Diving & marine glossary

24 terms

Plain-language definitions of the diving, biology and reef terms you'll meet across the site - from anatomy and toxins to reproductive biology and marine phenomena.

Toxins

What the animal actually carries, how it is delivered, and what to do about it.15

Ciguatera fish poisoning

Poisoning from reef fish that have accumulated ciguatoxins up the food chain - tasteless, cooking-proof, and capable of lasting for months.

Conotoxins

Cone snail venom peptides - a hundred or more per species, each shaped for one target in a nervous system, and the source of a painkiller stronger than morphine.

Grammistin

The frothing skin toxin of soapfishes, released as a lathering mucus when the fish is stressed - and the origin of their name.

Ichthyotoxin

A poison aimed at fish rather than at mammals, usually attacking the gills - including pardaxin, the Red Sea sole secretion that makes a shark let go.

Neurotoxin

A poison that jams nerve signaling rather than damaging tissue - it kills by stopping the breathing muscles, with the victim fully conscious.

Ostracitoxin (pahutoxin)

The boxfish defense: a soap released from the skin that destroys the gills of every other fish in a confined volume, itself included.

Palytoxin (PTX)

One of the most poisonous non-protein substances known, carried by common zoanthids - and it has hospitalized people who only cleaned an aquarium.

Paralytic shellfish poisoning (PSP)

Saxitoxin picked up from algal blooms by shellfish and some reef crabs: tasteless, unaffected by cooking, and treated only by keeping the victim breathing.

Poison

A toxin that harms when eaten or touched, with nothing injecting it - the pufferfish version of chemical defense.

Saponins (holothurin)

Soap-like defensive compounds of sea cucumbers and sea stars: they lather in water, take cell membranes apart, and can empty an aquarium.

Sesquiterpenes

The chemistry that keeps soft corals from being eaten and stops competitors settling next to them - and a standing source of drug leads.

Sulfuric acid (as a weapon)

Tritons, tun shells and some side-gilled slugs secrete free sulfuric acid near pH 1 to subdue armored prey - stomach acid, applied from the outside.

Tetrodotoxin (TTX)

The pufferfish poison: about a thousand times more potent than cyanide by weight, unaffected by cooking, and with no antidote.

Venom

A toxin actively injected through a spine, fang or sting. If the animal has to put it into you, it is venom.

Verrucotoxin (VTX)

The stonefish venom protein: it attacks the heart and bursts red blood cells, and the pain it causes is considered among the worst in nature.

Biology

Words that describe how an animal lives and where.3

Demersal

Living on or just above the bottom rather than in open water - the habit of flatfish, gobies, groupers and most of what you photograph on a sandy slope.

Endemic

A species that lives in one region and nowhere else on earth - in this catalogue, one found in the Red Sea alone.

Nematocyst (cnidocyte)

The single-use stinging capsule of jellyfish, anemones and corals - it fires in under a millionth of a second, and works whether or not the animal is alive.

Reproduction

How reef animals breed - and why so many of them change sex.5

Gonochoric

Separate sexes for life - an animal is male or female and stays that way, which on a reef is less common than you would expect.

Hermaphroditic

Carrying both sexes - either at the same time, or by changing from one to the other partway through life, as clownfish and most wrasses do.

Iteroparity

Breeding repeatedly across a long life - the strategy of most reef fish, and the reason a big old female matters more than a small one.

Oviparous

Laying eggs that develop outside the body - the strategy of most fish here, from the broadcast spawners to the shark that leaves a mermaid's purse.

Semelparity

Breeding once and dying - everything spent on a single reproductive event, as octopuses and squid do.

Phenomena

Things the reef does that need explaining before they make sense.1

Biofluorescence

Absorbing blue light and re-emitting it as green, orange or red - not the same thing as bioluminescence, and far more common on a reef than anyone realized.