By Andrea Quattrini, Postdoctoral Researcher, Harvey Mudd College
Parasites infect fishes in the deep sea, such as this copepod infecting the cutthroat eel Synaphobranchus. Video courtesy of Ivan Hurzeler and DEEP SEARCH 2019 - BOEM, USGS, NOAA, ROV Jason, ©Woods Hole Oceanographic Institution. Download larger version (mp4, 106.5 MB).
Parasitism is an important symbiosis—or interaction between two different species living in close physical association—found in marine communities. Different types of marine parasites, including worms, isopods, and copepods, infect a variety of host species, including crabs and fishes. This infection often changes the behavior of the hosts, which can result in changes to the number of individuals and species living within a community. Parasites are not all bad, however, as they can decrease the numbers of a species that may be a dominant competitor, which can enable rare species to thrive. Parasites have also recently been recognized as important components in food webs—or the many feeding relationships that occur among members of a community. Animals that eat parasites off hosts or eat the hosts that are infected with parasites can increase the overall energy flow within a system. The importance of parasites in marine communities is clear, yet they are often overlooked in marine community ecology studies. Thus, we have a limited understanding of the multitude of effects that they have in marine ecosystems—particularly in the deep sea.
Fishes host a variety of internal (endo-) and external (ecto-) parasites; both of which can alter behavior of hosts. In the deep sea, both types of parasites commonly infect fishes. One of our recent studies (Quattrini and Demopoulos 2016) examined the prevalence of ectoparasite infections on several species of deep-sea fishes observed using remotely operated vehicle (ROV) surveys in the northeast Atlantic Canyons region (including Okeanos Explorer expeditions in 2013 and 2014). Approximately 1 out of 100 individuals and 1/3 of all fish species we observed had ectoparasites. One of the most common types of parasites we observed were copepods. Copepods in the family Sphyriidae were the only species of copepod to infect the cutthroat eel, Synaphobranchus sp. We saw this same interaction on a Synaphobranchus sp. during our first ROV Jason dive at Richardson Hills (J2-1128). Other ectoparasites were also observed on fishes, including small isopods in the family Gnathiidae.
Many questions remain about the roles of parasites in deep-sea ecosystems. For example, what impacts do they have on the size of populations (or the number of individuals living within a particular location)? How do parasites contribute to the overall food web within an ecosystem? Is their presence a sign of a healthy ecosystem? In shallow-water reef ecosystems, “cleaner stations” are common. Fishes with ectoparasites visit these “cleaner” stations to have their parasites removed by shrimps and other, often smaller fishes. These ectoparasites are thus part of food webs on coral reefs, and they are signs of healthy ecosystems. It is completely unknown whether something like this exists in deep-sea coral ecosystems. But what is clear, however, is that parasitism is a relatively common interaction in the deep sea, and much is to be learned about the relative importance of this symbiosis in marine communities.
