MEPS 436:101-118 (2011)  -  DOI: https://doi.org/10.3354/meps09219

ABSTRACT: Transition zones between marine and freshwater environments are characterized by a pronounced salinity gradient and concomitant variation in invertebrate species richness. Here we use the β-diversity concept to depict the species turnover of macrobenthic species along the salinity gradient of the Baltic Sea with salinities ranging from 34 in the transition zone to the North Sea to less than 5 in the Bothnian Sea. Based on 250 data sets from 72 locations that were grouped into 2 habitats defined according to their depths and sediment types (shallower: 15 to 19 m, fine to medium sand; deeper: 20 to 35 m, silt to silty sand), we calculated the ­Jaccard dissimilarity index (β_1–J) as a measure of species turnover. To keep the focus on the salinity gradient, sediment characteristics and the time period covered by the data sets (spring and summer 1995 to 2005) were predefined. The mean hydrographic parameters, including temperatures, salinities and dissolved oxygen (DO) concentrations of the sample locations were derived from model ­calculations based on data gathered over a 3 yr period before sampling. At the deeper stations, the total number of macrofaunal species was 255, while at the shallower ones, 172 taxa were found. Statistical analyses revealed salinity to be the main structuring factor for macrobenthic species turnover. High correlations between the β_1–J index and mean salinities in both habitats (Spearman’s rank correlation coefficient ρ = 0.88 in shallower and ρ = 0.86 in deeper areas) confirmed these findings. β-diversity values with median β_1–J varied between 51 and 65% within the salinity classes eu-, poly-, α-meso- and β-mesohaline, while values of 75 to 100% characterized between-group comparisons. Furthermore, these high β-diversity values depict a discontinuous change in the communities and are found at salinities of around 10, 18, and 30, which ties in fairly well with the existing salinity boundaries postulated by the Venice System.

KEY WORDS: Species turnover · β-diversity · Salinity gradient · Macrofauna · Venice System · Baltic Sea