Can the Continuous Plankton Recorder (CPR) be used to infer sardine diet?

Knowledge on the impact of climate variability in the diet of planktivorous fish is limited by the laborious work involved in stomach content analysis, impractical for large scale studies. Routine measurements of plankton such as the Continuous Plankton Recorder (CPR) survey provide valuable information of the temporal variation of phyto- and zooplankton prey availability for higher trophic levels. Sardines are a world-wide distributed and commercially important planktivorous fish, at the basis of the pelagic marine food web. Being predominantly non-selective filter-feeders, their diets closely correspond to the water plankton species and a significant relationship was recently found between Sardina pilchardus feeding intensity and remotely sensed chlorophyll alpha . Data of sardine stomach prey composition and CPR were obtained during 2003 for the same location off the west coast of Portugal, an area characterised by strong seasonality of plankton abundance and composition, mainly governed by upwelling events. Phyto- and zooplankton prey in sardine stomachs were identified to the lowest possible taxa and their numerical and volumetric abundance was registered, as well as their contribution to the prey carbon content. The seasonal variation of the abundance and composition of sardine diet was then compared to the abundance and composition of the water plankton obtained with the CPR at the same time and for the same area where the fish were collected, in order to evaluate if CPR data can be used to proxy sardine prey availability and diet composition at large temporal scales.

Long-Term Retrospective Analysis of Mackerel Spawning in the North Sea: A New Time Series and Modeling Approach to CPR Data

We present a unique view of mackerel (Scomber scombrus) in the North Sea based on a new time series of larvae caught by the Continuous Plankton Recorder (CPR) survey from 1948-2005, covering the period both before and after the collapse of the North Sea stock. Hydrographic backtrack modelling suggested that the effect of advection is very limited between spawning and larvae capture in the CPR survey. Using a statistical technique not previously applied to CPR data, we then generated a larval index that accounts for both catchability as well as spatial and temporal autocorrelation. The resulting time series documents the significant decrease of spawning from before 1970 to recent depleted levels. Spatial distributions of the larvae, and thus the spawning area, showed a shift from early to recent decades, suggesting that the central North Sea is no longer as important as the areas further west and south. These results provide a consistent and unique perspective on the dynamics of mackerel in this region and can potentially resolve many of the unresolved questions about this stock

US NOAA Fisheries and UK SAHFOS CPR surveys: comparison of methods and data

The US National Oceanic and Atmospheric Administration (NOAA) Fisheries Continuous Plankton Recorder (CPR) Survey has sampled four routes: Boston–Nova Scotia (1961–present), New York toward Bermuda (1976–present), Narragansett Bay–Mount Hope Bay–Rhode Island Sound (1998–present) and eastward of Chesapeake Bay (1974–1980). NOAA involvement began in 1974 when it assumed responsibility for the existing Boston–Nova Scotia route from what is now the UK's Sir Alister Hardy Foundation for Ocean Science (SAHFOS). Training, equipment and computer software were provided by SAHFOS to ensure continuity for this and standard protocols for any new routes. Data for the first 14 years of this route were provided to NOAA by SAHFOS. Comparison of collection methods; sample processing; and sample identification, staging and counting techniques revealed near-consistency between NOAA and SAHFOS. One departure involved phytoplankton counting standards. This has since been addressed and the data corrected. Within- and between-survey taxonomic and life-stage names and their consistency through time were, and continue to be, an issue. For this, a cross-reference table has been generated that contains the SAHFOS taxonomic code, NOAA taxonomic code, NOAA life-stage code, National Oceanographic Data Center (NODC) taxonomic code, Integrated Taxonomic Information System (ITIS) serial number and authority and consistent use/route. This table is available for review/use by other CPR surveys. Details of the NOAA and SAHFOS comparison and analytical techniques unique to NOAA are presented.

