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Existing viewpoints and theories of selective grazing by copepods are briefly reviewed in order to formulate explicit hypotheses to be tested experimentally. Based on these hypotheses, a series of grazing experiments was run to determine (1) the extent of the selective ingestion capabilities of Acartia clausi and (2) how these capabilities were affected by previous feeding histories. Groups of copepods were separately preconditioned on a small diatom (Thalassiosira pseudonana), a large diatom (T. fluviatilis), or a plastic sphere. The ingestive behavior was then examined on various combinations of spheres and food particles. Spheres offered alone were not ingested. In mixtures of diatoms and spheres, the copepods avoided ingesting spheres intermediate in size between the sizes of the diatoms. The copepods either ingested particles on either side of the spheres, or ignored all particles less than the size of the largest spheres. The pattern observed depended upon the size of the preconditioning food. However, if the spheres were larger than the largest food particles, the copepods still selectively ingested the food particles. The above results demonstrate that A. clausi has a complex grazing behavior consisting of (1) more efficient grazing on larger particles within its particle-size ingestion range; (2) the ability to alter “effective” setal spacing to optimize feeding behavior (i.e., the ability to increase efficiency of capture of food particles, and to avoid non-food particles); and (3) the ability for post-capture rejection of non-food particles when they interfere with the ingestion of food particles on which the copepod has been preconditioned. The behavioral patterns observed depend heavily on the food preconditioning and the presence or absence of non-food particles. These results clearly indicate that a simple “mechanistic” explanation of selective grazing is insufficient.

Association between copepods and bacteria was observed in many scanning electron micrographs. Particular sites on the copepods were selectively colonized by bacteria; the joints of segments and legs, swimming legs and depressed parts of the body surface were found to be densely covered with bacteria. In comparison, bacterial attachment to copepod skeletons in fecal pellets excreted by chaetognaths was not selective; bacteria were sparsely found all over the copepod. Between 9 to 30% of copepods in Tokyo Bay waters had attached bacteria in January and April 1983.

The chaetognath Sagitta crassa Tokioka, which is abundant in Tokyo Bay, may seize and ingest several copepods within the space of a few minutes under laboratory and natural conditions. This chaetognath consumed about a third of its daily ration within 2 h after receiving a supply of food. After partial ingestion of a copepod, S. crassa occasionally relinquished its prey, which was immobile and appeared to be paralyzed. Large numbers of bacteria were found on the exoskeleton of a released copepod, instead of the expected holes from piercing by chaetognath teeth. S. crassa had a mean digestion time of 2.2 and 2.8 h for Acartia clausi Giesbrecht and Tigriopus japonicus Mori, respectively. The digestive efficiency of Sagitta crassa was determined gravimetrically and it ranged from 56 to 93%, depending on the food items, with a mean of 83%.

Over a period of about 3 years, 120 quantitative zooplankton samples were taken at five stations of the Valli of Comacchio, a wide shallow-water lagoon system of the north Adriatic Italian coast which has seasonally limited manregulated communications with the sea. The high density of the meroplanktonic forms and the prevalence of phytal copepods, mainly harpacticoids, over the typical euplanktonic ones, such as calanoids, are the main characteristics of the zooplankton assemblages of these lagoons. Acartia clausi , the only representative marine calanoid, was a passive immigrant in the valli. The zooplankton structure showed striking analogies with that of similar brackish environments lacking in free water exchanges with sea, e.g. the ‘dead’ Lagoon of Venice. Statistical analyses carried out on density data assessed significant differences between mean station densities of total zooplankton, polychaete trochophores and copepod nauplii. A significant year-station interaction variance for phytal harpacticoids was detected. The main source of variability of the zooplankton was represented by strong seasonal fluctuations of the various systematic groups which resulted in a fairly characteristic and recurrent pattern of their occurrence year by year.

Carbon, hydrogen and nitrogen content were investigated in natural populations of the crustacean copepod Acartia clausi collected during 1980–1982 from different areas near Marseilles, France — the coastal area of Cortiou which receives waste waters from the Marseilles Conurbation; the eutrophic and polluted Golfe de Fos, with its open basins; and the offshore areas of the Marseilles' Gulf. Energy equivalents were determined in order to examine the ecological role of A. clausi from a bioenergetic point of view. Carbon content ranged from 38.9% of body dry weight (DW) in the open sea off Marseilles to 45.5% of DW in an open basin at Fos in winter, nitrogen content from 10.4% of DW in the open sea off Marseilles in winter to 13.6% of DW in the open basins at Fos in summer. These values agree with the ranges reported in the literature for non-lipidic copepods. Carbon to nitrogen ratios ranged between 3.22 and 3.80. In the open basins at Fos, the mean value in summer (3.30) was significantly different from that in winter (3.70). In the Cortiou area, no seasonal differences emerged. For the three areas, energy equivalents ranged from 4.28 to 5.00 cal mg-1 DW. Highest values were recorded for the populations of the Cortiou area and of the open basins at Fos, i.e., from environments where particulate organic matter is abundant and relatively invariable. In these populations, the energy equivalent per unit dry weight did not change significantly throughout the year. The values recorded agreed with the means reported in the literature for non-lipidic species, but were far below those recorded for species which are able to store lipids. A. clausi is one of the most abundant copepod species throughout the year in the plankton of these coastal areas, and its steady energy content, with little seasonal variation, makes it an important element in the bioenergetics of the northwest Mediterranean coastal ecosystems.

