Influence of environmental factors on selenium flux in two marine invertebrates

The influence of certain environmental factors on the flux of selenium through marine biota has been studied, using Mytilus galloprovincialis and Lysmata seticaudata as test organisms of commercial interest. Over a selenium concentration range in sea water spanning 3 orders of magnitude, bioaccumulation of selenium by mussels was strongly dependent upon the ambient selenium concentration in sea water. Mussels accumulated Se (+4) to a much greater extent than Se (+6) and bioaccumulation was dependent upon temperature and mussel size. The presence of varying amounts of mercury did not significantly alter selenium uptake kinetics in mussels. Shrimp accumulated selenium to a lesser degree than mussels, the difference in concentration factors being due to the large amount of sorbed isotope lost with shrimp molts. Once incorporated, selenium was lost more rapidly from shrimp than from mussels. Temperature influenced selenium loss from mussels but did not alter the elimination rate in shrimp. Neither the chemical form of selenium nor mercury concentration in the organism affected loss of selenium from mussels. Elimination of selenium from shrimp was dependent upon the route of uptake; more rapid loss was noted from individuals which had absorbed the isotope directly from water than from those which had accumulated selenium via the food chain. In general, long-term selenium turnover rates were quite similar for both species; biological half-times ranged from 58 to 60 days for shrimp and 63 to 81 days for mussels. In the case of mussels, turnover rates measured in animals maintained in the laboratory differed somewhat from those determined from individuals held in field enclosures. Observed variations in flux rate may have been due to differences in food availability in the two experimental systems.Based on a communication given at the International Symposium on Interaction Between Water and Living Matter, Odessa, USSR, 6–10 October, 1975.     

The influence of ration level on growth and statolith increment width of the tropical squid Sepioteuthis lessoniana (Cephalopoda: Loliginidae): an experimental approach

Juvenile squids were grown in individual 2.6-l floating enclosures and were fed either a high- or a low-ration diet of fish and the crustacean Acetes. Squids were maintained for a maximum of 44 days in two experiments. The high-ration individuals reached a significantly larger size in both experiments (27, 25.5 mm mean mantle length, ML) compared to their low-ration siblings (19 mm mean ML) in both experiments. The statolith increment widths prior to the start of the experiment were significantly wider (between 3 and 4 μm) compared to the increment widths after the start of the experiment (between 2 and 3 μm) both for the low- and the high-ration squids. High-ration squids also had significantly wider increments and larger statoliths than their low-ration siblings. Even though we detected consistent trends in daily statolith increment widths for the different feeding regimes, we could not detect variation in increment widths at a daily level of resolution (i.e. as a result of differences in day-to-day food intake at an individual level). This was probably due to the relatively consistent diet experienced by each individual. These experiments revealed that ration level influences squid growth rate, statolith size and daily statolith increment width. Received: 30 March 2000 / Accepted: 30 October 2000     

Turnover and vertical transport of zinc by the euphausiid Meganyctiphanes norvegica in the Ligurian Sea

Participatory turnover time is defined as the time required to cycle an element in a system through a given material in that system. The participatory turnover time of ionic zinc by the adult Meganyctiphanes norvegica population in the Ligurian Sea ranged between 498 and 1243 years, depending upon the available food supply, and considering the food chain as the only route for zinc accumulation by the population. A total-impact turnover time was calculated as the sum of the participatory turnover time for live individuals plus the time required for dead euphausiids to lose 90% of their zinc to the water. Carcasses lost zinc to the water slower than either feces or molts, and so established the maximum loss time for all particulate excretion products; nevertheless, total-impact turnover time for zinc did not differ significantly from the participatory turnover time. The net vertical transport of zinc by M. norvegica from the sea surface to any specified depth can be calculated as the sum of the dissolved zinc excreted below the depth plus the concentrations of zinc left in feces, molts, and carcasses after they have sunk to the specified depth. Carcasses sink the fastest and lose the smallest fraction of their zinc concentration during descent; fecal pellets sink the slowest and lose the greatest fraction of their zinc concentration, and molts are intermediate. Nevertheless, feces represents the major route for delivering zinc to the bottom of the Ligurian Sea (2500 m), because concentration of the element in the pellets is so much higher than in carcasses or molts. Excretion of dissolved zinc into the water at the vertical migration depth of the living population during daylight hours was also inconsequential. Feces zinc represented over 80% of the total zinc transported to the sea floor if only marginal food supplies were available to the euphausiids, and over 90% if food was in sufficient supply. M. norvegica can effect a net transport of about 98% of its body zinc concentration below 500 m daily, in conditions of sufficient food supply and assuming that no released products are eaten during descent. If the food supply in the Ligurian Sea is considered only marginal throughout the year, M. norvegica can still effect a daily net transport below 500 m of about 36% of its body concentration, and about 6% of its body concentration will reach 2500 m daily.     

