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Transparent exopolymer particles (TEP) play an important role in aggregation, phyto- plankton bloom dynamics and the fate of organic carbon. Various types of plankton are known to release exopolymers that contribute to the TEP pool. Little is known, however, about other potential sources of TEP and TEP precursors in the oceans, especially in nearshore waters. Suspension-feeding bivalves can form dense assemblages in coastal waters and can process large volumes of water dur- ing feeding activities (e.g. 5 l h -1 g -1 dry wt). They secrete mucus to maintain clean body surfaces and to aid in capturing and transporting food material. We hypothesized that mucopolysaccharides, which are released from bivalves in dissolved or particulate form, contribute to the TEP pool. To test this hypothesis, laboratory experiments were carried out to measure the concentration of TEP and DOC in chambers with actively feeding oysters Crassostrea virginica over a 9 h period. Field experi- ments were conducted to measure TEP and DOC production by oysters in situ, using clear Plexiglas chambers on an intertidal sand-flat in New Brunswick, Canada. TEP concentrations were determined with an Alcian blue staining technique and spectrophotometric detection. DOC concentrations were determined using high-temperature catalytic oxidation (HTCO) with a platinum catalyst. Laboratory results indicated that oysters significantly enhanced TEP and DOC concentrations compared to con- trol levels over 9 h. Likewise, field experiments demonstrated elevated TEP concentrations in exper- imental chambers compared to control treatments. Our results support the hypothesis that oysters contribute to the production of TEP in coastal marine ecosystems.

Particle feeding on suspended and deposited material is a common mode of food collection among many groups of the Metazoa. In particular, many members of the Mollusca, most notably the bivalves, have specialized in particle feeding. Because suspension- and deposit-feeding activities often play significant roles in ecosystem processes, particular attention has been given to the mechanisms of particle feeding by these molluscs, and to the impacts of environmental factors upon these mechanisms. Early studies of the feeding organs of bivalve molluscs were descriptive and emphasis soon was placed upon the actual uptake of particulate material from the environment and identification of this material. Introduction of electronic particle counters led to a better understanding of the rates and efficiencies at which particle removal occurred, and the interface between food availability in the ocean and responses of these animals to temporal and spatial variability. While some early workers inferred the capabilities of these animals to select particles, it was the introduction of more advanced technologies (e.g., flow cytometry, video endoscopy, confocal microscopy) that allowed more detailed studies of the mechanisms associated with particle uptake and selection by these animals. These techniques have provided a more comprehensive analysis which clearly demonstrate that the mechanisms associated with particle feeding and selection are complex, with species-specific processes based upon both physical and chemical characteristics of the particles. In this review, we summarize prior research on particle selection in suspension- and deposit-feeding bivalve molluscs, discuss current theory and controversy regarding these processes, and propose areas for further study. In particular, more research is needed to elucidate the mechanisms responsible for particle selection, particulate characteristics that impact selection, and the intrinsic and extrinsic factors that mediate these processes.

Attempts have been made, especially in Asia, to displace harmful algal blooms (HABs) by spraying ‘china clay’ and ‘loess’ over affected coastal waters. The impact of this technique on benthic communities and processes is not known. We examined the effects of yellow loess on clearance rates of the benthic, filter-feeding invertebrates, Crassostrea virginica (Gmelin 1791), C. gigas (Thunberg 1793), Mytilus edulis (Linnaeus 1758), M. trossulus (Gould 1850), Argopecten irradians (Lamarck 1819), and Crepidula fornicata (Linnaeus 1758). An Obelia species of hydroid was also studied and the percent time open was analysed. Depletion rates were measured using a range of loess concentrations suspended in culture with unicellular algae (Rhodomonas lens) in 0.45 μm filtered seawater. The effects of loess on clearance rates and behaviour were species-specific. C. virginica was not impacted until clay concentrations reached 1.0 g L−1, while A. irradians showed a significant decrease at 0.01 g L−1. M. edulis showed a significant decrease in clearance rates at the 1 and 10 g L−1 concentrations. For hydroids, the percent time open was significantly lower than the control at 0.01, 0.1, and 10 g L−1. We clearly demonstrate that loess has a significant negative impact on filter-feeding invertebrates. The use of clay as a strategy for mitigation of HABs should be approached with extreme caution. While the control of active blooms may eventually be possible, it may not necessarily be an environmentally advisable or responsible approach to dealing with HABs.

