Fish Distribution and Habitat Complexity on Banks of the Strait of Sicily (Central Mediterranean Sea) from Remotely-Operated Vehicle (ROV) Explorations

Abstract

The Strait of Sicily was recognized internationally as an "Ecologically or Biologically Significant Area" by the Contracting Parties of the Convention on Biological Diversity in 2014. However, basic aspects of its fish diversity are still unknown and most of the information comes from traditional trawl surveys. This paper provides the first detailed description, using a Remotely Operated Vehicle (ROV), of the composition and depth distribution of the demersal fish assemblages found on banks of the Strait of Sicily and the related habitat complexity from 35 to 240 m depth. A total of 24 families and 52 fish species were recorded and depth was consistently associated with a significant proportion of the variation of the fish assemblage. The highest species richness was observed at the shallowest depth layer (0-50 m) and significantly decreased, remaining almost constant, in deeper layers. Similarly the highest abundance was recorded at 0-50 m, where C. julis represented the most abundant species, and decreased progressively throughout the whole depth gradient. Although the factor habitat complexity explained only a small proportion of the fish assemblage variation, significant differences among different degrees of habitat complexity were observed, together with a general positive trend for species richness and abundance with increasing habitat complexity. The ROV also allowed us to observe some rare or poorly known fish species such as Scorpaenodes arenai, Hyporthodus haifensis, Myliobatis aquila, Gadella maraldi, Epinephelus caninus and Lappanella fasciata. These findings show that banks serve as reservoirs for fish abundance and biodiversity and that immediate environmental conservation and management actions represent a priority not only for Italy but also for other countries which share the same area.

Fig 1. Study area.

Investigated banks of the Strait of Sicily following the official delimitation of the Italian Hydrographic Institute of the Navy. (Base map from Natural Earth).

Fig 2. In situ photographs of benthic habitats in banks of the Strait of Sicily.

(A) Helicolenus dactylopterus on soft sediment, low relief; (B) rhodolith beds, low relief; (C) colonies of Eunicella cavolinii on medium relief bedrock; (D) Macrofauna assemblage forming a medium relief habitat; (E) Savalia savaglia on high relief bedrock with a school of Anthias anthias in the background; (F) high relief coralligenous habitat; (G) school of A. anthias swimming close to fan-shaped Corallium rubrum on a high complexity habitat; (H) Ghost net on soft sediment.

Fig 3. Multidimensional Scaling (MDS) of the composition of fish assemblages among different depth ranges.

Triangle = 0–50 m; square = 51–100 m; rhombus = 101–500 m; circle = 151–200 m.

Fig 4. Correspondence analysis (CA) per sampling depth.

Ordination diagrams for the first two canonical axes of the correspondence analysis performed on species relative abundance data per sampling depth. Species codes as in Table 2.

Fig 5. Preferred depth for fish on banks of the Strait of Sicily.

Weighted average depth ± max/min depth.

Fig 6. Multidimensional Scaling (MDS) of the composition of fish assemblages among different degrees of habitat complexity.

Circle = low complexity; triangle = medium complexity; rhombus = high complexity.

Fig 7. Correspondence analysis (CA) per Habitat complexity.

Ordination diagrams for the first two canonical axes of the correspondence analysis performed on species relative abundance data per Habitat complexity. Species codes as in Table 2.

Fig 8. Representative demersal fish species from the banks of the Strait of Sicily.

(A) Epinephelus caninus; (B) Scorpaenodes arenai; (C) Gadella maraldi; (D) Macroramphosus scolopax; (E) Hyporthodus haifensis; (F) Callanthias ruber; (G) Myliobatis aquila; (H) Phycis phycis.