Crustaceans - shell shockers
Extracted from The Sea that Never Sleeps by Douglas David Seifert, read the full feature in the DIVE night diving special
The crustaceans – crabs, shrimp and lobster – are invertebrates encased in hardened shells acting as armour but are so irresistible as prey to so many other reef inhabitants that even that protection is not enough.
The majority of crustaceans rely upon concealment, either under the substrate or hiding in reef crevices. Crustaceans are among the most abundant and diverse animals, with more than 67,000 species roaming the oceans and near-shore environments.
One of the most colourful of the shrimps is the enigmatic broken-back or marbled shrimp, also known as saron shrimp. They are often colourfully patterned shrimp, with seemingly furry sensory hairs on some of their appendages, which hide among rubble and boulders and reef clefts by day, but by night boldly position themselves in open spaces on the reef.
Hermit crabs are crustaceans with armoured bodies but relatively soft and unprotected abdomens and tails. Nature’s solution to this vulnerability is to house the hermit crab within the shell of a dead gastropod. As the hermit crab grows, it must find larger and larger shells, but until its dwelling becomes too cramped, the hermit crab has a moveable fortress in which it can hide, should it come under attack by a predator only to pick up its home and make a run for it one the danger has passed.
Hermit crabs are largely nocturnal and one species – the anemone hermit crab (Dardanus pedunculatus) – lives in a symbiosis with a species of sea anemone that favours the mobile lifestyle, providing some measure of stinging protection for the hermit crab while in return being exposed to wide areas in which to feed.
Other species of crab that use other animals as cover during their nocturnal perambulations are the decorator crab (Majoidea) and the diminutive boxer crab, or pom-pom crab (Lybia tessellata).