Copepod Concentrations Research Articles

Laboratory rearing of marine calanoid copepods

Cohorts of 100 newly hatched (<48 h) Pseudocalanus sp. nauplii were reared to maturity in replicate in a flow-through apparatus at 5 ° C and four phytoplankton concentrations (200, 100, 50, and 25 μg carbon · 1−1). The life stage distribution of each cohort was measured by subsampling (nauplii) and silhouette photography (copepodids) at discrete intervals throughout the experimental period to determine the effect of food concentration on cohort development. The flow-through apparatus maintained constant paniculate carbon and nitrogen concentrations during the experiments. Silhouette photography eliminates the need to sacrifice animals so that rearing at field concentrations of copepods was possible. Phytoplankton were grown in chemostats which provided a simple means of maintaining sterile cultures for extended periods and a continual source of cells of constant chemical composition. A stock culture apparatus maintained source populations of copepods with only minimal handling.

Growth, food, and vulnerability to damage of the ctenophore Mnemiopsis mccradyi in its early life history stages

Newly hatched larvae of ctenophores are so delicate that they can be killed by copepods larger than nauplii. The larvae can withstand starvation for a week, but they need very high concentrations of nauplii to sustain rapid growth, and grow very slowly above 1 mm unless food of larger size is available. Over the first 7 days, larvae can double their weight seven times. Individual growth rate is extremely variable, even among the offspring of a single parent. Although newly hatched larvae have food in their guts &lt;30% of the time, a single food item (nauplius) of similar dry weight contains some 20 times more carbon than the ctenophore. As the larva grows, its consumption rate rapidly increases, the gut remaining full all the time, if food of larger size is available. These complex interactions of both high growth and high mortality of larvae are related to unnaturally high copepod concentrations in the laboratory. Patchiness in nature, however, at present ill defined quantitatively, may provide the explanation for the population’s success.

Potential effect of phytoplankton colony breakage on the calculation of zooplankton filtration rates

Substantial net production of short chains of the diatom Skeletonema costatum occurred in grazing experiments conducted with Acartia hudsonica (=A. clausi). A general model was then constructed to evaluate the influence of colony breakage during grazing on the calculation of zooplankton filtration and ingestion rates. Breakage can lead to either over-or underestimation of these rates. The magnitude of error is related to breakage probability, particle size distribution, size of the largest colonies, length of the experiment, copepod concentration and actual filtration rates. Size distributions similar to those described in the literature as manifestations of a complex selection for size and particle abundance can be generated by the grazing model under conditions of a uniform filtration rate accompanied by colony breakage. Unless the rate of breakage exceeds the rate of removal and causes net particle production, the occurrence of breakage may go undetected.

A preliminary study of zooplankton sound scattering layers in Balsfjorden: Structure, energetics, and migrations

Abstract An investigation of zooplankton generated Sound Scattering Layers (SSLs) using both echosounders and net sampling methods, was started in Balsfjorden, a Norwegian fjord situated within the Arctic circle, in April 1977. The results of some of the preliminary work over a 24 h period from 5–6 April are presented. Samples were taken in and out of the SSL with a Beyer's Low Speed Midwater Trawl, and demonstrated that the SSL was mainly due to concentrations of euphausiids, chaetognaths, and calanoid copepods. The results are also presented of analyses of dry weight, lipid, protein, carbon, nitrogen, ash, and caloric value showing that these factors were up to 30 times more concentrated in the SSL than outside it. The species composition and abundance of zooplankters in the SSL changed diurnally indicating the dynamic nature of the assemblage. Acoustic profiles taken with a 120 kHz precision echosounder, showed the SSL to have a text-book pattern of diurnal migration, apparently related to changes in incident and sub-surface radiation. Migration speeds of the SSL ranged from 8.1–24.2 m per h. Hydrography and phytoplankton are examined as possible factors influencing migration. The implications of zooplankton SSLs in fjords are considered in terms of ecological energetics as well as resource biology.

