Geukensia Demissa Research Articles

Late stage bivalve larvae in a well-mixed estuary are not inert particles

Depth-specific sampling at a single location was used to examine the vertical distribution of pediveliger larvae of bivalve mollusks in the York River, an estuary of Chesapeake Bay, Virginia. The water column at the sampling site was usually well mixed, lacking consistent temperature or salinity gradients for larvae. Four species showed strong vertical stratification when collected simultaneously at three depths. Pediveliger stage larvae of a clam (Cyrtopleura costata), an oyster (Crassostrea virginica), and a shipworm (Bankia gouldi) were most abundant near the benthos, and least abundant near the surface. A mussel (Geukensia demissa), showed the reverse trend, with most pediveliger larvae near the surface. Tidal stage had a slight effect on two species (C. costata andC. virginica), but only to increase the relative abundance of larvae near the benthos during flood tide. Otherwise, neither tidal phase nor light levels (night versus day) had detectable effects on distribution patterns. Sampling very close to the sediment-water interface provided no evidence that pediveliger larvae spent a significant proportion of their time in this location. While the behavior of precompetent bivalve larvae may tend to retain them within an estuary, that of competent-to-metamorphose pediveliger larvae does not appear to have that function. Pediveliger larvae may regulate their depth to best locate potential settlement substrate. Such an hypothesis is consistent with adult habitat zones of at least some of these species in Chesapeake Bay. Removing competent-to-settle larvae from analyses of larval distributions in estuaries will enhance or clarify depth distribution patterns observed for earlier-stage larvae.

Seston available as a food resource for the ribbed mussel ( Geukensia demissa) in a North American, mid-Atlantic saltmarsh

We studied the composition of the <25 μm seston size fraction as a food resource potentially available to suspension feeding ribbed mussels, Geukensia demissa, over an annual cycle in Canary Creek saltmarsh, Delaware Bay. There were significant seasonal variations in the concentration of particulate organic carbon (POC), particulate organic nitrogen (PON), and total carbohydrate, but not cellulose. The concentration of cellulose, measured by hydrolytic cellulase enzyme assay, was relatively low (seasonal range 24 to 35 μg l −1) and only comprised from 3% of total carbohydrate in May 1996 to 13% in November 1995. We used the biomass of microalgae, estimated from chlorophyll a, and abundance of free-living bacteria and heterotrophic nanoflagellates to calculate each component's equivalent carbon content. Microalgae were the most dominant carbon source (62% annually) among the four identified components (phytoplankton, bacteria, heterotrophic nanoflagellates, and cellulose) in all seasons except in August 1995 when carbon from bacteria was most abundant (55%). The annual average carbon equivalents of heterotrophic nanoflagellates and cellulose were relatively small (2 and 4%, respectively). The total concentration of POC in the seston was much greater than the carbon derived from the four identified components. The proportions that these identified components contributed to POC varied seasonally and combined only accounted for 8–24% of POC. Based on these estimates, the bulk of the POC in Canary Creek marsh was not associated with any of the four components we identified. We suggest that this uncharacterized material was some type of non-lignocellulosic, amorphous detritus of unknown utility as a food resource for ribbed mussels.

Tidal and seasonal variations in the quantity and composition of seston in a North American, mid-Atlantic saltmarsh

We determined the concentration of seston, particulate organic matter, and biological components (chlorophyll a, bacteria, and heterotrophic nanoflagellates) for <25 μm size fraction seston over five seasons in Canary Creek saltmarsh, Delaware Bay, USA. This material is the potential food resource for suspension-feeding ribbed mussels, Geukensia demissa, that inhabit the marsh intertidal zone. For eight tidal cycles each season we collected water six times at hourly intervals from mid-flood tide to mid-ebb tide. Although the concentration of seston did not vary seasonally, there were significant seasonal variations (analysis of variance, P<0.05) in seston components, with chlorophyll a concentration being highest in May and bacteria and heterotrophic nanoflagellates most abundant in August. Seston composition also varied within each tidal cycle with a magnitude as great as the seasonal variation. We conclude that ribbed mussels are subject to an unpredictable food supply that varies in composition and concentration on the order of hours and days. In contrast to the pronounced temporal changes, seston characteristics did not differ significantly among sampling locations within the marsh, or between samples collected close to the sediment surface and from the upper water column. Resuspension of sediment particles caused by tidal flow was not evident in tidal creeks and there were no dominant patterns in total seston concentration corresponding to tidal stages (flood tide, high slack water, and ebb tide) over the five sampling months. The abundance of biological components in the seston, including chlorophyll a, bacteria, and heterotrophic nanoflagellates, were significantly greater during high flood tide and high slack water than during ebb tide. The decline of biological components, particularly chlorophyll a in the ebb tide, indicates that this temperate saltmarsh imported organic material produced in the Delaware estuary.

