Fishing Out Marine Parasites?
By Chelsea Wood Awards: Haderlie, Myers |
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| Imagine a pristine marine ecosystem. Chances are poor that the picture at right has popped into your mind. The pile of monogenean flatworms in that petri dish are just a few of the worms removed from the gills of a single large predatory fish collected at Palmyra Atoll. Though we often associate parasites with environmental degradation, many parasite groups are highly sensitive to environmental impacts. I'm interested in the hypothesis that industrial fishing has driven a long-term decline in fish parasites, because fishing acts on exactly the parts of host populations that are most important for parasitism to flourish: |
 A few of the monogenean worms removed from the gills of a single wahoo (Acanthocybium solandri) collected on Palmyra Atoll. |
| - Many parasites need their hosts to be densely packed in order to successfully transmit among them. Think about a person with the flu riding a subway car - that flu will spread more efficiently if the car is packed full than if our patient is sharing the space with only a few other people. Fishing thins out fish populations, and in a sparser fish population, it may be harder for parasites to make their way from host to host. |
 A copepod parasite (Clavellotis dilatata) removed from the gills of a nearshore fish collected off the coast of central Chile. |
| - Other parasites are transmitted from prey to predator during predation events. We call this process trophic transmission, and populations of trophically transmitted parasites need lots of predator-prey interactions to ensure completion of their complex life cycles. By reducing the abundance of predators, a fishery reduces the number of these opportunities for transmission. |
 Clavellotis dilatata in its natural habitat, attached to the gill arch of its fish host (look for the two egg sacs and you'll find the parasite!). |
Palmyra Atoll, August 2009.
Photo courtesy of John McLaughlin. |
- Finally, large-bodied fish tend to carry the most parasites. Fishermen everywhere are after "the big one", and so they tend to take exactly those fish that are carrying the heaviest parasite burdens - meaning that those parasites are removed from their populations, and can't contribute new parasites into the next generation.
In these ways, certain groups of parasites may have declined in lockstep with their fish hosts over the history of industrial fishing. Through my dissertation research, I'm hoping to figure out whether we've been "fishing out marine parasites", and if so, which parasite groups have been the hardest hit. My research takes me to the Northern Line Islands, central Chile, and the California coast. To read more about what I'm up to, visit http://sites.google.com/site/chelsealwood. |
