ 25 Physical interaction under current temperature ________________________________ 26 Physical interaction under warmer temperature _______________________________ 28 Effect of P. caribaeorum surface chemical compounds ___________________________ 29 Data acquisition __________________________________________________________ 31 RESULTS ___________________________________________________________ 33
Competitive interactions survey _____________________________________________ 33 Physical interaction under current temperature ________________________________ 34 Physical interaction under warmer temperature _______________________________ 35 Effect of Palythoa caribaeorum surface chemical compounds _____________________ 38 DISCUSSION _______________________________________________________ 41 ACKNOWLEDGEMENTS _____________________________________________ 45 REFERENCES ______________________________________________________ 46 CONCLUSÃO _______________________________________________________ 56
12 APRESENTAÇÃO
Comunidades e populações dos ecossistemas mais variados compartilham de
uma mesma característica, dependem dos recursos disponíveis no ambiente para sua
sobrevivência. Em nível de indivíduo, quando dois organismos apresentam certa ou
total sobreposição de nicho ecológico, presume-se que deve haver competição pelos
recursos necessários a cada um quando estes forem limitados (MacArthur and Levins
1967). Esta limitação pode ocorrer por diversas vias, como por exemplo a variação
sazonal de recursos alimentares, e a disponibilidade de espaços físicos a serem
ocupados quando se tratando de recursos abióticos.
O espaço físico em ambientes recifais é um dos recursos mais limitados e
limitantes para organismos sésseis que se fixam na matriz recifal (Jackson 1977). A
falta de espaço aberto e apto à colonização faz com que organismos vizinhos se tornem
competidores em busca de expansão ou sobrevivência (Jackson 1977). Em recifes de
corais, que são aqueles construídos majoritariamente por corais escleractíneos (que
depositam esqueleto calcário), a diversidade desses organismos é elevada e
competidores de corais, como as algas, costumam apresentar abundância discreta. Já em
outros tipos de recifes, como os marginais, aqueles que ocorrem em condições que não
são as consideradas ótimas (Kleypas et al. 1999), a diversidade e abundância de corais
são reduzidas, tornando a abundância de competidores elevada. A competição entre
corais e outros organismos em ambos os tipos de recifes pode comprometer o estado de
saúde dos corais (Rasher and Hay 2010).
Os ambientes recifais estão entre os sistemas mais diversos do mundo (Connell
1978; Martínez et al. 2007), tornando essas formações cruciais para a manutenção de
processos ecossistêmicos, bem como das comunidades humanas associadas (Moberg
13 muitas espécies e são fundamentais para o ciclo de vida de muitas delas (Coni et al.
2013). Dessa forma, eles agregam uma enorme variedade de organismos que integram
uma complexa rede de interações e de manutenção da diversidade (Moberg and Folke
1999).
Corais são organismos sensíveis a variações de temperatura e sofrem com os
impactos globais como o aquecimento dos oceanos (Hughes et al. 2017). Estes
organismos perdem grande parte da sua fonte energética (Falkowski et al. 1984) quando
estão em temperaturas elevadas (Glynn 1983) e ficam menos resistentes aos
competidores por não poderem alocar energia suficiente para combatê-los (McClanahan
et al. 2009). Esse fenômeno é conhecido como o branqueamento de corais e tem
acontecido com maior frequência e intensidade à medida que os oceanos aquecem por
conta das mudanças climáticas (Hughes et al. 2018).
O branqueamento de corais se caracteriza pela interrupção da relação de
simbiose entre esses organismos e microalgas, chamadas zooxantelas, que vivem em
seu tecido e lhes conferem pigmentação, alimentação e proteção contra raios solares
(Buddemeier and Fautin 1993). A interrupção dessa simbiose pode se dar por conta de
diversos motivos, sendo um deles a elevação de temperatura. As zooxantelas aumentam
suas taxas reprodutiva e fotossintética com o aumento da temperatura, causando uma
superproliferação e produção excessiva de oxigênio que leva ao estresse oxidativo dos
corais. A resposta destes é expulsar as zooxantelas total ou parcialmente de seus tecidos.
Como consequência, os corais perdem a coloração e grande parte do seu alimento, a
glicose proveniente da fotossíntese realizada pelas zooxantelas (Falkowski et al. 1984;
Burriesci et al. 2012).
O branqueamento em massa de corais tem levado à perda desses organismos em
14 riqueza de espécies sustentada pelos ambientes recifais (Pratchett et al. 2018). Essa
perda se deve ao fato dos corais serem os maiores responsáveis pela complexidade
estrutural dos recifes (Graham and Nash 2012), e esta, por sua vez, ser a responsável
pela riqueza agregada a esses ambientes (Darling et al. 2017).
Recifes marginais não são necessariamente formados por corais ou com alta
abundância desses organismos (Mies et al. 2020), ainda assim a presença de corais
contribui para a riqueza desses ambientes. Assim, esses ambientes podem apresentar
respostas ao aquecimento dos oceanos diferentes das observadas em recifes de corais
nos centros de diversidade como os da região do Caribe e Indo-Pacífico (Mies et al.
2020). Recifes marginais também podem nos dar uma ideia de como será o futuro dos
recifes atualmente dominados por corais frente ao aquecimento dos oceanos.
Nos recifes brasileiros, considerados marginais, um dos mais importantes
agregadores de complexidade estrutural é o hidrocoral Millepora alcicornis Linnaeus,
1758 (Leão and Dominguez 2000; Leão et al. 2003). Essa espécie também apresenta
uma relação de simbiose com as zooxantelas e, portanto, também é impactada pelo
aquecimento dos oceanos. O zoantídeo Palythoa caribaeorum Duchassaing e
Michelotti, 1860, é bastante comum nos recifes brasileiros (Aued et al. 2018) e sua
distribuição também será afetada com o aquecimento dos oceanos (Durante et al. 2018).
