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Recruitment success at the early life stages is a critical process for zooplankton demography. Copepods often dominate the zooplankton in marine coastal zones and are prey of the majority of fish larvae. Hypotheses interpreting variations of copepod recruitment are based on the concepts of 'naupliar predation,' 'nutritional deficiency,' and 'toxic effect' of diatom diets. Contradictory laboratory and field studies have reached opposite conclusions on the effects of diatoms on copepod reproductive success, blurring our view of marine food-web energy flow from diatoms to higher consumers by means of copepods. Here we report estimates of copepod feeding selectivity and reproduction in response to seasonally changing phytoplankton characteristics measured in a highly productive coastal upwelling area off the coast of central Chile. The variable phytoplankton diversity and changing food quality had a strong and highly significant impact on the feeding selectivity, reproduction, and larval survival of three indigenous copepod species. Seasonal changes in copepod feeding behavior were related to the alternating protozoan-diatom diets, mostly based on dinoflagellates and ciliates during winter and autumn (low highly unsaturated fatty acids [HUFA]/polyunsaturated fatty acids [PUFA] availability), but switched to a diet of centric and chain-forming diatoms (high HUFA/PUFA availability) during the spring/summer upwelling period. Ingestion of diatom cells induced a positive effect on egg production. However, a negative relationship was found between egg hatching success, naupliar survival, and diatom ingestion. Depending on the phytoplankton species, diets had different effects on copepod reproduction and recruitment. In consequence, it seems that the classical marine food web model does not apply to some coastal upwelling systems. Key words: copepod feeding; egg production; hatching success; larval survival; marine food web; phytoplankton diversity.

A new mixed layer multi-nutrient ecosystem model, incorporating diatoms, non-diatoms and zooplankton is described that models the role of iron in marine biogeochemical cycles. The model results at Kerfix confirm the suggestions that underwater light levels have a more limiting effect on phytoplankton growth than iron supply and this model is also used to calculate C budgets.

Seasonal changes in diversity and community structure of planktonic copepods at a shelf site in Sagami Bay, Japan was studied in relation to cross-shelf interaction of species components. Seasonal mesozooplankton samples were collected from the shelf station (St. M) of the north-west part of Sagami Bay from 1995 to 1997. Vertical multi-layered samples were collected near the center of Sagami Bay (St. P) in June 1996. A total 185 copepod species were identified from the two stations. We observed a clear seasonal succession in calanoid diversity and community structure at St. M from a simple shelf water community (> 11 species) during spring blooming periods to highly diverse and mixed communities (ca 20-30 species) of shelf water species coupled with various Kuroshio Current species during late summer to autumn. Cluster and non-metric multidimensional scaling ordination analyses showed two distinct calanoid community groups. One group, which included samples of St. M and the surface layer of St. P, consisted of shelf water species, such as Calanus sinicus, Ctenocalanus vanus, Paracalanus spp., and Kuroshio species, such as, Canthocalanus pauper, Scolecithrix danae, etc. The other cluster was restricted to the samples collected from mid and deep layers at St. P, which consisted of meso- and bathypelagic species and Oyashio species (cold-current species, such as Neocalanus cristatus, Pseudocalanus spp., Eucalanus bungii and Metridia pacifica). In the mid and deep layers at St. P, the population of dormant copepodid stage V (CV) of Eucalanus californicus and C. sinicus were dominant. The deep CV population of C. sinicus might be ecologically discriminated from the surface and shelf water population due to their larger body length and dormant life cycle. E. californicus was also collected at the shelf site during each spring bloom period, whereas the population might descend into the mid- and deep-layers of the central bay before summer. Our results suggest that the seasonal fluctuation of community structure in the shelf water was controlled by both physical (Kuroshio Current) and biological factors, i.e., spring bloom and ontogenetic vertical migration of E. californicus. In particular, transport and diffusion processes of Kuroshio Current in Sagami Bay played a key role in controlling the shelf water calanoid community., Introduction Copepods are the most abundant and diverse mesozooplankton in marine habitats and are considered as a major component of secondary producers in the marine food web. In temperate shelf [...]

