Growth, survivorship, and habitat choice in a newly settled seagrass gastropod, Strombus gigas

Abstract

GrowthABSTRACT: The roles of nutrition, predation, and habitat choice were tested as mechanisms for shaping natural distribution of newly settled queen conch in seagrass Thalassia testudinum meadows in the central Bahamas. Small animals from 3 size classes were enclosed at 2 sites in 3 different habitats across a seagrass gradient (bare sand, low-density seagrass, medium-density seagrass) for 3 wk. Medium (11 mm shell length) and large (22 mm) newly settled conch grew faster in both seagrass habitats than on bare sand, but differences were not significant for small (5 mm) conch. Small and medium conch grown on sand, however, weighed more than those of the same length grown in seagrass. In laboratory habitat-choice experiments, newly settled conch preferred living seagrass and seagrass detritus over bare sand. Medium conch tethered in the 3 habitats at both sites suffered very high mortality (50 to 96% killed in 11 d), with those tethered in medium-density seagrass showing an advantage. Juvenile conch over 1 yr old are primarily associated with medium-density seagrass, but younger animals have been observed on sand. Results from this study show that nutrition is adequate on sand for newly settled conch, but an ontogenetic shift from sand into seagrass is unlikely because predation occurs before food becomes limiting or a habitat choice can be made. Nevertheless, post-settlement mortality is high regardless of where conch settle in the seagrass gradient, and predation is the most important mechanism influencing distribution.

What constitutes essential nursery habitat for a marine species? A case study of habitat form and function for queen conch

“…Because the smallest juveniles are often found in bare sand or rubble environment rather than in seagrass (Iversen et al 1987, Sandt & Stoner 1993, it has been hypothesized that settlement occurs on the shallow, bare substrata, where foods in the form of sediment-dwelling diatoms are abundant. Subsequent experiments conducted on a fine scale within nursery grounds (Ray & Stoner 1995) revealed that growth rates of 5 mm conch in sand were equivalent to those in adjacent seagrass, but slightly larger juveniles (11 and 22 mm) had significantly higher growth rates (and survival; see below) in seagrass. It remains unknown whether the observed size-related shift in juvenile conch away from sand habitat results from ontogenetic migration or differential mortality.…”

“…Prey abundance was also one of several statistically significant components in distribution models for age-0 winter flounder in a New Jersey estuary (Stoner et al 2001). Growth can be a sensitive indicator of food quality at a site, and growth in transplanted animals has been used as a metric for habitat quality for a variety of marine fishes (Cowan et al 1992, Sogard 1992, Rooker & Holt 1997, queen conch (Martín-Mora et al 1995, Ray & Stoner 1995 and other invertebrates (Mintz et al 1994, DeMontaudouin 1996. Several of these studies have shown that growth is not readily predicted from benthic habitat classification.…”

“…Laboratory and field experiments show that juvenile conch of all sizes have strong preferences for habitats with above-ground structure (Stoner & Waite 1990, Sandt & Stoner 1993, Ray & Stoner 1995, Ray-Culp et al 1999, and field experiments with juveniles ranging between 5 and 80 mm indicate that the relationship between seagrass density and conch survivorship is dome-shaped, with maximum survival at ~600 shoots m -2 (Marshall 1992. While the mechanisms for this function are unknown, conch nursery grounds are often associated with seagrass meadows with intermediate shoot density.…”

Different early post-settlement strategies between American lobsters Homarus americanus and rock crabs Cancer irroratus in the Gulf of Maine

“…2). Association of individuals with protective habitats has been shown for other large invertebrates, e.g, where it is also linked to predator avoidance in several species of spiny lobsters (Jernakoff 1990, Booth & Phillips 1994, Yoshimu.ra et al 1994, gem clam (Ahn et al 1993), and queen conch (Ray & Stoner 1995).…”

Ontogenetic changes in habitat use by postlarvae and young juveniles of the blue crab

“…High organism abundances in complex habitats may be due to flow-induced transport (Eckrnan 1983, Eckrnan & Nowell 1984, Butman 1987, reduced predation (decapod crustaceans, Heck & Thoman 1981; spiny lobster, Herrnkind & Butler 1986, Lipcius et al 19998; queen conch, Ray & Stoner 1995;amphipods, Ryer 1987; Atlantic cod, 'Addressee for correspondence. E-mail: jjorth9vims.edu Tupper & Boutilier 1995), abundant living space, and food availability (snails, Bronmark 1985;amphipods, Hacker & Steneck 1990; juvenile spiny lobster, Herrnkind & Butler 1986; epifaunal invertebrates, Schneider & Mann 1991b; juvenile blue crab, Perkins-Vissser et al 1996).…”