Zooplankton boom and ice amphipod bust below melting sea ice in the Amundsen Gulf, Arctic Canada

Early summer in the Arctic with extensive ice melt and break-up represents a dramatic change for sympagic–pelagic fauna below seasonal sea ice. As part of the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL), this investigation quantified zooplankton in the meltwater layer below landfast ice and remaining ice fauna below melting ice during June (2008) in Franklin Bay and Darnley Bay, Amundsen Gulf, Canada. The ice was in a state of advanced melt, with fully developed melt ponds. Intense melting resulted in a 0.3- to 0.5-m-thick meltwater layer below the ice, with a strong halocline to the Arctic water below. Zooplankton under the ice, in and below the meltwater layer, was sampled by SCUBA divers. Dense concentrations (max. 1,400 ind. m⁻³) of Calanus glacialis were associated with the meltwater layer, with dominant copepodid stages CIV and CV and high abundance of nauplii. Less abundant species included Pseudocalanus spp., Oithona similis and C. hyperboreus. The copepods were likely feeding on phytoplankton (0.5–2.3 mg Chl-a m⁻³) in the meltwater layer. Ice amphipods were present at low abundance (<10 ind. m⁻²) and wet biomass (<0.2 g m⁻²). Onisimus glacialis and Apherusa glacialis made up 64 and 51% of the total ice faunal abundance in Darnley Bay and Franklin Bay, respectively. During early summer, the autochthonous ice fauna becomes gradually replaced by allochthonous zooplankton, with an abundance boom near the meltwater layer. The ice amphipod bust occurs during late stages of melting and break-up, when their sympagic habitat is diminished then lost.     

Some studies on the ecology of limnetic crustacean zooplankton in Lake Begnas and Rupa,Pokhara Valley,Nepal

Monthly zooplankton samples taken during the period February, 1977 to February, 1978 in the deepest portion in two shallow sub-tropical Lakes, Begnas and Rupa in the Pokhara Valley, Nepal were studied. Four peaks of zooplankton abundance were noted. Adult and copepodid Copepoda were numerically dominant in both lakes with 56% Copepoda, 24% Cladocera and 20% nauplii in Lake Begnas and 48% Copepoda, 36% Cladocera and 16% nauplii in Lake Rupa. Other forms like Chaoborus larvae occurred sporadically in both lakes. An occurrence of the rare Limnocnida nepalensis (Coelenterata: Limnomedusae) in Lake Rupa was also noted during April and May, 1977. Although both of these lakes had already been ranked as eutrophic, the absence of calanoids, relative abundance of Bosmina longirostris and higher gross primary production in Lake Rupa is an indication of a higher trophic condition than that of Lake Begnas.     

Predaceous feeding habits of Limnocalanus macrurus

Limnocalanus macrurus, a large, glacial-relict copepod, hasbeen assumed an omnivore or a herbivore; predaceous habits ofthe species are unknown. The predaceous feeding habits of Limnocalanusfrom Lake Michigan were studied in the laboratory using naturalprey. Predation rates were highest on copepod nauplii. Copepoditesof Diaptomus spp. and Cyclops spp. were preyed upon at lowerrates. Limnocalanus preyed selectively upon nauplii <300µm. Small cyclopoid copepodites (<–750 µm)were also selected over large copepodites. Experiments usingtwo prey types showed that nauplii were selected over all copepodites,and that no selectivity existed for either diaptomid or cyclopoidcopepodites. Predaceous feeding habits began in the fourth copepoditestage of Limnocalanus. Predaceous feeding rates of Limnocalanuschanged seasonally being highest in late spring and autumn andlowest in summer and early winter. Since Limnocalanus also feedson net-phytoplankton, predation rate changes may be relatedto changes in the relative abundance of large phytoplanktonand naupliar prey in nature. Limnocalanus predation may be animportant factor in structuring the zooplankton community. Present address: Great Lakes Research Division, University Michigan,Ann Arbor, MI 48109, USA     

Seasonality and abundance of some dominant crustacean zooplankton in Lake Awasa,a tropical rift valley lake in Ethiopia

