Description: Growth rates of the cold-water corals (CWC) Madrepora oculata, Lophelia pertusa, Desmophyllum dianthus and Dendrophyllia cornigera were measured over 8 mo under controlled conditions (12°C in the dark, fed 5 times a week) by means of the buoyant weight technique. Additionally, linear growth rates were measured in M. oculata and L. pertusa for 2 and 1 yr, respectively. The weight measurements revealed growth rates, expressed as percent growth per day (mean ± SD), of 0.11 ± 0.04 for M. oculata, 0.02 ± 0.01 for L. pertusa, 0.06 ± 0.03 for D. dianthus and 0.04 ± 0.02 % d–1 for D. cornigera. Growth in M. oculata was significantly higher (p 〈 0.0001) than in the other 3 CWC species. For M. oculata and L. pertusa, also linear growth was recorded. These values (mean ± SD) were 0.014 ± 0.007 and 0.024 ± 0.018 mm d–1 for M. oculata and L. pertusa, respectively. This is the first study that compares the growth rates of 4 different CWC species under the same experimental conditions of water flow, temperature, salinity and food supply. These corals have different growth rates, both in terms of total weight increase and linear increase, and these growth rates can be related to interspecific physiological differences. Data on growth rates are essential to understand the population dynamics of CWC as well as the recovery capacity of these communities after disturbance.

Description: Little is known about the basic biology of deep-water coral species. In this study, we experimentally assessed the rates of ingestion of Artemia salina adults and nauplii by the 4 Mediterranean cold water coral species Dendrophyllia cornigera, Desmophyllum cristagalli, Madrepora oculata, and Lophelia pertusa. All species ingested A. salina in adult and nauplii forms. L. pertusa showed the highest grazing rate for both prey types, whereas M. oculata showed the lowest capture rates among the 4 species, and was practically unable to ingest adult prey. Capture rates of the 4 coral species ranged between 5 and 8 adult A. salina, and 50 and 280 nauplii polyp–1 h–1. Surprisingly, both capture rates and carbon uptake (adult Artemia ingestion: 994 to 3542 µg C polyp–1 h–1; nauplii ingestion: 78.1 to 462 µg C polyp–1 h–1) were within the range of values found in some tropical corals (which often ingest 0.004 to 3600 prey items polyp–1 h–1). The results show that the capture rates and energy input of the studied cold water coral species appear to be on a level that is comparable to that of other corals, even tropical zooxanthellate species.

Description: Octocorals are an important part of many ecosystems as they add three-dimensional complexity to the benthos and thereby increase biodiversity. The Mediterranean red coral (Corallium rubrum, L. 1758) is a longevous octocoral that is harvested commercially, yet natural and anthropogenic influences on its population size structure are little understood. This study found that some harvested red coral populations had a significantly different size structure when compared to populations at the nearby Marine Protected Area (MPA) of Medas Islands at the Spanish Costa Brava (NW Mediterranean). Eighty-nine percent of the red corals in the harvested Costa Brava area are less than 10 years old and 96% of all colonies have not yet grown more than second-order branches. The size/age distribution of the harvested population is notably skewed towards younger and smaller colonies. Thus, although red coral is still abundant, its population structure is strongly distorted by harvesting. The results confirm that MPAs are useful to distinguish between anthropogenic and natural influences on population structure. However, 14 years of protection appears to be an insufficient recovery time for a longevous octocoral population such as red coral.

Description: Gorgonians are passive suspension feeders, contributing significantly to the energy flow of littoral ecosystems. More than in active suspension feeders (such as bivalves, ascidians and sponges) their prey capture is affected by spatial and temporal prey distribution and water movement. Corallium rubrum is a characteristic gorgonian of Mediterranean sublittoral hard bottom communities. This study found a high variability in the annual cycle of prey capture rate, prey size and ingested biomass, compared to other Mediterranean gorgonians. Detrital particulate organic matter (POM) was found throughout the year in the polyp guts and constituted the main proportion of the diet (2544%). Crustacean fragments and copepods (1446%) accounted for the second major proportion, while invertebrate eggs (915%) and phytoplankton (811%) constituted the smallest part of the diet. To verify the importance of detrital POM in the energy input of this precious octocoral species, in situ experiments were carried out during the winterspring period. The results confirm the importance of detrital POM as the main source of food for C. rubrum [0.13±0.04 μg C polyp−1 h−1 (mean±SD)]. This study also compares the prey capture rates of two colony size classes and two depth strata: Within the same patch, small colonies (〈6 cm height) captured significantly more prey per polyp (0.038±0.09 prey polyp−1 h−1) than larger colonies (〉10 cm high) (0.026±0.097 prey polyp−1 h−1) and showed a higher proportion of polyps containing prey (17% compared to 10%). Comparing colonies of similar size (〈6 cm height) revealed that the colonies situated at 40 m depth captured significantly more prey (0.038±0.09 prey polyp−1 h−1) than the ones at 20 m (0.025±0.11 prey polyp−1 h−1). One pulse of copepods was recorded that constituted 16% of all captured prey during the 15-month period studied in one of the sampled populations. The data suggest that the variability of hydrodynamic processes may have a higher influence on the feeding rate than seasonal changes in the seston composition. The carbon ingestion combined with data on the density of the exploited population results in 0.49.6 mg C m−2 day−1. The grazing impact of current, heavily exploited and small-sized populations is comparable to that of larger Mediterranean gorgonians, suggesting that unexploited red coral populations may have a high impact compared with other passive suspension feeders.