Mesozooplankton distribution, metabolism and feeding were investigated in the slope water oceanic anticyclonic eddy (SWODDY) AE6 during the cruise Gigovi-0898, which was conducted in August 1998 in the Bay of Biscay. According to the distribution of isotherms at 200 m depth, the sampling area was divided into three zones: SWODDY centre (C), edge (E) and outside the SWODDY (O). Multivariate analysis identified four different zooplankton assemblages. Such separation was closely related to the structure of the SWODDY, with each grouping associated to a particular zone of this mesoscale structure. Thus, two of the groups were located at the SWODDY centre and outside (groups C and O, respectively), whereas the two remaining station groupings ([T.sub.WE] and [T.sub.NS]) were situated at the SWODDY margin. The assemblages C and O differed clearly from each other in their taxonomic composition. In contrast, [T.sub.WE] and [T.sub.NS] were separated because of the differences observed in numerical abundance rather than by a different composition. Some taxa were found exclusively outside the SWODDY, while others were confined to the centre, suggesting a large degree of isolation of the SWODDY with respect to the surrounding waters. Phytoplankton and mesozooplankton biomass followed a similar pattern, with highest values in the SWODDY centre, although the differences between zones were significant only for phytoplankton. The highest grazing impact for both phytoplankton standing stock (3.4%) and primary production (12.7%) was observed outside the SWODDY. Ammonium released by mesozooplankton accounted for between 25.3% (outside the SWODDY) and 44.4% (SWODDY centre) of total phytoplankton nitrogen demands. The percentage of total phosphorus required to be fulfilled by phosphate excretion ranged from 14.0% at the edge to 17.5% outside. Mesozooplankton underwent intense vertical migrations, especially at the SWODDY edge. The role of the mesozooplankton in the biological pump releasing metabolic end-products below 200 m at night time is proposed as one of the main sources of downward export of biogenic material in these systems.

Gonad maturation processes were studied in Pseudocalanus spp. females from Georges Bank and Cape Cod Bay (northwest Atlantic) using a combination of morphological analysis and experiments. For light microscopy of the oocytes, females of different maturation stages were preserved immediately after capture. The maturation processes during the spawning cycle were described from observations of live females which were exposed to feeding and starvation at two temperatures, 8 and 15[degrees]C, for 12 days. The gonad morphology of these females was examined in 24 h intervals, and spawning events were recorded. Both light microscopy and whole animal observation revealed that oocytes during maturation change in shape and size, in the morphology of the nucleus, and in the appearance of the ooplasm. Due to these modifications of oocyte morphology and due to oocyte migration, the morphology of the gonads changed distinctly during a spawning cycle. Five oocyte development stages were identified by light microscopy and related to a macroscopic system of four gonad development stages, that can be applied to whole animals and allows the identification of females ready to spawn. The experiment showed that food and temperature had strong effects on gonad maturation processes. High proportions of mature females were found when food was available, whereas the proportion of immature females increased shortly after exposure to starvation. Compared to 15[degrees]C, gonad maturation at 8[degrees]C was prolonged and thus spawning frequency was lower. The final maturation processes at food saturated conditions were slower than the embryonic development, and no indication was found that mature oocytes are stored in the diverticula waiting to be released. The duration of the interspawning interval would thus be determined by the duration of final oocyte maturation which is dependent on both temperature and food supply.

The Baltic Sea is a very suitable site for stoichiometric studies, since its subbasins differ in their concentration of elemental components, and primary production can therefore be either nitrogen or phosphorus limited. To reveal if the nutrient limitation of mesozooplankton mirrors that of the primary producers, carbon, nitrogen and phosphorus content of both seston and grazers (Acartia sp., Centropages hamatus, Daphnia cristata, Eurytemora affinis, Limnocalanus macrurus, Temora longicornis) were measured in midsummer in the Baltic proper, the Gulf of Finland and the Gulf of Bothnia. The mineral ratios of the different taxa were equal, apart from L. macrurus with notably higher C:P and N:P ratios. Molar C:N ratios were relatively stable (5.1-6.3), whereas C:P and N:P ratios fluctuated more (41-144 and 6.6-24). However, zooplankton elemental composition and limitation did not depend on the limiting nutrient of the phytoplankton, the seston mineral ratio or the sea area. Both the seston--zooplankton elemental imbalance and the food threshold ratio indicated phosphorus limitation of most of the grazers. While L. macrurus may be C or N limited, the possible P deficiency of the other studied taxa suggest that the Baltic Sea zooplankton may act as a potential phosphorus sink, as the freshwater secondary producers do.