A combinação do fator ‘aumento de temperatura’ com o fator ‘competição por espaço’ resulta em um cenário de impacto para os recifes que deve ser investigado a fundo.
Com o intuito de avaliar como o aquecimento dos oceanos pode modular os
efeitos da competição entre Millepora alcicornis e um competidor comum, o zoantídeo
Palythoa caribaeorum, fizemos experimentações em campo e em laboratório
reproduzindo a interação em temperatura atual e futura, e observando os efeitos sobre
15 tecido de M. alcicornis e que esses danos seriam potencializados em temperaturas
maiores. Descobrimos que, em condições atuais de temperatura, P. caribaeorum
danifica M. alcicornis através de mecanismos físicos e químicos, e que M. alcicornis
demonstra recuperação do dano dentro de 10 dias após o fim do contato. Um aumento
de 3 °C na temperatura prejudica a recuperação de M. alcicornis e torna o aspecto físico
do contato mais importante do que o aspecto químico. A taxa de sobrecrescimento de P.
caribaeorum em M. alcicornis tende a subir com a intensificação dessa interação à
medida que o oceano aquece, levando à perda de complexidade estrutural e,
consequentemente, de diversidade em recifes onde a interação ocorre.
REFERÊNCIAS
Aued, A.W., Smith, F., Quimbayo, J.P., Cândido, D. V., Longo, G.O., Ferreira, C.E.L.,
Witman, J.D., Floeter, S.R., and Segal, B. 2018. Large-scale patterns of benthic marine
communities in the Brazilian Province. PLoS One 13(6): e0198452. doi:10.1371/journal.pone.0198452.
Buddemeier, R.W., and Fautin, D.G. 1993. Coral Bleaching as an Adaptive Mechanism.
Bioscience 43(5): 320–326. doi:10.2307/1312064.
Burriesci, M.S., Raab, T.K., and Pringle, J.R. 2012. Evidence that glucose is the major
transferred metabolite in dinoflagellate-cnidarian symbiosis. J. Exp. Biol. 215(19):
3467–3477. doi:10.1242/jeb.070946.
Coni, E.O.C., Ferreira, C.M., de Moura, R.L., Meirelles, P.M., Kaufman, L., and
Francini-Filho, R.B. 2013. An evaluation of the use of branching fire-corals (Millepora
spp.) as refuge by reef fish in the Abrolhos Bank, eastern Brazil. Environ. Biol. Fishes
16 Connell, J.H. 1978. Diversity in Tropical Rain Forests and Coral Reefs. Science (80-. ).
199(4335): 1302–1310. doi:10.1126/science.199.4335.1302.
Darling, E.S., Graham, N.A.J., Januchowski-Hartley, F.A., Nash, K.L., Pratchett, M.S.,
and Wilson, S.K. 2017. Relationships between structural complexity, coral traits, and
reef fish assemblages. Coral Reefs 36(2): 561–575. doi:10.1007/s00338-017-1539-z.
Durante, L.M., Cruz, I.C.S., and Lotufo, T.M.C. 2018. The effect of climate change on
the distribution of a tropical zoanthid ( Palythoa caribaeorum ) and its ecological
implications. PeerJ 6: e4777. doi:10.7717/peerj.4777.
Falkowski, P.G., Dubinsky, Z., Muscatine, L., and Porter, J.W. 1984. Bioenergetics
Symbiotic Coral. Bioscience 34(11): 705–709.
Glynn, P.W. 1983. Extensive ‘Bleaching’ and Death of Reef Corals on the Pacific Coast of Panamá. Environ. Conserv. 10(2): 149–154. doi:10.1017/S0376892900012248.
Graham, N.A.J., and Nash, K.L. 2012. The importance of structural complexity in coral
reef ecosystems. Coral Reefs 32(2): 315–326. doi:10.1007/s00338-012-0984-y.
Hughes, T.P., Anderson, K.D., Connolly, S.R., Heron, S.F., Kerry, J.T., Lough, J.M.,
Baird, A.H., Baum, J.K., Berumen, M.L., Bridge, T.C., Claar, D.C., Eakin, C.M.,
Gilmour, J.P., Graham, N.A.J., Harrison, H., Hobbs, J.-P.A., Hoey, A.S., Hoogenboom,
M., Lowe, R.J., McCulloch, M.T., Pandolfi, J.M., Pratchett, M., Schoepf, V., Torda, G.,
and Wilson, S.K. 2018. Spatial and temporal patterns of mass bleaching of corals in the
Anthropocene. Science (80-. ). 359(6371): 80–83. doi:10.1126/science.aan8048.
Hughes, T.P., Kerry, J.T., Álvarez-Noriega, M., Álvarez-Romero, J.G., Anderson, K.D.,
Baird, A.H., Babcock, R.C., Beger, M., Bellwood, D.R., Berkelmans, R., Bridge, T.C.,
17 Dalton, S.J., Diaz-Pulido, G., Eakin, C.M., Figueira, W.F., Gilmour, J.P., Harrison,
H.B., Heron, S.F., Hoey, A.S., Hobbs, J.-P.A., Hoogenboom, M.O., Kennedy, E. V.,
Kuo, C., Lough, J.M., Lowe, R.J., Liu, G., McCulloch, M.T., Malcolm, H.A.,
McWilliam, M.J., Pandolfi, J.M., Pears, R.J., Pratchett, M.S., Schoepf, V., Simpson, T.,
Skirving, W.J., Sommer, B., Torda, G., Wachenfeld, D.R., Willis, B.L., and Wilson,
S.K. 2017. Global warming and recurrent mass bleaching of corals. Nature 543(7645):
373–377. doi:10.1038/nature21707.
