Roles of tidal and wind-generated currents in transporting white shrimp (Penaeus setiferus) postlarvae through a South Carolina (USA) inlet

The temporal and spatial abundance of postlarval Penaeus setiferuswas studied from plankton samples in oceanic and estuarine watersnear the North Edisto Inlet, South Carolina (USA), during threecruises in 1993 and 1994 (May 1993, August/September 1993 andJune 1994). Each covered a full cycle of neap-spring tides.On each cruise, bongo nets were towed at three stations acrossthe inlet throat on nightly flood tides. During the first twocruises, tows were made at surface and near-bottom depths inthe inlet, while sampling was confined to surface depths duringthe last cruise. Plankton tows were also made outside the inletalong transects extending in a cross-shelf direction and alongan arcuate transect around the inlet mouth. Stations along thearcuate transect were intensively sampled over a full tidalcycle during the last cruise. Extensive oceanographic and meteorologicalobservations were obtained from moored instrument arrays andshipboard sampling in order to relate fluctuations in tidal,lunar and wind phenomena to temporal changes in postlarval density.Densities of postlarvae were greater in the inlet throat thanat stations offshore. A significant interaction of postlarvaldensity among inlet stations and depth was noted in May. Forother cruises, no significant differences in density were notedamong stations across the inlet, but postlarvae were concentratedat the surface. The lack of a consistent horizontal salinitygradient and obvious pattern in water masses across the inletmay explain why postlarval densities did not consistently differlaterally in the inlet. Greater densities generally occurredduring the first quarter moon, although a clear relationshipof larval density to the spring-neap cycle was not observed.Highest mean densities of ingressing postlarvae in surface floodtide collections from the inlet were generally associated withdownwelling onshore winds which generate onshore flow near thesurface. The similarity between the time series curves of postlarvaldensity and the tidal component of currents just offshore ofthe inlet suggests that tidal transport may facilitate movementinto the estuary. Based on increased postlarval density at thesurface during early strong flood tides and a reduced densityat depth in the inlet, we hypothesize that postlarval P setiferusare utilizing selective tidal stream transport.     

Short-term changes in the mesozooplanktonic community in theSeine ROFI (Region of Freshwater Influence)(eastern English Channel)

Discrete-depth, hourly mesozooplankton samples were collectedover a 92 h period in May 1992 at an anchor station within theSeine Region of Freshwater Influence (ROFI) (English Channel).The mesozooplankton community defined as a euryhaline marineassemblage was dominated by the calanoid copepods Acartia spp.,Temora longicornis and Centropages hamatus, the cladoceran Evadnenordmanni and the appendicularian Oikopleura dioica. The semi-diurnaltidal current was the dominant factor in determining the short-termtemporal changes in the community in terms of density and speciescomposition so that zooplankton patches displayed oscillatingmotion in relation to tidal advection. Although a few species(e.g. Pleurobrachia pileus) exhibited higher densities aroundlow tide, maximum densities were observed for most species (e.g.T.longicornis and E.nordmanni) around high tide, according tosalinity variations. Diurnal changes were only reported forcyclopoid copepods (i.e. Halicyclops sp. and Cyclopina sp.)which wer$$$ mainly endobenthic during the day and moved intothe water column at night. Besides temporal changes in depth-averageddensities, most species exhibited vertical migrations at dieland/or tidal periods. Tidal vertical migrations were reportedonly for a few taxa and could be the result of passive mechanisms(e.g. vertical mixing) rather than of active behaviour. Dielvertical migrations were observed in most of the abundant taxa.While this migration pattern did not appear to be an adaptationto predator avoidance within the Seine ROFI, it could regulatehorizontal transport of organisms and promote their retention.The consequences of the short-term mesozooplankton fluctuationsfor sampling designs are discussed.     

Tidally driven distribution of phytoplankton blooms in a shallow, macrotidal estuary

