Egg production by Acartia tonsa in Long Island Sound

The egg production of adult Acartia tonsa females in Long IslandSound, NY, during and after the fall bloom, was measured inshort-term (8 h) incubations in natural seawater, and estimatedfrom the egg-ratio method, using preserved samples of eggs andfemales. Egg production, as estimated from the in cubation technique,closely tracked changes in chlorophyll concentration with time.The fecundity estimates from the egg-ratio method were significantlylower than from the incubation method in September but werenot significantly different in October. We suggest that a comparisonof the egg production rates using these two techniques may bea useful way of gaining some insight into the extent of eggpredation in the field. We attribute differences between eggratio and incubation fecundities in September to ctenophorepredation.     

Predation by Acartia tonsa Dana on planktonic ciliates and rotifers

In laboratory experiments, adults and nauplii of the calanoid copepod Acartia tonsa Dana feed on planktonic ciliates and rotifers. Adults have a higher clearing rate for planktonic ciliates and rotifers than for phytoplankton. Adult copepods have a maximum clearing rate of ≈200 ml copepod⁻¹ · d⁻¹ for large ciliates, with lower clearing rates for small ciliates. Nauplii have higher clearance for small than for large ciliates. Addition of ciliates or rotifers to the diet of A. tonsa enhances egg production; this effect is due to improved food quality. Microzooplankton may be an important component of the diet of A. tonsa even when phytoplankton are plentiful. Selective predation by copepods probably influences the population dynamics of planktonic ciliates and rotifers in coastal waters.     

DMSP-consuming bacteria associated with the calanoid copepod Acartia tonsa (Dana)

DMSP-consuming bacteria (DCB) were recovered from the body and fecal pellets of the copepod Acartia tonsa (Dana). The most probable number of DCB associated with starved A. tonsa was 9.2x10(2) cells copepod(-1). The abundance of DCB recovered from the copepod body increased to 1.6-2.8x10(4) after the copepod fed on DMSP-containing alga. DCB abundance associated with fecal pellets averaged 1.2x10(4) cells pellet(-1). In enrichment cultures, the DCB grew with a doubling time of 1.1-2.9 days, and consumed DMSP at a rate of 4.5-7.5 fmol cell(-1) day(-1). The apparent DMSP-to-DMS conversion efficiency was 25-41% for DCB from copepod body, and 99% for DCB from fecal pellets. Our study demonstrated that copepods and their fecal pellets may harbour dense populations of DCB, and that the copepod-bacteria coupling represents a novel mechanism for DMSP consumption in the water column.     

Do viruses affect fecundity and survival of the copepod Acartia tonsa Dana?

Naturally occurring viruses are extremely abundant in aquaticsystems, and they infect bacteria, cyanobacteria, prokaryoticand eukaryotic phytoplankton, heterotrophic nanoflagellates,fish and mammals. Viral infections of single-celled organismshave been studied intensively in the past decade, but littleis known about the effects of viruses on aquatic metazoans,other than for some economically important species. Becausezooplankton assemblages are often dominated in number and biomassby copepods, we used them as model organisms to study the effectsof naturally occurring viruses on higher trophic levels. Weattempted to induce viral infection in laboratory-reared culturesof the estuarine copepod Acartia tonsa Dana by exposing themto elevated concentrations of natural viruses in seawater. Wefound no negative effects of such exposure on copepod fecundity,larval survival or adult survival.     

Diel variations in Acartia tonsa feeding, respiration and egg production in a Mediterranean coastal lagoon

Short-term changes in abundance, feeding, respiration and spawningby the copepod Acartia tonsa were studied during four 24 h periodsat two stations in a Mediterranean lagoon in May and June of1989 and 1990. Nightly increases of abundance in the upper layer,attributed to nocturnal upward migration, were observed in threeout of the four time series. Nevertheless, occasional dailyincreases were observed too, so that no clear diel patternsin abundance could be defined. Contrarily, diel patterns seemedto appear: (i) for feeding (higher at the beginning of the night),based on gut fluorescence and clearance and ingestion rate measurements;(ii) for respiration (lower at night and based on 8 h incubationperiods); and (iii) for spawning (higher at the end of the night,based on experimental data). The origin of these patterns, aswell as their relationships to environmental data and theirpossible association, are discussed with regard to the availableliterature.     

