Stefano Ambroso

Variation in lipid and free fatty acid content during spawning in two temperate octocorals with different reproductive strategies: surface versus internal brooder

AbstractThis study investigates the energetic investment during spawning of two Mediterranean gorgonians characterized by different reproductive strategies: Corallium rubrum (internal brooder) and Paramuricea clavata (surface brooder). Sexual products (number of oocytes and spermatic sacs) were quantified, and biochemical characteristics (lipid content and free fatty acid content and composition) were determined to investigate the parental energetic investment and demand in reproduction. Results suggested that the majority of the energetic cost was due to reproductive activity (i.e., gametogenesis and spawning). The two species exhibited different life history strategies, with P. clavata investing more energy in reproduction than C. rubrum. However, P. clavata is reproductively more sensitive to inter-annual changes in environmental conditions.

In situ observations on withdrawal behaviour of the sea pen Virgularia mirabilis

Sessile marine organisms respond to environmental disturbance and predation by means of different adaptive strategies. Sea pens (Octocorallia, Pennatulacea) are colonial cnidarians adapted to survive on the muddy and sandy bottoms of the continental shelf and slope. Some of them can withdraw partially or completely into the sediment on an apparent rhythmic but unsynchronized procedure (Langton et al. 1990). Withdrawal into the sand or mud by sea pens tend to be preceded by the closure of the polyps and the expulsion of the water contained within the colony (Hoare and Wilson 1977). Only a few contractions are generally sufficient for the animal to hide into the mud and some colonies can withdraw into the sediment within few seconds if disturbed. The reasons for suchwithdrawal and extension behaviour of sea pens are not well understood, and the existing information is equivocal. Hoare and Wilson (1977) described a possible tidal-based rhythm for Virgularia mirabilis while Wilson (1975), using time-lapse photography, found a 22to 27-h rhythm for this species that was independent of lighting and tidal regime. Anyhow, there is a lack of in situ observations to provide evidence for this type of behaviour in the field. Here, observations are presented for the first time on the withdrawal behaviour of Virgularia mirabilis (for identification, see Greathead et al. 2007). They were made at ca 100 m depth bymeans of a Remotely OperatedVehicle (ROV) in themobile bottoms of the continental shelf, showing that this species retracts smoothly and with the polyps fully expanded (see Fig. 1 and Online Resource 1).

Ophiuroid biodiversity patterns along the Antarctic Peninsula

Benthic ecological surveys using standardized methods are crucial for assessing changes associated with several threats in the Southern Ocean. The acquisition of data on assemblage structure over a variety of spatial scales is important to understand the variation of biodiversity patterns. During the ANT XXIX/3 (PS81) expedition of RV Polarstern, three different regions at the tip of the Antarctic Peninsula were sampled: the northwestern Weddell Sea, the Bransfield Strait, and the northern boundary of the South Shetland Archipelago in the Drake Passage. The aim of this study was to characterize the distribution and biodiversity patterns of ophiuroid assemblages in these regions and depths. We quantified different community parameters in terms of the number of species, abundance, and biomass. Additionally, we calculated various components of species diversity (alpha, beta, and gamma diversity) over the three regions. Based on the benthic surveys, we collected 3331 individuals that were identified to species level (17 species). Overall, species diversity, as measured based on rarefaction, species richness and evenness estimators, was higher in the Bransfield Strait compared to the Weddell Sea and Drake Passage. Two deep stations in the Weddell Sea showed high dominance only of Ophionotus victoriae. Significant differences in the patterns of alpha diversity were found among the regions but not between depth zones, whereas beta diversity showed no differences. Regarding the resemblance among the ophiuroid assemblages of each region, there was a significant gradient from east to west with a maximum distance between the stations in the Drake Passage and the Weddell Sea. This study provides a baseline for detecting potential effects related to climate change, and it furnishes a basis for the implementation of monitoring schemes of Antarctic assemblages.

Animal Forests in Deep Coastal Bottoms and Continental Shelf of the Mediterranean Sea

Several studies using Remotely Operated Vehicles and manned submersibles have recently provided quantitative information on animal forests dominated by gorgonians, black corals, and sponges dwelling at 40–200 m depth in the Mediterranean Sea. These assemblages have received relatively little attention during the last decades due to the fact that they are found below scuba diving depths, and most submersible-based research has been traditionally conducted below 200 m depth. However, these communities are among the most threatened by the impact of fishing pressure, since the larger proportion of fishing activities, especially bottom trawling on soft bottoms and passive gears on hard grounds, concentrate between 50 and 200 m depth. This chapter reviews the recent advances in the study of the spatial and bathymetric distribution patterns of these animal forests, their species composition, ecology, and conservation status.

Pristine populations of habitat-forming gorgonian species on the Antarctic continental shelf

Declines in the abundance of long-lived and habitat-forming species on continental shelves have attracted particular attention given their importance to ecosystem structure and function of marine habitats. The study of undisturbed habitats defined as “pristine areas” is essential in creating a frame of reference for natural habitats free of human interference. Gorgonian species are one of the key structure-forming taxa in benthic communities on the Antarctic continental shelf. Current knowledge of the diversity, distribution and demography of this group is relatively limited in Antarctica. To overcome this lack of information we present original data on pristine and remote populations of gorgonians from the Weddell Sea, some of which display the largest colony sizes ever recorded in Antarctica. We assessed the distribution patterns of seven gorgonian species, a morphogroup and a family in front of the Filchner Ronne Ice Shelf (Weddell Sea) by means of quantitative analysis of video transects. Analysis of these videos showed a total of 3140 colonies of gorgonians with the highest abundance in the southern section and a significantly clumped distribution. This study contributes to the general knowledge of pristine areas of the continental shelf and identifies the eastern Weddell Sea as a hotspot for habitat-forming species.