DIVE LOG JUNE 2025 issue 412

STAYIN ALIVE THE DEFENCES OF SEA SLUGS - Part 2 Passive Defences

Behaviour By far, the best defence is without doubt the avoiding altogether of an encounter with a predator. Many sea slugs are nocturnal, only emerging at night to feed and to mate. This reduces significantly their exposure to bottom foraging fish that hunt using their eyesight during daylight hours. Others live a reclusive lifestyle beneath rocks or old coral plates or down in narrow crevices, never leaving that safety unless the food supply there is exhausted. The more primitive of the sea slugs live an infaunal (burrowing) lifestyle, many only emerging from the protection of the silt or sand to mate and spawn. Appearance Camouflage , by appearance, is a strategy

used by many sea slugs to avoid detection. Many have evolved to match the texture and/or colour of their background substrate that is often their food source whether that be plant or animal such as sponges, hydroids, bryozoans, algae or corals to such a degree that they are virtually invisible unless one knows where and what to look for. Some are known to “mimic” unrelated, that is non-dietary life forms in their habitat. Not Cognitive We must remember that in reality they are not “trying” to “mimic” at all. All the changes that are wrought to their appearance are random reproductive mutations that have proved to be advantageous to the sea slug through selection pressure in the habitat, assisted in their survival and then passed on to offspring.

Above:

Above: Found secluded beneath the overturned shell this specimen of Pleurobranchus peronii is exposed from occupying its usual daylight haunt for self-protection against predators. At night, however, it will be found foraging across the open substrate for food.

Above: Not quite infaunal living but making the most of the silty substrate to mask its presence is this specimen of Dendrodoris atromaculata . The combination of the rough tuberculate sur face of the notum and the dark patched and sandy colouration, sprinkled all over with silt works very well.

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DIVE LOG Australasia #412 - June‘25

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