ASSESSMENT OF PREY AVAILABILITY FOR DIAMONDBACK TERRAPINS IN A CONNECTICUT SALT MARSH

Wheeler Marsh in Milford, Connecticut provides habitat for diamondback terrapins (Malaclemys terrapin), a unique estuarine turtle. To assess potential prey availability, the distribution and abundances of marsh snails (Melampus bidentatus), mud snails (Ilyanassa obsoleta), marsh mussels (Geukensia demissa), and fiddler crabs (Uca spp.) were studied in several sub-habitats (marsh surface, marsh edge, creek bank, and mudflats) of five tidal creeks. Almost all terrapins have been found in one section of the marsh, Turtle Creek, where all four prey species were present in large numbers. However, high numbers of some prey were found in other sections of the marsh as well, suggesting that resource availability may not be the primary determinant of terrapin distribution. The physical structure, plant density, and tidal amplitudes of salt marsh creeks may also be important determinants of terrapin distribution via their influence on resource accessibility.

Response of Growth and Density of a Population of Geukensia demissa to Land-Derived Nitrogen Loading, in Waquoit Bay, Massachusetts

Nutrient enrichment is a widespread phenomenon affecting coastal waters, including salt marshes. As land-derived nitrogen loading in estuarine waters increases, chlorophyll concentrations in the water also increase. We hypothesized that such increases might increase growth of the food-limited population of Geukensia demissa, which is a dominant component of salt marshes. To test this, we conducted a regional scale experiment in three estuaries of Waquoit Bay, Massachusetts that receive different nitrogen loading rates. A stable isotope experiment on mussel tissues and on particulate organic matter (POM) showed that mussels within an estuary fed on POM characteristic of that estuary, demonstrating the direct linkage between POM and mussels within an estuary. In addition, we measured age-specific shell growth rates of mussel populations using two different methods: indirectly, shell growth of mussels indicated by internal shell-lines was measured by fitting the data to the von Bertalanffy equation, and directly, mussels were transplanted from one estuary to the other two, and their actual shell growth rates after 80 days were measured. Growth rates of mussels in the Waquoit Bay estuaries varied with age of the mussel, tidal elevation, and with mean concentration of chlorophyll in the water. Mussels grew best in the lower intertidal zone, at the marsh banks. Young mussels grew faster than older mussels. Growth rates increased in response to presumed greater food supply across the estuaries, only for younger mussels. The significant differences we found among the mussels from different estuaries indicate a response to higher concentrations of food particles available in estuaries subject to higher nitrogen loads.

Macroinvertebrate and fish populations in a restored impounded salt marsh 21 years after the reestablishment of tidal flooding.

During the last two decades, the State of Connecticut has restored tidal flow to many impounded salt marshes. One of the first of these and the one most extensively studied is Impoundment One in the Barn Island Wildlife Management Area in Stonington, Connecticut. In 1990, twelve years after the re-establishment of tidal flooding, the density of the marsh snail Melampus bidentatus, the numerically dominant macroinvertebrate of the high marsh, in Impoundment One was about half that in reference marshes below the breached impoundment dike. By 1999 the densities of Melampus above and below the dike were not significantly different, but the shell-free biomass was greater above the dike as a result of the somewhat larger number and size of the snails there. Twenty-one years after the renewal of tidal flooding, three marsh macroinvertebrates (the amphipods Orchestia grillus and Uhlorchestia spartinophila and the mussel Geukensia demissa) were significantly less abundant in the previously impounded marsh than in the reference marshes, whereas another amphipod (Gammarus palustris) was more abundant above the breached dike where conditions appeared to be somewhat wetter. In 1991 the fish assemblage in a mosquito-control ditch in Impoundment One was similar to that in a ditch below the breached dike; however, the common mummichog Fundulus heteroclitus appeared to be less abundant in the restoring marsh. By 1999 the number of mummichogs caught in ditches was significantly greater in Impoundment One than in the reference marsh, but the numbers of mummichogs trapped along the tidal creek were comparable above and below the dike. The results obtained in this study and those of other restoring marshes at Barn Island indicate the full recovery of certain animal populations following the reintroduction of tidal flow to impounded marshes may require up to two or more decades. Furthermore, not only do different species recover at different rates on a single marsh, but the time required for the recovery of a particular species may vary widely from marsh to marsh, often independently of other species.