Two primary zooplankton clusters are described for the California Current System of the Pacific Ocean, using data obtained from the California Cooperative Oceanic Fisheries Investigations (CalCOFI). One consists mainly of diatoms typical of enriched marine regions; the other is comprised of species commonly found in the North Pacific Ocean's offshore central region. Interannual variability is not found in either cluster beyond seasonal variability.

Day/night zooplankton sampling in Kosterfjorden, Sweden, gave information on population succession, vertical distribution and feeding of Calanus finmarchicus over 17 months. Copepodid Stage 1 and 2 (C-I, C-II) were present from December to August, indicating reproduction during most of the year. Mating and breeding for the overwintering generation mainly took place in February/March, resulting in peak abundance of C-I in March/April. Secondary breeding periods were in April and July/August, but the resulting recruitment from these were low. The relative recruitment success in the first spring was around 13 times higher than during the second spring. Low temperature in the surface water early in the year and depression of the spring phytoplankton bloom may have caused the failure in the second year. Population biomass peaked at > 15 g dry weight [m.sup.-2] during the numeric peak of the youngest stages in March/April. A more sustainable level of high biomass of 8 to 10 g dw [m.sup.-2] was gradually built up during summer, mainly due to a continuous accumulation of C-Vs. Adults and C-Vs comprised the overwintering population, with 7 to 14% and 85 to 93%, respectively, for the 2 years, but only C-Vs staying in the deep water were in a resting state. Adult males showed a strong diurnal vertical migration (DVM) of the usual type from spring to early autumn and a reversed DVM during the cold season. They were in a feeding state throughout the year. Adult females showed the usual type of DVM during summer to autumn, but commonly a reversed DVM during winter to spring. They were usually in a feeding state, with no pronounced differences between surface and deep water or between day and night. C-Vs aggregated in the deep water from October to March and performed DVM in April to June. They were commonly feeding in the deep water between March and June but showed no or very low feeding activity there from July to February. C-Vs in the surface water were commonly feeding and showed the highest proportion of feeding in autumn, when the population in the deep water was inactive. C-V constituted up to nearly 100% of the population biomass, and therefore must be of profound ecological importance. Defined by this dominant role, the population of C. finmarchicus can be characterised as having an active period of feeding, reproduction and development from February to July with a following 6 to 7 months of resting in the deep water, when development is arrested and no feeding occurs.

Analysis is presented on zooplankton samples taken from the Antarctic Ocean region between Cape Town, South Africa, and the Antarctic continent. Highest densities were discovered at the Antarctic Polar Front, lowest densities at the Subantarctic Front, and copepods formed the majority of the zooplankton samples.

Research is presented on zooplankton samples taken from the Antarctic Ocean region between Cape Town, South Africa, and the Antarctic continent. Highest biomass and abundances were discovered in the Marginal Ice Zone, the Subantarctic Front, and the Antarctic Polar Front, with the largest grazing impact found at the Polar Front Zone.

Research is presented concerning the analysis of linear stability of a Nutrient-Phytoplankton-Zooplankton ocean ecosystem model in understanding how biological dynamics are influenced by vertical mixing.

Measurements of backscatter signal intensity and vertical velocity made with an acoustic doppler current profiler (ADCP) on the Hebridean Continental Shelf are discussed and interpreted. Topics include evidence of diel vertical migration, weakening of the migration signal midway through the time series, and possible advection of the migrating zooplankton away from the ADCP.

It is well-known that zooplankton make an important contribution to the diets of corals and other anthozoans. However, zooplankton is an important dietary component only for a few alyconacean corals. Scleractinian coral's ability to capture zooplankton may be affected by flow rates and colony morphology. A new study investigates the rates of zooplankton capture by corals in the reefs at Discovery Bay, Jamaica. The study supports previous studies showing that zooplankton capture rates are limited by low flow speeds.

