Ingestion of the dinoflagellate, Pfiesteria piscicida, by the calanoid copepod, Acartia tonsa

The dinoflagellate, Pfiesteria piscicida, can form harmful algal blooms in estuarine environments. The dominant copepod species usually found in these waters is Acartia tonsa. We tested the ability of A. tonsa to graze the non-toxic zoospore stage of P. piscicida and thus serve as a potential biological control of blooms of this algal species. A. tonsa grazed the non-toxic zoospore stages of both a non-inducible P. piscicida strain (FDEPMDR23) and a potentially toxic strain (Tox-B101156) at approximately equal rates. Ingestion of P. piscicida increased with cell concentration and exhibited a saturated feeding response. Both the maximum number of cells ingested (I_max) and the slope of the ingestion curve (α) of A. tonsa feeding on P. piscicida were comparable to these ingestion parameters for A. tonsa fed similar-sized phytoplankton and protozoan species. When these laboratory ingestion rates were combined with abundance estimates of A. tonsa from the Pocomoke Estuary and Chesapeake Bay, we found that significant grazing control of the non-toxic zoospore stage of P. piscicida by A. tonsa would only occur at high copepod abundances (>10 copepods L⁻¹). We conclude that under most in situ conditions the potential biological control of blooms of P. piscicida is exerted by microzooplankton grazers. However, in the less saline portions of estuaries where maximum concentrations of copepods often occur with low abundances of microzooplankton, copepod grazing coefficients can be similar to the growth rates of P. piscicida.     

Feeding rates and productivity of the copepod Acartia bifilosa in a highly turbid estuary; the Gironde (SW France)

Acartia spp. are the dominant copepod species in the Gironde estuary, seaward of the turbidity maximum area. Acartia bifilosa develop a large population in spring and early summer whereas Acartia tonsa appear in late summer. High values and high variability of chlorophyll a/suspended particulate matter ratio are found seaward of the turbidity maximum area. Feeding rates of A. bifilosa were measured by fluorometry. Phytoplankton ingestion was found to be highly variable, between 8 to 80% of copepod carbon body weight. Except for adult females, copepods were heavier in summer than in winter. PB ratios, estimated by the instantaneous growth rate method, varied from 0.03 d^–1 to 0.14 d^–1. The gut contents and P/B ratios of Acartia bifilosa were related to chl a/SPM ratio. From those data, and a few obtained for A. tonsa, it is concluded that only in summer months phytoplankton ingestion is enough to maintain secondary production.     

Morphological aspects of subitaneous and resting eggs from Acartia josephinae (Calanoida)

A. josephinae collected along the Salento Peninsula (Ionian and Adriatic Seas) laid two types of eggs, under laboratory conditions, and they are described for the first time. Under a light microscope subitaneous eggs looked smooth on the surface, but scanning electron microscopy revealed that the surface was not perfectly smooth but tubercular with many small protuberances. Resting eggs had long and thick spines whose apical part was multi-branched. The use of egg morphology as a taxonomic character, in the systematic of copepods, is proposed.     

Egg production of the copepod Acartia tonsa: The influence of hypoxia and food concentration

Low dissolved oxygen conditions, or hypoxia, occur in estuaries and impact more than just the obvious commercially important species. Copepods are an important link in the food web, and the influence of hypoxia upon them is relatively unstudied. Using the copepod Acartia tonsa, a study of the impact of hypoxia on egg production was conducted. A. tonsa had reduced egg production at low dissolved oxygen concentrations (DO), with the lowest egg production occurring at 0.53-ml/l O₂ concentration. Another experiment was conducted to determine if, by increasing food concentration, the affect of hypoxia could be mitigated. The results indicate that increased food did not offset the impact that hypoxia had on egg production of A. tonsa. These results suggest that as A. tonsa experiences hypoxia in the wild, population numbers will decrease. Thus, if hypoxic conditions increase in scope and duration, declines in copepod abundance may lead to a decline in the abundance of species that depend on them as food. These species may be of commercial importance (e.g., fish, crabs, and oysters).     

