Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Climate impacts on environmental systems3.1.5 Phenology of marine speciesRelevancePhenology is the study of annually recurringlife-cycle events of species, such as the timing ofmigrations and flowering of plants. In the marineenvironment, phenology indicators include thetiming of the spring phytoplankton bloom andthe peak in abundance of other marine organisms.Change in phenology is one of the key indicatorsof the impacts of climate change on biologicalpopulations. Because marine species have differentsensitivities to changes in temperature, thesechanges may lead to large shifts in the marine foodweb that can ultimately affect the food available tofish, birds or marine mammals. Differing responseshave been seen across various levels of the food web(Thackeray et al., 2010).Changes in the phenology of different planktonspecies are seen as a factor contributing to thedecline in North Sea cod stocks, which was causedinitially by over-fishing, and they have probablyaffected other fish populations (such as sandeels) that are an essential food source for seabirds(Beaugrand et al., 2003; Edwards and Richardson,2004; Frederiksen et al., 2006).In the North Sea, work on pelagic phenology hasshown that plankton communities, includingfish larvae, are very sensitive to regional climatewarming. Responses to warming vary betweentrophic levels and functional groups, which maycreate a so-called 'trophic mismatch' betweenone species and their food source (Thackerayet al., 2010) (see also Section 3.4 for terrestrialecosystems). The sexual maturation of decapodalarvae has been found to be particularly sensitiveto water temperature and is therefore regardedas representative of phenological changes in theshelf-sea environments (Lindley, 2009). Other taxathat also have their seasonal development closelytriggered by temperature changes are also highlysensitive (e.g. echinoderm larvae, dinoflagellates,copepods).Past trendsThe zooplankton growing season indicator showsthe annual timing of peak seasonal abundanceof decapoda larvae from 1958–2009 in the centralNorth Sea (Figure 3.4 left). A shift towards an earlierseasonal peak is clearly visible, in particular since1988. Since the 1990s the seasonal development ofdecapoda larvae has occurred 4–6 weeks earlier thanthe long‐term average (baseline mean 1958–2009).This trend towards an earlier seasonal appearanceof decapoda larvae during the 1990s is highlycorrelated with SSTs (Figure 3.4 right). Even thoughdecapoda larvae are not routinely identified tospecies level, a recent study has shown that thesephenological shifts are a response at the specieslevel, and not simply different seasonal timings bydifferent species (Lindley and Kirby, 2010).Key messages: 3.1.5 Phenology of marine species• Temperature increases in the ocean have caused many marine organisms in European seas to appearearlier in their seasonal cycles than in the past. Some plankton species have advanced their seasonalcycle by 4–6 weeks in recent decades.• Projections of the phenological responses of individual species are not available, but phenologicalchanges are expected to continue with projected further climate change.• Changes in the plankton phenology have important consequences for other organisms within anecosystem and ultimately for the structure of marine food -webs at all trophic levels. Potentialconsequences include increased vulnerability of North Sea cod stocks to over-fishing; and changes inseabird populations.Climate change, impacts and vulnerability in Europe 201297