Food selection capabilities of the estuarine copepod Acartia clausi

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.     

Phaeocystis pouchetii blooms in the East Frisian coastal waters (German Bight,North Sea)

In 1982 and 1983, blooms of the planktonic alga Phaeocystis pouchetii were studied in the East Frisian coastal waters off Norderney, FRG. Morphological variability of the colonies, population development, effects on inorganic nutrient and oxygen budget, and the role in the seasonal plankton bloom sequence were investigated. in both years two separate Ph. pouchetii blooms occurred in late spring and early summer that were formed by the globosa-type exclusively. The pouchetii-type was only present during the interval between the first and second blooms in 1982. Growth conditions for Ph. pouchetii seem to be most favourable after a breakdown of a diatom bloom when the silicate reserves have been exhausted, phosphate concentrations are relatively low, but a rich supply of dissolved inorganic nitrogen is available. Contrary to diatom blooms, Ph. pouchetii blooms result in a high production of particulate organic carbon (POC). Another characteristic is the release of great amounts of dissolved organic substances, which cause extensive sea foam formation during the peaks and the subsequent breakdown of the blooms. Due to increased assimilation during mass development and intense disintegration after the breakdown, variations of the oxygen content of the water are significant. Presumably the intensity of blooms has increased in the past decade as indicated by sea foam formation which has actually been excessive in some years.     

Copepod grazing during a declining spring phytoplankton bloom in the Northern North Sea

Grazing rates of larger (Calanus finmarchicus) and smaller (Acartia clausii Pseudocalanus elongatus etc.) copepods on naturally occurring phytoplankton populations were measured during a declining spring phytoplankton bloom. During the initial period, dominated by Chaetoceros spp. diatoms, constant ingestion rates were observed in Calanus finmarchicus at suspended particulate concentrations above 300 g carbon l^-1. Average daily intake during this time amounted to 35 to 40% of body carbon and reached a maximum of 50%. The feeding response of the smaller copepods was not so well defined, although a maximum daily intake of 56% body carbon was recorded. In both groups, feeding thresholds were at particulate concentrations around 50 g C l^-1. The feeding response of C. finmarchicus was correlated with both a change in their own population and in the food cell type. Linear regressions describing the concentration-dependent feeding response were: ingestion rate (IR)=1.16 total particulate volume (TPV)-36.15 during the initial part of the period compared with IR=0.41 TPV-12.18 for the latter period. C. finmarchicus filtered out slightly larger (x 1.2 diameter) particles than the small copepods and, in both groups, some filtering adjustment was made to accomodate to modal changes in the phytoplankton population from 20–30 m to 10 m diameter cells. Particle production during feeding was frequently evident in the smallest size ranges of particles and the ratio of particle production to ingestion rate was greater at low feeding rates.     

Salinity tolerance,salinity preference and temperature tolerance in the high-shore harpacticoid copepod Tigriopus brevicornis

Tigriopus brevicornis (O. F. Müller) were collected in 1992 from rock pools close to U.M.B.S. Millport, Isle of Cumbrae, U.K. and acclimated to various combinations of salinity and temperature for at least 1 wk prior to laboratory experiments. Higher salinities of acclimation enhanced tolerance to high salinity stress, while tolerance of low salinities was hardly affected by acclimation salinity. Acclimation to low temperature (10°C) extended the survivable salinity range for T. brevicornis. High-salinity acclimation enhanced the survivable temperature range. Copepods acclimated to 60 survived significantly lower and higher temperatures than did 34-acclimated individuals. At high temperature, 75-acclimated female copepods had the highest median lethal temperature, 38.9°C. Females were significantly more resistant to high temperatures than males. The copepods were seen to have a very low median lethal temperature when frozen into solid ice for 2 h; 50% mortality occurred at-16.9°C in 10°C, 34-acclimated T. brevicornis. Salinity preference experiments demonstrated an ability to discriminate between salinities differing by as little as 3. Copepods acclimated to 34 chose salinities near their acclimation salinity; individuals acclimated to 5 favoured slightly higher salinities, while copepods acclimated to 60 chose rather lower salinities.     

Suspension-feeding by herbivorous calanoid copepods: A cinematographic study

Many planktonic calanoid copepods are commonly described as filter-feeders. Direct observations using high-speed micro-cinematography indicate that these animals are suspension-feeders. They capture and handle the food particles not passively according to size and shape but, in most cases, actively using sensory inputs for detection, motivation to capture, and ingestion.     

