Characterizing biochemical fluctuations within the gastric cavity of solitary cup corals

Master Thesis subject (30 ECTS)
The role of the gastric cavity of corals as hotspot for microbial mechanisms of ecosystem-scale relevance is still rather unexplored. Biochemical conditions within these semi-closed, often anoxic, microniches likely foster metabolic pathways not present in the well-oxygenated surrounding seawater environment. Solitary cup corals living off the south coast of Portugal will allow shedding light on the overlooked relations established between coral hosts and the microbial communities inhabiting their gastric cavity. As a first step to understand such relations we propose to characterize the biochemical variation of this microniche, both spatially (microgradients inside the gastric cavity) and temporally (upon different external conditions). Solitary corals are often disregarded in comparison to their colonial homologs. Furthermore, azooxanthellate corals (without photoautotrophic endosymbionts) lack the capacity to build reefs and are not considered ecosystem keystone species. Solitary cup corals such as the ones living off the south coast of Algarve (Portugal) seem to accumulate a double jeopardy regarding their conservation and that of the habitats they occupy, because of being neither colonial nor zooxanthellate. With this study we ultimately aim at placing these corals in the conservation spotlight by using them as model systems to study the biochemistry of the gastric cavity of invertebrates and infer on potential metabolic pathways active within thes microenvironments. Because the coral’s gastric cavity is a semi-closed sub-environment, it experiences conditions divergent from the surrounding seawater environment, with permanent or temporary anoxic conditions, low but fluctuating pH and high nutrient concentrations. It is therefore possible that the gastric cavity functions as hotspot for biological activity and offers the necessary conditions for metabolic pathways that complement those present in the surrounding ecosystem. Exploring the coral gastric cavity in this project will contribute to characterize this spatially and temporally dynamic system and identify the range of physicochemical conditions experienced by the microbial communities inhabiting such system. The aim is to follow changes in the chemical signature of the gastric cavity environment over time and upon external influence (feeding versus starvation of the host), but also to unravel its internal spatial variability and the putative existence of micro-niches within this cavity. SCUBA-diving will be used to collect coral samples off the south coast of Portugal (based at CCMAR) covering different locations and spatial scales. Target scleractinian species include Caryophyllia smithii and C. inornata, Leptopsammia pruvoti, Balanophyllia regia, Polycyathus muellerae, Phyllangia mouchezii, Hoplangia durotrix, Paracyathus pulchellus and Pourtalosmilia anthophyllites. Sample numbers will be kept low to reduce impact on the ecosystem. Representative specimens will be brought back alive and pre-acclimatized to the aquaria system of CCMAR, in which life-history traits will be studied contributing to elucidating on activity and reproduction of solitary corals in captivity. As a proof of concept, corals were already kept alive in this aquaria system. Mesocosm experiments, including a reduced set of species, will employ feeding/starvation incubations using nauplii of Artemia salina, as well as temperature and nutrient manipulation. Samples will be taken will blunt micro-needles (to avoid epithelium perforation) before treatment and regularly over the course of days. Different times of the day will be compared as zooplankton ingestion occurs mostly during the night. Microscale spatial-temporal variation within the gastric cavity will be monitored throughout mesocosm experiments using microsensors (oxygen, redox potential, pH). Standard samples will be collected with microneedles for characterization of organic and inorganic nutrients with particular emphasis on various nitrogen, sulfur and phosphorus chemical species. Samples will be pooled from more than one coral organism when necessary to obtain amounts needed for particular assays. Databases summarizing differences in the physicochemical composition between distinct hosts, incubation treatments and microniches within the gastric cavity will be analyzed using specific R packages for multivariate statistics.
Relevant experience with biochemical assays, excellent written and spoken English, demonstrated capacity to handle experimental setups, motivation to do long working hours in the lab, willingness to work both independently and as part of a larger team.
Number of students: 
academic year: 
Contact person email: 
contact person first name: 
Dr. Pedro Frade
Other people involved: 
Prof. dr. Ester Serrão as promoter and Dr. Aschwin Engelen as co-supervisor.
Reference Number: RP-39951