UK Marine Life Identification Guide: What You'll Actually See While Diving
Identify common UK marine life: grey seals, lobsters, crabs, jellyfish, fish, and invertebrates. Complete guide for British waters diving.
Not sure which setup is right for you?
Take Our QuizUK waters host 8,000+ marine species. Cold, nutrient-rich currents support biodiversity matching tropical reefs. Colors are muted but abundance is significant.
Common Fish Species
Wrasse Family
Ballan wrasse: Largest UK wrasse (30-40cm), green-brown coloration, thick lips, curious behavior. Common on rocky reefs, kelp forests, wreck structures. Often approach divers closely.
Cuckoo wrasse: Males blue-orange, females pink-red, 15-25cm. Sex-changing species (all born female, dominant females transition to male). Common on reefs and wrecks.
Rock cook wrasse: Small (10-15cm), brownish, found around rocks and kelp. Often in groups.
Bass
European sea bass: Silver, streamlined, 30-60cm. Hunt in small groups around wrecks, reefs, estuaries. Slow-growing (7-9 years to maturity), heavily protected with catch limits and seasonal restrictions.
Flatfish
Plaice: Orange spots on brown background, diamond-shaped, 30-50cm. Sandy bottoms, often buried with only eyes visible.
Turbot: No orange spots, rounder shape, aggressive predators, can reach 70cm.
Dabs: Smaller (15-25cm), rough skin texture, sandy areas.
Scorpionfish
Short-spined sea scorpion: 10-15cm, mottled brown-red, excellent camouflage. Spines mildly venomous (painful but not dangerous). Common among rocks and kelp.
Long-spined sea scorpion: Similar size, longer spines, deeper water (15-30m).
Conger Eels
Large (1-2m common, up to 3m recorded), grey-brown, live in wreck holes, crevices, rocky overhangs. Nocturnal hunters, often visible during day with head protruding from hole.
Not aggressive despite appearance. Bites occur when hands enter dark holes (avoid this).
Dogfish (Sharks)
Lesser-spotted dogfish: 60-80cm, brown with dark spots, often resting on sandy bottoms. Harmless, docile.
Greater-spotted dogfish (bull huss): Larger (1-1.2m), bigger spots, less common.
Crustaceans
Edible crab (brown crab): Large (carapace 15-25cm), brown-red shell, massive claws. Under rocks, in crevices, on wrecks.
Velvet swimming crab: Smaller (8-12cm), red eyes, aggressive temperament, rear legs flattened for swimming. Will display claws if approached.
Spiny spider crab: Long legs, triangular body, often covered in algae and sponges for camouflage. 10-15cm body, 20-30cm leg span.
European lobster: Blue-black, large claws, 30-40cm common, up to 60cm. Under rock overhangs and in wreck holes. Nocturnal.
Squat lobsters: Small (5-8cm), compressed body, under rocks and in crevices. Not true lobsters.
Starfish
Common starfish: Five arms, orange-red, 10-25cm diameter. Rocks, kelp, occasionally sandy areas.
Spiny starfish: Seven arms (usually), pale purple-brown, covered in short spines, 15-30cm diameter.
Cushion star: Pentagonal shape, five short arms, yellow-orange, 5-10cm.
Brittlestars: Thin arms, small central disk, 10-20cm arm span. Often in large groups on sandy bottoms. Arms break easily.
Sea Urchins
Edible sea urchin: Large (10-15cm), red-purple, short spines. Rocky areas, kelp forests.
Common sea urchin: Smaller (5-8cm), green-purple, longer spines. Can dominate areas where predators absent.
Jellyfish
Moon jellyfish: Translucent white, four horseshoe-shaped gonads visible, 10-30cm diameter. Mild sting, barely felt through wetsuit. Very common year-round.
Lion's mane jellyfish: Large (30-50cm bell, tentacles 1-2m+), brown-red, powerful sting. Causes intense pain, large red welts, blistering. Summer-autumn, particularly northern UK.
Compass jellyfish: Brown radial markings, 20-30cm, moderate sting. Painful but not dangerous. Summer-autumn.
Barrel jellyfish: Very large (40-90cm), cauliflower appearance, white-blue with purple edge. Mild sting. Summer, southwest England.
Portuguese Man O' War: Blue-purple float (10-15cm), long blue tentacles (up to 10m). NOT technically jellyfish. Very severe sting, requires medical attention. Rare but increasing, particularly after westerly storms.
Anemones
Beadlet anemone: Red-brown, 5cm diameter, closed resembles red blob. Rocky areas, very common.
Snakelocks anemone: Long green tentacles with purple tips, 8-10cm diameter, doesn't fully retract. Contains photosynthetic algae.
Dahlia anemone: Large (10-15cm), thick short tentacles, brown-red-white.
Plumose anemone: White, feathery appearance, 10-20cm tall. Wrecks, pier pilings, rocky overhangs.
Nudibranchs (Sea Slugs)
UK hosts 100+ species. Common types:
Sea lemons: Yellow-orange, warty texture, 5-10cm. Feed on sponges, found on rocks.
Sea hares: Large (15-25cm), brownish, rabbit-ear-like tentacles. Kelp forests and seagrass.
Flabellina: Small (2-5cm), colorful, feathery appendages. Various species with different color patterns.
Cephalopods
Common cuttlefish: 30-40cm, can change color and pattern instantly. Intelligent, curious, sometimes approach divers. Summer breeding aggregations in some areas.
Common octopus: 60-80cm total length, eight arms with suckers. Changes color for camouflage and communication. Intelligent, shy, usually hide in crevices.