Grazing and ingestion rates of nauplii,copepodids and adults of the marine planktonic copepod Calanus helgolandicus

The average grazing and ingestion rates of all stages of the marine planktonic copepod Calanus helgolandicus (Calanoida) from nauplius stage IV to adults were measured experimentally at 15°C in agitated cultures. The chain-forming diatom Lauderia borealis and the unarmoured dinoflagellate Gymnodinium splendens were offered as food. The food concentrations were close to natural conditions and ranged from 36 to 101 g of organic carbon per liter. The medium body weights expressed in g of organic carbon of almost all larval stages raised at 49 g C/1 were identical with the weight of the same stages caught in the Pacific Ocean off La Jolla, California, USA. In a log-log system, grazing and ingestion rates increased almost linearly with increasing body weight. Grazing rates ranged from 4 to 21 ml/day/nauplius stage IV to 286 ml to 773 ml/day/female. Ingestion rates increased from 0.2 g to 0.8 g C/day/nauplius stage IV to 18 g to 69 g C/day/female. Grazing and ingestion rates per unit body weight decreased gradually with increasing body weight. The daily ingested amount of food decreased from 292 to 481% of the body weight (g C) of nauplius stage V to 28–85% of the body weight of adult females. Grazing and ingestion performances of all stages increased with increasing particle size. Grazing rates decreased and ingestion rates increased with increasing food concentrations. The published data on food intake of the different age groups of C. helgolandicus show that the young stages of herbivorous planktonic copepods can play a major part in the consumption of phytoplankton in the sea due to their high grazing and ingestion rates.     

Salinity tolerance of benthic estuarine diatoms as tested with a rapid polarographic measurement of photosynthesis

Measurements of net photosynthesis of benthic estuarine diatoms were made by polarographic registration of oxygen saturation. A measuring cell was constructed in which media with salinities of 2.0 to 100.7 were pumped over the algae between measurements. Diatoms from unialgal cultures and mixed populations from intertidal flats appeared to be highly tolerant of extreme salinities. During short-term exposures (20 min) the net photosynthesis of the algae did not drop below 70% of the initial values, within the salinity range 4.0 to 60.0. Prolonged exposure (up to 6 h) gave essentially the same results. Populations of benthic diatoms, sampled from field stations with mean salinities of about 30, 12, and below 5, showed only gradual differences in their tolerance of salinities between 2.0 and 33.7. Two species, Navicula arenaria and Nitzschia sigma, were cultured in media ranging in salinity from 8.0 to 45.0 and from 2.0 to 45, respectively. The tolerance to changing salinity was only slightly affected by the salinity of the medium in the preculture. The role of salinity in the production and distribution of intertidal diatoms is discussed.     

Particle-Size-dependent maximum grazing rates for Temora longicornis fed natural particle assemblages

The hypothesis that lower retention efficiencies of filter-feeding copepods for small particles should result in different ingestion rate versus food concentration curves for different-sized foods was tested using Temora longicornis (Müller) fed natural phytoplankton. The copepods were fed different natural phytoplankton assemblages, which varied in their species and size distribution. Volume ingestion rates were an asymptotic function of food concentration, with maximum ingestion rates measured at food concentrations exceeding 5 to 10x 10⁶ m³ ml^-1, which were less than those occurring in the natural waters in which the copepods and phytoplankton were collected. Maximum volume ingestion rates increased linearly by a factor of 3.5, as the diameter of the particle forming the peak in the food size distribution increased fron 5 m (primarily microflagellates) to 30 m (mostly large diatoms). These results suggest that natural and pollutant-induced size reductions in natural phytoplankton could markedly decrease the volume of food consumed by filter-feeding copepods.Contribution No. 243 of the Marine Sciences Research Center     

Plankton inhabiting the surface layer of the southern and southwestern lagoon of New Caledonia

In the southern and southwestern coral reef lagoon of New Caledonia and the adjacent oceanic waters, 42 neuston samples were collected from the upper surface layer (0 to 10 cm) along nine transects from the coast to the coral barrier reef and the open ocean immediately beyond the reef, in March and April 1979. There was a progressive numerical decrease in zooplankton densities from the coast to the reef and from the reef to the open sea. Generally, 80 to 95% of the surface plankton consisted of holoplankton and 5 to 20% of meroplankton. Zooplankton was very abundant in littoral bays with a marked eutrophication. In a few samples collected in very shallow waters close to coral patches, cladocerans were numerous and constituted up to 75% of the total plankton, whilst in other samples collected above greater depths, copepods made up 60 to 85% of the total plankton. In the coral reef lagoon of south and southwest New Caledonia, typically hyponeustonic copepods (pontellids) often comprised 5% of the total copepod populations.     

