Temperature and development in larvae of the turbot Scophthalmus maximus

Turbot (Scophthalmus maximus L.) were reared at 12 and 16°C until 26 d after hatching. At both temperatures, starting at the neural plate stage, somites were initially formed every 75 min. Expressed as a percentage of development time (DT, fertilisation to 90% larvae hatching) somite formation occurred relatively earlier during embryogenesis at 12°C (45% DT) than at 16°C (55% DT). At 12°C, after the 32-somite stage the rate of somite formation decreased to one every 300 min. The larvae hatched after 6 d at 12°C and 3 d at 16°C at a relatively primitive stage of development, prior to the opening of the mouth and anus, with unpigmented eyes, and a straight gut. Temperature altered the relative timing of organogenesis in the larval stages. At 12°C, the following characters appeared (in this order): swimbladder>loop in the gut (at the time of yolk exhaustion)>caudal fin. In contrast, at 16°C, the caudal fin appeared at the same time as the loop in the gut. At 16°C, spines formed on the head in the region of the otic capsule at the time the swimbladder formed and the yolk was exhausted, but were absent in 12°C larvae. At both temperatures, in 1 d-old larvae the myotomes just behind the yolk-sac contained 200 inner muscle fibres (presumptive white muscle). The initial growth of inner muscle was largely due to hypertrophy, but by 26 d at 12°C and 11 d at 16°C hyperplastic growth became important, as evidenced by a significant increase in the number of small fibres (<10 m²). By 26 d the average number of inner muscle fibres had increased to 341 at 12°C and 988 at 16°C. New muscle fibres were added in distinct germinal zones at the dorsal and ventral apices of the myotomes. Metamorphosis was associated with a thickening of the superficial (presumptive red) muscle layer and the appearance of tonic muscle fibres.     

Characterization of urease activity in three marine phytoplankton species,<Emphasis Type="Italic"> Aureococcus anophagefferens</Emphasis>,<Emphasis Type="Italic"> Prorocentrum minimum</Emphasis>, and<Emphasis Type="Italic"> Thalassiosira weissflogii</Emphasis>

The availability of different forms of nitrogen in coastal and estuarine waters may be important in determining the abundance and productivity of different phytoplankton species. Although urea has been shown to contribute as much as 50% of the nitrogen for phytoplankton nutrition, relatively little is known of the activity and expression of urease in phytoplankton. Using an in vitro enzyme assay, urease activities were examined in laboratory cultures of three species: Aureococcus anophagefferens Hargraves et Sieburth, Prorocentrum minimum (Pavillard) Schiller, and Thalassiosira weissflogii (Grunow) Fryxell et Hasle. Cultures of P. minimum and T. weissflogii were grown on three nitrogen sources (NO₃^m, NH₄⁺, and urea), while A. anophagefferens was grown only on NO₃^m and urea. Urease was found to be constitutive in all cultures, but activity varied with growth rate and assay temperature for the different cultures. For A. anophagefferens, urease activity varied positively with growth rate regardless of the N source, while for P. minimum, urease activity varied positively with growth rate only for cultures grown on urea and NH₄⁺. In contrast, for T. weissflogii, activity did not vary with growth rate for any of the N sources. For all species, urease activity increased with assay temperature, but with different apparent temperature optima. For A. anophagefferens, in vitro activity increased from near 0-30°C, and remained stable to 50°C, while for P. minimum, increased in vitro activity was noted from near 0-20°C, but constant activity was observed between 20°C and 50°C. For T. weissfloggii, while activity also increased from 0°C to 20°C, subsequent decreases were noted when temperature was elevated above 20°C. Urease activity had a half-saturation constant of 120-165 wg atom N l^у in all three species. On both an hourly and daily basis, urease activity in A. anophagefferens exceeded nitrogen demand for growth. In P. minimum, urease activity on an hourly basis matched the nitrogen demand, but was less than the demand on a daily basis. For T. weissflogii, urease activity was always less than the nitrogen demand. These patterns in urease activity in three different species demonstrate that while apparently constitutive, the regulation of activity was substantially different in the diatom. These differences in the physiological regulation of urease activity, as well as other enzymes, may play a role in their ecological success in different environments.     

