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Shell planting to enhance oyster recruitment and habitat in Delaware Bay, NJ was reinitiated in 2005 with 3 y of federal funding. Since then, annual plantings of locally available surf clam and ocean quahog shell have been funded by the oyster fishery. The cured shell is deployed directly onto sites already containing commercially viable numbers of market-sized oysters in areas that are routinely fished sustainably. The locations targeted to receive shell plants vary and are selected to provide the greatest benefit throughout the fished reef tract. Annual sampling that included shell plants from 2005 through 2017 permitted evaluation of their performance. New oysters set and survive preferentially on newly planted shell during the first season and later at the same level as native shell for at least 10 y so that the benefit of once-added shell is retained for over a decade. Recruitment to shell plants enhances "good" sets and makes a critical difference during years of "poor" set. Plant substrate, now with oysters of its own, significantly outperforms native substrate in recruitment and survival of oysters in the second and third years post-planting, with enhancement declining exponentially over the first 4 y. An estimated half-life for this decline is just under 1 y. Beyond 3 y, the plant-based substrate continues to perform at least as well as native substrate. Size–frequency analysis shows that first-year oysters on planted substrate are larger than those on native substrate and that this difference carries through the fourth year of a plant. The volume contributed by live and dead oysters on planted substrate increases over the first 5 y until the contribution to the reef from planted substrate volume matches that of native substrate, thus carrying the enhancement forward through time. Annual survey data from the first 4 y of shell plants show that on seven of eight beds, live plus dead oyster density (number m–2) was up to 2.8× greater on planted sites than on non-planted sites. Change in density averaged positive over time on both planted and non-planted sites but was greater on planted sites. Shell plants on beds in the Delaware Bay fishery provide 3–4 y of enhanced oyster productivity and continue to double the local native substrate productivity as they age, maintaining an active and productive fishery. [ABSTRACT FROM AUTHOR]

Parasites and pathologies of oysters and mussels were sampled yearly from 1995 to 2010 from the Gulf of Maine to Alaska and the Great Lakes as part of the National Oceanic and Atmospheric Administration Status and Trends Mussel Watch Program. Sentinel bivalves included mytilid mussels, dreissenid mussels, and oysters. This comprehensive dataset provides a unique opportunity to examine long-term temporal dynamics of parasites, pathologies, and physiological indices of these sentinel bivalves. Temporal dynamics fell into a few clear categories. Significant differences between years occurred commonly for parasites, pathologies, and physiological indices; the absence of significant change over time was more noteworthy. In a few cases, these trends were characterized by multiyear increases or decreases in value within the time series. Such behavior might be produced by a multiyear cycle and, in fact, such behavior was much more common along the southern East Coast, the Gulf Coast, and Southern California where a relatively short cycle, El Niño-Southern Oscillation (ENSO), is well documented. More interestingly, for a number of parasites, pathologies, and physiological indices, significant trends existed across the time series. These trends substantively exceed the time span of climate cycles influencing these regions such as ENSO and the North Atlantic Oscillation. A few of these longer term coherent trends were continental in scale, being observed across sentinel taxa and multiple coasts. Continental scale trends were restricted to the physiological indices such as length. Regional trends were important for a subset of parasites, pathologies, and physiological indices. In general, the regional trends were produced by single-celled proliferating parasites such as Perkinsus marinus, the major pathologies, and certain physiological indices. The multicellular eukaryotes and the gregarines often showed significant year-to-year changes without trend. Temporal trends were prominently represented by oyster parasites on the Atlantic and Gulf Coasts and by mytilid parasites on the West Coast. Pathologies by contrast had strong temporal signals in northeastern mytilids. [ABSTRACT FROM AUTHOR]