Temporal variation and distribution of trace metals in freshwater and fish from Calabar River, S.E. Nigeria

An investigation on the abundance and distribution of trace metals (Fe, Cu, Zn, Mn, Cr, Cd and Pb) in water, and nine species of fish samples from Calabar river was carried out in 1992. The concentrations of iron (6000–7240gl^–1), zinc (4910–7230gl^–1), and cadmium (3–7gl^–1) showed moderate pollution while those of copper (420–630gl^–1), manganese (23–48gl^–1), chromium (<10–20gl^–1) and lead (<1–10gl^–1) in water were well below WHO permissible levels. Significant seasonal changes (0.001p0.25) were obtained for iron, copper, zinc, manganese and cadmium in water. Furthermore, iron, zinc and cadmium showed statistically significant spatial changes (0.005p0.10). Of the nine fish species studied, no statistically significant relationship between body weight and the concentrations of the metals was observed. The concentrations of the metals per mean total body weight apparently decreases in the order Fe>Zn>Cu>Mn>Pb>Cd=Cr and were within the limits that were safe for consumption.     

Distribution of glycosylglycerols and oligosaccharides in the marine environment and their ecological significance in the deep sea

Determination of low molecular weight carbohydrates in marine environments indicated that 1-O--D-galactosylglycerol, 6-O--D-galactosyl-1-O--D-galacto-sylglycerol, sucrose, laminaribiose and laminaritriose are widely distributed in seawaters, suspended and sinking particles, and sediments in coastal as well as in deep-sea waters [e.g. Mikawa Bay and Sagami Bay, Kumano Nada (offshore Japan), and northwest North Pacific Ocean, Bering Sea and Antarctic Ocean: collections during 1978–1984]. Identification of these glycosylglycerols and oligosaccharides in algal cells such as a flagellate (Olisthodisus luteus), blue-green algae (e.g.Trichodesmium sp.) and a diatom (Reptocylindrus denicus) strongly suggests that these sugars are photosynthetically produced by algae in the euphotic zone and are then rapidly transported to the deep sea as sinking particles which can be collected by sediment-trap experiments. The rapid decay rate of low molecular weight carbohydrates by microorganisms suggests that the transported sugars provide energy substrates for microorganisms living in the deep sea.Please address all requests for reprints to Dr. Handa at Nagoya University     

Upwelling-generated plankton strandlines: important predictable food sources for seabirds at Husvik,South Georgia

Sustained strong offshore winds generate upwelling in the fjords of northern South Georgia. Deepwater plankton is pumped by upwelling towards sandy beaches at the heads of the fjords; calanoid copepods, chaetognaths and pteropods are stranded by the sand filter in large quantities on falling tides. Local benthonic species (harpacticoid copepods and amphipods) are present in the plankton but do not strand. Strandlines are very rich (<4 kg wet mass m^-2) and provide large fractions of the food of kelp gulls, sheathbills and terns in the austral summer. Birds can only exploit fresh strandlines, since air-drying of the plankton soon makes it too salty to eat.     

Carbon-isotope ratio gradients in western arctic zooplankton

Zooplankton from 87 stations in the Bering, Chukchi and Beaufort Seas sampled in 1985, 1986 and 1987 showed a geographic gradient in stable carbon-isotope ratios (¹³C). The zooplankton most depleted in ¹³C were found in the central and eastern Beaufort Sea and those most enriched were from the Bering and Chukchi Seas. Average ¹³C values ranged from-20.9 to-26.7 for copepods and from-19.4 to-25.1 for euphausiids. Euphausiids show a minimum of 1.0 enrichment relative to copepods throughout the study area. Relative biomasses of the major zooplankton taxa varied significantly across the Alaskan Beaufort Sea in October 1986, with euphausiids dominating in the west and copepods in the east. These differences in taxonomic composition affected the weighted ¹³C values for total zooplankton and may produce an even more pronounced geographic gradient in zooplankton ¹³C than that found within a single taxon. The bowhead whale Balaena mysticetus migrates between wintering areas in the Bering Sea and summering areas in the Beaufort Sea and feeds over this geographic range. The zooplankton ¹³C gradient is the probable source of ¹³C oscillations found along the baleen plates of this planktivore.     