Temperature effects on the metabolism of larvae of the Antarctic starfish Odontaster validus, using a novel micro-respirometry method

Oxygen consumption of individual larvae of the Antarctic sea-star Odontaster validus was measured during the 50-day period following fertilisation. Values ranged from 0.76 pmol O₂ h^-1 for one specimen at the coeloblastula stage to 77.6 pmol O₂ h^-1 for one bipinnaria larva. At 0°C the mean oxygen consumption rate of an individual larva increased from 10.9 pmol O₂ h^-1 (standard error of the mean, SEM, 0.13) for a gastrula larva, 13 days post-fertilisation, to 25.4 pmol O₂ h^-1 (SEM 3.5) at the bipinnaria stage (50 days post-fertilisation). Gastrulae reared at -0.5°C did not have significantly different oxygen consumption rates between days 13 and 45 post-fertilisation (mean=11.4 pmol O₂ h^-1). Individual metabolic rates were highly variable, covering more than a 40-fold range. At 2°C gastrula oxygen consumption was on average 45% higher (17.35 pmol O₂ h^-1), giving a Q₁₀ temperature effect of 4.4. For bipinnaria, mean oxygen consumption in 2°C larvae (31.4 pmol O₂ h^-1) was not significantly different from that in larvae at -0.5°C, suggesting bipinnaria metabolism may be less sensitive to temperature change than earlier stages. At 2°C the bipinnaria stage was reached at 30-35 days compared with 45-50 days at 0°C, giving a Q₁₀ of 4.5 for temperature effects on development. The method here used a new, highly sensitive micro-respirometry method that is inexpensive and straightforward in design. Individual larvae of O. validus were held in 35- to 50-µl respirometers. These larvae have very low metabolic rates, and published work on such organisms have utilised at least 25 individuals per chamber. The oxygen content of the respirometers was measured using a 25-µl sample injected into a couloximeter. Oxygen consumption rates down to -1 pmol h^-1 can be detected. Under optimum conditions oxygen consumption of a single larva of -4 pmol O₂ h^-1 was measured with an accuracy of ᆨ%. Values of ~15 pmol h^-1 could routinely be measured with this accuracy. This method would allow oxygen consumption to be evaluated in individual field-caught larvae of most marine ectotherms.     

Temperature-induced ontogenetic plasticity in sea bass (Dicentrarchus labrax)

We studied the ontogeny of Dicentrarchus labrax comparatively under constant rearing temperatures of 13, 15 and 20°C. At hatching, yolk-sac larval morphometry differed significantly between the temperatures and especially between the two extremes, while at the end of the yolk-sac larval stage, it mainly differed between the two lower temperature regimes and that of 20°C. Compared with the two lower temperature conditions, at 20°C D. labrax presented a significant ontogenetic acceleration which was morphologically expressed either as a significantly smaller total length (TL) at feeding onset, notochord flexion and fin differentiation, or as shifts of the allometric inflection points of 8 out of the 15 morphometric characters studied. Additionally, temperature significantly affected the allometry coefficients, with a decreasing growth intensity as the temperature difference decreased. The rate of TL growth increased under elevated temperature conditions throughout the entire ontogenetic period, except during the early larval period (feeding onset to metamorphosis onset), at which time D. labrax presented equal growth rates at 15°C and 20°C. The results are discussed with respect to the ontogeny of the functional morphology and the meanings of temperature-induced ontogenetic plasticity for the survival of fish larvae.     

Burrowing behaviour and sediment reworking in the heart urchin Brissopsis lyrifera Forbes (Spatangoida)

Sediment reworking due to burrowing and feeding was studied in the spatangoid Brissopsis lyrifera, at two different temperatures (7°C and 13°C). Spine activity and burrowing behaviour were recorded with a real-time video camera. Reworked sediment volume was calculated from tracks produced by the heart urchin. Ingestion rates were measured by feeding the heart urchins with luminophores. Temperature had a significant effect on the bioturbation activity of B. lyrifera. At 13°C reworked sediment volume due to burrowing was 22 ml sediment h^-1 and at 7°C 14 ml sediment h^-1. The ingested amount of sediment was 0.08 and 0.02 g dry sediment h^-1 in 13 and 7°C, respectively. Reworked sediment volume due to burrowing was 60-150 times higher than the volume ingested. The large reworked volume is a consequence of B. lyrifera moving with a rocking motion through the sediment. The spines were continuously transporting sediment around the test with 5-min metachronal wave cycles.     

