The effects of tidal currents on the rhythm of feeding and digestion in Pecten maximus L.

The orientation of individuals in two populations of Pecten maximus L., from the west coast of Ireland, shows that they have a marked preference to face directly into a tidal flow. In both localities examined there was a reversal of tides and the members of the populations were divided equally for flood and ebb tides. Twenty-four hour in situ studies of the animals were made and at all stages of the tide individuals facing either due east or west were observed. A cyclical feeding pattern imposed by the reversal of tidal flow is proposed.The pH of various parts of the digestive tract was investigated and showed a wide range of values. The most acid region was that of the stomach. The variations in pH of all of the regions of the gut examined throughout a 24-h period closely followed the pattern of the tidal cycle.Histological analysis of the stomach and digestive diverticula of representative samples of scallops taken at regular intervals over the 24-h periods clearly indicated a diphasic pattern of digestion within the tubules of the digestive diverticula. A close correlation between the phases of intracellular digestion, the pH variations in different regions of the gut, and the tidal cycle indicate distinct feeding cycles in Pecten. Those scallops facing into the ebb current show the same diphasic patterns as those individuals facing the flood current, but are 6 h out of phase. The cycle is considered as a duplication of a diphasic feeding pattern. The tubules themselves undergo a digestive process similar to that in Lasaea rubra (Montagu). The digestive cells phagocytose food material, begin intracellular digestion, and increase in size until they obscure the lumina. The dispersal of waste material and residual bodies is accomplished dramatically by a dehiscence of the tubule cells together with a loss of both digestive and crypt cells. New tubules are regenerated from the apices of those tubules breaking down. In any section of the diverticula tubules in two different conditions are found. The cycle of digestion takes 24 h and in order to facilitate feeding at each 12-h tidal cycle the tubules are equally divided into two phases with one 12 h behind the other.     

A PLANIMETRIC STUDY OF MORPHOLOGICAL VARIABILITY IN THE DIGESTIVE DIVERTICULA OF LITTORINA LITTOREA (LINNAEUS) AND MYTILUS EDULIS LINNAEUS

The inter-and intratubular morphological variability in thedigestive diverticula of Littorina littorea and Mytilus edulishas been investigated by planimetric procedures. Five parametershave been measured: mean epithelial thickness (MET), mean diverticularradius [MDR], mean luminal radius (MLR), MLR/MET ratio and MET/MDRratio. The results indicate that irrespective of the patternof tubule organization within the digestive diverticula (whethertubule types are clustered or not), variability between individualsis greater than that between zones of the digestive gland. Thishas implications for the design of sampling strategies in investigationsof the morphology of digestive diverticula in physiologicaland pathological studies. The variability in the epithelialthickness within diverticular sections is of minor relevancein assessing the overall condition of the digestive gland inthese studies, because variability in epithelial thickness betweentubules is significantly greater than within tubules in bothspecies. (Received 10 March 1989; accepted 16 October 1989)     

The tidal rhythm of feeding and digestion in the pacific oyster, Crassostrea gigas (Thunberg)

A study has been made of the processes of extra- and intracellular digestion in the Pacific oyster, Crassostrea gigas (Thunberg) over two 24-h cycles in winter and summer.The results show that the digestive processes are discontinuous and related to the tidal cycle. Variations in tidal height resulting from a diurnal inequality of the tide affect both the relative dissolution of the crystalline style and the relative lengths of the constituent phases of the intracellular digestive process in the digestive diverticula. On a seasonal basis the style is present for a greater length of time in winter and, conversely, remains dissolved longer in summer. A seasonal variation in the structure of the digestive tubules has also been found.The results confirm conclusions reached earlier that the processes of extracellular digestion in the stomach and intracellular digestion in the digestive diverticula of intertidal bivalves are both discontinuous, alternate, and irrevocably interrelated since breakdown of the digestive cells of the digestive diverticula following intracellular digestion results in the dissolution of the crystalline style. The arrival of food in the stomach has a minimal effect upon the style. Moreover, the cytological structure of the digestive diverticula of C. gigas undergoes a series of synchronized changes related to the tidal cycle.     