Hypoxia and seasonal temperature: Short-term effects and long-term implications for Acartia tonsa dana

Far more attention has been given to the short-term lethal impacts of reduced dissolved oxygen on commercially important fish and crabs than to the long-term sublethal impacts on these same species, or on lower trophic levels. This study demonstrates that chronic, sublethal effects of hypoxia on the copepod Acartia tonsa, a critical component of many pelagic coastal food webs, can lead to significant decreases in population growth. The results of laboratory experiments conducted at 15 °C (winter) and 25 °C (summer), under conditions of normoxia (Controls), sublethal hypoxia (1.5 ml l^− 1) and lethal hypoxia (0.7 ml l^− 1) show that egg production female^− 1 day^− 1 was significantly lower at 0.7 ml l^− 1 compared to Controls at both temperatures, while egg production female^− 1 day^− 1 was significantly lower at 1.5 ml l^− 1 compared to controls in both summer experiments and in one of the two winter experiments. Survival was significantly decreased in the 0.7 ml l^− 1 treatment compared to Controls and the 1.5 ml l^− 1 treatment. Copepods developed more slowly and matured at smaller adult body sizes at both temperatures under both lethal and sublethal hypoxia compared to normoxia. Under summer temperatures, egg production was reduced by hypoxia exposure on two counts: (1) exposure to hypoxia during development resulted in smaller adults, which translated into lower egg production, and (2) egg production was still significantly lower in hypoxia treatments compared to Controls even when differences in body size were taken into account. While copepods collected in winter and exposed to winter temperatures and hypoxia also matured at smaller body sizes than copepods exposed to normoxia, egg production in winter was almost entirely attributable to this reduction in body size. These results suggest that coastal hypoxia may have a significantly greater impact in the summer months, when copepod populations are most abundant and growing at their most rapid rate of the year. With the anticipated increases in global temperatures, hypoxia may have even greater impacts on pelagic food webs.     

Acartia tonsa: a species new for the Black Sea fauna

The presence of Acartia tonsa in Black Sea waters (South Crimean coast, Ukraine) is reported for the first time. A. tonsa may be a recently introduced species in the Black Sea. Morphological features of the adults have been shown by S.E.M.     

Fitness consequences for copepods feeding on a red tide dinoflagellate: deciphering the effects of nutritional value, toxicity, and feeding behavior

Phytoplankton exhibit a diversity of morphologies, nutritional values, and potential chemical defenses that could affect the feeding and fitness of zooplankton consumers. However, how phytoplankton traits shape plant–herbivore interactions in the marine plankton is not as well understood as for terrestrial or marine macrophytes and their grazers. The occurrence of blooms of marine dinoflagellates such as Karenia brevis suggests that, for uncertain reasons, grazers are unable to capitalize on, or control, this phytoplankton growth—making these systems appealing for testing mechanisms of grazing deterrence. Using the sympatric copepod Acartia tonsa, we conducted a mixed diet feeding experiment to test whether K. brevis is beneficial, toxic, nutritionally inadequate, or behaviorally rejected as food relative to the palatable and nutritionally adequate phytoplankter Rhodomonas lens. On diets rich in K. brevis, copepods experienced decreased survivorship and decreased egg production per female, but the percentage of eggs that hatched was unaffected. Although copepods showed a 6–17% preference for R. lens over K. brevis on some mixed diets, overall high ingestion rates eliminated the possibility that reduced copepod fitness was caused by copepods avoiding K. brevis, leaving nutritional inadequacy and toxicity as remaining hypotheses. Because egg production was dependent on the amount of R. lens consumed regardless of the amount of K. brevis eaten, there was no evidence that fitness costs were caused by K. brevis toxicity. Copepods limited to K. brevis ate 480% as much as those fed only R. lens, suggesting that copepods attempted to compensate for low food quality with increased quantity ingested. Our results indicate that K. brevis is a poor food for A. tonsa, probably due to nutritional inadequacy rather than toxicity, which could affect bloom dynamics in the Gulf of Mexico where these species co-occur.     

