Physiological performance of the cold-water coral Dendrophyllia cornigera reveals its preference for temperate environments

Cold-water corals (CWCs) are key ecosystem engineers in deep-sea benthic communities around the world. Their distribution patterns are related to several abiotic and biotic factors, of which seawater temperature is arguably one of the most important due to its role in coral physiological processes. The CWC Dendrophyllia cornigera has the particular ability to thrive in several locations in which temperatures range from 11 to 17 °C, but to be apparently absent from most CWC reefs at temperatures constantly below 11 °C. This study thus aimed to assess the thermal tolerance of this CWC species, collected in the Mediterranean Sea at 12 °C, and grown at the three relevant temperatures of 8, 12, and 16 °C. This species displayed thermal tolerance to the large range of seawater temperatures investigated, but growth, calcification, respiration, and total organic carbon (TOC) fluxes severely decreased at 8 °C compared to the in situ temperature of 12 °C. Conversely, no significant differences in calcification, respiration, and TOC fluxes were observed between corals maintained at 12 and 16 °C, suggesting that the fitness of this CWC is higher in temperate rather than cold environments. The capacity to maintain physiological functions between 12 and 16 °C allows D. cornigera to be the most abundant CWC species in deep-sea ecosystems where temperatures are too warm for other CWC species (e.g., Canary Islands). This study also shows that not all CWC species occurring in the Mediterranean Sea (at deep-water temperatures of 12-14 °C) are currently living at their upper thermal tolerance limit. © 2014 Springer-Verlag Berlin Heidelber

Trophic ecology of the facultative symbiotic coral Oculina arbuscula

Symbiotic corals are trophically complex, relying on both auto- and heterotrophy. Here, the nutrition of the temperate facultative symbiotic scleractinian coral Oculina arbuscula was investigated under natural conditions. Nutrition of symbiotic and aposymbiotic colonies during spring and fall was assessed by determining the carbon and nitrogen isotope signature of their tissues, photosynthetic endosymbionts and different potential food sources (plankton and particulate organic matter) in seawater and sediment. The nutrition of symbiotic colonies was primarily derived from their endosymbionts, regardless of the season. However, aposymbiotic colonies of O. arbuscula relied preferentially on sediment organic matter as well as pico- and nanoplankton (<10 µm). As this small planktonic fraction (that includes phytoplankton) has been overlooked as a potential food source for symbiotic scleractinian corals, this study provides new insights into this feeding mode in these reef-building organisms

The Deep‐water corals of Cyprus: Environmental settings and ecological features (CYprus Cold‐corals Levantine SeA, Eastern MEditerraneaN: CYCLAMEN)

The recently started research project CYCLAMEN (CYprus Cold-corals Levantine SeA, Eastern MEditerraneaN), will conduct the first detailed study of cold-water coral communities in eastern Cypriot waters. Cold-water coral habitats have been found during exploratory surveys. The 2-yr long project will include the environmental characterization of the area, as well as the study of the spatial distribution of cold-water coral communities. In addition to the study of the biology of the coral species, genetic and eco-physiological studies will be included. This project is the first of its kind in Cyprus and will additionally have an associated scientific outreach programme in order to bring these ecosystems, still poorly known, to the general public. The project is led by the Spanish Institute of Oceanography (IEO), and relies on the participation of research Institutions in Cyprus: The Cyprus Institute (CyI) and the NGO Enalia Physis Environmental Research Centre (EPERC); France: Aix-Marseille University – Mediterranean Institute for Biodiversity & Ecology (AMU-IMBE); Greece: The Hellenic Centre for Marine Research (HCMR); Mónaco: Centre Scientifique de Monaco (CSM); United Kingdom: National Oceanography Centre (NOC), and Spain: Universitat de Barcelona (UB). Here we present the conceptual frame of the project, the background knowledge and the first obtained results in the oceanographic cruise carried out in summer 2015

Cold-water corals research in the lab and in the field: (1) growth rates of four CWC species maintained in aquaria, (2) new research areas: the Galicia Bank and the Avilés canyon (Atlantic and Cantabrian Sea), a scientific and methodological approach