Jackson, J.B.C. 1977. Competition on Marine Hard Substrata: The Adaptive
Significance of Solitary and Colonial Strategies. Am. Nat. 111(980): 743–767.
doi:10.1086/283203.
Kittinger, J.N., Finkbeiner, E.M., Glazier, E.W., and Crowder, L.B. 2012. Human
Dimensions of Coral Reef Social-Ecological Systems. Ecol. Soc. 17(4): art17.
doi:10.5751/ES-05115-170417.
Kleypas, J.A., McManu, J.W., and Mene, L.A.B. 1999. Environmental limits to coral
reef development: Where do we draw the line? Am. Zool. 39(1): 146–159.
doi:10.1093/icb/39.1.146.
Leão, Z.M. a. N., Kikuchi, R.K.P., and Testa, V. 2003. Corals and coral reefs of Brazil.
In Latin American Coral Reefs. Elsevier. pp. 9–52.
doi:10.1016/B978-044451388-5/50003-5.
Leão, Z.M.A.N., and Dominguez, J.M.L. 2000. Tropical coast of Brazil. Mar. Pollut.
Bull. 41(1–6): 112–122. doi:10.1016/S0025-326X(00)00105-3.
MacArthur, R., and Levins, R. 1967. The Limiting Similarity, Convergence, and
18 Martínez, M.L., Intralawan, A., Vázquez, G., Pérez-Maqueo, O., Sutton, P., and
Landgrave, R. 2007. The coasts of our world: Ecological, economic and social
importance. Ecol. Econ. 63(2–3): 254–272. doi:10.1016/j.ecolecon.2006.10.022.
McClanahan, T.R., Weil, E., Cortés, J., Baird, a H., and Ateweberhan, M. 2009.
Consequences of coral bleaching for sessile reef organisms. In Coral Bleaching.
doi:10.1007/978-3-540-69775-6_8.
Mies, M., Francini-Filho, R.B., Zilberberg, C., Garrido, A.G., Longo, G.O., Laurentino,
E., Guth, A.Z., Sumida, P.Y.G., and Banha, T.N.S. 2020. South Atlantic coral reefs are
major global warming refugia and less susceptible to bleaching. Front. Mar. Sci.
7(June): 514. doi:10.3389/FMARS.2020.00514.
Moberg, F., and Folke, C. 1999. Ecological goods and services of coral reef ecosystems.
Ecol. Econ. 29(2): 215–233. doi:10.1016/S0921-8009(99)00009-9.
Pratchett, M.S., Thompson, C.A., Hoey, A.S., and Cowman, P.F. 2018. Coral
Bleaching. Edited ByM.J.H. van Oppen and J.M. Lough. Springer International
Publishing, Cham. doi:10.1007/978-3-319-75393-5.
Rasher, D.B., and Hay, M.E. 2010. Chemically rich seaweeds poison corals when not
controlled by herbivores. Proc. Natl. Acad. Sci. 107(21): 9683–9688. doi:10.1073/pnas.0912095107.
19
CAPÍTULOÚNICO
Can ocean warming help zoanthids outcompete branching hydrocorals?
A ser submetido para a revista ‘Coral Reefs’20
Can ocean warming help zoanthids outcompete branching hydrocorals?
Lonzetti B. C.1, Vieira E. A.1, Longo G. O.1*1
Laboratório de Ecologia Marinha, Departamento de Oceanografia e Limnologia, Universidade Federal do Rio Grande do Norte, Natal, RN, 59014-002, Brasil.
______________________________________________ * Corresponding author: Guilherme O. Longo
Email: guilherme.o.longo@gmail.com Telephone number: +55 84 3342 4969
21 ABSTRACT
Competitive interactions between sessile organisms in reef environments generally occur through physical contact, given the spatial limitation in these environments. Ocean warming is one of the factors that can affect the outcomes of these interactions, changing the competitive ability and recovery capacity of the organisms. The Intergovernmental Panel on Climate Change predicts and average increase of 3 °C in the temperature of the Atlantic Ocean for the year 2100, under highest greenhouse gas emission projection. The hydrocoral Millepora alcicornis is one of the only branching coral species in Brazil, contributing to structural complexity in reef environments. The zoanthid Palythoa caribaeorum is one of the most important coral competitors in the Western Atlantic. Both species compete with each other from the coast of Florida to southeastern Brazil. If M. alcicornis withstands the 3 °C increase in temperature, it will continue to compete with P. caribaeorum, which will still occur in reef areas in the Caribbean and northeastern Brazil, despite minor distribution shifts. Going beyond predictions of species distribution, the effect of ocean warming on species interactions is poorly known. Because interactions can be modulated by ocean warming, we studied the competitive interaction between P. caribaeorum and M.
alcicornis through field and laboratory experiments, addressing in particular: the effect
of physical contact on the health of M. alcicornis (field and laboratory); the recovery potential of M. alcicornis after the end of contact (field and laboratory); whether this interaction is mediated by chemical compounds present on the surface of P.
caribaeorum (field and laboratory); and how ocean warming can affect these processes
(laboratory: 27 °C vs. 30 °C). We found that physical contact with P. caribaeorum causes more damage than with its control in the field and in the laboratory at 27 °C. The recovery of M. alcicornis in the laboratory at 27 °C and in the field occurred within 10 days. Filamentous algae colonized the area of M. alcicornis that had contact with P.
caribaeorum in the laboratory at 30 °C, jeopardizing its recovery. Contact with
chemical extract of P. caribaeorum in the laboratory at 27 °C and in the field caused more damage to M. alcicornis than contact with its control. Contact with the extract and its control caused equal damage to M. alcicornis in the laboratory at 30 °C. Our results indicate that P. caribaeorum outcompete M. alcicornis through physical and chemical mechanisms, and that an increase of 3 °C in the ocean temperature impairs the recovery of M. alcicornis and makes the physical aspect of contact more important than the chemical. The rate of P. caribaeorum overgrowth in M. alcicornis tends to increase with the intensification of this interaction as the ocean warms, which can lead to a loss of structural complexity and, consequently, of diversity in reefs in the Caribbean and Brazil. Understanding how ocean warming can affect competitive interactions in reef environments is essential to project the future of these ecosystems.
