Scaling climate effects from individual physiology to population responses

Although a few compelling case studies have demonstrated biological effects of global warming, a common denominator of these studies is that they tend to focus on populations, communities, and ecosystems. However, it is necessarily individuals that feel and respond to changes in the environment. The sum of environmental influences on an individual determines its survival and ability to reproduce and grow, which are the links between individual traits and population dynamics. A central component of climate change and of great physiological importance is an increase in temperature. In this project we have therefore examined to which extent temperature affects maturity, spawning and early life stages survival. The project has resulted in major advancements in knowledge within this research field, based on integration of experimental studies, field sampling, time series analyses and further developments of migration models (consulting also data-storage tag information). A spawning temperature above 10 deg C results in negative effects on a series of reproductive traits: 1) increased prevalence of atresia (resorption of developing oocytes), 2) declining levels of estradiol, 3) significantly altered gene expressions, and 4) decreasing sperm activity (velocity). Consulting the data-storage tag information, environmental temperature stands out as being important for selection of spawning depth, but an individual seems to return very much to the same spawning ground indicating a well-developed adaptive capacity in this regard. Improvements in geolocation algorithms have been important, but further works continue. Barents Sea cod show delayed spawning time at higher water temperature. This unexpected result may be explained by longer periods of feeding at high latitudes, i.e., near the ice edge, and thus lower experienced temperature during gonad maturation (prior to spawning). We found that larger cod typically spawn earlier than smaller cod, supporting our original hypothesis that this earlier spawning will increase the chances of the larvae matching temporally the advanced peak prey (zooplankton) availability in warmer waters, which is a basis for enhanced survival. In contrast, small cod appears not to spawn sufficiently early despite the higher temperatures, resulting in more of a mismatch with larval prey. Consequently, the early spawning of large females seems to be a precondition for increased early stage recruitment in warm years. The 3.5 year project is now ended (December 2020). Several articles have already been published, and new ones will appear in 2021.

Prosjektet har resultert i en klar forbedring av kunnskapsgrunnlaget: En gytetemperaturer over 10 grader C har en klar negativ effekt på en serie av reproduktive responser, som: 1) flere hunner viser atresi, 2) fall i østrogennivå, 3) endringer av genuttrykk for en rekke gener, 4) fall i spermaktivitet. Vanntemperatur er viktig for hvilket dyp torsken står i under gytingen, men torsken gyter mye i det samme området og dermed viser en adapsjon. Det er videreutviklet metodikk (geolokalisering) for å følge torskens vandring. Vi fant at torsk i Barentshavet gyter senere når temperaturen øker. Dette uventede resultatet ses i sammenheng med et lengre fødeopphold nær iskanten nord i Barentshavet som fører til at temperaturen under modningen faller. Imidlertid stor torsk gyter noe tidligere enn mindre torsk, som indikerer at det vil være et bedre samsvar mellom gytetidspunkt og våroppblomstringen og dermed økt mulighet til å finne føde (dyreplankton) for larvene fra stor torsk.

Although a few compelling case studies have demonstrated biological effects of global warming, a common denominator of these studies is that they tend to focus on populations, communities, and ecosystems. However, it is necessarily individuals that feel and respond to changes in the environment. The sum of environmental influences on an individual determines its survival and ability to reproduce and grow, which are the links between individual traits and population dynamics. A central component of climate change and of great physiological importance is an increase in temperature. In this project we therefore focus on the temperature dependence of female maturation and spawning dynamics and the characteristics of early life-history stages using a key species in arcto-boreal waters as our model: the Atlantic cod. Our preliminary data led to the hypothesis that large cod are able to spawn earlier in warm years, matching peak zooplankton availability for their larvae, which is a basis for enhanced survival. In contrast, small cod would not spawn sufficiently early despite higher temperatures, resulting in more of a mismatch with larval prey. Consequently, the early spawning of large females is a precondition for increased early stage recruitment in warm years. To assess the magnitude of this effect, the project is designed to quantify temperature-dependent physiology and spawning performance in cod, assess its consequences at the population-level, predict new optimal life histories, and assess management implications. The focus will be on Northeast Arctic cod, but comparative studies will also be undertaken with North Sea/Scottish cod. The project will combine physiological experiments, field data, tagging studies, environmental data, and quantitative ecological and evolutionary modelling to develop predictive-type models to address the effect of climate warming on teleost productivity and recruitment.