Genetic dis/similarities between western Mediterranean and eastern Atlantic populations of the honeycomb worm <i>Sabellaria alveolata</i> (Polychaeta: sabellariidae)

Thanks to their ability to build three-dimensional bioconstructions, Sabellaria worms strongly regulate community structure and ecosystem functioning in coastal ecosystems. Such reefs and the degree of connectivity between them are crucial for identifying population units that are relevant in conservation strategy and management. To help bridge the gap in connectivity information about the Sabellaria alveolata reefs, this study is focused on the genetic characterization of some populations along the Italian coast to compare them with other Mediterranean and Atlantic reefs; explore the correlation between genetic and geographical distances; and infer the extent of connectivity between these populations. Ten reefs were investigated: seven in the Mediterranean and three in the Atlantic. A region of 608 nucleotides in mtCOI was sequenced in six reefs from Tyrrhenian Sea (Latium, Italy) and in a reef from the Atlantic French coast. Sequences from two Portuguese and one Sicily populations were obtained from the Barcode of Life Data (BOLD) Systems database for comparison. The spatial comparative analysis revealed the smallest genetic differences within the Atlantic populations and the greatest differences between the Atlantic and the Mediterranean populations, thus demonstrating a general decrease in genetic similarity with increasing geographical distance, as the genetic distance regression on geographic distance, clustering and ordination analyses supported. A striking genetic distance emerged between the populations of Latium and that of Sicily, showing, in particular, a considerably higher number of differences with Sicily than the Atlantic populations. Our results are in line with the surface circulation entering from Gibraltar, the internal hydrodynamic regime of the Mediterranean and with the concept of cells of ecosystem functioning, that support, on one hand, the internal connectivity between the Tyrrhenian reefs and, on the other hand, a barrier to connectivity between the Sicilian and Tyrrhenian reefs.