Growth And Development Of Veined Rapa Whelk Rapana Venosa Veligers

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

Selective feeding behavior of larval naked gobies Gobiosoma bosc and blennies Chasmodes bosquianus and Hypsoblennius hentzi: preferences for bivalve veligers

Naked gobies Gobiosoma bose, striped blennies Chasmodes bosquianus, and feather blennies Hypsoblennius hentzi provide important intermediate links within the trophic structure of estuarine oyster reef communities. Predator-prey interactions between planktonic larvae of these fishes and larval eastern oysters Crassostrea virginica may influence recruitment success within oyster reef communities. These 3 species of oyster reef fish larvae were cultured from wild nests and used in multifactorial laboratory feeding experiments with larval oysters or hard clams Mercenaria mercenaria as well as wild plankton as prey items to determine the effects of predator age, predator concentration, and prey type on feeding selectivity of these fishes. Predator age significantly influenced feeding behavior of naked gobies and feather blennies. Predator concentration did not significantly effect feeding behavior for any of the 3 fish species. Prey type significantly affected feeding behavior of feather blennies and naked gobies. Naked gobies consumed bivalve veligers preferentially at all veliger concentrations. Feather blennies consumed veligers preferentially at concentrations as low as 12% of the available prey field. Striped blennies were less specialized in their feeding patterns but still consumed bivalve veligers preferentially at prey field concentrations as low as 11% veligers

Observations Of Distribution, Size, And Sex Ratio Of Mature Blue Crabs, Callinectes Sapidus, From A Chesapeake Bay Tributary In Relation To Oyster Habitat And Environmental Factors

Blue crabs Callinectes sapidus (Rathbun, 1896) \u3e 100 mm carapace width were sampled from a constructed oyster reef (1996 and 1997), a sand bar (1997) and a natural oyster bar (1997) in the Piankatank River, Chesapeake Bay, USA to describe habitat use, sex ratios, and demographics across a gradient of habitat types. Patterns of blue crab catch-per-unit-effort (CPUE), and demographics were similar on the oyster reef in 1996 and 1997. Average annual CPUE on the reef was 6-8 crabs pot(-1) with maximum CPUE of 15 crabs pot(-1). Daylength and water temperature significantly affected reef CPUE with more crabs observed in late August and early September. In 1997, average annual CPUE at the natural oyster bar was higher (9 crabs pot(-1)) than on the reef or the sand bar (both 6-7 crabs pot(-1)). Observed differences in habitat use may relate to site-specific differences in depth and tidal current as well as the presence of living oyster (biogenic) substrate. A transition in the sex ratio of crabs was observed as daylength declined seasonally. In May, males were 3-5 times more abundant than females at all sites but by early September, as daylength and water temperatures declined, female crabs were 3-4 times more abundant than males at all sites. The median size of males and females increased from spring into summer and female crabs were typically larger than males from the same habitats across all habitat types. The largest female crabs were observed in habitats with oysters. Biogenic oyster habitats are important estuarine habitats for blue crabs as well as oysters

Veined Rapa Whelk (Rapana Venosa) Range Extensions in the Virginia Waters Of Chesapeake Bay, USA

Three recent range extensions for the Chesapeake Bay, Virginia, veined rapa whelk (Rapana venosa) population are described. These extensions into Tangier Sound, the mid James River estuary, and to Cape Henry at the Bay mouth extend respectively, the northern, western, and southeastern boundaries of the occupied rapa whelk range in Virginia waters. Salinity and tidal circulation mediate the distribution of adults and larvae of this animal. During dry years (e.g., 2001 and 2002) adult rapa whelks may move up-estuary in western tributaries like the James River, given increased salinity and available habitat and food resources. Declines in salinities (or return to normal salinities) will either kill the rapa whelks in the upriver habitats or force a return to downstream habitats

Age And Growth Of Wild Suminoe (Crassostrea Ariakensis, Fugita 1913) And Pacific (C-Gigas, Thunberg 1793) Oysters From Laizhou Bay, China

