Challenging Ecological Norms: Why “A Crab Is Never Just a Crab”

The conventional view of ecosystems focusing on distinct species may be oversimplified, according to researchers, including Ana Born-Torrijos from NIOZ. They argue that understanding the ecology of wild-caught animals requires considering the diverse community of microbes and parasites within them. The researchers highlight the importance of recognizing animals as ecosystems themselves, as they host a variety of parasites and microbes in various tissues. Ignoring these components may lead to incorrect conclusions about the ecology of the animals and the ecosystems they inhabit.

Various parasites, such as nematodes, cestodes, trematodes, isopods, and copepods, can infect fish, crabs, snails, and other animals. These parasites can impact the morphology, behavior, and metabolism of animals, influencing their roles within the local food chain. The researchers emphasize that understanding the ecological roles of animals requires considering the interactions with the diverse range of parasites and microbes that inhabit them.

In understanding the food chain, stable isotopes of nitrogen can be used to determine the position of animals along the chain. The accumulation of heavy isotopes in an animal's nitrogen pool with each step in the food chain helps indicate the feeding relationships within the ecosystem. This method allows researchers to comprehend the complex interactions between different species and their roles in the food web.

The review article emphasizes how an animal's stable isotope values can be influenced by parasite infections. Parasites, even when not causing severe illness, can alter the behavior of their hosts. For instance, a coral fish infected by a particular isopod species may exhibit reduced foraging outside the reef compared to uninfected individuals of the same species. These behavioral changes induced by parasites can be detected through shifts in the chemical composition of the host animal, providing insights into the intricate relationships within ecosystems.

The article not only reviews the knowledge accumulated in the last decade regarding parasite-host interactions but also outlines ongoing research efforts. Born-Torrijos, through a Marie Skłodowska-Curie Actions Postdoctoral Fellowship, is conducting experimental tests to unravel the influence of parasites on their hosts. For example, experiments involve crabs infected or uninfected with a rhizocephalan, a parasitic barnacle. By manipulating the crabs' diet and observing changes in stable isotopes, researchers aim to distinguish the effects of parasitic infections from dietary influences. This experimental approach seeks to understand how infection impacts host metabolism and subsequently influences isotopic composition.

This underscores the importance of considering the parasitome, the entirety of parasites inhabiting an animal, in ecological research. While the microbiome (microorganisms on the skin and in the intestines) is well-studied, the parasitome is posited as an equally critical aspect. Neglecting the influence of parasites, according to Born-Torrijos and colleagues, can lead to a distorted understanding of food webs in ecological studies, emphasizing the need for a more comprehensive approach to studying host organisms. To learn more, go to the Royal Netherlands Institute for Sea Research’s article on SciTechDaily https://scitechdaily.com/challenging-ecological-norms-why-a-crab-is-never-just-a-crab/