The zooplankton of a Rift Valley lake in Ethiopia, Awasa, was sampled at 3 stations for 2 years (1986 and 1987) concurrently with various meteorological and limnological measurements. The spatial and temporal variation in abundance of some numerically dominant crustaceans, Mesocyclops aequatorialis similis (Copepoda), Thermocyclops consimilis (Copepoda) and Diaphanosoma excisum (Cladocera) is discussed. Temporal (months, sampling dates) rather than spatial (station) variability accounts for more than 50% of the total variance in zooplankton abundance but horizontal patchiness exists during periods of high zooplankton density. Sampling errors were generally low, except for counts of cyclopoid nauplii (subsampling) and Diaphanosoma (inter-replicate variance). Zooplankton showed distinct seasonality associated with the mixing cycle of the lake. Total numbers increased to more than 200 000 m⁻³ during the unstratified period (July to September). Low numbers were evident during stratification (February to May) when zooplankton numbers did not exceed 15 000 m⁻³. Individual zooplankton species and age classes showed variable seasonal amplitudes, ranging from 6.4 (nauplius 3) to 44.8 (copepodite 3 of Mesocyclops). We discuss some possible causes for zooplankton seasonality in Lake Awasa, and also review zooplankton seasonal cycles in other tropical lakes, especially African ones.     

Zooplankton in a Danube River Arm near Rusovce (Slovakia)

Poor quantity of zooplankton was recorded in a Danube arm situated on the right side of the Danube River in Slovakia (river km 1857) in 2002 and 2003. All over the year the arm is significantly influenced by groundwater by reason of seepage. Because of low mean water temperature (12°C) and poorly developed macrovegetation in particular, the arm reminds gravel pit-like. The annual average of zooplankton biomass was low and ranged from 0.35 g m⁻³ (2002) to 1.28 g m⁻³ (2003), because of low crustacean abundance. Total cladoceran abundance was excessively low in both years and ranged from 3.5 N L⁻¹ (2002) to 16.6 N L⁻¹ (2003). Small species, Bosmina longirostris and Chydorus sphaericus were dominant. Only four adult Copepoda — Cyclops vicinus, Thermocyclops crassus, Eurytemora velox and Eudiaptomus gracilis — were recorded in quantitative samples of both years. In the zooplankton assemblage dominated rotifers (Synchaeta pectinata, Synchaeta oblonga, Polyarthra dolichoptera and Keratella cochlearis) which represented 78% and 67% of total abundance respectively. The total of 19 species of rotifers, 34 Cladocera species and 16 taxa of Copepoda were found.     

The longitudinal distribution and community dynamics of zooplankton in a regulated large river: a case study of the Nakdong River (Korea)

The longitudinal distribution and seasonal dynamics of zooplankton were examined along a 200-km section of the middle to lower Nakdong River, Korea. Zooplankton was sampled twice a month from January 1995 to December 1997 at five sites in the main river channel. There was considerable longitudinal variation in total zooplankton abundance (ANOVA, p < 0.001). All major zooplankton groups (rotifers, cladocerans, copepodids and nauplii) increased significantly with distance downstream along the river. There also were statistically significant seasonal differences in zooplankton abundance at the sampling sites (ANOVA, p < 0.01). Zooplankton abundance was high in spring and fall and low in summer and winter. The seasonal pattern of rotifers was similar to that of total zooplankton. This reflected the fact that rotifers (Brachionus calyciflorus, B. rubens, Keratella cochlearis and Polyarthra spp.) strongly dominated the zooplankton community at all locations. Among the macrozooplankton, small-bodied cladocerans (e.g. Bosmina spp.) dominated; the abundance of large-bodied cladocerans (e.g. Daphnia) was negligible (0–5 ind. l^–1). Among the environmental variables considered, partial residence time seemed to play the most important role in determining characteristics of the river zooplankton community.     