The seven species of small copepod common in Loch Striven have been studied from vertical tow-net hauls taken there throughout the year 1933. These copepods were Pseudocalanus minutus, Paracalanus parvus, Microcalanus pygmaeus, Centropages hamatus, Temora longicornis, Acartia clausi and Oithona similis.In general, the copepods began to reproduce about the time of the spring diatom increase in March or April, and produced a succession of broods throughout the summer; apart from the first these broods were not as a rule so clearly marked as in Calanus. Microcalanus begins to breed before the spring increase and has clearly marked broods like Calanus.

The life histories of the small planktonic copepods of Plymouth were studied during 1947. The samples were taken at Station L4 with Harvey measuring nets, and are thus truly quantitative.The main species concerned were Pseudocalanus elongatus, Paracalanus parvus, Centropages typtcus, Temora longicornis, Acartia clausi, Oithona similis, O. nana, Oncaea venusta and Corycaeus anglicus.The species common in summer—all but the last three of the above—behaved in a very similar way, producing probably five generations in the course of the year, but differing from each other in the relative and absolute abundance of the different stages at different times of the year.

1. The development times to hatching of eggs of several kinds of copepods were studied at controlled temperatures. Data are analyzed from several geographical populations of Pseudocalanus minutus, a large form of Pseudocalanus, Calanus finmarchicus, C. glacialis, Acartia clausi, and Tortanus discaudatus.2. Belehraek's temperature function, expressed as D = a(T - α)b, where D is development time, T the temperature, and α, a and b are constants, was fitted to the results. Assuming that b is the same ( - 1.68, the mean of fitted values) for all species results in several regularities.3. The scale correction or "biological zero" α varies little within species, but seems positively related to environmental temperature. C. glacialis, with the most northerly range, has the lowest value of α, and A. clausi and T. discaudatus, which are the most southerly, have highest values of α. Temperature adaptation per se may be considered in relation to this parameter alone.4. The proportionality coefficient a varies signif...

Seasonal variations appeared in the metabolism-temperature curves of Centropages typicus, Temora stylifera, Acartia clausi and Calanus helgolandicus . The respiration rate was higher during the cold season than during the hot season. The Q 10 between 10° and 18°C was higher under warm conditions. Between 10° and 14°C, it was higher during the cold than during the hot season; reversal conditions appeared between 14° and 18°C. A temperature adaptation by a process described by Bullock seems the principal cause of the observed variations. On the other hand, the succession of different generations appeared to be responsible for temporary changes in the respiratory level and in the Q 10 .

1. The most noticeable response of marine plankton to light, under laboratory conditions, is the formation of groups on the lighted (or opposite) side of the vessel containing them.2. Specimens from such groups were tested under different conditions of illumination, and in all cases they moved in thedirectionof the light quite irrespective of accompanying changes ofintensityin the surroundings.3. Groups form around the line of direction of the light, or the resultant direction when the light is scattered or falling from more directions than one, this being the direct result of individuals moving along the mean path of incidence of the light.4. The behaviour of individuals was examined more closely to distinguish between the two possible ways in which the directed movement could have been brought about, viz. (i) reactions to bilateral inequalities of illumination (here called “true topotaxis”), and (ii) reactions to changes in total illumination of light-receptors (a type of “phobotaxis”). For a number of species it was clearly a case of “true topotaxis,” and very probably for at least the majority of the rest.5. In two very different cases, namely,Acartia clausiandPoecilochaetus serpens, there was no orientation of the body, but nevertheless efficient orientation of the path of movement. It is believed that this is the first occasion on which such behaviour has been described.6. The observations described point to the fact that movement in the direction of incidence of the light, however this may be affected, is general among a wide range of the smaller, free-living, bilaterally symmetrical, marine animals, and would tend to dominate other possible response to light. This behaviour on the part of individuals provides a substantial basis for attempted explanations of the correlations, that have been demonstrated by ecological workers, between the vertical distribution of populations and light-intensity.