Suspension-feeding bivalve molluscs can assume a large ecological role by linking benthic and pelagic ecosystems. Therefore, a knowledge of the factors that influence feeding rates and processes at the level of the individual is important in understanding bivalve-dominated environments. We examined the roles of diet quality and concentration on particle processing by the ctenidia of four species of bivalves: the mussels Mytilus edulis L. and Mytilus trossulus Gould, and oysters Crassostrea virginica (Gmelin) and Crassostrea gigas (Thunberg). Bivalves were delivered diets of three different qualities at three different concentrations (1–2×103, 104, 105 particles ml−1). The high-quality diet consisted of the cryptophyte Rhodomonas lens Pascher et Ruttner; the low-quality diet consisted of particles prepared from ground Spartina sp. detritus; the medium-quality diet consisted of a 50:50 mixture (by particle number) of both particle types. Particle transport velocities on the ventral groove and dorsal tracts were then measured by means of video endoscopy. Ventral-groove transport velocities of M. edulis were the most responsive, demonstrating a significant increase with increasing diet quality, and a significant decrease with increasing diet concentration. Transport velocities in the ventral groove and dorsal tracts of C. virginica were not significantly affected by changes in diet quality, but significantly increased with increasing diet concentration. Transport velocities of M. trossulus and C. gigas demonstrated little change with diet quality or concentration, indicating that responses are species specific. Our data suggest that differential control of particle transport on the bivalve ctenidium is one of the underlying mechanisms that contribute to compensatory feeding responses exhibited by the entire organism.

Previous studies have demonstrated that bivalve molluscs respond to changing food conditions through processes such as preferential selection and ingestion of particulate matter. Little is known, however, about the underlying mechanisms accountable for these responses. To further explain feeding processes at the level of the pallial organs, we determined pallial cavity residence times, or the amount of time it took particles to travel from the inhalant aperture to the stomach, in two species of bivalves, Crassostrea virginica and Mytilus edulis, under conditions of differing particle quality, particle concentration, and temperature. From these residence times, particle-handling times on the labial palps were determined. Diets of three different qualities were tested, including Rhodomonas lens cells, particles prepared from ground Spartina sp. detritus, and a 50/50 mixture of both. Bivalves were delivered one of the three diets along with 10-μm fluorescent polystyrene beads (tracer), removed from feeding chambers at intervals from 30 s up to 20 min, and placed in liquid nitrogen to halt particle transport. Digestive systems of bivalves were then dissected and examined for the presence of tracer beads. Particle-residence times in the pallial cavity and handling times on the labial palps of C. virginica were significantly affected by changes in diet type. Particle-handling times on the palps decreased with increasing diet quality and ranged from 2.2 min (100% R. lens) to 22.8 min (100% ground Spartina sp.), accounting for 88% and 99%, respectively, of the total time particles spent in the pallial cavity. In contrast, diet quality had little effect on particle-residence times in the pallial cavity of M. edulis. However, residence times were affected by temperature and diet concentration. Temperature significantly affected residence times at particle concentrations of both 20 and 100 particles μl−1, whereas particle concentration affected residence times at 20 °C, but not at 5 °C. Particle-handling times on the labial palps ranged from less than 1 to 5.5 min, depending on temperature and concentration, accounting for 50% to 82%, respectively, of the total time particles spent in the pallial cavity. We suggest that (1) observed interspecific differences in particle handling on the labial palps may be due to differences in palp morphology and function, and (2) particle sorting and selection on the labial palps is a rate-limiting step of pre-ingestive feeding processes in by bivalves.

