Low diversity or poorly explored? Mesophotic molluscs highlight undersampling in the Eastern Mediterranean

Paolo G. Albano,Bruno Amati,Gil Rilov,Michele Azzarone,Cesare Bogi,Bruno Sabelli

doi:10.1007/s10531-020-02063-w

Abstract

Mesophotic assemblages are the next frontier of marine exploration in the Mediterranean Sea. Located below recreational scuba diving depths, they are difficult to access but host a diverse array of habitats structured by large invertebrate species. The Eastern Mediterranean has been much less explored than the western part of the basin and its mesophotic habitats are virtually unknown. We here describe two mesophotic (77–92 m depth) molluscan assemblages at a rocky reef and on a soft substrate off northern Israel. We record 172 species, of which 43 (25%) are first records for Israel and increase its overall marine molluscan diversity by 7%. Only five of these species have been reported in recent surveys of the nearby Lebanon, suggesting that our results are robust at a broader scale than our study area and that the reported west-to-east declining diversity gradient in the Mediterranean needs a reappraisal based on proper sampling of the eastern basin. We found only four (2%) non-indigenous species, represented by seven (0.5%) specimens. These results suggest that pristine native assemblages still thrive at this depth in Israel, in contrast to the shallow subtidal heavily affected by global warming and biological invasions, calling for strong conservation actions for these valuable but vulnerable habitats.

Highlights

Mesophotic ecosystems are located between * 40 m and * 150 m depth where low light is a dominant abiotic feature (Lesser et al 2009; Cerrano et al 2010)
We record 172 species, of which 43 (25%) are first records for Israel and increase its overall marine molluscan diversity by 7%. Five of these species have been reported in recent surveys of the nearby Lebanon, suggesting that our results are robust at a broader scale than our study area and that the reported west-to-east declining diversity gradient in the Mediterranean needs a reappraisal based on proper sampling of the eastern basin
These results suggest that pristine native assemblages still thrive at this depth in Israel, in contrast to the shallow subtidal heavily affected by global warming and biological invasions, calling for strong conservation actions for these valuable but vulnerable habitats

Summary

Introduction

Mesophotic ecosystems are located between * 40 m and * 150 m depth where low light is a dominant abiotic feature (Lesser et al 2009; Cerrano et al 2010). 2016; Corriero et al 2019; Chimienti et al 2020), bivalves (Cardone et al 2020) and sponges (Bo et al 2011; Idan et al 2018) Notwithstanding the depth, these communities are under anthropogenic pressure due to stressors such as climate warming (Cerrano et al 2000; Garrabou et al 2001, 2009), fishing and trawling (Rossi 2013; Bo et al 2014). Molluscs are a taxonomically and functionally diverse phylum and some species can be important ecosystem engineers (Gutierrez et al 2003). They show a high level of correlation with overall species richness and community patterns on both hard and soft substrates (Ellingsen 2002; Smith 2005).

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Results

Conclusion