The Mysterious Eye Parasite Of The Greenland Shark

The frigid waters of the Arctic may seem like an unlikely place to find sharks, yet the Greenland shark (Somniosus microcephalus) calls this harsh environment home. These large, slow-moving predators are highly adapted to the extreme cold, with antifreeze proteins coursing through their veins. But even these mighty sharks must contend with persistent parasites.

A fascinating relationship exists between Greenland sharks and small copepods that attach to their eyes. This peculiar pairing raises many questions about the dynamic between host and parasite. What does the parasite look like? How does it impact the shark’s vision? And how do the sharks cope? Unraveling the mystery of this eye parasite provides a portal into the hidden world of Arctic marine life.

In this article, we’ll explore what’s known about the peculiar eye parasites that plague Greenland sharks while also peering into the shadowy depths to uncover what remains unknown. Understanding this complex parasitic relationship sheds light on the remarkable biology of the Greenland shark and the challenges of survival in the frigid Arctic seas.

What Is the Greenland Shark Eye Parasite?

The tiny pest that plagues the eyes of Greenland sharks is known scientifically as Ommatokoita elongata. This parasite is a copepod – a type of small crustacean – that attaches itself to the corneas of the sharks’ eyes.

At just a few millimeters long, Ommatokoita elongata is dwarfed by its massive Greenland shark hosts, which can grow over 5 meters in length. The female parasite has an elongated body with a distinctive egg sac at the rear, while males are smaller with no egg sac. The copepods use hooked antennae and sharp appendages to anchor to the surface of the shark’s eye.

While a variety of marine life can be afflicted by parasitic copepods, Ommatokoita elongata is specially adapted to thrive on the eyes of cold-water sharks like the Greenland shark. The parasite penetrates the corneal tissue and likely feeds on mucus and cells from the surface of the eye.

This bizarre pairing of shark and crustacean has puzzled scientists striving to understand how and why the parasites target the eyes. Unlocking these secrets provides insights into the shadowy lives of Greenland sharks in the deep Arctic waters they inhabit.

How Does Ommatokoita Elongata Attach to The Shark’s Eye?

The lifecycle of Ommatokoita elongata is synchronized with its shark hosts. The adult female parasite produces eggs which hatch into nauplius larvae that float freely in the ocean. When a larva encounters a Greenland shark, it quickly attaches itself to the surface of the cornea using specially adapted antennae and mouthparts.

Once attached, Ommatokoita elongata penetrates the outer corneal tissue using sharp mouth hooks. A bulbous structure at the front of the parasite’s body acts like an anchor, allowing the parasite to bore deeper into the shark’s eye. This firm attachment prevents the parasite from being dislodged as the shark swims.

Researchers believe the parasite secretes enzymes or other compounds to dissolve the shark’s corneal tissue, allowing the copepod to fuse its body to the surface of the eye. The parasites also provoke little immune response, likely using chemicals to suppress inflammation and evade the shark’s defenses.

This array of highly specialized adaptations allows tiny Ommatokoita elongata to cling tenaciously to the eyes of the world’s largest predatory shark.

What Effects Do the Parasites Have on The Shark’s Vision?

The presence of Ommatokoita copepods in its eyes appears to significantly impact a Greenland shark’s vision. The parasites damage the corneal tissue as they feed, destroying sensitive photoreceptor cells in the process.

  • Multiple parasites on a single eye can entirely coat the cornea in a dense layer that likely impairs light detection and blurs vision.
  • Scarring and erosion of the corneal surface from the parasites also reduces visual acuity.
  • In severe cases, the shark’s lens may become exposed or extruded as structural integrity is lost, blinding the shark entirely in that eye.

Yet remarkably, Greenland sharks seem capable of surviving with minimal vision loss. Researchers hypothesize that the sharks rely more on other finely-tuned senses while hunting in the inky Arctic depths:

  • Advanced olfactory systems allow Greenland sharks to detect minute traces of blood and chemicals.
  • Special gel-filled pits along their heads can detect faint electrical signals from prey.
  • Lateral lines running down their bodies sense minute water movements.

With multiple sensory backups, Greenland sharks appear equipped to cope with their pesky ocular parasites.

What Is the Prevalence of Eye Parasites in Greenland Sharks?

The eye parasite Ommatokoita elongata is remarkably common in Greenland shark populations across the Arctic. Studies have found that over 90% of Greenland sharks observed in the wild are infected with the parasites.

  • In eastern Greenland waters, 100% of sharks examined had copepods embedded in their eyes.
  • Around Iceland, 95-98% of Greenland sharks hosted parasites, with an average of 10 parasites per eye.
  • In the St. Lawrence Estuary, researchers found copepods in the eyes of 11 out of 13 sharks surveyed.

