Life on the edge: do biomechanical and behavioral adaptations to wave-exposure correlate with habitat partitioning in predatory whelks?

Abstract

The rocky littoral is a highly stressed but species rich environment in which adaptive trade-offs underlie the specialization that permits habitat partitioning by closely-related species. Habitat partitioning by prey species is generally attributed to differential tolerances to physiological stresses and competition for resources. Partitioning by predators is, however, less understood and also mainly related to thermal tolerance. We test the hypothesis that differential biomechanical and behavioral adaptations to wave action can result in habitat partitioning of mobile predators using 2 Mediterranean whelks. Stramonita haemastoma is found mainly at wave-exposed habitats on lower midlittoral or shallow (1 to 3 m) subtidal rocks. By contrast, Hexaplex trunculus is found only subtidally in more quiescent littoral environments (shallow bays and lagoons or deeper in wave-exposed sites). Morphologically, S. haemastoma is squatter than H. trunculus and the ratio of its foot surface area to the maximum projected surface area of its shell is 35% higher, making S. haemastoma less prone to dislodgment by waves. Mechanically, at least a 2-fold higher force (12 N) is required to dislodge S. haemastoma from the substrate, probably due to its larger foot, because tenacity per foot area was similar between species. The feeding technique and foraging behavior of S. haemastoma is also adapted to life in high-energy environments. Higher feeding rates and much shorter prey handling time compared to H. trunculus allow this species shorter foraging bouts that reduce the risk of dislodgment and increase predation success in wave-exposed areas. H. trunculus thrives in low-flow habitats where food density is low compared to shallow subtidal rocks. This is compensated for by a broader diet than S. haemastoma, feeding on any available food item, including conspecifics, and by reducing adhesion when not feeding, thus saving energy. S. haemastoma is more adapted to survive desiccation conditions than H. trunculus, which may exclude the latter from intertidal habitats. Our findings suggest that habitat partitioning between the whelks is maintained mainly by a 'distinct preferences' mechanism that might be relevant for other benthic predatory species.

Intra- and interspecific variation of attachment strength in sea urchins

“…For organisms possessing a simple holdfast (e.g. barnacles or gastropod molluscs), the scaled attachment force correlates with the tenacity, as the size of the adhesive organ is generally proportional to the size of the animal (Grenon & Walker 1981, Rilov et al 2004. This is, however, not necessarily the case for organisms possessing a multi-tethered holdfast (e.g.…”

“…This is similar to the situation described for whelks, but different from the case of limpets. Rilov et al (2004) studied 2 Mediterranean whelks, Stramonita haemastoma from a wave-exposed habitat and Hexaplex trunculus found only subtidally in more calm littoral environments. The 2 species possess the same tenacity, but the former is less prone to dislodgment by waves due to a more streamlined shell and a larger foot.…”

Slow-moving predatory gastropods track prey odors in fast and turbulent flow

“…This concept of physical stress affecting the strength of trophic interactions led to some interesting research (e.g. Menge, 1978;Power et al, 1988;Peckarsky et al, 1990;Hart, 1992;Rilov et al, 2004) and has proven to be especially productive in studies of marine rocky intertidal habitats (Menge, 2000). For example, comparison of benthic community dynamics between different flow regimes in a Maine estuary showed that crab predation was most important in low-flow sites, whereas recruitment and particle delivery dominated the high-flow sites (Leonard et al, 1998).…”

Spatial patterns in the population structure of the whelk <em>Stramonita haemastoma</em> (Linnaeus, 1766) (Gastropoda: Muricidae) in the Canarian Archipelago (eastern Atlantic)

“…Spatio-temporal variability in the population structure of this species has been attributed to differences in abiotic processes, such as habitat structure and the degree of wave exposure (e.g. Richardson and brown, 1990;Rilov et al, 2001Rilov et al, , 2004brown et al, 2004). Similarly, limited prey availability, in terms of abundance and biomass, has been suggested to be a possible mechanism behind the low abundances and growth rates of these intertidal carnivores on some coasts (mckillup and butler, 1983;burrows and Hughes, 1990;mckillup and mckillup, 1997;ota and Tokeshi, 2000).…”