Respiration and nitrogen-excretion studies were carried out on several species of zooplankton (Meganyctiphanes norvegica, Phronima sedentaria, Acartia clausi and Sagitta setosa) under starvation. Although all the species were mainly ammonotelic, apparently a significant amount of organic nitrogen was excreted; the validity of the measurements and their significance are discussed. The effect of duration of starvation showed for M. norvegica and A. clausi two different patterns of behaviour, which were chiefly a function of the rate of biomass turnover of the species studied. The rates of metabolism, chemical composition, and reaction to starvation varied with season in M. norvegica. The physiological balance of the experimental animals was examined by calculating the protein carbon equivalent to respiratory and excretory catabolism, and by use of atomic O:N ratios. Starved individuals catabolized more protein carbon than can be accounted for by the amount of respiratory oxygen utilized. A hypothesis, which suggests that there are three levels of resistance to starvation, is proposed to explain this paradox, and its metabolic basis is discussed.

Fatty acid composition of the plankton in Narragansett Bay, Rhode Island, varies in relation to the seasonal succession and productivity of populations. The ratio of palmitoleic acid to palmitic acid declines during vernal warming from 2.0 to ca. 0.3, reflecting the change in dominance from diatoms to flagellates. In the zooplankton, the ratio is twice as high in Acartia clausi, the winter dominant copepod, as in the summer species, Acartia tonsa. Palmitoleic acid and palmitic acid vary reciprocally throughout the year; so do oleic and stearidonic acids. If palmitic and oleic acids, the less saturated members of each covariate pair, arc related by multiple linear regression to zooplankton standing crop, 52% of the variation over an annual cycle is explained. During a poor year for Calanus finmarchicus in Rhode Island Sound, the fatty acids vary independently of each other, in agreement with previous findings for free amino acids.

In marine plankton, the patterns of seasonal succession and free amino acid composition reveal several features in common. Fret amino acid levels are generally higher in summer than in winter communities: major changes occur during periods of community change in late spring and early winter, These levels also appear to be an index of physiological condition and productive capacity. The variations arc quantitative in terms of concentration per unit tissue weight; relative compositions are the same in both the summer and the winter dominant copepods ( Acartia tonsa and Acartia clausi). Factor analysis reveals an extremely high degree of intercorrelation within the free amino acid pools. The phytoplankton-microzooplankton, consisting primarily of diatoms and larval crustaceans in varying proportions, has greater consistency of quantitative change (one amino acid in relation to all others) than does the zooplankton. Furthermore, the amino acid communality of an estuarine phytoplankton-microzooplankton community is surprisingly high.

Investigation of the food of larval and post-larval fish from the townets has been continued throughout the year (1918) in the same way as previously, by examining the contents of stomach and intestine in the fresh state. From May 24th a new big net made of stramin, with a wooden frame 36 inches by 25 inches, was used in addition to the ordinary tow-nets. Any live specimens, and these were chiefly caught in the big net, were kept in small aërated aquaria standing in running water and fed with plankton in order to see, when possible, what food they ate. In this way a few post-larval fish went through the metamorphosis into the adult form. Details of these will be found in another paper in the same number of the Journal (page 9).The tow-nettings were regularly examined by Miss Webb in order to see whether the fish were feeding on what was commonest at the moment, and this was found to be usually the case, so far as the Copepods were concerned, although most of the young fish seemed to select their food to a certain extent. In any month the Copepods which are at that time commonest in the plankton are those most eaten by the young fish, but most of them have preferences and select in various degrees. Thus in June Calanus finmarchicus and Acartia clausi were the commonest Copepods, Temora longicornis coming next, Pseudocalanus elongatus and Oithona similis not occurring so frequently. The commonest young fish in the tow-nets in the same month were the Whiting, Pollack, Rockling and Ballan Wrasse (Labrus bergylta).

When adult females of Calanus pacificus are fed on monospecific cultures of centric diatoms which grow as single cells, a predictive relationship is found between feeding behavior of the copepods and size and concentration of food particles. Ingestion rate of copepods increases linearly with cell concentration up to a maximal rate. This maximal ingestion rate, expressed as carbon, is the same for copepods feeding on diatoms ranging in diameter from 11–87 µ. As the size of food particles increases, the carbon concentration at which this ingestion rate is achieved decreases. Thus females of C. pacificus can obtain their maximal daily ration at relatively low carbon concentrations of large cells.