Today, populations of eastern oysters, Crassostrea virginica, are commonly limited by disease mortality. Resistance to MSX disease has developed in a number of cases, but the development of resistance to Dermo disease would appear to be limited, despite the high mortality rates and frequency of epizootics. Can aspects of the host's genetics or population dynamics limit the response to the disease despite the apparent opportunity afforded by alleles conferring disease resistance or tolerance? To answer this question, we use a gene-based population dynamics model, configured for C. virginica, to simulate the development of disease resistance using mortality as the agent of selection. Simulated populations were exposed to 4 levels of mortality covering the range in mortality observed in Delaware Bay in the l990s. In each case, disease resistance increased in the simulated population over time, normally proportional to the increase in mortality rate imposed by the disease. However, simulations show that the population responds even at its most rapid rate on multidecadal to half-century timescales. As the mortality rate declines with increasing disease resistance, the rate of further improvement in disease resistance likewise declines. Thus, disease resistance develops over decadal timescales at a 40%-per-year mortality rate, but, as mortality rate falls to 25% per year, the rate of further development of disease resistance extends to half-century timescales. The discouraging profundity is that a mortality rate of 25% per year, yielding a rate of selection profoundly slow, is still very high. In northern climes, significant decrements in oyster abundance will occur. Evidence from fisheries retrospectives suggests that oysters cannot withstand a constant removal at this scale without compromising population integrity noticeably. So, a mortality rate that grievously limits the development of disease resistance still sorely strains the species' ability to maintain a vibrant population necessary to its long-term survival. [ABSTRACT FROM AUTHOR]

We evaluate a 54-y survey time series for the Delaware Bay oyster beds in New Jersey waters to identify the characteristics of regime shifts in oyster populations and the influence of MSX and Dermo diseases on population stability. Oyster abundance was high during the 1970s through 1985. Oyster abundance was low at the inception of the time series in 1953, remained low through 1969, and has been low since 1985 and very low since 2000. Natural mortality was low in most years prior to the appearance of MSX in 1957. From 1957 through 1966, natural mortality generally remained above 10% annually and twice exceeded 20%. Natural mortality remained well below 15% during the 1970s and into the early 1980s when oyster abundance was continuously high. The largest mortality event in the time series, an MSX epizootic that resulted in the death of 47% of the stock, occurred in 1985. Mortality rose again with the incursion of Dermo in 1990 and has remained above 15% for most years since that time and frequently has exceeded 20%. The primary impact of MSX and Dermo diseases has been to raise natural mortality and ultimately to cause a dispersed stock to retreat into its habitat of refuge in the moderately low salinity reach of the bay. The time series of oyster abundance on the New Jersey oyster beds of Delaware Bay is dominated by two regime shifts, the 1970 abundance increase that was maintained for about 15 y thereafter, and the 1985 abundance decrease that continues through today. These two regime shifts ushered in long-term periods of apparent constancy in population dynamics. The 1985 regime shift was induced by the largest MSX epizootic on record that produced high mortalities throughout a population distributed broadly throughout its habitat range after 15 y of high abundance. A putative new regime commenced circa 2000 as a consequence of a series of Dermo epizootics. Mortalities routinely exceeded 20% of the population annually during this period, with the consequence of a greater degree of stock consolidation than any previous time in the 54-y record. Extreme consolidation of the stock would appear to be a characteristic of the population's response to Dermo disease. The 1970-1984 and post-1985 regimes each were ushered in by a confluence of events unique in the 54-y time series. Each was characterized by a period of relative stability in population abundance. However, the stability in total population abundance belies a more dynamic process of stock redistribution during both time intervals, demonstrating that the appearance of constancy in stock abundance is not necessarily a result of invariant stock dynamics. Rather, the Delaware Bay oyster time series suggests that regime shifts delimit periods during which differential, often offsetting, local trends impart similar abundance levels, and thus constancy at the level of the stock masks substantive changes in local population dynamics potentially fostering future catastrophic changes in population-level attributes. Understanding such regime shifts will likely determine the success of decadal management goals more so than measures designed to influence population abundance. [ABSTRACT FROM AUTHOR]

