Two years ago, while diving near County Antrim in Northern Ireland, Libby Keatley came across a peculiar sight. It was a sea slug, also known as a nudibranch, with a transparent body displaying orange streaks and twig-like projections along its back. “It caught my attention because it looked very unique and unlike anything I had encountered before,” she recalls.
Keatley summoned her diving partner, Bernard Picton, an expert on sea slugs and a leader in UK sea slug research. He captured it in a plastic bag and, upon returning to his laboratory, verified that it was a recently discovered species. In recognition of Keatley’s contribution, he named it Dendronotus keatleyae.
Keatley recalls that three years ago, she was not familiar with nudibranchs or believed that they exclusively inhabited tropical regions. This demonstrates that anyone can gain knowledge, regardless of their experience in a laboratory, simply by noticing unusual or distinctive features.
A small but expanding community of novice nature enthusiasts have found sea slugs to be the perfect subject for their interests. These creatures possess the same beauty as butterflies, but unlike their fluttering counterparts, they remain still and allow for close observation and photography. Despite being distant relatives of the dull and slimy land-dwelling slugs found in gardens, sea slugs have a much more charming and appealing appearance. Many species are adorned with vibrant and dazzling colors as a means of defense against potential predators. Some even have the ability to blend in with their environment, which is often made up of brightly colored seaweeds and sponges.
There are a plethora of sea slugs waiting to be explored in the waters of the United Kingdom, with approximately 150 identified species in the northern Atlantic region. Despite their diminutive size, typically less than the width of a finger, there is a sense of excitement in sighting one. “That’s what I find most appealing about them,” explains Keatley.
Keatley takes me on a dive in Strangford Lough, located an hour’s drive south of Belfast. This area is known for being one of Europe’s largest sea inlets and a popular spot for wildlife enthusiasts, with its diverse population of seabirds, seals, and even bottlenose dolphins. By experiencing this hobby firsthand, Keatley shows me how it has garnered a global community of scuba divers and amateur photographers, while also contributing to scientists’ understanding of the changing oceans.
Beneath the surface, there is a plethora of activity taking place. During high tide, the Irish Sea carries in a mixture of particles and nutrients, providing sustenance for a diverse range of underwater species and the predators that rely on them.
Keatley looks out over the uninviting green, murky water. “There is an entire hidden world just below the surface,” she reassures me.
Keatley’s partner and fellow enthusiast, Phil Wilkinson, and Picton, who recently revised a guidebook for sea slugs in the north Atlantic with Christine Morrow, are diving with us. Morrow is keeping an eye on us from the shore. She believes that nudibranchs are highly captivating and can easily captivate people.
We put on tight, waterproof suits, gloves and hoods made of a synthetic rubber called neoprene. We also carry heavy scuba diving equipment and weights as we make our way into the water. Once we reach a depth of ten meters, the temperature drops to a chilling 10 degrees Celsius and visibility is limited to just a few meters. However, after a short while, Keatley directs my attention to a minuscule sea slug resembling a group of pale pink raspberries.
We discover a greater number of sea slugs than I have ever witnessed, even in warm oceans: vibrant pink ones and see-through ones adorned with finger-like projections tipped in shiny turquoise; another is white with yellow spots and has a pair of bunny ears used for smelling rather than hearing. We come across a group of sea slugs resembling tiny fried eggs drizzled with spicy chili sauce, and Keatley directs our attention to a peach-colored specimen hitchhiking on a hermit crab. It consumes tiny hydroids – related to jellyfish – that thrive on the crab’s shell.
Keatley experienced a resurgence in her childhood passion for nature through her newfound interest in spotting sea slugs. After learning to scuba dive in January 2019, she quickly became enamored with the enchanting underwater realm. She admits, “I was constantly craving more. The more I saw, the more I wanted to discover, and the more I discovered, the more my fascination grew.”
Eager to showcase the fascinating creatures with loved ones, Keatley acquired a waterproof camera and started sharing pictures on Instagram. She receives assistance in identifying species from fellow enthusiasts and experts through Facebook groups.
In just one year, she became a certified diver and began offering her services as a volunteer for Seasearch’s Northern Ireland division. This group of divers and snorkelers is dedicated to citizen science, collecting data on various species and environments. The accuracy of their findings is verified and then added to the national NBN Atlas, a database for biodiversity.
Keatley recalls that his initial dive experience with Seasearch left him feeling like he had finally found his niche. He was surrounded by others who shared his passion and interests. Filled with a desire to contribute and make a difference in a place he adored, Keatley was motivated to give back.
During the summer and fall seasons, she and other Seasearch divers conduct monthly underwater surveys of the coasts of Northern Ireland. In 2021, Keatley discovered a new species of sea slug during one of these surveys. In between dives, she also assists in coordinating virtual presentations and workshops to train volunteers in identification and photography techniques.
Terry Gosliner, an experienced expert in nudibranchs from the California Academy of Sciences, has aided in identifying numerous species. He supports individuals who are contributing to the discovery and research of sea slugs. “We do not have an adequate number of scientists to fully observe and understand the happenings in this field,” he remarks.
The practice of citizen science has a lengthy history, particularly among British hobbyist naturalists like Charles Darwin. It is currently gaining popularity, particularly in the realm of sea slugs, due to the numerous online forums, Facebook groups, and communities like iNaturalist that allow professionals and amateurs to collaborate in identifying and mapping species. There are also contests and competitions for underwater photography, with special categories for the best photos of nudibranchs. Citizen scientists are able to witness the direct impact of their observations, which encourages them to continue their involvement, according to Gosliner. “We are currently experiencing a golden era of truly comprehending the significance of citizen science.”
This is not just about finding new species but also documenting their movements as the planet heats – and sea slugs are on the move. In August 2022, a rainbow-coloured sea slug was seen by a Seasearch diver in the Isles of Scilly, a first for the UK. The species is commonly found in France, Spain and Portugal and was spotted again in May this year, in a rockpool on a beach in Falmouth.
In June of last year, Keatley discovered a sea slug near County Donegal in the north-west region of Ireland. This species was previously only documented as far north as Pembrokeshire in the UK.
“If you are familiar with nudibranchs, you would easily recognize this species. It is unique and cannot be mistaken for any other.”
According to Gosliner, citizen scientists are often the ones who first recognize species appearing in unexpected locations. He emphasizes the importance of regular individuals with a passion and knowledge in the field, as they act as guardians of environmental changes and make crucial observations.