Seasonal changes in biochemical composition of the bivalve Lima hians from the Clyde Sea Area

Seasonal changes in the tissue weight and biochemical composition of the bivalve Lima hians (Gmelin) from a station in the Skelmorlie Bank, Clyde Sea Area, were studied during 1969–1971. The composition of an animal of standard size was calculated for each sampling date to give information on seasonal changes independent of shell growth. Increases in tissue weight took place between April and July as the gonad developed and reserves were built up. Between July and March tissue weight fell, at first rapidly as a result of spawning in the population, and later more slowly as reserves were utilized. Differentiation of the gonad began during the winter, at the expense of stored reserves, but was greatly accelerated during the spring due to increased food from the plankton. The lipid and nitrogen content of a standard animal rose to a pre-spawning maximum in July and then fell. Carbohydrate content also rose during this period, but continued to rise to reach maximum values in September. Carbohydrate and nitrogen both declined during the winter, but there was little indication of any net utilization of lipid during the winter months. The tissues of the ripe female contained more lipid than the male, and the tissues of the ripe male contained more nitrogen than those of the female. The total calorific content of the tissues of the male was greater than that of the female.     

Seasonal changes in biochemical composition of the bivalve Abra alba from the Clyde Sea Area

Seasonal changes in the body weight and composition of Abra alba (W. Wood) from south of the Little Cumbrae in the Clyde Sea Area (UK) were studied during 1969–1971. The composition of a specimen of standard size was calculated for each sampling data to provide information on seasonal changes independent of shell growth. Increase in body weight took place rapidly in early summer as the gonad developed and reserves were built up. Spawning in July resulted in a fall in body weight, and this was followed by a slower fall during the autumn and winter as reserves were utilized. The changes are related to seasonal fluctuations in food availability and temperature, which are reflected in the amount of pigment (phaeophytin) retained in the tissues.     

Seasonal variations in biochemical constituents during the reproductive cycle of the female dog cockle Glycymeris glycymeris

In an attempt to describe the biochemical events associated with the main stages of the annual and reproductive cycles of the female dog cockle Glycymeris glycymeris L., we studied seasonal variations in the various stages of oocyte development of the ovaries, and the glycogen, total protein and total lipid content of five body tissues – adductor muscle, foot, tunic coat, visceral mass and mantle. From November 1991 to November 1994, microscopic examination of the ovaries and measurement of the tissue concentrations of glycogen, total proteins and total lipids in these five body tissues were made monthly on ten female dog cockles originating from the sea area around Douarnenez (south Brittany, France). Morphological studies revealed that in the population investigated the annual cycle is characterised by three major periods: a first period of vitellogenesis extending from February/March to April/May and preceding a spawning in spring; a second period of vitellogenesis extending from May/June to September/October and leading to either no spawning, a single autumnal spawning event, or to two spawning events in summer and autumn; and a third period extending from October/November to February/March and characterised by a high level of oocyte lysis. In the muscular body tissues of the dog cockle, i.e. the adductor muscles, the foot and the tunic coat (the muscular envelope containing the visceral mass), the concentrations of glycogen, total proteins and total lipids underwent very similar variations during the annual cycle. During each stage of vitellogenesis, a typical glycogen–protein–lipid sequence was observed in the muscular tissues that was characterised firstly by a peak of glycogen concentration 2 to 3 mo before spawning, followed by a peak in total proteins 1 mo before spawning, and finally by a peak in lipid content just before spawning. A similar glycogen–protein–lipid sequence was also recorded in the first half of the winter period. However, these events were followed by general atresia affecting all oocytes in the gonad. Maximum energetic value of biochemical constituents in females coincided with peaks in lipid content in the visceral mass and mantle. These biochemical events occurred principally immediately before and at the end of oocyte lysis (December/January). A drop in the total energetic value, affecting mainly the visceral mass and the mantle, was recorded each year during the period January to March, coinciding with the period of shell growth in this species. Our data clearly indicate that in female G. glycymeris all muscular tissues contribute to the storage of glycogen and proteins, and suggest that glycogen may be the source of energy triggering vitellogenesis. Biochemical and microscopic observations revealed that oocyte development takes place during the first half of winter, but that these oocytes undergo atresia in December/January. The metabolites produced from oocyte lysis could contribute to somatic growth, which occurs in late winter. Received: 3 March 1997 / Accepted: 23 July 1997     

