Comparing deep-sea fish fauna between coral and non-coral "megahabitats" in the Santa Maria di Leuca cold-water coral province (Mediterranean Sea)

Abstract

Two experimental longline surveys were carried out in the Santa Maria di Leuca (SML) cold-water coral province (Mediterranean Sea) during May-June and September-October 2010 to investigate the effect of corals on fish assemblages. Two types of "megahabitat" characterized by the virtual absence of fishing were explored. One was characterized by complex topography including mesohabitats with carbonate mounds and corals. The other type of megahabitat, although characterized by complex topographic features, lacks carbonate mounds and corals. The fishing vessel was equipped with a 3,000 m monofilament longline with 500 hooks and snoods of 2.5 m in length. A total of 9 hauls, using about 4,500 hooks, were carried out both in the coral megahabitat and in the non-coral megahabitat during each survey. The fish Leucoraja fullonica and Pteroplatytrygon violacea represent new records for the SML coral province. The coral by-catch was only obtained in the coral megahabitat in about 55% of the stations investigated in both surveys. The total catches and the abundance indices of several species were comparable between the two habitat typologies. The species contributing most to the dissimilarity between the two megahabitat fish assemblages were Pagellus bogaraveo, Galeus melastomus, Etmopterus spinax and Helicolenus dactylopterus for density and P. bogaraveo, Conger conger, Polyprion americanus and G. melastomus for biomass. P. bogaraveo was exclusively collected in the coral megahabitat, whereas C. conger, H. dactylopterus and P. americanus were found with greater abundance in the coral than in the non-coral megahabitat. Differences in the sizes between the two megahabitats were detected in E. spinax, G. melastomus, C. conger and H. dactylopterus. Although these differences most probably related to the presence-absence of corals, both megahabitats investigated play the role of attraction-refuge for deep-sea fish fauna, confirming the important role of the whole SML coral province as a refuge area from fishing.

Figure 1. Santa Maria di Leuca cold-water coral (CWC) province in the Mediterranean Sea and bathymetric framework within the southern Apulia margin (APLABES project - Corselli, 2010).

Figure 2. Longline stations in the coral megahabitat (C) and non-coral megahabitat (NC) in the Santa Maria di Leuca cold-water coral province (Northern Ionian Sea) (Map by Savini et al., submitted).

Figure 3. Non-parametric multidimensional scaling of relative abundance index in number (N/1000 hooks) computed for all the stations carried out in the SML coral province (▴ = coral megahabitat; ▾ = non-coral megahabitat) (Fourth root transformation; Global R = 0.14, not significant).

Figure 4. Non-parametric multidimensional scaling of relative abundance index in number (N/1000 hooks) computed for the stations using J-hook 9 in the SML coral province (▴ = coral megahabitat; ▾ = non-coral megahabitat) (Fourth root transformation; Global R = 0.33; p<0.005).

Figure 5. A live colony of Madrepora oculata with the presence of the solitary Desmophillum dianthus corals collected by longline in the coral megahabitat of the SML cold-water coral province.

Figure 6. Percentage of colonies of cold-water coral species collected by longline in the coral megahabitat of the SML coral province.

Figure 7. Colony of Lophelia pertusa collected by longline in the coral megahabitat of the SML cold-water coral province.

Figure 8. Colonies of Madrepora oculata and Leiopathes glaberrima collected by longline in the coral megahabitat of the SML cold-water coral province.

Figure 9. Length-frequency distribution of Etmopterus spinax, Galeus melastomus and Conger conger in the coral megahabitat (C) and non-coral megahabitat (NC) in the SML cold-water coral province.

Figure 10. Length-frequency distribution of Helicolenus dactylopterus, Merluccius merluccius and Micromesistius poutassou in the coral megahabitat (C) and non-coral megahabitat (NC) in the SML cold-water coral province.

Figure 11. Length-frequency distribution of Pagellus bogaraveo, Phycis blennoides and Polyprion americanus in the coral megahabitat (C) and non-coral megahabitat (NC) in the SML cold-water coral province.