The influence of the ebb tide on the abundance and distributionof bloom-forming species, as well as the mechanisms for theselection of those species which remain, were investigated inthe shallow, tidal-flushed Urdaibai estuary, north Spain. Phytoplanktonwas collected monthly from May to September 1998 during differenttidal conditions (neap-spring) at five stations along the salinitygradient of the estuary. During the neap tides of May, Leptocylindrusdanicus dominated in the lower estuary, together with Thalassiosiraguillardii and Peridinium foliaceum in the upper segment; T.guillardiiexperienced the broadest displacement along the estuary. Duringthe June and July cruises, coinciding with mid-tidal amplitudesand high temperatures, Peridinium quinquecorne densely aggregatedin the upper estuary at the slack high tide, whereas Chaetocerossalsugineum bloomed at the intermediate stations. Cyclotellaatomus and Protoperidinium achromaticum reached high concentrationsin the upper zone only during the late stages of the ebb. Duringthe spring tides of September, Prorocentrum minimum, Heterocapsapygmaea and Heterocapsa rotundata appeared in the lower marineestuary, being washed out at low tide. By contrast, the diatomsSkeletonema costatum, Thalassiosira guillardii and Cyclotellaatomus were the most abundant species in the upper reaches,peaking during the ebb. Physical trapping and high water residencetimes served to retain blooming species in the upper estuary.The intense growth of the estuarine diatoms may compensate forthe advective seaward losses of cells during the ebb, thus allowingthe development of stable populations in the estuary. Only Peridiniumquinquecorne seems to combine an endogenous tidal rhythm witha photic response to remain in the tidal area of the estuary.     

Zooplankton growth rates: the larvaceans Appendicularia, Fritillaria and Oikopleura in tropical waters

The growth rates of Appendicularia sicula, Fritillaria borealissargassi, Fritillaria haplostoma, Oikopleura dioica and Oikopleuralongicauda were determined from microcosms incubated in situat 23C in Jamaican waters. Experiments were conducted fromoligotrophic offshore waters, through mesotrophic Lime Cay andeutrophic Kingston Harbour in both natural and nutrient-enhancedphytoplankton communities. Length-weight relationships werecalculated for two of these species: O.longicauda log W=2.47log TL –6.10 and F.haplostoma log W=2.44 log TL –7.37,where weight (W) is in micrograms and trunk length (TL) is inmicrometres. Instantaneous growth rates averaged 1.7–2.5day^–1 for the five species and were observed as high as3.3 day^–1 These instantaneous rates are equivalent todaily specific growth rates averaging 4.6–11.4 and rangingup to 28. In larger genera, growth rates were related positivelyto picoplankton and nanoplankton concentration, and negativelyto the biomass of larvaceans, but in the smallest species growthwas unrelated to these factors. However, because the variabilityin these two factors within microcosms exceeded their naturalrange of variability, growth rates of larvaceans may normallybe unlimited by resources or population density effects. ¹Present address :Monterey Bay Aquarium Research Institute 7700Sandholdt Road, Moss Landing, CA 95039-0628, USA ²Present address :Bedford Institute of Oceanography PO Box 1006,Dartmouth, Nova Scotia B2Y 4A2, Canada     

Temporal and spatial distribution of the ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt in the St Lawrence, Canada

The occurrence of the potentially ichthyotoxic dinoflagellateGyrodinium aureolum Hulburt is reported for the first time inthe Lower Estuary and Gulf of St Lawrence. Taxonomic identificationusing an iramunochemical tagging method suggests a close taxonomicproximity between the species found in the St Lawrence and G.aureolumpresent in European waters. In 1993, G.aureolum was observedalong the entire coast of Quebec and in offshore waters of theGulf of St Lawrence. At the coastal stations, G.aureolum showedlarge week-to-week variations, but higher densities were observedduring late August and early September. Bloom concentrations(10⁶ cells 1^–1) were only observed in the GaspéCurrent at Mont-Louis, on the north coast of the Gaspd peninsula.In the central part of the Gulf, G.aureolum was concentratedin the upper 5 m of the stations directly influenced by thefreshwater run-off of the St Lawrence Estuary. Results fromprincipal component analysis indicate that G.aureolum favorsenvironments with high nitrogen recycling activity.     

Seasonal variability of phytoplankton populations in the middle Adriatic sub-basin

The seasonal variability of phytoplankton assemblages in themiddle Adriatic sub-basin is described. The investigated areacrossed the middle Adriatic from the Italian to the Croatiancoasts. Hydrographic data, chlorophyll (Chl) a and phytoplanktonwere collected on a seasonal basis from May 1995 to February1996. Highest phytoplankton densities (up to 6 x 10⁶ cells dm^–3)were observed in spring and autumn in the western side, withinthe diluted waters. The vertical distribution of Chl a exhibiteda pronounced subsurface maximum associated, in coastal waters,with micro-planktonic diatoms. Phytoplankton assemblages weredominated by phytoflagellates in all the periods investigated.Diatom maxima were observed in spring and autumn: their verticaldistribution generally reflected the Chl a pattern and in thewestern coastal area peaks are due to large diatom species (Pseudo-nitzschiaspp.). In offshore waters, dinoflagellates strongly prevailover diatoms and provide a relevant contribution to the totalbiomass, especially in highly stratified conditions. Coccolithophoridswere mostly encountered in surface layers and their highestcontribution to the total biomass was observed in the LevantineIntermediate Water.     

