Grazing Patterns of the Periwinkle and Their Effect on Sessile Intertidal Organisms

Abstract

The periwinkle, Littorina littorea, a common gastropod herbivore in the New England intertidal, strongly affects two abundant, sessile organisms, the green alga Enteromorpha and the barnacle Balanus balanoides. At very low densities, Littorina can maintain initially bare areas clear of Enteromorpha while higher densities are required to eliminate established patches. At low periwinkle densities, Enteromorpha interferes with Balanus settlement, while at high densities, Littorina appears to dislodge newly settle barnacle cyprids. Balanus abundance is greatest at intermediate Littorina densities. Experimental manipulation of periwinkle behavior through the use of partial cages shows that Enteromorphia can persist due to an interaction between snail behavior and surface irregularities. Certain areas are consistently missed which would normally be reached by a randomly moving grazer. There is no such refuge for Balanus. These results suggest that behavior—mediated effects may play an important role in maintaining diversity in the rocky intertidal.

Parasites alter community structure

“…Edible algae account for only a very small proportion of the total biomass of macroalgae on rocky shorelines (Ϸ7% of total initial macroalgal cover in our experiment; refs. 43 and 44), but constitute an important food and habitat resource for a variety of intertidal organisms (21,45,46). Although the increase in edible algae found in this experiment was modest in terms of total algal abundance, it represents a substantial change in available edible algae.…”

“…Changes in the abundance of ephemeral species can strongly influence the abundance and composition of invertebrate fauna inhabiting a given patch of macroalgae (21,45,46). For example, when L. littorea are excluded from exposed intertidal rock habitats, increases in the percent cover of ephemeral macroalgae reduce the availability of substrate suitable for barnacle recruitment, and the resulting absence of barnacle tests reduces blue mussel recruitment (45). Because high parasite prevalence in snails has a similar effect on grazing in a given area as reduction in snail density, high infection levels, like reduced snail density, may exert far-reaching effects in the intertidal community.…”

Effects ofFucus vesiculosus covering intertidal mussel beds in the Wadden Sea

“…This was also observed in our study. The fact that Littorina fittorea reached higher densities on mussel beds free of F. vesiculosus is surprising, when taking into account that food and fe~ding mechanisms are similar to Littorina mariae -in that diatoms as well as ephemeral or juvenile macroalgae are preferred foods (Lubchenko, 1978(Lubchenko, , 1983Lein, 1980;Enright et al, 1983;Petraitis, 1983;Watson & Norton, t985;Imrie et al, 1990). However, the common periwinkle is known to graze on a broad range of surfaces, and in K6nigshafen it preferably associates with solid substrata (Wilhelmsen & Reise, 1994).…”

Variability and community organization in moderately exposed tropical rocky shore algal communities as influenced by different consumer groups

“…One way predation can structure a community is by limiting the foraging power of gastropods by forcing them frequently into predator avoidance behavior Garrity et al1986;Power et al 1989). On the other hand, grazing by herbivorous fishes and molluscs can reduce the biomass of algal covers, smother young recruits and open spaces for other recruits (Underwood 1980 and1981;Petraitis 1983;Underwood et al 1993;Freidenburg et al 2007). Scaled up and repeated studies of comparable design on tropical rocky shores however are lacking, which indicates an imbalance of efforts compared to temperate shores.…”