Lately Iíve been reading about jellyfish. There have been reports of large swarms of them in southern waters, getting tangled in fishermenís nets, as well as washing ashore. Warnings have been issued in places like Honolulu about encountering stinging jellyfish on the beaches. Several animals collected seem to be larger than normal, feeding on the constant nutrients flowing from land. On Cape Cod these animals are mainly confined to the warmer months of the year. The most common species is the moon jelly (Aurelia aurita). This animal is a few inches in length and has four pinkish gonads in its clear center. The body is bell-shaped and moves by forcing water out of its body. In fact the animal lacks circulatory, respiratory, or excretory systems. Like most jellyfish, it has tentacles with stinging cells called nematocysts. Moon jellies mainly feed on plankton. They have both a sessile polyp stage, and a motile medusa stage. The moon jelly is relatively harmless to humans, but there is another species that should definitely be avoided. That is, of course, the Portuguese man-of-war (Physalia physalia). This large colonial jellyfish travels via the Gulf Stream and can end up on Cape Cod beaches in the summer. It is easily recognized by its foot long purple float that looks like a small sail on the surface. However, the danger lies below where the tentacles with their poisonous nematocysts may stretch as long as fifty feet. I know someone who was badly stung when he touched a stranded man-of-war on a beach several years ago. These animals retain their toxicity even after coming ashore. The jellyfish belong to the phylum Cnidaria which also includes the coral and the freshwater hydras. There does appear to be an increase in jellyfish populations around the world. Some speculate that this rise in numbers is due to climate change. A warmer ocean creates ideal conditions for jellyfish survival. These animals appear to be better adapted to higher nutrient concentrations, including the subsequent drop in dissolved oxygen as algae blooms occur. Large populations of jellyfish can easily consume many of the eggs and larvae of fish species. Not only do jellyfish increase in population under these conditions, but they may also increase in size when feeding in areas of sewage and other pollution runoff. We usually suspect an environmental problem when a species suddenly declines. However, as we can see with the jellyfish, an increase can also serve as an environmental signal that something is wrong.
Copyright Gil Newton 2009 Thanks to Chris Dumas for logo image.