Short term spatial — temporal distribution patterns of zooplankton in Admiralty Bay (Antarctica)

The present work analyses the abundance and species composition of mesozooplankton in relation to different patterns of wind speed and tides in Admiralty Bay. The plankton was sampled on 12, 13 and 15 March 1989 with a 385 m mesh size conical-cylindrical net by R.V. Barão de Teffé. In Martel Inlet, the zooplankton standing stock reached 25,223 individuals 100 m^–3 during the high tide. Under north-west winds, the abundance of the dominant species Ctenocalanus citer and Fritillaria borealis followed the tidal cycle. Weak south-west winds promoted the input of plankton even during low tide. Throughout the Bay, the highest densities of plankton (446–2,899 individuals 100 m^–3) were observed in surface waters flowing towards the Bransfield Strait. Surface waters flowing through the Bay and the inlets showed different species composition to surface waters flowing towards the Bransfield Strait.     

Nutrient status of phytoplankton communities in Norwegian waters (marine, brackish, and fresh) as revealed by their chemical composition

The chemical composition of nutrient-saturated cultures of Emilianiahuxleyi, Amphidinium carterae, and Staurastrum luetkemuelleriwas studied. The variation in chemical composition of naturalphytoplankton communities in the North Sea, the Trondheimsfjord,and a eutrophic lake was also studied. Nutrient status was evaluatedby measurement of the algal protein/carbohydrate, N/C, P/C,and N/P ratios. Tests for P-deficiency were carried out by measuringthe increase in ATP upon addition of phosphate. At saturationthe N/C ratio was {small tilde}0.14 in marine species and {smalltilde}0.05 in Staurastrum. Saturation P/C ratios (excludingpolyphosphates) were species-dependent, ranging from 0.017 (Skeletonema)to 0.006 (Amphidinium). Amphidinium and Staurastrum store polyphosphateswhen grown in P-rich media; true marine planktonic species donot. Natural communities tended to be close to nutrient saturationat low biomass densities and nutrient deficient at high densities.In the North Sea, nitrogen was clearly limiting. In waters offthe Møre coast and in the Trondheimsfjord, growth wasnearly balanced with respect to N and P at high salinities (>25)and clearly P-limited in brackish fjord waters. In dense communities,the N/P ratio was inversely related to salinity. Freshwatercommunities were clearly P-limited, but responses were dampenedwhen daphnia or whitefish were introduced, due to increasedexcretion of nutrients. ¹Contribution No. 212, Trondheim Biological Station, N-7001Trondheim, Norway.     

FORAGING ACTIVITY OF HELCION PRUINOSUS (PATELLOGASTROPODA) ON A SOUTH AFRICAN BOULDER SHORE

Foraging activity of the mid-shore limpet Helcion pruinosuswas monitored on an exposed boulder beach in the Eastern Capeof South Africa. Numbers of limpets active in 10 fixed quadratswere monitored and compared in different seasons and during springand neap tides. Foraging excursions were mainly associated with nocturnallow tides, limpets only emerging from beneath rocks when theywere completely uncovered by the receding tide, and they hadall retreated to beneath rocks before being splashed by theadvancing tide. The number of animals active was greater onfull moon spring tides. Significantly more limpets were activeon an autumn spring tide than on similar tides in other seasons. ^* To whom correspondence should be addressed. (Received 27 March 2000; accepted 5 July 2000)     

Transport of microbial biomass through the North Inlet ecosystem

Tidal fluctuations and transports of total microbial biomass (measured as adenosine triphosphate [ATP]) were investigated at three marsh creeks comprising the major transfer points between the North Inlet marsh and the adjoining aquatic ecosystems. Two creeks, Town Creek and North Jones Creek, form the inlet mouth and are the only marsh-ocean exchange points. The third creek, South Jones Creek, connects to a brackish water embayment. The creeks were simultaneously sampled every 1.5 hours for 50 consecutive hours during neap tides (four tidal cycles) and 50 consecutive hours during spring tides of each season. At the inlet, ATP concentration fluctuated in phase with the tide during winter and fall and out of phase with the tide during the spring. Fluctuation patterns at South Jones Creek were irregular. The highest ATP concentrations were during the spring (mean=2.17 mg of ATP per m³) and the lowest concentrations were during the winter (mean=0.65 mg of ATP per m³). Net transports of ATP varied from tidal cycle to tidal cycle with regard to direction of transport (import or export) and magnitude. Net transports were small compared to large instantaneous transports and only 4 of 22 determinations of net transport were different from zero transport.     