Seasonality of feeding and nutritional status during the austral winter in the Antarctic sea urchin Sterechinus neumayeri

The seasonal pattern of food intake and tissue energy status was measured over a 2 year period for two populations of the common Antarctic echinoid Sterechinus neumayeri living on contrasting substrata at Rothera Point, Adelaide Island, Antarctica. Food intake was estimated from faecal egestion, and both tissue mass and energy content assessed. Food availability was intensely seasonal, in that water column chlorophyll content and sediment pigment content varied markedly throughout the year. In response, both urchin populations showed an extremely seasonal cycle of faecal egestion, indicating a strong seasonality of feeding activity. Urchins from North Cove living on soft sediment fed at a considerably higher rate, and had a significantly larger Aristotle's lantern, than those in South Cove, 1 km away, living on hard substrata and taking a more cosmopolitan diet. Faecal egestion in both populations was zero for a 7 month period in the austral winter of 1997, and again for a 4 month period in 1998. During the austral summer of 1997/1998, 84% of the total annual energy intake took place in the period January to March. Significant decrease in gut tissue mass provided energy for maintenance in early winter, although progressive reduction of both gonad energy content (but without a detectable change in gonad mass) and body wall organic mass provided energy during the late winter period. The mass of reproductive tissue showed large differences between the two sites, but there was no marked decrease associated with spawning. Tissue proximate composition was assessed stoichiometrically from elemental composition and also checked by direct assay; gonad tissue was richer in lipid than gut tissue, though both were dominated by protein and contained only small amounts of carbohydrate. These data suggest that the very strong seasonality of food intake does not pose a significant energetic challenge for this species.     

Incorporation of dietary sterols by the sea scallop Placopecten magellanicus (Gmelin) fed on microalgae

The anatomical distributions of sterols and the incorporation of dietary phytosterols into different organs were studied in two populations of sea scallops, Placopecten magellanicus Gmelin, collected in 1989 from Georges Bank (Nova Scotia) and St. Pierre Bank (Newfoundland), respectively. In contrast to the well-established organ-specific lipid classes and fatty-acid compositions usually found in marine animals, the major organs of wild sea scallops (adductor muscle, digestive gland, gonads, gills and mantle) had the same sterol compositions. In order to know if anisomyarian bivalves require a uniform anatomical distribution of sterols, wild scallops were subjected to a microalgal diet containing high concentrations of brassicasterol, -sitosterol and cholesterol. The sterol composition of the scallop adductor muscle was not changed by 6 wk of feeding on the experimental diet. In contrast, the proportions of brassicasterol, -sitosterol and cholesterol in the digestive gland, and of brassicasterol and cholesterol in the male gonad, increased significantly (p<0.05). These results showed that the typical even anatomical distribution of sterols of bivalves can be disrupted by a drastic change in diet and is therefore not subject to strict internal regulation. Furthermore, the P. magellanicus results indicate that, although sea scallops may be capable of sterol biosynthesis, the incorporation of unmodified dietary phytosterols plays an influential role in establishing their sterol composition.ORNL is managed by Martin Marietta Energy Systems for the US Department of Energy, under contract DE-ACOS-8-10R21400     

Compositional topography of melon and spermaceti organ lipids in the pygmy sperm whale Kogia breviceps: Implications for echolocation

The forehead of the pygmy sperm whale Kogia breviceps contains a large melon of fatty tissue in front of a small, fat-filled, cornucopia-shaped spermaceti organ. This unique anatomical structure may possibly play an acoustical role in the whale's echolocation system, similar to the fatty melon sound lens postulated for dolphins. To better understand its function, we have studied the compositional topography of the K. breviceps melon and spermaceti organ lipids. The fatty head tissues of an adult K. breviceps were serially sectioned into 9 transverse slices. Appropriate tissue samples were cut from every other slice, and analyzed for % lipid and lipid class composition. Wax esters and triglycerides were the only major lipids present; their average carbon number in each sample was determined by gas-liquid chromatography (GLC). Our topographical analyses of K. breviceps melon indicate 3 regions of distinctive lipid composition: a fat-poor melon exterior, an outer melon of medium fat content having % triglyceride>% wax ester, and a fat-rich inner melon having % wax ester>% triclyceride. The spermaceti organ contains a fat-rich core of very high wax-ester content (84 to 99%), surrounded by a fat-poor case. Average carbon numbers of both wax esters and triglycerides were lowest in the inner melon and the spermaceti organ. At the rear of the spermaceti organ lies the museau de singe, an apparent sound generator. The lipid topography data plus anatomical and acoustical considerations suggest that the K. breviceps melon/spermaceti organ system may function as an acoustical transducer, directing and refracting sound waves from this source for the purpose of echolocation.     

