A Description of Marine Parasitism

A Description of Marine Parasitism

Ecologists use certain terminology to describe relationships between animals. Animals that frequently interact are said to have a symbiotic relationship, which can be mutualistic, commensal, or parasitic. Most people are familiar with parasitism, where one creature benefits at the expense of its host. The ticks on a dog are a commonly known parasite. Marine parasites are less well known, however they do play an interesting part in their respective ecosystems.

The Importance of Understanding Parasites

For every marine fish species there are 3-4 parasites of the Animal kingdom (as opposed to parasitic bacteria) according to Dr. Harry Palm, a professor of zoology at the Heinrich-Heine Unviersity in Germany. Dr. Palm cites on his webpage “Marine Parasitology” that there may be up to 43,200 marine fish parasites, making these creatures a significant part of the ocean’s Animal kingdom. Ocean parasites are important to study not only because of their disease causing ways but also as biological indicators. Biologists can study a long-living parasite to determine the seasonal migrations of its host as well as the environmental conditions of the area.

The Parasite Lifestyle

Parasites don’t infect their hosts out of spite. Rather, they rely on their host for food and a place to live. A parasite can live on the surface of its host. Called ectoparasites, these include copepods that eat skin flakes and sea lice that suck blood. There are also endoparasites which complete their lifecycle within their host, for example roundworms hatched within the host’s stomach. Some parasites may inhabit different hosts throughout their lifecycle, e.g., when a person eats a bad fish a worm can travel from fish to human. However, not all parasites cause disease.

Parasites and Disease

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W.F. Perrin et al say in the 2002 book Enclyopedia of marine mammals that many parasites coexist peacefully with their hosts – so long as the host is healthy. Sea lice and stomach worms are generally harmless. However, if a creature is starving or becomes ill for other reasons the host may feel the effects of the parasites.

The Sunfish Has Many Marine Parasites

The sunfish Mola mola can grow six feet long and weigh 2,200 pounds. It is the world’s heaviest bony fish and, perhaps less impressively, well known for its parasites. Roughly forty different genera of parasites have been found on the Mola mola according to Dr. Tierny Thys’s webpage “Ocean Sunfish > Life History”. The many types of sunfish parasite include flatworms, roundworms, protozoans, and small crustaceans. Parasitic crustaceans are not like the crabs found on a dinner plate. Living on the Mola mola are sea lice of the class Branchiura and copepods only a millimeter long.

Marine Parasites That Affect Humans

Marine parasites are often too small to gain much attention, that is until one infects a human. A person eating uncooked fish may unintentionally eat the small Anisakis simplex which can cause stomach pain and vomiting as the worm bores its way into the human’s stomach tissue. The disease caused by this worm is called anisakidosis.

Trichinella is another type of worm that can be caught from eating uncooked fish. The symptoms caused by this ocean parasite can last for months according to the Center for Disease Control’s Fact Sheet “Trichinellosis”.

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