IMPACTS OF CLIMATE CHANGE ON PLANKTON

Philip C. Reid
Sir Alistair Hardy Foundation for Ocean Science

Executive Summary

Major changes have taken place in both the plant (phyto-) and animal (zoo-) plankton of the seas around the British Isles over the last few decades. They include a:

pronounced stepwise change (regime shift) in marine ecosystems since the mid- 1980s,
northerly movement of warmer water plankton by 10° latitude in 40 years and a similar retreat of colder water plankton to the north
Considerable changes in the seasonal timing (phenology) of the plankton have been observed
pronounced change in the composition and abundance of the phyto-and zooplankton
large increase (400% for sea urchins) in the larval stages of animals living on the bottom in the North Sea since the mid 1980s
~50% increase in phytoplankton biomass and an associated long-term decline in zooplankton biomass that includes a 70% decline in the important copepod genus Calanus in the North Sea since the late 1950s
Increase in biodiversity although the species (mostly copepods) are smaller and production is likely to be less.

The observed changes have been significantly linked to regional hydroclimatic variability (SST, salinity, oceanic inflow, wind strength and direction, visibility, nutrients and water column stability) that is associated with climate warming, the North Atlantic Oscillation and in particular Northern Hemisphere temperature. It is the significant statistical association with the latter index of hemispheric warming that suggests that the changes are a regional response to climate warming engendered by greenhouse gases. The observations for the above bullet points primarily come from the 75 year old Continuous Plankton Recorder survey, but are confirmed by other single point time series such as at Helgoland and through intercomparison with satellite measurements.

Modelling studies are still at an early stage although inclusion of the plankton data in new modelling approaches to fishery assessment is giving promising preliminary results. Likely much higher sea temperatures in UK waters in the future will lead to further large changes in plankton as temperature appears to be a major factor in the composition of communities and in the timing (phenology) of populations.

Other factors such as eutrophication, fisheries and in the future acidification may also contribute to plankton variability, but they are believed, by general consensus, to be less important than hydroclimatic forcing. In contrast the changes in the plankton have had a major impact on fish stocks with a decline in gadoid biomass, especially cod, and can also explain the marked reduction in returns of salmon to home waters. A climate link has also been established between plankton, sandeels and seabirds There is regional variability in the patterns of change seen in the plankton, but the general trends described above are characteristic of all waters around the UK.

Level of Confidence

MEDIUM

Medium. A high level of confidence is suggested in the information axis primarily on the basis of information from the Continuos Plankton Recorder survey although there is a great deal of other plankton data that is backing up the messages coming from the survey. Modelling is still at an early level, but preliminary work with GAMS, Neural Networks and intercomparison with satellite derived data is helping to confirm a strong linkage between plankton variability and hydroclimatic change with a strong relationship to temperature. It should not be too long before it is possible to forecast possible scenarios for UK seas with higher sea temperatures. Unfortunately, we cannot derive a confidence level for potential shifts like the mid 1980s regime shift that has had such a major impact on the UK marine environment. Thus on average the information available is high, but the confidence in interpretation moderate.

Key Sources of Information

Charting Progress: State of Plankton section (Reid et al., 2005) in Marine Habitats and Species http://192.171.163.165/Climate%20Encyclopaedia/pdfs/chartprogress-3.pdf

ICES Working Group: Zooplankton Ecology annual reports other documents
http://www.ices.dk/committe/occ/wgze.htm

SAHFOS Ecological Status Report for 2004/5
http://192.171.163.165/annual_reports/annual%20report%202005/ecological%20status%20(ebook).pdf

SAHFOS web site
http://www.sahfos.org/

Please acknowledge this document as: Reid, P. C. (2006). Impacts of Climate Change on Plankton in Marine Climate Change Impacts Annual Report Card 2006 (Eds. Buckley, P.J, Dye, S.R. and Baxter, J.M), Online Summary Reports, MCCIP, Lowestoft, www.mccip.org.uk