Environmental Geochemistry of Soils and Waters of Susaki Area, Korinthos, Greece

Soil and water samples were collected from the Susaki area of Korinthos and analysed for heavy metals in order to evaluate their environmental impact. The geology of the studied area includes ultrabasic rocks and Neogene and Quaternary deposits whereas magnesite veins are found within the ultrabasic rocks. In the north part of the studied area post volcanic emissions of H₂S, CO₂ and H₂O vapor continue to the present day. All the samples were analysed for heavy metals by the ICP method. The element ranges (in g g^–1) for soil samples are: Cu 11–63, Pb 5–256, Zn 21–604, Ni 183–2665, Co 12–124, Mn 456–1434, As 5–104, Sr 44–730, V 21–84, Cr 163–2346, Ba 48–218, Zr 3–41, Y 3–13. The metals Pb, Zn, Ni, Co, Cr, Fe, Cu, Mn, As and Sr are enriched in the Susaki soils. The element ranges for water samples are: Cu 65–103ppb, Pb<10ppb, Zn<5ppb, Ni 21–163ppb, Co 2–12ppb, As<30ppb, Cr<20ppb, Ba 36–785ppb, Sb<10ppb, W<10ppb, Bi<30ppb, Mn 0.0–0.9 g g^–1, Fe 0.01–0.22 g g^–1, Na 843–3076 g g^–1, K 98–278 g g^–1, Si 39–65 g g^–1, P 0.1–0.2 g g^–1. There is a natural pollution of soils with elevated concentrations of Ni, Co, Mn, Fe and Cr due to the presence of ultrabasic rocks. Another natural case of As pollution of soils is due to the volcanic activity and the geothermal field in the area. The geochemical data of ground waters and also the ¹⁸, D data showed a mixing in different proportions between sea water and meteoric water.     

The “red tides” of Malta

A 5 year survey of Marsamxetto Harbour, Malta, was carried out to investigate some factors contributing to red tides and to identify the causative organisms. Red tides occurred usually in May but, less predictably, also during June – August. Causative organisms included the diatom Chaetoceros sp., and the dinoflagellate genera Prorocentrum, Peridinium, Ptychodiscus, Gonyaulax, Ceratium and Cochlodinium. Early summer red tides occurred at a time of increasing insolation, and water temperature, prevailing onshore winds and salinities in the range 34.4 to 36.6 A consistent feature was a quick rise in sea temperature of more than 2 C^o during the week preceding red water. Red tides later in the year coincided with higher temperatures and salinities and calm weather.     

Accumulation of 14C-1-naphthalene by an oceanic and an estuarine copepod during long-term exposure to low-level concentrations

Accumulation of the bi-cyclic aromatic hydrocarbon ¹⁴C-1-naphthalene in adult female Calanus helgolandicus Claus and adult female Eurytemora affinis Poppe in sea water concentrations of hydrocarbon ranging from 0.2 to 992 g/l was studied during exposure periods of up to 15 days as part of an investigation of the possible effects on marine zooplankton of persistent exposure to low levels of petroleum hydrocarbons. With both species the body levels of radioactivity increased rapidly during the first few days of the exposure period, but after exposure for 7 to 8 days to sea water containing 50 g hydrocarbon/l an equilibrium condition was approached; in some experiments where E. affinis was exposed to 1.0 and 10 g hydrocarbon/l for 15 days there was no further increase in body levels of radioactivity after 7 to 8 days. Using a low concentration of hydrocarbon (1 g/l), the quantity of radioactivity accumulated after 10 days was found to be nearly fifty times greater in the smaller species, E. affinis, than in C. helgolandicus, when expressed in terms of body weight. After they had been exposed to the hydrocarbon for several days the copepods contained a considerable proportion of radioactivity that was no longer identifiable as naphthalene and was presumably present as metabolites. Radioactivity accumulated in the copepods after several days was rapidly lost after they were transferred to uncontaminated sea water: e.g. C. helgolandicus lost nearly 90% of its body level of radioactivity in 24 h. Thereafter the rate of loss was greatly reduced, and 5% of the original body level of radioactivity still remained in the copepods at the end of 11 days. Experiments on the breakdown of naphthalene added at low concentrations to sea water samples containing natural microbial populations indicated degradation rates of 0.1 to 0.2 g/l/24 h in oceanic water, and 2.6 g/l/24 h in inshore water samples. The results are discussed in terms of the possible transfer of hydrocarbon to a higher trophic level in areas subjected to constant low-level inputs of petroleum hydrocarbons.     