22 INTRODUCTION
Reefs aggregate organisms by providing habitat, refuge and food, resulting in a
complex network of interactions and maintenance of diversity (Moberg and Folke
1999). The arrangement of these environments counts with substrate physical space
often as a limiting factor to sessile organisms’ settlement (Jackson 1977). Therefore,
corals are generally in contact with a variety of other organisms, such as algae. Some
seaweeds produce anti-herbivory or competition-suppressor secondary metabolites (Hay
2009), that are allocated rather on the surface than inside seaweeds (Nylund et al. 2007;
Longo and Hay 2017) and are deployed on corals upon contact (Rasher and Hay 2014).
Such contacts lead to either physically or chemically mediated competitive interactions
that can result in coral microbiota destabilization (Pratte et al. 2018), bleaching and
necrosis (Rasher and Hay 2010). These outcomes can be followed by coral death
(Bonaldo and Hay 2014) and subsequent overgrowth by the competitor (Diaz-Pulido et
al. 2009), favoring a dominance that reduces reef diversity.
The outcome of competitive interactions between corals and other reef
organisms can change with ocean warming (e.g. reduced coral
photosynthesis/respiration ratio; Brown et al. 2019) and acidification (e.g. increased
coral tissue loss and mortality rate; Diaz-Pulido et al. 2011; Del Monaco et al. 2017).
The Intergovernmental Panel on Climate Change’s (IPCC) latest projection using
business as usual greenhouse gases emissions (Representative Concentration Pathway
(RCP) 8.5) foresees a 3 °C average increase in the temperature of the Atlantic Ocean for
the year 2100. With ocean warming, corals’ symbiosis with dinoflagellates can be
disrupted by the thermal stress, resulting in coral death if higher temperatures persist for
a prolonged period of time (Hughes et al. 2018). The loss of dinoflagellates leaves
23 dinoflagellates’ photosynthesis (Burriesci et al. 2012). By these mechanisms, ocean warming can indirectly affect corals’ ability to compete, since thermal-stressed corals have less energy to allocate in competition efforts and so are more prone to be
outperformed by their competitors. However, added to the fact that most
coral-competition studies investigated coral-seaweed interactions (but see Cruz et al. 2016),
few studies have assessed how temperature modulates the outcome of a
coral-invertebrate interaction (see Almeida Saá et al. 2020), which is a common interaction in
several reefs worldwide (Grace 2017; Roth et al. 2018).
As reefs structural complexity is largely supported by coral cover, specifically
by branching species, coral loss leads to reef flattening (Graham and Nash 2012). Since
richness and diversity on these environments are positively linked to their structural
complexity (Darling et al. 2017), reduced coral cover implicates in less rich and diverse
reefs (Rogers et al. 2018). In the context of global changes, understanding how ocean
warming will affect corals’ competitive interactions can provide important information
to foresee reef health in future warming scenarios.
Considering that coral-invertebrate competitive interactions may also negatively
affect coral health (Cruz et al. 2016), with consequences for reef structural complexity,
and that the outcome of this interaction may be modulated by ocean warming, we
investigated the interaction between the branching hydrocoral Millepora alcicornis
Linnaeus, 1758 and the zoanthid Palythoa caribaeorum Duchassaing and Michelotti,
1860 under current and warmer temperatures predicted for the year 2100. Unlike in
other reef systems, branching corals such as the ones from the genus Acropora and
Montipora do not occur in Brazilian reefs. Among the few branching coral species in
Brazil is M. alcicornis, which is the main structural complexity aggregator in Brazilian
24 benthic organisms (Leão and Dominguez 2000; Leão et al. 2003; Leal et al. 2013, 2015;
Coni et al. 2013). The zoanthid P. caribaeorum is a fast-growing and
chemically-packed competitor (Ciereszko and Karns 1973; Bastidas and Bone 1996) that tends to
overgrow its competitors (Suchanek and Green 1981; Almeida Saá et al. 2020) and
commonly occurs in Brazilian reefs (Aued et al. 2018). Both species co-occur across the
Atlantic Ocean (M. alcicornis – from Florida, USA, to Southeast Brazil; and P.
caribaeorum – from Florida, USA, to Santa Catarina, Brazil) at shallow depths (Sebens
1982; Lewis 2006). If M. alcicornis withstands the 3 °C temperature increase projected
by the IPCC for 2100, it will continue to compete with P. caribaeorum, as this species,
despite having its distribution affected, will still occur in reef areas such as the
Caribbean and the Northeast of Brazil (Durante et al. 2018). By manipulating the
interaction between these species, we experimentally investigated in the field and in the
laboratory (i) the impact of P. caribaeorum direct contact on M. alcicornis, (ii) M.
alcicornis damaged tissue recovery, (iii) how ocean warming will modulate the
outcome of this interaction and (iv) if P. caribaeorum chemical compounds play a role
in the interaction. We expected: (i) direct contact with P. caribaeorum to cause M.
alcicornis tissue damage; (ii) M. alcicornis damaged tissue to recover better under
current temperature than warmer; (iii) P. caribaeorum direct contact to cause greater
damage under warmer temperature than current; (iv) P. caribaeorum chemical
compounds to play a role in the interaction.
