Search

Une synthese des articles portant sur la reponse du benthos a la pollution des mers parait indiquer que les communautes constituees de l'endofaune macroscopique et de la meiofaune ont des profils repetables de reponse a la contamination des sediments qui sont generalement observables a des niveaux taxonomiques eleves (meme a celui du phylum). Ces reponses semblent etre alimentees a la fois par des caracteristiques ecologiques et physiologiques intrinseques des taxons superieurs : p. ex., les crustaces (particulierement les amphipodes et les harpacticoides) et les echinodermes sont sensibles aux substances toxiques tandis que les polychetes, les oligochetes et les nematodes (particulierement les depositivores non selectifs) tirent parti de l'enrichissement en matieres organiques. L'application de ce modele aux resultats obtenus dans le cadre du projet GOOMEX fait intervenir la toxicite et l'enrichissement en matieres organiques comme facteurs. Les resultats des tests de toxicite et les rapprochements entre des concentrations observees de contaminants et des niveaux d'effets connus paraissent indiquer que les metaux sont les principaux agents de la toxicite. Nous parvenons aux conclusions suivantes : 1) les forages produisent des effets durables dans l'environnement sedimentaire autour des plates-formes de production gaziere, 2) les effets combines de la toxicite et de l'enrichissement en matieres organiques sont probablement a l'origine des reponses facilement detectables de la meiofaune benthique et de l'endofaune macroscopique jusqu'a 100-200 m et 3) le fait de ne pas detecter de signes d'exposition ou d'effets subletaux chez le poisson et la plupart des grands invertebres est le resultat de leur grande mobilite par rapport a l'echelle des changements dans l'environnement et de leur exposition negligeable aux hydrocarbures et a d'autres contaminants.

Les populations de macro-epifaune a proximite de trois plates-formes d'exploitation gaziere ont ete etudiees dans le cadre de la GOOMEX (Gulf of Mexico Offshore Operations Monitoring Experiment) a l'aide d'une strategie de collecte a champ proche (50-100 m) et a champ eloigne (3 km). Lorsqu'il existait des differences relatives aux prises par unite d'effort (PPUE) et a la taille, ces differences etaient specifiques de l'espece et du site. Les effets sur la taille n'etaient pas attribuables uniquement au dimorphiemse sexuel. Les differences touchant la taille et l'abondance ne variaient pas en meme temps. On n'a pas observe de reposes generales a la presence de la structure meme de la plate-forme ni a d'autres caracteristiques communes aux plates-forme ni a d'autres caracteristiques communes aux plates-formes d'exploitation gaziere. Les differences quant a la taille et aux PPUE etaient specifiques du site (plate-forme), ce qui indique que l'epifaune a reagi aux caracteristiques physiques et chimiques uniques de chacune des plates-formes. La frequence des differences champ proche-champ eloigne statistiquement significatives a diminue avec l'accroissement de la profondeur, tout comme la frequence des differences significatives saisonnieres et liees au moment du prelevement, a la fois pour la taille et les PPUE, ce qui indiquerait que les plates-formes influent davantage sur la structure de la communaute adjacents en eau peu profonde et que la saisonnalite et les comportements pourraient etre des promoteurs importants de ces effets. Les differences significatives n'etaient pas moins frequentes chez les especes plus mobiles (crevettes penaides) que chez les etoiles de mer et les petoncles beaucoup moins mobiles. En consequence, des populations discrete de l'epifaune mobile maintiennent leur coherence pendant des periodes importantes, ce qui permet aux effets differentiels produits par la proximite de la plate-forme de se manifester chez certains des invertebres les plus mobiles du plateau continental.

To investigate the application of the size-frequency distribution in paleoecology, the size-frequency distributions for a series of assemblages obtained from two cores taken in Copano Bay, Texas are examined from four perspectives. These four perspectives are the size-frequency distribution of each of the dominant species and three measures of the size-frequency distribution for the assemblage as a whole, defined according to the maximum size of the species, the maximum size of the assemblage, and the maximum size of a group of assemblages. In each case, the size-frequency distribution was evaluated in terms of abundance and converted by a hindcasting model to two indices of trophic structure, paleoproduction and paleoingestion. Significant temporal changes in community structure identified in this way included changes in environmental optimality, food supply, persistence of population dynamics, and the division of resources amongst small and large species. Paleoingestion was consistently bimodally distributed when plotted by size class because small and large species contributed substantially to energy flow. Only the larger size classes accounted for significant paleoproduction. Thus the smaller size classes included small, long-lived species that reached near-maximum size. Habitat optimality was identified by examining the degree to which individuals reached a fraction of their species' maximum size. Significant downcore changes in habitat optimality occurred only for the large species in the assemblage; those potentially most affected by changes in food supply. Species replacement in the community included not only guild replacement but also size replacement. The size-frequency distribution for the community was persistent over hundreds of years whereas those for the individual species frequently were not. So, too, was the distribution of paleoproduction and paleoingestion amongst the size classes. Thus, unlike the population dynamics of each species, the population dynamics and the distribution of energy flow through the constituent size classes was a temporally persistent feature of community structure and represents a valuable parameter in the analysis of the fossil record. A change in assemblage maximum size likely records variations in food supply. Variations in assemblage maximum size and the replacement of chemoautotrophic species with filter-feeding ones suggests that a substantial increase in food supply occurred over the last 400 yr at this site.

A size-structured, time and vertically-dependent model was used to investigate the effects of water column structure on the distribution of larvae of the oyster Crassostrea virginica. Formulations used to model larval growth and behavior are based upon laboratory studies. Simulated vertical larval distributions obtained for conditions representative of a well-mixed, partially stratified and strongly stratified water column illustrate the effect that salinity and temperature gradients have on moderating larval swimming and hence on larvae vertical location. For well-mixed conditions, smaller larvae are dispersed throughout most of the water column. For strongly stratified conditions, the smaller-sized larvae cluster within the region of strong salinity change. Intermediate-sized larvae cluster within or directly below the region of strong salinity change. The oldest larvae are found near the bottom for all salinity conditions since their location is determined primarily by sinking rate. Additional simulations show that diurnal salinity changes interact with larval behavioral responses to create patchy larval distributions Finally, simulations show that the inclusion of an upwelling or downwelling velocity can overwhelm the behavioral responses of smaller larvae and result in much different vertical distributlons. The simulated vertical larval distributions show that changes in larval migratory behav~or which are brought about by changes in the vertical sal~nity gradient can significantly alter larval distribution patterns. These, when combined with horizontal advective flows, have important implications for larval dispersal.

We examine the use of paleoproduction (the net production of somatic tissue over an individual's lifetime) and paleoingestion (the energy required to sustain the animal over its life span) in habitat tier and feeding guild analysis of paleocommunities, using modern death assemblages from a variable salinity bay. Community attributes evaluated by the abundance of the constituent species differed markedly from the same attributes described by paleoproduction or paleoingestion. Examination of the guild and tier structure from the perspective of paleoproduction and paleoingestion identified significant temporal changes in environmental optimality, probably related to changes in food supply, and in the division of resources amongst small and large species. Significant downcore changes in habitat optimality occurred only for the large species in the assemblage; those potentially most affected by changes in food supply. Tier structure was less variable than guild structure because species replacement always occu...

