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130. Plagued with sea lice (copepods)


This Undulated Moray Eel (Gymnothorax undulatus) is plagued with sea lice.

Sea lice are copepods, which are small crustaceans that live in every aquatic habitat. Most of them are free-living species, but some prefer a parasitic lifestyle and settle on the skin of a host, where they feed on the mucus, epidermal tissue, and blood of their host.

These parasitic species are found on almost every group of animals in the ocean, from sessile sponges to migrating whales. Many sea louse species (sea louse is the singular form of sea lice) are specific with regard to host genera, meaning that one species of sea louse will be found on different species of fish but all within the same fish family. They have a quite complex life cycle. Because they have a rigid external skeleton (exoskeleton), they have to moult at the end of each stage, so from egg over larva to adult, they undergo several moults.

Although they are not harmful, most fish prefer to have them removed at different cleaning stations on the reef by cleaner shrimps and/or cleaner wrasses. Copepods form a valuable food source for many different fish species. Non-parasitic copepods feed on phytoplankton (plants), therefore they form an important step in the aquatic food chain, a link between a plant-based food source (microscopic algae) and predation. The itching effect sometimes observed by bathers is not caused by copepods or sea lice but probably by the planktonic larval stages of cnidarians like jellyfish or anemones.

An ironic detail; many of these small parasitic and non-parasitic copepods are themselves infected with Dinoflagellates, a gut parasite.


Most underwater videographers would prefer to film colourful nudibranchs, impressive animals like sharks, majestic creatures like manta rays, and even strange-looking critters such as mantis shrimp. However, sometimes the most rewarding underwater images that an underwater videographer or photographer can collect are shots of the really bizarre and weird species. Images of unusual marine life (I guess that most scuba divers do not go diving to see parasites) present an opportunity for us to expand our understanding of the underwater world.

Furthermore, strange and bizarre critters often evoke strong emotional responses, such as shock, awe, or disgust, which can be a powerful motivator for exploration. These intense emotional reactions may be why people are often drawn to horror movies, haunted houses, or other forms of entertainment that play on our fears and anxieties. Not that scuba divers watching these underwater video clips need to fear a sea lice infestation on their next dive, but capturing footage of unusual marine life can help us appreciate the incredible diversity of the underwater world and inspire us to protect it for future generations. So, while the allure of more conventional underwater subjects is undeniable, there is something uniquely fascinating about capturing the bizarre and the weird in our oceans.

From the underwater videographer's point of view, it is a challenge to film such small critters. Tiny moving subjects can easily cause focus fluctuations, so it is recommended to use a diopter and ensure enough footage is taken. Afterward, while editing, just select the best shots.

Join us on a journey of discovery and entertainment as we explore fascinating marine wildlife topics and explore the many exciting underwater adventures on our YouTube channel and our Facebook page!

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