The rare, giant gorgonian Ellisella paraplexauroides: demographics and conservation concerns

摘要

A striking occurrence of the gorgonian coral Ellisella paraplexauroides off the Chafarinas Islands (western Mediterranean) requires serious conservation attention owing to considerable damage initiated by small fishing operations. Although this gorgonian is among the largest Atlantic-Mediterranean invertebrates, its biology remains virtually unknown. The studied population, established within an area of regulated fishing, was in unusually shallow waters (12-32 m). Density averaged 0.5 colonies m~(-2) (max 5 m~(-2)); colony volume averaged 48 ml (max 511 ml), height averaged 76 cm (max 167 cm), and number of branches averaged 16 (max 72). Allometric growth revealed increasing branching and thickening once colonies reached approximately 60 cm in height. Size distribution suggested moderate to low recruitment. Three geographic zones of fishing pressure (A-C) were semi-quantitatively identified, based on the activity of a small-scale fishing fleet: 'A had the highest level of fishing pressure (frequent gillnetting, trolling lines, and occasional trawling); 'B' had the lowest level (occasional gillnetting and fishing lines), and 'C an intermediate level. Most fishing gear was tangled in the gorgonians in zones A and C. Mortality and colony damage were significantly higher in zones with intensive and poorly regulated fishing activity and appeared unrelated to predation or disease. In high-pressure zone A, about half (44.6%) of the colonies were dead, while about 82% of the surviving colonies showed significant damage, with a large number of epibionts disrupting colony functioning. The Chafarinas population of E. paraplexauroides is likely a unique Mediterranean relic from a Mau-ritanian-Senegalese Pleistocene interglacial expansion but is now being seriously impacted by illegal fishing.