Most studies regarding the neuroanatomy and neurophysiology of molluscan ctenidia have focused on isolated ctenidial tissue preparations. This study investigated how bivalve molluscs modulate their feeding rates by examining the effects of a variety of neurotransmitters, including serotonin, dopamine, and the dopamine agonist apomorphine on both isolated ctenidial tissue and in intact members of two commercially important bivalve species: the blue mussel, Mytilus edulis; and the bay scallop Argopecten irradians. In particular, we examined the effect of changes in: 1) beat of the lateral cilia (in vitro), 2) distance between ctenidial filaments and/or plicae (in vivo), and 3) diameter of the siphonal openings (in vivo) on alteration of bulk water flow through the mantle cavity. Important differences were found between isolated tissue and whole animals, and between species. Drugs that stimulated ciliary beat in vitro did not increase water processing rate in vivo. None of the treatments increased water flow through the mantle cavity of intact animals. Results suggest that A. irradians was primarily modulating lateral ciliary activity, while M. edulis appeared to have a number of ways to control water processing activity, signifying that the two species may have different compensatory and regulatory mechanisms controlling feeding activity.

Predicting the fate of nanoparticles in aquatic environments requires knowledge of how these materials interact with the organic and inorganic constituents in aqueous media. This work explored the behavior of three types of titanium dioxide nanoparticles (rutile and anatase) in natural seawater, artificial seawater, and Milli-Q water and determined the percent incorporation of the nanoparticles in marine snow, an important hetero-aggregation in the ocean. Dynamic light scattering, zeta potential, field-emission scanning electron microscopy, and inductively coupled plasma mass spectrometry were used to examine the particles over three time intervals (

The technique of endoscopic video observation was used to study feeding processes of Placopecten magellanicus (Gmelin), collected from Bull Arm, Newfoundland in August 1991 and 1992, under near-natural feeding conditions. The fate of captured particles depended on the extent of ingestive or handling capacity saturation. Under low (1 to 10 particles μl-1) to medium (10 to 20 particles μl-1) particle concentrations, most particles were incorporated in continuous anteriorly directed slurries in the dorsal ciliated tracts of the gill arch and dorsal bends. As particle concentration or exposure time to the lower particle concentrations increased, four endogenous mechanisms of ingestion volume control were increasingly observed: (1) rejection of dense mucus-particle masses from the principal filament troughs onto the ventrally beating cilia and associated currents of the ordinary filament plicae, counter to and below the incoming pallial current maintained by the principal filament cilia; (2) intermittent stopping of the anteriorward flow in the dorsal ciliated tracts; (3) reduction or cessation of input from the principal filaments to the dorsal ciliated tracts; (4) detachment of the dorsal bends from the mantle to establish a shunt from the infrabranchial to the suprabranchial cavity. Chemical and histochemical tests of purified fluid withdrawn from the dorsal ciliated tracts indicate that mucus is present at all particle concentrations. Mucus therefore participates both in normal feeding and in ingestion volume control on the bivalve gill, although different mechanisms, and types of mucus, effect transport of material in the dorsal (feeding) and ventral (cleaning) ciliated tracts.

As the application of nanomaterials to science and technology grows, the need to understand any ecotoxicological effects becomes increasingly important. Recent studies on a few species of fishes and invertebrates have provided data which suggest that harmful effects are possible. The way in which nanoparticles are taken up by aquatic organisms, however, has been little studied. We examined uptake of nanoparticles by two species of suspension-feeding bivalves (mussels, Mytilus edulis; oysters, Crassostrea virginica), which capture individual particles1 microm with a retention efficiency of15%. Given this limitation, it would appear that nanoparticles could not be ingested in large numbers. During certain times of the year, however,70% of suspended particles are incorporated within aggregates that are100 microm in size. Therefore, we delivered bivalves fluorescently labeled, 100-nm polystyrene beads that were either (1) dispersed or (2) embedded within aggregates generated in the laboratory. Results indicate that aggregates significantly enhance the uptake of 100-nm particles. Nanoparticles had a longer gut retention time than 10-microm polystyrene beads suggesting that nanoparticles were transported to the digestive gland. Our data suggest a mechanism for significant nanoparticle ingestion, and have implications for toxicological effects and transfer of nanomaterials to higher trophic levels.

