Shirley M. Baker

Particle Transport in the Zebra Mussel, Dreissena polymorpha (Pallas)

The capture, transport, and sorting of particles by the gills and labial palps of the freshwater mussel Dreissena polymorpha were examined by endoscopy and video image analysis. More specifically, the morphology of the feeding organs in living zebra mussels was described; the mode and speeds of particle transport on the feeding organs was measured; and the sites of particle selection in the pallial cavity were identified. Particle velocities (outer demibranch lamellae, 90 microm s(-1); inner demibranch lamellae, 129 microm s(-1); marginal food groove of inner demibranchs, 156 microm s(-1); dorsal ciliated tracts, 152 microm s(-1)), as well as the movement of particles on the ctenidia and labial palps of D. polymorpha, are consistent with mucociliary, rather than hydrodynamic, transport. Particles can be sorted on the ctenidia of zebra mussels, resulting in a two-layer transport at the marginal food groove of the inner demibranch. That is: preferred particles are transported inside the marginal groove proper, whereas particles destined for rejection are carried superficially in a string of mucus. Sorting also occurs at the ventral margin of the outer demibranch; desirable particles are retained on the outer demibranch, whereas unacceptable particles are transferred to the inner demibranch and ultimately excluded from ingestion. We suggest that the structure of homorhabdic ctenidia does not preclude particle sorting, and that some ecosystem modifications attributed to zebra mussels may ultimately be due to ctenidial sorting mechanisms.

RANGE AND DISPERSAL OF A TROPICAL MARINE INVADER, THE ASIAN GREEN MUSSEL, PERNA VIRIDIS, IN SUBTROPICAL WATERS OF THE SOUTHEASTERN UNITED STATES

Abstract The tropical Asian green mussel, Perna viridis (Bivalvia: Mytilidae) is a recent invader in the Caribbean Basin, including the subtropical southeastern United States. In this study we examined the (1) range of P. viridis in the southeastern United States, (2) relative abundance of P. viridis across habitats and (3) density of P. viridis in Tampa Bay, FL. The invasion and spread of P. viridis in the southeastern United States was estimated by a combination of first-hand qualitative sampling and second-hand observations. There were apparently at least two discrete introductions, each followed by natural dispersal. The initial invasion was discovered in Tampa Bay in 1999, and was followed by rapid spread of P. viridis south as far as Marco Island, FL, but limited spread northward. In 2002, a second invasion occurred in northeast Florida, separated from the west Florida population by 650 km of coastline. On the east coast, P. viridis appeared to be distributed discontinuously between South Carolina and the Indian River Lagoon, FL by 2007. The literature concerning native distribution, habitat use and invasion history, and vectors of P. viridis is also reviewed.

Physiological Status and Biochemical Composition of a Natural Population of Unionid Mussels (Amblema plicata) Infested by Zebra Mussels (Dreissena polymorpha)

Abstract We compared the physiological status and biochemical composition of unionid mussels (Amblema plicata) from a riverine population with and without attached zebra mussels (Dreissena polymorpha). Unionid specimens were collected from Lake Pepin, Mississippi River, WI and MN, where both infested and noninfested unionids were experiencing local increases in water clarity. Infested specimens had higher ammonia excretion rates, lower respiration to nitrogen excretion ratios and lower clearance rates than noninfested specimens. Infested specimens also had lower carbohydrate and protein contents. Zebra mussel infested unionids had depleted energy stores and we hypothesize that they were starving, relative to noninfested individuals from the same location. This comparison helps to clarify the nature of zebra mussel impacts on unionids by showing that direct attachment is a very important component of the effect of zebra mussel populations on unionids.

