Alan Power

Genetic sex determination, gender identification and pseudohermaphroditism in the knobbed whelk, Busycon carica (Mollusca: Melongenidae)

We report perhaps the first genic–level molecular documentation of a mammalian–like ‘X–linked’ mode of sex determination in molluscs. From family inheritance data and observed associations between sex–phenotyped adults and genotypes in Busycon carica, we deduce that a polymorphic microsatellite locus (bc2.2) is diploid and usually heterozygous in females, hemizygous in males, and that its alleles are transmitted from mothers to sons and daughters but from fathers to daughters only. We also employ bc2.2 to estimate near–conception sex ratio in whelk embryos, where gender is indeterminable by visual inspection. Statistical corrections are suggested at both family and population levels to accommodate the presence of homozygous bc2.2 females that could otherwise be genetically mistaken for hemizygous males. Knobbed whelks were thought to be sequential hermaphrodites, but our evidence for genetic dioecy supports an earlier hypothesis that whelks are pseudohermaphroditic (falsely appear to switch functional sex when environmental conditions induce changes in sexual phenotype). These findings highlight the distinction between gender in a genetic versus phenotypic sense.

Hand Harvesting Quickly Depletes Intertidal Whelk Populations

Abstract: With the collapse of the offshore whelk trawl fishery in Georgia, interest has increased in harvesting whelk from inshore areas where trawling is prohibited. This study examines the effects of hand harvesting on local intertidal populations of whelk. Over a 34 day period from 27 February to 1 April 2006, 1,824 whelk were hand harvested at low tide: 91.2% knobbed, Busycon carica (Gmelin, 1791); 4.7% lightning, Busycotypus sinistrum (Hollister, 1958); 4.1% channeled, Busycotypus canalicalatus (Linnaeus, 1758); and one pearwhelk, Busycotypus spiratus (Lamarck, 1816). Significantly greater numbers of knobbed and lightning female whelk were found than males. Mean shell lengths for females were consistently larger than males of all species. The study period was divided into three collection periods that were separated by approximately one week. The numbers of whelk harvested and their mean shell lengths significantly decreased between sampling periods as stocks were depleted. All species and sexes were active in both daytime and nighttime; however, significantly more knobbed and channeled whelk were harvested when sampling occurred closer to the middle of the night and significantly fewer toward the middle of the day. Nocturnal feeding is likely a cryptic adaptation to avoid predation and desiccation, and many whelk presumably remain buried on the intertidal flats during diurnal exposure. This study was conducted in the period leading up to copulation and egg-laying on the intertidal sandy-mud flats in inshore areas in coastal Georgia. Nocturnal hand harvesting at this time of the year could very quickly have detrimental impacts to local whelk stocks. Further implications of this work for an intertidal hand harvest supplemental whelk fishery are discussed.

Ecological Succession on Restored Intertidal Oyster Habitat in the Tidal Creeks of Coastal Georgia

ABSTRACT Microhabitat availability resulting from spatial complexity on oyster reef allows niche overlap and enhances benthic-pelagic coupling within a localized area; however, in Georgia, little is known regarding the temporal succession patterns of resident species on constructed reef. The purpose of this research is to evaluate the development and relative habitat value of man-made oyster habitat by monitoring oyster growth and the colonization by structurally important and resident oyster reef community species. Sixteen sampling units of commercial spat sticks in densities of 81/m2 were deployed prior to the oyster reproductive season during April 2004. Two sampling units were extracted every 3 mo starting July 2004 and assessed for biomass; oyster shell height and growth rate; oyster, barnacle, and mussel density per 0.01 m2; and species and phyla richness. Maximum oyster growth rate (0.39 mm/day) occurred during January 2005, with mean oyster shell height peaking at 83.56 ± 1.31 mm by May 2005. Oysters, barnacles, and scorched mussels appeared concurrently on sampling units during July 2004, and ribbed mussels appeared in October 2004. There were significant positive relationships between oyster and mussel (ribbed and scorched) densities (P < 0.0001), but none were detected between oyster and barnacle densities. Reef species rapidly colonized sampling units (24 of 31 species by October 2004), and a significant correlation between biomass and species (R2 = 0.91) and phyla (R2 = 0.96) richness was observed. Settlement and optimal growth of structurally important species on vertically elevated man-made oyster reef enhanced habitat availability and supported rapid colonization of reef-associated species.

A CAUTION AGAINST INTERPRETING AND QUANTIFYING OYSTER HABITAT LOSS FROM HISTORICAL SURVEYS

ABSTRACT Comparisons of historical surveys and fishery data have led to the popular belief that during the past century, more than 90% of oyster habitat has been lost through overfishing, disease, storms, and alterations to water quality and natural flow in the state of Georgia. Using handheld GPS computers, we conducted an on-the-ground inventory of living intertidal oyster reefs at four separate locations, and have concluded that previous surveys were not comprehensive or accurate enough to facilitate a reliable quantitative assessment of habitat loss. Alternatively, we have shown that intertidal oyster reefs are remarkably resilient and may occur in greater abundance today than when first documented in 1891. Rather than a collapse of oyster stocks, declining trends in fishery landings reflect the social and economic challenges associated with an unsustainable canning industry during the early 20th century. In addition, we challenge the axiom that the condition of existing intertidal reef habitat has deteriorated. Areas of shell deposits attributed to exhausted beds in historical assessments may in fact represent naturally occurring coastal features. Nonetheless, enhancement and conservation efforts are worthy efforts, because intertidal oyster habitat increases the health and resiliency of coastal Georgia by providing essential fish habitat, flood control, erosion abatement, and pollution reduction services. We propose that detailed GIS inventories like the ones conducted in this study can establish accurate baseline data to document reliably future changes in distribution, abundance, and condition, particularly with respect to the growing threats from development, sea level rise, and ocean acidification.

GAMETOGENIC CYCLE OF THE PONDEROUS ARK, NOETIA PONDEROSA (SAY, 1822), FROM CEDAR KEY, FLORIDA

Abstract The gametogenic cycle of the ponderous ark, Noetia ponderosa (Say, 1822), was studied in a Cedar Key, Florida population between March 2001 and January 2003. Ponderous arks are dioecious, and no hermaphrodites were found in this study (n = 592). The sex ratio of females to males was 0.84:1.00, but was not significantly different from parity. On the Gulf coast of Florida, the ponderous ark dribble spawns over most of the year, peaking in the summer and fall months and with the least spawning activity occurring during the spring when gametes are maturing. A small percentage (5.2%) was found infested with an undescribed digenetic trematode. The Cedar Key area has an important commercial hard clam (Mercenaria mercenaria) aquaculture industry, and the implications of these findings on the potential for its diversification based on this species are discussed.