Hydrolytic enzymes in the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis

Hydrolytic enzyme activities were determined in tissue extracts of the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis. The following activities were measured in field samples and characterized according to their mean specific activities and their pH optima: protease, aminopeptidase, amylase, N-acetylglucosaminidase, -glucosidase, chitinase, carboxylesterase, phosphatase. Many of the enzyme activities are correlated, indicating their control by the same factors (i.e. nutritional conditions). Differences found between the phosphatase activities and the apparent lack of the chitinolytic system in B. gracilis reflect the differences in body composition and food specialization in both ctenophores, respectively. The low amylase and -glucosidase activities in both ctenophores agree with the low carbohydrate content of their prey. In spite of high carboxylesterase activities, no lipolytic activity was detected in either of the ctenophores. In a laboratory feeding experiment with P. pileus, the enzyme activities increased but did not reach the activities found in the field samples. In B. gracilis, seasonal variations of some enzyme activities are discussed in relation to the seasonal abundance of its prey, P. pileus.     

Herbivory and detritivory among gammaridean amphipods from a Florida seagrass community

The gammaridean amphipods Cymadusa compta (Smith), Gammarus mucronatus Say, Melita nitida Smith and Grandidierella bonnieroides Stephensen from a seagrass community in the Indian River estuary of Florida (USA) fed variously upon large drift algae, small algae epiphytic on seagrasses and seagrass leaf debris and detritus. Consumption was measured in the laboratory using an index (CI) equivalent to mg ingested mg^-1 amphipod day^-1. Observations revealed that the amphipods fed by macrophagy, an attack upon large algae and seagrass debris, and by microphagy, small particle detritus feeding and scraping of plant surfaces for diatoms and other epiphytic algae. C. compta was a macrophagous feeder with a generalized diet of algae and seagrass debris, preferring epiphytic algae and drift algae at mean rates of 1.10 and 0.87 CI, respectively. Gammarus mucronatus fed upon epiphytes and seagrass debris equally at mean rates of 0.90 and 0.97 CI, respectively. The diet of M. nitida condisted primarily of epiphytes, consumed at an average rate of 1.05 CI. Grandidierella bonnieroides fed in a specialized microphagous manner, grooming plant surfaces for small particle detritus and diatoms at an approximate CI rate of 1.45. Assimilation of plants ingested, as reflected by carbon-14 uptake, varied similarly among the 4 amphipods. Epiphytic algae appeared to be most useful as food, providing means of 41 to 75% carbon-14 uptake as ingesta. Drift algae and seagrass debris were of less value, with means varying between 11 and 24 % of carbon-14 uptake by the amphipods. The data show a pattern of feeding which resembles resource partitioning of food both by size and kind. Other evidence, however, including population limitation by predators and an apparent overabundance of food, indicate that resource partitioning as seen may be an artifact, and one which has no co-evolutionary basis among the present species.Contribution No. 102 of Harbor Branch Foundation, Inc.     

Carbohydrate digestion in Penaeus monodon

Using crude homogenates from the digestive system of pond-cultured Penaeus monodon, carbohydrase activity was demonstrated toward a wide variety of substrates differing in sources and complexity. The largest concentration of this activity was found to be localised within the midgut gland. Multiple pH optima for the hydrolysis of starch suggested the presence of more than one amylase, which was confirmed by partial purification using chromatofocusing. Enzyme characterisation of the amylase activity suggested exohydrolysis in the form of a glucoamylase and possible endohydrolysis in the form of an -amylase. The complexity of the enzyme profile demonstrated in P. monodon is discussed in relation to possible sources of carbohydrate found in natural food items.     

