William E. Robinson

Faunal associations on scallop grounds in the western Gulf of Maine

Benthic photographic transects were made during 1986–1987 across productive scallop beds on Jeffreys and Fippennies Ledges, western Gulf of Maine, from a manned submersible at depths of 56–84 m. Three megafaunal invertebrates dominated at each site: the sabellid worm Myxicola infundibulum (Renier) (mean densities ranging from 3.3 ± 4.2 to 7.1 ± 9.6·m−2); the burrowing cerianthid anemone Cerianthus borealis Verrill (1.0 ± 1.2 to 2.0 ± 0.5·m−2); and the sea scallop Placopecten magellanicus (Gmelin) (0.2 ± 0.5 to 1.0 ± 2.2·m−2). All three species exhibited contagious distributions (i.e., occurred in largescale clusters or patches), which could be modeled by negative binomial functions. On Fippennies Ledge, where little scallop dredging occurred in 1986, but, where appreciable fishing was conducted in 1987, sea scallops were positively associated with M. infundibulum and negatively associated with C. borealis in both years. In contrast, the association between M. infundibulum and C. borealis changed from a significant negative association in 1986 to random in 1987. The marked increase in scallop dredging on Fippennies Ledge between 1986 and 1987 was apparently the cause of a significant decline in the mean densities of all three megafaunal species (70% decline in sea scallops; 25–27% decline in cerianthids and myxicolids), although the pattern of faunal association with the sea scallops remained intact. On Jeffreys Ledge, where intensive dredging had occurred prior to our 1986 sampling, the pattern of faunal association described for Fippennies Ledge was absent. Thus, natural faunal associations may be severely impacted by fishing operations. We propose that C. borealis controls the spatial distribution and patch size of both M. infundibulum and P. magellanicus by preying on the larvae of the latter two species.

Metal interactions within the kidney, gill, and digestive gland of the clam,Mercenaria mercenaria, following laboratory exposure to cadmium

Mercenaria mercenaria were exposed to 0.1 Μg Cd/ml seawater (109Cd + stable carrier) for either (1) periods of 1 hr to 31 days, or (2) a period of 3 days followed by depuration in clean seawater for 2 to 64 days. Cd accumulated at increasing rates in the kidney, but at decreasing rates in all other organs of the clam during the laboratory exposure period. Measurement of total Cd levels confirmed that109Cd was accumulated by the clam tissues and not simply exchanged. The overall rate of Cd accumulation was significantly greater (P < 0.05) for the kidney than for the gill, mantle, digestive gland, pericardial gland, adductor, or remaining viscera, but not significantly different among the other organs (P > 0.05). No loss of Cd or other detectable metals occurred even after 64 days depuration. The degree to which Cd accumulated in the kidney, gill, and digestive gland did not correlate with the concentrations of other metals already present in these organs (except with Zn in the digestive gland). Negative correlations between different metal concentrations were never observed. Comparison of metal interaction patterns between the kidney, gill, and digestive gland indicates that each organ relies on different mechanisms for sequestering metals.

Podocytes in bivalve molluscs: Morphological evidence for ultrafiltration

SummaryIn representatives from a survey of three major taxa of bivalves the pericardial glands were found in two distinct positions. In protobranches (Acila castrensis) and filibranch bivalves (Glycymeris subobsoleta, Chlamys hastata, Pecten caurinus, Placopecten magellanicus, Mytilus edulis andMytilus californianus) the pericardial glands are located on the auricular surface. In heterodonts (Mercenaria mercenaria, Clinocardium nuttallii andMya arenaria) the pericardial glands are found in an anterodorsal position to the pericardial cavity.The sites of ultrafiltration are described. They consist of podocytes with basally extending pedicels forming an interdigitating network apposed to a basal lamina. Other characteristics of this ultrafiltration barrier described are anionic sites on the basal lamina and presence of substructural components within the ultrafiltration slits between pedicels.The pathway for the ultrafiltrate in protobranchs and filibranchs is from the hemocoel through the basal lamina, through the ultrafiltration slits of the pedicel network, into the urinary spaces between the podocyte cell bodies and into the pericardial cavity. The pathway for the ultrafiltrate in heterodonts is from the hemocoel through the basal lamina, through the ultrafiltration slits of the pedicel network, into urinary spaces between the podocyte cell bodies, into the lumen of the pericardial gland tubules and into the pericardial cavity.All podocyte cells have electron dense granules, Golgi apparatus and vacuoles associated with their cytoplasm. Heterodont species have microvilli on the cell surfaces of the podocytes apposed to urinary spaces.In all cases the morphological sites of ultrafiltration were associated with the pericardial glands of the heart-pericardial complex.

Vanadium K-edge X-ray Absorption Spectroscopy Reveals Species Differences within the Same Ascidian Genera A COMPARISON OF WHOLE BLOOD FROM ASCIDIA NIGRA ANDASCIDIA CERATODES

Vanadium K-edge x-ray absorption spectroscopy (XAS) was used to examine whole blood preparations from the tunicatesAscidia nigra and Ascidia ceratodes. Each XAS spectrum exhibits a rising edge inflection near 5480 eV characteristic of vanadium(III) and an intensity maximum at 5484.0 eV. In A. ceratodes blood cells, intrinsic aquo-VSO4 + complex ion is indicated by an inflection feature at 5476 eV in the first derivative of the vanadium K-edge XAS spectrum, but this feature is notably absent from the first derivative of the vanadium K-edge spectrum of blood cells from A. nigra. A strong pre-edge feature at 5468.6 eV also uniquely distinguishes the vanadium K-edge XAS spectrum of A. nigra blood cells, implying that vanadyl ion represents ∼25% of the endogenous vanadium. However, the energy position of the rising edge inflection of the vanadium K-edge XAS spectrum of A. nigra (5479.5 eV) is 1 eV lower than that of A. ceratodes (5480.5 eV), the reverse of any expected shift arising from the endogenous vanadyl ion. Thus, in contrast to A. ceratodes, a significant fraction of the blood cell vanadium(III) in A. nigra is apparently in a ligation environment substantially different from that provided by water. These novel species-related differences may have taxonomic significance.

