Selectivity in feeding by the deposit-feeding bivalve Macoma nasuta

Macoma nasuta Conrad is primarily a deposit-feeding bivalve sucking the top millimeter of the sediment surface. Growth experiments show that surface sediment supports growth better than detritus falling from the water column. Gut clearance time is between 1 and 9 h (12°C). Fecal pellets are ejected in a regular rhythm. However, the total amount of feces per unit time shows considerable individual variation. Due to sorting in the mantle cavity, about 97% (dry weight) of the surface material is ejected again as pseudofeces. Selectivity by the bivalve is estimated by comparison of particle size and organic composition of sandy and muddy sediments and compared with feces produced by clams fed these sediments. Fecal pellets are in all cases richer in organic components than the sediment, indicating a high degree of selectivity. Ingestion and digestion of small animals (meiofauna) occur, but many of the ingested specimens survive. It is not possible to estimate the assimilation of organic matter by simple difference between the ingested sediment and the ejected feces. The difficulties in calculating energy budgets which arise from selective feeding and associated bacteria are discussed.     

Seasonal and tidal changes in the length of the crystalline style intertidally living Macoma balthica (Mollusca,Bivalvia)

Samples of Macoma balthica were collected during 1978 and 1979 from the westernmost part of the Dutch Wadden Sea. The length of the crystalline style in the stomach of this intertidal bivalve was studied through tidal and annual cycles. The length of the style was ca. half the shell length and changed slightly with the season. Maximum lengths were recorded in spring, the season of high food intake, and minimal values in autumn and winter. Changes in the length of the style also exhibited a tidal cycle, but with two maxima and two minima. Tidal fluctuations in style length amounted to ca. 5% only. The influence of enzymes and waste products from the digestive diverticula, the food intake as well as the influence of the pH on the length of the style are discussed.Communication No. 401 of the Delta Institute     

Endogenous circatidal rhythm in the Manila clam Ruditapes philippinarum (Bivalvia: Veneridae)

Manila clams, Ruditapes philippinarum, removed from their natural environment and maintained for 9 weeks in continuously immersed conditions exhibited a clear endogenous circatidal rhythm in oxygen consumption. The clams exhibited a semidiurnal rhythmicity in oxygen consumption after showing a diurnal pattern in the first few days (5 to 7 d) of the experiment. The results of the present study indicate that activity rhythms of clams are controlled not only by exogenous factors, but also by an endogenous circatidal periodicity. Received: 8 April 1998 / Accepted: 1 February 1999     

First evidence of gender-related differences in immune parameters of the clam Ruditapes philippinarum (Mollusca, Bivalvia)

For the first time, gender-related differences in some important functional parameters of haemocytes from the clam Ruditapes philippinarum have been studied. Clams were collected during the pre-spawning phase, when sex can be distinguished by microscopic observation of gonadal smears, in order to ascertain whether the two sexes reach the stressful spawning period with different degrees of immunosurveillance. Total haemocyte count (THC), haemocyte size frequency distribution, capability of haemocytes to assume the vital dye neutral red (NR, indicative of endocytotic activity), lysozyme-like and acid phosphatase activities in both haemocyte lysate (HL) and cell-free haemolymph (CFH), and superoxide dismutase (SOD) and catalase (CAT) activities in HL were all evaluated. No differences in THC values were found between the two sexes, but differing haemocyte size frequency distributions were observed: the fraction of larger haemocytes (7–9 μm diameter, 200 fl volume) was markedly increased in females and that of smaller haemocytes (<5 μm diameter, <200 fl volume) markedly increased in males. Interestingly, when haemocytes were observed under the light microscope, a significantly higher percentage of granulocytes was found in haemolymph from females, compared with that of males. Significantly increased NR uptake was recorded in female haemocytes. No significant variation in lysozyme-like activity was observed in HL, whereas in CFH, enzyme activity was significantly higher in females. HL acid phosphatase activity was significantly higher in males with respect to females; no significant variations in enzyme activity were observed in CFH. HL SOD and CAT activities were significantly higher in females than in males. Overall, on the basis of the cell parameters studied here, gender-related differences in immune parameters were found in R. philippinarum, indicating that females have more active haemocytes than males during the pre-spawning period.     

