Parasite detection and quantification in a variety of marine species
The underground and peculiar world of marine parasites...
When thinking about marine parasites, most people picture repulsive worm shaped creatures crawling inside the body of the host. I am sure you do too and not so long ago I was like you.
Thanks to my Professional Practice, I discovered the marine parasite universe by building a case study dataset about them. Let me tell you that there are quite some cunning species that found mischievous ways to use marine species to survive.
I want to show you in this page that marine parasites do not only correspond to the description above nor they are boring. There is actually a vast spectrum of them going from worms, barnacles, amphipods and even fungi-like species! You will find out about some parasite life-cycles that I particularly enjoyed myself while doing my research. Don't worry, they are not all disgusting.
Some interesting parasitic life-cycles you wouldn't have imagined of...
A "Trojan horse" strategy
The Pomphorhynchus laevis acanthocephalan worm is native from Europe rivers. Its second host forms a cyst as an immune response but it does not affect the infecting power of the worm. In the Rhine river, the parasite found a perfect shelter in the invasive dominant goby Neogobius melanostomus.
The cunning invasive eel parasite nematode Anguillicola crassus uses this characteristic to hide: the cyst is its Trojan Horse. Indeed, its second host have the capability to encapsulate it and kill it, preventing the nematode to infect its definitive host: the eel. But thanks to P. laevis cysts, the nematode enters the eel and infects its swim bladder impacting the european eel swimming performance and eventually causing its death during its spawning migration journey of 5,000 km. Because of that, the European eel was classified as a critically endangered species in the IUCN Red List in the 80's.
An endless parasitic life-cycle?
I'm sure you never imagined the beautiful sea anemones as parasites, and that they could take advantage of other marine species for their survival. Well, I am sorry to announce you that sea anemones are not that nice to everyone!
The lined sea anemone Edwardsiella lineata is a facultative parasite in the sea walnut comb jelly, Mnemiopsis leidy. It can transform into a parasitic stage to infect the sea walnut's gut and feed on partially digested food. What is surprising is that after being excised from the host and go back into its planula shape again, instead of becoming an adult polyp, it can also reinfect the comb jelly by changing its form AGAIN! Edwardsiella lineata was smart enough to find a perfect shelter with food and escape the ocean’s rough conditions for its small larva.
Bottom: Three stages in the life history of the lined sea anemone(A) The adult polyp.(B) The parasite.(C) The planula larva.(Abbreviations: mo mouth, ms mesentery, ph pharynx, tn tentacle.)
Pacific Chinook salmon linked to fried-egg jellyfish by an amphipod?
Hyperia medusarum hyperiid amphipod is an obligate parasite of gelatinous zooplankton when it is a juvenile: in order to survive it has to live in jellyfishes, ctenophores or salps. One of its definitive host is the fried-egg medusa, Phacellophora camtschatica.
The juveniles hide in the oral arms where they feed on nematocysts and possibly on preys caught by the jellyfish. Recent studies found H. medusarum in the Chinook salmon stomach. But the parasite had nematocysts in its foregut matching with the nematocysts from the medusa's oral arms.
This discovery creates an energetic link between the salmon and the jellyfish! We do not know yet if the salmon is either plucking hyperiids from medusa and therefore eating oral arms, or if that it is encountering hyperiids that have left their host for reproduction or some other purpose.
If you want to learn more in detail about the parasites you just discovered and about a fungi-like marine parasite, click here to read the three articles I wrote during this Professional Practice!
By summarizing 12 case studies, reading more than 40 papers, and writing 3 articles, I learned that marine parasites are very complex and diverse. The examples pictured here represent complex life-cycles with food web transmission, but there can be simpler life-cycles involving only one host. Marine parasites can castrate their host (quite common in crustaceans), can cause human diseases if we eat infected fish (these are called zoonotic diseases) or if we just touch the parasite (E. lineata causes the seabather’s eruption, a skin irritation disease).
However, marine parasites are a key factor in ecological components . They help regulate host populations and exert power over food webs. They are not just here to cause harm. Therefore, without them the whole marine ecosystem would be disrupted.
Not only I improved my writing skills, reading scientific papers and summarized them but also I increased my marine biology knowledge.
But I could not leave you without showing you magnificent pictures of what we usually imagine thinking about our beautiful marine parasites...