Feeding behaviour and migrations in a natural population of the copepod Acartia tonsa

This paper deals with the variations on feeding activities and diel migrations of Acartia tonsa Dana, the dominant copepod species in Berre lagoon (west Mediterranean French coasts).A 27 hour in situ study was carried out during June 1989, at a station located in the south west of the lagoon. Vertical profiles of salinity, temperature and dissolved oxygen taken each 12 hours showed a stratification of the water column in two distinct layers: (1) a superficial layer with higher temperature, moderate salinity, and high oxygen concentrations; (2) a colder, more saline and almost anoxic deep layer. In situ chlorophyll a measurements were made at –1, –3 and –5 m; concentrations were relatively homogeneous through the water column during the whole sampling period.Zooplankton samples were collected every 3 hours with a 200 µm mesh net, in three strata (0–2 m, 2–4 m, 4–6 m). A complete dominance of A. tonsa was observed in the zooplankton community. Our results point out clearly a nocturnal migration, with individuals concentrating in both superficial layers; thus an unimodal migratory pattern can be inferred. Gut flourescence measured following the Mackas & Bohrer technique (1976), showed higher values during night time, and values for females were the highest with wider day—night variations. Similar results were found in laboratory experiments with copepods fed with a culture of Dunaliella tertiolecta.Gut evacuation rate was measured in two laboratory experiments either mixing or separating males and females. Evacuation rate was 17.92 and 27.25 min for males and females respectively.Phytoplankton daily ration for A. tonsa calculated by gut flourescence and gut evacuation rate was particularly low, for it represents only 10% of the individual carbon weight.Moreover, grazing impact on phytoplankton is very restricted, it represents less than 1% of the daily phytoplankton stock.     

Gonad morphology,oocyte development and spawning cycle of the calanoid copepod <Emphasis Type="Italic">Acartia clausi</Emphasis>

Information on gonad morphology and its relation to basic reproductive parameters such as clutch size and spawning frequency is lacking for Acartia clausi, a dominant calanoid copepod of the North Sea. To fill this gap, females of this species were sampled at Helgoland Roads from mid March to late May 2001. Gonad structure and oogenesis were studied using a combination of histology and whole-body-analysis. In addition, clutch size and spawning frequency were determined in incubation experiments, during which individual females were monitored at short intervals for 8 and 12 h, respectively. The histological analysis revealed that the ovary of A. clausi is w-shaped with two distinct tips pointing posteriorly. It is slightly different from that of other Acartia species and of other copepod taxa. From the ovary, two anterior diverticula extend into the head region, and two posterior diverticula extend to the genital opening in the abdomen. Developing oocytes change in shape and size, and in the appearance of the nucleus and the ooplasm. Based on these morphological characteristics, different oocyte development stages (OS) were identified. Mitotically dividing oogonia and young oocytes (OS 0) were restricted to the ovary, whereas vitellogenic oocytes (OS 1–4) were present in the diverticula. The development stage of the oocytes increased with distance to the ovary in both, anterior and posterior diverticula. Most advanced oocytes were situated ventrally, and their number varied between 1 and 18, at a median of 4. All oocyte development stages co-occur indicating that oogenesis in A. clausi is a continuous process. These morphological features reflect the reproductive traits of this species. In accordance with the low numbers of mature oocytes in the gonads, females usually produced small clutches of one to five eggs. Clutches were released throughout the entire observation period at intervals of 90 min (median) resulting in mean egg production rates of 18–28 eggs female⁻¹ day⁻¹.     

