Temporal and spatial variability of phytoplankton and chlorophylla: lessons from the south coast of Norway and the Skagerrak

Abstract

Regular monitoring of phytoplankton has been carried out on the Norwegian Skagerrak coast three times a week since 1989, and samples from the upper 3 m of the water column have been analysed for chlorophyll a (Chl a) concentrations and dominant species. Selected potentially toxic or harmful species of phytoplankton have also been quantified. Chl a appears to fluctuate considerably on a short time scale (2-3 days), and simple analyses suggest that Chl a should be measured at least twice a week to obtain reliable annual estimates. By contrast, at the inshore monitoring station Chl a is significantly correlated with transect measurements across most of the Skagerrak, indicating a high spatial homogeneity. Hence, measurements at the inshore stations are likely to reflect concentrations over a large area and meteorological conditions are suggested to be the most likely driving force controlling the variability. The traditional view of a marked spring and autumn bloom in temperate stratified waters does not seem to be a predominant feature of the production cycle in the Skagerrak. In fact, Chl a concentrations >4 g l 1 rarely last for more than a week. In addition to short-term variability, there is also high inter-annual variability in the production cycle. This picture is reinforced by large variations in species composition of the phytoplankton community; the abundance of all species analysed varies substantially from one year to the next. 1998 International Council for the Exploration of the Sea

Routine quantification of phytoplankton groups—microscopy or pigment analyses?

“…Emphasis has been put on the occurrence of potentially harmful species and on seasonal succession of algal groups, their diversity, magnitude, and duration to monitor environmental changes (Pybus 1996, Gobler & Sañudo-Wilhelmy 2001, Edwards et al 2002. Phytoplankton monitoring has been used as an early warning system for potentially harmful algal blooms (Dahl & Johannessen 1998) and has resulted in indications of climatic changes, e.g. glacial melting in the Antarctic, where an increased dominance of cryptophytes was used as a sign of an increased input of melting water into the coastal regions of the Southern Ocean (Moline & Prézelin 1996).…”

Bifurcations in Marine Ecosystems

“…This bloom was dominated by red-tide dinoflagellates, the toxic Karenia mikimotoi, and large Ceratium spp. (Chapter 8; Dahl and Johannessen, 1998). The onset of the spring bloom occurred earlier in the season (about 21 d) during the most recent period.…”

“…However, the concept has become vague because of lack of consistent definitions of regimes and of regime shifts (deYoung et al, 2004;Overland et al, 2008). For example, Jarre et al (2006) listed 13 different definitions of regime shifts from the marine literature.…”

“…Instead, they appear to be more consistent with a long memory process with considerable autocorrelation at multiyear time scales, which can show persistent major deviations from a single century scale mean." In general, because of the difficulty of testing the underlying mechanism of shifts in large, open marine ecosystems (Collie et al, 2004;deYoung et al, 2004;Scheffer and van Nes, 2004), one can usually only come up with hypothesis of causal relationships.…”

A long-term perspective on the Chrysochromulina bloom on the Norwegian Skagerrak coast 1988: a catastrophe or an innocent incident?

“…1B) as well as monthly transects across Skagerrak, began in 1988. In the course of this work it has been found that Chrysochromulina spp., including C. polylepis, are common in the Skagerrak; their main season being May-June (Dahl & Johannessen 1998). Bloom duration and concentrations of Chrysochromulina spp.…”