Effects of symbiont elimination and reinfection on the life processes of the planktonic foraminifer Globigerinoides sacculifer

Laboratory experiments were carried out to determine the influence of symbiotic dinoflagellates (zooxanthellae) on the shell growth, longevity, and reproductive potential of Globigerinoides sacculifer (Brady). Its symbionts were eliminated by 72-h treatment with a photosynthetic inhibitor (DCMU). Symbiont elimination resulted in earlier gametogenesis (shortened survival time) and smaller shell sizes of G. sacculifer when compared to untreated foraminifera grown in sea water. Individuals kept in continuous darkness in untreated sea water also exhibited early gametogenesis, short survival times and small shell sizes. Aposymbiotic foraminifera formed on the average one or two chambers fewer per individual and their rate of shell size increase is slower than symbiont-bearing foraminifera. Symbionts were lysed within perialgal vacuoles of G. sacculifer when subjected to DCMU treatment or kept in continuous darkness. One DCMU-treated group was reinfected with symbionts from crushed G. sacculifer donors. Soon after reinfection, these foraminifera resumed a shell growth rate and exhibited developmental stages that were nearly equivalent to those of untreated individuals, as deduced from their shell size, frequency of sac-like chambers, rate of gametogenesis, and survival time. Our experiments indicate that the symbionts aid in calcification and that elimination of symbionts triggers gametogenesis, thus shortening the life span of the foraminiferal host. The results imply that shell growth in symbiont-bearing planktonic foraminifera occurs mainly in the euphotic zone and that they do not survive for long periods below it.     

Phytoplankton-zooplankton relationships in the Western Pacific Ocean and adjacent seas

Regressions of biomass and daily food requirements of herbivorous zooplankton on daily primary production were calculated, using assumptions based on data collected in various sea areas of the western Pacific Ocean and adjacent seas. A regression coefficient (1.470) of calculated herbivorous biomass on observed daily primary production is significantly higher than unity (P<0.01). This indicates that the herbivorous biomass sustained by unit amount of primary production is large in the more productive high latitudes, and small in the less productive tropical sea areas. This is attributed to relatively larger food requirements per unit biomass of the tropical herbivores as compared with those found in cold waters. Despite distinct areal differences in the herbivorous biomass-primary production ratios, the calculated daily food requirement of herbivores was in direct proportion to the daily primary production, when equilibrium had been established between phytoplankton and zooplankton. Under conditions of limited food supplies, the small body size of the tropical herbivores may be advantageous both in reducing the total energy consumption per individual, and in inducing rapid growth and reproduction. Therefore, the low ratio of biomass to primary production in the tropics could beregarded as a result of possible regulation of tropical herbivores to scarce food conditions rather than as evidence of failure of adaptation to such conditions.     

Sexual and asexual reproduction of Anthopleura dixoniana (Anthozoa: Actiniaria): periodicity and regulation

Reproduction of the sea anemone Anthopleura dixoniana (Haddon and Shackleton) from the high intertidal zone of southern Taiwan (120°41 E; 22°01N) was studied from April 1987 through March 1989. A. dixoniana spawns once a year, in July, and divides asexually by longitudinal fission throughout the year, with a peak in July. During the spawning season, sea anemones>3 mm pedal dise diameter can be sexed, and display a 1:1 sex ratio. Dividing sea anemones are significantly larger than non-dividing individuals, and increase in body size before fission. Under laboratory conditions, individuals kept at 28 C and fed had larger oocytes and a higher division rate than those kept at 18, 22, 25 or 32°C or starved. The division rate significantly influenced the oocyte diameter. The present study revealed for the first time, that a long photoperiod (14 h hight:10 h dark) significantly enhances the growth of oocytes in A. dixoniana under laboratory conditions.     