Description: The Mediterranean red coral (Corallium rubrum, L. 1758) is a characteristical gorgonian living in semidark habitats in the coralligenous zone of sublittoral hard bottoms. Despite being harvested commercially for the use of its red calcium carbonate skeleton in the jewelery industry, its ecology is still little understood. Thus the objective of this study was to increase knowledge on the population structure, reproduction and feeding ecology of red coral and to use these data to evaluate the efficiency of current management strategies of this species.The size/age structure of a population records valuable information, summarising the effects of mortality, recruitment and growth of past years. The six studied populations at the Costa Brava (NE Spain) consisted mainly of small/young colonies, as larger colonies are commercially exploited. Average size and age were estimated at 3 cm height and 7.5 years, whereas the species is capable of reaching 50 cm and 100 years. Furthermore, these young populations consist of colonies that have developed only few branches, offering considerably less three dimensional structure to the ecosystem than unharvested populations. One of the studied populations is located in a protected area, the Medas Islands Marine Park, and consisted of significantly larger/older colonies, thus allowing to distinguish harvesting effects from environmental ones.The reproductive output of red coral was found to significantly depend on colony size, having important implications for its management. Another aspect of potential importance for optimal harvesting is mesoscale variation of reproductive output. In a comparison of eight stations, however, we did not find significant differences, indicatig a homogenous reproduction. Colonies in deep water were found to spawn slightly earlier than shallow water ones, however, this phenomenon was observed only when temperature stratification in summer was particularly pronounced. Yet depth was not found to affect reproductive output itself, again in contrast to the demographic features.The trophic ecology is one of the key aspects of the biology of an organism, helping to understand its demography and reproductive biology. The main proportion of the diet of Corallium rubrum was found to be particulate organic matter, while crustaceans such as copepods played a smaller role due to the irregular capture. Red coral appear to be able to meet their energy requirements by constant access of resuspended detritic material, while taking advantage of occasional capture of large zooplankters. Prey capture rate per polyp is higher in small colonies, and also in colonies situated in deep water. We did not find a clear seasonal pattern in red coral feeding, as observed in some gorgonians, which indicates that changes in water movement have a stronger effect on the prey capture rate than the seasonal succession of the plankton. The grazing impact of red coral populations was estimated to be lower than that by other gorgonians, which is a result of its population structure being dominated by small colonies.Ecological data like those presented in this study are the base for ecosystem management, as they allow to calculate the secondary production of a population. We therefore used the demography and reproduction data to provide managment recommendations for red coral, by using the Beverton-Holt fishery management model to calculate maximum sustainable yield. The results show that the red coral fishery at the Costa Brava would reach its maximum yield only at a considerable age of first capture, whereas the colonies are harvested at a much younger age. This results in an estimated annual catch that is only a fraction of what could be harvested using an optimised management strategy. Furthermore, harvesting at this age provides a short reproductive period before capture, compared for example to the sustainable fishery of black coral in Hawaii. The comparison of calculated and declared harvests indicates considerable poaching activities and undeclared harvest. Finally, a recent rise in mortality confirms a non-sustainable level of harvesting.Concluding, the results confirm the paramount importance of data on the reproductive biology and population structure of a species for its management. In this study we investigated the effects of harvesting, spacial mesoscale variability and depth on the population structure, reproduction and feeding ecology of red coral. The data show that red coral populations at the Costa Brava are very young and have a diminished reproductive potential due to overharvesting, yet show a considerable impact on the seston. Protecting young colonies is proposed as the central management measure.