Lipid biochemistry and reproductive biology in two species of Gammaridae (Crustacea: Amphipoda)

Gammarus oceanicus Segerstråle, 1947 and Echinogammarus marinus (Leach, 1815) were sampled during the breeding season from Oslofjord in 1984, and their lipid composition examined in relation to reproductive condition. In G. oceanicus, female lipid content increased as the ovary matured. Both the amount of lipid stored and the rate of accumulation were greater in spring than in winter. Spring eggs contained 12.4 g lipid, of which 63% was triacylglycerol and 27% phospholipid. Both fractions decreased steadily during embryonic development. Winter eggs contained 19.2g lipid, of which 52% was triacylglycerol and 43% phospholipid. During the early stages of embryonic development the amount of phospholipid decreased sharply, whereas that of triacylglycerol increased, suggesting that some of the fatty acid released from phospholipid was sequestered temporarily as triacylglycerol. When newly spawned, both winter and spring eggs were richer in monoenoic fatty acids than adult amphipods and these acids were the major fuel consumed during development. 6 fatty acids were utilised more slowly than 3 acids, and egg carotenoid pigment content remained constant. Female E. marinus increased in lipid content as the ovary matured. Spring eggs contained 14.7 g lipid when newly spawned and this increased to 16.6 g during the early stages of development. This increase was entirely triacylglycerol, which declined in later stages; the source of the extra lipid was unclear. Eggs contained very little phospholipid or sterol, and both of these components remained at a steady low level during development. E. marinus eggs were not significantly rich in thonoenoic acids compared with adults, and saturated, monoenoic and polyenoic acids were utilised about equally during development. Both adults and eggs were rich in 20.46, which was utilised at a slower rate than the 3 polyunsaturated acids during embryonic development; again, egg carotenoid pigment content remained constant. In both species there was a decrease in the size of the egg (and as a result, of the newly hatched juvenile), but an increase in total reproductive output (i.e., the total weight of the egg clutch) per female as the breeding season proceeded. The reproductive output of an individual female is probably related to food availability during the period of ovarian maturation, whereas the size of an individual egg is dictated largely by feeding conditions for the juveniles once they are independent of the female. The different patterns of lipid utilisation during development found in this study emphasize the flexibility of response in the reproductive biology of gammarid amphipods. It is not yet possible, however, to relate the differing patterns in a simple way either to egg size or total female reproductive output. Two outstanding problems are the source of extra triacylglycerol during the early stages of development of E. marinus and the metabolic cost of brooding eggs.     

Oxygen-binding by haemocyanins from an ecological series of amphipod crustaceans

The oxygen-binding properties of haemocyanins (Hc) from three species of gammaridean amphipods, Gammarus locusta (L.) (subtidal), Echinogammarus pirloti (Sexton and Spooner), (intertidal, marine) and E. marinus (Leach) (intertidal, estuarine), one species of hyalid amphipod Hyale nilsonni Rathke (high intertidal, marine) and the talitrid amphipod Orchestia gammarellus (Pallas) (semi-terrestrial) have been studied. All the species were collected from the Firth of Clyde, Scotland, during the spring of 1992. The oxygen-carrying capacity of haemolymph from each species was low, although variable, and was correlated with the low concentration of Hc present. The Hc oxygen-affinity of native gammarid haemolymph was relatively high [partial pressure of oxygen required for half-saturation, P₅₀=4 to 5 torr (0.53 to 0.67 kPa)] at their respective in vivo pH values. At equivalent pH, however, Hc from G. locusta displayed a lower O₂-affinity than either Echinogammarus species. Gammarid Hcs had a large Bohr effect ( log P₅₀/ pH=-1.16 to-1.47). Resuspended Hc isolated from whole H. nilsonni showed similar O₂-binding properties to those of the gammaridean amphipods [P₅₀=6.3 torr (1.44 kPa) at pH=8.0; log P₅₀/pH=-1.20]. Comparable data for haemolymph from O. gammarellus showed that the Hc had a lower affinity for O₂ [P₅₀=14.1 torr (1.87 kPa) at in vivo pH] and exhibited a more moderate Bohr effect ( log P₅₀/ pH=-0.79). To eliminate the possibility that these differences were due to the different haemolymph constituents, each of the Hcs were pelleted and resuspended in physiological saline. The differences noted above persisted, demonstrating that they were due to inherent O₂-binding properties of the Hc molecules themselves. An increase in L-lactate resulted in an increase in Hc oxygen-affinity for both Echinogammarus species but not for O. gammarellus. This study has confirmed that there is a clear difference between Hcs from aquatic and semi-terrestrial amphipod genera. The results lend further support to the hypothesis that the move on to land by amphipod crustaceans is accompanied by a decrease in Hc oxygen-affinity, a decrease in the Bohr effect and a decrease in effector (in this case L-lactate) sensitivity.     