METHODS
We conducted the fieldwork on the Parrachos of Rio do Fogo, a shallow patchy
reef located within a marine protected area (APARC, Portuguese acronym for Coral
25 Northeast Brazil (Figure 1). This reef complex is located six kilometers offshore,
presents relevant scenic beauty for tourism, sheltering corals and a great diversity of fish
and other marine species (Maida and Ferreira 1997; Feitosa et al. 2002).
Figure 1 - A) Red dot indicating the Parrachos of Rio do Fogo in Rio Grande do Norte, Brazil (5°24’S, 35°36’W). B) Parrachos de Rio do Fogo viewed from the boat.
COMPETITIVE INTERACTIONS SURVEY
To determine the most common organisms competing with the hydrocoral
Millepora alcicornis (Figure 2), we photographed 42 colonies in a circular motion
around the colony aiming its basis. We then used the photo sequence of each colony to
visually estimate the contact percentage for each major group (i. e. crustose coralline
26
Figure 2 – Millepora alcicornis colony on the Parrachos of Rio do Fogo.
PHYSICAL INTERACTION UNDER CURRENT TEMPERATURE
In order to test the impact of physical competition between Millepora alcicornis and
Palythoa caribaeorum, we first simulated the contact interaction in the field. For that,
we took three healthy fragments (no sign of bleaching, epibionts or bioeroders;
measuring 6 to 8 cm) from 20 M. alcicornis colonies (n = 60) and disposed them
attached to stainless steel nails previously inserted on the reef flat matrix (Figure 3A
and 3B). Our replicates consisted of one fragment used as a manipulative control (no
contact), one subjected to contact with a chunk of P. caribaeorum simulating
competition with the zoanthid and one kept in contact with an inert mimic (kitchen
sponge without antibacterial and antimicrobial agents), which enabled us to separate the
27
caribaeorum chunks and its inert mimic had similar sizes (5 x 5 cm) and were kept in
contact with the hydrocoral fragments by a cable tie gently disposed around the pair of
fragment-contact treatment. We also held adjacent chunks of P. caribaeorum attached
alone to stainless steel nails for each replicate group. This was a precaution that enabled
the evaluation of health and survival of P. caribaeorum after cutting and detaching from
the substrate manipulation (all chunks survived and did not significantly differ in color).
We assessed fragments’ health through photographs of the contact area as close to them
as possible, in four steps: prior to contact introduction, 1, 3 and 13 days later. A ruler
was framed in all photos to set the size scale. On the first assessment (first day), contact
was removed, a photograph taken, and contact replaced. On the second assessment
(third day), contact was definitely removed. After 13 days, photographs were also taken
and they could give us an idea of damage duration and recovery.
Figure 3 – Millepora alcicornis fragments deployed on the reef flat. A) Fragment attached to a nail by a cable tie. B) Replicate group of fragments with treatments (from right to left): control fragment with no contact treatment; fragment in contact with Palythoa caribaeorum chunk; fragment in contact with the inert mimic dishwasher; and a chunk of P. caribaeorum that was followed up to evaluate survival and damage related to the experimental manipulation.
28 PHYSICAL INTERACTION UNDER WARMER TEMPERATURE
In order to test the effects of contact competition under controlled conditions in
laboratory and how different scenarios of temperature could modulate the outcome, we
took six healthy fragments (6 to 8 cm) from other 11 Millepora alcicornis colonies in
the field (n = 66), and transported them under sea water with aeration inside cooler
containers to replicate the same interactions in the lab under current and future
temperatures. Fragments were gently glued to squared plastic bases with a drop of
cyanoacrylate-based glue (Super Glue by Loctite®) (Dizon et al. 2008) (Figure 4A) and
evenly distributed (n = 33) in two identical aquaria (80 cm length, 50 cm width, 25 cm
height). Each aquarium was a closed seawater system with physical, biological and
chemical filtration, and in proper lighting conditions (4606.03 lux ± 327.41 SE; field
average for three months) with 12h photoperiod with simulated gradual dawn and dusk.
One aquaria was kept at 27 °C (field average for three months ± 0.13 SE) and the other
at 30 °C (RCP 8.5 projection for 2100; IPCC 2014) using a thermostat (Figure 4B).
Room temperature was maintained at 27 °C with an air-conditioning system.
Deployment of the plastic bases with fragments was ensured by attaching them to
aquarium bottom using Velcro®. We are aware that grouping contact treatments in one
single aquaria per temperature conditions, formally generates pseudo-replicates
(Underwood 1997). However, because the interactions and data collected were
restricted to the point of contact and that, excluding the contacted areas, corals remained
healthy regardless of the contact treatment, we used them as true replicates. We divided
the six fragments of each colony evenly in the aquariums, three fragments per aquarium.
This way we could control for contact and temperature treatments. We also held
adjacent chunks of P. caribaeorum deployed alone to each aquarium bottom. This was a
29 experimental manipulation. Since there was 100% survival rate and health maintenance
for this precaution procedure in the field, we decided to hold six (instead of one per
replicate group) adjacent chunks of P. caribaeorum in each aquarium (all chunks
survived and did not significantly differ in color, the health proxy). Salinity and pH
remained stable throughout the experiment and varied minimally among temperature
treatments (for the 27°C treatment: average salinity 38ppm; average pH 8.7; and for the
30°C treatment: average salinity 39ppm; average pH 8.8). We assessed fragments with
photographs of the contact area as closely to them as possible in six steps: prior to
contact introduction, 1, 3, 5, 13 and 23 days later. On the first assessment, contact was
removed, a photograph taken and contact replaced. On the second assessment, contact
was definitely removed. As we were conducting maintenance activities in the lab every
day, we could add the fifth and 23rd day assessments to better evaluate the recovering
process.