The benthic suspension feeding ascidian, Halocynthia pyriformis (Rathke, 1806), is often exposed to high concentrations of resuspended sediment in the Bay of Fundy. Resuspended sediment can change diet quantity and quality that may alter the ascidian's ability to feed and gain energy. The feeding activity of H. pyriformis exposed to bottom sediment was examined using standard physiological techniques and video endoscopy. Ascidians were exposed to natural seston plus additions of bottom sediment ranging in concentration from 0 to 46 mg l(-1). For each sediment concentration, clearance rate, ingestion rate, and retention efficiency of the ascidians was estimated using flow-through feeding chambers. Samples of suspended particles and feces were collected to estimate absorption efficiency and absorption rate. Results indicate that with increasing sediment concentration, ingestion rate increased to a constant level, absorption rate increased linearly despite a logarithmic decrease in absorption efficiency, and the retention of small particles (2-5mgr;m) increased while retention of larger particles (5-15mgr;m) decreased. As sediment concentration increased, squirting frequency increased and diameter of the siphon was reduced. Endoscopic observation of feeding structures and processes and the measurement of particle velocity was performed on ascidians exposed to 0 and 10 mg l(-1) of bottom sediment. An increase in squirting frequency at the high concentration facilitated the rejection of unwanted material and altered the structure and transport velocity of mucus. Mucus velocity was five times slower at 10 mg l(-1) than at 0 mg l(-1), however, the overall distance of mucus travel and the probability of clogging was reduced at 10 mg l(-1). H. pyriformis appears to compensate for episodic changes in the quantity and quality of available food particles by altering siphon-opening diameter, squirting frequency, structure and transport of mucus, and retention efficiency to maintain constant clearance rates.

Many species of microalgae release considerable amounts of their photoassimilated carbon into the water. This article reviews the impact of these released metabolites on the behavior and physiology of phytophagous suspension-feeding invertebrates (metazoans). The discussion is divided between planktonic (larvae and adult) and benthic suspension-feeders. Emphasis is placed on marine interactions, factors influencing microalgal metabolite production and methods of assessing their influence on suspension-feeders.

Bivalve molluscs form dense populations that exert profound effects on the particle loads and phytoplankton composition of coastal waters1. It has long been known that bivalves can select among different particle types, including selecting against those of poor nutritional value2,3,4,5, but because of difficulties in observing particle transport processes in the pallial cavity in vivo, the mechanism of selection was not known. We now use a combination of video endoscopy6 and flow cytometry7 to show that oysters can select living particles from non-living detritus on the gills. Our methods could aid the study of suspension feeding in many animal groups.

The feeding structures and mechanisms of the brachiopod species Terebratulina septentrionalis from the Bay of Fundy, eastern Canada and Terebratalia transversa from the west coast of Canada were examined, in vivo, with an endoscope linked to a video recording system. A diet consisting of various-sized, light-reflective particles and natural seston was given to both species. Our observations demonstrate that the lateral arms are the sites where most particle rejection occurs and the median coil is the site where particle acceptance occurs. Low particle retention may be attributed to the way particles move on the outer filaments. The combined effect of localized currents produces the large-scale flow through the lophophore. The lophophore's delicate hydrodynamics are easily disturbed by attempts to observe them. Only by relatively non-invasive techniques such as endoscopy can we accurately record normal feeding behaviour. Additional key words: lophophorate, Terebratulina septentrionalis, Terebratalia transversa The lophophore, the main organ of feeding and respiration in brachiopods, is a ciliated tentacular organ that acts as a ciliary pump, producing currents that flow through the mantle cavity. The two articulate species investigated in this study have plectolophous lophophores (Fig. 1), a complex type consisting of two lateral arms that lie on either side of a median coil. Two series of ciliated filaments fringe both the lateral arms and the median coil. At the base of these filaments is a ciliated food groove (brachial groove) covered by the flexible brachial lip. Particles captured on the ciliated filaments enter the brachial groove and are transported to the mouth for ingestion (Rudwick 1970). In plectolophous species, water enters through the lateral commissure and exits through the anterior part of the gape (Atkins 1959; Rudwick 1962; Savage 1972; James et al. 1992). One aspect of brachiopod physiology that has generated increasing interest is the mechanism of feeding, especially particle acceptance and rejection (Strathmann 1973, 1982; Gilmour 1978, 1981; Jorgensen 1981; Rhodes & Thompson 1992, 1993). Although many studies have addressed feeding processes (reviewed by James et al. 1992), there is still disagreement on the role of ciliary action on the inner and outer filaments (Strathmann 1973; Gilmour 1978; a Author for correspondence. E-mail: bmacdon@unbsj.ca LaBarbera 1981), as well as on the selectivity of brachiopod feeding (McCammon 1969; Rudwick 1970; Gilmour 1981; Thayer 1986). Previous studies have described the function of the lophophore from dissected structures, or surgically altered and narcotized animals, or from observations on intact animals yielding limited views (summarized in James et al. 1992). These invasive techniques could have altered the hydrodynamics within the lophophore and mantle cavity. Also, stress associated with surgery could have stimulated excess mucus production and caused the lophophore to function abnormally. In contrast, our study, using recently developed techniques in video endoscopy (Ward et al. 1991), allowed direct in vivo observations of feeding structures and mechanisms with minimal disturbance to the animals. No surgery was performed so that the animals remained intact. Our technique enabled us to observe, at a magnification of 150X, areas such as the inside of the median coil, that are impossible to view using conventional methods. The resulting video recordings allowed for post-observational analysis of events. The aim of this study was to investigate and describe lophophore activity in the articulate brachiopods Terebratulina septentrionalis (COUTHOUY 1838) and Terebratalia transversa (SOWERBY 1846) with respect to feeding, and to clarify some of the ways these brachiopods accept and reject particles. We report on parThis content downloaded from 157.55.39.231 on Wed, 05 Oct 2016 04:36:24 UTC All use subject to http://about.jstor.org/terms Endoscopy of feeding in plectolophous brachiopods < current inside coil < current outside coil

