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Simple Summary Some corals belonging to the orders Alcyonacea and Antipatharia have elongated, unbranched shapes, and are generally addressed as sea whips. The octocorals Viminella flagellum are the main sea whip species inhabiting the Mediterranean Sea, where they can form large colony aggregations known as coral forests. These habitats are of great conservation importance; they provide a suite of ecosystem goods and services, and their monitoring is essential to plan appropriate conservation strategies. One of the most important indicators on the status of a coral forest is its population structure, such as the frequency of different size classes within the coral population. This is very difficult to assess in sea whips because of the length and high flexibility. Here, we report on the findings of a newly discovered, monospecific forest of V. flagellum in Aeolian Archipelago (Mediterranean Sea), and we present a new method to study its population structure using video analysis. The results of the survey indicate that the Aeolian coral population was in good condition, without significant anthropogenic impacts. The new method presented here proved to be an effective and promising tool for the monitoring of this vulnerable marine ecosystem. It can be applied to every known population of V. flagellum as well as adapted to other sea-whip species. Abstract Coral forests are vulnerable marine ecosystems formed by arborescent corals (e.g., Anthozoa of the orders Alcyonacea and Antipatharia). The population structure of the habitat-forming corals can inform on the status of the habitat, representing an essential aspect to monitor. Most Mediterranean corals live in the mesophotic and aphotic zones, and their population structures can be assessed by analyzing images collected by underwater vehicles. This is still not possible in whip-like corals, whose colony lengths and flexibilities impede the taking of direct length measurements from images. This study reports on the occurrence of a monospecific forest, of the whip coral Viminella flagellum in the Aeolian Archipelago (Southern Tyrrhenian Sea; 149 m depth), and the assessment of its population structure through an ad-hoc, non-invasive method to estimate a colony height based on its width. The forest of V. flagellum showed a mean density of 19.4 ± 0.2 colonies m−2 (up to 44.8 colonies m−2) and no signs of anthropogenic impacts. The population was dominated by young colonies, with the presence of large adults and active recruitment. The new model proved to be effective for non-invasive monitoring of this near threatened species, representing a needed step towards appropriate conservation actions.

Coral forests are vulnerable marine ecosystems formed by arborescent corals (e.g., Anthozoa of the orders Alcyonacea and Antipatharia). The population structure of the habitat-forming corals can inform on the status of the habitat, representing an essential aspect to monitor. Most Mediterranean corals live in the mesophotic and aphotic zones, and their population structures can be assessed by analyzing images collected by underwater vehicles. This is still not possible in whip-like corals, whose colony lengths and flexibilities impede the taking of direct length measurements from images. This study reports on the occurrence of a monospecific forest, of the whip coral Viminella flagellum in the Aeolian Archipelago (Southern Tyrrhenian Sea; 149 m depth), and the assessment of its population structure through an ad-hoc, non-invasive method to estimate a colony height based on its width. The forest of V. flagellum showed a mean density of 19.4 ± 0.2 colonies m−2 (up to 44.8 colonies m−2) and no signs of anthropogenic impacts. The population was dominated by young colonies, with the presence of large adults and active recruitment. The new model proved to be effective for non-invasive monitoring of this near threatened species, representing a needed step towards appropriate conservation actions.

15 pages, 6 figures, 4 tables, Population dynamics, morphology, density, lipid contents and prey capture rates were studied in a patchy population of the tree-like passive suspension feeder Eudendrium racemosum (Cnidaria: Hydrozoa) during seasonal cycles. Density and size of colonies oscillated due to intraspecific competition (following the self-thinning rule) and predation (nudibranchs) showing size distributions in which alternatively large-and small-sized colonies were more abundant. Increase in the trophic impact on the water column was correlated with colony size (30.7 mg C m -2 d -1 in late spring-early summer compared with 10.2 mg C m -2 d -1 in the rest of the year). Lipid accumulation in the hydrocauli followed the same trend, being higher during the reproductive period (140 μg lipids mg -1 organic matter [OM]) compared with the rest of the year (70 μg lipids mg -1 OM). The short time cyclic variations reproduce, in a short time scale, the variations studied in other benthic suspension feeders, suggesting E. racemosum as a model organism to better understand the importance of large colonies in long-lived species in benthic-pelagic coupling processes. The accordance with the self-thinning rule found for this animal species strengthens the animal forest concept (a 3-dimensional live structure composed mainly by heterotrophic organisms such as gorgonians, bryozoans, and sponges), confirming the validity of the utilization, by marine ecologists, of the conceptual tools developed for terrestrial forest sciences. It is suggested that the impact of mature populations on benthic-pelagic coupling and biogeochemical cycles, simulated for long-lived species, could be validated by studying fast-growing species, in order to understand the importance of the preservation of complex structures and long-lived eco-engineering organisms in benthic habitats. © Inter-Research 2012, Support for this work was provided by a FPI fellowship from the ‘Ministerio de Educación y Ciencia’ and a Ramón y Cajal Contract (RyC-2007-01327) to S.R., by a CICYT grant and by the MAST-III-ELOISE European Union METRO MED Project. L.B. was supported by a Marie Curie Intra-European Fellowship within the 7th European Community Framework Programme (Project No. 221072