Space partitioning among damselfishes in the Caribbean coast of Panama: the role of habitat preferences

This study aimed to assess abundance and habitat use by juvenile and adult damselfishes, as much as the benthic cover of different reefs on Isla Colon, Bocas del Toro, Panama. Reefs were selected considering different levels of wave exposure and depths. Damselfish and benthic communities were distinct between reefs. The most abundant species in the sheltered deeper reef was Stegastes planifrons followed by S. leucostictus, and they were also recorded in the sheltered shallower reef. Low densities of S. partitus and S. variabilis were also observed in the sheltered deeper reef, as these species are apparently restricted to higher depths. Additionally, these reefs presented patches with high cover of live and dead massive coral. Shallow depths presented high abundances of S. adustus, indicating a preference of this species for shallow habitats and exhibiting a two-fold increase in abundance at higher wave surge. Also, Microspathodon chrysurus reached higher numbers in shallow depths. Furthermore, the exposed reef presented a high cover (%) of algae groups and the fire-coral Millepora alcicornis, acknowledged as a preferred habitat for M. chrysurus and other reef fish. In this study, distinct habitat uses were observed, with patterns regulated by depth and/or wave exposure levels and/or availability of specific benthic cover. For site-attached species as damselfish, habitat specialization, competition and/or non-random recruitment patterns have been found to rule distributional patterns. Similar results for damselfish relative abundances were found compared to studies conducted within Panama and other reefs throughout the Caribbean region over three decades ago, indicating strong habitat affinity for the most abundant species. However, severe reductions of habitat availability following coral mass-mortality events may have disrupted their distributional patterns.

Este estudo teve como objetivo avaliar a abundância e uso do habitat por juvenis e adultos de peixes-donzela, assim como as comunidades bentônicas em distintos recifes de Isla Colon, Bocas del Toro, Panamá. Os recifes foram escolhidos considerando diferentes níveis de exposição a ondas e profundidade. As comunidades de peixes e bentos estudadas se mostraram distintas. A espécie mais abundante em recifes com maior profundidade e abrigados foi Stegastes planifrons, seguida por S. leucostictus, que também foram observadas em recifes rasos abrigados. As baixas abundâncias de S. partitus e S. variabilis também foram observadas no primeiro recife citado e estas espécies foram aparentemente restritas à profundidade maiores. Adicionalmente, estes mesmos recifes apresentaram uma vasta cobertura de corais massivos, vivos ou mortos. Stegastes adustus apresentou sua maior abundância em baixas profundidades, indicando uma preferência por habitats rasos, aumentando em duas vezes com a exposição a ondas. Os recifes rasos também tiveram maior abundância de Microspathodon chrysurus. Além disso, o recife com maior exposição apresentou extenso percentual de cobertura por algas e o coral-de-fogo Millepora alcicornis, reconhecido habitat preferencial de M. chrysurus e outras espécies de peixes. Neste trabalho, diferentes padrões de uso do habitat foram encontrados, sendo regulados pela profundidade e/ou exposição e ainda a disponibilidade de determinada cobertura bentônica. Para espécies fortemente associadas ao substrato, a especialização, a competição e padrões não aleatórios do recrutamento são conhecidos determinantes dos padrões distribucionais. Este estudo apresentou resultados similares a outros conduzidos há 30 anos no Panamá e outros recifes do Caribe, indicando que as espécies mais abundantes mantêm forte afinidade com o habitat. Entretanto, severas reduções na disponibilidade de habitat, seguidas de eventos de mortalidade em massa, podem ter possivelmente afetado seus padrões de distribuição.

Variations in reactive oxygen release and antioxidant activity in multiple Symbiodinium types in response to elevated temperature.

As ocean temperatures rise, investigations into what the physiological effects will be on the symbiotic microalga Symbiodinium, and how these may play into the cnidarian bleaching response, have highlighted the contribution of reactive oxygen species (ROS). Previous studies have laid this groundwork using a limited number of Symbiodinium phylotypes, and so this study aims to expand this understanding by exploring the effects of sub-lethal elevated temperatures on the physiological response of seven genetically distinct types of Symbiodinium, including A1, B1, B2, C1, D, E1, and F2. The production of ROS (at 26 °C, 29 °C, 30 °C, and 31 °C) and activity of the antioxidants catalase (CAT) and superoxide dismutase (SOD) (at 26 °C and 31 °C) were measured as indicators of sensitivity or tolerance to heat stress. Symbiodinium types B1 and C1 were the most thermally sensitive, with C1 producing the highest amount of ROS at elevated temperatures. Types A1 and F2 were tolerant, having no increase in ROS production, and were the only types to increase both CAT and SOD activity with temperature stress. Type B2 had decreased ROS production and elevation of CAT activity, while type E1 had decreased levels of ROS production at elevated temperatures. Type D was the only Symbiodinium type to remain unaffected by elevated temperatures. These results are consistent with previous findings of relative sensitivity or tolerance to elevated temperatures, specifically with regards to types A1, B1, and F2. The inclusion of types B2, C1, D, and E1 provides further new evidence of how types differ in their thermal responses, suggesting differing mechanisms exist in the Symbiodnium response to higher temperature and highlighting the importance of establishing symbiont identity when exploring the response of intact associations to this type of stress.

