Killer jellyfish posing a threat to our fish

BOLINOPSIS: A genus of the Bolinopsis jellyfish that could pose a threat to our local eco system. It is the size and shape of a hard-boiled egg and is completely transparent, nearly invisible in water.
BOLINOPSIS: A genus of the Bolinopsis jellyfish that could pose a threat to our local eco system. It is the size and shape of a hard-boiled egg and is completely transparent, nearly invisible in water.

Scientists are concerned that an unclassified species of the genus Bolinopsis jellyfish could pose a threat to local aquaculture, fish stocks and even the already depleting numbers of cuttlefish.

Recently numerous types of jellyfish species in different habitats around Australia have been blooming in large numbers and an increase here could cause problems.

Australian Marine Stinger Advisory Services director Doctor Lisa-ann Gershwin said if the trend of increased numbers occurs here, this particular jellyfish could cause a lot of damage.

"The Spencer Gulf Bolinopsis is closely related to two very troublesome species," Dr Gershwin said.

"One is another species of Bolinopsis from Japan, which has cost millions of dollars in fisheries losses because of its huge appetite for fish eggs and larvae."

The other species is the Mnemiopsis, which was accidentally introduced into the Black Sea in the 1980s.

Within a few years it had eaten so much of the native marine life and multiplied so much that the population had grown to cover almost the entire Black Sea.

"At the height of the problem, it had become 95 per cent the biomass of the Black Sea, just this one species of jellyfish, and had completely crashed the Black Sea ecosystem and all fisheries," Dr Gershwin said.

Dr Gershwin said the potential threat by the Bolinopsis here was greater though as it is a superior species.

"The biology and ecology of Mnemiopsis and Bolinopsis are nearly identical, except that Bolinopsis is a slightly better predator and faster reproducer than Mnemiopsis," Dr Gershwin said.

As for local fish stocks, Dr Gershwin said the Bolinopsis needs large food supplies but doe not have many predators.

"So any conditions that create these situations could lead it to flourish," Dr Gershwin said.

"It eats fish eggs and larvae, as well as plankton so either production of a lot of fish, and therefore more available fish eggs and larvae, or else fewer fish being taken by predators, and therefore more fish producing babies, could be triggers.

"Plankton are triggered by any condition that produces algal blooms, such as sewage discharge, fertiliser runoff, aquaculture waste, or even in some cases changes in salinity.

"Because Spencer Gulf is a reverse estuary, that is, it is mostly saline near the top, it also has slower water flow and flushing rates than most gulfs, so any of these factors are exacerbated by slower dilution and greater potential for build up."

Without accurate numbers on the amount of jellyfish currently living within the Upper Spencer Gulf as well as how elements like the desalination plant and the declining number of cuttlefish are affecting the marine ecosystem, Dr Gershwin said she was unable to say what the risk level was.

"It is hard to predict what impact the Spencer Gulf Bolinopsis could have on the local ecosystem, without knowing what is happening in terms of its numbers relative to its predators and competitors," Dr Gershwin said.

"Its impact could range from catastrophic to literally no effect."

In general, jellyfish tend to be inferior competitors to most fish unless something happens to tilt the balance so that jellyfish then seriously outnumber fish.

Dr Gershwin indicated that a decline in cuttlefish could be just the thing that alters this marine balance.

"For example, if a species of fish that either eats Bolinopsis or competes with it has a bad year, then that could be enough to tip the balance," Dr Gershwin said.

"But if Bolinopsis can't get that upper hand, then it could stay "harmless" for a long time, just waiting for a good opportunity to bloom out of control.

"A few Bolinopsis are not necessarily a problem, but a few million are... because they are all hungry, so it's all about how many mouths are hunting for food."

Dr Gershwin has written a book based on observations of the Bolinopsis in the Spencer Gulf, along with the proposed desalination plant at Point Lowly, the cuttlefish issue, and the potential for problems.

She hopes to return to the area soon to finish her research and complete a description of the cuttlefish for classification.