Environmental controls on shell growth rates and δ<Superscript>18</Superscript>O of the shallow-marine bivalve mollusk <Emphasis Type="Italic">Phacosoma</Emphasis><Emphasis Type="Italic">japonicum</Emphasis> in Japan

Microgrowth patterns and the oxygen isotope composition of juvenile, shallow-marine bivalve mollusk shells of Phacosoma japonicum (Reeve) in Japan were analyzed and cross-calibrated with environmental parameters. Mark-and-recovery experiments indicate that a pair of two microgrowth lines and two microgrowth increments is produced every lunar day. This finding makes it possible to assign exact calendar dates to each portion of the shell. Average daily growth rates decrease by 61% from age two to three and 55% from age three to four. The length of the growing season and the growth rate are mainly controlled by temperature: shell growth ceases below 14.2°C (age two) and 16.8°C (age four) and is most rapid between 24.6°C and 27.2°C. Based on local temperature cycles, the growing season is longest in Seto Inland Sea, central Honshu (from May to November) and shortest at Hakodate Bay, North Japan (from June to October). The annual oxygen isotope profiles of the shells reflect the temperature cycle and the varying amounts of freshwater added to the seawater by precipitation. The most negative '¹⁸O values of -3.15‰ occur during the rainy season, i.e. during the monsoon and typhoon seasons. Growth rates are only slightly affected by salinity changes. Strongly reduced growth rates during the second half of the year at Seto Inland Sea and to a lesser extent at Tokyo Bay are explained by nutrient deprivation. Our study provides the basis for the use of P. japonicum in high-resolution ecological studies and environmental reconstructions.     

Combined effects of dissolved oxygen concentration and water temperature on embryonic development and larval shell secretion in the marine snail <Emphasis Type="Italic">Chorus</Emphasis><Emphasis Type="Italic">giganteus</Emphasis> (Gastropoda: Muricidae)

The present study was undertaken to determine the effects of both extracapsular oxygen concentration and temperature on embryonic development in Chorus giganteus. In normoxia increasing water temperature from 12°C to 18°C reduced by 15 days the median time required for the capsules to hatch. Hypoxia (oxygen content at 50% of air saturation) generated a low development rate and totally prevented both shell secretion and larval hatching from the egg capsule. Experimental transfer at weekly intervals, from normoxia to hypoxia and vice versa, induced a decrease and increase in the embryonic ash content, respectively, but did not affect the number of hatched larvae. Such an effect was more pronounced at 12°C than at 15°C or 18°C. The embryonic inability to produce a shell under hypoxia is likely to be a result of the low intracapsular oxygen concentration (IPO₂) generated as the combined effect of a low extracapsular oxygen concentration (environmental) added to the intracapsular embryonic oxygen demands, which lowers the IPO₂ still further. Under such conditions, a decrease in intracapsular pH is likely to take place, and, if so, embryos might divert carbonates away from shell calcification to balance such changes in pH.     

New insights into temperature-induced white muscle growth plasticity during Dicentrarchus labrax early life: a developmental and allometric study