Previous models of particle feeding have focused on optimal solutions for particle acquisition or absorption. We propose two conceptual approaches to treat particle feeders as an integrated system of compartments, in hopes of understanding critical limiting factors that might be overlooked by focusing on only one part. The compartment model treats a particle feeder as a series of structures that process particles, with characteristic residence times within compartments and transfer points between them. These might change with overall particle food value and proportion of poor particles. As a non-exclusive alternative, the pathway model considers particle transfer as being analogous to enzyme control systems, with feedback loops that may involve interactions such as negative feedback between compartments that engage in no direct transfer. We examine these models in the light of some studies of particle handling by the deposit-feeding bivalves Yoldia limatula, Macoma secta, and M. nasuta, and the suspension-feeding oyster Crassostrea gigas. In Y. limatula, palp overloading results in feedback that shuts down the particle-collecting palp proboscis. In Macoma, nearly all particles are rejected, suggesting that rejection is necessary because digestion and gut residence time are limiting factors. We suggest that a whole-system approach is important in understanding particle processing by deposit feeders and suspension feeders. Additional key words: feeding, deposit feeding, suspension feeding, symmorphosis The purpose of this paper is to provide a conceptual framework for analyzing the processing of food particles by bivalve molluscs. We model the component organ systems as a series of compartments with transfer points between them, but with potential feedback loops among all potential compartments. Because the various compartments-ctenidium, palp, gut, and their components-have differing structures and functions, mechanisms are necessary for transfers of particles between them, e.g., the mucus string that transports particles between the ctenidium and palp in suspension feeders. Owing to disparate evolutionary origins and inherent structural difficulties, the supply of particles from one compartment to the next might cause overloading or rates of particle supply from one compartment that are below the capacity of another. In other words, the particle-processing system found in bivalve molluscs and other organisms might not function optimally with fixed transfer rates. Alternatively, the system might consist of a series of components whose individual processing rates are fixed and perfectly adapted to each other, much as has been suggested in arguments for other complex systems (Taylor & Weibel 1981; Weibel et al. 1991). We will first present a general compartment model for examining particle feeders such as bivalve molluscs. We describe compartments specifically for a selected group of bivalve species and show how problems ranging from phylogeny to the study of particle transfer between compartment structures can be studied. We will also use another conceptual model, derived from enzyme pathway analysis, to point out how interactions among the compartments can be considered. Finally, we will present some data on two species of deposit-feeding bivalves and some preliminary data on a suspension feeder to demonstrate how this approach allows a sharpening of our understanding of particle feeding and processing. This content downloaded from 207.46.13.52 on Mon, 24 Oct 2016 04:13:08 UTC All use subject to http://about.jstor.org/terms Models of particle processing Bivalve particle feeding Benthic particle feeders are typically divided into deposit feeders and suspension feeders. These represent a continuum rather than two discrete modes, although specific mechanisms of collection and processing may differ. Within the superfamily Tellinacea, for example, we encounter a range of morphologies, from those best suited for suspension feeding to those more efficient at deposit feeding (Yonge 1949; Pohlo 1966, 1967). Many particle-feeding species, including bivalves, switch from deposit to suspension feeding, depending upon substratum and hydrodynamic conditions (Taghon et al. 1980; Dauer 1983; Miller 1984; Olafsson 1986; Miller et al. 1992). The food source for both feeding types, however, is often quite similar, as it may consist of material resupplied by storm and other resuspension events (Miller et al. 1984; Frechette et al. 1989; Judge et al. 1993). In both bivalve feeding types, particles are collected actively, followed