Life Saving 123: Marine Animal Defenses at Pulau Semakau

The rich habitat along the sea shore provides lots of feeding opportunities for animals. However, this comes at a price. Compared to animals on land or in the sea, inhabitants here are vulnerable to predators coming both from the sea and land. Consequently, many have evolved anti-predator defences so as not to end up at someone else's dinner table. Examples of these could be found during our exploratory walk at Pulau Semakau today.

The most basic anti-predator defence has got to be fleeing. If you can't catch me, you can't eat me. Those that do that exceedingly well all eluded my capture on camera. The focus today will thus be on those that could not get away fast enough.

If you cannot get away fast enough, then better hope that your enemies cannot see you.

The hairy crab (Pilumnus sp.) is covered with long hair that breaks up the crab's outline and binds sediments to help it blend with its surroundings. If that does not work, it will dash into the closest crevice for cover.

Taking camouflage one step further, cuttlefish and squids such as this big-finned reef squid (Sepioteuthis sp.) can change their colour to match their surroundings. Another trick they may use is to release a cloud of ink to confuse predators while they make their escape.

If you are as slow as a snail, more extreme tactics will have to be used. A turban snail (Turbo sp.) has a hard shell which it can retract fully into to protect its soft body.

On its foot is a trap-door-like operculum that seals up the

opening. The thick and tough operculum has a rounded surface and protects the snail from the prying pincers of crabs and other predators.

The shape and colour of the operculum resemble cat's eyes and is sometimes made into jewelry.

Sometimes, best defence is offense.

The flower crab (Portunus pelagicus) packs a nasty pinch from its sharp pincers. When threatened, the aggressive crab faces its aggressor head on, pincers ready. On top of that, it is heavily armoured with a shell packed with numerous spikes to discourage predators from swallowing it.

The hell's fire sea anemone (Actinodendron sp.) defends itself from any animal that dares to touch it with a painful sting. This comes from stinging cells tipped with venom and they look like little harpoons under the microscope.

If you are a small shrimp with minimal defensive powers, then it is best to find a powerful ally.

Apparently the stinging cells of sea anemones are so effective that the anemone shrimp (Periclimenes brevicarpalis) have found a way to take advantage of them by living among them for protection. But as if free protection is not enough, this species has been observed feeding on the tentacles of its host anemone!

Today's exploratory walk at Pulau Semakau also saw new records of 3 sea cucumber species for the island's shore. Even though they look helpless, sea cucumbers are able to protect themselves too. Some contain toxins or taste downright foul to predators, others try to confuse enemies by vomiting their guts and other organs out while some produce sticky threads to bind attackers in a gooey mess. Very neat.

From left: Ball sea cucumber (Phyllophorus sp.), Holothuria notabilis, and brown sandfish sea cucumber (Bohadschia vitiensis).

At the end of this trip, I still wonder how people squat over ankle-high water without getting their backsides wet. Must acquire this veritable skill.

Further reading:

1. Bruce, A. J. and Svoboda, A. 1983. Observations upon some pontoniine shrimps from Aqaba, Jordan. Zoologische Verhandelingen 205: 3-44.