Red tide in the upwelling region of Baja California1

Predominant organisms in a red water dinoflagellate bloom during the seasonal onset of coastal upwelling off Baja California were Gonyaulax polyedra, Ceratium furca, and Gymnodinium sp. The major part of the chlorophyll and the 14C assimilation in the area was related to the G. polyedra population. The maximum concentration of these organisms was associated with low salinity water of the surface California Current. The dinoflagellates remained in the area during the 20‐day cruise, although the vertical stability coefficient was low, with no steep temperature gradient. The high concentrations of small copepods suggest them as major grazers of G. polyedra.

Preliminary results from the GATE acoustic echo sounder : MANDICS P. A. and F. F. HALL Jr., 1976. Bull. Am. met. Soc., 57 (9): 1142–1147

Meganyctiphanes norvegica (M. Sars) will feed upon the centric diatom Thalassiosira weissflogii (Grunow) G. Fryxell & Hasle but cannot fulfil its energy requirement for metabolism on this food. Its daily metabolic requirement can be exceeded when the euphausiid feeds upon the copepods Calanus finmarchicus Gunner or Centropages typicus Krøeyer, but not when feeding upon the smaller copepods Pseudocalanus spp. or Acartia spp. When feeding upon a natural copepod assemblage Meganyctiphanes norvegica requires high concentrations of copepods to achieve its metabolic requirements, suggesting that the euphausiid may exploit vertically patchy concentrations of prey. Short-term predation rates on Pseudocalanus spp. were also used to estimate feeding rates. Feeding in Meganyctiphanes norvegica appears to be adapted to a spatially variable food supply and rapid exploitation of food sources concentrated into patches or layers. The filter area of the feeding basket of M. norvegica is proportionally smaller than the filter area of Euphausia superba Dana, but has the same allometric length exponent. The filter area probably reflects the difference between the primarily carnivorous diet of Meganyctiphanes norvegica and herbivorous diet of Euphausia superba.

Das Mesozooplankton im Sylter Wattenmeer (Nordsee)

1. Abundance and biomass of the quantitatively most important zooplankters (>150 µm) were investigated in the wadden sea between the island of Sylt and the North Frisian Coast from March until November, 1972. Zooplankton screened from 10 l surface water samples twice daily was counted under the microscope and calculated zooplankton carbon was taken as biomass measure. 2. In spite of the large number of meroplanktonic larvae present, calanoid copepods(Acartia clausi, Centropages hamatus, Temora longicornis andPseudocalanus elongatus) dominated with an average of 85% (including copepodites) of the zooplankton biomass (7.4 µg Cl−1). The great fluctuations in copepod stocks were not related to hydrographical changes during summer and autumn. 3. The copepod concentrations recorded were about one order of magnitude higher than those published from neighbouring wadden sea and coastal waters using plankton nets. 4. Only from June to September, other zooplankton groups were of quantitative significance, mainly the polychaete larvae, which made up 15% of the zooplankton biomass from July to September. A mass occurrence of harpacticoid copepods was restricted to the beginning of June until the beginning of July. Appendicularians were abundant from July to September.

Copepod and chlorophyll a concentrations in receiving waters of a nuclear power station and problems associated with their measurement

Copepod and chlorophyll a concentrations were measured in the sea-water mixing zone of cooling water from a nuclear power plant and in a control area (containing no cooling water). No significant differences ( P < 0.05) were observed between the two areas for these parameters; however, it is known that about 70% of the copepods and 80–100% of the phytoplanktonic photosynthesis are eliminated in the 95 000 m 3/h of sea water entrained through the power plant. From the data collected, which consisted of five replicate plankton tows or chlorophyll measurements at each of four stations on five dates, we calculated that our sampling program was not able to detect the ca. 5% reduction that occurred in the population size. In fact, we calculate that about 300 plankton tows are required per station to measure a ±5% change in copepod concentrations, 75 tows for a ±10% change and 20 for a ±20% change. For chlorophyll a an average of 88 samples are needed per station to measure a ±5% change, 22 for a ±10% change and 6 for a ±20% change. Considering this, because of tidal currents in coastal areas and the difficulty of repeatedly sampling the same water mass, we feel that it is virtually impossible to measure relatively small (<±20%) changes in plankton densities. The number of chlorophyll a samples needed for a ±20% change is not prohibitive. These data indicate the importance of determining the ability of a sampling program to measure a population change before concluding that a suspected pollutant has not affected the population. The study also shows the inability of conventional methods of measuring plankton densities to detect relatively small changes.

