Combining Methods to Better Estimate Total Fish Richness on Temperate Reefs: The Case of a Mediterranean Coralligenous Cliff

Abstract

Coralligenous habitat is considered as one of the most important special habitat types in the Mediterranean; however, due to its inaccessibility, little is known about it, although it is considered as one of the Mediterranean’s richest habitats in terms of species. Due to a low number of studies, it was presumed that the richness of coralligenous fish assemblages is underestimated using traditional visual census methods which are not applicable to the deep, steep, and vertical slopes of coralligenous cliffs and do not capture exhaustively cryptobenthic species commonly found in this habitat. This paper aims at producing a more complete assessment of fish assemblages on a coralligenous cliff by combining different methods, particularly the deep vertical transect visual census and square with anesthetics method. A total of 76 fish species were recorded on a single coralligenous cliff, supporting the opinion that coralligenous cliffs are important Mediterranean biodiversity hotspots. The analysis of species traits between species recorded by the different methods showed how complementary they are to better describe species compositions. Hence, the result of this study demonstrates that the combined use of methods is essential for a more exhaustive description of the whole fish community structure and for accurate estimates of the abundance and diversity patterns, particularly in complex habitats such as coralligenous cliffs.