Species identification websites

General sites

• Encyclopedia of Marine Life of Britain and Ireland (National Museums of Ulster)
• World Register of Marine Species
• MarLIN, The Marine Life Information Network
• British Marine Life Study Society
• Marine Species Identification Portal
• GB Non-native Species

Specific areas/taxa

• The online version of Picton & Morrow's sadly-out-of-print nudibranch Bible
• Scottish nudibranchs (but still useful even if you're not in Scotland)
• More nudis
• Online version of Picton et al. Sponge V (you can also download the PDF version)
• FishBase
• AlgaeBase
• Checklist and Atlas of the Seaweeds of Britain and Ireland (you can also download the PDF version)

Books, guides, etc.

• NHM Big Seaweed survey (ID guide for download, aimed at the more common species)
• Field Studies Council publications (Not free but very cheap)
• Field Studies Journal 1959-2003 (Most papers free to download)

Maps and search tools

• National Biodiversity Network
• EUNIS (European Nature Information System)
• JNCC (Joint Nature Conservation Committee)

Diving

Organisations

• British Sub-Aqua Club (BSAC) (The British way, though also available world-wide)
• Professional Association of Diving Instructors (PADI) (The world-wide way)
• Seasearch (Volunteer diving for marine surveying)

Dive shops/centres/boats

I have only listed places I've actually used (and liked...)

• Gozo Aqua Sports
• Blue-o-Two
• Deep Blue Diving (Fuerteventura)
• Reef Conservation International (Belize)
• Sark Diving Services
• Poole Diving ("Peveril Myth")
• Celtic Diving (Pembrokeshire)

Related information

• IOW & Solent tide times/tables
• Cromer (and other) tide times

Conservation

• Marine Conservation Society
• Project AWARE
• Hampshire & Isle of Wight Wildlife Trust
• Dorset Wildlife Trust
• UK Marine Protected Areas Centre