Suspension-feeding and assimilation efficiency in Lanice conchilega (Polychaeta)

In laboratory experiments, measurements of ingested ration, assimilated ration and assimilation efficiency in the polychaete Lanice conchilega (Pallas) were carried out at 12°C and at a food concentration of 40x10⁶ cells of Dunaliella marina/l. Over periods of 20 to 46 days, the ingested ration was determined photometrically by the continous automatic recording apparatus described by Winter (1973). The assimilated ration was calculated from the calorific content of the food ingested minus the calorific content of the faeces produced. Within the range of body size investigated (1.3 to 35.0 mg dry-tissue weight), the food intake (=filtration rate=F) was found to be a linear function of body size (W) according to the equation F=0.88 W ^0.32. The daily food intake-expressed as percentage of dry-tissue weight-decreased from 35.7 to 3.9% with increasing body size. The assimilation efficiency was found to vary between 70.6 and 77.2% and showed no significant correlation with body size. The absolute amounts of food retained from suspension and the assimilation efficiencies calculated for L. conchilega are within the range typical for obligatory suspension-feeding organisms. This implies that L. conchilega is capable of completely replacing deposit-feeding by suspension-feeding.This work was made possible through a research grant from the Deutsche Forschungsgemeinschaft in connection with the program Litoralforschung-Abwässer in Küstennähe.     

Population energetics of the intertidal isopod Cirolana harfordi

Laboratory experiments and field measurements generated a population energy-budget estimate for the isopod Cirolana harfordi (Lockington). Assimilation of food energy averaged 88% on a diet of fish. About 35% of assimilated energy is allocated for growth and reproduction, while the bulk of the remainder is used for maintenance and activity (respiration). The high growth efficiency of C. harfordi is discussed with respect to ecological efficiency and energy transfer in marine systems.     

Chitinolytic enzymes in the integument and midgut-gland of the shrimpPalaemon serratus during the moulting cycle

Chitinase andN-acetyl--D-glucosaminidase activity were quantified inPalaemon serratus (Pennant) integument and midgut gland during the moulting cycle. Studies were performed on specimens collected near Concarneau, France, in July 1989. The changes in specific activity are different in the two organs: in the midgut gland enzymatic activity is high throughout the whole moulting cycle with a weak peak at the early premoult Stage D1, whereas in the integument the activity of both enzymes is very low throughout post- and intermoult stages and rises only after premoult Stage D1. The highest specific activity is reached in D1 for chitinase and somewhat earlier (D1) forN-acetyl--D-glucosaminidase. The increase in specific chitinolytic activity coincides with an increase in ecdysteroids.     

Social organization of female sperm whales and their offspring: constant companions and casual acquaintances

Summary Associations among female sperm whales, Physeter macrocephalus, and their dependent offspring, off the Galapagos Islands were studied between 1985 and 1989. The whales were found in groups containing about 23 individuals, with each individual having approximately 12 constant (over years) companions. These permanent units associated with one another for periods of 6.5 days, although the rate and duration of these associations seemed to vary between years, perhaps because of differences in the food supply. The principal function of the closed units may be care of the offspring, and units in the same general area may derive benefit from feeding in a coordinated manner.Offprint requests to: H. Whitehead     

13C/12C ratios and the trophic importance of algae in Florida Syringodium filiforme seagrass meadows

