Temperature-dependent growth of Antarctic krill: predictions for a changing climate from a cohort model

Abstract

In the Southern Ocean, Antarctic krill Euphausia superba are the dominant prey item for many predators, and a changing climate may affect the biomass of krill available to both predators and the krill fishery. We projected growth trajectories for individual krill within cohorts and estimated how total biomass in an area available to both predators and the fishery may vary from year to year simply due to fluctuations in temperature. We used an existing temperature-dependent growth model and a time series of temperature data (1970 to 2004) for 2 regions in the Southern Ocean: (1) around the Antarctic Peninsula, and (2) around the island of South Georgia. The growth model predicted increasing individual size within a cohort (in terms of length and weight) with increasing temperature in the cooler Antarctic Peninsula region and decreasing individual size with increasing temperature in the warmer South Georgia region. Years with many cohorts of small individuals in the population resulted in biomass well below average, whereas years with many cohorts of large individuals resulted in biomass well above the average, suggesting that temporal changes in Southern Ocean temperatures may have profound effects on the total biomass in an area that is available to both predators and the fishery. Moreover, the effects of a potentially warming Southern Ocean on krill biomass will likely be more pronounced in the warmer regions occupied by krill.

Long-Term Effect of Photoperiod, Temperature and Feeding Regimes on the Respiration Rates of Antarctic Krill (<i>Euphausia superba</i>)

“…Krill is considered to be stenothermal and is sensitive to slight changes in temperature and other environmental changes [57]. Temperature has been shown to influence the frequency of moulting in krill, and thus overall growth rates, which can vary considerably, even within a narrow annual temperature range that is observed in the Southern Ocean [23,24,38,58,59,60].…”

Managing direct and indirect threats to marine ecosystems to balance multiple objectives

“…We described summaries of the mechanisms for environmental change for each of these drivers, the estimated impact on krill, observed impact from experiments, and then linked this information to the effect of a change in these physical variables on krill growth, spawning and hatching success, recruitment and survival parameters (see Table 6.2). Although there is spatial variability in the intensity of impacts from environmental change on krill, it is acknowledged that a rise in seasurface temperature beyond the threshold of survival for krill (~4°C) will consistently result in high mortality (Constable et al 2014;Hill et al 2013;Murphy et al 2007;Wiedenmann et al 2008). …”

“…Although there are a number of alternative models for evaluating Antarctic krill growth, few estimate growth as a function of temperature (Wiedenmann et al 2008). The model of Atkinson et al (2006) has been used in several previous studies (Atkinson et al 2009;Atkinson et al 2008;Wiedenmann et al 2008) to estimate krill Gross Growth Potential, which provides a measure of the ability of the habitat to support Antarctic krill growth, based on spatially-resolved, monthly averages of SST and CHL. To convert krill length to age, we used a von Bertalanffy growth equation to relate shell length l (mm) to age in years (t), based on Siegel (1987).…”

“…Negative response around Sth Georgia where water temperatures have already increased ) -further temperature increases could raise metabolic costs to an unsustainable level (Constable et al 2014;Hill et al 2013;Murphy et al 2007;Wiedenmann et al 2008). Modelled uniform 1°C temperature rise produces a pole-ward shift for euphasiids .…”

“…Modelled uniform 1°C temperature rise produces a pole-ward shift for euphasiids . Wiedenmann et al (2008) growth model predicts increasing individual size within a length and weight cohort with increasing temperature in cooler Antarctic Peninsula region (60-70°S), decreasing individual size with increasing temperature in warmer South Georgia region (50-60°S). Ice-associated primary production (including ice algal production) expected to decline in some areas (e.g.…”