Effect of intra- and interspecific interactions on the feeding behavior of two subtidal sea stars

Abstract

Competition and its effects are difficult to demonstrate, as they vary depending on the species present and the environmental conditions in each community. We conducted laboratory and field experiments to evaluate the effects of intra-and interspecific interactions on the use of food resources and behavior of the sea stars Leptasterias polaris and Asterias vulgaris, 2 major predators in subtidal communities of the northern Gulf of St. Lawrence. We demonstrate interference (encounter) competition between the two. For both species, the presence of the other (as detected by both contact and chemical signals) decreased feeding activity and provoked behavioral changes (avoidance, decrease in percentage feeding). These effects were reversible and short-lived, and were more pronounced when there was a shortage of food and when sea stars were exposed to simulated attacks by the other species (involving pedicellarial pinching). L. polaris seemed to be the inferior competitor as (1) it switched to less profitable prey size (smaller mussels, Mytilus edulis) when A. vulgaris was present, and (2) it avoided A. vulgaris and reduced its feeding activity when food was scarce. The dominance of A. vulgaris is possibly attenuated at our study site (near its northern distributional limit) by the reduction of its fitness when water temperatures are low (most of the year) and during the winter when it migrates to deeper water. Competition for food resources seems to occur periodically (mainly summer), in localized areas (patches and beds of mussels) or when sea stars form dense aggregations in which they are likely to interact frequently. Interactions, and thus the chance of competition, are less likely at greater depths. Coexistence seems to be permitted by both the attenuation of the dominance of A. vulgaris and by the great variations in how L. polaris and A. vulgaris interact (strongly affected by variations in prey availability, sea star abundance, and in the patterns of prey use by both sea stars).

Small macrobenthic invertebrates affect the mortality and growth of early post-settlement sea urchins and sea stars in subtidal cobble habitat

“…This is different from the sea stars Acanthaster planci and Nardoa novaecaladoniae, which had greater survival in cages where the other animals had been removed from coral rubble, likely due to the abundance of predators in the community (Keesing & Halford 1992, Keesing et al 1996. While interspecific competition can cause small adult Asterias rubens to reduce their feeding rates in the laboratory (Gaymer et al 2002), the present study gives no evidence for interspecific competition. In our study, sea stars had a different cause of mortality, possibly starvation, intraspecific (intrageneric) competition for food and/or cannibalism.…”

The role of Asterina stellifera (Echinodermata: Asteroidea) as a predator in a rocky intertidal community in southern Brazil

“…Asterina stellifera, a weak predator in this study, in contrast with other starfish that are important predators in North America and in Australia at similar subtropical latitudes (PAINE 1974, CAMERON et al 1991, NAVARRETE & MENGE 1996, GAYMER et al 2002 and may be keystone predators (MENGE et al (4) Osmolality (mOsm/kgH 2 O, mean ± 95% confidence intervals) of the coelomic fluid of Asterina stellifera when exposed to the salinities of 10, 35, and 45, in summer and winter (n = 10 for each group). The single value for water in each group was calculated considering salinity 1 = 30 mOsm/kg H 2 O (PROSSER 1973); (5) chloride concentration (mM, mean ± 95% CI) of the coelomic fluid of Asterina stellifera when exposed to the salinities of 10, 35, and 45, in summer and winter (n = 10 for each group).…”

“…Starfish are often the most abundant benthic predators of the subtidal and intertidal areas (CAMERON et al 1991, HIMMELMAN & DUTIL 1991, GAYMER et al 2001a where they prey intensively on most macro-invertebrates of both consolidated and unconsolidated substrates (HIMMELMAN & DUTIL 1991). They are very abundant and they aggregate on coastal rocks and reefs, thus maximizing the effects of predation ( PAINE 1971, 1974, CAMERON et al 1991, GAYMER et al 2002.…”

“…Starfish can be voracious predators that devastate some communities, such as Acanthaster planci (Linnaeus, 1758) on coral reefs (CAMERON et al 1991) sp. on mussels (GAYMER et al 2002). Not all asteroids, however, are so voracious and some may maintain heterogeneity and biological diversity of their communities (VERLING et al 2003).…”

Sea anemones and brittle stars: unexpected predatory interactions during induced in situ oxygen crises

“…Cereus also feeds almost exclusively on crustaceans, mainly amphipods and decapods (Chiniroglou and Koukouras 1992); echinoderms have never been identiWed as prey items. Conversely, studies on predators of ophiuroids in shallow-water habitats have focused on demersal Wsh (Witman and Sebens 1992;Rosenberg and Selander 2000), various crabs and shrimps (Wurzian 1977;Aronson 1987;Makra and Keegan 1999), the Norwegian lobster (Baden et al 1990a) and asteroids (Sloan 1980;Gaymer et al 2002), but have never included actinians.…”