CYCLIC ACTIVITY AND EPITHELIAL RENEWAL IN THE DIGESTIVE GLAND TUBULES OF THE MARINE PROSOBRANCH MAORICRYPTA MONOXYLA (LESSON)

Three cell types are present in tubules of the digestive glandof the marine prosobranch Maoricrypta monoxyla (Lesson). Histochemistry,and feeding and starvation experiments established that themain type, the digestive cell, is involved in endocytotic uptakeof food material from the lumen. Digestion of this materialoccurs within vacuoles, and indigestible material (indicatedby the dye trypan blue) accumulates in basal residual bodiescontaining lipofuscin pigment. Another cell type, the cryptcell, appears to secrete a glycoprotein, probably enzymaticin function. The third cell type contains large vacuoles butit has not been Established whether the contents are secretoryor excretory. The tubules undergo a cycle of digestive activity not relatedto the tidal cycle as in some marine molluscs, but probablyan indirect result of the feeding regime. The cycle begins withimmature tubules in which some endocytosis occurs. These developinto absorbing tubules involved mainly in food uptake. In maturetubules intracellular digestion occurs. At a later stage thetubules fragment to produce spherules which may conserve usefulmaterial, and finally they, disintegrate completely. Eighty per cent of the dividing cells in the epithelium occurin crypts, which are therefore considered to be the main sitesof epithelial renewal. The processes by which tubules may bereformed after breakdown are discussed (Received 28 September 1978;     

THE FUNCTIONAL MORPHOLOGY OF THE DIGESTIVE SYSTEM OF LYONSIA HYALINA CONRAD, 1831 (BIVALVIA: ANOMALODESMATA: PANDOROIDEA)

The anatomy and histology of the digestive tract of the suspensionfeeding bivalve Lyonsia hyalina were examined using microdissectionand conventional light microscopy. Lyonsia hyalina has a typeIV stomach which contains a major typhlosole that does not penetratethe left pouch, as in other members of the Pandoroidea. Theventral and posterior sorting areas of the stomach are sitesof vigorous ciliary activity. The gastric shield is locatedon the left and posterior stomach walls, underlain by tall basophiliccells with microvilli that project into the gastric shield.The style sac and midgut are combined, and contain the morphologicalcell types A-D seen in other bivalves. Many ciliated cells ofthe digestive tract appear to have high densities of apicalmitochondria. The ducts within the digestive diverticula arelined by epithelia containing a conspicuous brush border. Bothcrypt cells and digestive cells exist in the digestive tubules.The presence of numerous fragmentation spherules throughoutthe digestive diverticula indicates that intracellular digestionoccurs there. (Received 21 April 1992; accepted 1 October 1992)     

DISTRIBUTION OF DIGESTIVE TUBULES AND FINE STRUCTURE OF DIGESTIVE CELLS OF APLYSIA PUNCTATA (CUVIER, 1803)

The distribution of digestive tubules of Aplysia punctatahas been studied in animals under experimental feeding conditions.Histological analysis of the digestive gland has revealed twotypes of tubules, called tubules A and B. Tubules of type Awere composed of basiphilic cells (calcium, excretory and thincells) and tubules of type B were lined by large digestive cellsand basiphilic cells. The latter occur in small groups, usuallyin the corners of the tubules. Type A tubules are involved inion metabolism and show a diphasic cycle (absorptive and reconstitutive)according to the height and the stage of calcium cells. TypeB tubules are involved in digestive processes and display atetraphasic cycle (holding, absorption, fragmentative and reconstitutive)depending upon the height and the stage of the digestive cells.The tetraphasic cycle was compared with the four categoriesof tubules in bivalves. It is proposed that digestive processesmay be continuous in digestive cells of A. punctata. (Received 16 November 1999; accepted 1 October 2000)     

FORMATION OF MYO-INOSITOL AND PHYTIN IN RIPENING RICE GRAINS

With the view to elucidate the role of myo-inositol in the ripeningprocess of rice grains, its distribution, formation and conversionwere studied.

