bluuebunny/crossref_metadata_2025_split huggingface dataset:
Radiotracer determination of the diet of calanoid copepod nauplii and copepodites in a temperate estuary
Authors: Finlay Kerri , Roff John C 
Published: May 2004

Abstract
Many studies have focused on the consumption of specific prey items and clearance rates on natural food particles by copepod adults and copepodites, but few have addressed the feeding habits of the youngest stages, the nauplii. Because of the difference in size and shape between copepod developmental stages, corresponding differences in diet would be expected. This subject was addressed using a modification of a new method offering radiolabelled natural food particles (with 3H for heterotrophs and 14C for autotrophs) to nauplii and copepodites of the copepods in a temperate estuary. By measuring the uptake of the radiolabel by the copepods it was possible to determine clearance rates on different sizes and types of food particles. All copepods began feeding on food sources >2 μm in size, and feeding on heterotrophs by all species and stages was considerably lower than feeding on autotrophs. Overall, it appears that copepod nauplii have a comparable diet to the later stages in terms of food type and size and therefore it is unlikely that nauplii are a more efficient link between the microbial foodweb and the classical foodweb, at least in temperate estuarine waters.
Microzooplankton production in the oceans
Authors: Landry Michael R. , Calbet Albert 
Published: May 2004

Abstract
A literature synthesis of phytoplankton growth (μ) and grazing (m) rate estimates from dilution experiments reveals that microzooplankton account for most phytoplankton mortality in the oceans, averaging 60–75% of daily phytoplankton production (PP) across a spectrum of open-ocean and coastal systems. For reasonable estimates of gross growth efficiency (GGE=30–40%), such impacts imply that secondary production rates of microzooplankton (MP2°) are typically in the range 21–34% of PP. However, multiple trophic transfers within the microbial community can further enhance total microzooplankton production by an additional third to a half (MPtot=28–55% of PP). These estimates are 2–5 times typical values for bacterial production (10–15% of PP). Thus, in aggregate and on average, microzooplankton consume substantially more (6–7 times) production from phytoplankton than from heterotrophic bacteria. High grazing impacts and relatively high GGEs are consistent with population growth rates for microzooplankton and phytoplankton that are roughly equivalent under ambient conditions, which may be requisite for grazing regulation. Transfer efficiencies of microzooplankton production to mesozooplankton depend critically on the number of predatory interactions among micro-consumers, and may be one way in which systems differ substantially. Overall, the ability to quantify microzooplankton production in terms of more broadly measured rates of PP provides a potential avenue for broadening our understanding of ocean community dynamics through remote sensing and modelling.
Enumeration, measurement, and identification of net zooplankton samples using the ZOOSCAN digital imaging system
Authors: Grosjean Philippe , Picheral Marc , Warembourg Caroline , Gorsky Gabriel 
Published: May 2004

Abstract
Identifying and counting zooplankton are labour-intensive and time-consuming processes that are still performed manually. However, a new system, known as ZOOSCAN, has been designed for counting zooplankton net samples. We describe image-processing and the results of (semi)-automatic identification of taxa with various machine-learning methods. Each scan contains between 1500 and 2000 individuals <0.5 mm. We used two training sets of about 1000 objects each divided into 8 (simplified) and 29 groups (detailed), respectively. The new discriminant vector forest algorithm, which is one of the most efficient methods, discriminates between the organisms in the detailed training set with an accuracy of 75% at a speed of 2000 items per second. A supplementary algorithm tags objects that the method classified with low accuracy (suspect items), such that they could be checked by taxonomists. This complementary and interactive semi-automatic process combines both computer speed and the ability to detect variations in proportions and grey levels with the human skills to discriminate animals on the basis of small details, such as presence/absence or number of appendages. After this checking process, total accuracy increases to between 80% and 85%. We discuss the potential of the system as a standard for identification, enumeration, and size frequency distribution of net-collected zooplankton.
Comparative ecology of over-wintering Calanus finmarchicus in the northern North Atlantic, and implications for life-cycle patterns
Authors: Heath Michael R , Boyle Peter R , Gislason Astthor , Gurney William S.C , Hay Stephen J , Head Erica J.H , Holmes Steven , Ingvarsdóttir Anna , Jónasdóttir Sigrun H , Lindeque Pennie , Pollard Raymond T , Rasmussen Jens , Richards Kelvin , Richardson Katherine , Smerdon Gary , Speirs Douglas 
Published: May 2004