Dicentrarchus labrax is a major finfish of interest in Mediterranean aquaculture. As the development of its hatchery production had gone with an increase of its larval rearing temperature, we studied the effect of a constant high (20°C) and two lower (13 and 15°C) temperatures on its early white muscle growth, with developmental and allometric approaches. D. labrax, sampled at hatching and at three developmental stages corresponding to main events in fish early life (first exogenous feeding, notochord flexion and completion of fin ray counts), were histologically processed in order to follow changes in the white myotomal muscle size, cellularity and localisation of proliferative nuclei. Morphometric analyses showed that, for 13, 15 and 20°C incubated/reared D. labrax, the total cross-sectional area of white muscle increased slowly in eleutheroembryos shorter than 5.2 mm, and four times faster in longer fish (free-swimming larvae). White muscle growth occurred both by hypertrophy (increase in muscle fibre size) and hyperplasia (increase in total number of muscle fibres) in all sampled fish, but both processes were higher in free-swimming larvae than in eleutheroembryos. The morphometric establishment of a higher hyperplastic growth of white muscle in free-swimming larvae was confirmed at immunological level by a high occurrence of proliferative nuclei. Early thermal environment was demonstrated to affect the growth process of white muscle on a different way in eleutheroembryos and free-swimming larvae: in the former, white muscle hypertrophy was stimulated at 20°C and hyperplasia at lower temperature, whereas in the latter, both white muscle hypertrophy and hyperplasia were more stimulated at 20°C than at lower temperatures. This was verified at once when the fish length and the white muscle total cross-sectional area were used as explicative variables.     

Combined effect of temperature and food concentration on the grazing rate of the rotifer Brachionus plicatilis

We developed a predictive relationship to determine the grazing rate of Brachionus plicatilis at given temperatures and food concentrations; this function could be applied to experimental culturing and aquaculture practices. Grazing experiments were conducted at temperatures between 5°C and 40°C and at food concentrations, of the flagellate Isochrysis galbana, ranging between ~0 and 10⁶ ml^-1. In total, 136 grazing rates were determined, using the prey depletion method, for rotifers acclimated to treatments for 0.5 or 4 h. The response of grazing rate to temperature and food concentration was described using a model that combined a rectangular hyperbolic function for food concentration and a sigmoidal function for temperature. Using non-linear curve-fitting methods an equation was obtained: G=(452F)/(159000+F)Ǵ.94/(1+2190002T^-4.35) , where G is the grazing rate (flagellates rotifer^-1 min^-1), F is the food concentration (flagellates ml^-1), and T is temperature (°C). The equation indicates a maximum grazing rate of ~35 prey rotifer^-1 min^-1, above ~4᎒⁵ prey ml^-1 and 25°C.     

Temperature acclimation of upper and lower thermal limits and freeze resistance in the nonindigenous brown mussel, Perna perna (L.), from the Gulf of Mexico

Acute and chronic upper and lower thermal limits and freeze resistance were investigated in the nonindigenous brown mussel, Perna perna, from the Texas Gulf of Mexico coast in order to assess its potential distribution in North American coastal waters. This species' long-term, incipient lower and upper thermal limits were 7.5°C and 30°C, congruent with the seasonal ambient water temperature range of 10-30°C reported for other populations worldwide. Effects of temperature acclimation and individual size on survival time were most pronounced on chronic exposures to lethal temperatures approaching incipient lower or upper thermal limits. When exposed to temperature increasing at 0.1°C min^-1, the acute upper lethal limit was 44°C regardless of acclimation temperature or individual size. P. perna had a limited freeze resistance, being intolerant of emersion at -2.5°C. This species' narrow incipient thermal limits, limited capacity for temperature acclimation and poor freeze resistance may account for its restriction to subtidal and lower eulittoral zones of cooler subtropical rocky shores. Near extinction of P. perna from Texas Gulf of Mexico waters occurred in the summer of 1997 when mean surface-water temperatures approached its incipient upper limit of 30°C.     

A novel Vibrio sp. pathogen of the coral Pocillopora damicornis

A coral pathogen was isolated from the diseased tissue of Pocillopora damicornis in Zanzibar. The pathogenic bacterium, referred to as Vibrio coralyticus YB, was classified as a member of the genus Vibrio. Based on its 16S rDNA sequence, V. coralyticus is probably a new species. In controlled aquaria experiments at 26-29°C, inoculation of pure cultures of V. coralyticus YB either into the seawater or by direct contact onto the coral caused tissue lysis of P. damicornis fragments. At 29°C, lysis began as small white spots after 3-5 days, rapidly spreading so that by 2 weeks the entire tissue was destroyed, leaving only the intact bare skeleton. When an infected diseased coral was placed in direct contact with a healthy one, the healthy coral lysed in 2-4 days, further indicating that the disease was contagious. Inoculation with as few as 30 bacteria ml^-1 was sufficient to infect and lyse corals. Seawater temperature was a critical variable for the infectious process: infection and lysis occurred rapidly at 27-29°C, slowly at 26°C and was not observed at 25°C. The data suggest that the presence of V. coralyticus YB, even in low numbers, in seawater surrounding a coral reef will lead to tissue destruction of P. damicornis, when seawater temperatures rise.     