Effects of food on bacterial community composition associated with the copepod Acartia tonsa Dana

The estuarine copepod Acartia tonsa naturally carried diverse strains of bacteria on its body. The bacterial community composition (BCC) remained very conservative even when the copepod was fed different axenic algal species, indicating that the food per se did not much affect BCC associated with the copepod. In xenic algal treatments, however, copepod-associated BCC differed with each alga fed, even though the same bacterial source was used to inoculate the algae. In addition, starved copepods taken at the same location but at different times significantly differed in their BCC. Algal species composition and copepod life history therefore serve to regulate BCC associated with copepods, and spatial and temporal variations in algal species composition and copepod origin would alter bacteria–copepod interactions.     

Seasonal and fine-scale spatial variations in egg production and triacylglycerol content of the copepod Acartia tonsa in a river-dominated estuary and its coastal plume

We measured egg production rates of the estuarine calanoid copepodAcartia tonsa in Mobile Bay, an estuary in the northern Gulfof Mexico. Two stations were sampled approximately monthly,one at the mouth of the bay and the other just beyond the mouthin the salinity front between bay and coastal waters. Over thewhole year, temperature was the most important environmentalvariable controlling egg production. Rates increased with temperatureup to 30°C and 140 eggs female^–1 day^–1. We foundno evidence of food limitation. There was no correlation betweenegg production and phytoplankton abundance, nor increased eggproduction in response to supplements of phytoplankton addedto natural food, suggesting that non-phytoplankton food wasimportant in the diet. At the highest egg production rates,the amount of the storage lipid triacylglycerol (TAG) in adultfemales was greatly diminished, to <50 ng female^–1.This suggests that lipids in the diet can be very tightly coupledto egg production. Both egg production and TAG content of femalesshowed significant variability on spatial scales of 3–15km, especially in relation to the salinity front separat ingwater outwelling from the bay from open coastal water. For organismsthat are using copepods and their eggs as food, this variabilitywould result in a heterogeneous food environment, both in termsof the abundance of food and its nutritional content.     

Seasonal cycles in population abundances and egg production rates in the planktonic copepods Centropages typicus and Acartia clausi

Laboratory studies on the seasonal cycling of egg productionrates for Centropages typicus and Acartia clausi did not reflectseasonal changes in densities for these species at sea. Maximumegg production rates occurred from autumn to spring when populationabundances at sea were low. In late spring, an increment inpopulation numbers was followed by a drastic decline in eggdeposition which continued into summer. The percentage lossdue to mortality, calculated using egg data and total numberof copepodid stages CIII and CIV recorded at sea {small tilde}2weeks later, indicated greatest mortality (80–99%) fromeggs to copepodids during periods of high breeding intensity.These results suggest that high and low density phases in populationnumbers may be the outcome of variations in reproductive potentialand survival rates of eggs and immature stages rather than reproductivepotential per se.     

Evidence for hyporegulation in the calanoid copepod,Acartia tonsa

• 1.1. The euryaline calanoid copepod, Acartia tonsa, maintains haemolymph Na below that of the external medium in salinities above 34^o_oo (475 mM Na).
• 2.2. The measured transepithelial electrical potential. −9.97 ± 1.0 mV, indicates that Na is regulated out of electrochemical equilibrium.
• 3.3. Water osmotically lost in hyporegulation is replaced by Na-dependent absorption by the gut.
• 4.4. High osmotic water permeability is evidenced by the fact that with an increase in external salinity from 475 mM Na to 580 mM Na the copepod's drinking rate nearly doubles.
• 5.5. Sodium efflux measurements indicate that ionic permeability is much lower than other hyporegulating crustaceans.
• 6.6. The energetic advantage of hyporegulation in this species is considered.

