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Butterflies of the Sea

News item submitted by Agatha Ioannou
News item dated 13 Jan 2011


Due to their flash colouring and striking forms, nudibranchs hold the position under the sea that butterflies do on land. There are over 3,000 species of these marine gastropod molluscs, however, nudibranchs are generally poorly recorded and few are scientifically named. Some species have an external anatomy with textures and colors that mimick surrounding plants to avoid predators., whilst other nudibranchs have an intensely bright and contrasting color pattern that makes them especially conspicuous in their surroundings. Their bold coloration warns potential predators that the seaslugs are distasteful or poisonous.

Frontier-Fiji have been carrying out nudibranch surveys throughout 2010. On average, our researchers have recorded 30 individual nudibranchs per month. Nudibranch surveys are a simple yet extremely useful tool in establishing a comprehensive nudibranch species list for Gau. Unfortunately due to the highly variable nature of body forms within species, identification is sometimes not possible in which case detailed diagrams and notes are taken to identify at a later date. 

During the last few weeks of 2010, a total of 108 individual nudibranchs have been recorded and 16 new species were found not previously known to the island. There are currently 33 different known species of nubibranchs at Gau, however, a few are yet to be identified. The most abundant species was Loch's Chromodoris, Chromodoris lochi. Most sightings were seen to be stationary, closely followed by moving, feeding, or no record of activity. Nudibranchs live at virtually all depths of salt water, but reach their greatest size and variation in warm, shallow waters. The average depth of sightings was 7.8 m with a minimum depth of 2.5 m and a maximum depth of 15.1 m. The average size of sighted specimens was 2.6 cm, with the smallest being 0.5cm and the largest nudibranchs being 7cm. Many nudibranch species are incredibly small and may also be camouflaged or hidden in sediment and can therefore be hard to spot.  This is the major limiting factor to the nudibranch surveys, making it hard to determine the true number of nudibranchs present around Gau.  Hopefully 2011 with see further progress in Frontier’s research into the nudibranchs inhabiting the waters surrounding Gau.

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