Seasonal abundance, biomass, and taxonomic composition of copepods in El-Mex Bay (Southeastern Mediterranean region) were studied from autumn 2011 to 2012. Most species within the copepod communities displayed a clear pattern of succession throughout the investigation period. Generally copepods were the predominant group. They contributed numerically 57% of the total zooplankton counts with an average of 5083 organisms/m 3 and a total number of 203,333 individuals. The bay harbored 50 species belonging to 28 genera within 19 families and 4 orders under one class. Calanoids were represented by 24 species which formed 31.6% of total copepods predominantly Acartia clausi , Calocalanus pavo , Clausocalanus furcatus , Eucalanus crassus , Nannocalanus minor , Paracalanus parvus , Eucalanus subcrassus , and Temora longicornis . Cyclopoids comprised 13 species of which Acanthocyclops americanus , Halicyclops magniceps , Oithona attenuata , and Oithona nana were the most abundant adult copepods. Eleven Harpacticoid species were also recorded with Euterpina acutifrons , Microsetella norvegica , Onychocamptus mohammed being the most prevalent. It was found however, that two Poecilostomatoida species were rarely encountered in the plankton Oncaea minuta and Corycaeus typicus . Copepod larvae and copepodite stages formed the main bulk of copepod Fauna as noticed in the El-Mex Bay during the investigation period. Their percentage was 36.7% of the total count and their total numbers were 74,629 individuals with an average of 1866 organisms/m 3 . The persistent relationships between total copepod counts, copepod orders, and physico-chemical variables suggested that physical factors operate on the copepod communities, either directly to limit maximum distribution along the bay, or indirectly on abundance.

In laboratory experiments, mixed populations of two marine copepods (Acartia clausi and Eurytemora herdmani) when fed artificial food particles consisting of microcapsules that were either enriched with an encapsulated homogenate of naturally occurring phytoplankton or nonenriched preferentially ingested the enriched capsules. Beads or nonenriched capsules were either seldom ingested or not ingested at all. The observations demonstrate that filter-feeding in these species is a behavioral process, under sensory control, and that the copepods are able to discriminate between enriched and nonenriched food particles.

Twelve trace elements (antimony, arsenic, cadmium, chromium, cobalt, copper, iron, managenese, mercury, scandium, selenium and zinc) were determined by neutron activation analysis in a planktonic copepod ( Acartia clausi ) from Elefsis Bay of the Upper Saronikos Gulf, Greece. During the first cruise (January 1974) higher levels of most of these trace elements were found in this copepod collected from a polluted area of the bay. This trend however was not observed during the second cruise (February 1974) possibly due to the termination of the active vertical convection. Lower levels of cobalt, similar levels of iron and slightly increased levels of chromium were found in Elefsis Bay Acartia clausi from those reportedin Acartia clausi from the Bay of Roquebrune. Slightly increased concentrations of antimony and zinc as well as lower concentrations of arsenic and cadmium were found in Acartia clausi than those reported in other Copepoda. No significant differences were found for copper, manganese and mercury. More data are needed to confirm if higher levels of antimony, chromium and zinc found in Acartia clausi are due to the pollution of the bay.

Toxicity of heavy metals to marine organisms is a subject of interest because, due to technological development, the sea receives an increasing amount of heavy metals. Acute toxicity studies have played a major role in estimating the effects of heavy metals to marine organisms because survival is considered the best index of a pollutant stress, being in general the least variable. However, long term exposure to sublethal concentration of a pollutant may markedly alter the normal functioning of organisms and thus destroy a population as effectively as lethal doses. Therefore, the study of the effects of sublethal doses is indispensable if we want to set realistic standards of water qualtiy criteria. The purpose of this study was twofold: first to establish and characterize the sublethal effects of cadmium on different physiological processes (longevity, feeding, respiratory rates), and second to verify whether there exist differences in the effects of sublethal concentrations of cadmium between the two populations of Acartia adapted to differently polluted areas.

The two estuarine systems composing San Francisco Bay have distinct zooplankton communities and seasonal population dynamics. In the South Bay, a shallow lagoon-type estuary, the copepods Acartia spp. and Oithona davisae dominate. As in estuaries along the northeast coast of the U.S., there is a seasonal succession involving the replacement of a cold-season Acartia species (A. clausi s.l.) by a warm-season species (A. californiensis), presumably resulting from the differential production and hatching of dormant eggs. Oithona davisae is most abundant during the fall. Copepods of northern San Francisco Bay, a partially-mixed estuary of the Sacramento-San Joaquin Rivers, organize into discrete populations according to salinity distribution: Sinocalanus doerrii (a recently introduced species) at the riverine boundary, Eurytemora affinis in the oligohaline mixing zone, Acartia spp. in polyhaline waters (18–30‰), and neritic species (e.g., Paracalanus parvus) at the seaward boundary. Sinocalanus doerrii and E. affinis are present year-round. Acartia clausi s.l. is present almost year-round in the northern reach, and A. californiensis occurs only briefly there in summer-fall. The difference in succession of Acartia species between the two regions of San Francisco Bay may reflect differences in the seasonal temperature cycle (the South Bay warms earlier), and the perennial transport of A. clausi s.l. into the northern reach from the seaward boundary by nontidal advection.