The copepod genus Oncaea (Poecilostomatoidea) from the Lebanon: taxonomic and ecological observations

Eighteen species of the genus Oncaea, four of them polymorphic,have been collected from the inshore and offshore waters ofthe Lebanon. Three species are new additions to the Mediterraneanfaunal list, O.shmelevi, O.pumilis and O.rufa. The males ofthree poorly described species, O.bathyalis, O.ovalis and O.similis,the female of O.shmelevi and both sexes of O.tenella are redescribed.Oncaea media and O.mediterranea were the two most common representativesof the genus in the study area. Oncaea were most abundant inDecember and January and between March and May; they were mainlymesopelagic and oceanic. Many of the species recorded here havecosmopolitan distributions; some of the smaller ones are lesswell-known, but may prove in time to be as widespread as thelarger taxa.     

Red tide assemblage formation in an estuarine upwelling ecosystem: Ria de Vigo

Red tides are conspicuous in the upwelling system of Galicia(NW Iberian Peninsula). At present, there are conflicting hypothesesabout the generation site of these phytoplankton assemblages.It is interesting to know whether the rias can be sites of redtide formation or if they act only as accumulation sites ofpopulations advected from shelf waters. A study in the Ra deVigo, carried out during late September 1990, showed the developmentof a red tide assemblage, composed of Alexandrium affinis, Ceraiiumfusus and Gymnodinium catenaium, during a 2 week upwelling-downwellingcycle. Growth occurred at the bottom of the thermocline-topof the nutricline. Above this assemblage, a diatom assemblage(large diatoms) was blooming. Prior to the formation of thered tide, a subsurface chlorophyll maximum made up of smalldiatoms (Nilzschia f. seriaia, Chaeloceros socialis), smallflagellates (<30 µm) and small gymnodinid forms (<30µm) was observed. In the nutrient-depleted upper layer,several autotrophic and large heterotrophic dinoflagellatesdominated. It is suggested that the ratio between the velocityof upward water movement and the depth of the stratified upperlayer (flushing rate, day^–1) is the critical parameterwhich triggers active phytoplankton growth. It can be concludedthat upward water velocities of {small tilde}2.5 m day^–1and a stratified upper layer of 10 m depth (flushing rate 0.25day^–1) are the main physical constraints for red tidedevelopment.     

Evidence for tidally-induced vertical migration of some gelatinous zooplankton in the Wadden Sea area near Sylt

Gelatinous zooplankton is more abundant in the Wadden Sea area of North Sylt than in the adjacent North Sea. The hypothesis is tested that medusae maintain their position in the North Sylt Wadden Sea by ascending to the surface at flood tides and descending to the bottom during ebb tides, thus avoiding the strong ebb currents which could carry them out of this food-rich area. Surface sampling at a main tidal channel revealed great differences between high tide and low tide abundances of five species of medusae in the surface layer.Rathkea octopunctata, Sarsia tubulosa, Eucheilota macultata andPleurobrachia pileus were all more abundant around high tide than during low tide. Bongo net sampling in different depth layers revealed thatPleurobrachia pileus, Bougainvillia ramosa andEucheilota maculata showed a preference for the surface layers around high tide, whereas most of the individuals were found in the deepest layer around low tide. The results suggest tidally-induced vertical migration of medusae in tidal channels. This may assist maintenance of the populations in the Wadden Sea area near Sylt.     

