Anne Donval

Differential δ13C and δ15N signatures among scallop tissues: implications for ecology and physiology

There have been several studies where the isotopic composition of organisms has been determined seasonally, but fewer have examined separate organs. In this context, separate organs (e.g. gonad, digestive gland and muscle) of a suspension-feeder, the scallop Pecten maximus, were used to assess seasonal changes of both stable isotopes and biochemical components. Our study used multiple indicators [stable carbon and nitrogen isotope ratios, biochemical components and seston chlorophyll-a (chl a)] to track nutritive activity and energy allocation in P. maximus from the Bay of Brest (France). In addition to seasonal variation in the isotopic composition of P. maximus tissues, we found strong differences in the mean isotopic signatures of different organs. This has serious implications for interpretation of animal diets and potential use in animal physiology. Furthermore, we present evidence that seasonal variations of metabolism will cause changes in the isotopic composition not related to changes in the diet. Interpretation of isotopic data may require consideration of values from several separate organs. Finally, y 15 N appears powerful to track metabolite fates in the scallop P. maximus. D 2002 Elsevier Science B.V. All rights reserved.

Mode of particle ingestion in five species of suspension-feeding bivalve molluscs

In order to elucidate the mode of particle ingestion and the functional anatomy of the oesophagus in bivalves, a histological study was performed onMytilus edulis (Mytilidae),Crassostrea virginica (Ostreidae),Placopecten magellanicus, Chlamys varia, and juvenilePecten maximus (Pectinidae). Specimens were sampled from various sites in New Brunswick, Canada, and Brittany, France, from 1987 to 1989. The buccal, peribuccal, and oesophageal epithelia of all species contained a dense distribution of actively secreting mucocytes, although these were somewhat less abundant inCrassostrea virginica, which also has the shortest oesophagus. Mucocyte morphology, while constant within a family (Pectinidae), showed clear differences among families. Both acid and neutral mucopolysaccharides were secreted by the epithelial mucocytes of all species. Mucus and mucus-particle masses were observed in the peribuccal and buccal regions, as well as in the oesophageal lumina of all species, even in those specimens which had been maintained without feeding (Placopecten magellanicus) or held out of water for 48 h (C. virginica) prior to dissection and fixation. These results indicate that a basal level of mucus production and transport is continuous on the peribuccal, buccal, and oesophageal ciliated epithelia, regardless of the particle concentration in the external medium. Buccooesophageal glands, generally thought to be absent in the Bivalvia, were observed in one of the species examined (M. edulis). It is concluded that the mode of particle ingestion in these suspension-feeding bivalves is via ciliatransported mucus masses; the presence of buccooesophageal glands inM. edulis suggests a digestive role for the oesophagus in this species.

Monoamines and reproduction in Pecten maximus, a preliminary approach

Summary The distribution of serotonin-like immunoreactivity was studied in the central nervous system and the gonad of Pecten maximus. Cerebral and pedal ganglia contain a well developed serotonin-immunoreactive neuronal subpopulation, whereas positive neurons are scarce in the visceral ganglion. The distribution pattern of immunoreactive elements in the gonad indicate that serotonin is involved in peripheral neurotransmission of this organ. Seasonal variations of monoamines (serotonin, dopamine and noradrenaline) have been investigated in the nervous system using HPLC. Lower concentrations of serotonin are observed during winter in the central nervous system; dopamine levels of the visceral ganglion are correlated to gonadal growth.

Variations in food intake of Pecten maximus (L.) from the Bay of Brest (France): influence of environmental factors and phytoplankton species composition.

Previous studies carried out in the bay of Brest on daily shell growth of Pecten maximus have demonstrated that temperature is a major control on daily shell growth in contrast to food supply. However, repeated events of slow growth have been observed during diatom and dinoflagellate blooms. The aim of this study was to determine how fluctuations in environmental parameters influence P. maximus food intake and daily shell growth rate. In 1995, P. maximus food intake and growth were highest when Cerataulina pelagica (diatom) blooms occurred and lowest during Gymnodinium cf. nagasakiense (dinoflagellate) blooms. During blooms of other diatom species, P. maximus food intake and growth were high when the algal concentration did not exceed a critical threshold, dependent upon the dominant species and sedimentation rate of diatoms. These results demonstrate that the morphological and physiological features of phytoplankton bloom species strongly affect benthic microphytophagy, a component of benthic-pelagic coupling.

Nutritional strategies of the hydrothermal ecosystem bivalves

Studies of deep-sea hydrothermal bivalves have revealed that the species, which are strictly dependent upon the interstitial fluid emissions, derive their food indirectly via symbiotic relationships with chemosynthetic bacteria present in their gill tissues. As the gill plays the main trophic role, structural and ultrastructural modifications occur in the digestive tract. Scanning and transmission electron microscope studies reveal that the digestive system of species belonging to the genera Calyptogena, Bathymodiolus and Bathypecten have anatomical differences. In Calyptogena, the reduction of several parts of the digestive tract and the stomach content which is either empty or full, according to the various species examined indicate that the digestive system is hardly if at all functional. In Bathymodiolus, the labial palps are well developed, the stomach is always full with particles and the two cellular types, digestive and secretory, are present in the digestive gland. All these characteristics indicate that the digestive system is functional. In Bathypecten, the digestive tract is well developed and it seems that it plays the main trophic role. We conclude that the nutritional strategies of the hydrothermal vents bivalves are quite varied. They range from a normal trophic process, through a mixotrophic diet, to one based purely on chemoautotrophic bacteria. The strategy of each species is adapted to and influences its distribution.

