Doliolids in the German bight in 1989: Evidence for exceptional inflow into the North Sea

Abstract

Doliolids were found in samples taken with a Continuous Plankton Recorder (CPR) in October 1989 between 55°14'N 03°32'E and 55°20'N 06°13'E during a tow between Newcastle and Esbjerg. Densities were estimated at >100 m−3 for about 112 km of tow. A sub-sample of specimens in sufficiently good condition to be reliably identified were referred to Doliolum nationalis Borgert. Substantial numbers of doliolids were found on a CPR tow between Harwich and Gothenburg which passed through the same area in that month and specimens were found nearer to the Danish coast in November and south-west of Helgoland in December. The distribution of doliolids in CPR samples taken in the North Sea in the last three months of 1989 is shown in Figure 1.

Increasing prevalence of the marine cladoceran Penilia avirostris (Dana, 1852) in the North Sea

“…The well documented rise in SST and the increased incursion of oceanic water has led to large scale changes in the plankton community of the North Sea. It is interesting to note that P. avirostris was found in the southern North Sea in 1990 (Helgoland Roads time-series), the same time as an exceptionally large pulse of warm high salinity water entered the North Sea (Lindley et al 1990;Edwards et al 1999 The above results could suggest that P. avirostris has shifted northwards in its distribution in response to increased SSTs. The appearance of P. avirostris in the 1990s appears to have heralded the successful colonisation of the North Sea by the species, with a peak in abundance in 1999 and subsequently in 2003 (with a further increase in abundance in 2004 in the Helgoland Roads survey, Table 1), whereas previous occurrences do not appear to have established a viable population.…”

Evidence for decrease in size of lesser sandeels Ammodytes marinus in a North Sea aggregation over a 30-yr period

“…This was followed by an opposite scenario in the late 1980s and early 1990s, with elevated salinities and temperatures (Edwards et al 2002). Both these events were associated with profound changes in the biomass, community structure and phenology of plankton in the North Sea (Lindley et al 1990, Reid et al 1992, Edwards et al 2002. Data on fish stocks also indicated major changes in distribution, abundance and demography during these periods (Corten & van de Kamp 1992, Reid et al 2001, Beaugrand et al 2003.…”

New primary production in northwest European shelf seas, 1960–2003

“…Heath et al (1991) have previously reported unusually high anomalies of salinity during this period, coinciding with a peak since 1865 in the NAO index characterized by enhanced westerly winds and oceanic transport. Edwards et al (1999), Holliday & Reid (2001), and Lindley et al (1990) reported exceptional incidences of oceanic species in the plankton collected along European continental shelf routes by the continuous plankton recorder (CPR) during 1989 and 1997 to 1998, and changes in many aspects of the fisheries and marine ecology have been identified during this period, leading to it being referred to as a 'regime shift' (Reid et al 2001a,b, Weijerman et al 2005). In our study we can perhaps identify one of the processes underlying the so-called regime shift as being the injection of a significant mass of nitrate-nitrogen onto the shelf, which was then assimilated into the food web as new production.…”