Genetic analysis of Continuous Plankton Recorder (CPR) samples

Genetic analysis of Continuous Plankton Recorder (CPR) samples is enabling greater taxonomic resolution and the study of plankton population structure. Here, we present some results from the genetic analysis of CPR samples collected in the North Sea and north-eastern Atlantic that reveal the impacts of climate on benthic-pelagic coupling and the food web. We show that pronounced changes in the North Sea meroplankton are related to an increased abundance and spatial distribution of the larvae of the benthic echinoderm, Echinocardium cordatum. Key stages of reproduction in E. cordatum, gametogenesis and spawning, are influenced by winter and spring sea temperature (January-May). A stepwise increase in sea temperature after 1987, which has created warmer conditions earlier in the year, together with increased summer phytoplankton, may benefit the reproduction and survival of this benthic species. Competition between the larvae of E. cordatum and other holozooplanlcton taxa may now be altering the trophodynamics of the summer pelagic ecosystem. In the north-eastern Atlantic the genetic analysis of fish larvae sampled by the CPR has revealed an unprecedented increase in the abundance of juvenile snake pipefish, Entelurus aequoreiis since 2002. We argue that increased sea surface temperatures in winter and spring when the eggs of E. aqueoreus, which are brooded by the male, are developing and the young larvae are growing in the plankton are a likely cause. The increased abundance of this species in Atlantic and adjacent European seas already appears to be influencing the marine food web.

Molecular analysis of Continuous Plankton Recorder samples, an examination of echinoderm larvae in the North Sea

Analysis of the biological time series of plankton samples collected by the Continuous Plankton Recorder (CPR) in the North Atlantic and North Sea has shown a regime shift in the plankton in this region. Both the distributions of planktonic organisms and their timing of occurrence in the seasonal cycle have changed and these changes appear to ref lect global warming. In the North Sea the planktonic larvae of echinoderms have shown a recent dramatic increase in both relative and absolute abundance and their seasonal peak of occurrence has advanced by 47 days. The identity of the echinoderm larvae involved in this change has, however, remained equivocal. The small size of many organisms like echinoderm larvae combined with incomplete taxonomic keys hinders their visual identification and their fragility often means that useful morphological features are damaged during sampling by the CPR. Here, using new molecular methods applied to CPR samples, we show that planktonic larvae of the benthic Echinocardium cordatum dominate the North Sea plankton. We argue that since this species benefits from mild winters and warmer waters their numerical increase in the plankton is consistent with recent climatic changes that appear to be affecting the wider ecology of this region.

Ocean climate anomalies and the ecology of the North Sea

Long-term changes in the plankton of the North Sea are investigated using data from the continuous plankton recorder (CPR) survey. During the last 4 decades, there appears to have been 2 large anomalous periods within the plankton data set, one that occurred in the late 1970s and the other in the late 1980s. These anomalous periods seem to be largely synchronous with unusual ocean climate conditions that have occurred episodically over a timescale of decades. The unusual ocean climate conditions prevailing at these 2 time periods appear to contain important hydrographical elements that involve oceanic incursions into the North Sea. This paper, using data from the CPR survey and providing evidence from other studies, focuses on the relationship between the long-term changes in the biology of the North Sea and these 2 exceptional hydro-climatic events. Here, we suggest that while atmospheric variability and associated changes in regional temperatures have a dominant effect on the marine environment, oceanic influences on the ecology of a semi-closed environment such as the North Sea may have been underestimated in the past.

Decadal basin-scale changes in diatoms, dinoflagellates, and phytoplankton color across the North Atlantic

The Continuous Plankton Recorder (CPR) survey has been used to characterize phytoplankton and zooplankton space-time dynamics in the North Sea since 1931 and in the North Atlantic since 1939. Phytoplankton biomass is assessed from these samples by visual assessment of the green color of the silk mesh, the Phytoplankton Color Index (PCI), and the total count of diatoms and dinoflagellates. Species with a frequency of occurrence greater than 1% in the samples are used as indicator species of the community. We investigated (1) long-term fluctuations of phytoplankton biomass, total diatoms, and total dinoflagellates; (2) geographical variation of patterns; (3) the relationship between phytoplankton and climate forcing in the North Atlantic CPR samples; (4) the relative contribution of diatoms and dinoflagellates to the PCI; and (5) the fluctuations of the dominant species over the period of survey to provide more information on the processes linking climate to changes in the phytoplankton community. As a result of the differences in microscopic analysis methods prior to 1958, our analyses were conducted for the period ranging from 1958 to 2002. The North Atlantic was divided into six regions identified through bathymetric criteria and separated along a North-South axis. Based on 12 monthly time series, we demonstrate increasing trends in PCI and total dinoflagellates and a decrease in total diatoms.