The role of herbivores in a near future ocean: positive and negative effects of climate change on herbivore ecological function

Earth’s climate is characterised by abrupt change through its history, yet human induced climate change is warming and acidifying our oceans at unprecedented rates. Such alterations in the seawater’s chemical and physical properties are anticipated to disrupt a multitude of ecological processes leading to potential reductions in productivity and biodiversity of marine systems. Functional groups such as marine herbivores are renowned for meditating competition between benthic organisms, affecting the physical structure and primary production in marine systems, countervailing the deleterious effects of global and local disturbances. Within this context, it is important to not only understand how herbivorous species respond to climate change, but also how their overall functional role are affected and how this might have cascading effects on other species. In this thesis, I reveal that whilst populations of many species are forecast to collapse due to the effects of future climate, some herbivorous species may capitalize on environmental change and boost their densities by increasing the carrying capacity of the environment by actively modifying the habitat under an otherwise stressful condition. I also show that the modifications performed by herbivorous species trough the strengthening of positive interaction under ocean acidification can assist other species to densify, stimulating species coexistence and ecosystem function, and perhaps mitigate the deleterious effect of CO2 enrichment expected at population and community level. Therefore, under ocean warming the functional role of herbivores is eroded releasing opportunistic algae from trophic control which can potentially lead marine systems to undergo structural modification. I show that loss of this functional role, reduces the capacity of the system to control the expansion of opportunistic algae. The identification of the circumstances as to whether herbivores functional role in marine systems will strengthen or decrease provides insights into the impacts of ocean warming and acidification at local scale and their potential management.Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 201

Community structure of shallow rocky shore fish in a tropical bay of the southwestern Atlantic

Os costões rochosos do Atlântico Sul Ocidental sustentam ricas comunidades de peixes recifais. Apesar disso, o conhecimento sobre essas comunidades em zonas tropicais continua escasso, especialmente no Brasil. No presente trabalho avaliamos parâmetros das comunidades de peixes recifais, tais como composição e estrutura trófica, além de sua interação com variáveis físicas e bióticas, em quatro costões rochosos tropicais na Baía de Todos os Santos, costa leste do Brasil. Durante seis meses 80 censos visuais foram realizados, nos quais 3.582 peixes pertencentes a 76 espécies foram registrados. Os peixes herbívoros territoriais e as algas filamentosas dominaram em todos os costões. A variação espacial na estrutura da comunidade de peixes esteve relacionada com a composição bêntica e profundidade. A elevada abundância observada de peixes herbívoros territoriais e invertívoros móveis pode ser devido à alta cobertura de algas filamentosas e à baixa profundidade e exposição às ondas. Além disso, esse padrão também pode ser explicado pela baixa densidade de herbívoros errantes e grandes carnívoros, provavelmente devido à intensa pressão da atividade pesqueira. Assim, novos estudos são necessários para avaliar o real estado de conservação destes ambientes, uma vez que estão localizados em posição singular na Baía de Todos os Santos, conectando recifes internos e externos da área.Southwestern Atlantic Ocean rocky shores sustain important reef fish communities. However, those communities in tropical regions are not well understood, especially in Brazil. In this present article we assess community parameters of reef fishes such as composition, trophic organization and their relationships with physical and biological factors on four tropical rocky shores in Todos os Santos Bay, southwestern Atlantic. During six months, a total of 80 visual censuses were performed, in which 3,582 fish belonging to 76 species were recorded. Territorial herbivorous fish and turf algae were dominant at all the sites. The spatial variability of fish community structure was related to the benthic cover composition and depth. The high abundance of territorial herbivores and mobile invertebrate feeders could be associated with high levels of turf cover, low wave exposure and shallow waters. Moreover, this fact could be a consequence of the low density of roving herbivores and large carnivores probably due to the pressure of intense fishing activity. Thus complementary studies are needed to evaluate the actual conservation status of these rocky shore reefs, singularly located habitats connecting inner and outer reefs in Todos os Santos Bay

Mesophotic reef fish assemblages of the remote St. Peter and St. Paul's Archipelago, Mid-Atlantic Ridge, Brazil

Mesophotic reef fish assemblages (30-90 m depth) of the small and remote St. Peter and St. Paul's Archipelago (SPSPA), Mid-Atlantic Ridge, Brazil, were characterized using remotely operated vehicles. Ordination analyses identified distinct fish assemblages in the upper (30-50 m) and lower (50-90 m) mesophotic zones, the former characterized by high abundances of species that are also abundant at euphotic reefs (Caranx lugubris, Melichthys niger, Stegastes sanctipauli and Chromis multilineata) and the latter dominated by two mesophotic specialists (Prognathodes obliquus and Chromis enchrysura). Planktivores dominated fish assemblages, particularly in the upper mesophotic zone, possibly due to a greater availability of zooplankton coming from the colder Equatorial Undercurrent in mesophotic depths of the SPSPA. Turf algae, fleshy macroalgae and scleractinian corals dominated benthic assemblages between 30 and 40 m depth, while bryozoans, black corals and sponges dominated between 40 and 90 m depth. Canonical correspondence analysis explained 74 % of the relationship between environmental characteristics (depth, benthic cover and complexity) and structure of fish assemblages, with depth as the most important independent variable. Juveniles of Bodianus insularis and adults of P. obliquus and C. enchrysura were clearly associated with branching black corals (Tanacetipathes spp.), suggesting that black corals play key ecological roles in lower mesophotic reefs of the SPSPA. Results from this study add to the global database about mesophotic reef ecosystems (MREs) and provide a baseline for future evaluations of possible anthropogenic and natural disturbances on MREs of the SPSPA.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico-CNPqCNPqFundacao de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ)Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)Univ Sao Paulo, Inst Oceanog, Programa Posgrad Oceanog Biol, BR-05508120 Sao Paulo, SP, BrazilUniv Fed Paraiba, Programa Posgrad Ciencias Biol Zool, BR-58059900 Joao Pessoa, PB, BrazilUniv Fed Paraiba, Programa Posgrad Ecol & Monitoramento Ambiental, BR-58297000 Rio Tinto, PB, BrazilUniv Estadual Paraiba, Programa Posgrad Ecol & Conservac, BR-58109753 Campina Grande, PB, BrazilUniv Fed Pernambuco, Dept Oceanog, Ctr Tecnol & Geociencias, BR-50670901 Recife, PE, BrazilUniv Fed Paraiba, Ctr Ciencias Exatas & Nat, Dept Sistemat & Ecol, BR-58051900 Joao Pessoa, PB, BrazilInst Pesquisas Jardim Bot Rio De Janeiro, Rio De Janeiro, RJ, BrazilUniv Fed Sao Paulo, Inst Mar, Campus Baixada Santista, BR-11030400 Santos, SP, BrazilUniv Fed Rio de Janeiro, Inst Biol, BR-21944970 Rio De Janeiro, RJ, BrazilUniv Fed Rio de Janeiro, SAGE COPPE, BR-21944970 Rio De Janeiro, RJ, BrazilUniv Sao Paulo, Inst Oceanog, Dept Oceanog Biol, BR-05508120 Sao Paulo, SP, BrazilUniv Fed Paraiba, Dept Engn & Meio Ambiente, BR-58297000 Rio Tinto, PB, BrazilUniv Fed Sao Paulo, Inst Mar, Campus Baixada Santista, BR-11030400 Santos, SP, BrazilCNPq: 557185/09-2CNPq: 484875/2011-6Web of Scienc