Climate change is driving changes in the physical and chemical properties of the ocean that have consequences for marine ecosystems. Here, we review evidence for the responses of marine life to recent climate change across ocean regions, from tropical seas to polar oceans. We consider observed changes in calcification rates, demography, abundance, distribution and phenology of marine species. We draw on a database of observed climate change impacts on marine species, supplemented with evidence in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. We discuss factors that limit or facilitate species’ responses, such as fishing pressure, the availability of prey, habitat, light and other resources, and dispersal by ocean currents. We find that general trends in species responses are consistent with expectations from climate change, including poleward and deeper distributional shifts, advances in spring phenology, declines in calcification and increases in the abundance of warm-water species. The volume and type of evidence of species responses to climate change is variable across ocean regions and taxonomic groups, with much evidence derived from the heavily-studied north Atlantic Ocean. Most investigations of marine biological impacts of climate change are of the impacts of changing temperature, with few observations of effects of changing oxygen, wave climate, precipitation (coastal waters) or ocean acidification. Observations of species responses that have been linked to anthropogenic climate change are widespread, but are still lacking for some taxonomic groups (e.g., phytoplankton, benthic invertebrates, marine mammals).

/pdf/responses-of-marine-organisms-to-climate-change-across-2yqrxoj2dw.pdf

Responses of Marine Organisms to Climate Change across Oceans

The initial response of individuals to human-induced environmental change is often behavioural. This can improve the performance of individuals under sudden, large-scale perturbations and maintain viable populations. The response can also give additional time for genetic changes to arise and, hence, facilitate adaptation to new conditions. On the other hand, maladaptive responses, which reduce individual fitness, may occur when individuals encounter conditions that the population has not experienced during its evolutionary history, which can decrease population viability. A growing number of studies find human disturbances to induce behavioural responses, both directly and by altering factors that influence fitness. Common causes of behavioural responses are changes in the transmission of information, the concentration of endocrine disrupters, the availability of resources, the possibility of dispersal, and the abundance of interacting species. Frequent responses are alterations in habitat choice, movements, foraging, social behaviour and reproductive behaviour. Behavioural responses depend on the genetically determined reaction norm of the individuals, which evolves over generations. Populations first respond with individual behavioural plasticity, whereafter changes may arise through innovations and the social transmission of behavioural patterns within and across generations, and, finally, by evolution of the behavioural response over generations. Only a restricted number of species show behavioural adaptations that make them thrive in severely disturbed environments. Hence, rapid human-induced disturbances often decrease the diversity of native species, while facilitating the spread of invasive species with highly plastic behaviours. Consequently, behavioural responses to human-induced environmental change can have profound effects on the distribution, adaptation, speciation and extinction of populations and, hence, on biodiversity. A better understanding of the mechanisms of behavioural responses and their causes and consequences could improve our ability to predict the effects of human-induced environmental change on individual species and on biodiversity.

Behavioural responses to human-induced environmental change.

https://www.cell.com/current-biology/pdf/S0960-9822(09)01181-6.pdf

Impacts of climate change on marine organisms and ecosystems.

Broad-scale studies of climate change effects on freshwater species have focused mainly on temperature, ignoring critical drivers such as flow regime and biotic interactions. We use downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows and increased temperatures on four interacting species of trout across the interior western United States (1.01 million km2), based on empirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast a mean 47% decline in total suitable habitat for all trout, a group of fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temperatures beyond the species’ physiological optima and continued negative biotic interactions. Habitat for nonnative brook trout Salvelinus fontinalis and brown trout Salmo trutta is predicted to decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rainier winters. Habitat for rainbow trout, Oncorhynchus mykiss, is projected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than temperature influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our findings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations.

https://www.pnas.org/content/pnas/early/2011/08/09/1103097108.full.pdf

Flow regime, temperature, and biotic interactions drive differential declines of trout species under climate change

Climate change can affect organisms both directly via physiological stress and indirectly via changing relationships among species. However, we do not fully understand how changing interspecific relationships contribute to community- and ecosystem-level responses to environmental forcing. I used experiments and spatial and temporal comparisons to demonstrate that warming substantially reduces predator-free space on rocky shores. The vertical extent of mussel beds decreased by 51% in 52 years, and reproductive populations of mussels disappeared at several sites. Prey species were able to occupy a hot, extralimital site if predation pressure was experimentally reduced, and local species richness more than doubled as a result. These results suggest that anthropogenic climate change can alter interspecific interactions and produce unexpected changes in species distributions, community structure, and diversity.

https://science.sciencemag.org/content/sci/334/6059/1124.full.pdf

Climate Change, Keystone Predation, and Biodiversity Loss

Biotic interactions will modulate species' responses to climate change. Many approaches to predicting the impacts of climate change on biodiversity so far have been based purely on a climate envelope approach and have not considered direct and indirect species interactions. Using a long-term observational data set (>30 years) of competing intertidal barnacle species, we built a hierarchy of age-structured two-taxa population models (Semibalanus balanoides vs. Chthamalus montagui and C. stellatus combined as one taxon) to test if the presence of a dominant competitor can mediate climatic influence on the subordinate species. Models were parameterized using data from populations on the south coast of southwest England and verified by hindcasting using independent north coast population data. Recruitment of the dominant competitor, S. balanoides, is driven by temperature. The mechanisms of competition explored included simple space preemption and temperature-driven interference competition. The results indicate that interspecific competition between juvenile barnacles is important in regulating chthamalid density but not that of the dominant competitor S. balanoides. Simulations were carried out using alternative future climate scenarios to predict barnacle population abundance over the next century. Under all emission scenarios, the cold-water S. balanoides is predicted to virtually disappear from southwest England by the 2050s, leading to the competitive release of Chthamalus throughout the entire region and thereby substantially increasing its abundance and occupied habitat (by increasing vertical range on the shore). Our results demonstrate that climate change can profoundly affect the abundance and distribution of species through both the direct effects of temperature on survival, and also by altering important negative interactions through shifting competitive balances and essentially removing dominant competitors or predators. Climate change impacts on organisms are unlikely to lead only to straightforward, easily predictable changes in population size and distribution. The complex, indirect effects of climate change need to be taken into account if we are to accurately forecast the long-term effects of global warming.

/pdf/modeling-the-response-of-populations-of-competing-species-to-56w0e4jscn.pdf

Alan J. Southward

Papers

Modeling the response of populations of competing species to climate change