JM Harding

Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

2006

Journal

Journal Of Shellfish Research

Volume

25

Issue

3

First Page

941

Last Page

946

Abstract

Planktonic larvae of benthic fauna that can grow quickly in the plankton and reduce their larval period duration lessen their exposure to pelagic predators and reduce the potential for advection away from suitable habitats. Veined rapa whelks (Rapana venosa, Muricidae) lay egg masses that release planktonic veliger larvae from May through August in Chesapeake Bay, USA. Two groups of veliger larvae hatched from egg masses during June and August 2000 were cultured in the laboratory. Egg mass incubation time (time from deposition to hatch) ranged from 18-26 d at water temperatures between 22 degrees C and 27 degrees C. Four stages of rapa whelk veliger development along a time series from hatch to settlement were described using external morphological features. Rapa whelk veligers were measured at three-day intervals from hatching through the onset of spontaneous settlement. A four-parameter Gompertz growth model was used with length at age data from cultures of rapa whelk veligers to estimate maximum growth rates for June and August hatched groups. Larval rapa whelks settled at shell lengths of 1.18-1.24 mm after planktonic larval periods ranging from 24-42 d. Maximum larval growth rates observed in August (0.03 mm d(-1)) are 50% lower than maximum larval growth rates observed for June hatched rapa whelk veligers (0.071 mm d(-1)). Daily larval growth rates from hatch to first spontaneous settlement for rapa whelk veligers ranged from 0.002-0.099 mm d(-1) with maximum growth rates occurring between 12-18 d post hatch in June. Larval period duration, or the time from hatch to first spontaneous settlement, was 12 days shorter for June hatched larvae than for August hatched larvae. Water temperature was not significantly correlated with larval growth rates (mm d(-1)) in either June or August. Plasticity in larval period duration may enhance survival and dispersal opportunities for planktonic rapa whelk veligers.

Keywords

Veined Rapa Whelk; Rapana Venosa; Veliger; Plankton; Larval Growth Rate; Propagule Pressure; Muricid; Gastropod

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