Effects of salinity on endogenous rhythm of the Manila clam, Ruditapes philippinarum (Bivalvia: Veneridae)

The Manila clam Ruditapes philippinarum, an intertidal bivalve, was exposed to different salinity regimes (from 31.0–31.7‰ down to 20‰, 15‰, 10‰, 5‰), and the endogenous rhythm in its oxygen consumption was studied using an automatic intermittent-flow respirometer. When exposed to salinities reduced from 31.5‰ to 20‰ and 15‰ under otherwise constant conditions, the clams recovered a clear endogenous circatidal rhythm in their oxygen-consumption rate after having dampened periods of 12 h and 48 h, respectively. At salinities less than 10‰, however, the oxygen-consumption rate was depressed greatly at the beginning of the experiment for about 36 h and then increased to a level higher than normal, but the rhythm of oxygen consumption was not recovered. The results of this study indicate that the Manila clam, a euryhaline organism, cannot maintain a normal metabolic activity at a salinity lower than 15‰. All clams were dead after exposure at a salinity of 5‰ for 7 days. Received: 28 February 2000 / Accepted: 26 August 2000     

Levels of genetic polymorphism at two enzyme encoding loci in eight species of the genus Macoma (Mollusca: Bivalvia)

Levels of genetic polymorphism were surveyed at two enzyme loci (LAP, PGI) in 2 intertidal and 6 subtidal species of the bivalve genus Macoma living in the waters of the San Juan Islands (Washington and Canada). The temporal environmental variability-genetic variability hypothesis predicts that intettidal species should have greater levels of genetic polymorphism than subtidal species. This is not true for the genus Macoma. However, at the PGI locus, genetic polymorphism was proportional to niche breadth in both the intertidal and subtidal species, but only for intertidal species at the LAP locus. These results support the contention that temporal environmental variability is not necessarily important in maintaining genetic variability, but that environmental heterogeneity may select for increased polymorphism at some loci.     

Early development of the gill and implications for feeding in Pecten maximus (Bivalvia: Pectinidae)

Despite the importance of understanding feeding in the early stages of bivalve development, little information is available concerning the organogenesis of the bivalve gill. The present study used histological and scanning electron microscopical techniques to present a detailed account of gill development in the early stages of the scallop Pecten maximus L. (Bivalvia: Pectinidae). Live specimens from larval cultures were observed daily using light microscopy, while five scallops were sampled for electron and light microscopy every 2 to 3 d from Day 18 to 35, then weekly to Day 56, with a final sampling on Day 58. Although development was continuous, four distinct stages were identified (1-primordia, 2-homorhabdic unreflected, 3-homorhabdic reflected, 4-heterorhabdic), partially recapitulating the presumed phylogenetic evolution of this character in the Pectinidae. The absence of a ventral grcove in all stages suggests that the particle transport mechanism of pectinids evolved independently of such a structure, which is found in other bivalve families. Similarly, the absence of latero-frontal cilia in all specimens up to the largest observed (4 mm) indicates that the single row found in adults is a later development, rather than a vestige of a more abundant ciliation in ancestral forms. The anatomical data, together with in vivo observations of feeding in postlarvae, suggest that the developmental stages of the P. maximus gill correspond to critical changes in gill function. The early life of P. maximus may thus be characterized by distinct functional changes in feeding.     

Age and growth rate determinations for the Atlantic surf clam Spisula solidissima (Bivalvia: Mactracea), based on internal growth lines in shell cross-sections

Marked and recovered surf clams, Spisula solidissima Dillwyn, from Virginia (USA) deposited one internal growth line during a period of 11/2 years, probably in response to spawning during late summer. We have used these annual growth lines to make growth curves for two samples of New Jersey (USA) clams, one from inshore (1.8 km from shore, 15 m deep), the other from offshore (17.5 km from shore, 28 m deep) waters. The offshore and inshore clams grow at approximately the same rate until Age 3 years, after which time the growth rates differ, as does the ultimate lifespan; the offshore clams grow more rapidly and attain a greater age — up to 31 years. Comparison of our growth curves with other published curves revealed a close correspondence to a curve which was based on a study of growth over a 5-year period. Curves based on external growth lines probably underestimate growth rate in early life and overestimate it in later years.     

Peribuccal organs ofPlacopecten magellanicus andChlamys varia (Mollusca: Bivalvia): Structure,ultrastructure and implications for feeding

