Variability In Abundance Vertical-Distribution And Ontogenetic Migrations Of Thysanoessa-Longicaudata (Crustacea Euphausiacea) In The Northeastern Atlantic-Ocean

The vertical distribution, seasonal and ontogenetic migrations and seasonal variability in abundance of Thysanoessa longicaudata (Krøyer) were investigated using the Longhurst-Hardy Plankton Recorder for a 4 yr period (March, 1971 to May, 1975) at Ocean Weather Station “I” (59°00′N; 19°00′W) in the north-eastern Atlantic Ocean. Of 8 species of euphausiids identified at this position, the vast majority were T. longicaudata (for example, 99.5% of the total euphausiids in 1972 belonged to this species). From March to October the majority of calyptopes, furciliae and adults of T. longicaudata were found in the upper 100 m. The major spawning occurred in spring at a water temperature of 9° to 10°C and calyptopes and furciliae appeared in late April, reaching their maximum abundance in May. There was no evidence of large-scale diurnal migrations, although an extensive ontogenetic migration of young developmental stages was observed. The eggs were found from 100 m down to 800 m, the maximum depth of sampling, and the vertical distribution of the three naupliar stages showed a “developmental ascent” as they matured. During the main reproductive period in May, over 70% of all nauplii were below 500 m while more than 94% of Calyptopis Stage I were above 500 m with their maximum abundance in the euphotic zone (0 to 50 m). Calyptopis Stage I is the first feeding stage and it is this stage which shows the largest ontogenetic migration. Brief descriptions of the egg and nauplii are given.

Regime shifts in marine ecosystems: detection prediction and management

Regime shifts are abrupt changes between contrasting, persistent states of any complex system. The potential for their prediction in the ocean and possible management depends upon the characteristics of the regime shifts: their drivers (from anthropogenic to natural), scale (from the local to the basin) and potential for management action (from adaptation to mitigation). We present a conceptual framework that will enhance our ability to detect, predict and manage regime shifts in the ocean, illustrating our approach with three well-documented examples: the North Pacific, the North Sea and Caribbean coral reefs. We conclude that the ability to adapt to, or manage, regime shifts depends upon their uniqueness, our understanding of their causes and linkages among ecosystem components and our observational capabilities.

Temporal changes in plankton of the North Sea: community shifts and environmental drivers

This paper analyses long-term and seasonal changes in the North Sea plankton community during the period 1970 to 2008. Based on Continuous Plankton Recorder (CPR) data covering 38 yr, major changes in both phytoplankton and zooplankton abundance and community structure were identified. Regime changes were detected around 1978, 1989 and 1998. The first 2 changes have been discussed in the literature and are defined as a cold episodic event (1978) and a regime shift towards a warm dynamic regime (1989). The effect of these 2 regime changes on plankton indicators was assessed and checked against previous studies. The 1998 change represents a shift in the abundance and seasonal patterns of dinoflagellates and the dominant zooplankton group, the neritic copepods. Furthermore, environmental factors such as air temperature, wind speed and the North Atlantic water inflow were identified as potential drivers of change in seasonal patterns, and the most-likely environmental causes for detected changes were assessed. We suggest that a change in the balance of dissolved nutrients driven by these environmental factors was the cause of the latest change in plankton community structure, which in turn could have affected the North Sea fish community.

Rapid biogeographical plankton shifts in the North Atlantic Ocean

Large-scale biogeographical changes in the biodiversity of a key zooplankton group (calanoid copepods) were detected in the north-eastern part of the North Atlantic Ocean and its adjacent seas over the period 1960–1999. These findings provided key empirical evidence for climate change impacts on marine ecosystems at the regional to oceanic scale. Since 1999, global temperatures have continued to rise in the region. Here, we extend the analysis to the period 1958–2005 using all calanoid copepod species assemblages (nine species assemblages based on an analysis including a total of 108 calanoid species or taxa) and show that this phenomenon has been reinforced in all regions. Our study reveals that the biodiversity of calanoid copepods are responding quickly to sea surface temperature (SST) rise by moving geographically northward at a rapid rate up to about 23.16 km yr−1. Our analysis suggests that nearly half of the increase in sea temperature in the northeast Atlantic and adjacent seas is related to global temperature rises (46.35% of the total variance of temperature) while changes in both natural modes of atmospheric and oceanic circulation explain 26.45% of the total variance of temperature. Although some SST isotherms have moved northwards by an average rate of up to 21.75 km yr−1 (e.g. the North Sea), their movement cannot fully quantify all species assemblage shifts. Furthermore, the observed rates of biogeographical movements are far greater than those observed in the terrestrial realm. Here, we discuss the processes that may explain such a discrepancy and suggest that the differences are mainly explained by the fluid nature of the pelagic domain, the life cycle of the zooplankton and the lesser anthropogenic influence (e.g. exploitation, habitat fragmentation) on these organisms. We also hypothesize that despite changes in the path and intensity of the oceanic currents that may modify quickly and greatly pelagic zooplankton species, these organisms may reflect better the current impact of climate warming on ecosystems as terrestrial organisms are likely to significantly lag the current impact of climate change.