Over 380 stable carbon isotope (¹³C) analyses made during 1981–82 showed that Syringodium filiforme Kutz seagrass meadows in the Indian River lagoon of eastern Florida have food webs based on algal rather than seagrass carbon. Seagrasses averaging approximately-8 were isotopically distinct from algae epiphytic on seagrass blades (X=-19.3) and particulate organic matter in the water column X=-21.6. ¹³C values of most fauna ranged between-16 and-22, as would be expected if food web carbon were derived solely from algal sources. These results counter the idea that seagrass detritus is the dominant carbon source in seagrass ecosystems. Two factors that may contribute to the low apparent importance of seagrass in the study area are high algal productivities that equal or exceed S. filiforme productivity and the high rates of seagrass leaf export from meadows.     

Gut evacuation rates and pigment destruction in the Antarctic krill Euphausia superba

Krill grazing data collected during cruises in the region of the Antarctic Polar Front (S.A. Agulhas Voyage 70) and the South Georgia shelf (R.V. Africana Voyage 119) during the austral summer of 1993 were analyzed to estimate the variability of crucial parameters of the gut fluorescence technique in relation to food availability and krill feeding history. Gut evacuation rates (k) and passage or throughput times (1/k) varied in the ranges of 0.101 to 0.424 h^-1 and 2.3 to 9.9 h and were strongly correlated (p<0.001, r ²=0.98) to krill feeding activity (estimated as initial gut pigment content, G₀) but not to ambient chlorophyll a concentration. A significant differences was found when k values derived from incubations in filtered seawater and low charcoal particle concentrations (0.4 to 0.8 mgl^-1) were compared with values derived from krill fed high concentrations of charcoal (6 mgl^-1). The efficiency of gut pigment destruction was among the highest recorded for zooplankton organisms, 58.1 to 98.4%, and did not covary significantly (p>0.05) with ambient food concentration. However, the pigment lost per individual krill was strongly correlated with the total amount of pigment ingested (p<0.001, r ²=0.99). We suggest that both gut evacuation rates and pigment destruction efficiency may be realistically estimated only when krill is allowed to continue ingesting particles uninterruptedly. Charcoal particle concentration should be equivalent to the in situ wet weight of total seston per unit volume. An objective criterion for the standardization of the measurement and calculation of k values is also proposed.     

Analysis of an intertidal population of the amphipod Gammarus palustris using a modified version of the egg-ratio method

An intertidal population of Gammarus palustris Bousfield was sampled over a 23-month period and analyzed by a modified form of the egg-ratio method. Total numbers and size-frequency distributions revealed small numbers in the early spring which later increased to a peak in the summer months. This was followed by a marked reduction near the end of sumer and a subsequent rise in numbers during the early fall. Finally there was a second decrease to very low numbers in the late fall and early winter. Average brood size was calculated and used as an indication of food limitation. Attempts to correlate this with per capita rate of change (r), birth rate ( \((\hat b)\) and death rate ( \((\hat d)\) ) suggested that the population increase in the early summer was food-rather than predator-limited. The late summer decline appears to be the result of predation pressure as well as food limitation. The fall peak is attributed to juvenile release from ovigerous femals escaping previous predation and to an increase in adult males resulting from a release in predation pressure. The winter decline may be due to adverse environmental conditions.     

Feeding habits and food requirements of some amphipods in the Black Sea

Food composition and food requirements of four amphipod species of the Black Sea — Dexamine spinosa (Mont.), Amphithoe vaillanti Lucas, Gammarellus carinatus (Rathke), Gammarus locusta L. — were studied and an attempt made to assess the quantitative composition of the food, daily rhythms of feeding, and daily food rations. The composition of the food of the above-named amphipods is similar and consists primarily of seaweeds. Daily feeding intensity is characterized by a distinct increase during the dark period (D. spinosa, A. vaillanti); however, in G. locusta feeding intensity increases in the morning. The daily food rations of amphipods vary greatly (from 1.7 to 360% of the specimens' body weight), depending upon factors such as the kind of food, age, sex, the physiology of specimens, and the water temperature. The total quantity of food eaten by the populations of these amphipods in the coastal zone of the Black Sea amounts to 4000 g organic matter per square metre within 1 year.     