Phytoplankton standing stocks have shown a steady decline in Galveston Bay, Texas over the last 20 years. Phytoplankton provides the primary food resource for oyster populations in Galveston Bay. We used a time-dependent population dynamics model of oyster populations to examine the impact of a decline in phytoplankton stocks on oyster populations. Simulations were run with two different types of mortality: winter mortality, assuming that the oyster fishery is the primary source of mortality; and summer mortality, assuming that predators and disease are the primary source of mortality. All simulations showed the same qualitative trends. Market-size adults disappear from the population in about 4 years, with an approximate 15% decline in food supply. Submarket-size adults maintained an increasing or steady population density for 10–14 years, after which the populations crashed to near extinction in 2–4 years. The proximate cause was a cessation in reproductive activity when food supply ceased to be sufficient to generate a fall spawn, an approximate 60% drop in food from current levels in Galveston Bay. The temporal sequence of mortality affected the outcome very little. The simulations suggest that populations decline rapidly in response to declining food supplies because a minimum food level is required to support a market-size population and a minimal reproductive activity. The simulations suggest that a reduction in market-size individuals is the primary early-warning signal of decreased food supply within the affected population and that this warning signal might easily be mistaken for overfishing. Proper management requires the monitoring of food supply and the use of a mathematical model to assess the importance of observed declines in population abundance. Unfortunately, once the fishery is affected, little time may remain before the termination of spawning and population extinction.

The advent of molecular detection assays has provided a set of very sensitive tools for the detection of pathogens in marine organisms, but it has also raised problems of how to interpret positive signals that are not accompanied by visual confirmation. PCR-positive results have recently been reported for Haplosporidium nelsoni (MSX), a pathogen of the oyster Crassostrea virginica in 31 of 40 oysters from 6 sites in the Gulf of Mexico and the Caribbean Sea. Histological confirmation of the PCR results was not undertaken, and no haplosporidian has been reported from the numerous histological studies and surveys of oysters in the region. To further investigate the possibility that H. nelsoni is present in this region, we sampled 210 oysters from 40 sites around the Gulf of Mexico and Puerto Rico using PCR and 180 of these using tissue-section histology also. None of the oysters showed evidence of H. nelsoni by PCR or of any haplosporidian by histology. We cannot, therefore, confirm that H. nelsoni is present and widespread in the Gulf of Mexico and the Caribbean Sea. Our results do not prove that H. nelsoni is absent from the region, but taken together with results from previous histological surveys, they suggest that for the purposes of controlling oyster importation, the region should continue to be considered free of the parasite.

1. Eggs and sperm contain significantly more PAH (polynuclear aromatic hydrocarbon) than somatic tissues in oysters ( Crassostrea virginica ) taken from Galveston Bay. 2. The quantity of gonadal material was the most important correlate of PAH body burden. 3. Eggs, but not sperm, were enriched in chlorinated compounds (e.g. DDD, chlordane), while both eggs and sperm were enriched in total PCBs relative to somatic tissue. 4. Oysters may lose up to 50% of their total body burden of certain PAHs and pesticides in a single spawn.

A quantitative gonadal index was developed for oysters, Crassostrea virginica (Gmelin. 1791), using polyclonal antibodies from eggs and sperm. Percoll used in the purification of oyster eggs and sperm greatly improved the purity of antigens compared to filtering the egg or sperm through a fine mesh only. The antigen-antibody reaction was tested with indirect sandwich ELISA using alkaline phosphatase-conjugated goat anti-rabbit igG as a secondary antibody. Rabbit anti-oyster egg IgG and anti-oyster sperm IgG initially exhibited a weak cross-reactivity over somatic tissue. Absoring with acetone-dried oyster tissue powder removed this cross-reactivity. Both antisera exhibited strong specific immunological reactions to oyster eggs or sperm respectively. The quantity of eggs or sperm was measured using ELISA and a quantitative gonadosomatic index (dry wt of egg or sperm/dry wt oyster) (GSI) calculated. GSI from ELISA correlated with gonadal stage measured histologically. Monthly mean GSI of female oysters was highest during late spring to early summer (0·157–0·201) and lowest during early winter to early spring (0·002-0·000). Maximum GSI observed during the study was 0·422 for female oysters and 0·446 for male oysters. Female oysters produce 3·7–65·4 million eggs, with an average of 21·1 million during each spawning. A positive correlation was observed between the number of eggs produced and oyster size; the number of eggs in the gonad increased as oyster size (i.e. total dry wt) increased (r= 0·67); however, the relationship was non-linear. Large oysters contained proportionally fewer eggs. Prevalence of Perkinsus marinus parasitism was high, 90–100%, during the study, as was weighted incidence, 1·33 to 2·67, No statistically significant correlation was observed between infection intensity and the per cent weight of oyster eggs or egg number.

Bivalves are often used as sentinel organisms in monitoring programmes for trace organic contaminants. the animal's physiological state may be important in interpreting trends in contaminant body burden. Simultaneous evaluation of physiological state and organic contaminant concentration in bivalves typically involves removal of a lipid-rich cross-section of the body mass for histopathological and/or gonadal analysis. In this study, the bias introduced by this technique in the final trace organic concentrations, e.g. of polynuclear aromatic hydrocarbons, chlorinated pesticides and polychlorinated biphenyls, are evaluated on five different size groups of oysters. As a test case, we evaluated the use of this method in the NOAA's Status & Trends Mussel Watch (NS&T) Programme. the average biases introduced by this technique in the final trace organic concentrations in Gulf of Mexico oysters have been increasing since 1986 as a consequence of a continuous decrease in the size of the individuals sampled.

Crassostrea oysters are protandrous hermaphrodites. Sex is thought to be determined by a single gene with a dominant male allele M and a recessive protandrous allele F, such that FF animals are protandrous and MF animals are permanent males. We investigate the possibility that a reduction in generation time, brought about for example by disease, might jeopardize retention of the M allele. Simulations show that MF males have a significantly lessened lifetime fecundity when generation time declines. The allele frequency of the M allele declines and eventually the M allele is lost. The probability of loss is modulated by population abundance. As abundance increases, the probability of M allele loss declines. Simulations suggest that stabilization of the female-to-male ratio when generation time is long is the dominant function of the M allele. As generation time shortens, the raison d’etre for the M allele also fades as mortality usurps the stabilizing role. Disease and exploitation have shortened oyster generation time: one consequence may be to jeopardize retention of the M allele. Two alternative genetic bases for protandry also provide stable sex ratios when generation time is long; an F-dominant protandric allele and protandry restricted to the MF heterozygote. In both cases, simulations show that FF individuals become rare in the population at high abundance and/or long generation time. Protandry restricted to the MF heterozygote maintains sex ratio stability over a wider range of generation times and abundances than the alternatives, suggesting that sex determination based on a male-dominant allele (MM/MF) may not be the optimal solution to the genetic basis for protandry in Crassostrea.

