Description: Benthic suspension feeders have developed a variety of feeding strategies and food availability has often proven to be a key factor explaining their occurrence and distribution. The feeding biology of coral species has been the target of an increasing number of studies, however most of them focus on Scleractinia and Octocorallia, while information for Antipatharia is very scarce. The present study focused on Antipathella wollastoni, a common habitat-forming antipatharian in the Azores Archipelago, forming dense black coral forests between 20 and 150 meters. The objective of the study was to investigate the food preferences of the target species upon availability of different isotopically enriched food substrates and determine its ability to capture zooplankton prey under different flow speeds. The species was able to utilize different food sources including live phytoplankton, live zooplankton and Dissolved Organic Matter (DOM), indicating the ability to exploit seasonally available food sources. However ingestion of zooplankton enhanced Carbon (C) and Nitrogen (N) incorporation in coral tissue and metabolic activity, highlighting the importance of zooplankton prey for vital physiological processes such as growth and reproduction. The species displayed a high capacity to capture zooplankton prey over different flow rates, however capture rates were higher under 4 cm s-1, highlighting the ability of A. wollastoni to exploit high quantities of shortly available prey.

Description: The majority of octocoral species are found in waters deeper than 50m where they create three-dimensional and highly heterogenous habitats known as coral gardens. The Azores Archipelago is an octocoral biodiversity hotspot and coral gardens are one of the most prominent deep-sea communities encountered regionally. Although food availability and flow have been recognized as key factors in determining the dynamics of suspension feeder communities, very little information exists on how flow affects the feeding capacity of deep octocoral species. The study focused on two common habitat-forming octocoral species in the Azores, Dentomuricea meteor and Viminella flagellum, aiming at determining their ability to capture zooplankton prey under variable flow velocities. The rotifer Branchionus plicatilis was used as prey, while three flow velocities were established in recirculating 13L flumes: 3 cm/s, 6 cm/s and 9 cm/s. Both species efficiently captured zooplankton prey. Capture rates were lower under 3 cm/s, however no difference was detected between 6 and 9 cm/s. Dentomuricea meteor reached higher capture rates per polyp than V.flagellum, possibly due to their differences in polyp size and density.

Description: Coral gardens are considered to be hotspots of biodiversity and ecosystem functioning, due to the important structural and biogeochemical role of cold-water coral (CWC) species. Despite an increase in studies on deep reef-forming species, information on cold-water octocoral species is still very scarce. The present study focused on the feeding biology of two habitat-forming octocoral species typically encountered in seamounts in the Azores between 200 and 600m of depth: Dentomuricea aff. meteor and Viminella flagellum. We used an experimental approach aiming at determining the ability of the species to utilize different food sources including live phytoplankton (the diatom Chaetoceros calcitrans), Dissolved Organic Carbon (DOC) and live zooplankton (the rotifer Branchionus plicatilis). Food sources were isotopically enriched with tracers (13C, 15N) which allowed to trace the ingested food in different physiological processes, such as tissue incorporation, Dissolved Inorganic Carbon (DIC) respiration and excretion of Particulate Organic Carbon (POC) and Particulate Organic Nitrogen (PON).

Description: In the North Patagonian fjord region, the cold-water coral (CWC) Desmophyllum dianthus occurs in high densities, in spite of low pH and aragonite saturation. If and how these conditions affect the energy demand of the corals is so far unknown. In a laboratory experiment, we investigated the carbon and nitrogen (C, N) budget of D. dianthus from Comau Fjord under three feeding scenarios: (1) live fjord zooplankton (100 2,300 mm), (2) live fjord zooplankton plus krill (〉7 mm), and (3) four-day food deprivation. In closed incubations, C and N budgets were derived from the difference between C and N uptake during feeding and subsequent C and N loss through respiration, ammonium excretion, release of particulate organic carbon and nitrogen (POC, PON). Additional feeding with krill significantly increased coral respiration (35%), excretion (131%), and POC release (67%) compared to feeding on zooplankton only. Nevertheless, the higher C and N losses were overcompensated by the threefold higher C and N uptake, indicating a high assimilation and growth efficiency for the krill plus zooplankton diet. In contrast, short food deprivation caused a substantial reduction in respiration (59%), excretion (54%), release of POC (73%) and PON (87%) compared to feeding on zooplankton, suggesting a high potential to acclimatize to food scarcity (e.g., in winter). Notwithstanding, unfed corals `lost' 2% of their tissue-C and 1.2% of their tissue-N per day in terms of metabolism and released particulate organic matter (likely mucus). To balance the C (N) losses, each D. dianthus polyp has to consume around 700 (400) zooplankters per day. The capture of a single, large krill individual, however, provides enough C and N to compensate daily C and N losses and grow tissue reserves, suggesting that krill plays an important nutritional role for the fjord corals. Efficient krill and zooplankton capture, as well as dietary and metabolic flexibility, may enable D. dianthus to thrive under adverse environmental conditions in its fjord habitat; however, it is not known how combined anthropogenic warming, acidification and eutrophication jeopardize the energy balance of this important habitat-building species.

Description: Knowledge on basic biological functions of organisms is essential to understand not only the role they play in the ecosystems but also to manage and protect their populations. The study of biological processes, such as growth, reproduction and physiology, which can be approached in situ or by collecting specimens and rearing them in aquaria, is particularly challenging for deep-sea organisms like cold-water corals. Field experimental work and monitoring of deep-sea populations is still a chimera. Only a handful of research institutes or companies has been able to install in situ marine observatories in the Mediterranean Sea or elsewhere, which facilitate a continuous monitoring of deep-sea ecosystems. Hence, today’s best way to obtain basic biological information on these organisms is (1) working with collected samples and analysing them post-mortem and / or (2) cultivating corals in aquaria in order to monitor biological processes and investigate coral behaviour and physiological responses under different experimental treatments. The first challenging aspect is the collection process, which implies the use of oceanographic research vessels in most occasions since these organisms inhabit areas between ca. 150 m to more than 1000 m depth, and specific sampling gears. The next challenge is the maintenance of the animals on board (in situations where cruises may take weeks) and their transport to home laboratories. Maintenance in the home laboratories is also extremely challenging since special conditions and set-ups are needed to conduct experimental studies to obtain information on the biological processes of these animals. The complexity of the natural environment from which the corals were collected cannot be exactly replicated within the laboratory setting; a fact which has led some researchers to question the validity of work and conclusions drawn from such undertakings. It is evident that aquaria experiments cannot perfectly reflect the real environmental and trophic conditions where these organisms occur, but: (1) in most cases we do not have the possibility to obtain equivalent in situ information and (2) even with limitations, they produce relevant information about the biological limits of the species, which is especially valuable when considering potential future climate change scenarios. This chapter includes many contributions from different authors and is envisioned as both to be a practical “handbook” for conducting cold-water coral aquaria work, whilst at the same time offering an overview on the cold-water coral research conducted in Mediterranean laboratories equipped with aquaria infrastructure. Experiences from Atlantic and Pacific laboratories with extensive experience with cold-water coral work have also contributed to this chapter, as their procedures are valuable to any researcher interested in conducting experimental work with cold-water corals in aquaria. It was impossible to include contributions from all laboratories in the world currently working experimentally with cold-water corals in the laboratory, but at the conclusion of the chapter we attempt, to our best of our knowledge, to supply a list of several laboratories with operational cold-water coral aquaria facilities.