Sponges and Tunicates
Sponges: Encrusting types cover rocks and wrecks. Colors: yellow, orange, red, white, purple. Breadcrumb sponge (bright yellow), boring sponge (bores into shells), purse sponge (vase-shaped).
Sea squirts (tunicates): Filter feeders. Star sea squirt (orange star pattern), Clavelina (transparent, colonial), Ciona (solitary, vase-shaped).
Marine Mammals
Grey seals: UK population ~120,000. Curious underwater, often approach divers. Farne Islands, Lundy, Pembrokeshire are seal diving destinations. Powerful jaws, maintain respectful distance.
Harbour seals: Smaller than grey seals, spotted coat. Less common at dive sites.
Dolphins: Common dolphins, bottlenose dolphins occasionally encountered offshore. Rare to interact with while diving.
Basking sharks: Second-largest fish (6-8m), plankton feeders, harmless. Summer visitors to southwest England, Scotland, Isle of Man.
Marine Life Behavior
Camouflage: Scorpionfish, flatfish, octopus, spider crabs can be nearly invisible until movement.
Night vs Day: Night diving reveals different species. Conger eels hunt, lobsters emerge, squat lobsters more active.
Seasonal Changes: Summer brings jellyfish blooms, cuttlefish breeding, bass schools. Winter shows different fish distributions, fewer visible invertebrates, but clearest water (plankton dies off).
Depth Zones: Different species at different depths. Shallow (0-10m): kelp forest species, wrasse, sea urchins. Mid (10-20m): mixed reefs, diverse fish. Deep (20m+): larger wrasse, conger eels, deepwater species.
Conservation
Protected species: European eel, basking shark, angel shark, skates, seahorses. Report sightings to marine conservation groups.
Overfished species: Bass (catch limits apply), lobsters (minimum sizes), edible crabs (minimum sizes).
Touch nothing: Oils from skin damage anemones, sponges, corals.
Marine Conservation Zones (MCZs): 91 sites across UK protect specific habitats and species. Know site rules before diving.
Species Identification Resources
Books: "British Sea Fishes" (FSC guide), "Nudibranchs of Britain and Ireland" (Bernard Picton)
Websites: MarLIN (Marine Life Information Network), UK Sea Fish
Apps: Marine Wildlife ID
Courses: BSAC Marine Life courses (Fish Identification, Invertebrate Identification)
Find Your Perfect Setup
Answer a few quick questions and get personalised recommendations.
Start the QuizFrequently Asked Questions
What marine animals can you see diving in the UK?
Common UK marine life: Grey seals (Farne Islands, Cornwall, Scotland), common/harbour seals (Scotland, East Coast), European lobsters (under rocks and in crevices, bright blue colour), edible crabs, spider crabs, velvet swimming crabs, conger eels (wreck residents, up to 2m length), dogfish (small harmless sharks), pollack (schools around wrecks), wrasse (ballan wrasse most common, colourful), bass (southern UK summer), and various flatfish. Occasional sightings: basking sharks (surface feeders, summer), porpoises, dolphins (rare underwater encounter), octopus (shy, nocturnal), and cuttlefish. UK lacks tropical diversity but species present are large and impressive. Grey seals are highlight of UK diving, rivaling any tropical encounter for wonder.
Are there dangerous marine animals in UK waters?
UK marine life is remarkably harmless compared to tropical: No venomous fish (no lionfish, stonefish, or scorpionfish), no aggressive sharks (basking sharks and dogfish are harmless), no venomous sea snakes, and no dangerous octopus species. Hazards are minimal: Weever fish (venomous spines, found in sand, painful sting but not life-threatening), jellyfish (Lion's Mane can sting, painful but not dangerous), conger eels (will bite if provoked, but shy), and spiny creatures (sea urchins, crabs have pincers). Most UK diving injuries come from environment (cold, currents, wrecks) not marine life. This is major advantage over tropical diving: you can focus on cold and visibility rather than worrying about deadly creatures. The cold water will kill you long before any animal does.
Where can you see grey seals while diving in the UK?
Top UK grey seal diving locations: Farne Islands (Northumberland): 5,000+ seals, best October-December during pupping season, seal interactions guaranteed, boat dives from Seahouses. Lundy Island (Devon): year-round resident seal population, east coast sites best, seals curious and approachable. Cornwall (Lands End, Isles of Scilly): scattered seal colonies, summer best, variable sightings. Scotland (Orkney, Shetland, Inner Hebrides): large populations but more wary than Farne seals. Wales (Pembrokeshire, Ramsey Island): growing population, shore dive access possible. Farne Islands offers most reliable and interactive seal encounters in UK. Book October-November for juvenile seals (most playful). Grey seals are curious and will approach divers; remain still for best interactions.
What jellyfish should UK divers watch out for?
Common UK jellyfish: Lion's Mane (large red/orange jellyfish, trailing tentacles up to 10m, painful sting, common summer/autumn, most concerning UK species), Barrel jellyfish (huge barrel-shaped, up to 90cm, harmless to humans, impressive but docile), Moon jellyfish (translucent, harmless, extremely common), Compass jellyfish (brown markings, mild sting, summer), and Blue jellyfish (blue/purple, mild sting). Lion's Mane is only UK jellyfish with painful sting: causes burning pain, redness, and welts. Treat with vinegar or seawater rinse (not freshwater). Serious reactions rare but possible. Avoid touching tentacles (sting even when detached). Most UK jellyfish are harmless. Exposure suit protects most of body; watch exposed face/hands.
Related Guides
Ready to find your perfect setup?
Our quiz matches you with the right gear for your diving style.
Take the Quiz - It's FreeNo email required