A study was conducted to probe the vertical distribution of deep-sea zooplankton in the Arabian Sea at a depth in the bathypelagic zone. The highest biomass concentrations were detected in the uppermost 150 meter of the water column, decreasing in concentration below this level. The decrease of mesozooplankton concentration with depth in oxygen minimum zone was stronger than in open-ocean areas where oxygen minimum zone is absent.

Two species of tintinnids, Favella taraikaensis and F. azorica, were fed a diet of the toxic dinoflagellate Heterocapsa circularisquama to determine their growth, grazing and feeding responses. Results showed that temperature and prey density affect feeding behavior of ciliates and high concentration of prey algae causes high ingestion rates but decreased growth rates. Furthermore, the grazing of F. taraikaensis cannot control the development of H. circularisquama blooms at high concentrations of H. circularisquama.

A model of particle dynamics reveals the likely cause of daily cycles in marine aggregate concentration. Researchers who discovered the daily cycles in 1993 suggested three possible causes of the phenomenon; turbulence, phytoplankton growth and grazing. Incorporating each of these processes into a model of particle dynamics showed that neither daily growth nor grazing cycles were sufficient to create the cycles, but the daily cycles of marine turbulence, which are due to differences in incoming radiation, clearly created cyclical patterns in marine aggregate behaviour.

A comparison of the abundance, community composition and vertical distribution of macroplanktonic and micronektonic groups in three different sites in the northeast tropical Atlantic, namely, oligotrophic, mesotrophic and eutrophic, was conducted. For the euphausiid and thecosome groups, the number of species declined from oligotrophic to eutrophic sites. Few species were dominant at the mesotrophic and eutrophic sites. For vertically migrating species, migration amplitude was noted to have generally declined from the oligotrophic site to the mesotrophic and eutophic.

The population dynamics and production rate of calanoid copepod Paraclanus sp. in Fukuyama Harbor, a eutrophic inlet in the Inland Sea of Japan were studied. The study indicated that Paraclanus sp. was present in the zooplankton population throughout the year. Egg production rates in the natural population was constant. Mortality between egg and NIII was high and fluctuating due to predation and the sedimentation of eggs from the water column.

The diets and diet composition of calanoid copepods Eucalanus elongatus, Undinula vulgaris, Centropages velificatus and Temora stylifera from the West Florida continental shelf were studied using bottle incubation methods. The study revealed that calanoid copepods have two feeding modes, active or quiscent, which is determined by changes in food concentration in the ecosystem. Although nanoplankton composed the largest portion of copepod dietary biomass, copepod diets are diverse. Diatoms, dinoflagellates and microzooplankton were part of the diets of the four copepod species.

The respiratory physiology of the summer diapausing eggs of the neustonic copepod Anomalocera patersoni was represented by a bell-shaped curve with low oxygen consumption at the start of diapause. Adenosine triphosphate levels were high right after spawning but there was a rapid ATP level decline with time. Summer eggs also had lower ATP contents than winter eggs indicating that colder temperatures induced higher metabolism rates during dormancy.

Microzooplankton grazing experiments in the South Atlantic and Atlantic sector of the Southern Ocean indicate significant linear correlations between dilution and apparent phytoplankton growth rates in the area. On the other hand, protozooplankton abundance in the area co-varies with chlorophyll concentrations at the surface and at the subsurface chlorophyll maximum.

The aggregation of ctenophores near the estuary bottom and diel vertical migration are important factors in the retention of Pleurobrachia (P.) pileus in the Seine estuary. The ctenophores show passive tidal advection and active diel vertical migration. Large numbers around low tide and significant diel vertical migration occur in the outer estuary. The spring distribution includes high abundances on the marine side of the estuary.

The effects of seasonal pack ice on the distribution of zooplanktons and other mesopelagic organisms were studied by examining the uppermost 100 m. of water in the northwestern Weddell Sea during the austral spring of 1992. Findings indicated that mesopelagic organisms are distributed nearer to the surface under pack ice than in open water. This makes them more vulnerable to predators such as surface-foraging seabirds.