     

Feeding,egg production,and egg hatching success of the copepods Acartia tonsa and Temora longicornis on diets of the toxic diatom Pseudo-nitzschia multiseries and the non-toxic diatom Pseudo-nitzschia pungens

In 1987, there was an episode of shellfish poisoning in Canada with human fatalities caused by the diatom Pseudo-nitzschia multiseries, which produced the toxin domoic acid. In order to examine whether domoic acid in this diatom serves as a grazing deterrent for copepods, we compared feeding rates, egg production rates, egg hatching success and mortality of the calanoid copepods Acartia tonsa and Temora longicornis feeding on unialgal diets of the toxic diatom P. multiseries and the similarly-sized non-toxic diatom Pseudo-nitzschia pungens. Copepods were collected in summers of 1994, 1995 and 1996 from Shediac Bay, New Brunswick, Canada, near Prince Edward Island, the site of the 1987 episode of domoic acid shellfish poisoning. Rates of ingestion of the toxic versus the non-toxic diatom by A. tonsa and T. longicornis were similar, with only one significantly different pair of values obtained in 1994, for which A. tonsa had a higher mean rate of ingestion of the toxic than the non-toxic diatom. Thus, domoic acid did not appear to retard grazing. Analyses of copepods with high performance liquid chromatography (HPLC) revealed that copepods accumulated domoic acid when feeding on P. multiseries. Egg production rates of copepods when feeding on P. multiseries and P. pungens were very low, ranging from 0 to 2.79 eggs female^–1 d^–1. There did not appear to be differential egg production or egg hatching success on diets of the toxic and non-toxic diatoms. Mortality of females on the toxic diet was low, ranging from 0 to 20%, with a mean of 13%, and there was no apparent difference between mortality of copepods feeding on toxic versus non-toxic diatoms. Egg hatching success on both diets, although based on few eggs, ranged between 22% and 76%, with a mean percentage hatching of 45%. Diets of the non-toxic diatom plus natural seawater assemblages supplemented with dissolved domoic acid, revealed similar rates and percentages when compared to previous experiments. In summary, none of the variables measured indicated adverse effects on copepods feeding on the toxic compared to the non-toxic diatom.     

Cryptic ecological diversification of a planktonic estuarine copepod, Acartia tonsa

The recent discovery of cryptic species in marine holoplankton, organisms that 'drift' in oceanic currents throughout their life cycle, contrasts with their potential for long-distance passive dispersal and presumably high gene flow. These observations suggest that holoplankton species are adapting to surprisingly small-scale oceanographic features and imply either limited dispersal or strong selection gradients. Acartia tonsa is a widespread and numerically dominant estuarine copepod containing deep mitochondrial lineages within and among populations along the northwestern Atlantic coast. In this study, we intensively investigated A. tonsa populations in Chesapeake Bay with the goals of testing species status for the deep lineages and testing for their association with environmental features over space and time. Phylogenetic analyses of DNA sequences from mitochondrial cytochrome c oxidase I (mtCOI) and the nuclear ribosomal internal transcribed spacer (nITS) resolved two concordant monophyletic clades. Deep divergence between the two clades (13.7% uncorrected sequence divergence for mtCOI and 32.2% for nITS) and genealogical concordance within sympatric populations strongly suggest that the two clades represent reproductively isolated cryptic species. Based on restriction fragment length polymorphisms of mtCOI, representatives from the two clades were found consistently associated with contrasting salinity regimes (oligohaline vs. meso-polyhaline) with an overlap between 2 and 12 PSU in samples from 1995 to 2005. Finding these patterns in one of the best-known estuarine copepods reinforces the conclusion that marine biodiversity is underestimated, not only in terms of species numbers, but also with respect to niche partitioning and the potential importance of ecological divergence in marine holoplankton.     

Observations on egg production rates and seasonal changes in the internal morphology of Mediterranean populations of Acartia clausi and Centropages typicus

Egg production rates in wild populations of Acartia clausi and Centropages typicus, sampled biweekly in the Gulf of Naples from October 1985 to July 1987, showed marked seasonal fluctuations with maximum values in early spring that proceeded the annual maxima for adult female densities in summer. A positive correlation between chlorophyll a concentrations and egg production was evident only during the early spring phytoplankton bloom. A strong diminution in egg deposition occurred later in spring and continued throughout the summer notwithstanding high chlorophyll concentrations. In winter, when population abundances for adult females were lowest, egg production rates were always higher than in summer. Differences in egg production rates coincided with pronounced morphological changes between summer and winter populations of both species. The most striking of these changes consisted, in winter, in the presence of a dark brown fluid-like mass of granular material that seemed to freely bathe the gonads. The presence of this substance only during periods of elevated egg production suggests that it may enhance egg production rates when the adult population reaches minimum annual levels. Such a mechanism of self-regulation may operate to dampen the effects of environmental variability thereby contributing to maintain a conservative structure in coastal copepod communities.     

