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Weakened Ecosystems Could Benefit Jellyfish

October 30, 2010

Researchers have been working to figure out how jellyfish may benefit from marine ecosystems weakened by climate change and overfishing.

Experts and scientists are concerned that an increase in jellyfish populations could prevent depleted fish stocks from recovering to historical levels.

European scientists, however, say more data is needed to identify what is happening beneath the sea.

Researchers from Ireland and the UK, who have been collecting samples from the Irish Sea since 1970, said they have recorded an increase in cnidarians — the division of the animal kingdom that includes jellyfish and coral — “with a period of frequent outbreaks between 1982 and 1991.”

“There does appear to have been an increase in abundance since 1994 for the Irish Sea,” said co-author Christopher Lynam of the Center for Environment Fisheries and Aquaculture Science (Cefas).

In recent years, there have been several examples of sudden blooms (swarms) of jellyfish in European waters, including the Irish, Mediterranean and Black seas, which have killed fish and been responsible for beach closings.

A swarm of mauve stingers in 2007 wiped out Northern Ireland’s only salmon farm, killing more than 100,000 fish.

However, Dr Lynam pointed out that the team’s study was dominated by the common moon jellyfish, which was not responsible for wiping out the salmon.

The main concern, the team wrote, was the establishment of mass blooms of jellyfish in which they become so established that it makes it nearly impossible for commercial fish stocks to recover.

“I don’t think that the hypothesis that jellyfish will come into an area and dominate, not allowing anything to come back again, is really supported,” Dr Lynam told BBC News. “Such a nightmare scenario does not seem to be the case, when you consider the data and studies that have been carried out.”

The team looked at whether factors such as climate changes and overfishing were responsible for increases in jellyfish abundance.

“It is quite a complicated set of possible linkages that need to be drawn, which we really only have a vague insight at the moment,” said Lynam. “For the recent period where we have good data, it appears as if sea surface temperature is the most important variable.”

“This does not necessarily prove it of course, but it does appear to be benefiting jellyfish.”

The increase in jellyfish populations has also been linked with overfishing. The researchers suggest that commercial fishing during the 20th century had resulted in a change in the Irish Sea’s ecosystem.

“The overexploitation of herring during the late 1970s was followed by a period of ecosystem instability in the 1980s in which the frequency of occurrence of cnidarian material… rose to high levels, indicating outbreaks of jellyfish,” wrote the team.

“If you take out a lot of the plankton feeders, there could be more food for jellyfish so they might become more abundant. There may be feedback mechanisms that we are not aware of, so there does need to be further study,” Dr Lynam added.

The team urged for the monitoring of jellyfish to continue.

Findings of the study are set to be published in the journal Global Change Biology.

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