Effects of temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis

To assess the effects of both temperature and food ration on gonad growth and oogenesis of the green sea urchin, Strongylocentrotus droebachiensis (O.F. Müller), individuals collected December 1996 (winter experiment) and June 1997 (summer experiment) were maintained for 3 months in one of four experimental treatments: (1) 3 °C and fed ad libitum (high ration), (2) 3 °C and fed one-seventh of the maximum ration (low ration), and (3) 12 °C and fed the high ration; (4) 12 °C and fed the low ration. All individuals were fed an artificial diet and exposed to only 1 h of light every day. At the end of both experiments, mean gonad indices of sea urchins fed the high ration had increased significantly (11–24% and 6–19% in the winter and summer experiments, respectively), while the gonad indices of individuals fed the low ration did not change. At the high ration (both experiments), the increase in gonad index of sea urchins occurred primarily as the result of a significant increase in the mass of nutritive phagocytes, as revealed by histological analyses. Primary oocytes were significantly larger in individuals held at 3 °C than at 12 °C throughout the winter experiment, regardless of food ration; during the summer experiment, primary oocytes were significantly larger in individuals receiving the high ration, regardless of the temperature at which they were held. These results suggest that: (1) food availability is the most important factor regulating energy storage and the relative size of gonads throughout the year, (2) temperature affects the rate of growth and maturation of primary oocytes during the later stages of oogenesis, and (3) once gametogenesis has been initiated, mature ova will be produced, even under conditions of low food availability. Conditions of high food availability in summer and low temperature in winter would thus favor reproductive output in sea urchin populations. Received: 1 March 2000 / Accepted: 4 October 2000     

Rates of fission, somatic growth and gonadal development of a fissiparous sea star, Allostichaster insignis, in New Zealand

Seasonal changes in population structure and incidence of fission were measured in intertidal and subtidal populations of Allostichaster insignis, a fissiparous sea star. Population size structure was stable over the course of the 1-year study. Sea stars in the subtidal zone attained greater maximum size (mean arm length, R = 35 mm) than those in the intertidal population (20 mm). Fission rates were greatest among small individuals (R < 20 mm). The frequency of fission ranged from 5 to 32% with peaks in early austral summer in the intertidal zone, and in autumn and winter in the subtidal zone. Sexual reproduction occurred in early spring in sea stars larger than 12 mm. The populations were heavily biased toward males. In the laboratory, A. insignis of three size classes (small, R = 9–13 mm; medium, 19–21 mm; and large, 29–31 mm) were fed mussels ad libitum or starved (not fed macroscopic food) for ∼1 year in a 3 × 2 factorial experiment. Small and medium-sized sea stars divided throughout the experiment and the ramets of most individuals regenerated sufficiently to divide again after 6–9 months. Unfed sea stars did not undergo fission (with one exception), had a higher mortality rate, and did not grow. Small, fed sea stars grew significantly faster than medium-sized or large individuals. At the end of the experiment, the pyloric caeca index (a measure of nutritional condition) was greater in fed than in unfed animals. Gonads (only testes were observed) developed in medium-sized and large, fed sea stars. Our field and laboratory results indicate that asexual reproduction in A. insignis predominantly occurs in small, well-nourished individuals. Ramets grow gradually through repeated fission and regeneration to a size (mean length of regenerating arms, R _r ∼ 20 mm) at which they begin to switch to sexual reproduction as the dominant reproductive mode.     