Published data indicate that spawning seasons for the Asian oyster Crassostrea ariakensis and the eastern oyster C. virginica overlap. Hybrids can form, but the larvae are not viable. If C. ariakensis is introduced into Chesapeake Bay and synchronous spawning occurs with native C. virginica. hybridization could reduce the production of viable larvae (=gamete sink). We examined the effects of gamete age, sperm concentration, and ratios of heterospecific gametes on fertilization rates and hybridization between the two species. Interspecific fertilization rates were consistently lower than intraspecific rates. Fertilization rates decayed linearly with gamete age, though intraspecific fertilization rates remained above 50% for 4-6 h, indicating that long dispersal of viable gametes is possible. Fertilization rates decayed in a log-linear manner with decreasing sperm density for intra and interspecific crosses. Fertilization rates declined significantly when sperm were (1) given a choice of eggs from each species to fertilize or (2) required to compete to fertilize eggs from a single species. Hence, a gamete sink will likely occur if these two species spawn synchronously. The magnitude of the gamete sink will depend on both gamete concentrations and the relative proportion of interspecific gametes in the water column. Furthermore, genetic analysis of individual 2-day old larvae indicated that C. virginica sperm was more likely to fertilize C. ariakensis eggs than any other interspecific cross. All else being equal, the removal of C. ariakensis eggs through this mechanism may provide C. virginica with a competitive edge. [ABSTRACT FROM AUTHOR]

The parasites Perkinsus spp. are relatively easily and inexpensively detected in host tissues, but available methods to detect free-living planktonic stages are technologically complex and expensive. As a result, few studies have been conducted to detect and quantify free-living stages during transmission. Here, we describe an adaptation of Ray fluid thioglycollate medium (RFTM) assay to detect and enumerate Perkinsus spp. parasites in environmental water samples. Recovery of in vitro cultured P. marinus was successful, but recovery rates were low. Filtration of water samples captured significantly more cultured P. marinus cells than centrifugation. Lipid supplementation during RFTM incubation enhanced recovery of cultured P. marinus, but not of naturally occurring Perkinsus spp. parasites. Comparisons between the modified RFTM filtration method and a more complex inimunoassay revealed that the two methodologies were equally sensitive, indicating that the RFTM filtration method may be confidently applied to environmental water samples to determine relative concentrations of Perkinsus spp. parasites. [ABSTRACT FROM AUTHOR]

Oyster shell is the preferred substrate for replanting oyster beds and restoring oyster reefs. If pathogens remain viable in tissues attached to shell, then planting shell may inadvertently serve as a vector for pathogen transmission. Limited local shell sources may exacerbate the problem by increasing the risk of spreading novel strains into new areas if shell is derived from other regions. In South Carolina, the primary source of oyster shell is currently the Gulf of Mexico, where the protozoan oyster pathogen Perkinsus marinus (Mackin et al. 1978) has been problematic. Although P. marinus is present in South Carolina waters, different strains exist in the two regions. Given the detrimental effects of P. marinus on oysters, protocols to minimize its spread via planting of shell are needed. We conducted a short-term, replicated experiment to follow changes in P. marinus abundance in oyster tissues by placing whole, intact oysters or shucked oysters in shell piles. The amount of oyster tissue present and parasite abundance declined precipitously after one month and was virtually eliminated by three months. Parasite persistence was dramatically longer in whole, unshucked oyster tissues as compared with those associated with shucked oysters. Viability of parasites after one month was, however, unclear. The results support the recommendation that the quarantine of shell for one month or more can dramatically reduce the potential risk of spreading P. marinus when planting oyster shell (=cultch) from other geographic areas. This recommendation is applicable to virtually any region, but several parameters such as effects of climatic conditions and shell pile configuration warrant further investigation as does the persistence of other pathogens on shell piles. [ABSTRACT FROM AUTHOR]