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 preceeded 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.

Zooplankton was collected as part of a biological investigation of the Eskimo Lakes and Liverpool Bay, the first study of its kind carried out on one of the major estuaries in the Canadian arctic. Of the 43 zooplankton species found in the system, copepods, polychaete and cirripede larvae, and rotifers were the most abundant. Principal component analysis showed five geographical groups of stations in the estuary, which was dominated by the character of the inflowing waters at both extremities, and in which salinity and water source were the strongest determinants of zooplankton composition. Essentially freshwater species originating in waters which feed the head of the system dominated at the innermost stations. Marine species from the Beaufort Sea prevailed at the outermost stations. The most abundant copepods in the system, Acartia clausi, Eurytemora herdmani, Pseudocalanus sp., Limnocalanus macrurus and Drepanopus bungei, occurred widely but reached maximum numbers in different parts of the estuary. The annual cycle of standing stock is one of extreme seasonality, with biomass peaks occurring in mid-summer. A mean annual biomass of 80 mg (wet weight) per m3 represents an especially low standing stock. This and the additional factors of low primary productivity and phytoplankton standing stocks suggest extreme oligotrophy within the estuary.

1. 1. The copepod Acartia clausi exhibited two laminarinases (exo- and endo-acting forms) purified by gel chromatography followed by affinity chromatography. Specific antibodies have been raised against the purified exolaminarinase antigen. 2. 2. A single band of protein appeared on a polyacrylamide disc gel electrophoresis; its mol. wt is 21,000. 3. 3. Biochemical properties of the purified enzyme showed a maximum activity at pH 5.2 and a temperature of 40°C with laminarin as substrate. The thermal stability of the enzyme and the effect of various cations on its activity were examined. The enzyme hydrolyses specifically the β(1–3) linked polysaccharides and had no activity against the α(1–4) or β(1–4) disaccharides or polysaccharides. 4. 4. The kinetic parameters Vm and Km vary with the temperature; the affinity constant (Ka) was maximum between 25–30°C. The Arrhenius plot defined two values of energy of activation: 7980 cal/mole and 17,506 cal/mole. 5. 5. From the purification scheme the exoacting form appears to be largely dominant over the endoacting form.

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Diel changes in the particulate environment and nutritional metabolism of neritic zooplankton were studied in the Bay of Villefranche-sur-mer (France) for 30 h during February. Although the survey was carried out over a period of negligible wind speed, the changes in the particle size spectra and species composition of the Zooplankton sampled suggested an abrupt and temporary oscillation in the water mass at the second sampling time. The rest of the 30-h period was characterized by gradual changes which usually returned to conditions close to, but different from, the starting ones. A clear diel rhythm was recorded for the biochemical composition of the phytoplankton, probably related to the periodicity of the photosynthetic metabolism. The feeding rate of Clausocalanus arcuicornis Giesbrecht, 1888, measured by gut fluorescence, also showed diel rhythmicity with maximum rate at night. Digestive enzyme activities were measured on the total Zooplankton population composed of five major species: Clausocalanus arcuicornis, Paracalanus sp., Calanus helgolandicus Claus, 1863, Acartia clausi Giesbrecht, 1889, and Oikopleura dioica Fol, 1859. The activities of the carbohydrases showed varying patterns of periodicity with one or two night maxima. The proteases showed a different pattern with acidic proteases peaking just before dawn and decreasing gradually during the day and no periodicity for trypsin-like activity. No association could be established between the enzyme changes and those of either the food supply or the species composition of the Zooplankton sampled, suggesting that both feeding and digestion diel rhythms are controlled by an internal clock. Influences of internal, external and experimental factors on the digestive enzyme activity rhythm are discussed. The resulting scheme of short term regulation was compared with that proposed earlier for medium term changes.