The protozoan Perkinsus (=Dermocystidium) marinus is the most important pathogen of eastern oysters (Crassostrea virginica) in the Gulf of Mexico. Prevalence of P. marinus has been related to salinity and temperature, with low temperatures and salinities usually limiting infection. In 1986, a yearly monitoring program was begun to describe the regional distribution and yearly trends in P. marinus prevalence and infection intensity in the Gulf of Mexico in connection with NOAA's Mussel Watch program. Between 1986 and 1989, prevalence and infection intensity dropped in the southeastern and southwestern Gulf, infection intensity most strongly, and rose in the Florida panhandle, prevalence most strongly. Infection intensity fell but prevalence rose on both sides of the Mississippi delta; central/north Texas remained essentially unchanged. The regional and temporal distribution of P. marinus in the Gulf of Mexico can be considered a product of two spatio-temporal phenomena. (1) A relatively stable spatial pattern exists each year with centers of infection on the order of 300 km. (2) A concordance in yearly shifts in prevalence and infection intensity occurs among sites on a scale of > 1,000 km. The spatial scale of concordant yearly changes is much larger than the scale of centers of infection, and probably originates in broad shifts in weather patterns as they affect temperature and salinity (via rainfall and river runoff). Long-term climatic changes are most likely responsible for these spatio-temporal shifts and, as such, P. marinus prevalence and infection intensity may eventually be predictable from climatic models. Our data demonstrate the importance of multi-year cycles, not just seasonal cycles and occasional heavy rains, in determining P. marinus prevalence and implicate salinity as the primary mediating factor. Summary Perkinsus marinus plagues most oyster populations in the Gulf of Mexico including nearly every commercial one. Sixty to eighty percent of all Gulf oysters are infected and summer mortalities are frequently high. The regional and temporal distribution of P. marinus in the Gulf of Mexico can be considered a product of two spatio-temporal phenomena. (1) A relatively stable spatial pattern exists each year, with centers of infection on the order of 300 km. (2) A concordance in yearly shifts in prevalence and infection intensity occurs among sites on a scale of > 1,000 km. The spatial scale of concordant yearly changes is much larger than the scale of centers of infection, and probably originates in broad shifts in weather patterns as they affect temperature and salinity (via rainfall and river runoff). P. marinus is known to respond to climatic variables such as temperature and rainfall (salinity). The productivity of oyster populations has also been related to changes in climate (Allen & Turner, 1989; Ulanowiczet al., 1980; Chatryet al., 1983), salinity being the most important variable. Our data demonstrate the importance of multi-year cycles, not just seasonal cycles and occasional heavy rains, in determining P. marinus prevalence and also implicate salinity as the primary mediating factor. Only a shift in climate could explain the concordance in yearly shifts in prevalence on a 1,200 km scale. The El Nino/Southern Oscillation is a good candidate for the agent responsible, although 4 years of data are not adequate to conclusively prove this conjecture. Regardless of the source, long-term changes in climate clearly exert a significant impact on P. marinus prevalence and infection intensity, probably through salinity, and likely impact oyster population dynamics and fishing success in the Gulf of Mexico as well.

The stratigraphic, taphonomic and biologic records from two cores in Copano Bay, Texas were analyzed to determine (1) whether variations in shell content with depth were caused by variations in carbonate preservation, carbonate production or sedimentation rate and (2) the extent to which characteristics of fossil assemblages, such as species composition, numerical abundance, biomass, and trophic and habitat structure, identified similar or different trends. Below the top few cm of the sedimentary column, variations in carbonate content with depth could be attributed to variations in carbonate production. Most biological attributes varied similarly with depth and, hence, time on both long (⪖100 yr) and short (∼10 yr) temporal scales. These variations could not be explained by any taphonomic process, sediment reworking and burial, or sedimentation rate. Despite a vigorous taphonomic milieu, to obtain the shell content of Copano Bay sediments requires the preservation of nearly all carbonate produced. Preservation of a large fraction of the shell carbonate added requires the preservation of most of the relatively large-shelled biota (large species and adults) which retain important evidence of changes in the community's history in this area. The results reemphasize the importance of large individuals and biomass in paleontologic reconstruction and suggest that changes in community productivity, which in paleontologic usage, must be carbonate productivity, are preserved in the fossil record.

As part of NOAA's Status and Trends Program, oysters were sampled from 43 sites throughout the Gulf of Mexico from Brownsville, Texas, to the Florida Everglades from 1986 to 1989. Oysters were analysed for body burden of a suite of metals and petroleum aromatic hydrocarbons (PAHs), the prevalence and intensity of the oyster pathogen,Perkinsus marinus, and condition index. The contaminants fell into two groups based on the spatial distribution of body burden throughout the Gulf. Arsenic, selenium, mercury and cadmium were characterized by clinal reduction in similarity with distance reminiscent of that followed by mean monthly temperature and precipitation. Zinc, copper, PAHs and silver showed no consistent geographic trend. Within local regions, industrial and agricultural and use andP. marinus prevalence and infection intensity frequently correlated with body burden. Contaminants and biological attributes followed one of three temporal trends. Zinc, copper and PAHs showed concordant shifts over 4 years throughout the eastern and southern Gulf. Mercury and cadmium showed concordant shifts in the northwestern Gulf. Selenium, arsenic, length, condition index andP. marinus prevalence and infection intensity showed concordant shifts throughout most of the entire Gulf. Concordant shifts suggest that climatic factors, the El Nino/Southern Oscillation being one example, exert a strong influence on biological attributes and contaminant body burdens in the Gulf. Correlative factors are those that probably affect or indicate the rate of tissue turnover and the frequency of reproduction; namely, temperature, disease intensity, condition index and length.

The 1995-1998 database from NOAA's National Status and Trends 'Mussel Watch' Program was used to compare the distributional patterns of parasites and pathologies with contaminant body burdens. Principal components analysis (PCA) resolved five groups of contaminants in both mussels and oysters: one dominated by polycyclic aromatic hydrocarbons (PAHs), one dominated by pesticides, and three dominated by metals. Metals produced a much more complex picture of spatial trends in body burden than did either the pesticides or PAHs. Contrasted to the relative simplicity of the contaminant groupings, PCA exposed a suite of parasite/pathology groups with few similarities between the sentinel bivalve taxa. Thus, the relationship between parasites/pathologies and contaminants differs significantly between taxa despite the similarity in contaminant pattern. Moreover, the combined effects of many contaminants and parasites may be important, leading to complex biological-contaminant interactions with synergies both of biological and chemical origin. Overall, correlations between parasites/pathologies and contaminants were more frequent with metals, frequent with pesticides, and less frequent with PAHs in mussels. In oysters, correlations with pesticides and metals were about equally frequent, but correlations with PAHs were still rare. In mytilids, correlations with metals predominated. Negative and positive correlations with metals occurred with about the same frequency in both taxa. The majority of correlations with pesticides were negative in oysters; not so for mytilids. Of the many significant correlations involving parasites, few involved single-celled eukaryotes or prokaryotes. The vast majority involved multi-cellular eukaryotes and nearly all of them either cestodes, trematode sporocysts, or trematode metacercariae. The few correlations for single-celled parasites all involved proliferating protozoa or protozoa reaching high body burdens through transmission. The tendency for the larger or more numerous parasites to be involved suggests that unequal sequestration of contaminates between host and parasite tissue is a potential mediator. An alternative is that contaminants differentially affect parasites and their hosts by varying host susceptibility or parasite survival.