Effect of selenite and seleniferous fly-ash leachate on growth and viability of the marine amphipod Allorchestes compressa

Juveniles of the amphipod Allorchestes compressa Dana were exposed to sodium selenite and to seleniferous leachate from coal fly-ash. A maximum acceptable toxicant concentration (MATC) for selenite of >44<93 g Se l^-1 is indicated by the results for growth and viability. Leachate:sea water mixtures produced effects which were consistent with selenite toxicity but quantitatively less drastic than expected from the pure selenite work, perhaps because of sulphate antagonism. The results are compared with selenium toxicity data for other aquatic species, and high-light the difficulties of using application factors as the basis for water-quality criteria.     

Dietary effects on oocyte yolk-composition inCapitella sp. I (Annelida: Polychaeta): Fatty acids and sterols

In 1988, immatureCapitella sp. I (initial biomass 80µg dry wt) were raised on four diets: Gerber cereal, TetraMin fish food,Ulva sp., and benthic diatoms. After 2 wk of culturing different populations on these diets, eggs were dissected from gravid females, frozen and analyzed for fatty acid and sterol composition. Eggs produced by worms on different food types were discriminated by fatty acid composition in a principal component analysis (PCA), with 18:1⁹, 18:2, 20:5 and 20:4 fatty acids showing the greatest differences between experimental groups. The sterol profiles of all eggs were dominated by cholesterol (cholest-5-en-3-ol) and cholest-5,24-dien-3-ol (>60%). A PCA of egg sterols discriminated between adult diets with cholesterol, 23,24-dimethyl-cholesta-5-en-3-ol, cholest-5,24-dien-3-ol and a C-29 stenol showing the greatest differences. In field populations ofCapitella sp. I, oocytes produced at different times of the year may have different levels of lipids depending on their dietary availability during vitellogenesis. Variations in oocyte composition may influence larval growth and development and thus have an impact on population dynamics. Alternatively, variations in fatty acid and sterol composition of oocytes may allow us to identify the food resources utilized by this species.     

Adaptation and equivalence in open-ocean phytoplankton

Two marine phytoplankton species of the North Atlantic Ocean have inherently differt growth responses to changing nutrient conditions. Yet they co-occur. Thus, they can be compared under the same conditions via equivalence, provided that their adaptedness is linked to their responsiveness as follows. If Species x is adapted to nutrient changes, then it is responsive to these conditions and, certainly, if it is responsive to these conditions, then it is adapted to them. There is another expression that is equivalent to this one (that says the same thing): either Species x is adapted and responsive to these conditions or it is neither adapted nor responsive to them. The option just mentioned is resolved so that Emiliania huxleyi as Species x is adapted and responsive and Cyclococcolithus leptoporus as Species x is not adapted and not responsive. All the frequently observed species in the winter half of the year, November to April, from 1961 to 1972 are like E. huxleyi in being adapted and responsive or like C. leptoporus in being unadapted and unresponsive.Contribution No. 5806 from the Woods Hole Oceanographic Institution     

Ecophysiology of the benthic amphipod Monoporeia affinis in an open-sea area of the northern Baltic Sea: seasonal variations in oxygen consumption and ammonia excretion

Seasonal variations in the oxygen uptake rate ( ) and ammonia excretion rate ( ) of the benthic deposit-feeding amphipod Monoporeia affinis vere studied in an open-sea population of the northern Baltic Sea during three consecutive years (1991 to 1993). In the early summer an increase in the weightspecific by 22% (standard 1-mg individual) was registered; an even more striking change was noted in the , which showed an increase in the early summer of ca. six times the extremely low winter/spring valnes. The metabolic changes observed could not be attributed to temperature, which remained at steadystate throughout the year, nor could seasonal variations in the biochemical composition of the amphipods explain the results. Therefor, it is evident that quality-food abundance following the sedimentation of the spring phytoplankton bloom induces the observed early-summer elevations in and . In turn, the marked decrease in the towards autumn reflects the gradual depletion of quality-food in the benthic environment. Atomic O: N ratios indicated that at the sampling location, M. affinis uses lipid almost exclusively for metabolic energy throughout the year, except in early summer when the use of lipid and protein was observed to be almost equal. Results also indicated a time-lag between sedimentation of the phytoplankton bloom and metabolic response in the amphipod population.     