Seasonal variations in the rates of aquatic and aerial respiration and ammonium excretion of the ribbed mussel, Geukensia demissa (Dillwyn)

Aquatic and aerial rates of oxygen consumption and ammonium excretion of ribbed mussels, Geukensia demissa (Dillwyn), collected from the mid-intertidal zone of a mid-Atlantic salt marsh, were measured under ambient conditions of food, temperature, and salinity over five seasons. Rates of aquatic respiration covaried with body size and season, as the rates were high and strongly related to mussel tissue weight in spring and summer but low and weight independent in winter. There was a significant interannual difference between summer of 1995 and 1996. Rates of aerial respiration also varied seasonally, with high rates of oxygen consumption in summer and low rates in winter. The magnitude of these seasonal variations were greater than those for aquatic respiration, and as a result, the ratio of aerial to aquatic respiration was higher in summer (0.61 and 0.52) than in winter (0.11). This indicates that G. demissa was able to actively regulate aerial respiration, thereby permitting high aerobic metabolism during prolonged periods of air exposure in summer. We hypothesize that such high rates of aerial respiration, during the seasons of high metabolic activity, are required to provide sufficient energy for mussels to facilitate food digestion during air exposure at low tide. Rates of ammonium excretion varied seasonally and increased with mussel weight in all seasons. The atomic ratio of oxygen to nitrogen (O:N), calculated from aquatic respiration vs. ammonium excretion, was significantly lower in autumn (26) than in other seasons (46–60) among which the O:N did not vary significantly.

Sperm Ultrastructure of Two Mollusk Species Geukensia demissa and Modiolus modiolus (Mytilidae, Bivalvia)

Sperm ultrastructure was studied in two Atlantic species of bivalve mollusks Geukensia demissa and Modiolus modiolus (Mytilidae). These spermatozoa have a classic structure common for species with external fertilization: the head of the spermatozoon of G. demissa and M. modiolus consists of an acrosome, including an acrosomal vesicle and periacrosomal material, a nucleus, and a middle part with two mutually perpendicular centrioles, surrounded by a ring of spherical mitochondria. The spermatozoa of G. demissa and M. modiolus differ in the general shape and size of the head (M. modiolus, 5.8 × 4 μm; G. demissa, 4.2 × 2.5 μm), as well as the structure of the acrosome and the number of mitochondria (M. modiolus, 8–12; G. demissa, 5–6). The spermatozoa of the Atlantic species M. modiolus and M. modiolus (M. kurilensis) from the Sea of Japan are close in ultrastructure, but differ in the number of mitochondria. This could possibly be a reason to consider M. modiolus from the Sea of Japan as a separate subspecies, M. modiolus kurilensis. In ultrastructure, the spermatozoa of G. demissa differ significantly from the spermatozoa of M. modiolus, but are similar to the spermatozoa of species of the genus Brachidontes.

Antibacterial activities of oyster ( Crassostrea virginica) and mussel ( Mytilus edulis and Geukensia demissa) plasma

Anti- Bacillus megaterium activity was measured in unfractionated plasma withdrawn from three common US East Coast bivalve molluscs: an oyster Crassostrea virginica and the mussels Geukensia demissa and Mytilus edulis. The activities of the plasma samples from these bivalves were also measured against a C. virginica pathogen Perkinsus marinus. Strong anti- B. megaterium activity was measured in plasma from C. virginica and M. edulis, but was not detected in G. demissa. Bactericidal activity was found in hemocyte extracts from all bivalves in this study, suggesting a cellular origin of cytotoxic humoral factors. Peptides (< 10 kDa) were separated from the plasma samples by ultrafiltration; weak antibacterial peptide activity was quantified in C. virginica peptides, but not in peptides from the mussels. In the case of P. marinus, plasma from M. edulis or G. demissa was strongly cidal as compared to plasma from C. virginica. This difference in activity probably reflects the low pathogenicity of this oyster parasite for the mussel species tested. In summary, the bactericidal activity of plasma proteins from these bivalves showed considerable interspecies variation and did not necessarily correlate directly with antiprotistan activity. When present, antibacterial and antiprotistan activities seemed to be associated with plasma proteins rather than < 10-kDa plasma peptides, with the possible exception of C. virginica anti- B. megaterium activity and the occasionally expressed anti- P. marinus activity of M. edulis peptides. The precise identity of the plasma protein(s) responsible for the antimicrobial activities measured have yet to be determined, but it is likely that agents other than, or in addition to, lysozyme play significant roles in the process.