Discrimination and comparison between relatively young (recently dead) and relatively old (less recently dead) shells has been an important component of studies on modern death assemblages. We employed amino acid dating to determine whether or not various shell and taphonomic attributes could be used to categorize Donax into age (time-since-death) categories (e.g., old vs. young). As expected, biological interactions and whether the specimen was a right or left valve were not time-dependent. Abraded shells, shells lacking sheen, those showing evidence of dissolution, fragments and chipped shells tended to be relatively old, but many old shells retained the species' original (living) characteristics with regard to all of these attributes except color and sheen. Shell color was the only attribute yielding a satisfactory division of shells into two age categories, old vs. young. The formation of a typical beach assemblage requires the gradual addition and taphonomic alteration of shells over many hundreds of...

Taphofacies have been based on the likelihood that considerable variability exists in taphonomic processes between different environments and that this variability produces predictable variations in taphonomic signature between assemblages. Three stations above storm wave base that differed little in sediment texture and depth were sampled on the inner continental shelf of central Texas. Taphonomic analysis revealed subtle gradients in sediment grain size and water depth that would not be revealed by most other analyses. These gradients may exist over very small spatial scales, equivalent to those within a single extensive outcrop. Not all taphonomic attributes are equally likely to be preserved in the fossil record. Those varying with depth in our study area, such as fragmentation and articulation, are more likely to be preserved than those documenting changes in sediment texture, such as variation in the frequency of dissolution features on the shells. Nevertheless, siting and sampling protocols are important when characterizing a taphofacies because within-habitat variation is potentially as large as between-habitat variation. Description of the average taphofacies for an environment must include documentation of the variation in taphonomic attributes within the sampled area because few conservative taphonomic attributes exist. Fragments, even those that are unidentifiable, retain significant taphonomic information and should not be ignored. Careful sampling should permit the simultaneous description of general taphofacies as well as the detection of important but unsuspected gradients in the environment.

The utilization of taphonomic information to formulate biostratinomic models for modern and ancient assemblages has become a potentially powerful tool in paleoecologic analysis. The division of fossil assemblages into discrete suites of taphonomically-similar material adds an extra dimension to the interpretation of depositional setting and paleoecologic structure (Brett and Baird, 1986; Speyer and Brett, 1986, 1988; Speyer, 1987). This approach uses the hypothesis that taphonomic alteration varies in a predictable way with depositional setting. In other words, each specific environment (e.g., low-salinity muddy bay, storm-dominated clastic shelf) is characterized by a unique suite of physical, chemical and biological processes: these processes imprint a unique and predictable “taphonomic signature” on the death assemblage.

Although taphonomic processes alter or destroy much of the preservable portion of the original community, many of these processes also imprint valuable paleoecological information about the fauna and the environment of deposition which might be employed in paleoenvironmental reconstruction (Brett and Baird, 1986; Speyer and Brett, 1986, 1988). Accordingly, taphonomic analysis of modern and ancient death assemblages has received much attention recently (Powell et al., in press; Parsons et al., 1988; Kidwell and Behrensmeyer, 1988) and a new concept, that of the taphofacies, has been developed (e.g., Speyer, 1988). Taphofacies are based on distinct suites of taphonomic characteristics, taphonomic signatures, imprinted on the shell material and on its relationship to the sedimentary fabric by mixtures of physical, biological and chemical processes, which potentially are unique for a given environment. Ideally, if unique taphonomic signatures can be identified and the formative processes understood in a wide range of modern environments, this baseline can be employed to make more accurate reconstructions of equivalent paleoenvironments.

Oysters from 48 Gulf of Mexico sites were examined for presence and infection intensity of the endoparasite, Perkinsus (= Dermocystidium) marinus (Mackin, Owen and Collier, 1950) as part of NOAA's Status and Trends Mussel Watch Program. Prevalence exceeded 75% at 25 sites. Infection intensity did not vary with sex or reproductive stage. Latitude, total polynuclear aromatic hydrocarbon (PAH) content and industrial and agricultural land use significantly affected the parasite's distribution. PAH and pesticide concentrations were latitudinally dependent, suggesting an impact of spawning frequency on uptake and depuration. P. marinus analysis complements the use of pollutant body burden for determining change in environmental quality because it responds differently than pollutant body burden to the biology and ecology of the oyster.

A bioenergetics model of the Manila clam (Ruditapes philippinarum) was built to simulate growth, reproduction and spawning in culture and fishery field sites in Marennes–Oleron Bay (French Atlantic coast). The model is driven by two environmental variables: temperature and food supply. Food supply and the clam's filtration rate determine soft tissue condition index, which in turn drives clam growth and reproduction. The model was calibrated and then validated using two independent data sets. This paper discusses the difficulty of comparing experimental data and individual model outputs when asynchronous spawning events occur in the studied population. In spite of this difficulty, the simulations reproduce the typical pattern of growth and reproduction of the Manila clam. Simulations showed that water column chlorophyll a concentration is not a perfect estimator of food resources for a near bottom suspension feeder such as the Manila clam and emphasize the lack of knowledge about Ruditapes philippinarum nutrition. The individual growth model presented in this paper will be integrated into a numerical population model describing the host– parasite–environment relationship in Brown Ring Disease, caused by the bacterium Vibrio tapetis. © 2007 Elsevier B.V. All rights reserved.

An individual-based model was developed to simulate growth of the hard clam, Mercenaria mercenaria, in response to temperature, salinity and food supply conditions. Unique characteristics of the model are that: (1) length and tissue weight are related only by condition index, so that weight, up to a point, can vary independently of length, and (2) age is decoupled from length. Tissue weight changes result from the difference in assimilation and respiration. Changes in hard clam condition are determined from a standard length-weight relationship for average hard clam growth. Changes in hard clam length (growth) occur only when condition index is greater than zero, which happens when excess weight for a given length is attained. No change in length occurs if condition index is zero (mean case) or negative (less weight than expected at a given length). This model structure resolves limitations that accompany models used to simulate the growth and development of shellfish populations. The length-frequency distribution for a cohort was developed from the individual-based model through simulation of a suite of genotypes with varying physiological capabilities. Hard clam populations were then formed by the yearly concatenation of cohorts with partially independent trajectories that are produced by cohort- and population-based processes. Development and verification of the hard clam model was done using long-term data sets from Great South Bay, New York that have been collected by the Town of Islip, New York. The ability to separately track length and age in the simulations allowed derivation of a general mathematical relationship for describing age-length relationships in hard clam populations. The mathematical relationship, which is based on a twisted bivariate Gaussian distribution, reproduces the features of age-length distributions observed for hard clam populations. The parameters obtained from fitting the twisted bivariate Gaussian to simulated hard clam length-frequency distributions obtained for varying conditions yield insight into the growth and mortality processes and population-dependent processes, compensatory and otherwise, that structured the population. This in turn provides a basis for development of theoretical models of population age-length compositions. The twisted bivariate Gaussian also offers the possibility of rapidly and inexpensively developing age-length keys, used to convert length-based data to age-based data, by permitting a relatively few known age-length pairs to be expanded into the full age- and length-frequency structure of the population.

