2 – Feeding and Digestion in Bivalvia

Annual internal growth increments in shells of hard clams (Mercenaria mercenaria) provide an accurate record of both growth history and some types of environmental change. These increments were used to determine age and growth rate of hard clams collected in 1984–1985 from ten sites in Narragansett Bay, Rhode Island, USA, and to assess geographic variation in growth within the bay. The regional comparisons were facilitated by modeling the clam growth using the von Bertalanffy equation and the ω parameter of Gallucci and Quinn. The optimum region for hard clam growth was near the head of the bay, with areas further north (Providence River) and south (lower bay) not as productive. The relationship between size and age was similar to that reported for hard clams from northern New Jersey. Using dendrochronological techniques, variations in growth were analyzed on a temporal (year-to-year) basis. The comparative longevity of the hard clams (individuals with 40 annual bands were encountered) demonstrated that sclerochronologies of several decades were possible. A 26 yr growth record based upon 100 individuals was established, covering the years 1959–1984. Significant temporal variations occurred in bivalve growth, and a broad trend of increasing growth indices over the last two decades of the record was noted. The yearly standardized growth index values were highly and positively correlated with mean annual water temperatures in Narragansett Bay for the same time interval. The incremental shell records of these bivalves provide a quantitative indication of marine climatic (temperature) variability and growth which can be used in hindcasting the effects of natural or anthropogenic environmental perturbations.

Sclerochronological records of temperature and growth from shells of Mercenaria mercenaria from Narragansett Bay, Rhode Island

https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=2676&context=vimsarticles

A review of recent information on the Haplosporidia, with special reference to Haplosporidium nelsoni (MSX disease)

Abstract It is well known that the incorporation of isotopically light metabolic carbon (C M ) significantly affects the stable carbon isotope (δ 13 C) signal recorded in biogenic carbonates. This can obscure the record of δ 13 C of seawater dissolved inorganic carbon (δ 13 C DIC ) potentially archived in the shell carbonate. To assess the C M contribution to Mercenaria mercenaria shells collected in North Carolina, USA, we sampled seawater δ 13 C DIC , tissue, hemolymph and shell δ 13 C. All shells showed an ontogenic decrease in shell δ 13 C, with as much as a 4‰ decrease over the lifespan of the clam. There was no apparent ontogenic change in food source indicated by soft tissue δ 13 C values, therefore a change in the respired δ 13 C value cannot be the cause of this decrease. Hemolymph δ 13 C, on the other hand, did exhibit a negative relationship with shell height indicating that respired CO 2 does influence the δ 13 C value of internal fluids and that the amount of respired CO 2 is related to the size or age of the bivalve. The percent metabolic C incorporated into the shell (%C M ) was significantly higher (up to 37%, with a range from 5% to 37%) than has been found in other bivalve shells, which usually contain less than 10%C M . Interestingly, the hemolymph did contain less than 10%C M , suggesting that complex fractionation might occur between hemolymph and calcifying fluids. Simple shell biometrics explained nearly 60% of the observed variability in %C M , however, this is not robust enough to predict %C M for fossil shells. Thus, the metabolic effect on shell δ 13 C cannot easily be accounted for to allow reliable δ 13 C DIC reconstructions. However, there does seem to be a common effect of size, as all sites had indistinguishable slopes between the %C M and shell height (+0.19% per mm of shell height).

A Large Metabolic Carbon Ccontribution to the δ13C Record in Marine Aragonitic Bivalve Shells

Abstract Between 1957 and 1959, a previously unknown sporozoan parasite, now designated as Haplosporidium nelsoni (formerly Minchinia nelsoni ), or MSX, killed 90–95% of the oysters in lower Delaware Bay. Native oysters have been studied for more than 20 years since then to determine long-term disease and mortality patterns resulting from this host-parasite association. Development of resistance to MSX-kill in native oysters has reduced disease mortality to about half the original level, even though the pathogen continues to be very active in the bay. Since the initial epizootic, MSX levels have fluctuated in a cyclic pattern with peaks every 6 to 8 years. Periods of low disease pressure follow very cold winters, while average or above average winter temperatures correlate with high MSX activity. During peak years, every oyster in the lower bay may become infected. Although the parasite is salinity limited, salinities in the lower bay, the area from which oysters are marketed, are nearly always favorable for MSX, and fluctuations in river flow have almost no effect on MSX in this region. Infection periods recur each summer. Some oysters die soon after becoming infected; others survive through winter, but die in spring as the pathogen compounds normal overwinter stresses. Many survivors are able to suppress or rid themselves of infections when temperatures approach 20°C in late spring. Resistance to MSX-kill in native oysters is not correlated with an ability to prevent infection, but with restriction of parasites to localized, nonlethal lesions. The persistence of “hot spots” for infection in areas where oysters are sparse, the lack of spores in infected oysters, and failure to transmit the disease experimentally lead to the hypothesis that an alternate or reservoir host produces infective stages of MSX.

History and spizootiology of Haplosporidium nelsoni (MSX), an oyster pathogen in Delaware Bay, 1957-1980.

Respiratory and pumping rates in the hard clam Mercenaria mercenaria were measured directly in running seawater; the quiatntity of oxygen used was calculated from the difference in concentrations in incurrent and excurrent water. A linear relationship between pumping and respiratory rates suggests regulation of water transport by, oxygen requirement rather than by feeding.

Oxygen Consumption and Pumping Rates in the Hard Clam Mercenaria mercenaria: A Direct Method

Comparison of In vitro salinity tolerance of the oyster parasite, Haplosporidium nelsoni (msx) and hemocytes from the host, Crassostrea virginica

Influence of selective breeding, geographic origin, and disease on gametogenesis and sex ratios of oysters, Crassostrea virginica, exposed to the parasite Haplosporidium nelsoni (MSX)

. A new species of ascetosporan parasitizing tissues of woodboring mollusks of the genus Teredo, including T. navalis Linnaeus, T. furcifera von Martens, and T. bartschi Clapp, is described from light and transmission electron microscopical observations. The new species is assigned the name Minchinia teredinis sp. n. (Phylum Ascetospora, Class Stellatosporea, Order Balanosporida, Family Haplosporidiidae). Plasmodia, sporonts, sporocysts, and mature spores are found in all host tissues, but primarily in the gill. Spores are obovate, operculate, and characterized by four projections from the epispore membrane. The species is found from Long Island Sound to Virginia on the east coast of the United States. The parasite causes extensive damage to host tissues and is correlated with reductions in host populations.

Harold H. Haskin

Papers

Oxygen Consumption and Pumping Rates in the Hard Clam Mercenaria mercenaria: A Direct Method

Comparison of In vitro salinity tolerance of the oyster parasite, Haplosporidium nelsoni (msx) and hemocytes from the host, Crassostrea virginica

Influence of selective breeding, geographic origin, and disease on gametogenesis and sex ratios of oysters, Crassostrea virginica, exposed to the parasite Haplosporidium nelsoni (MSX)

Minchinia teredinis n. sp. (Balanosporida, Haplosporidiidae), a parasite of teredinid shipworms.