Effects of deep-water coral banks on the abundance and size structure of the megafauna in the Mediterranean Sea

摘要

The Santa Maria di Leuca (SML) coral banks represent a rare example of living Lophelia-Madrepora-bearing coral mounds in the Mediterranean Sea. They are located between 350 and 1100 m in depth, in the northern Ionian Sea (eastern-central Mediterranean). Using a multi-beam echo sounder, side-scan sonar, high-resolution seismics and underwater video, the zones were identified for the sampling demersal fauna without damaging the coral colonies. During September-October 2005 experimental samplings were carried out with longlines and trawl nets inside the coral habitat and outside, where fishery exploitation occurs. No significant differences were shown between the abundance of fish recorded using longlines in the coral and non-coral habitat even though some selachians and teleosts were more abundant in the former than in the latter. Large specimens of rockfish (Helicolenus dactylopterus) and blackspot seabream (Pagellus bogaraveo) were commonly caught using longlines in the coral habitat. Data from trawling revealed refuge effects in the coral habitat and fishing effects outside. Significant differences were detected between the recorded abundances in the two study areas. Greater densities and biomasses were obtained inside the coral area, and fish size spectra and size distributions indicate a greater abundance of large fish inside the coral habitat. The SML coral habitat is a spawning area for H. dactylopterus. The remarkable density of the young-of-the-year of the deep-water shark Etmopterus spinax as well as of Merluccius merluccius, Micromesistius poutassou, Phycis blennoides and H. dactylopterus, indicates that the coral habitat also acts as nursery area for these demersal species, which are exploited outside. Considering the evidence of the negative impact of bottom trawling and, to a lesser extent, of longlining, the coral banks can provide a refuge for the conservation of unique species and habitats as well as in providing benefit to adjacent fisheries through the spill-over effect both of eggs, larvae, juveniles and adults.