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Vulnerability of reef-building corals towards global change

Publication . Dias, Marta; Vinagre, Catarina; Cabral, Henrique

Global warming is leading to large-scale coral bleaching and mass mortality, but also to increases in tropical storms' frequency and intensity. Storms allow fragmentation of reef-building corals and can lead to near-shore salinity reduction which, combined with ocean warming, will aggravate coral distress. In order to assess the susceptibility of different coral species to these environmental stressors, small fragments of nine coral species of the Indo-Pacific region were exposed to different thermal (26°C, 30°C, 32°C) and hyposaline (26°C-33psu, 30°C-33psu, 26°C-20psu, 30°C-20psu) experimental treatments for 60 days. Several parameters were assessed at different levels of biological organization: at the organism level (total and partial mortality, and coral condition based in bleaching levels), physiological level (growth rate and regeneration rate of artificially inflicted lesions), and molecular level (superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO)). Also, in order to test two different approaches to be applied in the monitoring of the effects of heat stress, some parameters were combined in integrated biomarker response indices, either in a molecular approach, approach A, using GST, CAT, LPO, and SOD, or in an approach that integrates the molecular, physiological and organism levels, approach B, using GST, CAT, LPO, SOD, partial mortality, and growth rate. Results indicate that Pocillopora damicornis and Stylophora pistillata were the most vulnerable at 30°C. Psammocora contigua, Turbinaria reniformis, and Galaxea fascicularis were the most tolerant species at 32°C. The species P. contigua and G. fascicularis were the most tolerant to low salinity (26°C-20psu). The species G. fascicularis was the only one capable of surviving the combined effect of high temperature and low salinity (30°C-20psu). Approach B, the most integrative approach, was considered the most adequate for evaluating the health of reef corals since it better discriminated the stress suffered by the tested species.

2020-01Doctoral thesis

Open access

Evaluation of thermal stress in tropical marine organisms in the context of climate warming

Publication . Madeira, Carolina; Vinagre, Catarina Maria Batista, 1978-; Diniz, Mário; Cabral, Henrique N., 1969-

The marine environment is already registering the impacts of climate change. The current increase in global temperature since pre-industrial times is disrupting life in the oceans, from the tropics to the poles. The key impacts for marine species as warming continues include shifting home ranges and altered life histories due to the direct effects of temperature on metabolism, life cycles and behaviour of organisms. These pervasive effects on species will also have a significant impact in the goods and services provided by the ocean to human society. However, the vulnerability of tropical marine species (e.g. reef fish and non-coral invertebrates) towards ocean warming is still far from clear, not only due to the gap of knowledge on general ecology and biology of most tropical species, but also because there is a lack of integrative approaches addressing physiological and molecular thermal compensation mechanisms, as well as a lack of adequate or optimized assessment tools for tropical habitats. Therefore, the aim of this thesis was to assess the vulnerability of marine species (fish, crustaceans and gastropods) from tropical reef environments to ocean warming (gradual temperature increase and heat waves), using molecular- (proteins and antioxidant enzymes), cellular (lipid peroxidation), tissue- (energy reserves), organism- (condition, critical thermal maxima) and sample population (acclimation rate, thermal safety margins, mortality) parameters to measure stress and performance. General methodologies included collecting animals from tropical shallow waters with hand nets, experimental assays testing acute and chronic thermal stress and thermal tolerance in the lab (following control and warming scenarios), periodic samplings of several tissue types and biomarker quantification (sample homogenization and posterior immunoassays, kinetic colorimetric assays and elemental analyses by isotope ratio mass spectrometry). Mathematical calculations were used for several performance parameters as well as stress indices. Multivariate (as well as multifactorial) statistical analyses were then performed for all datasets. Results revealed that chronically increased water temperatures (30˚C – 32˚C) elicited a time-dependent cellular stress response in all species tested, where chaperones and antioxidant enzymes showed the greatest fold-changes. The latter molecular responses were highly inducible in vital organs such as gills, liver and muscle, suggesting a relation to tissue function, metabolic- and oxygen diffusion rate which determine the flux of reactive oxygen species and damage potential in cells. Additionally, animals subjected to increased temperatures also showed poorer health status and decreased body condition with lower energy reserves when compared to control temperatures, although mortality levels remained unchanged. An acute exposure to increased thermal load revealed plastic upper thermal limits. However, thermal safety margins were generally low for shallow water species in reef environments, indicating a low ability to tolerate further future warming. This means that organisms will have to rely on subtidal habitats for thermal refugia as shallow water habitats (e.g. tide pools) become ecological traps where animals cannot escape heat. Overall, the results point to the importance of monitoring thermal change in the wild to provide decision makers with appropriate and detailed information to sustain conservation efforts in fragile tropical marine ecosystems.

2018Doctoral thesis

Open access

Functioning of coastal food webs : intertidal rock pools as a case-study

Publication . Mendonça, Vanessa; Vinagre, Catarina; Flores, Augusto

Rocky intertidal ecosystems have long attracted the attention of biologists, being viewed as natural laboratories, where biodiversity and species-interactions could be easily investigated. However, intertidal rock pools have received much less attention that the surrounding emergent intertidal platforms. The aim of this thesis was to provide new insights into the trophic ecology of intertidal rock pools through 1) the characterization of pools as proxies for the study of ma-rine food web networks; 2) the investigation of food web network robustness to species loss in temperate and tropical ecosystems; 3) the investigation of food web robustness to heat-waves in temperate and tropical ecosystems; 4) the description of seasonality in the food web net-works; and 5) the testing of the role of pools as preferential feeding grounds for transient fish species. It was concluded that intertidal rock pools can be used as proxies for the study of marine food web networks. Tropical food webs revealed higher robustness than temperate food webs, however the tropical food webs’ topology suffered more alterations after species loss. Food web networks presented similar robustness to the removal of species based on thermal vulnerability, however the tropical webs encompass more thermally vulnerable species and should, thus, suffer more species loss in a heat-wave context. The basic topology of temperate webs was stable throughout the year. Intertidal rock pools are likely used as preferential feeding grounds by early-stages of transient fish, as showed by the consistent similarity between stom-ach contents and prey availability inside the pool, observed for all species. Overall, this work opens a brand-new research avenue with the use of intertidal rock pools as proxies for the study of marine food web networks, while also shedding light into the particular vulnerability of tropical food webs and the important role of pools in fish early-life.

2020-01Doctoral thesis

Open access