1. myo-Inositol in the ripening rice grains was fractionated intofree-, phosphate ester- and phosphoinositide-forms. At the earlystage of ripening, a considerable part of myo-inositol was foundin free state, and at the end of ripening stage the most partwas found in phosphate ester-state, phytic acid. The contentof phosphoinositide in the grains was low during the ripeningperiod.
2. The occurrence of biosynthesis of myo-inositol inthe ripeningrice grains was confirmed by the observation ofincorporationof ¹⁴C into myo-inositol from ¹⁴C-sugars and itwas found, fromthe feeding experiment of myo-inositol- thatmyo-inositol doesnot undergo reactions further than phosphorylation.
3. The feeding experiment of glucose-l-³²P showed that the distributionpattern of ³²P in different fractions of grain material wasthe same as that of ³²P-phosphate, indicating that phytic acidis one of the final products of phosphorus metabolism in theripening rice grains.
4. These results led to the assumptionthat myo-inositol mightact as an acceptor of phosphorus toremove inorganic phosphorusin favor of starch synthesis byphosphorylase.

(Received September 12, 1962; )     

FEEDING PATTERNS OF FISSURELLA SPECIES ON ISLA DE MARGARITA, VENEZUELA: USE OF RADULAE AND FOOD PASSAGE RATES

Structural differences and functional wear of the radula inthree species of the gastropod Fissurella from Isla de Margarita,Venezuela, were examined using light and electron microscopy.Wear patterns indicate between 6 and 9 transverse rows of teethare comonly used during feeding. Mechanical wear was most noticeableon the cusps of the outer lateral tooth; this wear varied fromrounding (F. nimbosa) to blunting (F. barbadensis) to squaring(F. nodosa) of the cusps. Morphological changes were additionallycharacterized by a significant decrease in the cusp length ofmarginal cusps in F. nodosa and breakage of the central toothand inner lateral teeth in F. barbadensis. Interspecific differencesin wear patterns suggest that the rhipidoglossate radula maybe used differently by congeneric Fissurella. Despite considerable variation, rasping rates while feedingon the same substrate were comparable among species; however,food passage rates through the digestive system differed amongspecies studied. Fissurella barbadensis requires 12 hours topass its food through the digestive tract, taking almost twiceas much time as F. nodosa and F. nimbosa. These data highlightdifferences in the feeding ecology of Fissurella species andcorrelate well with individual activity patterns and grazinghabits. ^*Present address: La Salle University, Department of Biology,20th Street at Olney Avenue, Philadelphia, PA 19141, USA. (Received 4 October 1988; accepted 16 February 1989)     

Tidal influence upon appendicularian abundance in North Inlet estuary, South Carolina

Tidal influences on appendicularian densities were observedat North Inlet, South Carolina, by sampling along a transectwhich ran from a tidal creek to a station 5 km offshore. Oikopleuradioica was the dominant species in North Inlet, while Oikopleuralongicauda and Appendicularia sicula contributed marginallyto appendicularian numbers during midsummer and fall. A strongtide-dependent density pattern was clear for inshore waters.Low-tide densities of all three species showed a dramatic increasein an offshore direction. At high tide, densities were similarbetween all stations for O. dioica, while O. longicauda andA. sicula showed a less pronounced density gradient than atlow tide. Population densities within the inlet were greateron spring tides than neap tides and tidal influences were generallyconsistent between seasons. Appendicularians enter the estuaryin densities as high as 20 072 animals m^–3, indicatingthat tidal currents may be an important mechanism for exchangeof appendicularian biomass between coastal and estuarine waters. ¹Present address: Allan Hancock Foundation, University of SouthernCalifornia, Los Angeles, CA 90007, USA.     

THE PHYSIOLOGY AND FEEDING BEHAVIOUR OF TWO MARINE SCAVENGING GASTROPODS IN HONG KONG: THE SUBTIDAL BABYLONIA LUTOSA (LAMARCK) AND THE INTERTIDAL NASSARIUS FESTIVUS (POWYS)