Biomass and metabolic rates (total nitrogen and phosphorus excretion and respiration) were measured at 4 stations, representative of the lagoon environment, during high-water (Oct-Nov), dry (Dec-Jan) and rainy (July) seasons. In low-salinity waters (4o/oo) Acartia clausi is almost the only species, whereas a marine and diversified fauna is brought in from the ocean during the dry season. O/NT and O/PT atomic ratios between respiration (O) and total nitrogen (NT) and phosphorus (PT) excretions are high (15.1 and 111, respectively) and show a marked hydrocarbon feeding of zooplankton. Production was assessed from excretion via the net growth efficiency coefficient, K2 , calculated from N/P ratios for particles (a1), zooplankton excretion (a2) and constitution (a3). Daily productivity indices (i.e. daily production/biomass ratio) are high and equivalent to 1.2-3.8 day turn-over times. These high values may be ascribed to high temperatures (26.5-30 C) and phytoplankton richness (surface chlorophyll 'a' concentrations are always greater than 4 mg/m-3). Finally, the paper deals with trophic relationships between phyto- and zooplankton (ingestion /primary production ratio and transfer coefficient) and the question of relationships between zooplankton and predators.

Allen and Nelson1, who succeeded in keeping several Calanus alive for a few weeks in laboratory conditions, stated that it should be possible to rear Calanus in the laboratory without difficulty. Since then it has become apparent that the marine calanoid copepods are hard to rear and breed in laboratory conditions, and Crawshay2 has discussed some of the early difficulties. A. G. Nicholls (unpublished results) reared three adult female Calanus from eggs3, and Conover4 reared two adult female Calanus with considerable mortality. It is only recently, however, that marine calanoid copepods—Acartia tonsa Dana5 and Acartia clausi Giesbrecht6—have been bred through the first filial generation and beyond.

Field evidence is presented showing that hatching success in the copepods Acartia clausi and Calanus helgolandicus was greatly modified during 2 major late-winter diatom blooms in the North Adriatic (Mediterranean) Sea in 1997 and 1998 compared to post-bloom conditions in early sum- mer of 1997. In February of both years, diatoms represented >90% of the microplankton at all depths of inshore stations, and from 40 to 95% at different depths of offshore stations. The diatom blooms dif- fered between the 2 yr in that Skeletonema costatum (66.3%) and Pseudo-nitzschia delicatissima (23.2%) dominated in 1997, whereas the following February the bloom was almost entirely composed of P. delicatissima (80.6%). In June 1997, diatoms were much less abundant, even though they still comprised about 50% of the algal population at some of the more coastal stations; the diatom species composition in this period had shifted to a dominance of Chaetoceros decipiens and Dactlyliosolen fragilissimus. The population structure and vertical distribution of the copepods A. clausi and C. hel- golandicus were examined to determine the effects of these diatom blooms on population recruitment rates. A. clausi was the most abundant copepod sampled in June, constituting 47.7% of total copepod numbers, whereas low abundances were recorded in February 1997 (1.6%) and 1998 (1.8%). C. hel- golandicus numbers were also low in winter 1998 (0.82% of total copepod numbers). Egg production rates (EPR) for A. clausi were highest during the blooms, with values of 10.6 and 18.4 eggs female -1 d -1 in 1997 and 1998 respectively, compared to 6.2 eggs female -1 d -1 in June 1997. However the most dra- matic differences between bloom and post-bloom conditions were in terms of egg hatching viability, with mean values of 15.4 and 16.1% in February 1997 and 1998 respectively, as opposed to 89.1% in June. Fecal pellet numbers for females were highest in winter, indicating active feeding on diatoms. Total egg production rate (TEP, the product of EPR and total number of females m -3 ) was much greater in June (863 eggs m -3 d -1 ) than in February 1997 (17.6 eggs m -3 d -1 ) and 1998 (140 eggs m -3 d -1 ) due to the higher number of females in early summer. In turn, naupliar recruitment rates (TNR) were ex- tremely high in June (790.2 nauplii m -3 d -1 ) as opposed to February 1997 (2.8 nauplii m -3 d -1 ) and Feb- ruary 1998 (15.6 nauplii m -3 d -1 ). EPR for C. helgolandicus in February 1998 was low (9.7), with only 6.5% hatching viability. Values for TEP (54 eggs m -3 d -1 ) and TNR (4.7 nauplii m -3 d -1 ) were lower than for A. clausi. We conclude that the main factor responsible for reduced population recruitment rates of both species in winter was low hatching viability and that the bulk of annual recruitment in the North Adriatic Sea occurred in post-bloom conditions, since the mixed protistan community that succeeded the bloom was probably a better food source for copepod embryogenesis. The results are discussed in relation to laboratory findings on the toxic effects of diatoms on copepod reproduction.