Quantification of ontogenetic discontinuities in three species of oegopsid squids using model II piecewise linear regression

Growth trajectories of morphological characters may change during ontogeny, but this change is often overlooked or, at best, is estimated visually. An objective method was developed for determining discontinuities in morphological measurements of three species of oceanic squids: Chtenopteryx sicula (Vérany, 1851), Mastigoteuthis magna Joubin, 1913, and Brachioteuthis sp. 3. The specimens were collected on the Amsterdam Mid North Atlantic Plankton Expeditions (1980-1983) along a transect from 55°N to 25°N along 30°W. Discontinuities were quantified via an iterative, model II, piecewise linear regression (PLR) analysis, whereby the regression model incorporated a fixed breakpoint that was increased in each iteration across the range of dorsal mantle lengths (DMLs). The iteration with the lowest LOSS value was selected as the best estimate of the breakpoint. In C. sicula, 7 of 10 measured characters had a single breakpoint, and 5 of these occurred at 7-9 mm DML. In M. magna, only 4 of 12 characters had breakpoints, 3 of which occurred at 4-7 mm DML. More, larger specimens would likely yield additional breakpoints. In Brachioteuthis sp. 3, 12 of 14 characters had discernable breakpoints; 3 characters had 2 breakpoints. Most breakpoints occurred at 11-12 mm DML, and all were found at larger sizes than in the other species. This clustering of breakpoints into discrete size ranges may be considered an allomorphosis, and this rapid morphological change may correlate with rapid ecological change.     

The effects of feeding or addition of dissolved inorganic nutrients in maintaining the symbiosis between dinoflagellates and a tropical marine cnidarian

The availability of solid food (Artemia nauplii) and dissolved inorganic nutrients (ammonium, nitrate, phosphate) to the shallow-water marine hydroid Myrionema amboinense was manipulated for 1-8 days in order to investigate their role in the growth of intracellular symbiotic dinoflagellates (zooxanthellae) of the genus Symbiodinium. Symbionts from hydroids collected from the field or maintained under laboratory conditions (25°C, 12 h:12 h light:dark cycle, 80 µE m^-2 s^-1 fluorescent lighting) always exhibited a single peak in mitotic index (MI) at dawn. Symbionts in freshly collected field animals had an MI peak of about 15%. Symbiotic dinoflagellates in hydroids fed Artemia nauplii twice daily in the laboratory maintained this dawn peak of MI between 10% and 15%, but in the absence of feeding or added inorganic nutrients, this peak declined to less than 1% within 2-4 days. In contrast, when hydroids were placed in solutions containing ammonium (20 µM NH₄Cl), nitrate (10 µM NaNO₃), and a combination of ammonium and phosphate (2 µM Na₂HPO₄) immediately after collection, the algal MI remained between 5% and 15% for 4-7 days; the addition of 2 µM phosphate did not increase MI relative to unfed rates. When unfed animals were placed in dissolved nitrogen or fed Artemia, the symbiont MI increased from <1% to 10-17% within 2-3 days; P alone had no effect. However, the increase resulting from added inorganic nutrients was temporary, lasting only 5-7 days. These observations suggest that algal division in the host is maintained indefinitely in the field or by feeding particulate foods twice daily in the laboratory, but the addition of inorganic nutrients alone (ammonium, nitrate and ammonium/phosphate) appeared to support the completion of a maximum of one additional round of cell division. Nutrients required for continued growth and division of symbiotic dinoflagellates are linked to host feeding and host growth; without external food, neither host nor symbiont continue to grow. The same phenomenon is seen in zooxanthellate anemones, clams and corals, where total numbers of symbionts appear to be linked to changes in host-tissue biomass (protein), achieving relatively stable densities in M. amboinense, corals and other cnidarian symbioses, depending on their local environmental conditions. The results of the present study help explain the cellular responses of algal symbionts in reef-dwelling invertebrates to additions of dissolved inorganic nutrients to coral-reef ecosystems.     