Aspects of the physiology and feeding behaviour of the scavengingsnails, Babylonia lutosa and Nassarius festivus have been studiedand compared. N. festivus has a wider physiological tolerancethan B. lutosa; upper lethal temperatures being 31.5°C and28.5°C respectively and lower lethal salinities 15.5 and11.5. N. festivus was also more resistant to desiccation. N.festivus is adapted to an intertidal environment that is morevariable than the subtidal habitat of B. lutosa. The metabolicrate of adult N. festivus was two to three times higher thanthat of adult B. lutosa, the specific oxygen consumption rateof the former being 7.91±0.49x10^–6 mol of O₂.g^–1wet wt.hr^–1. This correlates with estimates of consumptionobtained for the two animals, B. lutosa eating, on average,6.57% of its wet tissue weight per day, N. festivus 15.33%.Standardization of the data for 2 g animals of both species,however, reveals no significant difference in terms of oxygenconsumption and thus the enhanced consumption by N. festivussimply reflects its smaller size. Both species are opportunisticfeeders and can survive long periods of starvation (>100days). The feeding strategies of the two are also different,N. festivus eating faster than B. lutosa, possibly because ofthe more ephemeral nature of carrion in the intertidal. Starvationaffected the feeding behaviour of N. festivus more than B. lutosaand N. festivus was able to perceive carrion from greater relativedistances than B. lutosa. (Received 27 February 1989; accepted 24 July 1989)     

Size, composition and distribution of particles related to wind induced resuspension in a shallow tropical lagoon

The size, composition and distribution of particles in the watercolumn were surveyed in a shallow area (1 m depth) of a tropicallagoon (Cte d'Ivoire) during a sequence of wind-induced resuspension.Water samples were collected hourly near the surface duringone tidal cycle. Three characteristic periods were distinguished:a calm period with low wind speed (average 1.2 m s^–1 awindy period with wind speed >3 m^–1 s (range between4 and 6 m s^–1) inducing sediment resuspension and a relaxationperiod during the decrease of wind velocity. From the analysisof several parameters (particle size and volume, bacteria. pico-and nanophytoplankton, ciliates and detritus), sediment resuspensioncaused a regular injection of particles from the bed. The finestparticles (1.5–6 µm: chlorophytes such as Chiorellaspp., picocyanobacteria such as Synechococcus) were the firstto be affected by wind-induced turbulence, whereas large particles(6–12 µm: diatoms. cyanobacteria such as Lyngbiaspp.) were dispersed into the water column at the highest windspeed. The fate of the different seston components differedaccording to their size. Therefore, wind-induced resuspensioncould greatly influence the food web organization through thequantity, quality and size of edible particles available ata given time.     

Feeding, growth and food conversion of the marine cladoceran Penilia avirostris

Ingestion and clearance rates, feeding behaviors and life historyvariables of the marine cladoceran Penilia avirostris were evaluatedover a range of food concentrations encountered in nature (0.01–3.0mm³ 1^–1 of Isochrysis galbana). Ingestion rates increasedand clearance rates decreased with increasing food concentration.No maximum feeding thresholds were observed over the range ofalgal concentrations offered. Weight-specific ingestion ratesdecreased with increasing body weight. Feeding behaviors suchas mandibular activity, abdominal claw rejections of cloggedfeeding structures and feeding appendage activity decreasedat a food level of 0.3 mm³ l^–1 of l. galbana. Peniliaavirostris had very poor survivorship at extremely low (0.01mm³ l^–1 and high (3.00 mm³ l^–1) food levels. Mortalitywas hardly affected at food levels of 0.03–1.0 mm³ l^–1Reproduction did not occur at food levels of     

ENVIRONMENTAL CONDITIONS, GROWTH AND PRODUCTION OF ANADARA SENILIS (LINNAEUS, 1758) IN A SENEGAL LAGOON

Two populations of Anadara senilis were sampled periodicallyin a lagoon of Senegal. Spatfall occurs in summer during therainy season. Population density decreases from about 50, 000.m^–2,two months after spatfall, down to 6, 750 one year later and750 after 28 months. The average growth, measured on the surfaceof the shell, following the umbo rim axis is 0.8 mm per month.The main reduction in growth rate occurs in winter and endsby the deposition of a growth ring. A second growth reductiontakes place during the rainy season and sometimes ends by aweak growth ring. The microgrowth increments are conspicuousand widest during spring equinox. They are not directly relatedto the tidal cycle, but it was impossible to determine if theyhave a tidal or a daily periodicity. (Received 11 February 1990; accepted 16 July 1993)     

Effects of prey motility and concentration on feeding in Acartia tonsa and Temora longicornis: the importance of feeding modes