Species of the genus Daphnia are generalized filter-feeders and potentially strong competitors, yet several species often coexist in the open waters of lakes. We investigated the population dynamics and competitive interactions of two Daphnia species in Gull Lake, Michigan. In each of 3 yr D. pulicaria was always common, while D. galeata mendotae became abundant only in late summer. The summer invasion of D. galeata mendotae was associated with a decline in abundance of D. pulicaria in some, but not all years. Decline of D. pulicaria was strongly predicted by the loss of oxygen from deep water during summer, which resulted in greater spatial overlap between the species, and by changes in the quality of the phytoplankton resources. We employed in situ enclosures to manipulate the density of each species and quantify the intensity of intra- and interspecific competition. Repeated competition experiments demonstrated that the relative exploitative ability of the species reversed from early to late summer. Strong interspecific competition was often observed, but its strength varied with juvenile or adult stage, and with season. Daphnia pulicaria juveniles were always affected strongly by interspecific effects, while D. galeata mendotae juveniles were impacted largely by intraspecific effects. The relative strength of intra- and interspecific competition on adults reversed from early to late summer for each species. The magnitude of intra- and interspecific effects on D. pulicaria adults was similar during early summer, but by late summer interspecific effects were much stronger than intraspecific effects. The reverse was true for D. galeata mendotae adults; interspecific effects greatly decreased in late summer. This seasonal shift in the nature of competitive interactions provides an explanation for seasonal succession in this Daphnia assemblage., Key words: Daphnia; interspecific competition; intraspecific competition; population dynamics; resource partitioning; seasonal succession; stage-structure; vertical migration; zooplankton. INTRODUCTION Competition for limiting resources forms the basis of much ecological and evolutionary [...]

A study of the distribution of chaetognaths in the pelagic waters of the Eastern Mediterranean Sea reveals that most of the species are found within a 50 m range from the surface of water. Only a few species are found deep in the sea. The study involves the investigation of twenty vertical hauls from four different regions of the Eastern Mediterranean sea. Sagitta bipunctata, Sagitta enflata, Krohnitta subtilis, Sagitta minima, Sagitta lyra and Sagitta serratodentata occur at higher levels, the first two species being abundant at levels about 50 m.

An acoustic study of zooplankton distributions in the sea suggests daily formation of gaps, which do not contain vertically migrating zooplankton, in the ocean. Local topography and reactions among migrating animals and predators influence gap formation and patch mechanisms that occur subsequent to gap formation. Patch dynamics, controlled by both ocean currents and animal behavior, intensifies spatial heterogeneity of zooplanktons and influence marine food webs in irregular topographic sites.

The distributions of the main zooplankton groups in the surface layer are determined. Results show that zooplankton densities are lower outside than inside the lagoon. Moreover, zooplankton is densely concentrated in littoral bays with a marked eutrophication. Generally, 80 to 95 percent of the surface plankton consists of holoplankton, and 5 to 20 percent of meroplankton. Lastly, water exchanges between the lagoon and the ocean are partially responsible for the plankton distribution in the upper surface.

The concentrations of cadmium, copper and lead in neuston organisms from the Atlantic Ocean were determined. The metal accumulation in nineteen taxa of the neuston community was correlated with the logarithmic regressions of the corrected weight. The results showed the role of ocean-surface dwelling marine organisms in the biogeochemical cycles of metals.

The influence of bioluminescence on the predatory success rates of a nocturnal teleosts, Porichthys notatus, was evaluated. Mysids (Holmesimysis costata) were kept in aquaria with different concentrations of the dinoflagellate Pyrocystis fusiformis. Luminiscent flashes and prey strikes were observed using infrared cameras. The success rates and concentration of the dinoflagellate were correlated up to concentrations of three to 15 cells per millimeter. Higher concentrations resulted in decreased predatory accuracy because of a more diffused and confusing target.