Wood-based diet and gut microflora of a galatheid crab associated with Pacific deep-sea wood falls

Wood falls in the deep sea have recently become the focus of studies showing their importance as nutrients on the deep-sea floor. In such environments, Crustaceans constitute numerically the second-largest group after Mollusks. Many questions have arisen regarding their trophic role therein. A careful examination of the feeding appendages, gut contents, and gut lining of Munidopsis andamanica caught with wood falls revealed this species as a truly original detritivorous species using wood and the biofilm covering it as two main food sources. Comparing individuals from other geographic areas from substrates not reported highlights the galatheid crab as specialist of refractory substrates, especially vegetal remains. M. andamanica also exhibits a resident gut microflora consisting of bacteria and fungi possibly involved in the digestion of wood fragments. The results suggest that Crustaceans could be full-fledged actors in the food chains of sunken-wood ecosystems and that feeding habits of some squat lobsters could be different than scavenging.     

Influence of maternal food availability on offspring dispersal

Prenatal effects caused by the maternal environment during gestation are known to contribute to the phenotype of the offspring. Whether they have some adaptive value is currently under debate. We experimentally tested the existence of such a maternal effect (food availability during gestation) on dispersal of offspring in the common lizard (Lacerta vivipara). Pregnant females were captured and kept in the laboratory until parturition. During this period, females were offered two rates of food delivery. After parturition, we released mothers and offspring at the mother's capture point. Dispersal of young was significantly affected by the mother's nutrition. To our knowledge, this is the first evidence of a prenatal effect on dispersal. Offspring of well fed mothers dispersed at a higher rate than those of less well fed mothers. As current hypotheses clearly predict the opposite result, our evidence calls for their reassessment. Dispersers are not always the least fit individuals or those coming from the poorest environments.     

Development and metamorphosis of the planktotrophic larvae of Rostanga pulchra (Mollusca: Nudibranchia)

Rostanga pulchra MacFarland, a small (1 to 2 cm) dorid nudibranch, lays an average of 7000 eggs in the laboratory during a period of 30 days in the summer. The veligers hatch 15 to 16 days after oviposition and it takes another 35 to 40 days to become competent for metamorphosis at a temperature of 10° to 15°C. Larval cultures were maintained initially at a concentration of 500 veligers per 100 ml of filtered sea water (antibiotics added). During the planktotrophic phase of development, the veliger grows from 150 to 300 m in shell length. Although the veligers are generalists in their food preference, the best result (faster growth) was achieved by feeding them with a combination of Monochrysis lutheri and Isochrysis galbana. The concentration of food cells was kept at 10⁴ cells per ml of culture media and was supplied every 2 to 3 days. A veliger which is competent to metamorphose is identifiable morphologically by its propodium, eyespots, rhinophores, and spiculated dorsal papillae. The entire metamorphic process lasts 24 h when a suitable substrate such as the food sponge Ophlitaspongia pennata is provided. The competent veliger is able to delay metamorphosis for at least 3 weeks. Juveniles were kept in the laboratory for 70 days and, during this period, grew to a length of 4.5 mm.     

Comparative study of vanadium biokinetics in three species of echinoderms

Vanadium-48 (as vanadate) was used to study the uptake, tissue distribution, depuration and food-chain transfer of vanadium through 3 species of echinoderms: the seastar Marthasterias glacialis L., the sea urchin Paracentrotus lividus Lmk. and the holothurian Holothuria forskali D.Ch.; all were collected from the littoral zone near Monaco. Uptake by all species was relativelyslow; after 3 wk exposure, isotopic equilibrium had not been reached and whole-body concentration factors ranged from 5 and 7 in the holothurian and sea urchin, respectively, to 18 in the seastar. Sixty-three to 77% of the incorporated radiotracer was associated with the body wall or test, suggesting surface sorption as the principal mechanism governing uptake from water. Stable vanadium measurements confirmed the preponderance of this element in the external hard parts of the echinoderms; however, concentration factors based on stable vanadium levels were significantly higher than those measured experimentally. Subsequent vanadium depuration rates were also species-dependent, with biological half-times for loss ranging from approximately 50 d in the sea urchin and holothurian to 123 d in the seastar. Food-chain transfer experiments indicated that seastars can assimilate and retain a large fraction of the vanadium ingested with food whereas sea urchins appear to lack this capability. The relative importance of the water and food input pathway in achieving vanadium levels in echinoderms is discussed in light of results of ⁴⁸V distribution in experimental individuals and stable vanadium distribution in samples from the natural environment.     