Basin scale distribution of zooplankton in the Ligurian Sea (north-western Mediterranean) in late autumn

Mesozooplankton biomass and abundance were evaluated in epipelagic waters at 59 stations covering the Italian sector of the Ligurian Sea (north-western Mediterranean) in December 1990. This region is characterised by a cyclonic circulation which encloses a central divergence zone and is associated with a main thermohaline front offshore the western Ligurian coast. At the end of autumn, mesozooplankton biomass (range: 0.80–4.24 mg DW m⁻³) and the abundance (range: 83.8–932 ind. m⁻³) were lower in the divergence zone. On the contrary, in the Ligurian frontal zone at the periphery of the divergence and on the eastern continental shelf the greatest values of biomass and abundance were recorded. Copepods and appendicularians dominated the mesozooplankton community, the main taxa being the copepods Clausocalanus spp. (46% of total zooplankton) and Oithona spp. (15%) and the appendicularian Fritillaria spp. (12%). Three hydrological sub-regions, i.e. the divergence, the eastern continental shelf and the periphery of the divergence, were characterised by different zooplankton communities and characteristic species. Environmental differences between the three zones were mainly related to changes in bottom topography, sea surface temperatures and quantity of particulate organic matter. Vertical mesozooplankton abundance and taxa distribution from the surface to 1,900 m depth were also examined in one station. The results showed that the bulk of the community was concentrated in the upper 200 m, small copepods being dominant particularly in the upper 50 m. The copepod community was more diversified in sub-superficial waters, with a maximum observed in the 200–400 m layer. The distributions of main zooplankton taxa described in epipelagic waters in the eastern Ligurian Sea in autumn were compared with their distribution at surface in the north-western Mediterranean obtained by sampling performed with the Continuous Plankton Recorder in 1997–1999. The analysis of the zooplankton community in CPR samples confirms the dominance of small copepods (Paracalanus spp., Clausocalanus spp., Oithona spp.) and appendicularians in the north-western Mediterranean in late autumn-winter and shows that their distribution is mainly related to the main mesoscale hydrographic features characterising this basin. Guest editors: S. Souissi & G. A. Boxshall Copepoda in the Mediterranean: Papers from the 9th International Conference on Copepoda, Hammamet, Tunisia     

Regional and seasonal variability of zooplankton collected using sediment traps in the southeastern Beaufort Sea, Canadian Arctic

Time-series sediment traps were deployed at six mooring sites in the southeastern Beaufort Sea from October 2003 to August 2004 during the cruise of the Canadian research vessel Amundsen within the framework of the Canadian Arctic Shelf Exchange Study (CASES). Trap-collected zooplankton (TCZ) at around 200 m water depth was dominated by copepods accounting for 74–93% of the total abundance throughout the year with increase in abundance at all sites during the fall. Seven distinct TCZ groups were identified through cluster analysis. Two marked seasonal shifts in TCZ composition from late fall to early winter and from spring to early summer were revealed at five sites at 200 m depth. The zooplankton was dominated by Oncaea spp., pteropods, and copepod nauplii in the late fall cluster and in the winter cluster, and by copepod nauplii in the summer cluster. A significant change in water temperature, salinity, and sea ice concentration was observed only with the spring–summer shift. The cluster analysis also revealed that TCZ composition at 200 m at a station located in the Cape Bathurst Polynya was markedly different from those at other sites through the study period by being characterized by the dominance of various copepodite stages of Metridia longa. This was probably due to a less prolonged period of sea ice cover, which provides favorable food conditions for the zooplankton community.     

Seasonal variations in biomass, abundance and composition of zooplankton in the subarctic waters north of Iceland

