Hey Ma, Pass the Jellyfish

The following was published in the Cranbrook Daily Townsman in the fall of 2009.

“I wish I was a jellyfish, floating on the sea
Riding on the currents sailing along so peacefully.” 
~ Bobs & Lolo

One of the most stunning natural history exhibitions I have ever seen was at the Monterey Bay Aquarium. Their jellyfish display featured a dark room with various sized aquaria back-lit such that their inhabitants glowed. Floating effortlessly, I could have sat entranced for hours watching, just going with the flow.

 According to recent work by marine biologists, we may have a lot more opportunity to ponder jellyfish. A review by four scientists published the June, 2009, issue of the scientific journal Trends in Ecology and Evolution cautions that “a more gelatinous future” is clearly in the offing unless we take steps now to change the way we treat and manage the oceans. Jellyfish outbreaks are being reported worldwide, often with disastrous effects.

Of course jellyfish are a natural part of ocean ecosystems. Fossil evidence suggests they were they dominated the Cambrian seas some 500 million years ago, long before other vertebrate and invertebrate life forms we know today had evolved. They remain important as food for not just other sea creatures, but humans as well. Many Asian cultures eat jellyfish – some 425,000 tonnes each year by some estimates.

More often, they are viewed as a nuisance at best and hazardous risk to human life at worst. The list of deleterious consequences is long: closed beaches, blockage of cooling intake pipes for coastal power generators, fouling fishing nets, killing farmed fish, reducing commercial fisheries. Most often, human interference with marine systems has led to great increases in jellyfish numbers around the world, and the potential consequences are not pleasant.

The causes of jellyfish increases are not surprising: overfishing, eutrophication, climate change and accidental introductions from ship ballasts. The largest problem seems to come from a reduction in small filter feeding fish populations. Two examples cited are the sardine fishery off the coast of Namibia and anchovies in the Black Sea. Both of these fish play key roles in suppressing local jellyfish numbers, largely by eating their larval stages. With the fish gone, the jellies quickly multiply and the adults assume the plankton-eating niche that the sardines and anchovies occupied. Jellyfish biology is such that a self-enhancing feedback system sets up leading to rapid increase in jellyfish numbers.

Increased runoff of fertilizers and sewage has also benefited jellies. Increased nitrogen and phosphorus is advantageous to phytoplankton (including red-tides). This comes at the cost of more silicon-based diatoms. Jellies prefer phytoplankton, while most fish, marine mammals, turtles and other species prefer diatoms. Jellyfish win again. Phytoplankton blooms can lead to low oxygen levels, something jellyfish deal quite well with, while other animal species cannot tolerate.

Climate change has similarly favoured jellyfish. Warmer waters have allowed potentially fatal species of jellyfish, such as the box jellyfish of northern Australia to expand southward toward more populated swimming beaches. Warmer temperatures lead to nutrient-poor surface waters, a condition, like eutrophication example above, that favours jellyfish.

Finally, the commercial shipping industry has played a role in inadvertently introducing jellyfish to new areas. Like many other species, they can become invasive and without natural predators or other forms of regulation they rapidly increase in numbers to the point of greatly altering native ecosystems. The Black Sea, Caspian Sea and Gulf of Mexico have all witnessed introduced jellyfish problems in recent years.

The concerns are significant. Our current actions are potentially driving the seas away from those dominated by diatoms and fish to one of phytoplankton and jellies. Some scientists have suggested that if current trends continue, our oceans could soon more resemble the warmer, more eutrophied Cambrian seas of 500 million years ago.

No one is suggesting that jellyfish are driving fish and whales to extinction. It’s just that jellies and their ancient, time-tested adaptations are able to quickly take advantage of the opportunities that have been provided to them.

Thankfully, there are several options available to us. Mostly, these involve reversing the actions that have allowed for the recent proliferation of jellyfish: over-fishing, eutrophication and climate change. If we don’t, the seas may well be a vastly different place than what we are familiar with today. And instead of singing the children’s song quoted at the top, we’ll be following the advice of fisheries scientist Daniel Pauly, “My kids will tell their children: eat your jellyfish!”