Growth rates of 4 Cold-water Coral (CWC) species (Madrepora occulata, Lophe/ia pertusa, Desmophyllum cristagalli and Dendrophyllia cornigera) from the Mediterranean Sea have been measured under the same and controlled laboratory conditions over a nine months period. Results showed that M. occulata grew faster than the other three species, which presented similar growth rates. These results are discussed and also compared with the growth of tropical coral species maintained in aquaria, but in different light and temperature conditions, which corresponded to the usual culture conditions of these corals. It appeared that the zooxanthellate tropical coral Galaxea fascicularis exhibited similar growth rates than the CWC M. oculata. Further we present new research areas on the Atlantic and Cantabrian continental margin, the Galicia Bank and the Aviles canyon, which are part of the zones studied in the Spanish LIFE project INDEMARES, as well as possible targets as Marine Protected Areas (MPAs) for the NATURA 2000 network. Both areas are studied considering an ecosystem approach, aboarding an integrated study of the physical scenario (hydrography, geomorphology), all ecosystem compartments (fish, endo-, epi-, and suprabenthic and benthopelagic fauna) and the trophic relationships between them. All this information, together with the study of the impact of the fisheries working in the areas, will be integrated in a trophodynamic mass-balance model and will be used to identify vulnerable ecosystems (VE) (as the CWC habitats are) and essential fish habitats (EFH). This methodological approach offers a holistic view of these deep-sea ecosystems and can be used to design more effective and successful management strategies for MPA

Effects of Light, Food Availability and Temperature Stress on the Function of Photosystem II and Photosystem I of Coral Symbionts

Background: Reef corals are heterotrophic coelenterates that achieve high productivity through their photosynthetic dinoflagellate symbionts. Excessive seawater temperature destabilises this symbiosis and causes corals to "bleach," lowering their photosynthetic capacity. Bleaching poses a serious threat to the persistence of coral reefs on a global scale. Despite expanding research on the causes of bleaching, the mechanisms remain a subject of debate.\ud \ud Methodology/Principal Findings: This study determined how light and food availability modulate the effects of temperature stress on photosynthesis in two reef coral species. We quantified the activities of Photosystem II, Photosystem I and whole chain electron transport under combinations of normal and stressful growth temperatures, moderate and high light levels and the presence or absence of feeding of the coral hosts. Our results show that PS1 function is comparatively robust against temperature stress in both species, whereas PS2 and whole chain electron transport are susceptible to temperature stress. In the symbiotic dinoflagellates of Stylophora pistillata the contents of chlorophyll and major photosynthetic complexes were primarily affected by food availability. In Turbinaria reniformis growth temperature was the dominant influence on the contents of the photosynthetic complexes. In both species feeding the host significantly protected photosynthetic function from high temperature stress.\ud \ud Conclusions/Significance: Our findings support the photoinhibition model of coral bleaching and demonstrate that PS1 is not a major site for thermal damage during bleaching events. Feeding mitigates bleaching in two scleractinian corals, so that reef responses to temperature stresses will likely be influenced by the coinciding availabilities of prey for the host

Coral Uptake of Inorganic Phosphorus and Nitrogen Negatively Affected by Simultaneous Changes in Temperature and pH

The effects of ocean acidification and elevated seawater temperature on coral calcification and photosynthesis have been extensively investigated over the last two decades, whereas they are still unknown on nutrient uptake, despite their importance for coral energetics. We therefore studied the separate and combined impacts of increases in temperature and pCO2 on phosphate, ammonium, and nitrate uptake rates by the scleractinian coral S. pistillata. Three experiments were performed, during 10 days i) at three pHT conditions (8.1, 7.8, and 7.5) and normal temperature (26°C), ii) at three temperature conditions (26°, 29°C, and 33°C) and normal pHT (8.1), and iii) at three pHT conditions (8.1, 7.8, and 7.5) and elevated temperature (33°C). After 10 days of incubation, corals had not bleached, as protein, chlorophyll, and zooxanthellae contents were the same in all treatments. However, photosynthetic rates significantly decreased at 33°C, and were further reduced for the pHT 7.5. The photosynthetic efficiency of PSII was only decreased by elevated temperature. Nutrient uptake rates were not affected by a change in pH alone. Conversely, elevated temperature (33°C) alone induced an increase in phosphate uptake but a severe decrease in nitrate and ammonium uptake rates, even leading to a release of nitrogen into seawater. Combination of high temperature (33°C) and low pHT (7.5) resulted in a significant decrease in phosphate and nitrate uptake rates compared to control corals (26°C, pHT = 8.1). These results indicate that both inorganic nitrogen and phosphorus metabolism may be negatively affected by the cumulative effects of ocean warming and acidification