In order to better understand the structure of bivalve peribuccal organs and relate this to existing functional paradigms of their role in feeding, the labial palps of two scallop species,Placopecten magellanicus from the Bay of Fundy, Canada (1985 and 1986), andChlamys varia from the Bay of Brest, France (1986), were examined using histological techniques and electron microscopy. The ridged palp surface displays a uniformly dense ciliation with relatively few mucocytes; these are essentially concentrated in the region of the secondary ledge and may, through their secretory activity, determine the fate of particle masses in this area. The mucus secretions of the ridged palp surface are qualitatively different from those of the smooth palp surface. Mucocytes are much more abundant on the smooth palp surface, where it is suggested that their homogeneous secretions attenuate the potentially adverse effects of anteriorly-directed cleansing and swimming currents. Two other cell types are found in the palp epithelia: ciliated cells, which are very numerous on the ridged surface and relatively rare on the smooth surface, and non-ciliated epithelial cells, which are very numerous on the smooth surface and rare on the ridged surface, where they are confined to the palp margin. In addition to the mechanical role of the ciliated cells and mucocytes, the ultrastructural characteristics of the ciliated and non-ciliated epithelial cells indicate a dichotomy of function between the ridged and smooth surfaces. The ridged surface epithelial cells present an ultrastructural specialization in the absorption of dissolved and colloidal matter, suggesting an accessory nutritive role, whereas the smooth surface simple epithelial cells show signs of active molecular synthesis. No specialised sensory cells were observed on the ridged surface; it is therefore not yet possible to conclude whether the labial palps are capable of selection based on individual particle characteristics.     

Sperm ultrastructure of the giant clam Tridacna maxima (Tridacnidae: Bivalvia: Mollusca) from the Great Barrier Reef

Using transmission electron microscopy, spermatozoa from a member of the Tridacnidae, or giant clams, are described for the first time and compared with spermatozoa of other bivalves, especially other heterodonts. The acrosomal vesicle of Tridacna maxima (Röding, 1798) is short (0.37?μm), blunt-conical, and exhibits a prominent basal ring. A narrow apical elaboration of the nucleus, the nuclear peg, projects deep into the basal invagination of the acrosomal vesicle. Aside from this specialization, the nucleus is a solid elongate-cylindrical structure (7.66?μm) that exhibits several small irregular lacunae. Four or occasionally three round-ovate mitochondria surround a pair of orthogonally-arranged, triplet-substructure centrioles. The proximal centriole is connected to a small indentation of the nuclear base by a thin layer of granular pericentriolar material, whereas the distal centriole is anchored to the plasma membrane by nine terminally-forked satellite fibres. The 9?+?2 pattern axoneme of the tail is continuous with the distal centriole. Comparison with other bivalves indicates a very close relationship between tridacnids and cardiids based on sperm ultrastructure. Specifically, the presence of a nuclear peg links Tridacna spp. with the cardiid genus Cerastoderma, but further information on the many unstudied genera is required to test the exact nature of this relationship. The sperm ultrastructure provides additional support for the recently proposed hypothesis that the Tridacnidae may be no more than a specialized subfamily of the Cardiidae.     

Seasonal variation in the balance between physiological mechanisms of feeding and digestion in Mytilus edulis (Bivalvia: Mollusca)

Seasonal variations in the balance between physiological mechanisms of feeding and digestion are considered among 45 to 57 mm shell length Mytilus edulis L. from southwest England. Mussels had been acclimated to standardised conditions of food availability in March, June and October, 1981. Results indicate that despite showing a negative relationship (P<0.001) with the efficiency of ¹⁵N absorption, coincident alterations of both ingestion rate (0.17 to 0.54 mg total Phaeodactylum tricornutum h^-1) and organic gut content (1.00 to 1.80 mg) represent significant mechanisms effecting the seasonal regulation of nutrient acquisition. Concurrent changes in absorption efficiency alone clearly exerted a relatively minor influence upon seasonal rates of absorption. Associated gut residence times of ¹⁵N-labelled material varied between 4 and 10 h. Furthermore, despite the ensuing deleterious effects, together with increased gut contents, absorption efficiencies among mussels that had been starved throughout acclimation were consistently maintained equivalent to those among individuals feeding normally. Such constancy was at least partially achieved by an increased residence time of material within diverticulae, relative to the digestive system as a whole. Finally, comparison of isotopic absorption efficiencies with those recorded for total organics and organic nitrogen has demonstrated differences of as much as 30% between gross and net uptake due, we suggest, to excretion of metabolically derived material within the alimentary canal.     

Reproductive habits and life cycle of the small clam Kingiella chilenica (Bivalvia: Cyamiidae) in an estuarine sand flat from the south of Chile

A population of the small clam Kingiella chilenica Soot Ryen 1959 was studied from March 1986 to December 1988 in an intertidal flat at Queule River, in the south of Chile. The life cycle and life history pattern of the bivalve were established contrasting population structure and dynamics to its reproductive habits. Individuals are gonochoristic and semelparous, presenting a typical annual life cycle. The species is a sequential brooder whose embryos undergo direct development. After the brooding season (summer through autumn), the adults disappear gradually (autumn through winter). Recruited juveniles overwinter during a relatively long period, undergoing rapid growth during the spring to attain the adult stage during the summer. The number of brooded embryos increases in proportion to adult length cubed. Life history traits of this bivalve are compared to those reported for other small brooder clams. Some basic tendencies become apparent when traits for semelparous versus iteroparous species are contrasted. As in other semelparous sequential brooders (Transennella tantilla, Gaimardia bahamondei), the relationship between brood size and shell length obseved in K. chilenica does not fit the allometry hypothesis for marine brooding invertebrtes that allometric constraints on the brooding space limit the fecundity of larger individuals. Also contrary to theoretical predictions, small body size does not limit the diversity of a clam's developmental patterns. Possible explanations for this finding are discussed.     