Reproductive biology and biochemical composition of the brooding echinoid <Emphasis Type="Italic">Amphipneustes lorioli</Emphasis> on the Antarctic continental shelf

The bathyal West Antarctic Peninsula (WAP) shelf experiences intense seasonal variability in primary production, with summer phytoplankton blooms yielding intense pulse of phytodetritus to shelf sediments. Echinoderms form a conspicuous proportion of the deposit-feeding megabenthos on the shelf and of these Amphipneustes lorioli was the most abundant irregular echinoid. To explore the reproductive response of A. lorioli to this seasonal production cycle, A. Lorioli was sampled at one location on the WAP shelf during four separate cruises between March 2000 and March 2001. Reproductive patterns were determined by histological analyses of gonad tissue, and elemental (CHN) analyses were used to estimate the nutritional and energetic status of the body tissues. Histological analysis of the brooding echinoid A. lorioli suggested a quasi-continuous gametogenic pattern in both the ovaries and the testes. Biochemical analysis of the gonads and the gut tissues were consistent with a continuous gametogenic cycle, showing no significant changes in the biochemical composition of the tissues among seasons. Size-frequency distributions of the embryo and juvenile echinoids within the adults’ brood pouches revealed a synchronous recruitment of embryos and juveniles in specific cohorts between different adult specimens. Whilst this occurrence of different cohorts of the developing brood may be an adaptation to limited brood space, there may also be an external factor influencing the synchrony between adult individuals. Nonetheless, a continuous gametogenic cycle and the lack of seasonal variation in the biochemical composition of gonad and gut tissues suggest that this deposit-feeding irregular urchin is exploiting a persistent sediment food bank in WAP shelf sediments throughout much of the year.     

Ecological investigations of the zooplankton community of balsfjorden,northern norway: The genital system in Calanus finmarchicus and the role of gonad development in overwintering strategy

The structure of the reproductive system in Copepodite Stages IV and V of the marine copepod Calanus finmarchicus (Gunnerus) is described, together with seasonal variations in gonad development and sex ratio, from Balsfjorden (69°21N; 19°06E), a subarctic fjord in northern Norway. The genital system in Copepodite Stage IV consists of a small gonad with two genital ducts. The gonad of Copepodite Stage V in its most immature condition resembles that seen in Copepodite Stage IV, whereas the sex of Stage V copepodites with mature gonads can be easily and reliably determined. The genital ducts are the key characters for separating males and females in Copepodite Stage V; potential males have one and potential females two genital ducts connecting the gonad to the genital opening on the first urosome segment. Adults males were rare compared to females, and were only in the majority at the end of January and beginning of February. The sex-ratio also favoured females in Copepodite Stage V. Seasonal peaks in the proportion of adult males reflected peaks of males in Copepodite Stage V, suggesting that seasonal variations in the adult sex-ratio are a direct result of a situation which has already been determined in Copepodite Stage V. The seasonal variation in gonad development in Copepodite Stages IV and V of C. finmarchicus reveals that the size of maturity of the gonad varies throughout the year. This study indicates that visible sex-differentiation in Stage V and moulting into adults occurs in Balsfjorden at least 2 months before spawning in April. Phytoplankton levels are immeasurable before the spring diatom increase starts at the end of March, implying that development and maturation of gonads are dependent upon internal energy resources, whereas the final act of spawning seems to require energy input from phytoplankton.     

