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Marine Heat Waves More Common and Lasting Longer Globally

A study done by the Marine Heatwaves International Working Group showed that there has been a 54% increase globally in the number of “marine heat wave days” per year since 1925.[1] Published in the Nature Communications journal and cited in News Deeply recently[2], the study cited the warm zone off the Western Australian coast in 2011 and the Gulf of Maine episode in 2012 as incidences of this trend. Average ocean temperatures have been increasing but these marine heat waves are also increasing in frequency and duration. The combination of the two are linked to factors that damage ecosystems and economies.

Figure 1 Graphic explanation of Marine Heat Waves, from http://www.marineheatwaves.org/all-about-mhws.html

Marine heat waves (MHWs) are “…prolonged periods of anomalously high sea surface temperatures… [that] have had severe impacts on marine ecosystems in recent years.” (Oliver et al., 2018). In Australia alone, Shark Bay in Western Australia lost 36% of its seagrass meadows and carbon storage, and the Great Barrier Reef suffered four mass coral bleaching events because of these extended periods of elevated sea surface temperatures.[3]

There are significant ecological and economic effects arising from these marine heat waves. They include:

“… sustained loss of kelp forests, coral bleaching, reduced surface chlorophyll levels due to increased surface layer stratification, mass mortality of marine invertebrates due to heat stress, rapid long-distance species’ range shifts and associated reshaping of community structure, fishery closures or quota changes and even intensified economic tensions between nations.” (Oliver et al., 2018)[4]

According to Eric Oliver, the study’s lead author, “…in the early 20th century, there was an average of two marine heat waves per year globally, but now there are three or four. While they used to last 10 days on average, they now last for an average of 13 or 14 days.”[5]

The study suggests that marine heat waves will continue to increase with the ongoing global warming.

Why does Wilderness Markets care about anemones and anemonefish? Because our work requires us to look not only at enterprises and fishery management, but at the entire ecosystem to properly account for business risks. Learn more about us.

[1] Oliver, E. C. J et al. (2018). Longer and more frequent marine heatwaves over the past century. Nature Communications, 9. doi: 10.1038/s41467-018-03732-9

[2] News Deeply. (2018). Executive Summary for April 13th. Oceans Deeply (Marine Heatwaves Are Longer, More Frequent). Retrieved from https://www.newsdeeply.com/oceans/executive-summaries/2018/04/13.

[3] McSweeney, R. (2018). Marine heatwaves have become ‘34% more likely’ over past century.  Carbon Brief. Marine heatwaves have become ‘34% more likely’ over past century. Retrieved from https://www.carbonbrief.org/marine-heatwaves-have-become-34-more-likely-over-past-century.

[4] Oliver, E. C. J et al.

[5] Willick, F. (2018). Ocean heat waves becoming more common, longer, new study finds. CBC. Retrieved from http://www.cbc.ca/news/canada/nova-scotia/marine-heat-wave-ocean-hot-spot-study-1.4611794

Climate Change Stresses Clownfish

Rising ocean temperatures are causing significant changes with devastating impact on the ecosystem. Worldwide, the warmer and more acidic ocean conditions in the tropics have caused mass bleaching of anemones and corals[1]. A new study published in the Proceedings of the Royal Society B supports findings from another recent study in the journal, Nature, that the bleaching of anemones has a severe impact on anemonefish, like clownfish and dire consequences for marine life in general.[2]

sea water nature ocean animal underwater swim biology fish sea animal coral coral reef invertebrate marine life clown fish reef tentacle mollusk nemo aquarium cnidaria hide toxic creature exotic hidden protection invertebrates anemones protect symbiosis underwater world meeresbewohner organism clownfish water creature anemone fish sea anemones sea anemone marine biology coral reef fish marine invertebrates pomacentridae

Clownfish in anemone. Used under Creative Commons from : https://pxhere.com/en/photo/559857

Findings

The latest study looked at the metabolic rates between fish from bleached and unbleached anemones. Even though there was no discernible difference in activity between the two groups of fish, the study found that the “[s]tandard metabolic rate of anemonefish from bleached anemones was significantly higher by 8.2% compared with that of fish residing in unbleached anemones, possibly due to increased stress levels.”[3] Reduced spawning frequency and lower fecundity are two of the negative impacts that were previously observed.

The study published in Nature in 2017 focused on the hormonal stress response and reproduction of anemonefish in bleached anemones. The 14-month monitoring study found a strong correlation between the anemone bleaching and the anemonefish’s stress response and reproductive hormones. Anemonefish in bleached anemones had a 73% decrease in fecundity compared to anemonefish in unbleached anemones. They spawned half as frequently, laid 64% fewer eggs, and experienced a significantly higher egg mortality in incubation. The authors were unable to determine why the bleaching of anemones would trigger a stress response in anemonefish. They offer the possibility that bleached anemones may provide less cover and have reduced neurotoxicity of venom which leads anemonefish to perceive a greater risk of predation. [4]

According to Beldade, Agathe, O’Donnell, & Mills (2017), there are “…[a]t least 50 species of fishes and facultative symbionts of sea anemones worldwide…as many as 12% (56/464) of coastal fish species depend directly, either for food or shelter, on organisms capable of bleaching. While the strength of such dependency varies greatly, if these species suffer even a fraction of the impact found for anemonefish, then a short-lived bleaching event could decrease the reproductive output of at least 12% of species, especially those highly dependent on corals or anemones.”

Takeaway

The two studies contribute to a growing library of research on the effects of global warming on marine life and highlights the importance of understanding how individual differences in stress responses influence a species’ chances of survival.

Why does Wilderness Markets care about anemones and anemonefish? Because our work requires us to look not only at enterprises and fishery management, but at the entire ecosystem to properly account for business risks. Learn more about us.

https://www.flickr.com/photos/60477809@N03/34860139102

Photo Credit: “q phia”; anemone fish on bleached anemone, fukui, siladen, 2017

[1] Norin, T, Mills, S. C., Crespel, A., Cortese, D., Killen, S. S., & Beldade, R. (2018). Anemone bleaching increases the metabolic demands of symbiont anemonefish [Abstract]. Proceedings of The Royal Society B. doi: 10.1098/rspb.2018.0282

[2] News Deeply. (2018). Executive Summary for April 13th. Oceans Deeply (Bleaching of Anemones Makes Life Harder for Clown Fish). Retrieved from https://www.newsdeeply.com/oceans/executive-summaries/2018/04/13.

[3] Norin, et al.

[4] Beldade, R., Blandin, A., O’Donnell, R., & Mills, S. C. (2017). Cascading effects of thermally-induced anemone bleaching on associated anemonefish hormonal stress response and reproduction. Nature Communications, 8. doi: 10.1038/s41467-017-00565-w