Social synchronization of circadian rhythms in deer mice (Peromyscus maniculatus)

Summary Deer mice (Peromyscus maniculatus), kept in individual cages under constant dim-light conditions, displayed steady free-running rhythms of activity, the period of which varied between individuals.When two previously isolated mice with different rhythms were placed in a common enclosure, under the same constant light conditions, they soon displayed a mutual synchronization of their activity rhythms. When separated again, the mice lost mutual synchronization (Figs. 1 and 2)The process by which mutual synchronization was attained in the common enclosure is typical of entrainment by an external synchronizer (Zeitgeber). Our results suggest that the activity rhythm of the dominant mouse entrains the activity rhythm of the subordinate, and is thus a social Zeitgeber.     

Feeding,starvation and metabolic rate in the shore crab Carcinus maenas

The relationship between food intake and metabolic rate (as measured by oxygen consumption) of Carcinus maenas (L.) was studied. The metabolic rate of feeding crabs which had been starved for a short period increased, and several days were required for it to return to its original level. During prolonged starvation, the metabolic rate of C. maenas fell in two stages. The first reduction was to about 60% of the feeding level; this occurred during the first week of starvation. There was then a further reduction to about 40% of the feeding level and, at this level of metabolism, the crabs were able to survive for 3 months, with only 50% mortality; most of this occurred in the last 2 weeks. Metabolic rate was found to affect food intake; crabs acclimated to 24°C took 2.4 times as much food as crabs acclimated to 10°C, although the metabolic levels of the two groups differed by a factor of only 1.4. From the results obtained when the crabs were starved and when starved crabs were fed, it is suggested that, during starvation, the metabolic rate of C. maenas first drops from the elevated feeding level to a level at which carbohydrate reserves are utilised, and subsequently to a minimum level at which lipid reserves and proteins are used.     

The organisation of collective foraging in the harvester termite Hodotermes mossambicus (Isoptera)

Summary The process by which the foragers build up a foraging system between the nest hole and the food source, starting from an initial random distribution, was investigated under conditions of both light and dark in the laboratory.The extent to which trail pheromone is used can be determined by observing the abdominal position of workers moving outside the nest and can be classified into three categories, namely no trail-laying, marking and directional trail-laying.When workers of this species emerge from the nest hole into light emitted from a certain direction they orientate photo-menotactically. First, they mark the area around the nest hole, moving in small loops; they then make larger exploratory loops without trail-laying. Once they find a source of food they return directly to the immediate vicinity of the nest hole. As the area around the hole has already been marked it is easy for the termites to locate the hole. When a piece of food has been deposited by the hole the termites display directional trail-laying behaviour by leaving a trail in the direction of the source of food, this trail being stronger nearer the nest and decreasing as it approaches its goal. Inexperienced explorers are biased in this direction with a statistically higher frequency. If successful they join in the foraging and repeatedly contribute to the trail, which then gradually brings together most of the foraging population.In darkness exploratory loops are made with continuous marking, always returning to the nest hole, whereby a scent gradient decreasing away from the hole is formed. Once a source of food has been discovered the termites are neither able to return directly to the nest hole nor to return along their outward marking trail. They leave marking trails making exploratory loops from the food source with successively increasing radii. Another scent gradient, decreasing outwards from the food, is created. If the termite reaches the increasing scent around the nest hole from the decreasing scent around the food source it will locate the hole chemotactically. As other food finders repeatedly cross from one field to the other the scents will combine and become concentrated, thus forming a foraging path.