Body temperature independence of solar radiation in free-ranging loggerhead turtles,Caretta caretta,during internesting periods

Body temperatures, ambient water temperatures, light intensities and vertical positions (depth) of eight loggerhead turtles, Caretta caretta, were monitored by small recorders during internesting periods from 1991 through 1993 off Wakayama Prefecture, Japan. Body temperatures of eight loggerhead turtles were higher than ambient water temperatures through-out their internesting periods. Light intensities were compared with body temperatures and no evidence was obtained to suggest that the raised body temperatures were caused by the direct influence of solar radiation. Body temperatures were kept higher than water temperatures in cloudy weather or even at night. Mean thermal differences between body and water temperatures were significantly different among individuals, and larger turtles had a greater mean thermal difference. Elevations in body temperatures of adult loggerhead turtles can reasonably be assumed to result from the accumulation of metabolically produced heat. Surfacing times (spent at depths shallower than 2 m) of seven turtles were only 10.3 to 38.9% of their internesting periods, with the exception of one turtle who spent 66.3% of her time at the surface. Loggerhead turtles did not seem to bask positively at the sea surface to absorb radiative heat.     

Effects of temporary starvation on the survival,and on subsequent feeding and growth,of oyster (Crassostrea gigas) larvae

Larvae of oysters, Crassostrea gigas, were maintained without food for 1 to 8 d after fertilization, and fed daily thereafter. There was little difference in survival and growth between controls and larvae kept without food for 2 or 3 d. Survival and growth rates were depressed in larvae starved for 4 or 5 d. For larvae starved for 6 to 8 d, survival was negligible or nil; even those larvae which survived the starvation period died later in the presence of food, apparently because of impaired digestion. Therefore, food availability in the first few days after spawning appears to be of paramount importance to the successful recruitment of Pacific oysters.     

Movement patterns of the seastar Heliaster helianthus in central Chile: relationship with environmental conditions and prey availability

The rates and patterns of feeding and displacement of predators constitute two of the most important plastic behavioral responses that allow individuals to respond quickly to changes in abundance of their prey, predation risks and to rapid alterations in environmental conditions. In this study, we quantified seasonal and spatial variation in displacement (net changes in location in 12 or 24 h periods) and prey consumed of marked individuals of the keystone seastar Heliaster helianthus at six sites spanning 600 km along the coast of north-central Chile. We evaluated the hypotheses that: (1) at sites with low availability (cover) of the main prey, the mussel Perumytilus purpuratus, Heliaster displays larger displacements and consumes a greater proportion of other prey (e.g. mobile species) than at sites with high mussel cover, (2) daily displacements will be correlated with sea surface temperature (SST) and (3) increased wave action will reduce seastar daily displacement. Our results show that Heliaster displacement is higher at sites with lower availability of P. purpuratus; and at these sites, a larger proportion of Heliaster individuals are observed feeding, mostly on other prey (e.g. limpets), which could offset the higher costs associated with increased movement. In addition, wave forces affected the activity of Heliaster negatively. Contrary to our expectations, the daily displacements did not show any relationship with SST measured on the day or the previous days of the surveys, despite the fact that average displacement was generally higher in summer than in winter months. Future studies should examine Heliaster movement during single foraging excursions and determine whether these responses affect the growth and reproductive output of individuals. Such information is vital to understand how changes in prey abundance and environmental conditions alter the behavior and energy budget of this predator and its ability to control prey populations.     