Chemolithoheterotrophy in a metazoan tissue: thiosulfate production matches ATP demand in ciliated mussel gills.

The ribbed mussel Geukensia demissa inhabits sulfide-rich coastal sediments with a distribution that suggests a preference for exposure to sulfide. Although sulfide is a respiratory poison, it is also a potent reductant. Geukensia demissa gill mitochondria can use sulfide as a respiratory substrate for ATP production, and the gills of this species exhibit sulfide-supported oxygen consumption that matches the energy demand of ciliary beating. Here, we demonstrate (i) that the major product of G. demissa gill sulfide oxidation is thiosulfate and (ii) that the rate of sulfide oxidation also matches the cellular energy demand, resulting in a ratio near unity of oxygen consumed to sulfide oxidized at both low and high ciliary beat frequencies. A value for this ratio of unity is consistent with electrons from sulfide oxidation entering the mitochondrial electron transport chain. In the gills of the blue mussel Mytilus edulis from sulfide-free conditions, this ratio is 3-5 times higher, indicating an uncoupling of oxygen consumption from sulfide oxidation. Whereas M. edulis gills exhibit anaerobic metabolism during sulfide exposure, G. demissa gills do not, indicating a difference in sulfide tolerance between the two mussel species.

Isolation and identification of an ice-nucleating bacterium from the gills of the intertidal bivalve mollusc Geukensia demissa.

In the fall, freeze tolerant intertidal invertebrates usually produce ice-nucleating proteins that are secreted into the hemolymph. These proteins help protect against freeze damage by insuring that ice formation is limited to extracellular spaces. Geukensia demissa, a freeze tolerant, salt marsh bivalve mollusc was examined for the presence of ice nucleating proteins. The ice-nucleating temperature (INT) of the hemolymph was not significantly different from artificial seawater of the same salinity indicating the lack of an ice nucleating protein in the hemolymph. The palial fluid did have an elevated INT, indicating the presence of an ice nucleator. The INT of the palial fluid was significantly reduced by boiling and filtration through a 0.45-&mgr;m filter. High INT was also observed in the seawater associated with the bivalves, and was demonstrated in water samples collected from salt marshes but not sand and pebble beaches. Moreover, the INT of water samples collected from a salt marsh decreased in the summer. All of these data suggest that the ice-nucleating agents in the hemolymph and the seawater are ice-nucleating bacteria. One species of ice-nucleating bacteria, Pseudomonas fulva was isolated from the gills of Geukensia. These bacteria could perform the same function as hemolymph ice-nucleating proteins by limiting ice formation to extracellular compartments.

Recruitment, Survivorship, and Age Structure of a New York Ribbed Mussel Population (Geukensia demissa) in Relation to Shore Level: A Nine Year Study

Age structure, recruitment, and survivorship of a Jamaica Bay, New York ribbed mussel (Geukensia demissa) population were studied over nine years at two shore elevations. Mussels were collected in November (following seasonal growth and recruitment) and March (to assay over-winter mortality). Larval recruits (0-class) averaged 55% of the population at the marsh edge compared with <9% at the higher elevation (6 m upshore). High larval settlement at the edge apparently depletes the larval supply available for settlement within the marsh interior. At the edge, the population generally contained 7 monotonically decreasing age classes compared to 15–20 age classes at the interior site. At the interior site, most 0-class mussels may not directly settle into existing mussel aggregations, but instead immigrate over a period of two years following settlement. The linear survivorship curve at the edge reflects 40–50% mortality every year. Over-winter mortality is sensitive to winter ice conditions. Simulations of reproductive output based on survivorship and fertility data combined suggest that mussel cohorts living in the marsh may approach the life time reproductive output of marsh edge mussels after about 15 years, a life span which is not uncommon at higher shore levels.