Contribution to the ecotoxicological study of cadmium,lead, copper and zinc in the mussel Mytilus edulis

The understanding of natural fluctuations of metal concentrations in mussels used as bio-indicators is indispensable for a good assessment of the disturbances due to pollution. We have studied thoroughly the factors which condition bioaccumulation by using controlled populations of mussels, Mytilus edulis L., sampled monthly over more than two years (March 1982–May 1984) in the Bay of Bourgneuf, France. Seasonal changes in metal levels have been recognized, maximum values being observed in winter and early spring and minimum in later spring and summer. Depending on metal and size group, the ratios between these maximum and minimum values varied between 1.56 and 3.43. The fluctuations in soft-tissue weight appear to be the main explanatory factor of seasonal variations in metal concentrations in mussels. Fluctuations in metal levels related to size of mussels were observed. Except for cadmium in mussels with a mean dry weight of soft tissues >0.2 g, a slight decrease in metal concentrations was observed for growing individuals: the regression coefficient b was -0.10, -0.11, -0.13 and -0.27 for Cd, Cu, Zn and Pb, respectively. The metals examined were rather uniformly distributed among the different groups of organs (visceral mass, gills and palps, remainder) and, consequently, several analyses of metals in different organs do not provide much more information than one analysis on the whole soft tissues. It is concluded that fluctuations related to size or season are reflected by only moderate differences in the maximum and minimum concentrations of metals in the mussels, but that they are nevertheless sufficient to conceal low chronic or short-term pollution, except at those sites where the normal environmental conditions are well-documented.     

Relationships between seston,available food and feeding activity in the common mussel Mytilus edulis

The feeding and metabolic rates of Mytilus edulis L. of different body sizes were measured in response to changes in particle concentrations ranging from 2 to 350 mg l^-1. Rates of oxygen consumption were not significantly affected by changes in seston concentration, whereas clearance rates gradually declined with increasing particle concentration. Pseudofaeces production was initiated at relatively low seston concentrations (<5 mg l^-1). Marked seasonal changes were recorded in the composition of suspended particulates (seston) in an estuary in south-west England. Total seston was sampled at frequent intervals throughout an annual cycle and analysed in terms of: particle size-frequency distributions, total dry weight (mg l^-1), inorganic content, chlorophyll a, carbohydrate, protein and lipid. The particulate carbohydrate, protein and lipid content provided an estimate of the food content of the seston. The results are discussed in terms of the food available to a nonselective suspension feeder, such as M. edulis, during a seasonal cycle. The effect of inorganic silt in suspension was mainly to limit by dilution the amount of food material ingested rather than to reduce the amount of material filtered by the mussel. In winter, the food content of the material ingested was 5%, and this increased to 25% during the spring and summer.     

Growth and content of energy reserves in juvenile sea scallops,Placopecten magellanicus,as a function of swimming frequency and water temperature in the laboratory

The effects of swimming frequency and water temperature on shell growth, tissue mass, and stored energy reserves of juvenile sea scallops, Placopecten magellanicus Gmelin, were examined in a factorial laboratory experiment spanning six weeks in July and August 1992. Individually tagged scallops of similar initial size (22.5±0.1 mm shell height, n=240) were induced to swim to exhaustion at three different swimming frequencies (every day, twice a week, or not at all) in two different water temperature regimes (4 to 7 or 7 to 13°C). The scallops were fed an ad libitum mixture of cultured microalgae. At the end of the experiment, cumulative increase in shell height, dry weight of soft tissues, condition index of dry adductor muscle (adductor muscle dry weight/soft tissue dry weight x 100) and total carbohydrate content of dry adductor muscle were measured for each scallop. Scallops at the higher temperature had significantly greater shell heights, and were in better metabolic condition as evidenced by significantly higher condition indices and muscle carbohydrate contents. The dry soft tissue weights did not differ significantly from their low temperature counterparts. Swimming frequency had no significant effect on shell height, dry tissue weight, or carbohydrate content, but condition index of the adductor muscle increased significantly with swimming frequency. These results show that not only was there no cumulative cost of swimming in terms of shell growth, total soft tissue weight, or carbohydrate content in young scallops, but that condition of adductor muscle tissue was higher in scallops that swam.     