Trophic modification of food quality by heterotrophic protists: species-specific effects on copepod egg production and egg hatching

Recent literature suggests that heterotrophic protists could improve the biochemical constituents of poor quality algae for subsequent use by higher trophic levels, a phenomenon dubbed “trophic upgrading”. We conducted experiments to test trophic upgrading effects on the omnivorous calanoid copepod Acartia tonsa. Two heterotrophic protists, Oxyrrhis marina and Gymnodinium dominans, were grown on three algal species of different nutritional qualities: Dunaliella tertiolecta, Isochrysis galbana and Rhodomonas salina. In parallel incubations, the copepods were fed the heterotrophic protists or the algae that the protists grew on. We measured the ingestion rate, egg production rate and egg hatching success of the copepods in each treatment. Comparison of the egg production efficiency (EPE; egg carbon production/carbon ingestion×100%) between parallel diet treatments allowed us to calculate the trophic upgrading index (TUI; ratio of EPE-heterotrophic protist to EPE-alga). The copepods ingested similar amount, or 20-30% more algae than heterotrophic protists. Daily rations ranged 50-122% of body C per day. Copepods feeding on O. marina that grew on D. tertiolecta had higher egg production rate and egg hatching success than copepods feeding on D. tertiolecta directly, and the resultant TUI between the two treatments was 19.7. Similarly, the copepod egg production was improved by G. dominans that grew on D. tertiolecta and the resultant TUI was 23.3. TUI was near 1 between I. galbana treatment and the parallel heterotrophic protist treatments, indicating no or little trophic upgrading effects on the copepod's egg production. However, egg hatching success was significantly lower with G. dominans growing on I. galbana. O. marina that grew on R. salina induced a lower EPE relative to the alga itself, yielding a TUI of less than 1. Biochemical data showed that the heterotrophic protists contained eicosapentanoic acid (EPA) and docosahexanoic acid (DHA) even when they fed on alga that lacked these essential fatty acids, which may explain some of the observed trophic upgrading effects and species-specific differences in our experiments. However, our data also suggested that dietary EPA and DHA could not be the sole factors regulating the copepod's reproductive output, and that egg production and egg hatching appeared to have different nutritional requirements and respond differently to the copepod's diets.     

Respiratory metabolism during embryonic subitaneous and diapause development in Pontella mediterranea (Crustacea,Copepoda)

Oxygen consumption and ATP content are reported for the planktonic marine copepod Pontella mediterranea during normal and diapause embryonic development. In subitaneous embryos that hatched without delay within 48 h, O₂ uptake increased linearly after spawning to reach maximum levels about 25 h later. By contrast, ATP levels were initially very high but decreased rapidly within the next 5 h to reach stable values thereafter. In diapause embryos, O₂ consumption followed the typical U-shaped curve described for insect diapause. An initial period of prediapause, which lasted for about 25 days, was characterized by elevated O₂ uptake. This was followed by a period of diapause in which O₂ consumption dropped to 25% of the values recorded during prediapause. This protracted period of dormancy, which lasted about 4 to 5 months, was followed by a period of high O₂ consumption possibly due to the breaking of diapause and resumption in development. ATP content during the pre-diapause period showed a similar trend as in subitaneous embryos with high initial levels that decreased with time for the first 20 days and remained stable afterwards.Abbreviations E embryo - EDTA ethylenediamine-tetraacetic acid - PCA perchloric acid - SW sea water - TEM transmission electron microscopy     

Space and time distribution of zooplankton in a Mediterranean lagoon (Etang de Berre)