Feeding experiments were conducted with the ambush-feeding copepodAcartia tonsa and the feeding-current-generating copepod Temoralongicornis. The copepods were offered a mixed diet of the dinoflagellateHeterocapsa triquetra and the ciliate Balanion comatum of similarcell size. The dinoflagellate was offered at a constant concentrationof 10–15 cells mL^–1, whereas the ciliate was offeredat a variety of concentrations, ranging from 7 to 57 cells mL^–1.Copepods with different feeding modes possess different mechanismsfor prey detection, suggesting that the two copepods would responddifferently to the two prey types. Both copepods had significantlyhigher clearance rates on the highly motile ciliate than onthe less motile dinoflagellate. In encounters between A. tonsaand its prey, we argue that this is due to the higher hydromechanicalsignal generated by the ciliate. The advection feeding copepodT. longicornis fed on the two prey according to their relativeconcentrations; in this case, we suggest that although B. comatumis capable of detecting feeding-current-generating predators,the feeding current velocity generated by T. longicornis isgreater than the escape velocity of this ciliate.     

Perceptive performance and feeding behavior of calanoid copepods

The goal of this study was to determine variables associatedwith calanoid feeding behavior, and thus, to improve our understandingof the basics of calanoid feeding rates. These variables includedperiods and frequency of appendage motion, rates of cell clearance,distance at which a copepod first reacts to a cell which iseventually captured, and rate of water flow through the areacovered by the motions of a copepod's feeding appendages. Theeffects of these variables on feeding rates were determinedfor copepodids and adult females of the calanoid copepod Eucalanuspileatus at phytoplankton concentrations covering the rangeencountered by this species on the south-eastern shelf of theUSA. Our results indicate that the distance at which E.pileatusperceives phytoplankton cells increases {small tilde}2-foldas food concentrations decrease from 1.0 to 0.1 mm³ l^–1.These results lead us to hypothesize that this is due to increasedsensitivity of chemosensors on the copepods' feeding appendages.This 2-fold increase in perceptive distance amounts to a near4-fold increase in perceived volume which is close to the 6-foldincrease in volume swept clear (VSC) from 1.0 to 0.1 mm³ l^–1of Thalassiosira weissflogii. We assume that the increases inVSC by planktonic copepods, when food levels are below satiation,are largely a function of the sensory performance of the individualcopepod.     

EFFECTS OF WOUND HEALING ON ZINC DISTRIBUTION AND ALKALINE PHOSPHATASE ACTIVITY OF HELIX ASPERSA (GASTROPODA: PULMONATA)

Helix aspersa were loaded with ⁶⁵zinc and after 2 and 5 daysstarvation there was no significant reduction in the zinc concentrationof the digestive gland and shell. Wounding of the optic tentacle,foot tissue and partial shell removal of H. aspersa resultedin deposition of ⁶⁵zinc in the wound area. Alkaline phosphataseshowed no increase in concentration at the sites of wounding. (Received 15 October 1985;     

Feeding behaviour of the rotifer Ascomorpha ovalis: functional response, handling time and exploitation of individual Ceratium cells

The planktonic rotifer Ascomorpha ovalis feeds on large dinoflagellates(e.g. Ceratium sp., Peridinium sp.) and is able to extract theircell contents by means of its virgate mastax. This paper presentsthe results of experiments on the feeding behaviour of laboratory-culturedAscomorpha with Cerarium furcoides as food algae. Ascomorphaare three times larger than their prey Ceratium (by volume),but with regard to total length, their prey was even 20% larger.Ascomorpha showed a hyperbolic functional response curve witha plateau of the feeding rate at 8 Ceratium cells animal^–1dar^–1 when concentrations of Ceratium were >100 cellsml^–1. The mean handling time (time for capturing and extractingone Ceratium cell) was 3 min. The shape of the functional responsewas better described by a curvilinear model than by a rectilinearmodel. However, handling times cannot be responsible for this,since they were too short to set limits on ingestion rates.At low food concentrations, encounter rates with prey seemedto limit the feeding rates of Ascomorpha, whereas at mediumto high food concentrations, Satiation effects (lower attackrates) seemed to set limits on the feeding rates. Ascomorphashowed a significant decrease in the exploitation of singleCeratium cells at high prey concentrations. This decrease couldbe explained by a saturation effect in which the partly filledguts of Ascomorpha did not permit the total extraction of thecontents of a Ceratium cell.     