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.     

Gut clearance and pigment destruction in a herbivorous copepod, Acartia tonsa, and the determination of in situ grazing rates

Gut clearance rates of starving and continuously feeding Acartiatonsa were estimated. During the initial 30 min the rates weresimilar (0.045 and 0.048 min^–1, respectively; 14°C)but thereafter starving animals expelled the remains of theirgut contents at half the rate (0.019 min^–1) of fed ones(0.048). Pigment destruction was estimated by (i) incubationexperiments over 3–4 days, (ii) silica to pigment ratioin algae and faeces and (iii) by gut filling experiments. Theincubations showed that 8% of the ingested pigments were destroyedto nonfluorescent residues during gut passage. The silica topigment ratio method gave an average of 11 % (1 –24) destructionand gut-filling experiments showed no systematic differencebetween ingestion measured as gut filling rate (fluorescence)and particle reduction. ¹Present address: Kristineberg Marine Biological Station, S-45034 Fiskebäckskil, Sweden     

Reproductive trade-off of the copepod Acartia tonsa in a hypersaline estuary of the Southwestern Atlantic. Temporal variations in the morphology of eggs

The purpose of the present work was to study the seasonal variations in egg production, morphology and hatching success in the cryptic species Acartia tonsa, taking into account variations in female size, population abundance and environmental factors in a turbid and hypersaline estuary. Sampling was performed during the austral warm (18–23°C and 32–36 salinity) and cold seasons (5–7°C; 32–38) in Bahía Blanca Estuary (BBE), Argentina, during 2007 and 2009. Field-collected females were incubated in the laboratory simulating in situ environmental conditions, and specimens from fixed samples were measured using optical and scanning electronic microscopy. Acartia tonsa’s marked seasonality in its reproductive traits was found to ensure its permanence in the water column all over the year. During the warm season, small-sized females were observed to invest their energy in the production of subitaneous eggs with high hatching success and smooth appearance (12.95?±?2.38 eggs f^?1 day^?1 and specific egg production rate (SEP) of 16.57%C f^?1 day^?1). During the cold season, females invested C in body mass as well as in the production of resting eggs of three different morphotypes (6.56?±?3.2 eggs f^?1 day^?1 and SEP of 7.37%C f^?1 day^?1). Although these morphotypes were found to show differences in surface ornamentation, they exhibited the same delayed hatching behaviour. The eggs with shorter spines were found to integrate the resting egg bank in BBE. Our findings confirming a delayed egg hatching behaviour and a great tolerance to low temperatures and high salinities in the A. tonsa population in BBE suggest that this possible strain is a valuable phenotype for aquaculture.     

Turbulence decreases the hydrodynamic predator sensing ability of the calanoid copepod Acartia tonsa

The copepod Acartia tonsa is very sensitive to hydrodynamicsignals, including those made by approaching predators, andresponds with a vigorous escape jump. Whether the presence ofmoderate turbulence changes this ability to detect hydrodynamicsignals was investigated by comparing the response of copepodsto velocity gradients created by a siphon flow in turbulentand still water. Turbulence decreased the distance at whichA. tonsa initiated escapes from the siphon and increased thecapture rate, indicating decreased sensitivity to hydrodynamicsignals, but did not trigger unnecessary escape reactions thatmight produce fatigue.     

Nitrogen excretion by the calanoid copepod Acartia tonsa: results of mesocosm experiments

Rates of excretion of NH₄⁺ urea and dissolved primary amines(DPA) by Acartia tonsa were measured over two 24-h periods inestuarine mesocosms. Animals (     

Occurrence of human-associated yeasts in bivalve shellfish from Long Island Sound.

Candida parapsilosis, C. tropicalis, and Torulopsis glabrata were the human-associated yeasts most frequently isolated from quahogs, oysters, and mussels collected from four estuarine areas along the northern shore of Long Island Sound. Some inconsistency and seasonal variation in the occurrence of these and other yeast species were noted. In particular, C. albicans densities were greatest during colder months in the more heavily polluted waters. A total of 347 yeasts were isolated and cultured at 37 degrees C and, of these, 219 of 62% were human-associated forms. Generally, these yeasts in the animals sampled reflected the overall pollution status of the estuary from which they were taken. This study represents a clear demonstration of potentially pathogenic yeasts in a valuable marine resource.