Are Calanus spp. shifting poleward in the North Atlantic? A habitat modelling approach

Abstract

Chust, G., Castellani, C., Licandro, P., Ibaibarriaga, L., Sagarminaga, Y., and Irigoien, X. 2014. Are Calanus spp. shifting poleward in the North Atlantic? A habitat modelling approach. – ICES Journal of Marine Science, 71: 241–253. In the last decade, the analysis based on Continuous Plankton Recorder survey in the eastern North Atlantic Ocean detected one of the most striking examples of marine poleward migration related to sea warming. The main objective of this study is to verify the poleward shift of zooplankton species (Calanus finmarchicus, C. glacialis, C. helgolandicus, C. hyperboreus) for which distributional changes have been recorded in the North Atlantic Ocean and to assess how much of this shift was triggered by sea warming, using Generalized Additive Models. To this end, the population gravity centre of observed data was compared with that of a series of simulation experiments: (i) a model using only climate factors (i.e. niche-based model) to simulate species habitat suitability, (ii) a model using only temporal and spatial terms to reconstruct the population distribution, and (iii) a model using both factors combined, using a subset of observations as independent dataset for validation. Our findings show that only C. finmarchicus had a consistent poleward shift, triggered by sea warming, estimated in 8.1 km per decade in the North Atlantic (16.5 per decade for the northeast), which is substantially lower than previous works at the assemblage level and restricted to the Northeast Atlantic. On the contrary, C. helgolandicus is expanding in all directions, although its northern distribution limit in the North Sea has shifted northward. Calanus glacialis and C. hyperboreus, which have the geographic centres of populations mainly in the NW Atlantic, showed a slight southward shift, probably responding to cool water penetrating southward in the Labrador Current. Our approach, supported by high model accuracy, shows its power in detecting species latitudinal shifts and identifying its causes, since the trend of occurrence observed data is influenced by the sampling frequency, which has progressively concentrated to lower latitudes with time.

Mare Incognitum: A Glimpse into Future Plankton Diversity and Ecology Research

“…These attributes make them a key group for monitoring the impacts of climate change on biodiversity and ecosystem functioning (Richardson, 2008). So far, SDMs have seldom been applied to study plankton biogeography, with only a handful of studies on phytoplankton (Irwin et al, 2012;Pinkernell and Beszteri, 2014;Brun et al, 2015;Rivero-Calle et al, 2015;Barton et al, 2016) and some more on zooplankton (e.g., Reygondeau and Beaugrand, 2011;Chust et al, 2014b;Villarino et al, 2015;Brun et al, 2016;Benedetti et al, in press). This is due not only to the limited data availability for model development, but also due to several unaddressed methodological issues.…”

“…Moreover, disentangling the effects of anthropogenic climate change on plankton distribution and phenology shifts from other drivers (e.g., climate variability, population dynamics) is equally challenging (Chust et al, 2014b). In particular, the combination of controlling factors, together with systematic biases in sampling effort can lead to biases in estimated trends.…”

Reduced up-regulation of gene expression in response to elevated temperatures in the mid-Atlantic population of Calanus finmarchicus

“…Ongoing climate change, particularly seawater warming, is affecting and will continue to affect predominant copepods of the genus Calanus, resulting in distributional changes with consequences for higher trophic levels Chust et al, 2014;Olsen et al, 2011;Reygondeau and Beaugrand, 2011a). While a previous study has already revealed differences in the thermal stress response between closely related Calanus species , the degree of variation in responses of different Calanus populations is largely unknown.…”

“…The highest population densities of C. finmarchicus are found along the south-west to north-east axis of the North Atlantic where temperatures range between 4°C and 9°C (Planque and Batten, 2000;Sundby, 2000). Since the 1960s a consistent northward shift of C. finmarchicus distribution has been detected (Beaugrand et al, 2002;Chust et al, 2014). In the North Sea this decrease in the abundance of C. finmarchicus has been associated with an increase of the more southern species C. helgolandicus, which has a lower lipid content and different phenology than C. finmarchicus Bonnet et al, 2005).…”

“…The effects of temperature increase on C. finmarchicus distribution are documented by Chust et al (2014) and a further northward shift is predicted, particularly at the southern edge of distribution where seawater temperatures might exceed the thermal niche for C. finmarchicus for several months in a year by 2100 (Helaouët et al, 2011;Reygondeau and Beaugrand, 2011a). Thus, knowledge on physiological and gene expression plasticity among populations of C. finmarchicus to elevated temperatures may be of particular interest and importance to reduce uncertainties of climate change impacts.…”