Annual variation in the growth rate of Yoldia notabilis (Bivalvia: Nuculanidae) in Otsuchi Bay,northeastern Japan,analyzed using shell microgrowth patterns

Annual variation in the growth rate of the protobranch bivalve Yoldia notabilis (collected in Otsuchi Bay, northeastern Japan between 1989 and 1991) was determined by measuring shell length at successive growth lines. Factors affecting growth rates were assessed by examining long-term environmental data. Shell cross-sections of Y. notabilis showed a clear pattern of internal growth lines which formed simultaneously with the annual external lines on the outer shell surface. Hence, they were used as an age marker. A maximum lifespan of 17 yr was determined for this species, and a sigmoidal growth curve was obtained by the internal growth line analysis. Examination of the growth lines also revealed a large annual variation in growth rate, fluctuating as much as 32-fold during the past 9 yr. The variation correlated negatively with water temperature and positively with chlorophyll a content in the water column. It is suggested that the variation in annual growth rate is dependent on food supply during the spring phytoplankton bloom which varies from year to year according to the flow of the cold Oyashio current each spring.     

Factors influencing particle selection and feeding rate in the polychaete Cistenides (Pectinaria) gouldii

Feeding behavior of the deposit feeding polychaete Cistenides (Pectinaria) gouldii was examined to determine factors affecting particle selection and feeding rate. Worms were found to select large particles preferentially and particle size selection increased with worm size. Particle selection behavior was unaffected by changes in sediment bacterial abundance. Feeding rates were affected by sediment size, bacterial density and worm size. Generally feeding rates increased in sediment containing more food, although the response was worm size specific. When viewed in a theoretical construct these results were inconsistent with predictions of deposit feeder optimal foraging models. Alternative explanations, such as morphological constraints placed upon the polychaete, may explain C. gouldii feeding behavior.     

Variable feeding behavior in three species ofMacoma (Bivalvia: Tellinacea) as a response to water flow and sediment transport

Many species of tellinacean bivalves mainly deposit-feed but are also known to vary their feeding behavior in response to predation and to the availability of suspended organic matter relative to that of sedimentary organic matter. This study showed that three species of the Pacific genusMacoma (Macoma nasuta Conrad, 1937,Macoma secta Conrad, 1837, andMacoma inquinata Deshayes, 1855, from the San Juan Islands, Washington, USA) varied their deposit-feeding behavior in response to water flow near the sediment-water interface and to sediment transport. In the summers of 1987, 1988 and 1989, water velocity was varied in a large racetrack flume, in order to change both water velocity and bottom sediment transport. In quiet water, the inhalant siphon was protruded far from the siphon hole. As water velocity increased, with little or no sediment transport, the deposit-feeding radius decreased. Qualitative observations suggested that this was related to the drag on the siphon. InM. secta, the distance of siphon protrusion was not related to body size. Under conditions of higher near-bottom water velocity, combined with bottom sediment transport, some individuals ceased to deposit-feed, while others sustained feeding by ingesting sediment within the siphon hole, at least 1 cm beneath the sediment-water interface. These results suggest that hydrodynamic conditions are a major determinant of feeding behavior, and previous explanations of variable feeding behavior as a response to predation may have to be adjusted to accommodate this expanded set of responses.     

Siphon nipping facilitates lethal predation in the clam Mesodesma mactroides (Reeve, 1854) (Mollusca: Bivalva)

In soft sediment marine communities, fishes frequently bite off extended siphons of buried clams; the consequential shortening of the siphon is known to reduce burial depth of the clams, secondarily increasing their vulnerability to lethal excavating predators. In this study, siphon nipping on the yellow clam, Mesodesma mactroides, was simulated by removing the top 6.6–30% of siphons. This caused a burrow reduction in 25–75%, respectively, compared to control individuals with intact siphons, in field and laboratory trials. To examine subsequent consequences of reduced burial depth, we exposed nipped and intact clams to potential predators in the laboratory simulating the observed natural clam abundance. Artificially nipped clams were consumed twice as much as control clams. The present results suggest that sympatric croppers contribute to the stock recovery failure by facilitation of lethal predation and that re-seeding to increase the local abundance of M. mactroides should be an essential aspect of conservation efforts in South America.     