Effect of sexual maturation on the tissue biochemical composition of<Emphasis Type="Italic"> Octopus vulgaris</Emphasis> and<Emphasis Type="Italic"> O</Emphasis>.<Emphasis Type="Italic"> defilippi</Emphasis> (Mollusca: Cephalopoda)

Changes in the protein, lipid, glycogen, cholesterol and energy contents, total amino acid and fatty acid profiles of Octopus vulgaris and O. defilippi tissues (gonad, digestive gland and muscle) during sexual maturation (spermatogenesis and oogenesis) were investigated. Both species showed an increase of amino acids and protein content in the gonad throughout sexual maturation (namely in oogenesis), but allocation of these nitrogen compounds from the digestive gland and muscle was not evident. The major essential amino acids in the three tissues were leucine, lysine and arginine. The major non-essential amino acids were glutamic acid, aspartic acid and alanine. With respect to carbon compounds, a significant increasing trend (P<0.05) in the lipid and fatty acid contents in the three tissues was observed, and, consequently, there was also little evidence of accumulated lipid storage reserves being used for egg production. It seems that for egg production both Octopus species use energy directly from food, rather than from stored products. This direct acquisition model contrasts with the previous model for Octopus vulgaris proposed by ODor and Wells (1978: J Exp Biol 77:15–31). Most of saturated fatty acid content of the three tissues was presented as 16:0 and 18:0, monounsaturated fatty acid content as 18:1 and 20:1 and polyunsaturated fatty acid content as arachidonic acid (20:4n-6), eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3). Though cholesterol is an important precursor of steroid hormones, this sterol content exhibited variations that do not seem to be related with the maturation process. Moreover, significant differences (P<0.05) were obtained between genders, suggesting that perhaps there is a greater physiological demand for cholesterol during spermatogenesis than oogenesis. If the component sterols of octopus are of a dietary origin, considerable variation in the cholesterol content between species might be expected on the basis of the sterol composition of their prey. The glycogen reserves increased significantly in the gonad and decreased significantly (P<0.05) in the digestive gland and muscle of O. vulgaris (these trends were not evident in O. defilippi). Glycogen may play an important role in the maturation process and embryogenesis of these organisms, because carbohydrates are precursors of metabolic intermediates in the production of energy. It was evident that sexual maturation had a significant effect upon the gonad energy content, but the non-significant energy variation (P>0.05) in the digestive gland and muscle revealed no evidence that storage reserves are transferred from tissue to tissue. The biochemical composition of digestive gland and muscle may not be influenced by sexual maturation, but rather by other biotic factors, such as feeding activity, food availability, spawning and brooding.Communicated by S.A. Poulet, Roscoff     

Seasonal changes in biochemical composition of the bivalve Nucula sulcata from the Clyde Sea Area

Seasonal changes in the body weight and composition of Nucula sulcata Bronn from south of Little Cumbrae Island in the Clyde Sea Area (UK) were studied during the period August, 1969 to April, 1971. The composition of an animal of standard size was calculated for each sampling date to give information on seasonal changes independent of shell growth. Increase in body-tissue weight took place between May and October as the gonad developed and as reserves were built up. Spawning in the population took place in November, resulting in a rapid fall in body weight, and an increase in tissue water-content. These processes were less well defined in 1970 than in 1969, but the same general pattern was followed in both years. Ripe males showed a consistently higher tissue weight than females, but the female gonad contained significantly greater quantities of lipid. The changes are compared with those for other bivalves from the same general area.     

Comparative biochemical composition of ploidy groups of the lion-paw scallop (<Emphasis Type="Italic">Nodipecten subnodosus</Emphasis> Sowerby) supports the physiological hypothesis for the lack of advantage in triploid mollusc’s growth in food-rich environments

Induction of triploidy in aquatic organisms has increased worldwide in the last two decades, mostly because triploids have better growth than diploids. According to a physiological hypothesis, partial or total sterility of triploids allows the accumulation of reserves in muscle and other tissues instead of being transferred to the gonad. The present study analyzes lipid, protein, carbohydrate, and fatty acid levels in muscle and gonads of Nodipecten subnodosus triploids and diploids over 18 months from June 2001 to December 2002. An important increase in gonadosomatic index of diploids scallops was observed from May to June 2002 reaching the highest values in August. Such increase was not observed in triploid scallops. Changes in biochemical composition in female gonad were in general related to the accumulation of reserves during gonad development of diploid scallops. This accumulation was lower for triploid scallops, in accordance to their sterility, especially for carbohydrates and acylglycerides. Adductor muscle index as well as protein and carbohydrate levels in muscle increased in both ploidy groups during the reproductive period indicating no mobilization of reserves to sustain gonad development in both ploidy groups. These results partially support the physiological hypothesis on the advantage of triploids: in a rich food locality no mobilization of reserves is needed to sustain gametogenesis. This, together with a possible lower efficiency of energy assimilation at high food concentration for triploids, may be the reason for an apparent lack of superiority of N. subnodosus triploids in terms of adductor muscle growth. Only the levels of particular highly unsaturated fatty acids levels (namely 20:4n-6 and 20:5n-3) in muscle of diploid and triploid decreased during the reproductive period, indicating a possible transfer of selected fatty acids to gonads, even in triploids. The muscle of triploids has a slightly but significantly higher proportion of 22:6n-3 compared to diploids, which can have implications for the nutritional and commercial value of triploid adductor muscle.     