Abstract
Data from plankton net and Optical Plankton Counter sampling during 12 winter cruises between 1994 and 2002 have been used to derive a multi-annual composite 3-D distribution of the abundance of over-wintering Calanus finmarchicus in a swath across the North Atlantic from Labrador to Norway. Dense concentrations occurred in the Labrador Sea, northern Irminger Basin, northern Iceland Basin, eastern Norwegian Sea, Faroe–Shetland Channel, and in the Norwegian Trench of the North Sea. A model of buoyancy regulation in C. finmarchicus was used to derive the lipid content implied by the in situ temperature and salinity at over-wintering depths, assuming neutral buoyancy. The Faroe–Shetland Channel and eastern Norwegian Sea emerged as having the highest water column-integrated abundances of copepodites, the lowest over-wintering temperature, and the highest implied lipid content. The results are discussed in the context of spatial persistence of populations, seasonal patterns of abundance, and relationships between over-wintering and lipid accumulation in the surface waters.
Mesozooplankton size-fractionated metabolism and feeding off NW Spain during autumn: effects of a poleward current
Authors: Isla José Alejandro , Anadón Ricardo 
Published: May 2004

Abstract
Two consecutive cruises were carried out off NW Spain in October 1999 in an attempt to obtain information on the poleward current that affects the hydrodynamics of this area during autumn and winter. The stations sampled were divided into three zones: coastal (C), between the saline intrusion and the coast; poleward current (P), where salinity at 100-m depth was >35.85; and oceanic (O), outside the poleward current. Phytoplankton biomass, integrated through the photic zone, was similar for the three zones. Conversely, mesozooplankton biomass showed high spatial variation, with the lowest values associated with the high-salinity current. There was a decreasing trend in the relative importance of the biomass of the largest size class (>1000 μm) from coastal to oceanic zones. The lowest percentages of both Chl a and primary production ingested daily by copepods were measured at the poleward current stations. Specific metabolic rates were not significantly different between zones. The total amount of carbon respired and the NH4 and PO4 released were highest in coastal areas and lowest within the poleward current, in agreement with the pattern observed for mesozooplankton biomass. Diel vertical migrations were more marked in the coastal areas, decreasing gradually towards the oceanic stations. The role of mesozooplankton in promoting the flux of carbon, nitrogen, and phosphorus followed the same spatial distribution. Overall, the contribution of mesozooplankton to biogeochemical cycles seems to be minor in the poleward current compared to the other two zones, possibly as a consequence of the low biomass associated with this current.
Composition and temporal distribution of cirripede larvae in Southampton Water, England, with particular reference to the secondary production of Elminius modestus
Authors: Muxagata Erik , Williams John A , Sheader Martin 
Published: May 2004

AbstractSouthampton Water, an estuary on the south coast of England, has been the focus of a number of studies to determine the seasonality and productivity of its pelagic community. Although recognized as important in previous studies, the meroplankton component and, in particular, the cirripedes have been largely ignored, though they rank second to the Copepoda in abundance. In order to estimate the contribution of barnacle larvae to the pelagic community, 42 quantitative zooplankton samples were collected from a fixed station within the estuary during a period of 19 months (from 12 January 2001 until 16 July 2002). As expected, barnacles were the second most abundant group averaging 13% of the total population, and accounting for up to 60% on some occasions. Eight barnacle species were identified: Elminius modestus, Balanus improvisus, Balanus crenatus, Semibalanus balanoides, Verruca stroemia, Chthamalus stellatus, Sacculina carcini, and Peltogaster paguri. Of these E. modestus was the most abundant and frequent, dominating the Cirripedia fraction throughout the year, but being outnumbered by B. crenatus from February to May. Secondary production was calculated for E. modestus and mean daily rates of 0.077 mg C m−3 d−1 (28.08 mg C m−3 yr−1) were found.
A comparative study of Calanus finmarchicus mortality patterns at five localities in the North Atlantic
Authors: Ohman M.D , Eiane K , Durbin E.G , Runge J.A , Hirche H.-J 
Published: May 2004