Discard reduction is a component of the statutory requirements of the Sustainable Fisheries Act. One species of concern is scup, Stenotomus chrysops, discarded in the Loligo pealei fishery. Initially, regulations were imposed restricting the fishery in time and space to avoid areas and times associated with high scup discarding. Modified gear was required in 2003 on any boat fishing in areas otherwise closed to the fishery to reduce scup discarding. The purpose of this study was to evaluate the success of the 2003 net regulations and the potential influence of time-area closures (GRAs) in achieving a reduction in scup discarding. The regulations are based on three expectations. (1) Reduction in discarding in the Loligo squid fishery will materially reduce total scup discarding. (2) Exclusion of Loligo squid fishing vessels from the GRAs will result in these vessels fishing in areas that inherently produce fewer scup discards without equivalently increasing discarding in other sensitive species. (3) The use of a square-mesh large-mesh section in the extension will reduce scup discarding to the extent that otherwise would be achieved if the boats fished outside the GRAs without the economic cost imposed by redeploying the fleet. Analysis of the NMFS-NEFSC observer database offers no support for the belief that Expectation 1 has been met. Squid catches were too low to sustain a directed fishery in the northern GRA during this study. Thus, had this area been open, limited scup discarding would have occurred. In this study, squid catches averaged 1025 kg tow(-1) in the southern GRA. Thus, had the GRA been open, Loligo fishing would have taken place. Yet, in the 34 tows taken by two vessels, not a single scup was caught. Redeployment of the fleet clearly increased scup discarding in 2003. Thus, Expectation 2 was not met. Field tests demonstrated that the implemented net modification can produce reduced catches of mostly smaller-sized finfish without impairing squid catch, but the data also indicate that this result may not be routinely achieved. Thus, Expectation 3 was not completely met. Implementation of the 2003 net regulation was likely premature, in that the specification was not adequate to guarantee the desired results. The history of the scup discarding issue in the Loligo squid fishery demonstrates that discard reduction cannot be accomplished without adequate prior evaluation of the sources of discards, without the requisite and concomitant experimental evaluation of the results of regulatory reform, and without adequate commercial-scale testing of prospective reforms prior to implementation.

The Illex illecebrosus fishery in the northwestern Atlantic Ocean is trawl-based. I. illecebrosus normally lives less than 1 year. One option for managing such a short-lived species is the use of catch and effort data obtained from fishing vessels during the fishing season to manage the fishery in real time. Verification of the accuracy of data reports is important. Conceivably, information contained in the data stream of vessel position and time provided by a remote data logger could be used to reconstruct the vessel’s activities to assess the reliability of industry reports. This study describes quantitatively the types of vessel operating activities that take place on a typical I. illecebrosus fishing trip and assesses the possibility of reconstructing these activities reliably from the simple data stream of vessel position and time. Seven activities were identified, six of which occurred commonly: steaming to and from port, searching, towing, set-up time between tows, steaming overnight and laying-to overnight. Processing the catch, as a discrete activity, occurred rarely. Each activity could be characterized in terms of its duration and distance traveled, the average vessel speed, and the tendency for vessel speed to change during the activity. Most activities were conducted in a linear manner. Accordingly, reasonable estimates of the distance and duration of these activities could be obtained simply from the knowledge of the starting and ending position and time. Analysis of search time and subsequent catch revealed that searching did not improve catch. More squid would have been caught had the vessels used this time for towing. Catch per unit effort (CPUE) can be calculated using duration or distance in the denominator. In this set of fishing trips, the two were equivalent. Catch bore a nonlinear relationship with CPUE. In particular, larger catches were associated with incrementally larger CPUEs. The uniqueness of each activity when described by its characteristic speed, duration and distance, and the consistency of these characteristics for each activity between vessels suggests that vessel behavior might be assessed remotely using a time series of position and time. Such a capability might be important in any real-time management plan where industry vessels necessarily must be depended upon for data on catch and CPUE.

A hydrodynamic–oyster population model was developed to assess the effect of changes in freshwater inflow on oyster populations in Galveston Bay, Texas, USA. The population model includes the effects of environmental conditions, predators, and the oyster parasite, Perkinsus marinus, on oyster populations. The hydrodynamic model includes the effects of wind stress, river runoff, tides, and oceanic exchange on the circulation of the bay. Simulations were run for low, mean, and high freshwater inflow conditions under the present (1993) hydrology and predicted hydrologies for 2024 and 2049 that include both changes in total freshwater inflow and diversions of freshwater from one primary drainage basin to another. Freshwater diversion to supply the Houston metropolitan area is predicted to negatively impact oyster production in Galveston Bay. Fecundity and larval survivorship both decline. Mortality from Perkinsus marinus increases, but to a lesser extent. A larger negative impact in 2049 relative to 2024 originates from the larger drop in fecundity under that hydrology. Changes in recruitment and mortality, resulting in lowered oyster abundance, occur because the bay volume available for mixing freshwater input from the San Jacinto and Buffalo Bayou drainage basins that drain metropolitan Houston is small in comparison to the volume of Trinity Bay that presently receives the bulk of the bay's freshwater inflow. A smaller volume for mixing results in salinities that decline more rapidly and to a greater extent under conditions of high freshwater discharge. Thus, the decline in oyster abundance results from a disequilibrium between geography and salinity brought about by freshwater diversion. Although the bay hydrology shifts, available hard substrate does not. The simulations stress the fact that it is not just the well-appreciated reduction in freshwater inflow that can result in decreased oyster production. Changing the location of freshwater inflow can also significantly impact the bay environment, even if the total amount of freshwater inflow does not change.

Eastern oysters (Crassostrea virginica) often undergo epizootics of MSX (Multinucleated Spore Unknown) disease, which is caused by the protozoan pathogen, Haplosporidium nelsoni. The disease has been present in oyster populations in the mid-Atlantic United States since the 1950s. During the 1980s and 1990s, it became established further north along the east coast of the United States. To investigate the factors underlying the northward progression of MSX disease, a model that simulates the host–parasite–environmental interactions was used. The model is physiologically-based and is structured around the transmission, proliferation and death rates of the parasite. Environmental conditions of temperature, salinity and oyster food supply provide the external forcing that results in variations in the biological rates. For this study, environmental data sets, both average and extreme, were obtained at a site in upper Chesapeake Bay for 1986 through 1995. This site is in the middle of one of the most productive oyster growing regions on the east coast of the United States; thus, both short- and long-term changes in the environment measured here realistically reflect conditions experienced by important oyster populations. The effect of short-term high-salinity (drought) or low-salinity (wet) conditions on MSX disease prevalence and intensity was relatively small because the average salinity regime already favors maximum parasite activity at this site. Even the extreme low salinity events were not low enough to significantly inhibit the parasite. Similarly, simulations using short-term high-temperature extremes for the same site showed only minor deviations from the average pattern because average temperatures were already high enough to support parasite development. In contrast, the measured low temperature conditions, applied for a single year, caused a dramatic reduction in parasite activity, which extended over a 2-year period. Additional simulations show that overall food supply to the host is of little consequence in determining the basic disease pattern; however, the timing of maximum food supply provided to the host, relative to specific times in the parasite life cycle, is important in determining whether or not the parasite attempts sporulation or undergoes density-independent growth. Simulations that test a sequence of changing environmental conditions show that when a year with cold winter temperatures (less than 3 °C) is followed by a year of low salinity (less than 15 ppt), prevalences and intensities of MSX disease are greatly reduced, with the disease becoming almost absent in the oyster populations; however, the disease returns when average environmental conditions return. Simulations using progressive cooling or warming conditions indicate that winter temperatures consistently lower than 3 °C limit the long-term development of MSX disease. These simulations support the suggestion that climate warming is a contributing factor to the northward spread of MSX disease.

