The magnitude and characteristics of the response of Arctic marine ecosystems to the challenges resulting from climate change are not known. Among the drivers of change, temperature plays a fundamental role, influencing biological processes from individual organisms to whole ecosystems, and sets the thresholds for species performance, abundance and distribution, and is responsible for massive shifts in ecosystem structure and function. The metabolic theory of ecology is generally invoked to ascertain the effects of global temperature changes on shifts in ecosystems, from individual size and species composition to global trophic status. However, as generally occurs with most scaling laws, there is a lively debate about its usefulness to predict something more than gross tendencies. In general, to explain variability is much more interesting than to predict average values. The successful performance of species and the trophic status of ecosystems are controlled by the balance between energy gains and losses. The temperature-induced mismatch between the positive and negative terms of the metabolic balance appears to depend on precise characteristics of their respective thermal windows, hardly identifiable by the averaging predictions made by the metabolic theory. As a case study, we discuss the response to temperature changes of the balance between ingestion and respiration rates of the copepod Calanus glacialis, a fundamental component of Arctic pelagic food webs. We suggest using the response of the metabolic balance (at the organismal, community or ecosystem level) to temperature changes to identify thermal thresholds leading to tipping points and nonlinear ecosystem shifts.

Self-regulation of population dynamics in nutrient-rich (eutrophic) ecosystems has been a fascinating topic for decades in ecological literature. Simple theoretical models predict population oscillations of large amplitudes in such systems, those predictions often being at odds with reality. Plankton communities possess a particular combination of two important properties, making them unique among ecosystems with eutrophication. These are: (i) the existence of a pronounced spatial gradient of the prey growth rate (through light attenuation with depth) and (ii) the presence of fast-moving predator (zooplankton) capable of quick adjustment of grazing load in vertical direction throughout the whole habitat. Surprisingly, the interplay of those factors is rarely taken into account while analysing stability of nutrient-rich plankton communities. In this paper, we construct generic plankton models (based on integro-differential equations) incorporating the light attenuation in the water column as well as food-searching behaviour of zooplankton. We found that the interplay between the two factors would stabilize a system at low species densities even for an ‘unlimited’ nutrient stock (infinite system's carrying capacity). Different possible scenarios of stabilization have been found. Since both the vertical gradient of light and the active food search by zooplankton in the column are common characteristics of real plankton communities, we suggest that the obtained mechanism of self-regulation is rather generic in nature. We argue that taking into account this mechanism would be important for understanding the dynamics of nutrient-rich low-chlorophyll ocean systems as well as major causes of non-seasonal plankton blooms.

The data for the present study were collected at 20 sampling stations in the Kara Sea along the transect from the Ob estuary to the deep sea St. Anna Trough in September 2007. Based on the...

Studies were conducted at the end of June 2011 in the coastal region of the northeastern part of the Black Sea. The bulk of the Noctiluca scintillanspopulation was observed in the thermocline and...

Noctiluca scintillansis a common and numerous component of the heterotrophic plankton living in the Black Sea. It can play a significant role in the trophic dynamics of the pelagial community. The...

Two copepod species, Calanus finmarchicus (a widespread North Atlantic species) and C. glacialis(an Arctic species), are dominant in the zooplankton of Arctic seas. We hypothesized that the...