Effects of Olisthodiscus luteus on the feeding and reproduction of the marine rotifer Synchaeta cecilia

The chrysophyte Olisthodiscus luteus is not ingested by Synchaetacecilia. It inhibits the feeding on other, acceptable food atO. luteus densities as low as 50 cells ml^–1 and reducessurvival and reproduction at O. luteus densities > 10³ cellsml^–1. The possible mechanisms and implications of thisphenomenon for the distribution and abundance of S. ceciliaare discussed.     

Feeding and growth rates of the doliolid, Dolioletta gegenbauri Uljanin (Tunicata, Thaliacea)

The goal of this research is to enhance our knowledge of thecontributions of doliolids to the planktonic community as consumersand secondary producers. The objectives are to quantify feedingand growth rates of Dolioletta gegenbauri gonozooids at fourfood concentrations and four temperatures in order to determinetheir impact as grazers throughout the water column. Althoughdoliolids are abundant in numerous regions of the coastal ocean,and are considered to be major planktonic grazers, data on ratesof feeding and growth are scarce. Laboratory experiments wereconducted at 16.5, 20, 23.5 and 26.5°C to quantify removalof a 50:50 volumetric concentration of Thalassiosira weissflogiiand Rhodomonas sp. at four different food concentrations of20, 60, 160 and 390 µg C l^–1. Results from theseexperiments suggest that clearance rates are similar at concentrationsfrom 20 to 60 µg C l ^–1, and decrease as the foodconcentrations increase to 160 and 390 µg C l ^–1.The ingestion rates increase over a range of phytoplankton concentrationsfrom 20 to 160 µg C l ^–1, then decrease when abnormallyhigh concentrations of 390 µg C l ^–1 are offered.Clearance and ingestion rates increase as temperature increasesfrom 16.5 to 26.5°C. The exponential growth rates rangefrom k = 0.2–0.7, with the lowest rates occurring at thehighest food concentration. Growth rates increase with increasingtemperature from K = 0.1–0.3 at 16.5°C to 0.45–0.7at 26.5°C. In each case, the small- and medium-sized zooidshad higher growth rates than the larger gonozooids. These resultssuggest that doliolid feeding and growth rates are a functionof environmental food concentrations and temperatures, and implythat they can be important consumers in a changing neritic environment.     

Differential allocation of male-derived nutrients in two lampyrid beetles with contrasting life-history characteristics

Across diverse animal taxa, sperm is transferred from malesto females during mating within a spermatophore produced bymale accessory glands. In some insects, male spermatophoresprovide females with nutrients that may be used to increasereproductive output or for somatic maintenance, while in othersno such benefits have been detected. Boggs suggested that variationin the current function of spermatophores may be explained byconsidering ecological and life-history factors. This studyexamined spermatophore function in Ellychnia corrusca and Photinusignitus (Coleoptera: Lampyridae), two beetles that exhibit markeddifferences in adult diet, adult life span, and overwinteringstage. During mating, males of both species transfer to femalesa complex, proteinaceous spermatophore, which is subsequentlydigested in a specialized sac within the female reproductive tract.Males of each species were injected with ³H-radiolabeled aminoacid mixtures and mated with conspecific females. The fate of spermatophore-derivedproteins was determined by dissecting females at various timesafter mating with these radiolabeled males. Females of thesetwo species showed markedly different patterns of incorporationof spermatophorederived nutrients. P. ignitus females incorporatedthe majority (62%) of spermatophore-derived protein into maturingoocytes within 2 days after mating. In contrast, in E. corruscaa large percentage of radiolabel (46%) appeared in female fatbody at 6 days after mating, with a threefold lower allocationto maturing oocytes compared to P. ignitus. These findings supportthe prediction that short-lived, nonfeeding females are selectedto allocate a greater proportion of male-derived nutrients toreproduction, while longer-lived, feeding females are selectedto allocate a greater proportion to somatic reserves and maintenance.These results suggest that life-history characteristics maybe useful in explaining observed differences in spermatophorefunction across taxa.