Mercury as an environmental hazard, especially with regard to human health, has been of concern since the Minamata disaster. From 1966 to 1970 a chlor-alkali plant in Point Comfort, Texas released mercury-enriched wastewater (up to 29.9 kgHg/day) into Lavaca Bay (TWQB 1977). Since 1970 the Texas Department of Health (TDH) has periodically closed and then re-opened portions of Lavaca Bay to the harvesting of crabs and finfish based on their levels ( 0.5 ppm Hg wet weight) of mercury. A 1988 closure remains in effect as of this writing. Mercury contamination in Lavaca Bay organisms thus continues to be a problem 22 years after the chlor-alkali plant ceased releasing mercury into the bay. The goal of the following research was to better understand the behavior of mercury in Lavaca Bay. Oysters have been widely used as indicator species in metal pollution studies. Most such programs have focused on the concentrations of metals in oysters from different geographic areas. This study, however, investigated the rate and amount of mercury a [open quotes]clean[close quotes] oyster would accumulate when transplanted to a contaminated estuary and the rate of mercury depuration by contaminated oysters placed in a clean environment. The oysters were additionally analyzed formore » Ba, Cu, Fe, P, and Zn to test for the possible involvement of these metals in mercury accumulation and depuration. 17 refs., 3 figs., 2 tabs.« less

Three models are combined to investigate the effects of changes in environmental conditions on the population structure of the Eastern oyster,Crassostrea virginica. The first model, a time-dependent model of the oyster population as described in Powell et al. (1992, 1994, 1995a,b, 1996, 1997) and Hofmann et al. (1992, 1994, 1995), tracks the distribution, development, spawning, and mortality of sessile oyster populations. The second model, a time-dependent larval growth model as described in Dekshenieks et al. (1993), simulates larval growth and mortality. The final model, a finite element hydrodynamic model, simulates the circulation in Galveston Bay, Texas. The coupled post-settlement-larval model (the oyster model) runs within the finite element grid at locations that include known oyster reef habitats. The oyster model was first forced with 5 yr of mean environmental conditions to provide a reference simulation for Galveston Bay. Additional simulations considered the effects of long-term increases and decreases in freshwater inflow and temperature, as well as decreases in food concentration and total seston on Galveston Bay oyster populations. In general, the simulations show that salinity is the primary environmental factor controling the spatial extent of oyster distribution within the estuary. Results also indicate a need to consider all environmental factors when attempting to predict the response of oyster populations; it is the superposition of a combination of these factors that determines the state of the population. The results from this study allow predictions to be made concerning the effects of environmental change on the status of oyster populations, both within Galveston Bay and within other estuarine systems supporting oyster populations.

Rates of burial and transport of molluscan remains are essentially unknown for deeper continental shelf and slope environments, especially over periods of years. An understanding of the rates of taphonomic loss are critical to paleoecological analyses and to paleoenvironmental studies in general. The post-depositional history of organic remains is highly dependent on the length of time the material remains at or near the sediment/water interface. In order to measure these rates, 100 gastropod and bivalve shells were scattered over a marked area of sea bottom at 21 sites in seven environments of deposition (EOD9s) in the Gulf of Mexico and at five EOD9s on the Bahamas platform edge. A total of over 2600 shells were deployed. Each site was thoroughly documented with video photography. After one year in the Bahamas and after two years in both the Gulf of Mexico and Bahamas, these sites were re-photographed and video-taped to measure rates of burial and movement of shells. Shell condition (e.g., articulation, encrustation, and color loss) for those shells that remained exposed was also determined. Shells deployed in Gulf of Mexico petroleum seep sites, on the open continental shelf, and on the continental slope experienced high rates of burial (0.5-3.0 cm) within two years. Shells at these sites generally were not transported or disturbed, and disarticulation rates were low. In the Bahamas, shells on the platform shelf were completely buried within one year. On the steep platform edge from 70 to 300 m, shells on hardground ledges remained exposed, whereas shells in carbonate sands were buried by up to 3.5 cm of sediment. Transport was more common on the steep slopes of the platform edge. Net sedimentation rates for the outer continental shelf and slope of 0.01-0.06 cm yr-1 are well below our observed burial rates of 31 cm yr (super -1) . Thus, burial rate may be somewhat independent of sedimentation rate due to local reworking of sediments by storms at shallower depths and mechanisms such as deep bottom currents or bioturbation at deeper sites. Therefore, the potential for fossil preservation in offshore areas with low sedimentation rates may be much greater than previously assumed.

A mixed assemblage of lucinid and mussel shells were placed in mesh bags and left at a site of autochthonous death assemblage formation in a petroleum seep community on the Louisiana upper continental slope for a period of 3 yr. Upon recovery, the shells were assessed for taphonomic alteration and compared to a control assemblage of unaltered shells. The data verify a basic assumption of taphofacies analysis; that evidence of taphonomic processes preserved with the assemblage does in fact document the primary taphonomic processes that biased the assemblage from the original assemblage of living preservable organisms. Significant variability in taphonomic rates existed between shells from locations 10 m apart, as is typical of autochthonous assemblages, so that small-scale variability in the taphonomic process was important

Identifying ancient cold seep faunas is intertwined with the problem of distinguishing autochthony from parautochthony. Cold seep faunas are autochthonous assemblages. Taphofacies from an allochthonous microtidal inlet, a parautochthonous inner shelf and an autochthonous upper slope (representing cold seep faunas) were compared to identify their distinguishing characteristics and to facilitate cold seep recognition. The taphonomic signature of the allochthonous inlet assemblage is dominated by abrasion and edge alteration. Bivalves are completely disarticulated

Chemoautotrophically-based benthic communities on the Louisiana continental slope are currently producing the only significant localized, autochthonous shell accumulation in the northern Gulf of Mexico shelf and slope region. These sites are well below storm wave base and are not subject to anthropogenic disturbance. Five distinctive biofacies are associated with petroleum seepage, dominated respectively by vestimentiferan tubeworms, lucinid, thyasirid and vesicomyid clams and mytilid mussels. The taphonomy of petroleum seeps includes dissolution as the most pervasive mode of shell alteration throughout all the biofacies

Downcore changes in carbonate content can be produced by varying rates of taphonomy, physical and biological reworking or changes in rates of carbonate addition. Only the latter can be used to investigate changes in carbonate productivity in the living community. Only the latter indicate unequivocal changes in community structure. The stratigraphic, taphonomic and biologic records from two cores in Copano Bay, Texas were analyzed to determine (1) whether variations in shell content with depth were caused by variations in carbonate preservation, carbonate production or sedimentation rate and (2) the extent to which characteristics of fossil assemblages such as species composition, numerical abundance, biomass, and trophic and habitat structure, identified similar or different trends. Below the top few cm of the sedimentary column, variations in carbonate content with depth could be attributed to variations in carbonate production. Most biological attributes varied similarly with depth and, hence, time on both long (≥ 100 yr) and short (~ 10 yr) temporal scales. These variations could not be explained by any taphonomic process, sediment reworking and burial, or sedimentation rate. Despite a vigorous taphonomic milieu, explaining the shell content of Copano Bay sediments requires the preservation of nearly all carbonate produced. Doing so requires the preservation of most of the relatively large-shelled biota (large species and adults) which retain important evidence of changes in the community's history in this area. The results reemphasize the importance of large individuals and biomass in paleontologic reconstruction and suggest that changes in community productivity, which in paleontologic usage, must be carbonate productivity, are preserved in the fossil record in some assemblages. Taphofacies analyses might be used to identify such assemblages.

