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Feeding rates and selectivity of the calanoid copepods Calanus helgolandicus and Para-Pseudocalanus spp. on natural assemblages of microplankton were evaluated in the English Channel and western Celtic Sea during non-bloom and bloom conditions in April 2002. Ingestion rates of total chlorophyll- a were low at non-bloom stations where the phytoplankton community was dominated by cells 5 μm size fraction was dominant. Protozooplankton contributed to the copepod diet in all experiments, C. helgolandicus clearance and ingestion rates were highest for the ciliate Myrionecta rubra (626–1347 ml cop − 1 d − 1 ; 0.3–27 μg C cop − 1 d − 1 ). C. helgolandicus ingested between 1 and 18 μg C cop − 1 d − 1 (1–12% body C) from phytoplankton + protozooplankton food sources. The total carbon ingested by Para-Pseudocalanus spp. was lower (0.5–6 μg cop − 1 d − 1 ) but this was equivalent to between 6 and 78% of body carbon being ingested daily. Our data suggest that C. helgolandicus selected prey according to size; this was not the case for Para-Pseudocalanus spp. which became more selective as chlorophyll- a concentration increased. Grazing impact of the entire copepod community on protozooplankton was assessed. We found that at non-bloom stations between 12 and 17% of the protozooplankton community was being removed daily by the copepod community, whereas during the peak of the bloom the proportion being removed daily was only 2%. We conclude that during the spring bloom period copepods gained the majority of their carbon from phytoplankton ingestion but during non-bloom periods, protozooplankton and the ciliate M. rubra made a significant contribution to copepod diet.

Net sampling within the vicinity of the Crozet archipelago, in the Indian Ocean sector of the Southern Ocean, was conducted during late spring/summer (November 2004-January 2005) to describe the composition, distribution and grazing impact of mesozooplankton, and to investigate their relationships with the prevailing oceanographic regime in the area. The mesozooplankton community was intimately linked with the large-scale physical circulation in the region. To the west and north of the Islands, the sub-Antarctic Front (SAF) presented a strong biogeographic boundary between subtropical and sub-Antarctic species. South and east of the SAF, the mesozooplankton community was dominated by Polar Frontal Zone (PFZ) copepod species. Cluster analysis of mesozooplankton abundance data identified two main communities in the PFZ, termed here Island and Oceanic. Island stations, representing the proposed iron-fertilised productive region north of the archipelago, contained an abundance (mean of 2269 ind m(-3)) of the neritic copepod Drepanopus pectinatus, whose presence indicated that the water had interacted with the Crozet Island shelf at some point. D. pectinatus was present in samples north of Crozet up to the SAF, confirming that water passing the Crozet Islands could be transported, throughout the region to the north. The Oceanic stations, south of the Islands and within the SAF, contained similar mesozooplankton abundances and biovolume to the Island stations suggesting little enhanced impact of the iron-fertilised phytoplankton bloom through the mesozooplankton food web. Copepod community grazing pressure, in both Island and Oceanic stations, during November and December was small ( < 7% of chlorophyll-a standing stock per day, < 35% primary production per day). By January, a phytoplankton bloom had developed at some of the Island stations (up to similar to 3000 mg C m(-2) d(-1)) and grazing pressure was < 1% of chlorophyll-a standing stock per day. At the oceanic stations, primary productivity had reduced from similar to 460 to similar to 200 mg C m(-2) d(-1), typical values for high-nutrient low-chlorophyll (HNLC) waters, and the copepod community grazing pressure had increased to similar to 90% of daily primary productivity. This suggests that a combination of grazing and micronutrient availability controls phytoplankton biomass in HNLC waters to the south of Crozet, while grazing had little impact on the "iron- fertilised" bloom north of the Crozet Islands. The intense seasonal phytoplankton bloom around Crozet may therefore be exported to the sea floor rather than fuelling the higher trophic levels. (C) 2007 Elsevier Ltd. All rights reserved.

Oithona spp. is considered the most abundant and ubiquitous copepod genus in the marine environment, often outnumbering calanoid copepods throughout the year. Previous studies have argued that one of the reasons for such success is that the respiration rate of Oithona spp. is insensitive to temperature changes and lower than in calanoids. However, comprehensive data on the thermal biology of this important copepod genus is lacking. In this study, the respiration rate of adult female O. similis from the English Channel, was measured over the temperature range 4 to 25°C. The respiration rate of O. similis changed exponentially with temperature (ln O2-rate = -3.59 + 0.114 T, df = 35, r 2 = 0.85, p < 0.001, Q10 = 3.1) similar to that of other poikilotherms. Over the temperature range examined, O. similis basic metabolic cost varied from a minimum of ~1.4% body-C d -1 at 4°C to a maximum of 23% body-C d -1 at 25°C, corresponding to an energy demand of ~3% and 32% body-C d -1 respectively. The respiration rate of O. similis, from the present study, is ~8 times lower than that of a calanoid copepod of equivalent body weight estimated from published empirical metabolism-temperature data. We suggest that these differences in metabolic rates may account for the year-round persistence and higher abundances of Oithona spp. over calanoid copepods, particu- larly in oceanic and oligotrophic environments where food resources may be limiting for calanoid copepods.