Reproductive cycle and gametogenesis in the black abalone Haliotis cracheroidii (Gastropoda: Prosobranchiata)

Seasonal changes in gonald size and stages of gametogenesis in the black abalone Haliotis cracheroidii were related to changes in environmental parameters. H. cracheroidii showed an annual reproductive cycle terminating in a synchronized spawning in late summer. Gametogenesis was initiated immediately after spawning. Gametes were present in the gonad through the winter months. Gametogenesis was initiated a second time in the spring months. Maximal gonad growth (to a gonad index of 20%) occurred during summer months prior to spawning. Changes in gonad size andperiods of initiation of gametogenesis revealed no apparent correlation with changes in seasonal water temperature. Changes in gonad size showed no apparent relation to change in day length. Total polysaccharide levels in foot tissue changed seasonally, indicating that food availability is probably not a factor in directly regulating gonad growth. Gonad index data for the chiton Katharina tunicata (collected over a 10 year period) showed no apparent correlation to seasonal change in water temperature.     

Reproduction and genetic variation in the deposit-feeding sea star Ctenodiscus crispatus

The gonad index in the deposit-feeding asteroid Ctenodiscus crispatus (Retzius) in the Gulf of Maine (USA) is seasonally less variable than in any other sea star, ranging from 2.99 to 4.98% of dry body weight in females and from 2.28 to 3.42% in males, and varies in concert with, rather than reciprocal to, the pyloric caecum index. Biochemical composition and, hence, caloric content, of the gonads also show little seasonal change, suggesting that reproduction is aseasonal and continuous in this population. Oocyte development is asynchronous, all females having a full size range of oocytes (from less than 30 m to greater than 400 m diameter) throughout the year. Seasonally determined size-frequency distributions of juveniles, oocyte cytology and size-frequency distributions, responsiveness of adult females to 1-methyladenine, and oxygen uptake rates indicate that variations in reproductive intensity are superimposed on continuous reproduction, and seem related to changes in phytoplankton production rather than to temperature. The rich neutral lipid content (ca. 50% of total lipid) and large egg size (>400 m) in the ovaries suggest that development is direct. The population is extremely variable genetically, polymorphism among 13 enzyme-coding genes being 77% and average heterozygosity being 0.174. The reproductive pattern and genetic variation in the eurybathic C. crispatus are similar to those in deep-sea echinoderms. This may be related to the constancy of the population's detrital food source, to small-scale heterogeneity of its physical environment, and to low individual vagility.     

Fouling organisms in the port of Mar del Plata (Argentina). I. Siphonaria lessoni: ecological and biometric aspects

The present paper deals with ecological aspects of the pulmonate gastropod Siphonaria lessoni (Blainville, 1824), a common member of fouling communities in Mar del Plata's port (38°0817 S, 57°3118 W). Populations on colonized panels of an experimental raft were studied during three annual cycles, to determine feeding habits, growth and various factors which restrict their distribution on floating substrata. Although S. lessoni is harmless as a fouling organism, its grazing on the algal belt clears a part of the substratum's surface, which is then quickly colonized by truly aggressive organisms such as Balanus amphitrite.     