Development of ecosystem indicators for the Suwannee River estuary: Oyster reef habitat quality along a salinity gradient

The Suwannee River watershed is one of the least developed in the eastern United States, but with increasing urbanization it is facing potential long-term alterations in freshwater flow to its estuary in the Gulf of Mexico. The purpose of this study was to develop biological indicators of oyster reef state along a natural salinity gradient in the Suwannee River estuary in order to allow the rapid assessment of the effect of changing freshwater input to this system. Percent cover and density of three size classes of living oysters, as well as the abundance of several predominant reef-associated invertebrates, were measured along a broad salinity gradient in the estuary and were correlated with salinity estimates from a long-term database for the preceding 12–24 mo. All eastern oyster,Crassostrea virginica, parameters (percent cover and density of three size classes) were significantly and negatively related to salinity. Data from samples collected near the lower intertidal were more closely dependent upon salinity than were samples from the higher intertidal at the same sites. Salinity differences were most closely reflected in differences in total oyster cover. This relationship corresponded with a general decline in oyster habitat with increasing distance from the mouth of the Suwannee River. Species richness was significantly and positively correlated with allC. virginica parameters (percent cover and density of three size classes), but the relationship explained only about half the variability. Density data of the hooked mussel,Ischadium recurvum, and a mud crab,Eurypanopeus depressus, were positively and strongly correlated withC. virginica parameters, likely reflecting the abundance of habitat provided byC. virginica shells. All of the biological indicators measured responded similarly along the salinity gradient, indicating they provide reliable indices of the effect of changing salinities in the Suwannee River estuary over the previous 1 or 2 yr. Some areas of positive relief defined as reefs 30 years ago are no longer oyster habitat, suggesting an ongoing decline, but nearshoreC. virginica were abundant. *** DIRECT SUPPORT *** A02BY003 00002

Assessment of Cellular and Functional Biomarkers in Bivalves Exposed to Ecologically Relevant Abiotic Stressors

An understanding of the complex effects of the environment on biomarkers of bivalve health is essential for aquaculturists to successfully select field culture sites and monitor bivalve health in these sites and in hatcheries. We tested several whole-organism (functional) and cellular-level biomarkers as indicators of health of the cultured, stress-tolerant northern quahog (hard clam) Mercenaria mercenaria. We performed single- and dual-stressor experiments that were consistent with available water quality data from a clam culture area on the Gulf coast of Florida. Clams from the culture area were exposed over a 14-d period to low O2 (hypoxia), elevated temperature, hyposalinity, and a combination of elevated temperature and hyposalinity. There was no clear relationship between the functional and cellular-level biomarkers, with most of the treatment effects being detected at the whole-organism level but not the cellular level. Survival and burial ability were significantly affected by elevated temperature and by the combination of elevated temperature and hyposalinity. Glycogen content decreased over the experiment duration and did not differ significantly among treatments. There were no significant changes in expression patterns of eight stress proteins or in the levels of oxidatively damaged RNA. The results highlight the importance of investigating the effects of multiple stressors in short-term, controlled laboratory conditions and suggest that such cellular-level biomarker assays should be paired with functional biomarkers to better understand the responses of highly stress-tolerant species.

Zebra Mussels (Dreissena Polymorpha) Attached to Native Mussels (Unionidae) or Inanimate Substrates: Comparison of Physiological Rates and Biochemical Composition

ABSTRACT We compared the physiological rates and biochemical composition of dreissenid mussels (Dreissena polymorpha) from a riverine population that were attached to unionid mussels (Amblema plicata) or to rocks. Specimens were collected from Lake Pepin, Mississippi River, Wisconsin and Minnesota. Unionid-attached specimens had greater oxygen uptake and ammonia excretion rates than did rock-attached specimens. However, unionid-attached specimens also had lower carbohydrate and lipid contents. Our results indicate that there are physiological costs of attaching to unionids, at least under some circumstances. Interspecific competition for a limited food resource may negatively impact not only the unionids, but the attached dreissenids as well. This conclusion challenges the assumption that dreissenids benefit from attaching to unionid mussels.

