A herring in the North Sea, a crab in the Wadden Sea or an anemone fish on a coral reef, ... biologists like to think in terms of individual species that all have their own place within food webs in ecosystems across the world. "But that is surely too simplistic thinking," NIOZ researcher Ana Born-Torrijos and colleagues warn in this month's cover story of the scientific journal Trends in Parasitology. "If you ignore the different parasites that live in and on an animal, you might draw very wrong conclusions about its ecology," Born-Torrijos said. "Wild-caught animals should not be considered single individuals, but rather as entire ecosystems by themselves, hosting a variety of microbes and parasites which can be found in virtually every tissue."
Fish, crabs, snails and other animals can be infected by a multitude of parasites. These include nematodes, cestodes, trematodes, isopods or even copepods that spend part of their lives in the gills of fish. Those parasites can affect the morphology, the behavior and also the metabolism of animals in many different ways, in that way, those parasites also influence where an animal fits in the local food chain.
When Born-Torrijos depicts the food chain as a slowly ascending graph, algae and plants as so-called primary producers, which convert sunlight into 'edible' energy are in the lower left corner. At the very top right of the graph are the top predators, such as seals in the Wadden Sea. In the review article, the researchers describe how an animal's stable isotope values may differ depending on whether they are infected with parasites or not. "That's because parasites can change the behavior of a host, even without making that host really sick. For example, a coral fish infected by a specific species of isopod, appears to forage much less outside the reef than uninfected individuals of the same species. This is then reflected in the chemical composition of the animal."