Shell height at age estimates from Suminoe (Crassostrea ariakensis) and Pacific (C. gigas) oysters from a natural oyster reef in Laizhou Bay, China were compared with shell height at age estimates from triploid C. ariakensis of known age from the Rappahannock River, Virginia. C. ariakensis and C. gigas reach shell heights in excess of 76 mm (3 inches) within 2 years after settlement regardless of the source location. This fast growth appears to continue through at least we 4 or age 5 in wild individuals, because the growth trajectories for both specie, had not reached asymptotic height in (he oldest individuals collected. Estimates of the asymptotic maximum height (SHmax) from fitted Von Bertalanffy (VB) growth models were greatest for Chinese C. ariakensis (244.0 mm, standard error of the mean [SE] 30.4) and near the maximum shell height (227.0 mm) measured at the time of collection. Maximum shell heights measured on live Chinese C. gigas (173.0 mm) and Rappahannock C. ariakensis (190.0 mm) were also within the standard error estimates for the SHmax estimates from the fitted VB models for Chinese C. gigas (158.6 mm, SE 20.3) and Rappahannock C. ariakensis (183 mm, SE 19.1). Fitted VB growth curves were not significantly different between species within the same habitat, within species in different habitats or between species in different habitats. The ratio of shell height to shell width and shell height to shell inflation for triploid C. ariakensis was significantly less than similar ratios observed in wild C. ariakensis and C. gigas oysters

Fish species richness in relation to restored oyster reefs, Piankatank River, Virginia

Fish assemblages in relation to “reef” structures in marine habitats have been and continue to be topics for research addressing ecological and management questions. Much effort has been spent describing and defining fish assemblages, or groups of species, associated with tropical coral reefs (e.g., Sale 1991 and chapters therein), temperate hard bottom or rocky reefs (e.g., Sedberry and Van Dolah, 1984; Ambrose and Swarbrick, 1989), tropical lava flows (e.g., Godwin and Kosaki, 1989), and artificial “fishing” reefs (e.g., Chandler et al., 1985; Hueckel and Buckley, 1987; Bohnsack, 1989; Feigenbaum et al., 1989; Rountree, 1989; Stephan and Lindquist, 1989). Temperate oyster reefs, another natural reef type, host diverse finfish assemblages that are just beginning to be described (e.g., Wenner et al. 1996; Mann and Harding, 1997; Luckenbach et al. 1998 and references therein). Before Eastern oyster (Crassostrea virginica) populations were significantly reduced by environmental degradation, fishing pressure, and disease, oyster reefs dominated the intertidal areas of Chesapeake Bay and supported complex ecological communities including many fish species. The living shell matrix created by these predominantly intertidal, estuarine reefs provides structural heterogeneity and vertical relief that attract and sustain fishes from many trophic levels similar to living coral reefs (Roberts and Ormond, 1987; Ebeling and Hixon, 1991; Friedlander and Parrish, 1998). Recreationally and commercially valuable piscivorous finfishes including striped bass (Morone saxatilis), bluefish (Pomatomus saltatrix), and weakfish (Cynoscion regalis) were and are integral components of trophic networks that depend on oyster reefs (Mann and Harding, 1997, 1998). These pelagic finfishes use oyster reefs as both feeding and nursery grounds (e.g., Breitburg, 1998; Mann and Harding, 1997, 1998; J. Harding and R. Mann, unpubl. data)

Estimates of naked Goby (Gobiosoma bosc), striped blenny (Chasmodes bosquianus) and Eastern oyster (Crassostrea virginica) larval production around a restored Chesapeake Bay oyster reef

Naked gobies (Gobiosoma bose) and striped blennies (Chasmodes bosquianus) rely on oyster reefs for nesting sites, feeding grounds, and refugia from predation by upper level piscivores. Seasonal densities of Eastern oysters (Crassostrea virginica), naked gobies, and striped blennies on Palace Bar Reef, Piankatank River, Virginia were quantified and used to develop species-specific larval production estimates. Densities of oyster adults, juveniles, and articulated shell valves (the result of recent mortality) did not significantly change from November 1995 to November 1996. Naked goby and striped blenny densities varied with substrate type and season; peak fish densities for both species were observed in August 1996. Areas where shell substrate dominated the bottom supported fish densities up to 14 times greater than those observed in habitat areas lacking shell. Larval production and recruitment estimates for Palace Bar Reef oysters are of the same order of magnitude as observed field densities. Benthic fish production estimates are within an order of magnitude of adult densities and are similar to previous recruitment estimates for Chesapeake Bay naked gobies. Species-specific production estimates for both oysters and fishes are sufficient to sustain observed adult densities on Palace Bar Reef, Piankatank River, Virginia