Appendicularians have some of the highest growth rates among metazoans but they are usually outnumbered by the slower growing copepods in mesozooplankton communities. We present experimental evidence that the eggs and juveniles of the appendicularian Oikopleura dioica are actively consumed by various copepod species. Clearance rates of Calanus helgolandicus, Candacia armata, Centropages typicus, Eucalanus crassus, and Temora longicornis on eggs of O. dioica were usually above 300 ml copepod-1 d-1. The ingestion rates of C. helgolandicus on O. dioica eggs did not reach saturation even at the highest egg concentrations (4,560 eggs L-1). Although C. helgolandicus, C. typicus, and C. armata preyed actively on 1-mm-long O. dioica (approximately 0.2 mm in trunk length), predatory pressure decreased with increasing appendicularian size. We suggest that the association of dense appendicularian populations with phytoplankton blooms could be explained by their opportunistic response to beneficial conditions before copepod densities become high enough to cause a decline in appendicularian populations due to predation. Our results indicate that, in addition to the direct shunt of biomass from picoplankton to fish, appendicularians can occupy a similar role to that of microzooplankton in the ocean. They represent an intermediate step in the less efficient, picoplankton–appendicularia–copepod-fish food chain.

Diatoms dominate spring bloom phytoplankton assemblages in temperate waters and coastal upwelling regions of the global ocean. Copepods usually dominate the zooplankton in these regions and are the prey of many larval fish species. Recent laboratory studies suggest that diatoms may have a deleterious effect on the success of copepod egg hatching. These findings challenge the classical view of marine food-web energy flow from diatoms to fish by means of copepods. Egg mortality is an important factor in copepod population dynamics, thus, if diatoms have a deleterious in situ effect, paradoxically, high diatom abundance could limit secondary production. Therefore, the current understanding of energy transfer from primary production to fisheries in some of the most productive and economically important marine ecosystems may be seriously flawed. Here we present in situ estimates of copepod egg hatching success from twelve globally distributed areas, where diatoms dominate the phytoplankton assemblage. We did not observe a negative relationship between copepod egg hatching success and either diatom biomass or dominance in the microplankton in any of these regions. The classical model for diatom-dominated system remains valid.

Long-term research in the western English Channel, undertaken by the marine laboratories in Plymouth, is described and details of survey methods, sites, and time series given in this chapter. Major findings are summarized and their limitations outlined. Current research, with recent reestablishment and expansion of many sampling programmes, is presented, and possible future approaches are indicated. These unique long-term data sets provide an environmental baseline,for predicting complex ecological responses to local, regional, and global environmental change. Between 1888 and the present, investigations have been carried out into the physical, chemical, and biological components (ranging from plankton and fish to benthic and intertidal assemblages) of the western English Channel ecosystem. The Marine Biological Association of the United Kingdom has performed the main body of these observations. More recent contributions come from the Continuous Plankton Recorder Survey, now the Sir Alister Hardy Foundation for Ocean Science, dating from 1957; the Institute for Marine Environmental Research, from 1974 to 1987; and the Plymouth Marine Laboratory, which was formed by amalgamation of the Institute for Marine Environmental Research and part of the Marine Biological Association,,from 1988. Together, these contributions constitute a unique data series-one of the longest and most comprehensive samplings of enviromnental and marine biological variables in the world. Since the termination of many of these time series in 1987-1988 during a reorganisation of UK marine research, there has been a resurgence of interest in long-term environmental change. Many programmes have been restarted and expanded with support from several agencies. The observations span significant periods of warming (1921-1961; 1985-present) and cooling (1962-1980). During these periods of change, the abundance of key species underwent dramatic shifts. The first period of warming saw changes in zooplankton, pelagic fish, and larval fish, including the collapse of an important herring fishery. During later periods of change, shifts in species abundances have been reflected in other assemblages, such as the intertidal zone and the benthic fauna. Many of these changes appear to be related to climate, manifested as temperature changes, acting directly or indirectly. The hypothesis that climate is a forcing factor is widely supported today and has been reinforced by recent studies that show, responses of marine organisms to climatic attributes such as the strength of the North Atlantic Oscillation. The long-term data also yield important insights into the effects of anthropogenic disturbances such as fisheries exploitation and pollution. Comparison of demersal fish hauls over time highlights fisheries effects not only on commercially important species but also on the entire demersal community. The effects of acute ("Torrey Canyon" oil spill) and chronic (tributyltin [TBT] antifoulants) pollution are clearly seen in the intertidal records. Significant advances in diverse scientific disciplines have been generated from research undertaken alongside the long-term data series. Many concepts in marine biological textbooks have originated in part from this work (e.g. the seasonal cycle of plankton, the cycling of nutrients, the pelagic food web trophic interactions, and the influence of hydrography on pelagic communities). Associated projects currently range.from studies of marine viruses and bacterial ecology to zooplankton feeding dynamics and validation of ocean colour satellite sensors. Recent advances in technology mean these long-term programmes are more valuable than ever before. New technology collects data on finer temporal and spatial scales and can be used to capture processes that operate on multiple scales and hell) determine their influence in the marine environment. The MBA has been in the forefront of environmental modelling of sheaf seas since the early 1970s. Future directions being pursued include the continued development of coupled physical-ecosystem models using western English Channel time-series data. These models will include both the recent high-resolution data and the long-term time-series information to predict effects of future climate change scenarios. It, would be beneficial to provide more spatial and high-resolution temporal context to these data, which are fundamental for capturing processes that operate at multiple scales and understanding hoiv they operate within the marine environment. This is being achieved through employment of technologies such as sateillite-derived information and advanced telemetry instruments that pro vide real-time in situ profile data from the water column.