Dissolution rates of silica from diatoms decomposing at various temperatures

In a study of silica dissolution from diatoms, the rate coefficient (K) h^-1 of raw diatom cells was estimated as 4 to 5 times smaller than that of the acid-digested siliceous skeletons. The dissolution rate coefficient at early stage (K₁) can be predicted as a function of temperature (T°C): in K₁=+T, where is the frequency factor depending on the properties of diatom species, ranging from -7.35 to-`0.38, and the temperature coefficient is 0.0833 for all species. Activation energies were calculated to be 1.37 to 1.38 Kcal mol^-1. This equation suggests that the rate coefficient K₁ increases by a factor of 2.27 for each 10 C° rise in temperature. This equation will also be applied to a new approach for the fate and behavior of biogenous silica settling through a water column by introducing the term temperature into a model.     

Silicon and the ecology of marine plankton diatoms. II. Silicate-uptake kinetics in five diatom species

The variation of the rate of silicate uptake with varying silicate concentration in the medium was investigated in short-term experiments with the following marine diatom species:Skeletonema costatum, Thalassiosira pseudonana, T. decipiens, Ditylum brightwellii, andLicmophora sp. The uptake conformed to Michaelis-Menten kinetics only after a correction had been made for reactive silicate that apparently could not be utilized by the diatoms. The magnitude of this correction was in the range of 0.3 to 1.3 g-at Si/l. Mean values of the half-saturation constant of silicate uptake were calculated for the different species. The lowest value was found inS. costatum (0.80 g-at Si/l) and the highest inT. decipiens (3.37 g-at Si/l). Growth limitation by low silicate concentrations could be a cause of species succession in marine plankton-diatom blooms.     

Aqua regia extractable trace elements in surface soils of venezuela

Surface soils (0–15 cm) were sampled at 10–20 km intervals along two transects in Venezuela. One (1162 km, 70 samples) ran west to east parallel with the Caribbean coastline, the other (920 km, 92 samples) ran south to north from the frontier with Brazil to the Caribbean shore. Sampling took place in both a wet and a dry season. Trace metals were extracted from dried, sieved (<2 mm) soil with boiling aqua regia followed by analysis by ICP or flame AAS. Metal values did not differ significantly between the two seasons and dates were averaged. Geometric mean values for the west–east transect were: Cr=41.5, Cu 17.9, Cs 3.6, Li=13.9, Mn=294, Ni=21.3, Pb=17.4, Sr=39.4, V=60.4 and Zn = 83.7g g^–1, respectively. Similarly, for the south–north transect Cr=21.3, Cu=4.3, Cs=1.1, Li=2.0, Mn=55.7, Ni=4.4, Pb=6.1, Sr=13.3, V=28.2 and Zn=16.7g g^–1, respectively. A classification of samples by lithology showed surface soil composition to be related to rock composition. Metal values were low in the soils in the south of the country, in the Guyana highlands (Gran Sabana). Low Zn contents were prevalent. Lead contents were affected by roadside fallout from vehicles using leaded petrol except that high Pb contents of soils in the Gran Sabana were of more complex origin.     

A comparative study of photoadaptation in four diatoms isolated as endosymbionts from larger foraminifera

Four endosymbiotic diatoms were isolated from 2 species of larger foraminifera collected in the Red Sea and Hawaii. The photoadaptive responses of the cultured diatoms were measured at 312, 19 and 7 W cm^-2. Two of the diatoms (Fragilaria shiloi and Nitzschia laevis), both isolated from Amphistegina lessonii, grew fastest at 312 W cm^-2. The other two diatoms (N. valdestriata and N. panduriformis) which were isolated from Heterostegina depressa, grew best at 19 W cm^-2. Of the four diatoms, F. shiloi grew best at high light levels. Also in F. shiloi, chlorophyll c content per cell was directly proportional to light intensity; in contrast chlorophyll a and carotenoids increased to maxima at 19 W cm^-2. The chlorophyll a and c and carotenoid content of N. valdestriata were also maximal at 19 W cm^-2. Photosynthetic rates, measured by respirometry, suggested that the diatoms were photoinhibited at higher light intensities and did well at moderately low light intensities (175W cm^-2). The photocompensation points of all 4 diatoms were about 2% of the light available in the spring at 1-m depth at Elat on the Red Sea. At Elat the photocompensation point would lie between 40 and 50 m if the algae were free in nature. The amount of attenuation of light by the shells of the host has not yet been measured. Presumably photocompensation of the algae within hosts is reached at depths less than 40 m.