The seasonal variations in biomass, abundance and species composition of zooplankton in relation to hydrography and chlorophyll a were studied in the subarctic waters north of Iceland. The sampling was carried out at approximately monthly intervals from February 1993 to February 1994 at eight stations arranged along a transect extending from 66°16′N–18°50′W to 68°00′N–18°50′W. The mean temperature at 50 m depth showed a clear seasonal pattern, with lowest water temperatures in February (∼1.1°C) and the highest in July (∼5.4°C). The spring growth of the phytoplankton began in late March and culminated during mid-April (∼7.0 mg Chl a m⁻³). Both the biomass and the abundance of total zooplankton were low during the winter and peaked once during the summer in late May (∼4 g m⁻² and ∼38,000 individuals m⁻²). A total of 42 species and taxonomic groups were identified in the samples. Eight taxa contributed ∼90% of the total zooplankton number. Of these Calanus finmarchicus was by far the most abundant species (∼60% of the total zooplankton). Less important groups were ophiuroid larvae (∼9%), Pseudocalanus spp. (∼8%), Metridia longa (∼4%), C. hyperboreus (∼3%), Acartia longiremis (∼2%), chaetognaths (∼2%) and euphausiid larvae (∼2%). The dominant copepods showed two main patterns in seasonal abundance: C. finmarchicus, C. hyperboreus and C. glacialis had one annual peak in numbers in late May, while Pseudocalanus spp., M. longa and A. longiremis showed two maxima during the summer (July) and autumn (October/November). Ophiuroid larvae and chaetognaths (mainly Sagitta elegans) peaked during the middle of July, while the number of euphausiid eggs and larvae was greatest from May to July. The succession in population structure of C. finmarchicus indicated its main spawning to be in April and May, coincident with the phytoplankton spring bloom. A minor spawning was also observed sometime between August and October. However, the offspring from this second spawning contributed only insignificantly to the overwintering stock of C. finmarchicus. Received: 12 September 1997 / Accepted: 1 March 1998     

Spatio-temporal variations of the zooplankton abundance and composition in a West African tropical coastal lagoon (Grand-Lahou,Côte d’Ivoire)

Zooplankton constitutes a sensitive tool for monitoring environmental changes in coastal lagoons; however, the available information on zooplankton communities is not sufficient to optimize their rational management. The relationships between zooplankton distribution and environmental factors were studied in a tropical lagoon to test whether the indicator properties of zooplankton assemblages could be used to monitor water quality, in a context of expected eutrophication provoked by an increasing anthropogenic activity. Twenty-one (21) stations were sampled monthly from January to December 2004. The community was composed of 65 taxa including Copepoda, Rotifera, and Cladocera. Copepoda was the most abundant group (81% of total numbers). The main zooplankton species were Oithona brevicornis, Acartia clausi, and Brachionus plicatilis. The highest zooplankton abundance (171–175 ind. l⁻¹) was recorded during the long, dry season (February–April) and the lowest (40–45 ind. l⁻¹) during the rainy and the flood periods (June–July). At a spatial level, the lowest abundance was observed in the estuarine zone. During the dry seasons (December–April and August–September), marine zooplankton taxa were abundant near the channel of Grand-Lahou, and brackish water taxa dominated in the other sites. Multivariate analyses (Co-inertia) showed that the composition of zooplanktonic communities and their spatio-temporal variations were mainly controlled by salinity variations closely linked to the climatic and hydrological context. The role of the trophic state on zooplankton communities could not be clearly evidenced. Our results and a comparison with previous studies in the neighboring, highly polluted Ebrié Lagoon suggest that the ratio between Oithona and Acartia abundance could be used as biological indicator for the water quality. Handling editor: S. I. Dodson     

Zooplankton Distribution in Tropical Reservoirs,South China

The zooplankton of 18 reservoirs of South China was investigated in 2000. 61 Rotifera species, 23 Cladoceras and 14 Copepodas were identified. The most frequent Rotifera genera were Keratella, Brachionus, Trichocerca, Diurella, Ascomorpha, Polyarthra, Ploesoma, Asplanchna, Pompholyx and Conochilus. Bosmina longirostris, Bosminopsis deitersi, Diaphanosoma birgei, D. brachyurum and Moina micrura were typical of Cladocera in the reservoirs. Phyllodiaptomus tunguidus, Neodiaptomus schmackeri and Mesocyclops leuckarti were the most frequent Copepoda and M. leuckarti dominated Copepoda in most reservoirs. High zooplankton species richness with low abundance was characteristic of the throughflowing reservoir, whereas low species richness with low abundance was found in the reservoir with the longest retention time. Relative high abundance and medium species diversity were the distinction of intermediate retention time reservoirs.     

