Marine Matters: Consider the Jellyfish
Thursday, August 11, 2016 11:18 AM
Earlier this month, on the western coast of Wales, an onshore wind pushed thousands of blue jellyfish, called Velella, onto the region’s shore. Velella have a comb that floats above the water which acts as a sail, sending the deep blue jellyfish moving before the wind, in this case en masse into the coast of Wales.
Back here on the East Coast, the clinging jellyfish, normally found in the Pacific, has turned up in Connecticut, New Jersey and Massachusetts. The tentacles of the dime-sized jellyfish, which attaches to eelgrass and seaweed, pack a mean sting. The gentleman who encountered one while swimming in an embayment in New Jersey ended up in the local hospital’s emergency room. And in Myrtle Beach, South Carolina, hundreds of beach-goers were stung by congregations of jellyfish (technically called smacks) in early August. Officials with the state’s Natural Resources Department said the influx was due to steady southeast winds and particularly warm water along the coast.
There’s a lot not to like about these animals without a heart, brain or respiratory system. You would have to stretch your imagination broadly to find anything cute or cuddly about a jellyfish. They are proliferating greatly throughout the world as a result of a conflux of environmental factors, such as warmer ocean temperatures, overfishing of jellyfish predators, and diminished oxygen levels, none of which are indications of healthy oceans.
In the Gulf of Maine, we have two non-stinging jellyfish species — the small moon jelly and the smaller comb jelly — and one stinging — the lion’s mane jelly. Don’t mess with a lion’s mane jellyfish: it can grow to seven feet wide trailing long, potentially painful tentacles. Jellyfish with tentacles are called medusae. Medusae reproduce in a particular manner. The male releases sperm into the water, the female ingests it. She releases fertilized eggs that hatch into larvae that drift about before settling on a hard substrate, like a rock or wharf piling. Then it transforms itself into a polyp, which looks like a small tube. When conditions are right, the polyp divides itself into a stacked series of saucer-like clones called ephyra that break off one by one and swim away. Each is identical to the other.
Invasion of the clones!
Jellyfish are carnivorous animals. The stinging cells in their tentacles are called nematocysts and are used to inject a killing toxin in prey. Those toxins can be pretty fierce: the tiny box jelly, found off the coasts of Australia and other Pacific countries, can cause cardiovascular collapse in its victim within two to five minutes.
These oddly beautiful yet vaguely creepy creatures also have a peculiar ability to survive in the most unwelcoming of ocean environments, the “dead zones” that have appeared throughout the world’s oceans. A “dead zone” is a patch of water in which most of the dissolved oxygen has been depleted due to an overabundance of nutrients deposited by local rivers. The Northern Gulf of Mexico “dead zone” caused by nutrients from the Mississippi River is approximately 6,824 square miles in size this year. Fish and most other marine species avoid the areas because they can’t breath within them.
That lack of oxygen doesn’t bother jellyfish, however. Jellyfish are largely made up of a gel called mesoglea. Mesoglea is water and a whole lot of dissolved oxygen; a jellyfish’s active tissues (and there aren’t a whole lot of those) are embedded in the gel. When they are in a low-oxygen area, the tissues draw needed oxygen from the gel. This technique makes sense because jellyfish evolved a long, long time ago, when the earth’s oceans had much less oxygen in them than they do today. They don’t need a lot of oxygen to live their rather brief lives, and when the supply is tight they draw it from within themselves.
The oceans will continue to reflect the results of our warming world for many decades if not centuries in the future. Jellyfish populations are likely to continue to increase as a result. While I am not fond of the creatures, it is slightly reassuring to realize that in Asia the boom in jellyfish poses benefits both of a medicinal and culinary variety. Jellyfish are eaten in several Asian countries on special occasions, served salted and dried to give them a delicate crunch. And in Chinese, jellyfish are considered a means for curing arthritis and lowering blood pressure.