Tunichromes, vanadium, and vacuolated blood cells in tunicates

Summary This review covers three aspects of tunicate blood: its yellow/green pigmentation, vanadium content, and vacuolated blood cells. The yellow/green pigmentation is due to a class of organic compounds called tunichromes. A systematic procedure of isolation, purification, and structure determination carried out on blood of Ascidia nigra yielded a family of tunichromes called TC An-i, i = 1, 2, 3. Tunichrome An-1, for example, has the formula C26H25N3O11, moleculer weight 545 dalton; it has a central triglycyl moiety to which three phenolic groups are attached. An assay for free tunichrome has been developed leading to the discovery of such compounds in four additional species. Tunichromes may be involved in vanadium binding, since a ground blood cell pellet placed on a Sephadex LH–20 column and eluted with increasingly polor solvents yields a green band that contains tunichromes and vanadium. Additionally, there is in vitro evidence for vanadium/tunichrome complexes of definite stoichiometry. However,...

Isolation and characterization of granules from the kidney of the bivalveMercenaria mercenaria

Intracellular and extracellular granules are found in most bivalve kidneys. We examined the composition of kidney granules from the infaunal bivalveMercenaria mercenaria (L.) collected in 1985 from Cataumet Bay, Bourne, and Waquoit Bay, Falmouth, Massachusetts, USA. Small granules are numerically dominant, but large granules dominate the samples on the basis of weight. Large granules (estimated diam. >15 μm) are composed primarily of metals (28% by weight) with Mn (8%), Ca (8%), Zn (4%) and Fe (4%) as the major contributors. Non-metal elements (P, C, H, N, S) together constituted 21% of the granule dry weight, though organic content (0.02% protein, 0.3% carbohydrate and 0.5% lipid) was low. Small kidney granules (≤10 μm diam.) and digestive gland granules fromM. mercenaria had significantly higher C, H, and N contents than larger kidney granules. Our results, taken together with those from other bivalve species, suggest that kidney granule formation and subsequent increase in size is a continuous process of lysosomal maturation, residual body release and extracellular accumulation of predominately inorganic elements.

IRON ACCUMULATION IN TUNICATE BLOOD CELLS. I. DISTRIBUTION AND OXIDATION STATE OF IRON IN THE BLOOD OF BOLTENIA OVIFERA, STYELA CLAVA, AND MOLGULA MANHATTENSIS

The iron concentration, oxidation state, and distribution in blood plasma and blood cells of three iron containing tunicateS were determined. Preliminary studies are reported on the possible role of plasma proteins in iron uptake. Iron(II) concentration in the millimolar range was found in the blood cell cy toplasm ofall three species; no iron(III) in solution was detected in blood cells. Over 70% of the total iron in the cells is associated with the membranes. Although the iron concentration in S. clava blood cells is substantially greater than that in B. ovifera cells, the iron to protein ratio by weight is similar in both species. SDS-electrophoresis of B. ovifera blood showed two protein subunits com mon to both plasma and blood cells. These two subunits are most likely the major components ofthe high molecular weight protein found in the plasma. This protein was shown to bind iron(III) when iron(III) citrate was added to the plasma.

In vivo incorporation of14C-phenylalanine into ascidian tunichrome

Ascidia ceratodes exposed to14C-phenylalanine in the surrounding seawater incorporates the radiolabel into newly biosynthesized tunichrome molecules. Radioactivity can be detected in tunichrome extracted from circulating blood cells within one day following initial exposure to the radiolabel; weak activity (≤4 μCi/mol tunichrome=22 nmol phenylalanine/mol tunichrome) is detected in 1 to 10 days; significantly higher amounts of radiolabel (57 μCi/mol tunichrome=318 nmol phenylalanine/mol tunichrome) appear 20 days after seawater exposure. Therefore, phenylalanine can function as a precursor in the biosynthesis of tunichrome.

Accumulation of 109cadmium in extracellular granules in the kidney of the bivalve mollusc Mercenaria mercenaria (L.)

Abstract As part of an ongoing investigation of the transport, accumulation and excretion of metals in the infaunal eulamellibranch Mercenaria mercenaria (L.) organisms were exposed to radioactive cadmium followed by an autoradiographic study of the kidney tissue to determine the morphological sites of cadmium accumulation. Preliminary results of these studies indicate that cadmium is associated with large extracellular granules in the lumina of the kidneys. The presence of radioactive cadmium was determined morphometrically by counting developed silver grains on sections coated with a photographic emulsion. The results were statistically significant (99·9 % confidence—Students t-test) to show that more radioactive cadmium was associated with large granules than with the background tissue.

Subcellular distribution of metals within the kidney of the bivalve Mercenaria mercenaria (L.)

Abstract 1. 1. The subcellular distribution of nine transition metals (plus four additional elements) was measured in the kidney tissue of the quahog, Mercenaria mercenaria. 2. 2. Elemental analyses of the subcellular fractions indicated three main patterns of metal distribution within kidney cells. 3. 3. Barium, iron, manganese and lead were associated primarily with kidney granules. 4. 4. Cadmium, copper, potassium and magnesium were found mainly in the cytosolic fraction. 5. 5. Calcium, phosphorus and zinc were found in all isolated fractions, probably reflecting the important roles that these elements play in bivalve metabolism. 6. 6. The organelle composition of the isolated subcellular fractions was determined using marker enzyme assays and microscopic techniques.