Development of gene expression markers of acute heat-light stress in reef-building corals of the genus Porites.

Coral reefs are declining worldwide due to increased incidence of climate-induced coral bleaching, which will have widespread biodiversity and economic impacts. A simple method to measure the sub-bleaching level of heat-light stress experienced by corals would greatly inform reef management practices by making it possible to assess the distribution of bleaching risks among individual reef sites. Gene expression analysis based on quantitative PCR (qPCR) can be used as a diagnostic tool to determine coral condition in situ. We evaluated the expression of 13 candidate genes during heat-light stress in a common Caribbean coral Porites astreoides, and observed strong and consistent changes in gene expression in two independent experiments. Furthermore, we found that the apparent return to baseline expression levels during a recovery phase was rapid, despite visible signs of colony bleaching. We show that the response to acute heat-light stress in P. astreoides can be monitored by measuring the difference in expression of only two genes: Hsp16 and actin. We demonstrate that this assay discriminates between corals sampled from two field sites experiencing different temperatures. We also show that the assay is applicable to an Indo-Pacific congener, P. lobata, and therefore could potentially be used to diagnose acute heat-light stress on coral reefs worldwide.

Patterns of coral ecological immunology: variation in the responses of Caribbean corals to elevated temperature and a pathogen elicitor.

Disease epizootics are increasing with climatic shifts, yet within each system only a subset of species are identified as the most vulnerable. Understanding ecological immunology patterns as well as environmental influences on immune defenses will provide insight into the persistence of a functional system through adverse conditions. Amongst the most threatened ecosystems are coral reefs, with coral disease epizootics and thermal stress jeopardizing their survival. Immune defenses were investigated within three Caribbean corals, Montastraea faveolata, Stephanocoenia intersepta and Porites astreoides, which represent a range of disease and bleaching susceptibilities. Levels of several immune parameters were measured in response to elevated water temperature and the presence of a commercial pathogen-associated molecular pattern (PAMP) - lipopolysaccharide (LPS) - as an elicitor of the innate immune response. Immune parameters included prophenoloxidase (PPO) activity, melanin concentration, bactericidal activity, the antioxidants peroxidase and catalase, and fluorescent protein (FP) concentration. LPS induced an immune response in all three corals, although each species responded differently to the experimental treatments. For example, M. faveolata, a disease-susceptible species, experienced significant decreases in bactericidal activity and melanin concentration after exposure to LPS and elevated temperature alone. Porites astreoides, a disease-resistant species, showed increased levels of enzymatic antioxidants upon exposure to LPS independently and increased PPO activity in response to the combination of LPS and elevated water temperature. This study demonstrates the ability of reef-building corals to induce immune responses in the presence of PAMPs, indicating activation of PAMP receptors and the transduction of appropriate signals leading to immune effector responses. Furthermore, these data address the emerging field of ecological immunology by highlighting interspecific differences in immunity and immunocompetences among Caribbean corals, which are reflected in their life-history characteristics, disease susceptibilities and bleaching-induced mortality.

What are the physiological and immunological responses of coral to climate warming and disease?

Coral mortality due to climate-associated stress is likely to increase as the oceans get warmer and more acidic. Coral bleaching and an increase in infectious disease are linked to above average sea surface temperatures. Despite the uncertain future for corals, recent studies have revealed physiological mechanisms that improve coral resilience to the effects of climate change. Some taxa of bleached corals can increase heterotrophic food intake and exchange symbionts for more thermally tolerant clades; this plasticity can increase the probability of surviving lethal thermal stress. Corals can fight invading pathogens with a suite of innate immune responses that slow and even arrest pathogen growth and reduce further tissue damage. Several of these responses, such as the melanin cascade, circulating amoebocytes and antioxidants, are induced in coral hosts during pathogen invasion or disease. Some components of immunity show thermal resilience and are enhanced during temperature stress and even in bleached corals. These examples suggest some plasticity and resilience to cope with environmental change and even the potential for evolution of resistance to disease. However, there is huge variability in responses among coral species, and the rate of climate change is projected to be so rapid that only extremely hardy taxa are likely to survive the projected changes in climate stressors.