Abstract
We compare the patterns of stage-specific mortality of Calanus finmarchicus at five localities across the North Atlantic Ocean during the spring–summer period of active population growth: Georges Bank, a continental shelf locality in the NW Atlantic, based on 30 broadscale survey cruises in the US GLOBEC program; the northern North Sea, studied during the historic FLEX program with sampling four times daily for 73 days; Ocean Station M in the central Norwegian Sea, based on an 80-day daily time-series; and Lurefjorden (sampled weekly in late winter–early summer) and Sørfjorden (sampled monthly), two fjords in southwestern Norway characterized by markedly different guilds of predators. The mortality estimation methods included Wood's Population Surface Method, the Vertical Life Table (VLT) method, and a modified VLT, according to the study site and copepod recruitment schedules. Contrary to assumptions implicit in many simulation models and indirect methods for estimating zooplankton mortality, both rates and stage-specific patterns of mortality of C. finmarchicus vary appreciably across the North Atlantic. Characteristics of local environments, including the predator field in particular, appear to strongly influence mortality schedules in different regions. In at least two sites (Georges Bank and Ocean Station M), mortality rates of early stages of C. finmarchicus are density-dependent. We attribute this density-dependent mortality to egg cannibalism, which introduces non-linear population responses to changing environmental conditions. Region-specific biological interactions can substantially modify the effects of physical climate variability and render simple linear relationships between climate and zooplankton abundance unlikely.
Interannual abundance patterns of copepods during an ENSO event in Icy Strait, southeastern Alaska
Authors: Park Wongyu , Sturdevant Molly , Orsi Joseph , Wertheimer Alex , Fergusson Emily , Heard William , Shirley Thomas 
Published: May 2004

Abstract
Interannual copepod abundance (number m−3) and sea surface temperatures (SST, 2-m depth) were examined from four stations in Icy Strait, southeastern Alaska, monthly from May to September, 1997–2002. SST was generally lowest in May (≅7°C), increased rapidly to a summer peak (≅12°C), and declined again by September. SST was relatively high in the El Niño year, 1998, and was low during a regional cold event, 2002, compared to other years. Overall, copepods constituted 18.8% of the total biomass and 88.2% of zooplankton abundance, and included >34 species. The common copepod species were grouped into two size classes by total length (TL), those >2.5 mm (11.4% biomass, 24.2% abundance) and those <2.5 mm (7.4% biomass, 64.0% abundance). In order of dominance, large species included Metridia ochotensis, Calanus marshallae, M. pacificus, and Neocalanus spp. and small species included Pseudocalanus spp., Acartia longiremis, and Centropages abdominalis. Overall, the small species were more abundant than the large species. Densities of large copepods were relatively low compared to those of small copepods during El Niño (1998) and a cold year (2002), suggesting that large copepods with long lifespans are more sensitive to ocean climate fluctuation.
Vertical and seasonal distribution of eight Clausocalanus species (Copepoda: Calanoida) in oligotrophic waters
Authors: Peralba Àurea , Mazzocchi Maria Grazia 
Published: May 2004

Abstract
Copepods of the genus Clausocalanus Giesbrecht, 1888 are among the most abundant calanoids in the Mediterranean Sea, both in coastal and offshore regions. The vertical distribution of C. arcuicornis, C. furcatus, C. jobei, C. lividus, C. mastigophorus, C. parapergens, C. paululus, and C. pergens, which co-occur in the upper 200 m in the Gulf of Naples (Tyrrhenian Sea), was investigated during an annual sampling cycle conducted at an offshore station in 2002. The quantitative data on distribution of each species were analysed in relation to the environmental parameters. The patterns that we observed in the seasonal cycles and vertical distribution provided insights on the ecological niches of the eight Clausocalanus species.
Identifying global synchronies in marine zooplankton populations: issues and opportunities
Authors: Perry R.Ian , Batchelder Harold P , Mackas David L , Chiba Sanae , Durbin Edward , Greve Wulf , Verheye Hans M 
Published: May 2004