Zooplankton Dynamics in the Hyper‐Eutrophic Nakdong River System (Korea) Regulated by an Estuary Dam and Side Channels

Zooplankton in the main channel of the Nakdong River and in three tributaries was sampled from June 1994 to September 1995. Planktonic rotifers (Brachionus spp., Keratella spp., and Polyarthra spp.), cyclopoid nauplii and small cladocerans (Bosmina longirostris) were numerically dominant. There was considerable longitudinal variation of zooplankton biomass in the main channel as well as spatial heterogeneity among the major tributaries. In the middle region of the main channel, between river kilometer (RK) 170 and 150 above the estuary dam, total zooplankton abundance sharply increased from less than 100 ind. L^—1 to more than 1,000 ind. L^—1. In a downstream direction toward the estuary dam, phytoplankton biomass increased while total zooplankton biomass decreased. However, as shown by the increasing transport of zooplankton biomass, zooplankton was diluted in the reach of the estuary dam. Advective effects from major tributaries appear to be the contributory factor for the higher zooplankton biomass in the middle region. Overall, rather the external factors (flushing, retention) than internal factors (e.g., phytoplankton) appear to be responsible for changes in zooplankton abundance toward the river mouth.     

Plankton community composition and vertical migration during polar night in Kongsfjorden

The polar night in the Arctic is characterized by up to six months of darkness, low temperatures and limited food availability. Biological data on species composition and abundance during this period are scarce due to the logistical challenges posed when sampling these regions. Here, we characterize the plankton community composition during the polar night using water samplers and zooplankton net samples (50, 64, 200, 1500 μm), supplemented by acoustics (ADCPs, 300 kHz), to address a previously unresolved question–which species of zooplankton perform diel vertical migration during the polar night? The protist community (smallest plankton fraction) was mainly represented by ciliates (Strombidiida). In the larger zooplankton fractions (50, 64, 200 μm) the species composition was represented primarily by copepod nauplii and small copepods (e.g., Microcalanus spp., Pseudocalanus spp. and Oithona similis). In the largest zooplankton fraction (>1500 μm), the euphausiid, Thysanoessa inermis, was the most abundant species followed by the chaetognath Parasagitta elegans. Classical DVM was not observed throughout the darkest parts of the polar night (November–mid-January), although, subtle vertical migration patterns were detected in the acoustic data. With the occurrence of a more distinct day–night cycle (i.e., end of January), acoustical DVM signals were observed, paralleled by a classical DVM pattern in February in the largest fractions of zooplankton net samples. We suggest that Thysanoessa spp. are main responsible for the acoustical migration patterns throughout the polar night, although, chaetognaths and copepods may be co-responsible.     

Seasonal variability in copepod ingestion and egg production on the Faroe shelf

Copepod community ingestion rates of Calanus finmarchicus, Temora longicornis, Acartia longiremis and Pseudocalanus spp., and egg production rates of C. finmarchicus and T. longicornis, were studied in relation to phytoplankton composition, abundance and biomass on the Faroe shelf during a one-year cycle. The phytoplankton community during winter was mainly composed of small flagellates and the copepods of Pseudocalanus spp. As the spring bloom progressed, diatoms increased in abundance and dominated the biomass throughout summer. C. finmarchicus increased in numbers in early spring, while T. longicornis and A. longiremis dominated the community during summer and autumn. While no response in ingestion rates was observed for A. longiremis and Pseudocalanus spp. with increasing diatom biomass, both ingestion rates and egg production of C. finmarchicus and T. longicornis, generally increased, showing a dependence upon diatoms for production. The daily ingestion for C. finmarchicus females was 7% and 22% of body biomass during the pre-bloom and bloom period, respectively, while for T. longicornis females it was 33% and 56% and for A. longiremis females 22% and 33%, respectively. C. finmarchicus accounted for more than 80% of the total copepod ingestion in May, but in mid- and late summer, T. longicornis and A. longiremis dominated, and represented 80–90% of the total copepod ingestion. The proportion of reproductively mature C. finmarchicus increased as the phytoplankton biomass increased. Most of the time there was good agreement between herbivorous ingestion rates and calculated carbon demand for the observed egg production. However, both species showed a peak in egg production prior to the phytoplankton spring-bloom. Handling editor: J. Padisak.     