Hemoglobin Structure and Function in the Rat-Tailed Sea Cucumber, Paracaudina chilensis

The rat-tailed sea cucumber, Paracaudina chilensis, has abundant hemoglobin-filled hemocytes in its perivisceral coelom, water vascular system, and hemal system. The perivisceral oxyhemoglobin consisted of 34 kDa dimers and molecules with an apparent molecular weight of ca. 50 kDa. The perivisceral hemoglobin had a high oxygen affinity with a P50 of 1.5 mm Hg at 15°C. It exhibited cooperative oxygen binding with a Hill coefficient of 1.26 to 1.86. Oxygen affinity appeared to be pH dependent, but the effect was not significant. The heat of oxygenation was -11.2 kcal mol-1. At high hemoglobin concentrations, the perivisceral hemoglobin oxygen affinity was lower and the apparent pH effect and cooperativity were increased. Perivisceral and water vascular hemoglobins had spectral characteristics similar to those of other invertebrate and vertebrate hemoglobins. The perivisceral hemoglobin appeared to be electrophoretically heterogeneous and was structurally distinguishable from water vascular hemoglobin. The oxygen affinity of water vascular hemoglobin was not different from that of the perivisceral hemoglobin in spite of the difference in structure and location in the animal. The exceptionally high oxygen affinity hemoglobin of P. chilensis, a burrowing sea cucumber, may be adaptive to this animals oxygen-limited habitat.

Continuous water quality monitoring for the hard clam industry in Florida, USA

In 2000, Florida’s fast-growing hard clam aquaculture industry became eligible for federal agricultural crop insurance through the US Department of Agriculture, but the responsibility for identifying the cause of mortality remained with the grower. Here we describe the continuous water quality monitoring system used to monitor hard clam aquaculture areas in Florida and show examples of the data collected with the system. Systems recording temperature, salinity, dissolved oxygen, water depth, turbidity and chlorophyll at 30 min intervals were installed at 10 aquaculture lease areas along Florida’s Gulf and Atlantic coasts. Six of these systems sent data in real-time to a public website, and all 10 systems provided data for web-accessible archives. The systems documented environmental conditions that could negatively impact clam survival and productivity and identified biologically relevant water quality differences among clam aquaculture areas. Both the real-time and archived data were used widely by clam growers and nursery managers to make management decisions and in filing crop loss insurance claims. While the systems were labor and time intensive, we recommend adjustments that could reduce costs and staff time requirements.

Self-Adhesive Wire Markers for Bivalve Tag and Recapture Studies

Abstract: Bivalves are good candidates for tag and recapture studies because the accrual of shell material provides a stable record of growth. Obtaining measurements for tagged individuals over time relies on the resilience of markings or tagging devices to environmental stress as well as the readability of identifying markings upon capture. Tagging devices should also be easy and quick to apply in order to minimize potential stress to the animal during extirpation from the water. A variety of methods to attach devices to the inside and outside of bivalve shells have been used in tagging studies. This paper describes a low cost, commercially available, self-adhesive numbered tag for application to clams and other bivalves. Tests of the tag demonstrate its resilience to severe conditions over a short time scale with a ninety-five percent recovery of individuals with tags remaining intact. Ninety-four percent recovery of individuals with tags intact was also achieved in long-term studies. No problems with legibility of tags recovered occurred in any of the tests.

INVESTIGATION OF PERKINSUS SPP. IN AQUACULTURED HARD CLAMS (MERCENARIA MERCENARIA) FROM THE FLORIDA GULF COAST

Abstract Aquacultured hard clams (Mercenaria mercenaria) from Florida were examined for Perkinsus spp. using culture in Rays Fluid Thyioglycollate Medium (RFTM) and PCR. Clams were negative for P. marinus-specific PCR, but low-level infections were observed by RFTM culture and by genus-specific PCR. In contrast, P. marinus was frequently detected in wild oysters, indicating possible host specificity for this parasite.