I compiled literature observations of abundances of invertebrate zooplankters associated with marine snow aggregates in the euphoric zone. Abundances, normalized with ambient concentrations of colonizers, scale with equivalent aggregate radius raised to power 2.27. Different taxonomic groups showed different affinities for aggregates and copepods and crustacean nauplii were the dominant groups on aggregates. The encounter volumes (volume searched to find one aggregate) are substantial, e.g., [is greater than] 1 liter for a 1-cm aggregate, suggesting that some zooplankters actively search for aggregates. The scaling of the enrichment of invertebrates in aggregates over ambient water with aggregate radius (r) was significantly different from that of bacteria, [varies][r.sup.-0.73] and [varies][r.sup.-2.25], respectively, and for aggregates larger than 0.1 cm radius, invertebrates were one to several orders of magnitude more enriched than bacteria. Tentative estimates of the remineralization and degradation rates of aggregates due to the activity of invertebrate colonizers suggest that aggregate carbon is turned over within one to a few days. This is similar to or faster than turnover rates due to microorganisms. It is also estimated that between 20 and 70% of aggregate carbon is degraded by invertebrate colonizers before a sinking aggregate leaves a 50m-deep euphotic zone. Thus, the majority of aggregated material may be degraded within the euphoric zone due to the combined activity of colonizing invertebrates, other grazers, and microorganisms.

Ctenophores are gelatinous marine invertebrates that prey upon zooplankton. The two main ctenophoran orders that affect planktonic communities are the Cydippida and the Lobata. The Cydippida possess two elongate tentacles. [...]

Nick Loomis never would have predicted he'd grow up to study marine science. 'I'm actually from Nebraska. We don't exactly have a lot of oceans out there,' he said. 'To [...]

Research was conducted in shelf waters and the water masses related to the Subtropical Convergence east of New Zealand in the austral winter and spring of 1993. The objective of the study was to measure the biomass, composition and grazing rates of three size fractions of mesozooplankton. Results and the fact that spring populations were actively growing indicate that mesozooplankton diets were largely microzooplankton.

Ecol. Lett. doi: 10.1111/j.1461-0248.2009.01391.x (2009) In an ecological system with two predator and two prey species, theory predicts two ways in which the species' population dynamics can become coupled. If [...]

Distribution of and Feeding by the Copepod Pseudocalanus Under Fast Ice During the Arctic Spring LANDFAST SEA ICE INHIBITS PRImary production in the water column in the Canadian Arctic Archipelago [...]

A hundred species of gelatinous zooplankton were collected using specialized sampling methods. These zooplankton species, taken from various depths ranging from one meter to 3,500 meters, were then examined and their bioluminescence spectra measured. Results showed that maximal wavelengths for all species was between 440 and 506 nm. Wavelengths of ctenophores were found to be longer than those of medusae and siphonophores. Deep-dwelling species were also discovered to have shorter wavelengths than shallow-water species.

Research was conducted to examine the acoustic discrimination of two zooplankton species using bifrequency sonar 38 kHz and 120 kHz. Two species of Mysidacea, which were similar in shape but not in size and with differing behavioral patterns, were observed and discriminated. Only Siriella jaltensis was detected at 38 kHz while both were observed at 120 kHz. Results indicate that the 38 kHz is a good frequency to detect Siriella while 120 kHz is not a good frequency for the detection of the larger Siriella.

The differences in species composition and predator abundance of the marine macrozooplankton, Euphausia pacifica, were examined in terms of physical variability and the species' significance to the total diet of the demersal fish assemblages. Data were collected from the research cruises undertaken by the Tohoku National Fisheries Research Institute of the Fisheries Agency of Japan. It was observed that the predators of E. pacifica in shallow waters were more diverse than in deep waters during May but the opposite occurred during Nov. The species was more abundant near the sea bottom.

Research was conducted to measure and compare grazing rates by microzooplankton on total phytoplankton, picophytoplankton and bacteria in different water masses. Grazing rates by microzooplankton feeding on bacteria, picophytoplankton and total phytoplankton were measured in Subtropical Convergence, subantarctic and subtropical waters in winter and spring 1993. Results indicate that microzooplankton may have an important role to play in the transfer of carbon to higher trophic levels throughout much of the year.