Abstract
Abstract This study compared the diversity parameters and structures of encrusting assemblages in two habitats situated at two levels of shallow rocky shore: hydrolittoral and littoral along the Baltic Sea system. We investigated the variability and level of distinctiveness of the hydrolittoral encrusting fauna based on species biodiversity and distribution, and compared these features with those of communities inhabiting the adjacent shallow littoral zone (3-m depth). Structural similarities and differences between the encrusting assemblages from adjacent hydrolittoral and littoral zones were studied within 14 locations distributed along the northern coastline of the Baltic Sea. Multivariate analysis indicates that salinity had the greatest influence on the structure of the investigated assemblages. Most of the observed hydrolittoral assemblages contained the same species as the littoral zone. This result indicated a shared common species pool with similar large-scale patterns of species distributions with some variability in the dominating species between zones. The similarity between species composition of the hydrolittoral and littoral assemblages decreased with increase of salinity. Additionally, with higher species richness and the occurrence of marine specialists adapted to hydrolittoral conditions, the role of the rock size in the frequency of species occurrence and assemblage diversity was less significant.
Highlights
We investigated encrusting assemblages inhabiting rocks in the Baltic Sea hydrolittoral zone in comparison to the adjacent littoral zone along a salinity gradient
Along the gradient of increasing salinity, the spatial trends in the hydrolittoral zone, including species composition and increased diversity of encrusting assemblages, were found to be similar to those reported for other macrobenthic communities from deeper regions of the Baltic Sea (Bonsdorff & Pearson, 1999; Westerbom et al, 2002) and in particular, as this study clearly indicated, the nearby littoral
Among the environmental variables we studied, salinity showed the strongest relationship with the large-scale pattern of encrusting assemblages
Summary
Coastal marine communities are affected by a variety of physical, chemical and biological disturbances (e.g. Bonsdorf & Pearson, 1999; Hanninen & Vuorinen, 2001; Eriksson & Bergstrom, 2005; Rousi et al, 2011) that modify recruitment conditions, influence species richness, diversity and distribution (Bonsdorff, 2006; Haanes & Gulliksen, 2011).In marginal marine habitats, such as the intertidal zone, stress is considered to be a structuring factor for benthic community zonation, especially for those sessile organisms sensitive to disturbances (Olenin, 1997; Araujo et al, 2012). Intensified coastal disturbance is associated with tidal basins, where factors such as increased wave action, sea level changes or, in some areas, winter ice formation are observed (Barnes & Arnold, 1999; Araujo et al, 2012). The Baltic Sea is considered to be a nontidal basin, seasonal and daily sea level variability can be significant and, over shorter time scales, the sea is affected by meteorological forcing (Johansson et al, 2001; Zaitseva-Parnaste et al, 2009). These conditions can affect supralittoral or ‘hydrolittoral’ zone (the latter term being used in this study). Position along the land–sea gradient can directly influence physical and biological processes across the water column, mainly by controlling their intensity and influencing community composition (Terlizzi et al, 2007)
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