Advertisement call duration indicates good genes for offspring feeding rate in gray tree frogs (Hyla versicolor)

Indicator or ”good genes” models of sexual selection predict that mating preferences allow females to choose mates that are genetically superior. Female gray tree frogs (Hyla versicolor) prefer male advertisement calls of long call duration, which can be indicators of enhanced offspring growth performance. We tested the effects of father’s call duration and the presence of a caged predator (dragonfly naiad) on tadpole activity and growth in a factorial experiment, controlling for maternal and environmental effects. The effect of food availability (a repeated measure) on tadpole activity was also examined. Tadpoles responded to predator presence and to high food availability by decreasing activity and feeding. Tadpoles exposed to a caged predator were smaller after 14 days than those exposed to an empty cage, suggesting that spending less time feeding carries the cost of reduced growth. Offspring of males with long versus short calls responded similarly to the presence of a predator. Nonetheless, offspring of long-calling males spent more time feeding than did offspring of short-calling males, except when a predator was present but no food was available. Increased time spent feeding may contribute to enhanced offspring growth and, therefore, to the indirect benefit that a female may realize by selecting a mate with long calls. However, because the behavioral differences depended on the environment, and because the fitness consequences of such behavioral differences should also vary with the environment, the benefit of mating with a long-calling male may depend on the conditions encountered by the offspring. Received: 15 February 2000 / Revised: 24 September 2000 / Accepted: 16 October 2000     

Particle-size selection by Pseudopolydora paucibranchiata (Polychaeta: Spionidae) in suspension feeding and in deposit feeding: influences of ontogeny and flow speed

Pseudopolydora paucibranchiata Okuda suspension feeds and deposit feeds at the sediment-water interface, where it is exposed to a variety of particles differing in physical characteristics and nutritional value. In flume experiments (conducted in August 1994 and May 1995) with two sizes of either suspended or deposited beads, I measured particle-size selection separately in each feeding mode. The same influences of palp width and of ambient flow speed were observed in each mode. At velocities 0.74 cm s^-1 there were no relationships between palp width and the proportion of gut contents composed of large beads. At velocities 1.8 cm s^-1 worms with narrower palps ingested relatively fewer large beads (and more small beads) than did worms with wider palps. Palp width and body length were linearly related, and results were similar when analyzed with body length as the independent variable. As flow speed increased, selectivity changed in a worm-size-specific manner: worms with a palp width -1. Assuming that in the field (1) particle size is the principle criterion for selection, and (2) the amount of digestible food component in deposited and suspended particles, respectively, is related to particle surface area and volume, I hypothesize that changes in selectivity as velocity rises can cause juveniles to experience a decreasing profitability of suspension feeding and a simultaneously increasing profitability of deposit feeding. Juveniles could maintain a diet of high food value despite flow variations by adjusting the proportion of time they spend suspension feeding relative to deposit feeding.     

Advanced age for sexual maturity in the ocean quahog Arctica islandica (Mollusca: Bivalvia)

A study of gonadal state in 39 small specimens of Arctica islandica Linné collected in April 1976 from the Middle Atlantic shelf of North America suggests that sexual maturity is reached at a later age than has been reported for other shelf bivalves. Eight of the specimens had gonads in the undifferentiated state. On the basis of annual internal growth banding in the shells of these immature specimens, age ranged between 4 and 14 years. Average age was 9.38 years (standard deviation, s,= 3.54). Shell length ranged from 24 to 47 mm (average 38.85 mm, s=9.25). Differentiated gonads were found in specimens as young as 6 years. Age of maturity shows a wide range and may be dependent upon growth rate and locality.     

Epifluorescence microscopy,a technique for the study of feeding in Crassostrea virginica veliger larvae

Epifluorescence microscopy was applied as a new technique to observe the response of Crassostrea virginica veliger larvae to the algal foods Monochrysis lutheri or Chlorella autotrophica. Uptake, lysis, and digestion or rejection of these algae by oyster larvae were observed microscopically through the autofluorescence of chlorophyll a and its derivatives. Both species of algae were taken up by large numbers of larvae within 5 min after being added to larval cultures. The good growth of larvae obtained with M. lutheri as a food source was related to rapid uptake, lysis, and digestion of this alga. Larvae fed with C. autotrophica did not grow. Althogh C. autotrophica was also taken up rapidly by the larvae, there was no lysis or digestion of these algae and cells were eventually voided.