Survival of copepods passing through a nuclear power station on northeastern Long Island Sound, USA

About 70% of the copepods entering the cooling water system of a nuclear power plant on northeastern Long Island Sound (USA) are not returned to the Sound in the effluent. Copepod mortalities are caused by the mechanical or hydraulic stresses of passage, although our experimental design could not determine whether heat or chlorination could cause mortality in the absence of mortality induced by hydraulic stress. After passing through the power plant, copepods sink rapidly (ca. 2.5 times faster than controls). This leads to an increase in concentrations of copepods suspended in the deep water (25 to 30 m) of the effluent pond. About half of the live copepods collected at the discharge and held in situ died within 3.5 days, and 70% died within 5 days, whereas only 10% of those from the intake died in 5 days. About 60% of the copepods observed suspended in deep water in the pond were dead. The copepod mortality caused by the power plant reflects the loss in secondary production occurring below about 270×103 m2 of sea surface in Long Island Sound annually. This loss represents a reduction of about 0.1% in the annual secondary production over a 333 km2 area of Long Island Sound adjacent to the power plant. Highest losses occurred during the spring (April, 1.4×106 g dry weight), the lowest in autumn (November, 45.8×103 g). If the same copepod loss rate exists for all power plants in Long Island Sound, then secondary production in 1.69×106 m2, or 0.05% of the total copepod production may be lost annually. A comparison of the surface outflow from Long Island to Block Island Sound with the water entrained through Millstone Unit One, and the 70% copepod loss rate in the latter area, indicates that Unit One eliminates about 0.1 to 0.3% of the copepod production in eastern Long Island Sound. This calculation compares favorably with losses computed from production data.

Depth Distribution of the Carotenoid Pigments and Lipids of Some Oceanic Animals 1. Mixed Zooplankton, Copepods and Euphausiids

Analysis of the carotenoid pigment and lipid concentrations of groups of the smaller zooplankton organisms from different depths has suggested a midwater maximum for carotenoid concentrations and a slight depth-related increase in lipid content. Similar analysis of seventeen species of euphausiid has not indicated similar trends, but has shown a close relationship between size and pigment content in all species other than those ofStylocheiron,which have significantly lower pigment concentrations. Comparisons of the data of Fisher, Kon &amp; Thompson (1964) on the pigment and lipid concentrations of copepods with the known depth ranges of the various species have suggested a midwater maximum in pigment concentrations, but no consistent trends in the lipid concentrations. A midwater pigment peak is explicable in terms of pigment accessibility and requirement for protective coloration, and the significance of the pigments is discussed.

Respiration and osmotic behaviour of the copepod Acartia tonsa in diluted sea water

1. 1. Adult females of the euryhaline planktonic copepod Acartia tonsa show increased oxygen requirements when the salinity of the surrounding sea water is lowered. 2. 2. The rise in respiration occurring during an 8-hr period of exposure to the diluted medium ranges from 0·077 μl oxygen/mg dry weight/hr at 90% sea water (0·7 per cent increase) to 16·061 μl oxygen/mg/hr at the lowest salinity 30% sea water (101·4 per cent increase). 3. 3. The increased metabolic rate can persist in diluted sea water for more than 24 hr. 4. 4. The internal osmotic concentration of copepods transferred from full-strength sea water 50% sea water falls rapidly due to entry of water into the body. After 1 hr no further osmotic change can be detected.

A study on the organic productivity and the solubility product of CaCO 3 in the ocean by means of the radiocarbon C 14

