Long-term changes in the diel vertical migration behaviour of zooplankton

Abstract

Samples historically collected and analysed by the Continuous Plankton Recorder survey were used to examine long-term (1958 to 1994) patterns in the normal diel vertical migrat~on (NDVM) behaviour of 7 copepod taxa in the North Sea: Calanus finmarchicus C5-C6; Calanus spp. Cl-C4; Cenlropages typicus; Centropages hamatus; Temora longicornis; Acartia clausii and Para-Pseudocalanus (this last group included all Paracalanus and Pseudocalanus species). The ratio of night:day abundance near the surface was used as a measure of the extent of NDVM. For all 7 taxa, the extent of NDVM between 1958 and 1994 CO-varied wlth the abundance of herring Clupea harengusin the North Sea. Fisheries data show that during this period the herring stock was a good indicator of the overall abundance of planktivorous fish in the North Sea. These results suggest that changes in the abundance of planktivorous fish in the North Sea over recent decades have resulted in modifications in the NDVM behaviour of many zooplankton taxa.

Habitat selection by a marine copepod during the productive season in the Subarctic

“…Field data that are collected on relevant scales to permit analysis of habitat selection by marine zooplankton are scarce, especially from Subarctic and Arctic areas and even more so from advective and from oceanic areas (but see Hays et al 1996, Basedow et al 2008, Fossheim & Primicerio 2008. It is therefore no coincidence that most of our knowledge on habitat choice by zooplankton stems from limnetic areas and from modelling studies (Zaret & Suffern 1976, Neill 1990, Hugie & Dill 1994, Lampert et al 2003, Primicerio 2003.…”

Long-term changes in diel vertical migration behavior:more ups and downs

“…While they did find such a correlation, their analysis has been challenged by Hirst & Batten (1998), primarily on 2 grounds: (1) Hays (1995) and Hays et al (1996) did not properly assess the dark period, mistakenly including some light periods as dark and vice-versa, due to seasonally changing day-lengths; (2) they used an index of diel migration, their 'DVMindeX1 (changed in the second paper to 'N/D,nde,'), which was sensitive to sample size. Hirst & Batten (1998) proposed their own, which they confusingly termed 'DVM' (the usual abbreviation for the phenomenon of diel vertical migration itself-] will refer to the index as 'HB'), designed to remedy the sample-size sensitivity in N/Dmde,, the Hays index.…”

“…and Hays et al (1996) analyzed Continuous Plankton Recorder (CPR) records to determine if die1 vertical migrations (DVMs) of North Sea copepods had changed in response to changes in predator (chiefly herring) abundances between 1958 and 1996. While they did find such a correlation, their analysis has been challenged by Hirst & Batten (1998), primarily on 2 grounds: (1) Hays (1995) and Hays et al (1996) did not properly assess the dark period, mistakenly including some light periods as dark and vice-versa, due to seasonally changing day-lengths; (2) they used an index of diel migration, their 'DVMindeX1 (changed in the second paper to 'N/D,nde,'), which was sensitive to sample size.…”

“…As the number of days covered by a sampling program is decreased, eventually there would be no way to identify the signals as true DVM. The depth sampled is usually about 6.5 m (Hays & Warner 1993), not really a 'surface' sample, and it is seldom clear whether the copepods were feeding at this depth, merely passing through, or engaging in 'reverse' DVMs from the surface layer (Roe 1974, Hays et al 1996. Even assuming that the copepods do spend the dark hours within the phytoplankton maximum, as the depth of this varies through the year, the perceived migration regime must vary with it.…”

“…As well as Temora longicornis and adult (C5-C6) Calanus finmarchicus (discussed above), Hays et al (1996) examined the CPR records of 5 copepod groupings: Calanus sp. Cl-C4, Cen tropages typicus, Cen tropages hamatus, Acartia clausii, and a combined category of Paracalanus sp.…”