Diet,behaviour and reproduction of the whelk Buccinum undatum in the northern Gulf of St. Lawrence,eastern Canada

A laboratory experiment was used to examine whether a decrease in the width of sutures is the basis for shrinking of the test in echinoids under conditions of low food availability and whether the body condition of sea urchins is likely to be retained when shrinking occurs. This experiment was performed with H. erythrogramma specimens collected in January 1987 from Pt. Lillias in Corio Bay, Australia. Suture widths in the test and gonad volume were significantly less (relative to body volume) in Heliocidaris erythrogramma (Val.) in the low food treatment than the high food treatment after 4 mo. These results imply that sea urchins which shrink may have a poorer body condition and be less able to reproduce than sea urchins that do not shrink. A comparison of the expected to the observed changes in suture width showed that a decrease in suture width is involved in the shrinking of the test in H. erythrogramma and may be of sufficient magnitude to fully explain the observed reduction in test size. This suggests that the amount a sea urchin may shrink under low food conditions is constrained by the degree to which the sutures can be reduced in width.     

Mortality is associated with social rank in the clown anemonefish (<Emphasis Type="Italic">Amphiprion percula</Emphasis>)

Elucidating the causes of post-recruitment mortality is a vital step toward understanding the population dynamics of coral reef fishes. Predation is often considered to be the primary proximate cause of mortality. It has, however, proven difficult to discern the relative contributions of predation and other processes, such as competition for food, shelter, or mates, to patterns of mortality. To determine which other processes might be important drivers of mortality patterns, factors related to mortality in the clown anemonefish Amphiprion percula (Lacepède, 1802) were examined. Patterns of mortality will not be driven by predation in A. percula, because these fish are well protected from predators by their close association with sea anemones. Mortality rates were based on the disappearance of known individuals from a population of 201, in 57 groups, during a 1-year field study (in 1997), in Madang Lagoon, Papua New Guinea. Mortality rate of A. percula was low (14% per annum) compared to other coral reef fish, probably due to the protection from predators afforded by the anemone. Six factors (reef, depth, anemone diameter, number of individuals, density, and standard length) showed no association with the probability of mortality (P>0.05). Rank was the only factor associated with the probability of mortality (P<0.03); low-rank individuals (ranks 4–6) suffered a higher mortality rate than high-rank individuals (ranks 1–3) (P<0.01). The most likely explanation for this pattern was that competition for rank, amongst individuals within an anemone, resulted in some individuals evicting their subordinates. Individuals probably competed for rank because it conferred access to reproduction, and not because it conferred access to food or shelter. Such competition for reproduction will be intense whenever some individuals obtain a greater share of reproduction than others do, and it may be an important process influencing the dynamics of coral reef fish populations.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Communicated by J.P. Grassle, New Brunswick     

Physiological energetics of the intertidal sea anemone Anthopleura elegantissima

High-intertidal (H) individuals of the sea anemone Anthopleura elegantissima (Brandt) are exposed aerially up to 18 h each day, unlike low-intertidal (L) individuals which may be continuously immersed over many days. Thus, H anemones experience shorter feeding periods compared to L anemones. From 1980 to 1982, H and L anemones were observed and collected at the mouth of Bodega Harbor in North Central California (USA) to determine whether any physiological adaptations mitigate the energetic effects of reduced feeding time in H anemones. Weight of prey in coelenterons of H anemones was three times more than that of L anemones following a single immersion period. This difference is not due to slower digestion rates in H anemones. Prey residence time in coelenterons (4h) was equivalent in both groups. Different prey weights imply that ingestion rates were greater in H individuals. However, all anemones had similar weight-specific feeding-surface areas. Different prey-capture rates result from increased receptivity to prey in H anemones, rather than from increases in feeding surface. Absorption efficiency was inversely related to ration size in anemones from both shore positions. H individuals absorbed food more efficiently than L individuals fed equivalent rations. Ration, not exposure conditions, affected absorption efficiency. Daily growth rates were 1.5 to 1.8% and 1.2 to 1.4% of dry body weight in H and L anemones fed large rations (4.0 to 5.6% of dry body weight), respectively. H anemones fed smaller daily rations, approximating amounts of zooplankton captured naturally (1% of anemone dry weight), had higher growth rates and growth efficiencies than L anemones, which lost mass. Higher growth rates in H anemones, which are supported by higher prey-capture rates, result in attainment of minimum body size for reproduction in a relatively short period of time despite reduction in time available for feeding, thus improving relative fitness of these anemones in the upper intertidal zone.     

