Benthic communities in relation to wave exposure and spatial positions on sublittoral boulders in the Baltic Sea

Abstract

Boulders are an important substrate for Baltic Sea benthic communities. Although previous studies have examined benthic species on sublittoral boulders in the Baltic Sea, information on benthic assemblages and how they vary in relation to structuring factors is limited. The aim of the present study was to describe the benthic communities, including both algae and animal taxa, on sublittoral boulders in relation to spatial positions on the boulders (4 levels) and differences in wave exposure (2 levels). The multivariate results, including 29 algae and 25 animal taxa, from the field sampling showed a significant interaction between the 2 main factors. Changes in the biomass of both annual an perennial macroalgae as well as Mytilus edulis and Balanus improvisus, were found among different positions on wave-exposed boulders, a pattern which was less clear on boulders from sheltered sites, showing that water movement influences small-scale spatial patterns on sublittoral boulders. Apart from water movement, the physical factors substrate slope and light intensity were also associated with the small-scale patterns found in benthic communities. The difference in these factors may influence both settlement and post-settlement processes for both algae and animals, and possible mechanisms leading to the patterns found are discussed. KEY WORDS: Spatial patterns · Physical factors · Macroalgae · Mytilus edulis · Balanus improvisusResale or republication not permitted without written consent of the publisher algae and animals on sublittoral boulders (Kautsky 1989, Gilek et al. 2001), but to our knowledge no study has described the community composition or the small-scale patterns of occurrence for the whole macrobenthic community (including both macroalgae and animals) on sublittoral boulders in the Baltic Sea. The aim of the present study was, therefore, to describe the benthic plant and animal community composition, on a small scale, on sublittoral boulders in the Baltic Sea in relation to different positions on boulders and in relation to different degrees of wave exposure. MATERIALS AND METHODSThe study was carried out in June 2004 in the Askö area, in the northern Baltic proper (Fig. 1). The salinity in this area is relatively constant at around 7. During the winter months the watersurface temperature is ~0°C, while in July to August the temperature may exceed 20°C.On each of 3 wave-exposed (Sites 1 to 3) and 3 sheltered sites (Sites 4 to 6) ( Fig. 1) 3 randomly selected boulders were sampled.All the sites are located in a sparsely populated area. There is no freshwater or sewage water outflow close to any of the sites, and they are homogenous in salinity. The sites were chosen on a marine chart of the area. To determine the degree of wave exposure, a model developed by Isaeus (2004), based on effective fetch, wind direction and wind force, was used. The 3 wave-exposed boulders, which are open to waves from the south (the dominating wind direction), are all homogenous in wave exposure, as are the 3 sheltered s...

Spatial pattern of hydrolittoral rock encrusting assemblages along the salinity gradient of the Baltic Sea

“…The most frequent components of the brackish hydrolittoral assemblages, represented by barnacles and mussels (A. improvisus and Mytilus juv. ), have been observed in high biomass on exposed shores of the Baltic Sea (Wallin et al, 2011) and were considered to be the most frequent components of wave-exposed intertidal biotopes in the Northern Atlantic Ocean bioregion (Bartsch & Tittley, 2004). This confirms that A. improvisus is well adapted for survival in the highly hydrodynamic coastal rock belt of the Baltic Sea and is one of the dominant species in brackish communities.…”

Disturbance-related patterns in unstable rocky benthic habitats of the north-eastern Baltic coast

“…From the results of this study and those of Grzelak and Kuklinski (2010) and Wallin et al (2011), it appears that there are no boulder habitat specialists in the species depauperate regions of the Baltic Sea (i.e. the regions occurring further east of the entrance and in south-west).…”

“…The hypotheses investigated in previous similar studies that included B. improvisus (Grzelak and Kuklinski, 2010;Wallin et al, 2011) concerned habitat suitability, with distributions of living animals being of interest. These studies reported large densities of B. improvisus tests, which were comparable to the total densities of empty + occupied tests we found, but they did not mention the presence of any empty tests.…”

Effects of temperature change on mussel,Mytilus

“…For example, a recent review by Crain et al (2008) of marine ecosystem studies found that the interaction of environmental temperature with stressors ranging from pH to disease to overfishing could be additive (effects reflect sum of individual stressors), synergistic (effect greater than sum of individual stressors) or antagonistic (overall effect less than sum of individual stress effects). Many of these observations likely resulted from differential impacts operating at different trophic levels (Crain et al (Jones et al 1995) M. edulis (Berge et al 2006;Bibby et al 2008;Bechmann et al 2011) M. galloprovincialis (Michaelidis et al 2005;Kurihara et al 2008) Salinity M. edulis (Bussell et al 2008;Deschaseaux et al 2011) M. galloprovincialis (Solic et al 2010;Gombac et al 2011) Wave exposure M. edulis (Carrington 2002;Carrington et al 2009;Wallin et al 2011) M. galloprovincialis (Pfaff et al 2011) M. californianus Petes et al 2008) Food availability and temperature M. galloprovincialis (Schneider et al 2010) M. trossulus (Schneider et al 2010) Food availability and wave exposure M. californianus (Dahlhoff & Menge 1996) Food availability, temperature and wave exposure M. californianus (Dahlhoff et al 2002) Metal bioaccumulation and temperature M. edulis…”