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Jellyfish, the human factor

8 janvier 2016, 09:01

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Marine ecologists are warning of worse to come, and pointing the tentacle of blame at us. Some researchers fear that human changes to the marine environment may be leading to a tipping point in which jellyfish will rule the oceans, much as they did hundreds of millions of years ago in pre-Cambrian times.

The problem is that no one really knows what causes the blooms. Some believe that population explosions result from overfishing of their dining competitors and predators, which include more than 100 species of fish, and animals such as turtles. However, other researchers point out that overfishing also hits jellyfish by reducing their food availability.

Either way, what is clear is that jellyfish are simply better prepared than other marine life for many of the ways humans are changing the ocean environment, such as warmer temperatures, salinity changes, ocean acidification and pollution. In this sense, humans might be jellyfishes’ best friend.

For instance, pollution can cause algal blooms that reduce the water’s oxygen content. This hits muscular swimmers like fish hard, but jellyfish can cope far better with these conditions.

Warmer water encourages jellyfish reproduction, and they can also better tolerate population crashes because their reproductive strategies are complex and adaptable. Some species of jelly can clone themselves, whereas others reproduce sexually but also have a polyp stage – like corals, with which they are related – that allows large populations of immature individuals to multiply while waiting for the right conditions to mature into adulthood. Inthese ways, they can withstand impacts that devastate other marine species.

Even the coastal infrastructure we build seems to be working to their advantage. Rob Condon, a marine scientist at Dauphin Island Sea Lab in Alabama, says that the pontoons, piers and even drilling platforms help provide anchors for jellyfish polyps, encouraging local population explosions.