Figure 4 - Laboratory experiment setup. A) Millepora alcicornis fragment glued to squared plastic base deployed to aquarium bottom with Velcro®. B) The two aquaria setup with running seawater in a closed system and with proper lighting conditions.
EFFECT OF PALYTHOA CARIBAEORUM SURFACE CHEMICAL COMPOUNDS
In order to clarify if the chemistry of Palythoa caribaeorum played an important
role in the competitive outcome, we extracted chunks of P. caribaeorum (16 cm x 16
30 cm) from the study area and transported them to the laboratory in seawater with aeration
in containers. To acquire P. caribaeorum lipid-soluble surface extracts, in the laboratory
we poured 50 ml of hexane in a round mouth (5 cm diameter) glass recipient, drained
and discarded the seawater from the surface of the P. caribaeorum chunk by vertical
positioning and gently shaking it up and down and then attached the chunk to the recipient’s mouth with polyps facing the hexane. With the P. caribaeorum chunk pressed against the recipient to avoid hexane leakage, we turned the recipient upside
down and gently stirred it in a circular horizontal motion for 30 seconds with P.
caribaeorum polyps in contact with the hexane. We then transferred the solution to a
volumetric flask, coupled it to a rotary evaporator and separated the chemical
compounds found in P. caribaeorum form the hexane at a 30° C water bath. After that,
we transferred this extract to a smaller recipient, added an extra 15 ml of hexane to the
pre-used volumetric flask, vigorously shaking it to solubilize any remaining P.
caribaeorum extract, transferred this solution to the same smaller recipient already
containing P. caribaeorum extract and coupled this smaller recipient to the rotary
evaporator for a second round of separation of the chemical compounds found in P.
caribaeorum from the hexane. We repeated this whole process for four P. caribaeorum
chunks and in the end mixed all the extracts together. In this experiment we adapted an
extraction method for algae (Longo and Hay 2017), using hexane as a solvent because it
allows the acquirement of lipid-soluble metabolites from the surface of organisms
(Longo and Hay 2017), not penetrating wet cells or causing cell lysis if applied for 30
seconds (De Nys et al. 1998; Rasher and Hay 2010). We decided to use only surface
compounds from P. caribaeorum because it is a more realistic representation of what
happens in the interaction since the contact occurs surface to surface, where the
31 2007; Lane et al. 2009). It is worth stating that we do not know if the compounds tested
are produced by the zoanthid itself or by its inhabiting microbiota.
In a beaker, we poured 9.5 ml of water and 0.196 g of Phytagel™
(Sigma-Aldrich, USA), mixed for homogenization, microwave heated the solution for 10
seconds, added 1 ml of the mixed extracts after resuspending them in 4 ml of hexane (1
ml for each chunk), mixed again, poured this solution on a strips-cut form containing a
fine mesh bellow, allowed it to dry and cut the gel-mesh strips to obtain 1 x 2 x 0.3 cm
gel-mesh rectangles. We followed the same procedure for controls, but added 1 ml of
hexane instead of P. caribaeorum extract (sensu Longo and Hay 2017).
In the study area, we gently attached the extract and control strips to different
branches of the same M. alcicornis colony (n = 20 colonies) using cable ties. We
assessed the treatments after 24h by taking pictures of the contact areas using the
camera flash to standardize light conditions in all pictures. In the laboratory experiment,
we followed the same procedure of M. alcicornis fragments collection and aquaria
placement performed on the laboratory experiment conducted with chunks of P.
caribaeorum, but now for 20 colonies (four fragments from each). We gently attached
the extract and control strips to the fragments on 27° C (n = 40, two of each colony) and
30° C (n = 40, two of each colony) aquariums using cable ties. We assessed the
treatments after 24 h by taking pictures of the contact areas using the camera flash to
standardize light conditions in all pictures, following the same procedure described
above.
DATA ACQUISITION
We used IMAGEJ v. 1.52a (Schneider et al. 2012) to measure the impacted area (cm2 –
32 experiments. For the photos of the chemical experiments, we used the L*a*b* model on
Adobe Photoshop® to extract color values of the contact area, as done by other studies
(Yam and Papadakis 2004; León et al. 2006; Afshari-Jouybari and Farahnaky 2011).
The L*a*b* model consists of three parameters, one for luminance or lightness (L*),
and two color gradients ranging from green to red (a*) and blue to yellow (b*). Each
one of these parameters can be interpreted as follows: the higher the value, the greater
the lightness (L*), the more red (a*), and the more yellow (b*). In biological terms,
higher values for lightness represent brighter colors, meaning bleaching, and lower
values for a* and b* represent less healthy coral color.