In the Berre lagoon, a large brackish and swallow area near Marseille, the environmental factors (temperature, salinity, oxygen, suspended particulate matter and chlorophyll) generally display strong space and time variations. The rotifer Brachionus plicatilis and the copepod Acartia tonsa constitute the bulk of the zooplankton population during all the year. Their space and time distributions were studied in 23 stations distributed all over the lagoon, during four seasonal cruises (February, June, October, November), at surface and bottom layers. There is no marked difference in the horizontal and vertical distribution of the two species, (except in November when rotifers were prevailing in surface and copepods at depth) and in their time occurence. When the four series of data are pooled, correlation analysis show that A.tonsa is positively correlated with temperature, salinity and seston and negatively to oxygen and chlorophyll. B. plicatilis is positively correlated with temperature and seston, but also with chlorophyll, while salinity has a negative effect. The specific eggs number of both species is chlorophyll dependent. Considering seasonal cruises separately, some differences appear in the sense or the significance of these different correlations. The respective distribution of the two species is only partly dependent on the variation of the environmental factors: most of the variance remains unexplained, as indicated by the result of a stepwise multiple regression analysis using the most significant factors (temperature, salinity and oxygen explain 33 to 42% of the variance in Acartia, while temperature and salinity explain 27 to 28% of the variance in Brachionus). Thus, internal behavioral factors could also play a role in the distribution of organisms, particularly in some cases of aggregations of organisms observed during this study. As the two species occupied the same space habitat most of the year, they are potentially in competition for food. A way to optimize the food utilization could be the time separation of their feeding activity, nocturnal in Acartia and diurnal in Brachionus. Another way could be selective feeding upon food particles depending on their size (Brachionus being able to use finer particles than Acartia) or their quality (Brachionus being more herbivorous than Acartia) as demonstrated in some grazing experiments carried out in parallel.     

Respiration in Branchinella Kugenumaensis (Crustacea-Anostraca) inhabiting tropical astatic ponds

The oxygen consumption (routine rate) of Branchinella kugenumaensis, inhabiting tropical astatic ponds is measured at 28°C. Two distinct trends are observed in the oxygen consumption by this fairy shrimp; young, immature animals have a higher rate than the older, sexually mature animals. Branchinella kugenumaensis falls under the intermediate group of Bertalanffy, where respiration falls between the respiration surface proportional and the respiration weight proportional metabolism.     

Feeding of Acartia tonsa Dana (Copepoda,Calanoida): predation on nauplii of Canuella perplexa T. et A. Scott (Copepoda,Harpacticoida) in the sluice-dock at Ostend

Feeding experiments in which the zooplankton fraction of the Sluice-dock smaller than 200 μm is offered to Acartia tonsa, the dominant calanoid of this biotope, show that it feeds on the nauplii of Canuella perplexa, the dominant benthic harpacticoid. The ecological implications of this carnivorous feeding, occurring in the presence of natural phytoplankton concentrations, are briefly discussed.     

Life-history variation related to the first adult instar in daphnids derived from diapausing and subitaneous eggs

Vibrio cholerae is the causative agent of the severe dehydrating diarrheal disease cholera. This bacterium has been detected in many estuaries around the world and the United States. In this study we examine the abundance and distribution of V. cholerae in recreational beach waters and tributaries of Southern California. Water samples were taken from 11 beach locations adjacent to freshwater runoff sources between February 8th and March 1st, 1999. Water samples were also taken from rivers, creeks and coastal wetlands along the Southern California coast between May 19th and June 28th, 1999. In addition to the detection of V. cholerae, environmental parameters including temperature, salinity, coliphage counts, viable heterotrophic plate counts and total bacterial direct counts were also determined to understand the relationships between the presence of V. cholerae and environmental conditions. A direct colony hybridization method using an oligonucleotide probe specific for the 16S–23S intergenic spacer region of V. cholerae, detected V. cholerae in 3 of the 11 beach samples with the highest concentration (60.9 per liter) at the mouth of Malibu Lagoon. V. cholerae and coliphage were not correlated for beach samples, indicating that the presence of V. cholerae is independent of sewage pollution. V. cholerae were detected in all samples taken from rivers, creeks and wetlands of coastal Southern California where salinities were between 1 to 34 parts per thousand (ppt), but was not found at a freshwater sampling site in upper San Juan Creek. The highest density of V. cholerae was found in San Diego Creek with a concentration of 4.25×10⁵ CFU/L. The geographical distribution of V. cholerae was inversely correlated with salinity. High concentrations of V. cholerae were more frequently detected in waters with lower (but above 0) salinity. The results of this study provide insight into the ecology of this aquatic species and are potentially important to the understanding of the epidemiology of cholera on a global scale.     