THE BIOLOGY OF THE NORTHEASTERN PACIFIC TURRIDAE II. OENOPOTA

The habitat, diet, some reproductive and mortality factors forseveral shallow-water species of the boreal turrid genus Oenopotafrom the Puget Sound region were determined. All fed exclusivelyon tubicolous polychaetes. Oenopota fidicula was a dietary andhabitat generalise Oenopota elegans eats Schistocomus hiltoniand lives in areas of shell fragments. Oenopota excunata eatsTharyx multifilis and is a habitat generalist. Oenopota tabulataappears to be a dietary generalist, but lives only on or nearrocks. The widely-distributed species, O. levidensis, eats spionidpolychaetes, primarily Polydora species, or Owenia fusiformis,and is a habitat generalist. Feeding frequencies are low asare population densities; although O. levidensis sometimes exceeds15 animals m^–2. Crabs are major predators upon turridsin some areas, but mortality causes are generally obscure. Spawningwas observed in four species, but only O. elegans and O. levidensishad viable larvae. Development takes 13–15 weeks, 6–7weeks in a capsule and 6–7 weeks as planktonic veligers.There are no nurse eggs. Settling was not observed. ^*Present mailing address: Bamfield Marine Station Bamfield,B.C. VOR 1B0 CANADA (Received 30 May 1982;     

An immunofluorescent survey of the brown tide chrysophyte Aureococcus anophagefferens along the northeast coast of the United States

Surveys were conducted along the northeast coast of the USA.between Portsmouth, NH, and the Chesapeake Bay in 1988 and 1990,to determine the population distribution of Aureococcus anophagefferens,the chrysophyte responsible for massive and destructive ‘browntides’ in Long Island and Narragansett Bay beginning in1985. A species-specific immunofluorescent technique was usedto screen water samples, with positive identification possibleat cell concentrations as low as 10–20 cells ml^–1.Both years.A.anophagefferens was detected at numerous stationsin and around Long Island and Barnegat Bay, NJ, typically athigh cell concentrations. To the north and south of thus ‘center’,nearly half of the remaining stations were positive for A.anophagefferens,but the cells were always at very low cell concentrations. Manyof the positive identifications in areas distant from Long Islandwere in waters with no known history of harmful brown tides.The species was present in both open coastal and estuanne locations,in salinities between 18 and 32 practical salinity units (PSU).The observed population distributions apparently still reflectthe massive 1985 outbreak when this species first bloomed, giventhe number of positive locations and high abundance of A.anophagefferensin the immediate vicinity of Long Island. However, the frequentoccurrence of this species in waters far from this population‘center’ is disturbing. Aureococcus anophagefferensis more widely distributed than was previously thought. Numerousareas thus have the potential for destructive brown tides suchas those associated with the sudden appearance of the speciesin 1985.     

TEMPORAL VARIATION IN FORAGING BEHAVIOUR OF PATELLA GRANULARIS (PATELLOGASTROPODA) AND SIPHONARIA CONCINNA (BASOMMATOPHORA) ON A SOUTH AFRICAN SHORE

Foraging activity of two mid- to low- shore species of limpet,Patella granulans (Prosobranchia) and Siphonaria concinna (Pulmonata)from an exposed shore on the Eastern Cape coast of South Africawas monitored. In both species, activity was compared duringspring and neap tides and, in P. granularis between summer andwinter. Rhythms of activity of the two species were similar,with foraging excursions being mainly associated with nocturnallow tide times, although some P. granularis foraged during daytimelow tides. It is suggested that foraging excursions in P. granularisare triggered by wave action. Both species foraged further onspring tides than on neap tides and this is suggested to bea result of the limited time limpets have to forage. P. granulariswas also found to forage further during summer when comparedto winter and the possibility that seasonal micro-algal productivityinfluences foraging distances in limpets is discussed. The foraging activity of both species could be divided into3 distinct phases, a relatively rapid outward phase, a muchslower foraging phase and a rapid homeward phase. Whether ornot these limpets graze throughout an excursion is not known.S. concinna was found to home to a fixed scar, although duringthe experiment some scar-swapping occurred. P. granularis didnot home to a fixed scar but possessed a ‘home range’(approx. 5 cm²) to which it returned after each excursion. Patella granularis was found to move randomly during foraging,whilst S. concinna foraged in a non-random direction -whichtook individuals upshore. No tidal-influence is thought to bepresent in this case and the possibility of a learning componentin the foraging behaviour of certain limpet species in relationto the return to optimal feeding patches is discussed. (Received 18 May 1996; accepted 2 September 1996)     

Effects of temperature and salinity on the growth of the red tide flagellates Heterocapsa circularisquama (Dinophyceae) and Chattonella verruculosa (Raphidophyceae)

Growth responses of the red tide flagellates, Heterocapsa circularisquama(Dinophyceae) and Chattonella verruculosa (Raphidophyceae),were examined with 36 different combinations of temperature(5–30°C) and salinity (10–35 PSU). Heterocapsacircularisquama did not grow at or below a temperature of 10°C.The maximum growth rate of H.circularisquama (1.3 divisionsday^–1) was obtained with a combination of 30°C and30 PSU. In contrast, C. verruculosa did not grow at 10 PSU andat temperatures of 25°C or more. The maximum growth rateof C. verruculosa (1.74 divisions day^–1) was obtainedwith a combination of 15°C and 25 PSU. A significant temperature-salinityinteraction on growth was found by factorial analysis. Basedon the physiological characteristics obtained in the presentstudy, these novel flagellates have a potential for future outbreaksof red tides in pre viously unaffected waters.     