Data analysis
For the data on damaged area from the field experiment, after checking for the
absence of outliers and data normality and sphericity, we performed two-way repeated
measures ANOVA (p < 0.05), considering the effects of contact treatment (fixed, 2
levels: Palythoa caribaeorum and inert mimic), time (repeated, 3 levels: 1, 3 and 13
days), and the interaction between both. For significant factors, we conducted a
one-way ANOVA checking for data homogeneity and normality, considering the effects of
time (significant source, see results), and post hoc Tukey’s Test for pairwise
comparisons. For lab damage area data, after checking for the absence of outliers and
data normality and sphericity, we performed three-way repeated measures ANOVA (p <
0.05), considering the effects of contact treatment (fixed, 2 levels: P. caribaeorum and
inert mimic), temperature treatment (fixed, 2 levels: current and future) and time
(repeated, 5 levels: 1, 3, 5, 13 and 23 days), and the interaction among them. For
significant factors or interactions, we conducted two-way ANOVAs, considering the
effects of contact and temperature treatments for each time separately (except for the
33 comparison when factors or interactions were significant, checking for data
homogeneity and normality and applying Bonferroni correction for multiple
comparisons (p = 0.0125). We performed the analysis using the software Systat 12. For
the chemical experiment data, we compared ‘color’ of the damaged area between treatment and control, considering the three color parameters (L*, a* and b*) as
response variables. For that, we followed a multivariate approach building a similarity
matrix considering Euclidian distance. The similarity matrix was used to build a
non-metric multidimensional scaling plot (nMDS) for better visualization (Clarke 1993) and
to properly test the effects of treatment (field) and treatment and temperature
(laboratory) on color composition with PERMANOVA tests using 999 permutations
(Anderson 2001). For significant effects we performed a SIMPER analysis to obtain the
color parameters that were most important for the differences observed (Clarke 1993).
We performed these analyses using the software Primer 6.
RESULTS
COMPETITIVE INTERACTIONS SURVEY
The organisms that had the highest mean contact percentage per colony among the 42
surveyed Millepora alcicornis colonies were the epilithical algal matrix (58.38% ± 5.34
SE) and the zoanthid Palythoa caribaeorum (17.19% ± 5.54 SE; Figures 5A and 5B),
followed by crustose coralline algae (CCA) (14.14% ± 2.59 SE), macroalgae (9.29% ±
3.18 SE) and others (1% ± 0.95 SE). Considering that there is no clear evidence that the
epilithical algal matrix can inflict significant damage to corals via physical contact
(Jompa and McCook 2003a, 2003b; Pratte et al. 2018); that CCA is related to coral
34 zoanthid is a fast-growing and effective competitor (Bastidas and Bone 1996); we
conducted the experiments with the zoanthid P. caribaeorum.
Figure 5 – A) Palythoa caribaeorum on the Parrachos of Rio do Fogo. B) Competitive interaction between P.
caribaeorum and Millepora alcicornis on the Parrachos of Rio do Fogo.
PHYSICAL INTERACTION UNDER CURRENT TEMPERATURE
Contact with Palythoa caribaeorum caused a greater damage area on Millepora
alcicornis fragments compared to contact with the inert mimic (p < 0.05; Table 1). P. caribaeorum caused on average damages 1.84 times greater after one day of contact, 1.4
times greater after three days of contact and 1.66 times greater by the end of the 13 days
of experiment, when compared to the mimetic contact. Damage area peaked after the
first day of contact, stabilized until the third day and shrunk in about half by the 13th day
35
Table 1 - Two-way repeated measures ANOVA examining the area damaged by contact treatments on
Millepora alcicornis fragments (p < 0.05). Bold p-values stand for significant effects.
Between subjects Source Df MS F p Contact 1 79.27 8.48 0.006 Error 38 9.35 Within subjects Source Df MS F p Time 2 47.37 21.78 < 0.001 Time x Contact 2 4.61 2.12 0.13 Error 76 2.18
Figure 6 - Damage area (bleached or dead; cm2 mean ± SE) over time on Millepora alcicornis fragments in contact with Palythoa caribaeorum and inert mimic. Controls without any contact never experienced damage and so are not shown. Post hoc Tukey’s Test determined differences between days. Day 1 (A), day 3 (A), day 13 (B).
PHYSICAL INTERACTION UNDER WARMER TEMPERATURE
Damage extension depended on a combination of temperature, contact and time
(Table 2; Figure 7). After one day of contact, temperature interacted with contact
0 1 2 3 4 5 6 7 0 1 3 (contact removal) 13 Fr ag m en t d am ag e ar ea ( cm 2, m ea n ± S E)
Days after contact introduction
36 treatments (p < 0.01) showing that contact with inert mimic caused less damage than
contact with Palythoa caribaeorum at 27 °C (p < 0.05) and with inert mimic at 30 °C (p
< 0.05). Despite apparent for temperature, no treatment differed from the third to the
fifth day (contacts removed on the third day). From the 13th day onwards, Millepora
alcicornis fragments at 30 °C maintained greater damage areas compared to the 27 °C
temperature (p < 0.01), with average damages 1.61 times greater in the 13th day and
2.08 times greater in the 23rd day. The damage trajectory at 27 °C peaked on the third
day, showing signs of recovery from the 13th day (3rd ≠ 13th, p < 0.05) to the smallest
damage area on the 23rd. At 30 °C damage trajectory peaked on the third day, but did
not show signs of recovery until the 23rd day (3rd = 23rd, p > 0.05). In addition, 41% of
the M. alcicornis fragments (two treated with inert mimic and seven with P.
caribaeorum) at 30 °C had their damaged area partially colonized by algae on the 23rd
37
Table 2 - Three-way repeated measures ANOVA examining the impact of contact and temperature on
Millepora alcicornis fragments damaged area (p < 0.05). Bold p-values stand for significant effects.