Hyperosmotic volume regulation in the gills of the ribbed mussel, Geukensia demissa: rapid accumulation of betaine and alanine.

The content of betaine and alanine in gills of the ribbed mussel Geukensia demissa increases rapidly following transfer of the tissues from 250 to 1000 mOsm seawater (SW). Increases in alanine, proline and glycine account for most of the increase in the amino acid pool. The betaine content increases from 45 to 150 &mgr;mol/g dry weight within 12 h. Transfer of isolated gills from 250 to 1000 mOsm SW results in a temporary cessation of all ciliary activity. Within 20-40 min following transfer, ciliary activity has recovered. Recovery of ciliary activity precedes recovery of tissue hydration. The uric acid content of gills is unchanged by exposure to hyperosmotic media, suggesting that uric acid is not a store of nitrogen for alanine synthesis from pyruvate. In other organisms, the accumulation of betaine in response to hyperosmotic stress is a slow (days to weeks) process that probably involves changes in gene expression. The rapid, large increases in betaine reported here suggest that gene expression is not a factor in volume recovery by euryhaline bivalve tissues exposed to acute hyperosmotic stress.

Seasonal utilization of different seston carbon sources by the ribbed mussel, Geukensia demissa (Dillwyn) in a mid-Atlantic salt marsh.

Seston in salt marshes contains a temporally and spatially complex mixture of natural microparticulate organic material, including phytoplankton, vascular plant detritus, bacteria, heterotrophic nanoflagellates and benthic diatoms. Quantitative information is available concerning how suspension-feeding consumers, such as the ribbed mussel, Geukensia demissa (Dillwyn), utilize some of these components to satisfy their carbon demands. Despite this information there is still a limited understanding of how the relative nutritive contribution of these different dietary items may shift during the year associated with variations in both seston composition and the mussel's physiological condition. To investigate if the mussel's ability to use specific constituents of natural seston varies seasonally, we ran a series of pulse-chase 14C feeding experiments under ambient conditions in March, May, August and November 1996. Phytoplankton, cellulosic detritus, bacteria, heterotrophic nanoflagellates and benthic diatoms were radiolabeled and supplemented in small amounts to natural marsh water for feeding to mussels. The fate of 14C in mussel tissues, feces, respiration and excretion was quantified and contrasted among the different diet types and seasons. Microcapsules containing radiolabeled carbohydrate and protein were used as standards to differentiate possible between-experiment variations in seston composition from seasonal changes in the mussel's feeding and digestive physiology. Mussel clearance rates for all diets were highest in summer and autumn and lowest in winter and spring. In contrast, seasonal shifts in digestive physiology were only found for certain diets. The seasonal range of assimilation efficiencies for microcapsule standards (18-29%) and field-collected microheterotrophs (bacteria 76-93% and heterotrophic nanoflagellates 87-94%) did not differ significantly during the year, whereas summer and autumn assimilation efficiencies for cellulosic detritus (22-24%), phytoplankton (71-79%) and benthic diatoms (89-93%) were up to twofold greater than those in winter and spring (13%, 40-59% and 45-81%, respectively). We conclude that the digestive physiology (e.g., digestive enzyme production) of mussels responds to shifts in dietary components during the year.

Relationships among total lipid, lipid classes, and polychlorinated biphenyl concentrations in two indigenous populations of ribbed mussels (Geukensia demissa) over an annual cycle

Two indigenous ribbed mussel (Geukensia demissa) populations were sampled approximately every four weeks during 1997 to investigate the relationships among concentrations of total lipid, lipid classes, and polychlorinated biphenyls (PCBs). One population was located in a highly contaminated area near a Superfund site (New Bedford Harbor, MA, USA), while the other population was located at a relatively clean site (West Island, Fairhaven, MA, USA). Mussel tissue total PCB concentrations (quantified as the sum of 18 congeners) from the contaminated site were two orders of magnitude greater than those at the clean site. Total lipid and triacylglycerol (TG) also were higher at the contaminated site. No significant relationship (p > 0.05) was observed between total PCBs and total lipid at either location; however, the correlations at both sites increased when total PCBs were compared with total TG or, to a lesser extent, total nonpolar lipid. Principal component analysis and linear discriminatory analysis indicated that the two mussel populations could be distinguished by the proportions of their lipid classes, particularly the concentration of nonpolar lipids, which consisted mainly of TG. These results suggest that the standard method of normalizing organism PCB concentrations to total lipid may not be appropriate as a routine practice, especially when the organism has a relatively low total lipid content (<6% dry wt in this study).