by one or more particle-processing stages, which usually involve particle rejection by the ctenidium and palp before particles enter the gut. Some food particles then pass directly through a tubular gut while others may be shunted to a diverticular structure where complete intracellular digestion occurs. Benthic particle feeders can be examined with regard to two principal problems. How do they deal with (1) variation of particle load (volume of particles supplied per unit time), and (2) varying proportions of particles of differing quality? Both deposit feeders and suspension feeders are confronted with widely varying particle loads and ranges of quality. Deposit feeders deal with high loads of particles that are mostly indigestible and that may require rejection before appropriate particles enter the gut (Lopez & Levinton 1987). They deal with this problem partly by non-random search and particle-collection strategies (Taghon et al. 1978; Levinton 1980; Whitlatch & Weinberg 1982), by variation of ingestion rate when local patches of high quality particles are encountered (Taghon 1981; Taghon & Jumars 1984), and by rejection of low quality particles (Hylleberg & Gallucci 1975; Taghon 1982). The bivalve Macoma nasuta typically rejects over 95% of the material that enters its incurrent siphon (Hylleberg & Gallucci 1975). By contrast, some sea cucumbers feed nearly indiscriminately, and digestive processing must be a major consideration in maximizing energy uptake (Powell 1977; Sloan & von Bodungen 1980). Suspension feeders also deal with a wide variety of particle loads and with particles of varying quality. At extreme loading, suspension feeders may adjust pumping rates, but bivalve molluscs also collect particles on the ctenidium and then reject those that are non-nutritive in the form of pseudofeces (Ki0rboe et al. 1980). There is growing evidence for qualitative selection (Newell & Jordan 1983; Ward & Targett 1989; MacDonald & Ward 1994) even of similar-sized organic particles (Shumway et al. 1985). Ingestion rates and other feeding processes appear to respond to changing content of non-nutritive particles (Bayne et al. 1989; Iglesias et al. 1992). Depending upon the degree of non-nutritive particle loading, cockles may respond by altering rates of particle uptake and the degree of rejection of particles as pseudofeces (Iglesias et al. 1992). In sum, particle feeders appear to respond in manifold and complex ways to the two cardinal problems outlined above. Previous conceptual approaches Three distinct but certainly not contradictory approaches have been applied to the modeling of particle processing, as well as other functional problems. The first approach involves models that place constraints upon feeding. Certain features of bivalve feeding have been argued to have characteristic hydrodynamic properties, and several authors have devised models that limit bivalves to certain physical mechanisms of particle processing, such as mechanical transport (Whitlatch & Weinberg 1982; J0rgensen 1989). More general models of particle feeding predict that certain particle sizes are collected with less efficiency than others, owing to hydrodynamic constraints (Rubenstein & Koehl 1977; Shimeta 1993). Processing rates also may be fixed, which could lead to characteristic transfer rates and loadings in a particle-processing chain. The second approach involves development of compensation models of feeding. Compensation is a change in behavior (e.g., rate of water transport through the siphon) following a change in feeding conditions (e.g., change in particle concentration in the water) that increases the rate of food uptake by the animal over the rate that would be found if no compensation occurred. For example, some studies report changes in rate of inflow that compensate for changes in phytoplankton concentration (Bayne et al. 1988). These models implicitly assume an array of optimal solutions corresponding to changing conditions and that bivalves can adjust at least in the direction of these optimal states. Finally, optimal models are more explicit renditions of compensation models. Such models take a series of boundary conditions and predict an optimal solution to foraging or digestion. For example, Penry & Jumars (1987) argued that during deposit feeding, particles 233 This content downloaded from 207.46.13.52 on Mon, 24 Oct 2016 04:13:08 UTC All use subject to http://about.jstor.org/terms Levinton, Ward, & Thompson Fig. 1. Conceptualization of a bivalve mollusc as a system of compartments with transfer between

