Dead Jellyfish Blooms Vital To Deep Sea Ecosystem Health, Study Finds

February 7, 2015 in Animals & Insects

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Dead jellyfish blooms appear to be vital to the health of many deep-sea ecosystems, based on new research National Oceanography Centre that investigated the speed at which these dead blooms are eaten.

It had previously been thought that when large blooms of jellyfish died that they often simpy fell to the ocean floor and rotted, rather than being eaten, as the sheer quantity excluded the eating of all of the bloom — thereby depleting the oxygen on the ocean floor, and creating a dead zone of sorts. The new work suggests that these assumptions were off-base.

Jellyfish blooms

One of the researchers who worked on the study, Daniel Jones from the National Oceanography Centre, stated it thusly: “In recent years, anecdotal studies have suggested that when jellyfish blooms die off, massive quantities of the creatures can sink to the ocean floor to form ‘jelly-lakes’, which are not eaten then simply rot, depleting the oxygen on the ocean floor and repelling fish and other sea creatures. However, as our video footage indicates, it seems that ‘jelly-lakes’ may be the exception rather than the rule and that jellyfish carcasses are consumed at speed by a host of deep-sea scavengers such as hagfish and crabs.”

The work — performed by researchers from Norway, the UK, and Hawaii — utilized lander systems to observe how scavengers reacted to jellyfish and fish baits in the deep ocean off the coast of Norway. The research was done in regions with jellyfish blooms near the ocean surface, and showed quite clearly that when jellyfish fell to the ocean-floor that they were very rapidly consumed by scavengers.

Jellyfish deep sea crabs

Jellyfish are present in the worlds oceans in huge numbers — with jellyfish blooms seemingly becoming increasingly common as a result of overfishing, fertilizer pollution, and warming waters.

As a result of these growing numbers, what actually happens to these blooms after death has a fair amount of pertinence to a number of different things — including the carbon cycle. It had previously been assumed that when these blooms sank that the carbon they carried was mostly taken out of the system. This work shows that that doesn’t seem to be the case, it’s simply retained in deep sea ecosystems, fish, and microbial communities.

Image Credit: NOC; Public Domain

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