In this study, marker pigments analysed in incubation feeding experiments and monthly amino acid composition (AAC, weight percentage of total amino acids yields) of copepods collected over 1 yr from the field were used to estimate the food niche of 4 co-occurring copepod species: Acartia clausi, Oithona nana, Temora longicornis and Euterpina acutifrons. Both marker pigments and AAC of copepods are good indicators of copepod food niche. Marker pigments are indicators of the autotrophic food ingested by copepods and AAC is an indicator of both autotrophic and non-autotrophic food needed by copepods to maximise reproductive success. Marker pigments showed that copepod species fed selectively on the phytoplankton community and that copepod species had different diets. A. clausi fed mainly on chlorophytes and diatoms, E. acutifrons on diatoms and chlorophytes, T. longicornis on dinoflagellates and diatoms, and O. nana on dinoflagellates and prymnesiophytes. Each copepod species had its own specific AAC and, furthermore, there was a significant relationship between similarity in AAC among copepod species and similarity in the phytoplankton classes ingested by them, indicating that the differences in the AAC among copepod species were due to different food resources. As a higher copepod reproductive success is observed when the AAC of the food is more similar to the AAC of the copepods, this selective feeding behaviour could be due to the necessity of a diet with an AAC balanced in an optimal proportion. The food niche partitioning observed in this study might contribute to the coexistence of these copepod species in their habitat., Sí

Secondary production of a congeneric species group of Acartia Dana, 1846, was estimated during a summer-autumn period (from June to October 1989) using a calculation based on the size-frequency distribution. Our study area was Malaga harbour (SE of Spain), a shallow (10 m depth) and semi-isolated ecosystem with restricted circulation. Acartia was the dominant copepod in the water column. Co-occurring species were Acartia grani, Acartia clausi, and Acartia discaudata var. mediterranea. Estimated average production was 29.12 mg dry wt m-3 d-1 (13.10 mg C m-3 3 d-1). The high values of chlorophyll concentration suggest that copepods can always find sufficient food for growth at maximum rate. The results obtained were similar to previous estimates for other Acartia species in coastal areas.

8 pages, 1 figure, 4 tables, The transfer of matter and energy in planktonic food webs is determined by the encounter rate between predators and prey and subsequent attack and capture success. We tested if differences in swimming behavior and escape ability of 2 planktonic ciliates could explain differences in their susceptibility to predation from the calanoid copepod Acartia clausi. We chose 2 similarly sized ciliates, which exhibited very different swimming behavior: Strobilidium spiralis (Strobilidiina) and Metacylis sp. (Tintinnina). Behavioral analyses were combined with feeding incubations. The behavior of S. spiralis was characterized by slow upward and downward swimming interrupted by sudden jumps. Metacylis sp. showed a swimming pattern typical for many tintinnids, with steep helical trajectories and without jumps. Feeding experiments while A. clausi was incubated in a 1:1 mixture of both ciliate species showed a higher predation rate on Metacylis sp. According to behavioral observations, the copepod exhibited a 2-fold difference in ingestion rate between the ciliate species. Furthermore, film analyses revealed that S. spiralis escaped the attacking predator with rapid jumps while Metacylis sp. lacked any effective behavioral response to the approaching predator. We discuss the relative importance of velocities and dispersal rates in encounter processes and conclude that the escape response shown by S. spiralis significantly reduces the risk of predation. This study emphasizes the importance of mechanistic knowledge at the level of behavior and individual sensory abilities to improve present models of biogeochemical fluxes in the water column

An entire population of the copepod Acartia tonsa in the Patuxent River, Maryland, was infested with a stalked protozoan of the genus Zoothamnium. Each copepod had 25 to 200 ciliates attached around the appendages. The infestation occurred at the time when Acartia tonsa was being replaced as the dominant copepod by Acartia clausi.

In tow-nettings from Plymouth Sound, June 20th, 1935, Acartia clausi were abundant and inside these copepods, emerging from them and free in the water were very large numbers of larval trematodes, easily identified as Hemiurus communis. This is not a new record, for this parasite has already been described from the same Copepod in Plymouth waters in May and February (Lebour, 1923), but it has always been rare. In no case have more than two parasitised specimens been seen from these regions, and no seasonal appearance has been noticed. Much has been written about these trematodes which grow in the bodies of copepods until they are of such a large size that they inevitably kill the host and just before it dies emerge from between the joints, if not eaten before this with the copepod, but I think this is the first time that they have been recorded in any quantity at one time. Since my first communication Steuer (1928) has written about the geographical distribution of these hemiurids parasitising copepods and is of the opinion that all those in Northern seas belong to Hemiurus lühei and H. communis. In the Mediterranean the hemiurids known have not yet been found in copepods but usually in Sagitta, or are found living freely in the sea and these probably belong to H. rugosus which lives in the adult state in the pilchard.

