Tuesday, July 21, 2015

Life in a warming ocean

How will different marine species respond to climate change and which species are in greatest jeopardy due to their limited ability to escape warming waters? Two new studies provide insight from different angles.

Galeocerdo cuvier (Tiger shark)
In Eastern Australia, the ocean has been warming at a rate that's 4-times that of the global average. Many marine species have been appearing further south than they ever have before, while others have stayed put. The first study identifies which characteristics seem to be important for species to shift their ranges so quickly. 

As expected, swimming ability is important. Fish are stretching their ranges south faster than other organisms such as starfish and crustaceans. The researchers also found that animals that have large range sizes are also at equilibrium with their environment, and are therefore the most responsive to change and shift the fastest. The tiger shark, short-tail stingray and barren-forming urchin were some of the fish species with the largest range shifts in the region. Filter-feeding barnacles - omnivores that are notoriously invasive - also displayed some of the largest expansions of territory. Meanwhile the spotted handfish, a coastal species in the same region, hasn't extended its distributional range into cooler waters despite shifting temperatures.

We think that this is because species with large ranges are habitat generalists, so their ranges are currently limited more by temperature and not by habitat, allowing them to move freely when temperature changes.

Acanthochromis polyacanthus
Study no 2 examined how fish's genes responded after several generations living at higher temperatures predicted under climate change. Researchers  used a multi-generational rearing experiment to identify the molecular pathways associated with transgenerational thermal acclimation in the common reef fish, Acanthochromis polyacanthus. The project involved rearing fish at different temperatures for more than four years in purpose built facilities at James Cook University, and then testing their metabolic performance.

The research team sequenced and assembled transcriptomes of the different generations of fish and identified 53 key genes that are involved in long-term, multi-generational acclimation to higher temperatures. 

Metabolic genes were among the most upregulated transgenerationally, suggesting shifts in energy production for maintaining performance at elevated temperatures. Furthermore, immune- and stress-responsive genes were upregulated transgenerationally, indicating a new complement of genes allowing the second generation of fish to better cope with elevated temperatures. Other differentially expressed genes were involved with tissue development and transcriptional regulation. Overall, we found a similar suite of differentially expressed genes among developmental and transgenerational treatments. Heat-shock protein genes were surprisingly unresponsive, indicating that short-term heat-stress responses may not be a good indicator of long-term acclimation capacity.

The study is the first to reveal the molecular processes that may help coral reef fishes and other marine species adjust to warmer conditions in the future.

Understanding which genes are involved in transgenerational acclimation, and how their expression is regulated, will improve our understanding of adaptive responses to rapid environmental change and help identify which species are most at risk from climate change and which species are more tolerant.

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