Annual cycle of expression of connective tissue polypeptide markers in the mantle of the musselMytilus galloprovincialis

We suggest that gonad development in the mantle tissue of the bivalve molluscMytilus galloprovincialis Lmk. is an example of epithelial/mesenchymal interactions (i.e. soma/germline interactions) and morphogenesis in the adult state. According to this concept, the aim of the present study was to use biochemical and immunochemical methods for identifying and characterizing the mantle cell polypeptide markers whose expression is seasonally and morphogenetically regulated. We showed for the first time thatM. galloprovincialis mantle, of both males and females, contains polypeptides (with an apparent mol. wt of 45 to 53 kDa) specific for connective tissue (mantle connective tissue polypeptides; MCTPs). Electrophoretic, immunoblotting and immunofluorescent experiments demonstrated that MCTPs are primarily localized in the adipogranular (ADG) cells, and their expression in the mantle is seasonally regulated. There is a positive correlation between MCTP expression and connective tissue volume in the mantle. MCTPs are overexpressed during the rest period, when the mantle consists of connective tissue mainly, whereas mature gonads contain only trace amounts of MCTPs. Moreover, there is a temporal correlation between the onset and decrease of MCTP expression and the appearance and disappearance of the ADG cells in the mantle. MCTP localization in the mantle tissue should not be associated with the ADG cells only, because positive immunofluorescence was also detected in follicle membranes (but not in germ cells) and superficial mantle epithelium. Using immunoblotting and immunofluorescence, MCTPs were found in the connective tissue of the mantle, posterior adductor muscle and visceral mass, but not gills, foot or hepatopancreas. Possible mechanisms by which MCTPs could participate in the annual processes of mantle gonad/connective tissue development and involution are discussed.     

Seasonal grazing of Pseudocalanus minutus on particles

Grazing by Pseudocalanus minutus on naturally occurring partieles has been investigated over a 2 year period at 5 m depth, in a small coastal embayment in Nova Scotia, Canada. Large variations in the standing stock of particulate matter in the water from 5 m depth were associated with seasonal changes in phytoplankton, and at times with runoff from rivers. Each size group displayed seasonal changes, with high amplitudes occurring in the large-particle size ranges. P. minutus consumption was associated with seasonal changes in total particle concentration as well as with the concentration in each size group. The food uptake was correlated (P>0.01) with the particle concentration in all particle categories, except in the size range below 3.57 . Frequency of positive electivity indices increased with particle sizes up to 57 and then decreased. Observations on particle spectra revealed considerable seasonal variability in both particle sizes and copepod feeding patterns. P. minutus adapted to seasonal variations within the particle spectrum by shifting its grazing pressure from one size range to another. By taking advantage of every particle peak concentration, P. minutus revealed a strong opportunistic feeding behaviour, and a very efficient utilization of the standing stock. Maximum consumption was recorded in early spring, when P. minutus fed on large-size particles. Feeding took place in the medium and small-size ranges during the summer and part of fall. Food uptake was rarely less than 2.26% of body weight during the winter, and reached up to 55% and sometimes more in spring. The unselective feeding patterus demonstrated by P. minutus suggest certain ecological implications of feeding pressure on standing stock.     

Reproductive development of the barnacle Chthamalus malayensis in Hong Kong: implications for the life-history patterns of barnacles on seasonal, tropical shores

Hong Kong, lying just below the Tropic of Cancer (22°17′N, 114°09′E), experiences a strongly seasonal environment, with a cool almost temperate winter and a hot, tropical, summer. Histological sectioning of the gonads of the high-shore barnacle, Chthamalus malayensis Pilsbry, showed a seasonal trend in the development of its reproductive organs. Four stages of female gonad development were identified according to the cell types present: post-spawning, resting, growth and mature stages. The female gonad was mature from April to November, which was related to seawater temperatures, and entered a resting phase from December to March. Although the male gonad showed a seasonal developmental trend and reached maximum maturity in summer, the seminal vesicles were full of spermatozoa and functional throughout the year. The reproductive season of this species is therefore solely dependant upon the maturity of the female gonad. The estimated maximum number of broods per year was up to 10 and the maximum number of eggs produced per brood can reach 3,000 eggs. The minimum size for female gonad maturity was 6 mm rostro-carinal diameter (RCD) at which size, the barnacles were ~6-month old. Sperm production occurred at a smaller size (2 mm=2-month old). Compared with Chthamalus montagui and Chthamalus stellatus from temperate regions, C. malayensis produced a greater number of broods per year, had a longer reproductive period and faster gonad development. Chthamaloid barnacles in tropical regions may, therefore, invest more energy per year in reproduction during their life span. Contrary to the seasonal gonad developmental pattern of C. malayensis in the present study, however, C. malayensis in Singapore (which experiences only slight seasonal variation) had mature female and male gonads throughout the year, further supporting the strong role of climatic conditions effecting the reproductive biology of barnacles.