Genetic variability of macroalgae of the genus Cystoseira in the Gulf of Naples and analysis of the associated molluscs community

Abstract

The brown macroalgae of the genus Cystoseira are amongst the most important ecosystem engineering species along rocky coasts of the Mediterranean Sea establishing structurally complex and diversified habitat. Over the last few decades the disappearance of Cystoseira species has been recorded in wide geographical area as a consequence of anthropogenic impacts. In the Gulf of Naples a recent study to outline historical changes in macroalgal diversity highlighted a drastic decrease of Cystoseira species in the intertidal zones. The decline seems to be largely related to the habitat destruction. In order to assess the consequences of the current process of Cystoseira population fragmentation in the Gulf of Naples at species, population and community level and to provide tools for restoration and coastal management strategies, a multi-approach has been used. The diversity of the genus Cystoseira along the coasts of the Gulf of Naples has been investigated at species, genetic and ecosystem level. The species have been genetically characterized through the analysis of the plastidial psbA gene. Eight microsatellites and the RADSeq, a next-generation sequencing method, have been employed to test their usefulness for connectivity and population genetic studies. Overall Cystoseira associations in the Gulf of Naples show different pattern of genetic variability among and within the species. Cystoseira amentacea and Cystoseira crinita are more variable in terms of polymorphic sites and number of haplotypes compared to Cystoseira compressa and this seems to be related to the evolutionary history of these species rather than to their resilience to the environmental conditions. The molluscs community associated with three Cystoseira species have been characterized and the different pattern of associated diversity have been evaluated. The analysis at community level highlighted the importance of Cystoseira species as nursery for the recruitment of molluscs since only juvenile stages were found. Although the dominance of the bivalve Mytilus galloprovincialis, it is possible to identify some differences in the pattern of association of molluscs community. The three Cystoseira stands harbor a species-rich malacofauna assemblage, a total of 53 mollusc species were identified. The present study outlines the importance of using a multi-approach in the analysis of diversity at different scales of investigation. Moreover the results from the present study might be taken as an incentive for a series of protection and management strategies towards these important habitat forming species.