Boonea (= Odostomia ) impressa (Say) is an ectoparasitic gastropod commonly found on the American oyster Crassostrea virginica (Gmelin). Field and laboratory studies were conducted to quantify effects of the ectoparasite on the physiology of oysters. After 2 wk of parasitism, three and six Boonea impressa per oyster significantly reduced both organic and inorganic growth and survival of juvenile Crassostrea virginica under laboratory conditions. Furthermore, six Boonea impressa per oyster affected feeding behavior of Crassostrea virginica by significantly reducing filtration rates of juvenile oysters, and significantly increasing the number of valve adductions of adult oysters. Filtration rates returned to normal within 2 h after Boonea impressa were removed. Previous workers have considered adverse effects of parasitism by B. impressa only in terms of removal of nutrients from the host oyster. In this study reduction in growth of parasitized oysters could not be wholly explained by the metabolic energy requirements of the ectoparasites; we suggest that interference with the feeding behavior of oysters has a significant effect on growth and survival.

The brown tide bloom, which occurred in coastal embayments of Long Island (NY), Rhode Island, and New Jersey, during the summers of 1985 and 1986 (Carpenter and Cosper, 1986; Olsen, 1986; Sieburth et al., 1986), caused starvation and recruitment failure of bivalve populations (Bricelj and Siddall, 1986; Cosper et al., 1987; Tracey, 1988). Several mechanisms for these deleterious effects were postulated including harmful effects due to released metabolites from the brown tide alga, Aureococcus anophagefferens Hargraves et Sieburth (Cosper et al., 1987; Sieburth et al., 1988; Tracey et al., 1988).

Cell surface carbohydrates play important roles in cell recognition mechanisms. Recently, we provided ev- idence that particle selection by suspension-feeding bi- valves can be mediated by interactions between carbohy- drates associated with the particle surface and lectins present in mucus covering bivalve feeding organs. In this study, we used lectins tagged with fluorescein isothiocya- nate (FITC) to characterize carbohydrate moieties on the surface of microalgal species and evaluate the effect of oyster mucus on lectin binding. These analyses revealed that concanavalin A (Con A), one of six lectins tested, bound to Isochrysis sp., while Nitzschia closterium reacted with Pi- sum sativum agglutinin (PNA) and peanut agglutinin (PEA). The cell surface of Rhodomonas salina bound with PNA and Con A, and Tetraselmis maculata cell surface was characterized by binding with PNA, PEA, and Con A. Pre-incubation of microalgae with oyster pallial mucus sig- nificantly decreased the binding of FITC-labeled lectins, revealing that lectins present in mucus competitively blocked binding sites. This decrease was reversed by wash- ing mucus-coated microalgae with specific carbohydrates. These results were used to design a feeding experiment to evaluate the effect of lectins on sorting of microalgae by oysters. Crassostrea virginica fed with an equal ratio of Con A-labeled Isochrysis sp. and unlabeled Isochrysis sp. pro- duced pseudofeces that were significantly enriched in Con A-labeled Isochrysis sp. and depleted in unlabeled microal- gae. Selection occurred even though two physical-chemical surface characteristics of the cells in each treatment did not differ significantly. This work confirms the involvement of carbohydrate-lectin interaction in the particle sorting mech- anism in oysters, and provides insights into the carbohy- drate specificity of lectins implicated in the selection of microalgal species.