Zooplankton dynamic of Lake Prespa (Macedonia)

The composition and temporal abundance patterns of zooplankton community in Lake Prespa pelagic zone were studied throughout an annual cycle (October 2008–September 2009). Eighteen species (10 Rotifera, 5 Cladocera, 2 Copepoda, 1 Mollusca) were evidenced. It includes Arctodiaptomus steindachneri, an endemic calanoid of the Western Balkans. The zooplankton density varied during the investigated period and certain seasonal successions in temporal transpositions of their maximal development were noticed. The total zooplankton density was much higher in spring and summer period. The representatives of subclass Copepoda were dominant during the whole year. The dominant species was A. steindachneri. At the second place (with exception of the winter period) were the Cladocera representatives. The dominant species was Daphnia cucullata. At the third and fourth place were rotifers and larval form of Dreissena polymorpha, respectively. The quantitative presence of the Copepoda representatives was significantly lower in terms of the previous investigations. The Cladocera quantity reached high values during this period, particularly in summer. Such altering in the quantitative ratio between Copepoda and Cladocera in favor of the Cladocera, especially high quantitative presence of D. cucullata, typical for eutrophic lakes, imply of significant changes in zooplankton community and changes of the water quality in Lake Prespa pelagial.     

Mesh size and collection characteristics of 50-cm diameter conical plankton nets

This paper compares collection characteristics of #2-(363 µm), #10-(156 µm), and #20-(76 µm) mesh conical plankton nets: dimensions were 50-cm diameter by 1.6-m long. The #2-mesh net severely underestimated the abundances of Lake Michigan copepods and cladocerans with the exception of the largest species (Limnocalanus macrurus). Zooplankton abundance estimates were more similar for the #10- and #20-mesh nets collections. Nauplii, however, were severely undersampled by the #10-mesh net with abundance estimates approximately 8 to 12 times lower than for the #20-mesh net collections. Most other larger zooplankton were 50% more abundant in the 20-mesh net collections than in the #10-mesh net collections: such consistent differences occurred despite large variations in taxa size. This indicates that a sampling bias occurred other than the loss of zooplankton through the meshes of the #10 net. We hypothesize that, by incorrectly locating the flowmeter in the mouth of the plankton net, we underestimated the volume of water filtered by the easily-clogged #20-mesh net and therefore overestimated taxa abundances. We conclude that the #10-mesh net provided accurate estimates of microcrustacean zooplankton abundances except for nauplii. The #10-mesh net used in our study had a filtration area ratio of 3.06 and operated at a calculated average filtration efficiency of 98%. The #20-mesh net had a filtration area ratio of 1.86 and operated at calculated average filtration efficiencies ranging from 64.7% (41.7 m station) to 79.6% (6.3 m station). Calculations are presented which show how the filtration efficiencies of the nets used in our study could be improved by net redesign.     

Zooplankton assemblages in two reservoirs: one subjected to accentuated water level fluctuations,the other with more stable water levels

The abundance, composition and dynamics of zooplankton were followed in two reservoirs of the River Douro catchment. The Serra Serrada Reservoir is subject to marked fluctuations in water levels. The highest values of total phosphorus, soluble reactive phosphorus, nitrate, water colour and chlorophyll a were found during the minimum level phase. Rotifera was dominant except in late summer and autumn when the cladoceran Ceriodaphnia quadrangula or the copepod Tropocyclops prasinus replaced them as the dominant zooplankton. Among the rotifers the most common taxa were Keratella cochlearis, Conochilus sp. and Asplanchna priodonta. Maximum rotifer density was about 80,000 ind m⁻³ in 2000, 200,000 ind m⁻³ in 2001 and 100,000 ind m⁻³ in 2002. Among the crustacean zooplankton C. quadrangula achieved densities of up to 45,000 ind m⁻³ and T. prasinus, up to 80,000 ind m⁻³. Canonical correspondence analysis revealed a strong contribution of the variation in the stored water volume, temperature, total phosphorus, chlorophyll, nitrates, and water transparency to the observed, significant association between zooplankton assemblage and environmental variables. In the Azibo Reservoir, fluctuations in water level are smaller. Only total phosphorus, cholorophyll and conductivity varied seasonally. Cladocera and Copepoda were dominant during the whole study period. The most abundant taxa were Ceriodaphnia pulchella, Daphnia longispina, Diaphanosoma brachyurum, Bosmina longirostris and Copidodiaptomus numidicus. Cladocera achieved densities of up to 25,000 ind m⁻³ and Copepoda up to 15,000 ind m⁻³. Rotifera in general reached densities of up to 6,000 ind m⁻³. On the basis of canonical correspondence analysis only temperature and conductivity were significantly associated with zooplankton assemblage.     