Crabs are a major component of modern marine ecosystems, but are only rarely described in fossil assemblages. Studies of brachyuran taphonomy have examined either the fossil end-products of the taphonomic process or the very earliest stages of decay and decomposition. The next logical step is the analysis of modern crab death assemblages; i.e., studies that examine taphonomic loss in areas where the composition of the living assemblage is known. The authors studied crab death assemblages in shallow water sediments at several localities in an near Laguna Madre, Texas. Nearly every sample examined contained some crab remains, most commonly in the form of isolated claws (dactyl and propodus). A crab fauna associated with a buried grass bed contained abundant remains of the xanthid crab Dyspanopeus texanus, including carapaces, chelipeds, and thoraxes, as well as fragments of the portunid Callinectes sapidus and the majiid Libinia dubia. Crab remains may be an overlooked portion of many preserved benthic assemblages, both in recent and modern sediments.

Clam and mussel assemblages associated with petroleum seepage on the Louisiana continental slope form the only substantial shell accumulations below storm wave base on the northwestern Gulf of Mexico shelf and slope. Four distinct biofacies are present at the seeps, dominated respectively by mussels, lucinid clams, vesicomyid clams and tubeworms. Each primary seep site is typically composed of a series of not necessarily contiguous, autochthonous beds dominated by one biofacies. Mussels and tubeworms often co-occur, but neither normally co-occur with lucinid or vesicomyid clams. Lucinid and vesicomyid clam beds have the best chance of preservation. Despite essentially undisturbed accumulation in quiet water below storm wave base, concavity ratios rarely differ from 1:1 and frequency of articulation may be low. Dominantly concave-up valves previously reported in quiet water may result from man's fishing activities. Significant variability in shell orientation, frequency of articulation and concavity ratio between adjacent samples indicates that many individual stratigraphically-equivalent samples should be used in any taphofacies analysis of assemblages formed in low-energy environments. Lucinid beds which form below the sediment surface and vesicomyid beds which form on the sediment surface differed significantly in shell orientation and articulation frequency. Assemblages forming below storm wave base in low-energy environmentsmore » may comprise a wide variety of taphofacies depending upon whether formation occurs primarily beneath the sediment surface or on the sediment surface, despite contemporaneous formation under similar environmental conditions.« less

1. 1. Oysters were exposed for 2- and 5-day periods to increased salinity (26%.–38%.), anoxia, turbidity and drilling effluents. 2. 2. After two days, the FAA pool in the gill tissue of oysters exposed to 38%. salinity had elevated glycine, alanine and β-alanine levels; oysters exposed to anoxia showed elevated glycine and alanine and decreased aspartic acid levels. 3. 3. After 2 days, both oysters exposed to turbidity and to drilling effluents had increased cysteic acid levels. Glutamic acid and alanine levels were also elevated in oysters exposed to drilling effluents. 4. 4. After 5 days, glycine, alanine and β-alanine remained above control levels in oysters exposed to increased salinity whereas in those exposed to anoxia, turbidity and drilling effluents, a significant decrease in most amino acids occurred with the total FAA pool decreasing by 50%. 5. 5. The FAA pool's response was unique for each stress studied suggesting that the FAA pool may prove to be a useful diagnostic tool for determining a posteriori the causative agent responsible for a given stress response.

The effect of an ectoparasitic gastropod, Boonea (= Odostomia) impressa , on the energy bidget of its host, the American oyster, Crassostrea virginica , was examined. A model was developed from laboratory and field data, as well as from equations developed by Powell and Stanton (1985) . The model predicted that net productivity by large (7 cm length) oysters parasitized by 10 and 30 large (6 mm length) snails would be reduced by 21% and 63%, respectively. In contrast, net productivity in small (3 cm length) oysters would be reduced 25% by only 3 snails. Small oysters would have a negative energy balance when parasitized by 10 snails. The predicted reduction in growth was compared with measured growth in small and large oysters parasitized at abundances typical of Texas oyster reefs. Control oysters (no parasites) gained more shell weight than parasitized oysters. In four-week experiments conducted during the spring and fall, small control oysters gained 86% and 75% more weight than highly parasitized oysters. Large control oysters had 29% and 88% more shell deposition. Snail parasitism produced 75% mortality in small, highly parasitized oysters in the summer. In typical field populations in Texas bays, a minimal estimate of 4–12% of the energy otherwise available to the oyster for growth and reproduction is consumed by Boonea impressa .

1. 1. The ectoparasitic snail Boonea (= Odostomia) impressa is an important parasite of oysters. Although results varied among tissues and levels of parasitism, all oysters parasitized by B. impressa exhibited alterations in biochemical composition after 1 month. 2. 2. Few changes were observed in small (2–4 cm) or large (6–8 cm) oysters parasitized by 5 or 10 snails, respectively. In contrast, carbohydrate concentration decreased in small oysters parasitized by 15 or 25 snails and increased in large oysters parasitized by 30 snails. 3. 3. Decreased carbohydrate content probably resulted from direct removal of assimiliated carbon by B. impressa. Increased carbohydrate concentration may be due to the combined impact of B. impressa with infections by the protozoan Perkinsus (= Dermocystidium) marinus. P. marinus infection increased in intensity with snail parasitism. Increased lipid content in the mantle tissue of large oysters and increased taurine content in most oysters and oyster tissues could be similarly explained. 4. 4. Overall, mantle tissue was the most severely affected, possibly because snail parasitism produces direct injury to this tissue as well as the systemic impact caused by removal of assimilated carbon.

The effect of time averaging on species richness of the preservable component (animals with preservable hard parts) of living benthic communities was investgated using long-term (24–30 mo) data sets obtained by recurrent sampling in estuarine and euhaline (30–40 ppt) habitats. About 20–40% of all living species collected were preservable. Species richness of the living community increased with salinity and water depth. Cumulative species richness increased with increasing duration of study. The percentage of preservable species, however, declined with increasing depth. As many preservble species were collected over time in some physically variable estuarine habitats as were collected in the physically less variable, euhaline habitats. Changing environmental factors allowed different species to inhabit these estuarine areas as time passed, whereas species richness was usually higher in euhaline habitats at any particular time. Hence, species richness in the death assemblages may be as high in some physically variable, estuarine habitats as in more invariant euhaline habitats. The species composition of the preservable component of the living community was more persistent than the nonpreservable component. That is, on the average, species additions or replacements occurred more frequently in the nonpreservable component. This increased persistence of the preservable component, however, could not offset the inherently more rapid temporal changes in faunal composition that occurred in physically variable habitats. Therefore, the classic ecologic relationship between increased species richness and reduced environmental variability may not be preserved. Additional evidences must be used to distinguish between species-rich assemblages produced by time averaging of noncontemporaneous taxa in environmentally variable habitats and those produced by diversedcommunities in less variable habitats.