A comparative study of metabolic energy expenditure in the limpets Patella cochlear,P. oculus and P. granularis

Oxygen consumption of 3 species of Patella was measured in air and water at various temperatures. Measurements at constant temperature over a full tidal cycle showed no tidal or light-dark rhythms. Measurements under conditions simulating natural tidal, temperature and day-night cycles allowed calculation of daily respiratory energy budgets. P. cochlear occurs low on the shore, but experiences a food shortage due to intense intraspecific competition. Its rate of respiration is moderate, but metabolic expenditure is kept low because exposure to air is brief and body temperatures seldom rise above 23°C. P. cochlear has a respiratory rate-temperature (R-T) curve which peaks at 20°C and forms a plateau between 20° and 32.5°C. The midshore P. oculus has abundant food and adopts an exploitative strategy. Growth rate is very high, and this high turnover of energy is linked with a high metabolic rate, high Q10 (temperature coefficient) values, high body temperatures during the day-time low tide, and a respiratory R-T curve peaking at 32.5°C. Small P. oculus occur mainly in intertidal pools and respire faster in water, while larger individuals occur on bare rocks and respire faster in air over the upper temperature range. In contrast, the upper-shore P. granularis has little food, and conservation of energy is essential, particularly as its growth rate is moderate and its reprocurve output high. Respiratory losses are reduced by suppression of the R-T curve and low Q10 values, resulting in relative independence of temperature. Small P. granularis occur low on the shore and respire slower in water. Larger individuals occur at high levels due to migration, and respire slower in air. This further reduces respiratory energy losses. The patterns of respiration in these 3 species are thus related to food availability, resulting in exploitative or conservationist strategies.     

Intake and coversion of food in the fish Limanda limanda exposed to different temperatures

In the flat fish Limanda limanda L., feeding rate and conversion efficiency were studied as functions of body weight, sex, temperature and food quality. When offered herring meat at 13 °C (series I), females (live weights 1 to 150 g) consume more food than males; the magnitude of this difference is body weight-dependent. With increasing wieght, both females and males consume less food per unit body weight per day. Variations in daily ration are considerable; the range of deviation from mean feeding rate is about 60% for males and 40% for females. The range of deviation does not vary significantly among females and males of different body weights. At the same temperature level (13 °C; series II), females consume almost the same, or even less, cod meat than males. Among individuals of series I and II, there is a little difference in the feeding rate; however, herring-fed individuals obtain about 2 times more energy than cod-fed individuals. Each gram wet weight of herring meat yields 2001, each gram cod meat 1137, calories. Small individuals completely cease to feed at 3°C; they feed little at 8 °C. Larger females consume maximum amounts at 8 °C. Small individuals consume maximum amounts at higher temperatures. Thus, with increasing body weight (age), the temperature for maximum feeding shifts downwards. Feeding with cod or herring meat results in considerable changes in composition and calorific content of L. Limanda. The magnitude of these changes depends both on temperature and food quality. Food conversion efficiency values of herring-fed individuals are about 1 1/2 times higher than of cod-fed individuals. In series I and II, females are more efficient converters than males. In individuals weighing more than 50 g, conversion efficiency decreases in the order: 8°, 13°, 18° C; in smaller individuals this order is 13°, 18°, 8 °C. Conversion rate is about 2 to 5 times faster in individuals fed herring meat than those receiving cod meat. Conversion rate decreases in the order 13°, 8°, 18 °C in males, and in the order 18°, 13°, 8 °C in females; females of more than 80 g are exceptional in that they reach the maximum at 8 °C. From the data on food intake and food conversion, the biologically useful energy available for metabolism has been calculated for each test individual kept at 13° and 18 °C. At these temperature levels, the weight exponents are about 0.6; the a value or metabolic level for the 18 °C series is about 2 times higher than that at 13 °C. Thus, temperature affects metabolic rate but not the exponential value. The exponential value for the body weight-metabolism relation at 13 °C is for dab fed herring meat 0.9; the a value amounts to about half that for dab fed cod meat. Food quality, unlike temperature, alters not only the exponential value but also metabolic rate.