Influence of habitat on diet and distribution of striped bass (Morone saxatilis) in a temperate estuary

Striped bass (Morone saxatilis) are recreationally and commercially valuable finfish along the Atlantic seaboard of North America including the Chesapeake Bay estuary. Habitat use patterns for striped bass in relation to biogenic habitat types in Chesapeake Bay tributaries are poorly described although it is widely acknowledged that these piscivorous fishes use estuarine habitat for nursery and feeding grounds during development. Striped bass diet and distribution patterns were examined in relation to a gradient of biogenic habitats ranging from complex three-dimensional oyster reef through flat oyster bar to sand bottom habitat in the Piankatank River, Virginia. Striped bass were more abundant at both sites with oysters and oyster shell substrate than at the site with sand substrate. Striped bass in association with the three-dimensional oyster reef were larger and consumed more teleosts (e.g., naked gobies) than fish at either of the non-reef sites. Striped bass estuarine habitat use is positively correlated with the presence of oyster reef habitat that includes physical structure and food resources via complex trophic communities centered on the oyster reef

Rapa Whelk Rapana Venosa (Valenciennes, 1846) Predation Rates On Hard Clams Mercenaria Mercenaria (Linnaeus, 1758)

The recent discovery of adult veined rapa whelks Rapana venosa (Valenciennes, 1846) in the Lower Chesapeake Bay, U.S.A. offers cause for both ecological and economic concern. Adult rapa whelks are large predatory gastropods that consume bivalves including commercially valuable species such as hard clams, Mercenaria mercenaria (Linnaeus, 1758). Laboratory feeding experiments were used to estimate daily consumption rates of two sizes of whelks feeding on two size classes of hard clams. Large rapa whelks (shell length, SL \u3e 101 mm) are capable of consuming up to 2.7 g wet weight of clam tissue daily, equivalent to 0.8% of their body weight. Small whelks (60-100 mm SL) ingest an average of 3.6% of their body weight per day

A Comparison Of Dredge And Patent Tongs For Estimation Of Oyster Populations

Exploited oyster stocks on public grounds in Virginia waters are subject to regular surveys effected using a traditional oyster dredge and, more recently, patent tongs. Dredges provide semiquantitative data, have been used with consistency over extended periods (decades), and provide data on population trends. Surveys with patent tongs provide absolute quantification (number of individuals per unit area) of oyster stocks but are more labor intensive. Absolute quantification of dredge data is difficult in that dredges accumulate organisms as they move over the bottom, may not sample with constancy throughout a single dredge haul, and may fill before completion of the haul thereby providing biased sampling. Selectivity of dredges versus patent tongs with respect to oyster demographics has not been rigorously examined. The objective of this study is to compare demographic oyster data collected at the same sites in the same years from both gear types. Data for the study were taken from 1993 to 2001 surveys conducted in the James River, Virginia, by the Virginia Institute of Marine Science and the Virginia Marine Resources Commission wherein the same stations were sampled by both techniques. Dredge surveys give data in oysters per bushel and assume no selective retention of live oysters with respect to shell substrate by the dredge. Patent tong surveys provide data as per tong estimates of oysters by size class and shell by volume. The hydraulically operated, 1-m square tong used in VMRC/VIMS surveys is designed to sample on and below the reef surface and include elements of buried shell that are probably not well sampled by a dredge, although the sampling ensures collection of all oysters within the tong mouth. Oysters collected by both gear types were classified as small (25-75 mm) or market (\u3e75 mm SL) for comparisons across methods. Shell volumes collected in patent tong surveys were standardized to bushel increments assuming 35.28 L of shell per bushel. The summary plots of mean values from 1993 to 2001 and 1998 to 2001 illustrate differences related to sampling gear. More shell per unit oyster (lower bushel counts) are observed in a patent tong sample. The appropriate model for attempting to fit a predictive line is open to debate, and will be influenced by patent tong penetration as determined by the degree of consolidation of the underlying substrate. The available data do not strongly support the ability to predict a relationship between dredge and patent tong population estimates at this time