In August 2017, Australians (and eventually the whole world) went berserk over the case of the 16-year-old Sam Kanizay, a Melbourne teenager who was “attacked” by scavenging crustaceans on Brighton Beach. The pesky attackers were later identified as lysianassid amphipods (identification credit going to marine biologist Genefor Walker-Smith from the Museums Victoria1). Case closed? Not quite. An alternative insight from Niel Bruce, former senior curator of the Museum of Tropical Queensland2, saw the suggestion that another scavenging culprit was involved in the crime scene: cirolanid isopods. Albeit different, these same size crustaceans are known to occur in similar environmental conditions and reports propose that the cirolanids have a greater likelihood of biting humans than the lysianassids due to the attributes of wider and stronger mandibles (jaws).

Cymothoa epimerica, Parasitic Isopod
Cymothoa epimerica - Parasitic Isopod Image: Ben Diggles
© DigFish Services Pty Ltd

Drawing our attention towards isopods, it is undeniable that social media has helped propel our crustacean critters to quick fame, but has that popularity helped breach the knowledge gap of their real identity? Take for instance “The Bay Movie”3, which displayed that an increase in toxicity in Chesapeake Bay in the USA turned parasitic isopods of fish into mutant breeds that used humans as hosts and unleashed a horrifying plague that wiped out the population. This notion is simply untrue, but for someone who has never encountered such a specimen, could toxicity alter the physiology and morphology of animals to some degree that people can be poisoned from toxicity? (if not into some monstrous human parasite). Peculiar as this may sound, there was an incident where a customer in Puerto Rico filed a lawsuit against a leading supermarket chain4, claiming to have been poisoned from eating an isopod cooked inside a fish, which was revoked as isopods are not known to be harmful when ingested.

In order to address all rumours and curiosities, it has boiled down to this question, Are all isopods bad and harmful to humans?

Simple as the question may be, there isn’t a straightforward answer to it. Isopods aren’t “bad”, but a few have been to known to cause some damage. Why some? For one, there are as many as 10,000 isopod species within 11 suborders (order Isopoda) found on land, freshwater, brackish and marine waters. Species of the suborder Oniscidea are exclusively terrestrial, and are affectionately known as pillbugs, sowbugs, woodlice, gribble and rollie pollies and are common among hobbyist and pet collectors. The rest are aquatic, and predominantly marine. All isopods are also NOT endemic to one habitat as they have morphologically and physiologically adapted to their environments. Secondly, isopods have various feeding categories. This variety includes free-living predators (e.g. cirolanids), scavengers (e.g Bathynomus spp., a.k.a deep sea giant isopods); grazers (Idotea spp.), parasites (e.g. species from family Cymothoidae) and detritus feeders (e.g. from family Sphaeromatidae).

It is because of this diversity and different feeding behaviour that isopods can’t be treated the same. Every isopod has its important role in the environment, keeping the ecology in a ‘check and balance’ scheme. For example, if the giant isopod was not built for its scavenging nature, there will likely be heaps of marine carcasses pilling-up in the deep abyss. Additional significance of isopods ecologically are their use as biological indicators for environmental health, helping clean dead organic matter and form a vital food source for other animals.

With some of the positive known impacts, there are those that cause negative impacts as well. Probably the most famous isopod family to take the cake are the cymothoids, which are exclusively parasitic to fish and are known as “sea lice” or “fish lice”. Despite having nearly close to 400 known species in the family to attach on various parts of the body of fishes (e.g. buccal, gills, inside the flesh, or externally on the skin), social media has collectively regard the cymothoid as one species occurring worldwide: Cymothoa exigua. There are also reports that stated finding cymothoids attached on other invertebrates, although ample research of this family back as early as the 1880s has definitely debunked this hypothesis. It is for these irregularities that research is still on-going to address isopods from a local to global scale. My research, while studying as a PhD candidate at the University of Tasmania, saw me work exclusively on reviewing buccal-attaching isopods that are parasitic to fishes from Australian waters. In addition to the new species found, my research has helped address issues of fish host specificity, cymothoid distribution locally and worldwide, and potential species of aquaculture concern. As much as my research has resolved the taxonomic conundrum by providing full accounts of the species synonymy, species and generic diagnosis and keys; I hope this will raise the platform for further research to elucidate the ecological and economical roles and impact of these parasitic isopods.

There is a saying that “we fear what we don’t understand and cannot control” and this quote perfectly reflects the scenario of the isopods. Apart from being collectively labelled as sea-bugs or sea lice, isopods have been stereotyped to be harmful to humans. Isopods are not “bad” in character to deliberately impose harm, but rather it’s the nature of evolution and adaptation that has built the isopods to serve its ecological purpose. And although the case of Sam Kanizay is a once in a blue moon occurrence, the most likely damage isopods can cause is mainly in an economical capacity. This would include situations like massive fish mortalities from parasitic isopods, or boring holes in marine and estuarine timbers for ships and other architecture. Probably in the human context, this would be considered “bad” for the pockets.

So, if one were to ask “are all isopods bad and harmful to humans?” an alternative to a simple answer would be “Not at all, they are just misunderstood”.

Dr Melissa Beata Martin, Senior Lecturer and Researcher, School of Marine & Environmental Sciences, Universiti Malaysia Terengganu

More information

Melissa Martin previously received a Geddes Postgraduate Fellowship to visit the Australian Museum to work on the taxonomy and phylogeny of the buccal-attaching Cymothoidae (Crustacea: Isopoda) of Australia. Her trip to the Australian Museum has greatly aided in the resolution of many of the buccal-attaching cymothoids. Since graduating in 2016, she is back in Malaysia as a lecturer cum researcher at Universiti Malaysia Terengganu, passing on that acquired knowledge to budding marine biologist and marine scientist alike.

Further reading

  4. Williams, E. H.Jr, Bunkley-Williams, L. (2003) New records of fish-parasitic isopods (Cymothoidae) in the Eastern Pacific (Galapagos and Costa Rica). Noticias de Galápagos (62): 21-23.
  5. Blog: Ouch, an isopod caught my tongue!
  6. Blog: Fish tongue biters: more than one of a kind

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