Chitobiase of planktonic crustaceans from South Atlantic coast (Southern Brazil): Characterization and influence of abiotic parameters on enzyme activity

Chitobiase is one of the enzymes involved in chitin degradation in nature. It is produced and released by a variety of organisms from bacteria to fish. In crustaceans, it is associated with digestive function and acts on the epidermis during the molting process. In the present study, the influence of water pH, temperature and salinity on maximum chitobiase activity (MCA), as well as the enzyme affinity (Km) for a substrate, the methylumbelliferyl N-acetyl-ß-d-glucosaminide (MUFNAG) was evaluated in the copepod Acartia tonsa. Km values for chitobiases of other crustaceans from the Patos Lagoon estuary and Cassino Beach (Southern Brazil) were also determined. For A. tonsa, MCA was observed at pH 5-6 and 30-35 °C. The range of pH was quite similar to that reported for other aquatic organisms. However, the range of temperature was lower than that previously reported. For salinity, no previous studies have considered the influence of this parameter on MCA. For A. tonsa, MCA was observed in freshwater, showing a significant linear decrease with increasing salinity. Considering that maximum copepod survival and growth rates are observed between 15 and 25 ppt, these findings suggest that the observed enzyme activity in this range of salinity (68 to 47% of that measured in freshwater) is not a limiting factor for A. tonsa growth. However, the extremely decreased enzyme activity observed in salinity 30 ppt (33% of that measured in freshwater) suggests that chitobiase activity might be one of the limiting factor for copepod growth at 30 ppt salinity or higher. Km values (μM) determined for organisms evaluated in the present study (copepod A. tonsa = 20.77; mysid Metamysidopsis elongata atlantica = 14.67; nauplii barnacle Balanus improvisus = 18.19; decapod zoea = 14.30; decapod megalopa = 24.77) were lower than those reported for other crustaceans from Northern Hemisphere. Also, they were much lower than those of organisms from different taxonomic groups like bacteria and fungi, but much higher than in protozoans and dinoflagelates. These findings suggest that chitobiase might be differentially evolved in each specific group of organism, and even within different ontogenetic stages of the same species, for a better adaptation to cope with its respective environmental needs.     

The copepod Calanus finmarchicus: A potential vector for trophic transfer of the marine algal biotoxin, domoic acid

The marine algal biotoxin, domoic acid (DA), is produced by certain members of the diatom genus Pseudo-nitzschia. This neurotoxin has been responsible for several mass mortality events involving marine birds and mammals. In all cases, the toxin was transferred from its algal producers through marine food webs by one or more intermediate vectors. The ability of some copepod taxa to serve as vectors for DA has been demonstrated; however, the role played in DA trophic transfer by Calanus finmarchicus, which often dominates N. Atlantic zooplankton assemblages and is a primary dietary component of the highly endangered N. Atlantic right whale (Eubalaena glacialis), has been uncertain. In the present study, we examined the ability of C. finmarchicus to consume DA-producing algae and retain the toxin. Results of grazing and toxin accumulation/depuration experiments showed that C. finmarchicus consumed DA-producing Pseudo-nitzschia multiseries regardless of the presence or absence of morphologically similar, but non-toxic, P. pungens, across initial cell concentrations ranging from 1000-4000 cells mL^− 1. Furthermore, C. finmarchicus did not appear to preferentially consume or avoid either Pseudo-nitzschia species tested. After ingestion of P. multiseries, copepods accumulated DA and retained it for up to 48 h post-removal of the toxin source. These findings provide evidence for the potential of C. finmarchicus to facilitate DA trophic transfer in marine food webs where toxic Pseudo-nitzschia is present.     