Ribbed Mussel Nitrogen Isotope Signatures Reflect Nitrogen Sources in Coastal Salt Marshes

The stable nitrogen isotope ratio in tissue of the ribbed mussel (Geukensia demissa) was investigated as an indicator of the source of nitrogen inputs to coastal salt marshes. Initially, mussels were fed a diet of 15N-enriched algae in the laboratory to determine how the tissue nitrogen isotope ratio (δ15N) changed with time. Steady-state times were calculated and found to be size dependent, ranging from 206 to 397 d. This indicated that mussels are long-term integrators of δ15N from their diet and may reflect nitrogen inputs to a marsh. Next, indigenous mussels were collected from 10 marshes with similar hydrology and geomorphology in Narragansett Bay, Rhode Island, USA, and mussel δ15N values were evaluated as indicators of nitrogen source. Significant positive correlations were observed between δ15N in mussels and the fraction of residential development in the marsh watersheds. In contrast, mussel isotope ratios showed significant negative correlations with the fraction of combined agricultural and recreational land use. These correlations suggested that the mussel nitrogen isotope signature is influenced by nitrogen derived from human activities in the adjoining marsh watershed. A more detailed examination of these relationships indicated that land use practices in close proximity to marshes and estuarine characteristics may also influence the observed nitrogen isotope signature. A simple, empirical model based on the 10 watersheds was developed to predict mussel δ15N from land use characteristics. The predictive ability of the model was tested with data from 12 additional marshes having similar geomorphology as the original 10, but differing in hydrology and mode of nutrient input. The model showed that ribbed mussel nitrogen isotope signatures may provide information on the source of nitrogen to coastal areas. This could be of use in developing general policies or strategies for monitoring and assessing coastal eutrophication. In addition, the isotopic ratio of mussels is useful as a proxy for watershed land use practices when assessing ecological responses to nutrient enrichment in coastal marshes.

RIBBED MUSSEL NITROGEN ISOTOPE SIGNATURES REFLECT NITROGEN SOURCES IN COASTAL SALT MARSHES

The stable nitrogen isotope ratio in tissue of the ribbed mussel (Geukensia demissa) was investigated as an indicator of the source of nitrogen inputs to coastal salt marshes. Initially, mussels were fed a diet of 15N-enriched algae in the laboratory to determine how the tissue nitrogen isotope ratio (δ15N) changed with time. Steady-state times were calculated and found to be size dependent, ranging from 206 to 397 d. This indicated that mussels are long-term integrators of δ15N from their diet and may reflect nitrogen inputs to a marsh. Next, indigenous mussels were collected from 10 marshes with similar hydrology and geomorphology in Narragansett Bay, Rhode Island, USA, and mussel δ15N values were evaluated as indicators of nitrogen source. Significant positive correlations were observed between δ15N in mussels and the fraction of residential development in the marsh watersheds. In contrast, mussel isotope ratios showed significant negative correlations with the fraction of combined agricultural and recreational land use. These correlations suggested that the mussel nitrogen isotope signature is influenced by nitrogen derived from human activities in the adjoining marsh watershed. A more detailed examination of these relationships indicated that land use practices in close proximity to marshes and estuarine characteristics may also influence the observed nitrogen isotope signature. A simple, empirical model based on the 10 watersheds was developed to predict mussel δ15N from land use characteristics. The predictive ability of the model was tested with data from 12 additional marshes having similar geomorphology as the original 10, but differing in hydrology and mode of nutrient input. The model showed that ribbed mussel nitrogen isotope signatures may provide information on the source of nitrogen to coastal areas. This could be of use in developing general policies or strategies for monitoring and assessing coastal eutrophication. In addition, the isotopic ratio of mussels is useful as a proxy for watershed land use practices when assessing ecological responses to nutrient enrichment in coastal marshes.

Synthesis and wettability characteristics of model adhesive protein sequences inspired by a marine mussel.