The effects of changes in vertical and horizontal microscale gradients of oxygen and sulfide on meiofaunal distributions were examined in laboratory microcosms. Specifically, the effect of tube abandonment and reestablishment by macro-infauna on the distribution of subsurface turbellarians, gnathostomulids and gastrotrichs was studied. Meiofauna responded rapidly (within 6 h) to changing sediment chemistry, consistently trying to reoccupy optimal habitat. Every subsurface taxon had a preferred suboptimal habitat which it occupied primarily during transit from deteriorating to newly established optimal habitat. Only during this time did the distribution of ecologically similar taxa overlap substantially. Changes in oxygen and sulfide gradients could explain most but not all of the response; food availability might also be important. Oxybios consistently chose oxic suboptimal microhabitat. Thus behaviorally, as well as biochemically and ecologically, thiobios represent a distinct group among the meiofauna.

Life in the sulfide system requires the ability to withstand the toxic effects of long-term sulfide stress. The adaptations of sulfide-system interstitial metazoans to sulfide stress have been investigated using 35 S-sulfide. One possible adaptation, the total exclusion of sulfide at the body wall, could not be demonstrated. Sulfide-system turbellarians and gastrotrichs, however, consistently incorporated less 35 S-sulfide during a 2-h incubation period than their surface-dwelling counterparts. Analysis of autoradiographs of the sulfide-system acoels Myopea crassula , Solenofilomorpha funilis , and Pseudohaplogonaria sp., and the surface-dwelling proseriate Archiloa wilsoni revealed major differences in the concentration of 35 S label in the body wall relative to the internal tissues. Timed uptake and loss experiments plus data from autoradiography showed that the label in the body wall was not permanently bound but, instead, was easily lost. The data indicate that a sulfide detoxification system exists in the body wall which uses an as yet unknown scavenging system to trap much of the sulfide that enters, detoxifies it, and releases the end-product to the medium.

Criteria for taphonomic processes, including dissolution, breakage, abrasion, size sorting and shell orientation, were statistically correlated against environmental parameters representing shell source, depositional environment and depth of burial, using samples obtained from San Luis Pass, a microtidal inlet on the Texas coast. Core intervals were differentiated by cluster analysis into shell-poor sands, slightly shelly sands, shell-rich sands and shell gravels based on their percent carbonate and percent shell gravel content. Boundaries between these sedimentary classes represent thresholds in physical processes forming the shell deposits. We propose that this classification scheme for shelly sediments may be useful for field descriptions in a variety of depositional and tectonic settings. The death assemblages were predominantly composed of whole and fragmental molluscan shells. Most shells show the effects of physical taphonomic processes such as shell breakage, edge rounding, surface abrasion and size sorting. A significant minority of the shells show evidence of minor chemical alteration (dissolution). Patterns of dissolution, edge rounding and surface abrasion differed significantly on shells in a mixed-faunal assemblage derived from different habitats (bay, inlet/beach, inner shelf and unrestricted). Thus, the habitat where a species lived, rather than its final depositional environment, controlled most aspects of its taphonomy. Only shell orientation and size-frequency distribution were significantly affected by final environment of deposition. The hypothesis that a discrete high energy (hurricane) “event” can imprint a unique taphonomic signature is, consequently, false. Although hurricanes physically winnow shell material, a single “event” merely concentrates shells with preexisting characteristics without further significant alteration. Depth of burial was poorly correlated with most biostratinomic effects, including dissolution. Significant dissolution must occur only near the sediment-water interface. Accordingly, quantified taphonomic characteristics might be useful in identifying the original habitats of species deposited in mixed accumulations; “taphofacies” reflect not only the final depositional process, but also taphonomic processes in the habitat of origin.

1. 1. Three turbellarians, Kuma sp., Solenofilomorpha cf. funilis and Parahaploposthia thiophilus and a gastrotrich, Turbanella sp. were exposed to sulfide under oxic and anoxic conditions and the resulting changes in [ATP] and [ADP] monitored. 2. 2. [ATP] in the oxybiotic species, Kuma , decreased under all sulfide exposures. 3. 3. The other three species, all thiobiotic, were sulfide-tolerant with the degree of tolerance dependent on the presence or absence of O 2 . Parahaploposthia was more tolerant under anoxia, Solenofilomorpha under oxia. Turbanella was tolerant under either condition. 4. 4. The sulfide system is a heterogeneous zone comprising a number of microhabitats. Consequently, the metazoans inhabiting this system have developed a variety of metabolic adaptations to sulfide and O 2 appropriate for the microhabitat in which they live.

The death assemblage is an important source of data on the living community prior to sampling and between sampling occasions. Proper use of these data requires a knowledge of how death assemblages form from living communities. A large larval settlement and catastrophic mortality of the clam Mulinia lateralis provided an opportunity to test several hypotheses about death assemblage formation. Individuals of M. lateralis were added to the death assemblage in pulses resulting from episodic mortality, but each pulse rapidly disappeared—half of the shells were gone in 192 days. This loss was size-dependent; smaller shells disappeared at over twice the rate of larger shells. The size-frequency distribution for M. lateralis in the death assemblage was bi-modal because of the simultaneous death of two cohorts of different size frequencies. Individuals present in the death assemblage prior to the new settlement had been locally redistributed by physical processes after death. We hypothesize that larger pulses are preserved preferentially because they remain in the death assemblage longer, and, thus, these shells have a greater chance of being physically reworked beneath the taphonomically-active surface zone by storms. Consequently, death assemblages provide two distinct types of data; data on recent recruitment and mortality provided by pulses in the process of decay, and data on longer-term events provided by the accumulation of the remains of pulses that were buried beneath the surface zone and indefinitely preserved.

The pyramidellid snail, Boonea (= Odostomia) impressa (SAY), is an important ectoparasite of the oyster, Crassostrea virginica (Gmelin). The small-scale spatial distribution of snails was examined in 11 oyster populations in the Copano Bay - Aransas Bay area of the Texas coast. Snails were contagiously distributed (s2/>1) and positively spatially autocorrelated. Patchiness was better developed and patches were larger on enclosed reefs than on more exposed open-bay reefs, probably because higher wave energy and increased distance between oyster clumps limited clump-to-clump movement by snails on open-bay reefs. Small snails were consistently distributed differently from large snails because small snails were less host specific. As the snails grow, a narrowing of host preference results in a substantial change in spatial distribution. Snails were consistently more contagiously distributed than their hosts; however, snail distribution was not host-density dependent. Factors determining the spatial distribution of the host had surprisingly little effect on the distribution of snails. Snail aggregates apparently form randomly by chance meetings of a few snails and then grow by attraction of additional snails. Consequently, snail behavior, which determines the size and length of time a patch retains its integrity, and the age distribution of the snail population may be the two most important factors, besides population size, determining the impact of B. impressa on oyster populations.