Michael A Rice

The impacts of aquacultured oysters, Crassostrea virginica (Gmelin, 1791) on water column nitrogen and sedimentation: results of a mesocosm study

To determine effects of aquacultured oysters Crassostrea virginica (Gmelin, 1791) on the overlying water column, a mesocosm study was performed at the Marine Ecosystem Research Laboratory (MERL) from June to October, 2000. The MERL facility is located adjacent to Narragansett Bay and consists of fourteen 13,000-l mesocosm tanks designed to simulate the Bay environmental conditions. Two hundred oysters (c35 mm valve height; nominally filtering about 55 l/day/individual) were placed into three mesocosms, and three mesocosms were maintained without oysters as controls. Experiments were run with varying rates of water exchange in the tanks ranging from 0% to 100% per day (13,000 l/day). Parameters that were measured and compared between the two treatments included chlorophyll-a, particulate organic and inorganic matter, sedimentation, nitrate, ammonia, selected phytoplankton species and oyster growth rates. Oysters affected phytoplankton species composition and increased rates of sedimentation. Large diatoms were net sampled, and Nitzchia striata was predominant in mesocosms with oysters, while Skeletonema costatum dominated the control tanks. Ammonia excretion rates were determined for C. virginica using the salicylate–hypochlorite method. Ammonia excretion can be described by the allometric equation E=50.65w 0.699 when E is the ammonia excretion rate in Ag/h, and w is the soft tissue dry weight in grams. Based on rates of ammonia excretion by oysters and observed steady states of ammonia and other forms of inorganic nitrogen in mesocosm tanks, it can be hypothesized

Bacterial Community Profiling of the Eastern Oyster (Crassostrea virginica): Comparison of Culture-Dependent and Culture-Independent Outcomes

ABSTRACT Tissue-associated bacterial community profiles generated using a nested polymerase chain reaction—denaturing gradient gel electrophoresis (DGGE) approach and culture-dependent and culture-independent isolation techniques were compared. Oyster samples were collected from 2 harvest areas along the coast of Maine, in the United States. Profiles from both isolation strategies were evaluated using Sorensens index of similarity and cluster analysis of gel banding patterns. Culture-independent profiles were further evaluated using the Shannon diversity index. In general, the culture-dependent strategy resulted in a greater number of bands within a profile. Bacterial DGGE profiles were found to be highly similar within an isolation strategy, with a higher degree of unrelatedness between culture-dependent and -independent techniques. Cluster analysis identified bands present in the culture-dependent strategy and not the total DNA technique, and vice versa. Significant differences in community profiles between oyster-associated and seawater were observed, indicating a diverse group of specialist bacterial species inhabit and are able to proliferate within the oyster.

Gonadal Cycle of Northern Quahogs, Mercenaria mercenaria (Linne, 1758), from Fished and Non-fished Subpopulations in Narragansett Bay

Abstract To determine if population density in areas closed to fishing in Narragansett Bay is causing differences in the reproductive potential of the organisms, this study used two approaches to determine the reproductive condition of the animals. The first approach consisted in employing a gravimetric condition index (CI) to evaluate the general condition of quahogs from nine different sites, 3 sites open conditionally for fishing (conditional areas) and 6 sites closed to fishing. The second approach was a determination of gonadal index (GI) of a subset of the sample sites, by histological observation of gonadal tissue sections. Initial sampling included determination of CI only, and lasted from March 25 to Sep. 22, 2005. The subset of six of the sites was sampled the next year (2006), every three weeks from April 15 until Sep. 28 to determine CI and the gonadal index (GI). Results show that there is a significant difference between the CI of northern quahogs from conditional areas and quahogs from closed areas (P < 0.001). There is a significant difference in GI between sites at (P < 0.10). The GI in conditional areas was consistently higher than in closed sites indicating that maturation and reproductive stages are more prevalent in conditional areas than in closed sites. When sites were separated into three categories: conditional fishing sites; coves; and Providence River sites, the GI and CI of the conditional areas were always higher than the CI and GI of all the other sites. The coves had intermediate indices, and the Providence River sites always had the lowest indices. The results indicate that the populations of quahogs in the closed sites sampled are not completing the gonadal cycle as expected and that the reproductive capability of the quahogs in conditional areas is higher than those in closed areas. Possible explanations to this condition include lower water quality in the closed areas, low dissolved oxygen concentration especially during the summer, poor bottom conditions and high population density. Although, not one single characteristic of the environment is solely responsible for the reproductive condition of the quahog population, density appears to have significant effect.

Identification and Salinity Tolerance of the Western Hemisphere Mussel Mytella charruana (D'Orbigny, 1842) in the Philippines

ABSTRACT Beginning in 2014, mussels have been found by shellfishers in parts of the Philippines that are morphologically distinct from native mytilids. These mussels, with a thick black periostracum, were first found in Manila Bay near an international shipping port, and later in 2014 appeared in western Tambac Bay (approximately 16.28° N, 119.9° E). The next year (July 2015), they were found near the village of Tucok (Dagupan City; 16.0272° N, 120.3147° E), and more recently (early 2016) they have been observed in Longos, San Fabian, Pangasinan (16.1887, 120.4043). About 50 mussels from Tucok were preserved in 95% ethanol and sent to the University of Maine for genetic evaluation. Sequencing of mitochondrial cytochrome oxidase I polymerase chain reaction products identified the nonnative mussels as Mytella charruana, the charru mussel, native to the tropical Caribbean and western Pacific coasts of South America. Further analysis indicates that populations on the Caribbean Coast of South America are the likely source of the Philippine charru mussels. Two salinity tolerance experiments were also conducted; in the first experiment, Philippine charru mussels were conditioned at salinity 5 (similar to the salinity of the collection site) for 7 days, then subjected to a salinity shock by directly transferring them to different salinity levels (10, 15, 20, 25, 30, and 35) for 12 days. In the second experiment, replicate groups of mussels were conditioned in 30 salinity, then for each replicate, salinity was gradually increased by five increments every 5 days until all mussels had died. In both the experiments, all mussels survived at salinities below 35. In the rapid salinity change trial, byssus formation was absent in mussels subjected to salinity 35 shock, and all mussels in this treatment died before the end of the experiment. In the acclimation trial, some mussels survived to salinity 60, but were inactive, and all died when salinity reached 65. These salinity shock and acclimation trials suggest that charru mussels may be best suited to Philippine waters during and after the monsoonal rainy seasons when salinities are routinely below 35, and may be spread among different estuaries via larval transport during the monsoonal rainy season. On the basis of these criteria, charru mussels may be a potential species for aquaculture complementing the culture of the native Perna viridis, a species with a higher preferred salinity that is traditionally cultured in the dry season.