Artemia nauplius is the food usually used in the culture of Litopenaeus vannamei larvae. However, the production of Artemia cysts does not always meet the increasing demands of aquaculture. Thus, alternative diets need to be tested. The objective of this study was to determine the ingestion rate of the L. vannamei larvae fed on different offspring concentrations of Tisbe biminiensis, composed of nauplii and copepodites, and to estimate the best food concentration. Two types of ingestion rate experiments were made: one using flat bottom flasks without aeration, and another with conic bottom flasks with aeration. In the first type, larvae in the mysis 2 and 3 stages and postlarvae 1, 3, 5 and 7 were stocked individually in vessels containing 50 ml of seawater. In the other type, groups of 6 larvae in the stages mysis 2 and 3 were stocked in vessels containing 300 ml of seawater. In both experiments, the vessels containing seawater of salinity 31–33 were incubated for 24 h, at 25–30 °C and the photoperiod of 13 h light/11 h dark. Four treatments were tested with different copepod offspring concentrations as well as controls without shrimp larvae. In addition, controls using Artemia nauplii as food were also used to verify the physiological condition of tested larvae. In experiments using conic bottom flasks with aeration, the best concentration of copepods was about 5 copepod ml− 1 for mysis 2 and 3, respectively. The mean ingestion rate was 56.7 ± 9 and 188 ± 203 copepod larva− 1 day− 1 for mysis 2 and 3, in that order. In the other type of experiment, mysis 2 did not ingest copepods and mysis 3 ingested only 24.5 ± 10 copepod larva− 1 day− 1. In postlarval stages, the best concentration of copepod was about 10 copepod ml− 1 for postlarvae 1 to 3 and 20 copepod ml− 1 for postlarvae 5 to 7. The mean ingestion rate was 185 ± 69 copepod larva− 1 day− 1 for postlarva 1, 229 ± 45 copepod larva− 1 day− 1 for postlarva 3, 342.8 ± 98 copepod larva− 1 day− 1 for postlarva 5 and 293 ± 45 copepod larva− 1 day− 1 for postlarva 7. The results indicated some preference for naupliar over copepodite stages. To conclude, the offspring of T. biminiensis copepod were ingested by L. vannamei larvae in the mysis and postlarval stages and the ingestion rate increased with larval development. Thus, the offspring of T. biminiensis copepod are a potential live food to be tested in larviculture of L. vannamei.

Sôbre uma coleção de Copepodos, não parasíticos, da baía de Santos e suas adjacências: Est. I e II

This paper deals with the occurrence of Copepods in the Bay of Santos (State of Sao Paulo, Brazil) and its surroundings. During 1934-1945 the author collected plankton samples from that region not only to study its various components but especially to test its distribution in the contents of fish's stomachs. Thus, 1.136 samples were gathered, mostly from surface waters, since only 18.6% from intermediary and 8.8% from deep waters. According to the available literature, up to 1939, no important account had been given on the Copepoda from the coast of Sao Paulo and few works deal with this order from the Brazilian coast in general. Among them Van Douwe (1911; 1912), Wright (1927; 1935; 1936; 1936a; 1937), Kiefer (1935; 1936a; 1936&;) Chappuis (1936), Marsh (1933) and Schubart (1938-1942) who referred to some specimens from the north of Brazil. However, in all these works only brackish and fresh water specimens were considered. Later on, Oliveira (1945-1947) while carrying out researches on the micro crustacea from Guanabara Bay, presented interesting studies on marine species. A list is given of the commonest species collected and the author arrived to the following conclusions: a) excepting the genus Oithona, Paracalanus, Euterpina, Corycaeus and in certain months Acartia that, generally were found throughout the year, there was a great variation of species in the region investigated. b) In a general way, the author could not find that strict subdivision proposed by some authors who proved the existance of an absolute characteristical fauna on the surface, another intermediary one and still a bathipelagial one. This was due, perhaps, to the irregular catches and to the methods employed which could only be improved after 1947. c) Bright light did not cause the accumulation of organisms on the surface, excepting, obviously, the night catches; quite rich catches were made in misty days. d) Winds of high and medium speed had no great effect on the distribution of macroplankton while the rain seemed to help the concentration of Copepods on the surface, at least during the day; strong winds as well heavy rains drawn the plankton deeper down. e) The temperature influentiated the occurrence of material though slight changes had no great effect. f) As it was expected the zooplankton from the Bay of Santos presented the same characteristics as that from the open sea, though it proved to be poorer in quality and concerning some species, reacher in quantity. Some general considerations are made regarding the impure and contaminated water of a large city like Santos. While studying the research methods, the author gives slight references to the migration observed and to geographical distribution of some species.