Between subjects Source Df MS F p Temperature 1 53.86 5.01 0.03 Contact 1 6.03 0.56 0.46 Temperature x Contact 1 9.38 0.87 0.36 Error 40 10.75 Within subjects Source Df MS F p Time 4 43.08 44.56 < 0.001 Time x Temperature 4 7.70 7.97 < 0.001 Time x Contact 4 0.27 0.28 0.89
Time x Temperature x Contact 4 3.61 3.73 0.01
Error 160 0.97
Figure 7 - Damage area (bleached or dead; cm2 mean ± SE) over time on Millepora alcicornis fragments in 27°C and 30°C in contact with Palythoa caribaeorum and inert mimic. Controls without any contact never experienced damage and so are not shown. Post hoc Tukey’s Test determined the temperature treatments trajectory over time. 27 °C: day 1 (AB), day 3 (C), day 5 (BC), day 13 (AB), day 23 (A). 30°C: day 1 (A), day 3 (B), day 5 (B), day 13 (AB), day 23 (AB).
0 1 2 3 4 5 6 7 0 1 3 (contact removal) 5 13 23 Fra gme n t d am age area (c m 2, m ea n ± S E)
Days after contact introduction
38 EFFECT OF PALYTHOA CARIBAEORUM SURFACE CHEMICAL COMPOUNDS
In the field, the color composition of areas contacted by control and extract
treatments were different considering a significance level of 6% (PERMANOVA:
Pseudo-F = 2.94, p = 0.06; Figure 8), with extract treatment leading to a whiter color
(SIMPER: 64.72%). We opted to adjust the significance level based on the consistency
of the results obtained from the natural contact with Palythoa caribaeorum both in the
field and in the laboratory. Therefore, assuming a 6% chance of type I error instead of a
5% chance seemed reasonable. In the lab, we did not observe differences between the
color of areas contacted by control and extract gels (p = 0.53), but the temperature
treatments had an effect on the damaged areas color (PERMANOVA: Pseudo-F = 3.49,
p < 0.05; Figure 9), with the 30 °C treatment leading to a whiter color in both contact
39
Figure 8 – Bar plots of the color parameters L, a and b (graphs A, B and C, respectively) observed on
Millepora alcicornis branches in the field after 24h of contact with control and treated gels. The y-axis on
40
Figure 9 – Bar plots of the color parameters L, a and b (graphs A, B and C, respectively) observed on
Millepora alcicornis fragments in the laboratory after 24h of contact with control and treated gels under 27 °C
(blue background; ncontrol = 19; ntreated = 19) and 30 °C temperatures (orange background; ncontrol = 20; ntreated =
20). The y-axis on graphs A and C is cut for better data visualization.
41 DISCUSSION
We studied the competitive effects of the common zoanthid Palythoa
caribaeorum on the hydrocoral Millepora alcicornis and our results indicate a tendency
of P. caribaeorum outcompeting M. alcicornis, via both physical and chemical effects,
an outcome that tends to intensify in warmer temperatures predicted for the future.
Known for its notorious competitive ability (Bastidas and Bone 1996; Rabelo et al.
2013; Silva et al. 2015) and unpalatability to other organisms (Moore and Scheuer
1971; Gleibs et al. 1995), this zoanthid is also expected to restrict its distribution
towards the equator as ocean temperature increases (Durante et al. 2018). This indicates
that if M. alcicornis endures the predicted 3 °C warming for the year 2100, it would still
have P. caribaeorum as a competitor in the reefs of the Caribbean and northeastern
Brazil. While in other parts of the world many branching coral species aid structural
complexity to the reefs, M. alcicornis is one of the main species to add structural
complexity to Brazilian reefs (Leão and Dominguez 2000; Leão et al. 2003) and
experiences great mortality facing thermal stress events (Duarte et al. 2020). More
frequent and intense competitive interactions with P. caribaeorum is likely to occur in
the future and may be decisive for decreasing complexity and consequently diversity,
particularly in the Brazilian reefs where P. caribaeorum is abundant (Aued et al. 2018).
As P. caribaeorum is a common invertebrate in other important reef areas, the effects
observed here could become frequent and intense elsewhere, being a threat to other reef
systems including the Caribbean (Durante et al. 2018).
The greater damage caused by P. caribaeorum contact in the field could be
interpreted as a sign that chemical compounds on the surface of the zoanthid (Ciereszko
and Karns 1973) could be mediating the competitive interaction, an assumption
42 Bone 1996; Rabelo et al. 2013). Another sign of chemical activity appeared after the
first day of the lab experiment, where P. caribaeorum contact caused greater damage
under 27 °C when compared to P. caribaeorum mimic contact. By specifically testing
the effects of surface-chemical compounds, we found that P. caribaeorum extracts
contacting M. alcicornis in the field resulted in whiter areas if compared to controls. We
believe that the lack of significant difference between the extract and control contacts in
the lab was due to a marine heatwave (Hobday et al. 2016) striking the study area
during fragments collection, which may have compromised M. alcicornis health status
prior to the experiment commencement, even though no bleaching was observed. Still,
we consider that our findings reinforce previous assumptions of the role played by P.
caribaeorum chemical compounds during competitive interactions. However, when we
focus on the lack of significant difference between extract and control contacts under 30
°C temperature, another possible interpretation is that the temperature factor becomes
more important than the contact identity at a certain point of warming. This could
translate into any kind of physical contact being harmful in higher temperatures.
Despite the importance of chemical activity, organisms can also have other
harming mechanisms such as overgrowing and shading their competitors (Box and
Mumby 2007), causing anoxia (Haas et al. 2013) and shifts in microbiota (Pratte et al.
2018). P. caribaeorum mainly uses its rapid growth rate to overtop competitors without
physical contact as tactic (Almeida Saá et al. 2020), applying lateral aggression and
overtopping with physical contact upon the genus Millepora (Suchanek and Green
1981). Our experimental time span did not allow us to notice such overgrowing
outcomes, but observations in the field strongly confirm them. It was common to find
M. alcicornis greatly reduced in size because of being overtopped by P. caribaeorum.