Temperature adaptation in eurythermal cod (Gadus <Emphasis Type="Italic">morhua</Emphasis>): a comparison of mitochondrial enzyme capacities in boreal and Arctic populations

Activities of citrate synthase (CS), cytochrome c oxidase (CCO) and the electron transport system (ETS) were investigated in white muscle and liver of laboratory-maintained cod, Gadus morhua, from the North Sea, Norwegian coast and Barents Sea for an analysis of temperature acclimation and adaptation in aerobic metabolism. Cold acclimation within each population led to elevated activities of CS, CCO and ETS in white muscle. In liver, however, only North Sea cod showed cold-compensated CS activities, with CCO and ETS unchanged. In contrast, cold-acclimated Norwegian cod displayed unchanged enzyme activities, and Arctic cod showed elevated activities for CS, but decreased activities for CCO and no change in ETS. Between-population comparisons revealed clear evidence for permanent cold adaptation in white muscle of northern (Norwegian coast and Barents Sea) compared to boreal (North Sea) cod populations, reflected by higher activities of CS, CCO and ETS at the same acclimation temperature. Cold-compensated, mass-specific enzyme activities in liver were found in northern compared to boreal cod for CS and CCO, however, for ETS, after warm acclimation only. When evaluated as capacity in total liver, such activities were only found in northern populations in the case of CS at all temperatures, and for CCO and ETS at 15°C only. Hepatosomatic index (I_H) and liver lipid contents were highest in North Sea cod, with similar I_H but lower lipid contents in cold- versus warm-acclimated animals. An acclimation effect on I_H was found in Norwegian cod only, with higher I_H but unchanged lipid contents in the cold. In conclusion, permanent cold adaptation of muscle aerobic metabolism prevails in cod populations at higher latitudes, which is in line with permanently elevated rates of oxygen consumption observed in a parallel study. These differences reflect higher maintenance costs in cold-adapted versus cold-acclimated cod.     

Differences in life-cycle traits of<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> originating from 60°N and 69°N,when reared in mesocosms at 69°N

Two different Calanus finmarchicus (Gunnerus) cohorts originating from 60°N (Bergen) and 69°N (Tromsø) were investigated in equal environmental conditions to study their different physiological responses to the same environment. A two-plus-two-bag mesocosm study was carried out between March and July 1998, in Håkøybotn, Tromsø, in order to determine development and mortality rates of the two parallel cohorts of C. finmarchicus. For practical reasons, the cohort from Bergen was incubated 10 days earlier than the Tromsø cohort. Consequently, they were exposed to elevated food conditions as compared to the Tromsø cohort. A high initial mortality among the Bergen cohort could clearly be ascribed, by genetic discrimination, to "contamination" with C. helgolandicus. After this initial mass mortality, the mortality was constantly 0.03-0.04 day^у. In cohorts starting from naupliar stage I, there was no significant difference in development or growth, the median development time (NI-CIV) differing by only 7 days (~6%). The difference in development time can be explained to a large extent (~4 days) by temperature differences. This is substantiated with model simulations using a physiological model developed for C. finmarchicus. There was a time lag in incubation between the two cohorts, resulting in elevated temperature during incubation of the Tromsø cohort. A fraction of both cohorts differentiated sexually at stage CV, with males differentiating before females. Females from both cohorts produced eggs, but specific egg production differed significantly (P>0.001, t-test). This was supported by elevated RNA:DNA ratio in females from the Bergen cohort. Both cohorts demonstrated quite similar development and physiological growth rates and, consequently, are considered to belong to the same genetic population inhabiting the Norwegian Shelf. The study demonstrates that C. finmarchicus is capable of adaptation to changes in environment and, thereby, demonstrates a significant physiological plasticity.     