The osphradium in Placopecten magellanicus and Pecten maximus (Bivalvia, Pectinidae): histology, ultrastructure, and implications for spawning synchronisation

The bivalve osphradium is a band of putatively sensory tissue located in the gill axis, whose function is uncertain. In the present study, extending from 1987 to 1994, anatomical, histological, and electron microscopical techniques were used to elucidate the structure and ultrastructure of the osphradium in hatchery Pecten maximus L. and Placopecten magellanicus (Gmelin) (collected from Passamaquoddy Bay, New Brunswick, Canada). The osphradium consists of two distinct regions which run longitudinally on both sides of each gill axis: the osphradial ridge, and the dorsal tuft cilia region. The osphradial ridge was largely devoid of cilia other than those of the few free nerve fibres. The dorsal tuft cilia region contained free nerve fibres and ciliary tufts, separated by undifferentiated epithelial cells. No paddle cilia were observed under isosmotic fixation conditions, although under hypotonic conditions such cilia were quite common, suggesting an artefactual nature. Most of the cells of the osphradial ridge were highly secretory, the principal products being large pigment granules (in Pecten maximus) directly secreted by the Golgi bodies, and numerous small, electron-dense vesicles. These vesicles were arranged along extensive microtubule arrays in the basal region, indicative of axonal transport. These data support and extend Haszprunars hypothesis of the role of the osphradium in the reception of chemical spawning cues and in the synchronization of gamete emission. Together with independent data on nerve pathways, osphradial sensory modalities, and monoamine localisation, an anatomical pathway and neurophysiological mediator are postulated.

Histology, histochemistry and enzyme biochemistry in the digestive system of the endosymbiont-bearing bivalve Loripes lucinalis (Lamarck)

The structural and functional aspects of the digestive gland in the endosymbiont-bearing bivalve Loripes lucinalis were examined. Specimens were collected over a one year period (September 1991 to September 1992) from the Moulin Blanc beach, Bay of Brest, (Brittany, France). The two apertures leading from the stomach into the digestive diverticula are very large as are the digestive ducts and tubules. The main and secondary ducts possess no ciliated tracts and present a definite brush border. The structural aspects of the cells lining the ducts, in addition to the presence of abundant acid phosphatase activity, suggest that these cells are actively involved in absorption and intracellulgr digestion of food material. Lipid and glycogen are abundant throughout the digestive diverticula suggesting that this organ is the site of significant energy stores. The tubules contain the two classical cell types, namely the secretory and digestive cells. Also present within the tubules are extremely large acid polysaccharide-filled vacuoles which originate from the lysis of digestive and/or secretory cells. These vacuoles suggest an extensive process of tubule autophagy and regeneration. The intestine is lined with cilia and microvilli. The cytological features of the intestinal cells, together with an abundant acid phosphatase activity, suggest that these cells are capable of absorption and intracellular digestion. The wet weight of the gonad-digestive gland complex varied throughout the year between 12 and 61.2 mg with an average wet weight of 31.8 ± 8 mg. Following spawning, total wet weights dropped by 50%. The α-amylase activity was measured and an average β-amylase to protein ratio of 5.34 ± 1.09 U/g protein was obtained. It was observed that amylase activity expressed per g protein may vary with the animals physiological status. The temporal evolution of absolute α-amylase activity throughout the sampling period revealed that the variations in activity were dependent on a combination of environmental factors, including temperature and food levels. Digestive activity, however, did not seem to correspond to reproductive efforts.

Immunocytochemical detection of different (neuro)peptides in the central nervous system of the scallop Pecten maximus

Abstract 1. Immunocytochemical investigations with antibodies raised against several biologically active peptides have been carried out on cerebro-pedal and visceral ganglia of the scallop Pecten maximus, at different stages of reproductive cycle. 2. All antisera used (anti-FMRFa, anti-methionine-enkephalin, anti-somatostatin, anti-insulin, anti-APGWa and anti-αCDCP) revealed immunoreactive structures at any investigated stage. 3. Description and localization of positive neurons and fibres are given for each antiserum. 4. The highest numbers of reacting cells were found with anti-FMRFa and methionine-enkephalin whereas αCDCP-like material was the less abundant.

Cadmium in the waters off South Morocco: Nature of particles hosting Cd and insights into the mechanisms fractionating Cd from phosphate

In this study we report the distributions of total dissolvable cadmium and particulate cadmium from 27 stations in southern Moroccan coastal waters (22-30°N) which is part of the North-West African upwelling system. These distributions were predominantly controlled by upwelling of the North Atlantic Central Waters (NACW) and uptake by primary production. Atmospheric inputs and phosphogypsum slurry inputs from the phosphate industry at Jorf Lasfar (33°N), recently estimated as an important source of dissolved cadmium (240 tCd year−1), are at best of minor importance for the studied waters. Our study provides new insights into the mechanisms fractionating cadmium from phosphate. In the upper 30 m, the anomalies observed in terms of Cd:P ratios in both the particulate and total dissolvable fractions were related to an overall preferential uptake of phosphate. We show that the type of phytoplanktonic assemblage (diatoms vs dinoflagellates) is also a determinant of the fractionation intensity. In sub-surface waters (30-60 m), a clear preferential release of P (vs Cd) was observed indicating that remineralization in oxygen minimum zones is a key process in sequestering Cd. This article is protected by copyright. All rights reserved.