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Will jellyfish take over the world? Jeremy Hance mongabay.com June 16, 2009
It could be a plot of a (bad) science-fiction film: a man-made disaster creates spawns of millions upon millions of jellyfish which rapidly take over the ocean. Humans, starving for mahi-mahi and Chilean seabass, turn to jellyfish, which becomes the new tuna (after the tuna fishery has collapsed, of course). Fish sticks become jelly-sticks, and fish-and-chips becomes jelly-and-chips. The sci-fi film could end with the ominous image of a jellyfish evolving terrestrial limbs and pulling itself onto land—readying itself for a new conquest. While this scenario sounds ridiculous, all of it—except the last sentence, of course—could conceivably come to pass. Dr. Anthony Richardson calls this the ‘jellyfish joyride’ and it is already happening in parts of the ocean: diverse fish populations are being replaced by jellyfish.
Once jellyfish gain a foothold, Richardson says that if conditions are right they can establish a massive population at the expense of other ocean life: “the problem is that jellyfish might form an alternative ‘stable state’. What this means is that parts of the ocean might switch from being dominated by fish to being dominated by jellyfish.” In a new study appearing in Trends in Ecology and Evolution, Richardson and colleagues explore the causes behind the jellyfish infestation and the need for swift, decisive action to stem the jellyfish take-over. Jellyfish explosions are linked directly to human actions, including over-fishing, the input of fertilizer and sewage into the ocean, and climate change.
As an example Richardson points to Namibia where "intense fishing has decimated sardine stocks and jellyfish have replaced them as the dominant species.” Eutrophication is another human-caused change in the ocean that has likely contributed to jellyfish explosions. Eutrophication is an increase of nitrogen and phosphorous in the ocean, largely caused by fertilizer and waste runoff seeping into the oceans. This leads to algae blooms, which lower oxygen in the marine ecosystem creating so-called ‘dead zones’, which have been increasing dramatically around the world. According to Richardson, these low-oxygen waters give jellyfish the advantage: “fish avoid low oxygen water but jellyfish, having lower oxygen demands, not only survive but can thrive in these conditions as there is less predation and competition from fish.” Furthermore, Richardson and his colleague speculate that climate change may expand the traditional ranges of jellyfish at the expense of other marine species. “As water warms, tropical species are moving towards the Poles. This has been documented on land and in the sea. Many venomous jellyfish species are tropical (e.g. box jellyfish and irukandji) and…could move south into more densely populated subtropical and temperate regions,” Richardson says.
Once jellyfish appear en masse in an ecosystem they can make it very difficult for fish to stage a come-back. By feeding on fish eggs and larvae in addition to competing with fish population for zooplankton, the jellyfish successfully “suppress fish from returning to their normal population numbers,” says Richardson. “One can thus think of two alternate states with each being stable: one dominated by fish and the other by jellyfish. Unfortunately, when there is a jellyfish dominated state then this does not support the higher trophic levels of other fish, marine mammals, and seabirds.” In other words an ecosystem that loses fish also loses the species that depend on fish for survival. The study describes this state as a “monoculture of jellyfish”: an apt analogy since the situation shares similarities with other monocultures. When the rich biodiversity of tropical forests is replaced by a plantation growing a single species of tree, an area of rich variety becomes a desert in terms of biodiversity, as do ocean ecosystems when jellyfish become the dominant species. "We need to start managing the marine environment in a holistic and precautionary way to prevent more examples of what could be termed a 'jellyfish joyride'," Richardson says. Due to the difficultly of turning an ecosystem around once jellyfish have gained the upper hand, Richardson and his colleagues suggest focusing on “prevention rather than cure.”
“Cut our greenhouse gas emissions,” Richardson says. “This would reduce the likelihood of venomous tropical species, such as box jellyfish and irukandji, from moving into subtropical and temperate areas.” Certainly all of these recommendations would aid marine biodiversity and ocean productivity in other ways in addition to stemming the jellyfish take-over. If not tackled, a future ocean of jellyfish could have dire economic, social, and, of course, ecological repercussions. While jellyfish are edible, it is doubtful that they could serve as rich—or as diverse—a food source as marine fish. Richardson, who has tried jellyfish says “the best types are slightly crunchy. Not a strong taste and usually had with a sauce. Excellent diet food, as it has virtually no calories!” Far worse than civilization forced to turn to a jellyfish diet is the ocean emptied of fish, big and small, predator and prey; an ocean that no longer supports birds in great flocks or marine mammals at all. This would be an alien ocean, better suited for (bad) science-fiction than our actual future.  CITATION: Anthony J. Richardson, Andrew Bakun, Graeme C. Hays, and Mark J. Gibbons. The jellyfish joyride: causes, consequences and management responses to a more gelatinous future. Trends in Ecology and Evolution. June 2009, Volume 24, Number 6. Related articles Giant sea creatures discovered in Antarctica (03/21/2008) An eight week long survey of New Zealand's Antarctic waters has turned up giant creatures including jellyfish with 12-foot tentacles and 2-foot-wide starfish, as well as up to eight previously undiscovered species of mollusc, reports the Associated Press (A.P.). Black jellyfish, strange marine species discovered in deep ocean (10/17/2007) An expedition to an unexplored deep ocean basin south of the Philippine Islands has turned up a trove of previous undiscovered species including a black jellyfish, a transparent sea cucumber, and a tentacled worm that resembles a squid. SHARE THIS ARTICLE:
Tags: oceans jeremy hance overfishing climate change impact of climate change dead zone marine conservation Animal behvaior Fish Fishing animal behavior animals ecology environment green Australia strange
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