Seasonal fluctuations in sand temperature: effects on the incubation period and mortality of loggerhead sea turtle (<Emphasis Type="Italic">Caretta</Emphasis><Emphasis Type="Italic">caretta</Emphasis>) pre-emergent hatchlings in Minabe,Japan

Incubation period, hatching success, and emergence percentage in loggerhead (Caretta caretta) nests were quantified during the 1993 and 1995 nesting seasons and following incubation seasons in Minabe, Wakayama, Japan. Sand and nest temperatures were also monitored. Over the seasons, daily mean sand temperature at nest depth fluctuated between 18.0°C and 33.3°C, with a steep increase in the second week of July and a peak in late August. Temperatures inside the nest chambers were a few degrees above those of the surrounding sand at the end of incubation. The incubation period ranged from 46 to 82 days. A significant negative correlation was found between mean sand temperature and incubation period. The relationship conformed to the day-degree concept. There was no significant seasonal trend in hatching success, but many pre-emergent hatchlings were found dead in most of the clutches during the warmest part of the season. Emergence percentage was correlated with mean sand temperature calculated for 4 days before emergence, suggesting that mortality may be due to heat. This heat-related mortality is considered to be a common phenomenon at our study site, because the peak in emergences coincides with the peak in high temperatures. These temperature effects on hatchling mortality must be taken into account in estimates of hatchling sex ratios. Because sand temperatures already exceed the optimal thermal range for incubation, this population is vulnerable to even small temperature increases resulting from global warming.     

Effects of emersion and elevated haemolymph ammonia on haemocyanin–oxygen affinity of Cancer pagurus

The subtidal crab Cancer pagurus (L.) experiences involuntary periods of emersion associated with practices used in their marketing and distribution. During 24 h emersion, impaired gill function caused an increase of circulating total ammonia (TA=NH₃+NH₄⁺) of 0.35 mmol TA l^-1 (167%). The oxygen-binding characteristics of the haemocyanin of C. pagurus were examined at 10°C in the presence of total ammonia (0.2-1.0 mmol TA l^-1). The haemocyanin-oxygen affinity was decreased in the presence of TA ((logP₅₀/(log[TA]=0.16). Emersion induced significant acidosis and elevated circulating levels of haemolymph TA, lactate and urate, but all had returned to normal levels within 24 h of re-immersion. The accumulation of haemocyanin-modulating substances during 24 h emersion compensated partially (40%) for the effect of the acidosis, but the net effect of the emersion period was a significant decrease in oxygen affinity, corresponding to an increase of P₅₀ (10°C ) from 1.24 kPa (immersed) to 1.96 kPa (24 h emersion). The implications of the findings are considered in terms of the effects and adaptations to emersion.     

Evaluation of fatty acids as biomarkers for a natural plankton community. A field study of a spring bloom and a post-bloom period off West Greenland

An investigation of the fatty acid composition of a natural arctic plankton community was carried out over two fishing banks located between 63°N and 65°N off the West Greenland coast. Samples for fatty acid analyses, species determination and biomass assessments of the plankton community were taken at the depth of fluorescence maximum. High biomass and diatom dominance during the spring bloom and low biomass and flagellate dominance in the post-bloom period were reflected by the fatty acid profiles. The total amount of fatty acid ranged from 55 to 132 µg l^-1 during the spring bloom and from 1 to 5 µg l^-1 during the post bloom. Analysis of the fatty acids showed that when the plankton was dominated by diatoms of the genera Thalassiosira and Chaetoceros, the proportions of C16:1(n-7) and C20:5(n-3) were correspondingly high. C18s, and particularly C18:1(n-9), were more abundant when the plankton was dominated by small autotrophic flagellates, primarily haptophytes. We found a good positive correlation between the common diatom marker, C16:1(n-7)/C16:0, and the biomass percentage of diatoms (r=0.742, P<0.001), as well as between the biomass percentage of flagellates and total C18 fatty acids (r=0.739, P<0.001). This supports the use of these specific fatty acids and fatty acid ratios as general biomarkers of the plankton community. However, the fatty acids are not specific enough to sufficiently characterise the composition of the plankton community, and microscopical support is needed to verify observed trends.     

