Algae, macrofaunal assemblages and temperature: a quantitative approach to intertidal ecosystems of Iceland

Abstract

Algae and the associated macrofauna in two Icelandic intertidal ecosystems under cold and warm influence, respectively, were studied with respect to algae-macrofauna relationships and a possible effect of temperature on community structure. Two sites in Iceland were selected, Sandgerdi ligthhouse (64°8¢N 22°40¢W) on the southwestern coast, and Grimsey Island (66°33¢N 18°04¢W), in the north, on the Arctic Circle, where sea temperature is considerably lower (5°a pproximately). The biomass of algae and the number of species of algae and macrofauna were higher in Sandgerdi than in Grimsey, and the patterns of diversity, evenness, biomass and abundance also differed between the sites. In the intertidal zone of Sandgerdi, a total of 28 species of algae and 45 species of macrofauna were identified whereas only 16 algal species and 27 macrofaunal species were found in Grimsey. Canonical correspondence analysis (CCA) using algal biomass as the environmental variable were conducted, and revealed significant relationships between algae composition and the associated macrofauna; some macrofauna taxa showed specific trophic or refuge relationships with algal species. According to the CCA, Corallina officinalis showed the highest correlation with macrofaunal assemblages in both study sites. However, correlations between macrofauna and other algae differed between Grimsey and Sandgerdi. The present study, together with additional observations in Greenland waters, shows a general decrease of species richness and diversity towards the north which may primarily be due to the temperature regime.

Sources of organic matter for intertidal consumers on Ascophyllum-shores (SW Iceland): a multi-stable isotope approach

“…In the Ascophyllum-based food webs of the Icelandic coasts, suspension feeders were mostly represented by bivalves and barnacles, the most abundant taxa in these environments (Espinosa and Guerra-Garcia 2005). At all three sites, mussels and barnacles relied directly on POM.…”

“…1). Osar and Hvassahraun were distant from densely populated areas, and therefore the community structure at both sites was assumed to be controlled largely by natural biological and physical factors (Espinosa and Guerra-Garcia 2005). Both these sites were far from freshwater inlets and had similar tidal ranges (2.5-3.8 m) at spring tides (Ingòlfsson 1992(Ingòlfsson , 1996; the water temperature was about 10.0-11.5°C and the salinity at marine levels (but see http://www.hafro.is).…”

“…At each study site, we selected diVerent hard substrata (natural rocks in Osar and Hvassahraun and artiWcial substrate in Reykjavik harbour) abundantly colonised by Ascophyllum nodosum, which is the main primary producer in the area (Espinosa and Guerra-Garcia 2005). From each site, dominant macroalgae (Ascophyllum nodosum [Linnaeus] Le Jolis; Fucus vesciculosus Linnaeus) were collected by hand, and epiphytic material was removed from the thalli by gentle scraping.…”

“…Samples of seawater both from the Sandgerdi oVshore area (as true marine referential signal) and each sampling site were collected in 4 l glass bottles; the water was Wltered through precombusted (450°C, 4 h) Whatman GF/F Wlters for the isotopic analysis of the particulate organic matter (POM). All organisms abundantly found at all sites according to Espinosa and Guerra-Garcia (2005) were collected manually: the gastropods Littorina obtusata (Linnaeus, 1758), Buccinum sp., Linnaeus 1758, and Nucella lapillus (Linnaeus, 1758), the bivalve Mytilus edulis Linnaeus, 1758, the decapods Carcinus maenas (Linnaeus, 1758), the barnacle Semibalanus balanoides (Linnaeus, 1758), the sponge Halichondria panicea (Pallas, 1766) and starWsh Leptasterias muelleri (M.Sars, 1846). Having been cleared of epiphytes, the animals were kept alive in Wltered seawater for at least 24 h to allow for gut evacuation.…”

“…Their most characteristic macroalgae are Ascophyllum nodosum and Fucus spp. (Hansen and Ingólfsson 1993;Espinosa and Guerra-Garcia 2005). The food supply for benthic macrofauna is strongly inXuenced by tidal processes, which are responsible for the active transport of organic matter, mainly of macro-algal origin.…”