Three adhesive polyoctapeptides (X/Y-Gly-Tyr-Ser-Ala-Gly-Tyr-Lys)n (X, Thr and Ala: Y, Thr:Ala = 3:2), which are the C-terminal octapeptide sequences shared by all those consensus motifs of a ribbed mussel Geukensia demissa adhesive protein (RMAP), have been synthesized by the polycondensation of the active esters. The correlation between wettability and adhesion with the alternative substitution by hydrophobic Ala and hydrophilic Thr in the synthetic RMAPs in aqueous solution and as films on high and low surface free energy (sfe) surfaces has been investigated by surface chemical approaches. The side chain moieties of RMAPs arrange their local conformation to adapt to the inherent surface character, and they orientate on high and low sfe surfaces. On a high sfe glass the hydrophilic side chains of the RMAP molecules face toward the surface, and on a low sfe polyethylene (HDPE) the hydrophobic side chains face toward the surface. The bonding strengths of synthetic RMAPs on glass and HDPE with and without enzymatic oxidation have been examined. Increased starting concentration exhibited the strongest adhesive capability (7.5 kgf/cm2) on alumina due to the increased cohesion among RMAP molecules. As another factor to increase adhesive ability, the intermolecular cross-linking among RMAP molecules by tyrosinase increases their adhesive capability by about 20% on HDPE, glass, and alumina except iron.

ATP production from the oxidation of sulfide in gill mitochondria of the ribbed mussel Geukensia demissa.

The ribbed mussel Geukensia demissa inhabits intertidal Spartina grass marshes characterized by sulfide-rich sediments. Sulfide poisons aerobic respiration, and G. demissa may cope in this seemingly inhospitable environment by oxidizing sulfide in gill mitochondria. Well-coupled mitochondria isolated from G. demissa gills were used to investigate sulfide oxidation and ATP synthesis. State 3 respiration, maximally stimulated by 5 micromol l(-)(1) sulfide with a P/O ratio of 0.89 and a respiratory control ratio (RCR) of 1.40, remained refractory to sulfide at higher concentrations except in the presence of salicylhydroxamic acid (SHAM), an inhibitor of alternative oxidases. Sulfide-stimulated ATP production was 3-5 times greater than that stimulated by malate and succinate, respectively, giving an ATP/sulfide ratio of 0.63. The inhibition of sulfide-stimulated respiration and ATP production by the complex III inhibitors myxothiazol and antimycin A, respectively, suggests that electrons enter the electron transport chain before complex III. Combined with in vivo evidence for electron entry at cytochrome c, these data suggest that more than one type of sulfide-oxidizing enzyme may function in G. demissa gills. The SHAM-sensitive pathway of electron flux may be a critical component of a physiological strategy to tolerate sulfide. We conclude that G. demissa exploits the energy available from its reduced environment by using sulfide as a respiratory substrate for cellular ATP production.

Faunal Utilization of Created Intertidal Eastern Oyster (Crassostrea virginica) Reefs in the Southeastern United States

Oyster cultch was added to the lower intertidal marsh-sandflat fringe of three previously createdSpartina alterniflora salt marshes. Colonization of these created reefs by oysters and other select taxa was examined. Created reefs supported numerous oyster reef-associated faunas at equivalent or greater densities than adjacent natural reefs. Eastern oyster (Crassostrea virginica) settlement at one site of created reef exceeded that of the adjacent natural reefs within 9 mo of reef creation. After only 2 yr, harvestable-sizeC. virginica (>75 mm) were present in the created reefs along with substantial numbers ofC. virginica clusters. The created reefs also had a higher number of molluscan, fish, and decapod species than the adjacent natural reefs. After 2 yr the densities ofC. virginica, striped barnacle (Balanus amphitrite), scorched mussel (Brachidontes exustus), Atlantic ribbed mussel (Geukensia demissa), common mud crab (Panopeus herbstii), and flat mud crab (Eurypanopeus depressus) within the created reefs were equivalent to that of adjacent natural reefs. From these data it is evident that created oyster reefs can quickly acquire functional ecological attributes of their natural counterparts. Because the demand for oysters continues to increase in the face of dwindling natural resources, habitat creation techniques need to evolve and these approaches need to consider the ancillary ecological benefits reef creation may provide. Reef function as well as physical and ecological linkages of oyster reefs to other habitats (marsh, submerged aquatic vegetation, and bare bottom) should be considered when reefs are created in order to provide the best use of resources to maintain the integrity of estuarine systems.