ONLY a fraction of the plant food captured by zooplankton is converted into growth ; the rest is lost through incomplete assimilation, excretion and metabolism. The net growth efficiencies, K2 (percentage of assimilated food converted into growth) for haloplanktonic animals such as Calanus and related copepod species are generally lower than the percentage of assimilated food lost in metabolism (100-K2. In terms of calories, values of K2 quoted in a recent review by Corner and Davies1 range from 23–58 for C. hyperboreus, from 6–55 for C. helgolandicus, and from 14–29 for Acartia clausi. There are few comparable estimates of growth efficiencies for meroplankton species, such as molluscan larvae, but the data that does exist suggests that the values of K2 are considerably higher than those for copepods. Jorgensen calculated a value for K2 of 73% for Mytilus larvae and values of 62% and 63% for two gastropod veligers2, and from short-term feeding experiments with Ostrea edulis Walne estimated that 68–80% of the total food assimilated by the larvae is utilized for growth3. During larval development the daily level of assimilated food declined from 56% to 29% of the body weight.

A study of the seasonal succession of dominant copepod species was conducted during the period May, 1972 to June, 1973 in the Navesink River estuary, a tributary of the New York Bight. The replacement of the copepod Acartia tonsa by Acartia clausi, a phenomenon well-documented in the middle Atlantic estuaries for the late winter and early spring seasons, was not observed during this study, indicating that this succession may not take place in the Navesink. Instead, the more brackish-water calanoids, Pseudodiaptomus coronatus and Eurytemora affinis replaced A. tonsa, increasing in numbers markedly as the A. tonsa population declined. Although A. clausi is known to occur in temperatures and salinities comparable to those of the Navesink, this study supports the results of Yamazi (1966) that the occurrence of A. clausi in the Navesink is a rarity.

Seasonal changes in phytoplankton biomass and production, total zooplankton biomass, and biomass and potential production rates of the two dominant copepods, Acartia hudsonica (formerly called Acartia clausi) and Acartia tonsa are described for several stations in Narragansett Bay, R.I. Plankton in the bay behaved as a single population with simultaneous changes occurring at the upper bay (Station 5) and the lower bay (Station 1). Phytoplankton biomass was higher in the upper bay ( $$\bar x$$ =16.95 mg chl a·m−3) than in the lower bay ( $$\bar x$$ =6.37 mg chl a·m−3) and these 0269 0101 V differences in biomass were reflected in the phytoplankton production rates. The zooplankton, which was dominated by A. hudsonica in the spring and early summer and A. tonsa during summer and fall, showed no such consistent differences between the stations. Mean A. hudsonica biomass (St 1, $$\bar x$$ ;=82.7 mg dry wt·m−3; St 5, _ $$\bar x$$ ;=95.2 mg dry wt·m−3) exceeded that of A. tonsa (St 1, $$\bar x$$ ;=56.7 mg dry wt·m−3; St 5, $$\bar x$$ ;=60.0 mg dry wt·m−3). Potential production rates of the two Acartia 0269 0101 V spp. were strongly temperature dependent. Despite the higher biomass levels of A. hudsonica, low temperatures resulted in lower potential production rates ( $$\bar x$$ ; St 1=7.25 mg C·m−3 day−1; $$\bar x$$ ; St 5=10.77mg C·m−3 day−1) and biomass doubling times of up to 9.6 days. Potential production rates of A. tonsa at summer temperatures were high ( $$\bar x$$ ; St 1=19.0 mg C·m−3 day−1; $$\bar x$$ ; St 5=22.9 mg C·m−3 day−1) and biomass doubling times were generally less than one day.

Measurements of cephalothorax length were made on females and males of Centropages aucklandicus, Acartia clausi, Paracalanus parvus, and Clausocalanus arcuicornis, and on female Calanus australis for the period from April 1964 to May 1965. Centropages aucklandicus and A. clausi increased gradually in length during autumn and winter to maximal size in the spring and were smaller again in summer. Paracalanus parvus was larger in spring and smaller the rest of the year. Calanus australis and C. arcuicornis were large in spring, but during summer they were also large on occasion, possibly because offshore populations had been brought into the area. Length-temperature-phytoplankton correlations showed that in temperate New Zealand waters with a relatively narrow temperature range the seasonal variations in length of all the copepods studied were significantly related to the annual phytoplankton cycle; temperature was an important factor for only two of the species. Some of the species measured are primarily herbivorous whereas others, such as Centropages and Acartia, are probably omnivores. Data are lacking for carnivorous copepods. However, since the spring bloom acts as a stimulus to zooplankton reproduction, it is suggested that all copepods that feed on living food might attain maximal size at around the time of the spring bloom in temperate waters with a relatively narrow temperature range.