Ocean giants in a changing climate: Impacts and challenges facing marine species and their conservation

Background/Question/Methods   Concerns regarding the potential effects of climate change on marine megafauna largely have been focused on polar environments, where changes in ice coverage can dramatically affect habitat and prey availability. Less attention has been given to cetaceans and turtles in temperate and tropical waters even though climate change related impacts on these species may be similarly pervasive. In some cases, cetaceans living in nearshore waters may be able to shift their ranges in response to changing environmental regimes. In other areas, cetaceans may occupy oceanographic, genetic, or ecological “cul-de-sacs” where range shifts are precluded. Long-term, site-based research on cetaceans and sea turtles provide vital opportunities for identifying and understanding the ecological effects of climate change under these scenarios.

Results/Conclusions   The impacts of sea-level rise and changes in fresh-water regimes are being examined in Bangladesh. The fine-scale distribution of Ganges River and Irrawaddy dolphins in estuarine waters of the Sundarbans mangrove forest varies with changing salinity levels resulting from seasonal changes in freshwater flow and local geomorphic features. This enables predictions to be made, as well as monitoring interactive responses to sea-level rise and the declining availability of freshwater from upstream rivers. In Sarasota Bay, Florida, bottlenose dolphins exhibit strong site fidelity across at least four decades and five generations, even through dramatic and prolonged environmental perturbations. Dolphin communities remaining in warming waters may experience changes in their prey base and increased exposure to biotoxins, pathogens, and environmental contaminants that can impact survival and reproductive success. For marine turtles, climate related impacts vary. Like some other reptiles, the sex of marine turtle embryos is determined by incubation temperature. The Pearl Cays, Nicaragua nesting habitat may provide a buffer against warming temperatures, allowing production to shift towards more females as ambient temperatures increase and before sand temperatures become too high. Additionally, sea-level rise poses other serious threats such as increasing erosion and inundation of essential nesting habitat. For polar specialists such as the bowhead whale, migration and gene flow are likely to be affected by changes in sea ice cover as well as increasing human activity in the Arctic. Information is needed to identify and detect signals of climate change, predict where and how impacts on cetaceans and marine turtles and their habitats are likely to occur, and prioritize pro-active management actions to provide these animals and associated biota the greatest opportunity for adapting to changing environmental conditions.