This extremely high prevalence suggests the parasite is well adapted to find and infect its primary host. The abundance of Ommatokoita elongata also indicates most Greenland sharks must cope with impaired vision for much of their long lives, which can span over 400 years.

Yet some small populations of Greenland sharks exist nearly parasite-free. Sharks in the St. Lawrence Estuary had no eye parasites, possibly due to environmental differences. These rare copepod-free sharks may provide insights into the visual capabilities of Greenland sharks at their full potential.

How Do Greenland Sharks Cope with The Eye Parasites?

Given the extremely high prevalence of Ommatokoita elongata among Greenland sharks, these predators must have evolved ways to cope with the vision impairment caused by eye parasites.

  • Research shows the sharks rely more heavily on their other finely-tuned senses to find prey, minimizing their dependence on sight. Their advanced olfactory system and electroreceptive gel-filled pores on their heads allow them to accurately detect prey.
  • Greenland sharks seem behaviorally adapted to function even when blinded. In the dark Arctic depths, vision has limited utility, so the sharks likely evolved to depend less on seeing and more on smelling and sensing.
  • The sharks may periodically rub their eyes along the sandy seafloor to dislodge some parasites. However, such actions provide only temporary relief as new parasites soon recolonize the eyes.
  • Antifreeze proteins in their tissues may inhibit the copepods from anchoring as firmly to the eye surface, reducing parasite impacts. However, no shark studied has been parasite-free.

Despite coping mechanisms, eye parasites undoubtedly still hinder Greenland sharks. Further research is needed to fully understand how these resilient Arctic predators compensate for near-constant vision impairment from Ommatokoita elongate.

Are There Any Benefits for The Greenland Shark or The Parasite?

On the surface, the relationship between Greenland sharks and Ommatokoita elongata appears purely parasitic, with the copepod damaging its host’s eyes while reaping the benefits of a free meal. However, some evidence suggests potential mutual benefits in this unusual pairing.

For the parasite, the Greenland shark’s eye provides an ideal habitat with ample food and protection from predators. The shark’s cold, deep environment lacks many complex fish immune systems that could evict the parasites. By evolving to specifically target shark eyes, Ommatokoita elongata has access to a reliable niche.

For the shark, some research proposes the parasites may provide benefits like warning off predators or removing dead tissue. However, no definitive advantages have been identified, and the parasites likely impair more than aid their hosts.

Overall, Ommatokoita elongata appears to have evolved highly specialized adaptations to extract maximum benefit from its environment at the expense of its host’s vision. While Greenland sharks have found ways to cope, their ability to evade or dislodge the parasites remains limited. This one-sided arrangement firmly favors the parasites over the sharks they afflict.

What Research Has Been Done on This Parasitic Relationship?

The unique parasitic relationship between the Greenland shark and the copepod Ommatokoita elongata has intrigued researchers for decades. Several studies have uncovered insights into this shark-parasite pairing:

  • Taxonomic research first identified and described the parasite species in the early 1900s. Later anatomical studies revealed its specialized claws and anchor adaptations for attaching to the shark’s eye.
  • Field surveys have quantified the extremely high prevalence of Ommatokoita elongata across Greenland shark populations in the Arctic. This work established how commonly the sharks interact with the parasite.
  • Physiological studies have examined how the parasites damage the shark’s corneal tissue as they feed and take up residence in the eye. This research shed light on the impacts on shark vision.
  • Behavioral studies suggest Greenland sharks rely more on non-visual senses to compensate for vision loss from the parasites. This shows the shark’s adaptions to cope with parasitism.
  • Genetic analyses aim to clarify the evolutionary relationship between the Greenland shark and Ommatokoita elongata. This could reveal how long the association between the species has existed.

While many questions remain, continued research on this host-parasite relationship will uncover new insights into how Greenland sharks interact with a highly specialized parasite in the extreme Arctic environment.


The relationship between the Greenland shark and the parasitic copepod Ommatokoita elongata represents a complex and intimate interaction between species. The parasite has evolved highly specialized adaptations to live on the shark’s eyes, claws, and anchors, enabling it to attach and feed on corneal tissue. In turn, the shark has developed compensatory mechanisms to cope with the resulting vision loss, relying more heavily on its acute non-visual senses.

While the parasite clearly benefits from this arrangement, extracting nutrients at the expense of its host’s sight, evidence for advantages for the shark remains limited. The copepod’s presence may ward off some predators, but any such effects appear negligible against the certain impairment of vision. After centuries of coevolution, this lopsided relationship remains tilted firmly in favor of Ommatokoita elongata.

Continued research can provide deeper insight into how the Greenland shark perseveres as an apex predator despite near-constant harassment by eye parasites. Further studies quantifying the impacts of varying parasite loads on shark hunting and species interactions could reveal just how much the sharks lose from their pesky blinding guests. Biologists still have much to uncover about this intriguing case of parasitism in one of the most extreme.

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