Amphipods, isopods and surface currents: a case for passive dispersal in the Bay of Fundy, Canada

Six species of isopods and 18 species of amphipods were collectedin the neuston of the Bay of Fundy and adjacent waters. Collectionswere made over a grid of stations covering 2.4x10⁴ km² duringthree spring, three summer and two autumn surveys. No isopodsand only five species of amphipods were found in spring surveys.Isopods and amphipods were diverse and plentiful in the neustonin summer and autumn. Dominant isopods were Idotea baltica andI.metallica, and dominant amphipods were Calliopius laeviusculusand Parathemisto gaudichaudi. Amphipods and isopods reach theneuston of the Bay of Fundy in three ways. Idotea metallica,the only euneustonic species present, was probably advectedinto the Bay of Fundy from southern waters in summer, and didnot appear to overwinter in the Bay. Most species, includingI.baltica, were collected with drifting littoral vegetation,and we suggest that transport by surface currents is an importantfactor in dispersal of some shoreline crustaceans. Midwaterplankton, such as Parathemisto gaudichaudi, reached the neustoneither by advection in upwelling waters or by an extension oftheir normal diel vertical distribution.     

A 91-year record of seasonal and interannual variability of diatoms from laminated sediments in Saanich Inlet, British Columbia

Diatom seasonal succession and interannual variability werestudied using laminated sediments from Saanich Inlet, BritishColumbia, for the years 1900–1991. Frozen sediment coresallowed fine-scale sampling of laminae for each year. Thus,three ‘seasons’ for each year were identified basedon species composition. Thalassiosira species were indicatorsof spring deposition. Skeletonema costatum was abundant in samplesfollowing Thalassiosira, probably deposited in late spring andsummer. Rhizosolenia sp. was most abundant in fall/winter samples.Diatom stratigraphies were related to sea surface temperature,salinity, sea level and the Pacific North American Index (PNA)using canonical correspondence analysis (CCA). CCA showed thatspecies of a particular season generally had optima for temperatureand salinity characteristic of that time. Interannual changesin diatom species composition and abundance were most prevalentin the decades 1920–1940, with the exception of S.costatumwhich showed cyclic changes in abundance. Skeletonema was moreabundant during periods of cool temperatures, while littoraldiatoms were more abundant during times of heavy winter rains.Sea level was an important variable in CCA and while its relationshipto diatoms is not clear, it may be related to variations innutrient supply to diatoms in surface waters.     

Experimental studies into the feeding biology of rotifers in brackish water

Mass developments of rotifers of the genus Brachionus, and especiallyof B.quadridentatus, occur regularly in the largely hypertrophicchain of shallow waters (‘boddens’) south of theDarss-Zingst peninsula (Southern Baltic). Interest in the autecologyof the species is, therefore, considerable. Various food sourceswere used in laboratory experiments to ascertain the food requirementsof B.quadridentatus, determine its filtration and ingestionrates, and assess its food particle size-selection ability.Growth experiments showed that the chlorophyceans Nannochlorissp. and Chlorella vulgaris possess considerable nutritionalvalue for the species, whereas abundances declined when Microcystisfirma, detritus from Enteromorpha sp. and only bacteria (Pseudomonas),respectively, were provided as food sources. Filtration ratesvaried between 0.02 and 1.73 µl ind.^–1 h^–1,and ingestion rates between 121 and 5560 cells ind.^–1h^–1, depending on the filtration rate and algal concentration.Investigations into food particle size selection using fluorescentlatex particles revealed that particle size influences foodparticle intake. When particles of different sizes were mixed,the animals showed a preference for the larger particles andingested the smaller ones with a diameter of 1–2 µmless efficiently. The brackish water species Brachionus plicatiliswas studied besides B.quadridentatus in all experiments. Theformer species proved to be superior both in its range of utilizableparticle sizes and its growth rate. The experiments with laboratorycultures were backed up by studies performed with various rotiferspecies taken from natural populations.