PARASITES: PROFITING FROM CLIMATE CHANGE
Some creatures look set benefit from the ravages of a changing climate, at least temporarily…
LIKE SO MANY
divers and marine scientists of my generation, I was inspired by watching countless hours of The Undersea World of Jacques Cousteau: whales sharks, colourful coral reef fishes, and brilliant coral reefs! My first snorkelling experience came in seventh grade when I enrolled in a freediving course at the local YMCA in La Canada, California. After that class, I knew that my professional future belonged to the ocean. I received my open-water scuba certification at age
16, and my divemaster and instructor certification at age 21. I went on to complete Bachelor's, Master's and Ph.D. degrees in biology and marine science. Like the vast majority of divers, my focus when in the water was on the big and the spectacular – things that were easily seen.
My perspective changed radically when in 1997, I observed damselfish on a coral reef interrupting spawning to visit cleaning stations at dawn.
As many divers know, cleaner fishes and shrimps remove parasites from larger fishes. Broadly known as cleaning symbiosis, these interactions occur at stable locations on the reef known as “cleaning stations” that are easily identifiable to divers and to fishes that visit them. Since this chance observation, the primary focus of my research has been on the tiny things that make their living by consuming parts of larger organisms such as fishes – parasites, some of which are eaten by cleaners. Because parasites are difficult to see, they are typically ignored by most divers and even most scientists. Yet, they represent something of a smaller majority – over 50 percent of the living organisms on coral reefs. Every living thing that is visible to a diver is habitat for parasites, and even many parasites have parasites!
THE TICKS OF THE SEA
If one opens the gut of a cleaner fish, what stands out is the large numbers of a particular kind of parasite called a gnathiid isopod. In fact, larger cleaners such as the cleaner wrasses that are so common in Asian and Australian reefs can eat over 1,000 of these parasites each day.
Gnathiids are very similar to ticks and mosquitoes on land – the “ticks of the sea”. Like ticks and mosquitoes, gnathiids attach to their host long enough to secure a blood meal. It is during this feeding stage that they can be eaten by cleaners. After their blood meal, they drop off and hide in the reef, digesting their meal and molting to the next stage, and then feeding again. This continues until they have reached adulthood (only juvenile gnathiids feed on fish blood), when they do not feed, but reproduce, then die.
Gnathiids play a major role on coral reefs. The irritation they cause their host fish influences the behaviour of coral reef fishes such that they increase their interaction with cleaners. Large numbers