Climate Change Effects on Fish Populations

Abstract

Estuaries are a key aquatic ecosystem most likely to be influenced by climate change. These systems will be direct recipients of major changes to their physico-chemical conditions by riverine, marine, terrestrial, and atmospheric drivers associated with climate change. In addition to these changes, fishes in estuaries are increasingly subjected to habitat degradation, water pollution, and fishery exploitation, all of which are creating stressful conditions for an ichthyofauna already under significant natural environmental pressures. The major climate change drivers are alterations in river flow, salinity, temperature, dissolved oxygen, sea-level, and connectivity between habitats and ecosystems. The drivers likely to have less influence on estuary-associated fishes this century are increases in dissolved carbon dioxide, declines in pH, and the spread of tropical diseases and parasites. Alternatively, we simply have insufficient information to understand their influence. A review of climate change impacts on estuarine fish assemblages around the world indicates that these impacts are not distributed equally, i.e., they vary among estuaries and associated habitats, processes therein, as well as across biogeographic regions. Yet, one common aspect to all regions is the lack of baseline understanding of the biology of many estuarine fish species, including their environmental sensitivities and tolerances. This is especially the case in polar regions where even documentation of the estuary-associated fish assemblages is largely missing, but initial information suggests these are becoming dynamic and increasingly functional. Looking to the future, research should focus on filling the above gaps, as well as how other anthropogenic impacts in estuaries will interact and compound climate-related changes. The cumulative effects of such impacts will likely increase the vulnerability of fish species, communities, and estuarine ecosystems to climate change, but this has not been quantified. Harnessing the power of modeling approaches to anticipate the impacts of global and regional climate change on estuarine environments at ecologically relevant scales will be vital to assisting estuarine fish assemblages to weather the storm of climate change that is already upon us.

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