Foods of <Emphasis Type="Italic">Velella velella</Emphasis> (Cnidaria: Hydrozoa) in algal rafts and its distribution in Irish seas

The pleustonic hydrozoan, Velella velella, occurs throughout tropical to cold-temperate oceans of the world and sometimes are stranded in masses along hundreds of kilometers of beaches. In June 2009, we encountered algal rafts in the Celtic Sea containing many V. velella that we immediately preserved for gut content analysis. Available prey were enumerated from raft-associated fauna and zooplankton sampled nearby. The identifiable prey (331) in V. velella comprised 78% raft-associated prey (primarily harpacticoid copepods, cumaceans, small fish) and 22% pelagic prey (calanoid copepods, barnacle nauplii, fish eggs). Comparison of ingested with available prey showed selection for fish eggs and small fish, among others; therefore, the null hypothesis, that V. velella consumed all available prey equally, was rejected. Transport by wind and water concentrate Velella spp. in convergences with algal rafts, which suggests that they are important predators of raft—as well as pelagic fauna. A visual survey in September 2004 across the Celtic Sea and beach-stranding data show that V. velella is very abundant in Irish waters at times. Its circumpolar abundance, consumption of pelagic prey and production from symbiotic zooxanthellae, and mass deposition on beaches suggest that V. velella is important in open-ocean carbon cycling and in transport of pelagic production to landmasses.     

Possible involvement of microcystins in the unexplained mass mortalities of Lesser Flamingo (<Emphasis Type="Italic">Phoeniconaias minor</Emphasis> Geoffroy) at Lake Manyara in Tanzania

We examined the effects of food and light on the swimming behavior of nauplii of the cyclopoid Apocyclops royi (Lindberg, 1940) (Copepoda: Cyclopoida) and the calanoid Pseudodiaptomus annandalei Sewell, 1919 (Copepoda: Calanoida). Several behavioral parameters such as swimming patterns, speed, and trajectories exhibited distinct ontogenetic differences between the two species. When algae Isochrysis galbana (Haptophyta: Isochrysidales) were offered as food to the nauplii of A. royi, they showed fast circle swimming behavior, while nauplii of P. annandalei never exhibited such behavior, neither with, nor without algae. The different behavioral patterns between the nauplii of both species suggest they both have different foraging strategies in detecting and capturing food.     

The production and ingestion of faecal pellets by nauplii of marine calanoid copepods

The downward transport of organic matter as zooplankton faecalmaterial is influenced by copepods which fragment, ingest andrecycle some of the pellet contents. Most of this activity hasbeen attributed to the later copepodite stages and the adults,but little is known about the role of nauplii. Stage-relateddefaecation rates during the naupliar development of two speciesof copepod, Calanus helgolandicus and Pseudocalanus elongatus,were quantified in a series of laboratory experiments. The productionof faecal material commenced soon after the appearance of theNIII in both species and increased throughout naupliar development.The causes of the increase were the formation of larger pelletsby later stages in Calanus and an increased rate of productionby Pseudocalanus. Calanus nauplii, when supplied with algalfood at concentrations that would support full naupliar development,ingested or broke up the pellets of the smaller Pseudocalanusspecies at rates of 1.15 pellets nauplius^–1 h^–1This consumption increased to 2.96 pellets nauplius^–1h^–1 when the concentration of algal food was reduced toa limiting level. Pseudocalanus was not able to consume thepellets of Calanus. Ingestion of Pseudocalanus faecal pelletsby Calanus could supply a nutritional benefit to a food-limitednauplius.