By Micaela Porte
When wildlife enthusiasts, researchers and professors met recently at UCSD Kendall-Frost Mission Bay Reserve, they had one thing on their minds: the microscopic parasites that inhabit Mission Bay.
The presentation was delivered by Ryan Hechinger, a UC Santa Barbara Marine Science Institute professor, who stated that trematodes, such as the common flatworm, frequently make their way from marsh bird feces into host organisms, like a horned snail, California Achilles fish and fiddler crab, among others. From there, they perform a key role in the regulation of marsh bio-systems.
According to Hechinger, the parasites lay their eggs in a benign bird host’s intestines. The eggs then hatch in the marsh and make their way to their primary hosts. Over a period of a few years, the worms eventually fully colonize in their host—typically a horned snail—consuming and replacing the sex organs. After morphing with and occupying the snail for the remainder of its natural life, which could last up to 10 years, they replicate by essentially cloning themselves. Cloned larvae leave the colony to attach to secondary hosts, such as fish, crabs, and clams.
Organisms belonging to the Trematoda parasitic class will then develop a cyst colony attached to the heads of marsh fish and take over their brain. The exact methodology—whether via secretions or some other mechanism—remains unknown. Some scientists believe that the parasites bring on a dementia in their hosts, making them act in an irregular manner, such as swimming in a zig zag pattern. This often causes the sunlight to reflect off of their bodies, which in turn attracts the attention of predator birds who eat them. This begins the parasitic life cycle all over again, as they lay their eggs in the bird’s intestines. Scientists have found that where there are more parasites, there are more birds because the fish are easier to catch—all a part of nature’s amazing patterns.
Fortunately for humans, we cannot see any of these “infections” with 
the naked eye, and our immune systems can handle any trematode parasitic attack, reducing it to a skin rash, commonly referred to as a swimmer’s itch. Still, it’s suggested to wear boots and shoes in a marsh, and thoroughly cook all fish, as doing so will kill a parasitic infestation.
Hechinger and his graduate crew are on a multi-estuary field trip from Baja California to Monterey to collect samples and analyze data regarding the complex world parasites. This work is made possible in part because of rare research facilities like the Mission Bay Reserve.
Friends of the Mission Bay Marsh, an organization headed by wildlife photographer Roy Little, was invited to participate in the presentation, which took place at the Mission Bay Reserve’s Pacific Beach bungalow. The lecture was part of a series of presentations held in conjunction with marshland researchers and the reserve’s manager, Professor Isabelle Kay.
Micaela Shafer Porte
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