Jellyfish of UK Waters: Identification and Sting Treatment Guide

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Jellyfish stings are the most common marine injury for UK divers. Most stings are minor irritations. Some cause serious pain and require medical attention. Identification and proper first aid matter.

Common UK Jellyfish Species

Moon Jellyfish (Aurelia aurita)

Appearance: Translucent white, saucer-shaped, four horseshoe-shaped gonads visible inside bell, 10-30cm diameter, short tentacles.

Sting severity: Very mild. Most people feel nothing through wetsuit. Bare skin contact causes slight tingling at most.

Frequency: Very common, year-round, all UK coasts. Often in large blooms.

Compass Jellyfish (Chrysaora hysoscella)

Appearance: Brown radial markings resembling compass points, yellowish-brown, 20-30cm diameter, 24 long tentacles.

Sting severity: Moderate. Painful but not dangerous for most people. Causes red welts, burning sensation lasting several hours.

Frequency: Common summer-autumn (June-October), all UK coasts.

Lion's Mane Jellyfish (Cyanea capillata)

Appearance: Large (30-50cm bell common, up to 1m recorded), red-brown to dark purple, thick mane of tentacles underneath extending 1-3m (occasionally 10m+).

Sting severity: Severe. Powerful sting causes intense pain, large red welts, blistering. Tentacles retain stinging cells for hours after separation from bell.

Frequency: Common summer-autumn, particularly northern UK (Scotland, North Sea).

Barrel Jellyfish (Rhizostoma pulmo)

Appearance: Very large (40-90cm diameter), cauliflower-like appearance, white-blue with purple edge, no trailing tentacles (arms instead).

Sting severity: Very mild. Most people feel nothing. Mild irritation possible on sensitive skin.

Frequency: Common summer (May-September), southwest England, Wales.

Blue Jellyfish (Cyanea lamarckii)

Appearance: Blue-purple, 10-30cm diameter, similar structure to lion's mane but smaller and blue.

Sting severity: Moderate to severe. Similar to compass jellyfish but can be more painful.

Frequency: Summer-autumn, all UK coasts.

Portuguese Man O' War (Physalia physalis)

Appearance: Blue-purple gas-filled float (10-15cm), long blue tentacles (up to 10m). NOT technically a jellyfish (colonial organism).

Sting severity: Very severe. Extremely painful, systemic effects possible (nausea, fever, shock), requires medical attention.

Frequency: Rare but increasing (climate change effect). Summer-autumn, southwest England, Wales, Ireland after westerly storms.

Jellyfish Sting Mechanism

Nematocysts (stinging cells) trigger on contact, inject venom through hollow barbs. Thick wetsuits (5mm+) usually prevent penetration. Thin suits (3mm), bare skin, neck seals, faces are vulnerable.

Thousands of nematocysts on single tentacle. Multiple contacts = more venom = worse symptoms.

Sting Symptoms by Severity

Mild (Moon, Barrel): - Slight tingling or no sensation - Minor redness lasting 20-60 minutes - Usually no treatment needed

Moderate (Compass, Blue): - Immediate sharp pain - Red welts within minutes - Burning, itching sensation lasting 2-8 hours - Possible raised bumps or hives

Severe (Lion's Mane, Portuguese Man O' War): - Intense immediate pain - Large welts, blistering, tissue damage - Pain lasting 24+ hours - Systemic symptoms possible: nausea, muscle cramps, difficulty breathing, elevated heart rate, dizziness - Medical attention recommended

Allergic Reactions (Any Species): - Rapid swelling beyond sting site - Difficulty breathing, wheezing - Dizziness, fainting, confusion - Chest tightness - Requires immediate emergency response (call 999)

First Aid Protocol

Immediate Actions (in water): 1. Exit water calmly (panic increases heart rate, spreads venom faster) 2. Remove visible tentacle pieces (use gloves, knife edge, or rigid object - not bare fingers) 3. Signal buddy/surface support

Onshore Treatment:

For Lion's Mane, Portuguese Man O' War: 1. Rinse with seawater (NOT fresh water - fresh water triggers more nematocysts) 2. Remove tentacles using tweezers, gloves, or scraping motion 3. Immerse in hot water (40-45°C) for 20-40 minutes OR apply heat packs (heat deactivates venom) 4. Seek medical attention if severe pain, large sting area, or systemic symptoms

For Compass, Blue jellyfish: 1. Rinse with seawater 2. Remove tentacles 3. Hot water immersion (40-45°C) for 20 minutes 4. Over-the-counter antihistamine for itching 5. Hydrocortisone cream for inflammation 6. Monitor for allergic reaction signs

For Moon, Barrel jellyfish: 1. Rinse with seawater 2. Usually no further treatment needed

What NOT to Do: - Do NOT use fresh water (triggers nematocysts) - Do NOT apply vinegar (UK species respond poorly, may worsen - vinegar works for box jellyfish in Australia/Indo-Pacific, not UK species) - Do NOT rub with sand or towel (spreads nematocysts) - Do NOT apply ice (cold increases pain for UK species) - Do NOT urinate on sting (myth, ineffective)

Prevention Strategies

Seasonal Awareness: Peak jellyfish season June-October. Plan dives accordingly.

Surface Checks: Check surface conditions before splashing. Jellyfish often visible floating.

Entry/Exit: Descend/ascend with awareness. Jellyfish often concentrate in top 5m.

Current Zones: Jellyfish accumulate in current lines, eddies, behind headlands. Avoid during blooms.

**Wetsuit Coverage**: Full wetsuit (including hood, gloves) provides excellent protection. Exposed skin (face, neck seal areas) remains vulnerable.

Buddy Awareness: Trail diver watches for jellyfish approaching from behind/above.

Beach Reports: Check local dive shop reports, beach lifeguard warnings. Major blooms usually reported.

Bloom Conditions

Jellyfish blooms occur when: warm water, high plankton levels, calm seas, specific current patterns.

Blooms can contain thousands of jellyfish in concentrated areas. Diving during blooms is unpleasant and risky. Postpone dive or choose different site.

Portuguese Man O' War Warnings

UK sightings increasing (climate change effect). When sightings reported: - Avoid diving until bloom passes (usually 3-7 days) - If in water and encounter, exit immediately - Washed-up specimens on beach can still sting (tentacles remain active for hours after death) - Check Marine Conservation Society reports for sighting updates

When to Seek Medical Attention

Immediate emergency (call 999): - Difficulty breathing - Chest pain or tightness - Rapid swelling of face/throat - Confusion, loss of consciousness - Severe widespread pain

Seek medical advice (A&E or GP): - Portuguese man o' war sting - Large sting area (>30cm) - Severe pain not relieved by hot water - Signs of infection developing (increasing redness, pus, fever) - Sting near eyes or mouth - Child or elderly person stung

Dive Kit Additions

- Tweezers (tentacle removal) - Heat packs (chemical heat packs if hot water unavailable) - Antihistamine tablets - Hydrocortisone cream

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