Bio-optical properties and radiative energy budgets in fed and unfed scleractinian corals (Pocillopora sp.) during thermal bleaching

© 2019 The authors. Corals live in symbiosis with algal dinoflagellates, which can achieve outstanding photo - synthetic energy efficiencies in hospite approaching theo retical limits. However, how such photosynthetic efficiency varies with environmental stress remains poorly known. Using fiber-optic and electrochemical microsensors in combination with variable chlorophyll fluorescence imaging, we investigated the combined effects of thermal stress and active feeding on the radiative energy budget and photosynthetic efficiency of the symbiotic coral Pocillopora sp. At ambient temperature (25°C), the percentage of ab sorbed light energy used for photosynthesis under low irradiance was higher for fed (∼5-6%) compared to unfed corals (4%). Corals from both feeding treatments responded equally to stress from high light ex posure (2400 μmol photons m-2 s-1), exhibiting a de crease in photosynthetic efficiency, down to 0.5-0.6%. Fed corals showed increased resilience to thermal-induced bleaching (loss of symbionts) compared to unfed corals. In addition, while unfed corals decreased their photosynthetic efficiency almost immediately when exposed to thermal stress, fed corals maintained a constant and high photosynthetic efficiency for 5 more days after onset of thermal stress. We conclude that active feeding is beneficial to corals by prolonging coral health and resilience during thermal stress as a result of an overall healthier symbiont population

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

Environmental drivers of distribution and reef development of the Mediterranean coral Cladocora caespitosa

Cladocora caespitosa is the only Mediterranean scleractinian similar to tropical reef-building corals. While this species is part of the recent fossil history of the Mediterranean Sea, it is currently considered endangered due to its decline during the last decades. Environmental factors affecting the distribution and persistence of extensive bank reefs of this endemic species across its whole geographic range are poorly understood. In this study, we examined the environmental response of C. caespitosa and its main types of assemblages using ecological niche modeling and ordination analysis. We also predicted other suitable areas for the occurrence of the species and assessed the conservation effectiveness of Mediterranean marine protected areas (MPAs) for this coral. We found that phosphate concentration and wave height were factors affecting both the occurrence of this versatile species and the distribution of its extensive bioconstructions in the Mediterranean Sea. A set of factors (diffuse attenuation coefficient, calcite and nitrate concentrations, mean wave height, sea surface temperature, and shape of the coast) likely act as environmental barriers preventing the species from expansion to the Atlantic Ocean and the Black Sea. Uncertainties in our large-scale statistical results and departures from previous physiological and ecological studies are also discussed under an integrative perspective. This study reveals that Mediterranean MPAs encompass eight of the ten banks and 16 of the 21 beds of C. caespitosa. Preservation of water clarity by avoiding phosphate discharges may improve the protection of this emblematic species.Spanish Ministry of Economy and Competitiveness [CTM2014-57949-R]info:eu-repo/semantics/publishedVersio

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