Seasonal variability in the individual carbon content of the calanoid copepod Acartia bifilosa from the northern Baltic Sea

The seasonal variation in the carbon content of the calanoid copepod Acartia bifilosa was studied in the northern Baltic Sea. Monthly length-weight relationships were followed from November 1990 to October 1991 by analysing the organic carbon content of individuals, using a high temperature combustion method. The monthly length (L) on carbon (C) regressions of copepodites were best described by power functions (C = aL^b), where 75% to 88% of the variation could be explained by length. Nauplii length explained less of their carbon content (63–71 %). The carbon content per length was highest in summer when the nutritional situation was good and temperature at its highest. However, the carbon-length regressions differed significantly between months, except in winter, when two subsequent months had similar regressions. The results pointed out the importance of seasonal variation as well as the risk of making errors if biomass estimates based on length on carbon regressions are used. Carbon analysis should, if possible, be done on every sample or should at least be tested as to whether the regressions are consistent with the study material before estimations are calculated.     

Oxygen consumption and body temperature in yellow-bellied marmot populations from montane-mesic and lowland-xeric environments

Summary Yellow-bellied marmots characteristically live in montane-mesic environments, but in several areas in western North America, this species extended its range into lowland-xeric habitats. Body mass was significantly smaller in the lowland-xeric population from eastern Washington at 393 m than in the montane-mesic population from western Colorado at 2900 m. Oxygen consumption of marmots from montane-mesic and lowland-xeric environments was signiflcantly affected by ambient temperature (T_A) water regimen, population, and a population x water regimen x temperature interaction. Lowland-xeric animals had a higher metabolic rate at low T_As, but a lower metabolic rate at higher T_As than the montane-mesic aminals. Oxygen consumption was lower on a restricted-water regimen than on ad libitum water in both populations. Coefficients relating oxygen consumption to body mass were affected by T_A, water regimen, and population. These intraspecific coefficients are larger than the interspecific coefficients for all mammals. Body temperature (T_B) was affected significantly by T_A, water regimen, and population. T_A body mass, and a population x water regimen interaction significantly affected conductance. Conductance generally was higher in the lowland-xeric than in the montane-mesic marmots. Both populations increased conductance at high T_A, but the lowland-xeric population dissipated a much higher proportion of the heat by evaporative water loss (EWL) than did the montane-mesic population. Metabolic water production exceeded or equaled EWL at 5–20°C. Smaller body size, reduced metabolism at high T_A, and increased EWL at high T_A characterized the lowland-xeric population.Metabolic rates of yellow-bellied marmots were higher than predicted from body size during the reproductive season but decreased to 67% of that predicted from the Kleiber curve by late summer. Marmots minimize thermoregulatory costs by concentrating activity at times when the microclimate is favorable, by tolerating hyperthermia at high T_A in the field, and by having a conductance lower than that predicted from body size.Abbreviations DHC dry-heat conductance - EHL evaporative heat loss - EWL evaporative water loss - HP heat produced - T _A ambient temperature - T _n body temperature - M body mass     

A marine calanoid copepod (Temora longicornis) in a semi-stagnant coastal lagoon (Lake Grevelingen,S.W.-Netherlands)

The marine calanoid copepodTemora longicornis was introduced in saline Lake Grevelingen (S.W.-Netherlands), when the lake was continuously flushed with North Sea water in 1979, to enhance the reduced salinity. Development of the copepod proceeded suboptimally as a consequence of an unfavourable environment in the lake: 1. The phytoplankton assemblage, mainly consisting of crytomonad flagellates, less suitable for growth and reproduction of the adult stages. 2. An acute food shortage occurring at a crucial moment in the development. 3. A. pronounced salinity-and oxygen stratification in June, preventing further development ofTemora.Communication nr. 474 of the Delta Institute for Hydrobiological Research, Yerseke.