Abstract
Analyses of the influences of climate variability on local zooplankton populations and those within ocean basins are relatively recent (past 5–10 years). What is lacking are comparisons of zooplankton population variability among the world's oceans, in contrast to such global comparisons of fish populations. This article examines the key questions, capabilities, and impediments for global comparisons of zooplankton populations using long-term (>10 year) data sets. The key question is whether global synchronies in zooplankton populations exist. If yes, then (i) to what extent are they driven by “bottom-up” (productivity) or “top-down” (predation) forcing; (ii) are they initiated by persistent forcing or by episodic events whose effects propagate through the system with different time-lags; and (iii) what proportion of the biological variance is caused directly by physical forcing and what proportion might be caused by non-linear instabilities in the biological dynamics (e.g. through trophodynamic links)? The capabilities are improving quickly that will enable global comparisons of zooplankton populations. Several long-term sampling programmes and data sets exist in many ocean basins, and the data are becoming more available. In addition, there has been a major philosophical change recently that now recognizes the value of continuing long-term zooplankton observation programmes. Understanding of life-history characteristics and the ecosystem roles of zooplankton are also improving. A first and critical step in exploring possible synchrony among zooplankton from geographically diverse regions is to recognize the limitations of the various data sets. There exist several impediments that must be surmounted before global comparisons of zooplankton populations can be realized. Methodological issues concerned with the diverse spatial and temporal scales of “monitored” planktonic populations are one example. Other problems include data access issues, structural constraints regarding funding of international comparisons, and lack of understanding by decision-makers of the value of zooplankton as indicators of ecosystem change. We provide recommendations for alleviating some of these impediments, and suggest a need for an easily understood example of global synchrony in zooplankton populations and the relation of those signals to large-scale climate drivers.
A 9-year increasing trend in mesozooplankton biomass at the Hawaii Ocean Time-series Station ALOHA
Authors: Sheridan Cecelia C , Landry Michael R 
Published: May 2004

Abstract
Mesozooplankton biomass in the North Pacific Subtropical Gyre (NPSG), as measured by the Hawaii Ocean Time-series program at Station ALOHA (22.45°N 158°W), increased significantly from 1994 to 2002. The changes occurred at a rate of 60 mg DW m−2 yr−1 for night-time collections and 45 mg DW m−2 yr−1 for daytime collections. Principal components analysis indicates that the 9-year trend was driven by an increase in small (0.5–2.0 mm) zooplankton that do not migrate on a diel cycle. This plankton class is known to increase during the summer at Station ALOHA when the water column is most stratified, and a strong summertime response is also apparent within the long-term trend from 1998 through 2002. Both long-term and seasonal changes in zooplankton biomass at Station ALOHA can be linked to an enhanced role of nitrogen fixation in ecosystem productivity. Climate forcing from El Niño–Southern Oscillation (ENSO) events may have influenced nitrogen fixation, general ecosystem productivity, and thus zooplankton biomass in the NPSG. However, it is difficult to evaluate the effect of climate cycles in this region without the benefit of a longer time-series at Station ALOHA. Because biomass trends in higher-level consumers like mesozooplankton can have cascading influences on lower levels, understanding the relative roles of bottom-up climate influences and top-down trophic processes will be important in resolving long-term trends in community composition and structure in the subtropical North Pacific Ocean.
Effects of food concentration and diet on chromophoric dissolved organic matter accumulation and fluorescent composition during grazing experiments with the copepod Calanus finmarchicus
Authors: Urban-Rich Juanita , McCarty James T , Shailer Mark 
Published: May 2004