Annual reproductive cycle, spatial distribution, abundance, and size structure of Oreaster reticulatus (Echinodermata: Asteroidea) in Bocas del Toro, Panama

The structure, distribution, and population abundance of Oreaster reticulatus (Linnaeus, 1758) in 47,157 ha of shallow-water habitat in the archipelago of Bocas del Toro, Panama, were assessed from May to October 2000. The reproductive cycle of the sea star was studied in Isla Solarte, from February 2000 to February 2001. In total, 4,818 sea stars were recorded with a mean density of 149.7 ind. ha^-1, and a population of over 7 million was estimated for the archipelago. O. reticulatus was absent in ca. 50% of the evaluated areas, possibly due to high runoff and sedimentation; highest density was observed in an intermediate-runoff regime (255 ind. ha^-1). About 45% of the population was found in substrata dominated by seagrass (Thalassia testudinum) and coarse, calcareous sand, 51% occurred in habitats where coral reef patches were mixed with seagrass, and 4% exclusively on coral reefs. The average size, based on the major radius, was 9.5 cm (3-21 cm), with a population structure composed of ca. 83% juveniles and 17% adults. The average reproductive size, measured as major radius, was 15 cm, and the minimum was 7 cm. Both males and females with a maximum stage (IV) of gonad development were observed throughout the year. The gonad index showed three peaks of maximum reproductive activity, which is not comparable to studies from other localities. The reproductive cycle did not seem to be related to water temperature, which ranged from 27°C to 30°C, but may respond more closely to changes in local rainfall. This relationship was not statistically significant based on this 1-year study. These data provide a useful baseline for management of local populations in the face of an increasing harvest for the aquarium trade and as souvenirs.     

Metabolic properties of Northern krill, Meganyctiphanes norvegica, from different climatic zones. II. Enzyme characteristics and activities

Activities and characteristics of two metabolic key enzymes, citrate synthase (CS) and pyruvate kinase (PK), were studied in the Northern krill, Meganyctiphanes norvegica, with respect to adaptive properties under different thermal conditions. Krill were sampled during late winter/spring and summer from the constantly warm Ligurian Sea (12-13°C below the thermocline), the colder but also comparatively constant Clyde Sea (7-8°C), and the variable Kattegat (2-16°C). Both enzymes showed distinct tissue- and organ-specific activities, which were highest in the pleopods - the principal locomotive organs. The fourth and fifth abdominal segments, however, were used for routine investigation due to lowest variability. Specific activity of CS and PK did not differ between seasons in krill from the Kattegat or the Clyde Sea. In the Ligurian Sea, in contrast, specific CS activities were significantly lower during summer. Analysis of individual data illustrated a decrease of CS activity with size and an increase of PK activity with size. Taking these allometric effects into account, as emphasized by calculating the ratio between both enzymes, variation of CS and PK activities turned out to be solely dependent on body size, which differed between locations and seasons. Ligurian krill from the summer, however, were unique in that they showed a lower CS/PK ratio than would be predicted by the scaling effect. Thermal characteristics of each enzyme were similar between locations and seasons. During the winter, in Kattegat and Clyde Sea krill, K_m values (Michaelis-Menten constant) of CS towards acetyl-coenzyme A exhibited an almost constant level over the experimental temperature range of 4-16°C. During summer, however, K_m values were lower at 8°C in the Clyde Sea and at 12°C in the Kattegat. In Ligurian krill from the summer, K_m values were consistently lower than those of winter krill over the entire experimental temperature range. In conclusion, Kattegat and Clyde Sea krill show only minor adaptations to their respective thermal environments in terms of CS and PK characteristics. Ligurian krill, in contrast, exhibited decreased specific CS activity during summer, which might be compensated by elevated enzyme-substrate affinity as indicated by lower K_m values. Since temperature was constant during both seasons, this effect cannot be explained as a reaction to thermal conditions. Consequently, oligotrophic conditions in the Ligurian Sea during summer may entail a reduction in the somatic performance of krill, which is reflected by lower CS activity.