AbstractLaboratory experiments were conducted with Calanus finmarchicus copepodites IV–V to examine the effects of food concentration, food type, and life stage on chromophoric dissolved organic matter (CDOM) release from copepods. Changes in CDOM absorption and fluorescence were monitored by incubating copepods in rotating bottles for 24 h in the dark with controlled diets. Copepods were fed a range of food concentrations from 800 to 15 000 cells l−1 of either Thalassiosira weissflogii and Skeletonema costatum or Prorocentrum minimum in stationary and exponential growth phases. Results from these studies indicate that diet does have an effect on the amount and type of CDOM released by C. finmarchicus. A diet of either diatoms or dinoflagellates in exponential growth will result in a release of humic-like material, while feeding on senescent cells leads to a net input of protein-like material. Only at very high senescent cell concentrations (>5000 cells l−1) can humic-like material accumulate. This could lead to seasonal cycles in the amount and type of CDOM released by copepods, such that humic-like material will be released in the spring and at the height of phytoplankton blooms, while protein-like material will be added to the water as the bloom dies. The humic-like material found in these studies is blue-shifted compared to the standard humic material (Peaks A, M, and C) measured in seawater. The role of this humic-like material in the environment is currently unknown, but it could be important in absorbing UV radiation.
Spatial patterns of mesozooplankton distribution in the Southwestern Atlantic Ocean (34°–41°S) during austral spring: relationship with the hydrographic conditions
Authors: Marrari Marina , Viñas María Delia , Martos Patricia , Hernández Daniel 
Published: May 2004

Abstract
The mesozooplankton community was analysed in a large region of the Argentine Shelf (34°–41°S) on the main spring spawning ground of the anchovy (Engraulis anchoita), and its spatial pattern was related to the hydrographic conditions. Copepods smaller than 1 mm dominated the community. Three faunistic areas were identified by cluster analysis: northern coastal area (NCA), southern coastal area (SCA), and shelf area (SA), each with distinct physical conditions. The NCA, influenced by the Río de la Plata estuary, had relatively high temperature, the lowest salinity, and the highest stratification values. The SCA had the highest salinity and a vertically homogeneous water column. The SA, vertically stratified, was influenced by the Río de la Plata estuary and by Subantarctic shelf waters and had the lowest temperature values and the greatest depths. Canonical correlation analysis was used to analyse the relationship between zooplankton and physical variables and four zooplankton assemblages were identified. Group A included the copepods Calanus australis, C. simillimus, Clausocalanus brevipes, Centropages brachiatus, Drepanopus forcipatus, Oithona atlantica, and O. helgolandica, and was preferentially distributed in the SA. Group B, composed of the copepods Acartia tonsa and Corycaeus spp. and the cladoceran Pleopis polyphemoides, showed a strong preference for the NCA. Group C included Labidocera fluviatilis, Ctenocalanus vanus, Paracalanus spp., Calanoides cf. carinatus, Euterpina acutifrons, Oithona nana, and the cladoceran Evadne nordmanni, and was preferentially distributed in coastal areas (NCA and SCA). Group D only included the cladoceran Podon intermedius and was mainly located in high salinity waters of the SCA. Small, omnivorous, fast-reproducing species (groups B, D, and most of C) are better adapted to warmer variable and less productive coastal areas, whereas larger herbivorous species (most of group A) seem to better exploit colder stratified and more productive shelf waters. The mesozooplankton community provides adequate food for E. anchoita larvae in coastal areas and for adults in shelf waters.
Zooplankton variability and climatic anomalies from 1994 to 2001 in the Balearic Sea (Western Mediterranean)
Authors: Fernández de Puelles M. Luz , Valencia Joaquín , Vicente Laura 
Published: May 2004

Abstract
The long-term and seasonal changes in biomass and zooplankton abundance at a station off Mallorca Island (Balearic Sea) were studied in relation to the main physical and chemical conditions. The results are based on a total of 276 samples collected every 10 days during 8 years by means of oblique hauls from bottom to surface. At this neritic station (77-m depth) located in a hydrographic area between northern Mediterranean and Atlantic southern waters, salinity ranged from 37 to 38.4 psu and temperature from 13.4°C (February 1996) to 27.4°C (August 1998). With the exception of salinity, the other environmental parameters and the most abundant zooplankton groups showed irregular but seasonal cycles. Interannual variability was also observed, with higher zooplankton abundance during the cooler and more saline years when the influence of northern water was stronger. Zooplankton abundance decreased during a warm period in 1998. Copepods were the most abundant group (54%) and their abundance was significantly correlated with temperature (negatively) and salinity (positively). Here, we summarize the changes in the zooplankton community abundance and how hydrographic forcing and other climatic factors have changed during the period from 1994 to 2001 in the Balearic Sea (Western Mediterranean).