COMMENTS & OBSERVATIONS

Another good forecast saw us head back up to the blue water of Holbourne Island. Due to the slight NE breeze, we opted to dive Manta Reef again as the island provides protection, enabling us to anchor and dive in flat water. For the first dive we headed in an easterly direction in slightly deeper water, before turning and heading back to the boat in around 5 metres. The pickings for nudibranchs were a bit slim but we did encounter a distant relative in the form of Cassis cornuta (Horned Helmet) so for the second dive we headed west, again slightly deeper before heading back in the shallows. We had more luck this time and after checking our photos when we got home we came up with a reasonable tally.

The variety of Phyllidiidae takes some working out to identify and we ended up with 10 different species of this annoying lumpy group. This might be the last offshore dive for a while with wet weather and winds forecast to arrive this week.

Taxonomic Diversity:
Thirteen of the nineteen species sighted were nudibranchs, 12 being dorids comprising 10 x porostome (suctorial feeders), 1 x phanerobranchs (non-retractile gill), 1 x cryptobranch (retractable gill); and one cladobranch comprising 0 x aeolids, 1 x arminid and 0 x dendronotinids. Five x sacoglossans and one x cephalspidean (headshield slugs) complete the species count. A total of 38 specimens were sighted. Eleven of the nineteen species are spongivores.

Our Historical Data:
– We have now completed 14 surveys since our first survey here on 13/03/2023.
– We have recorded 68 species at this site.
– Our most frequently recorded species here are Elysia marginata (50%), Phyllidia varicosa (50%), Phyllidiella pustulosa (50%), and Phyllidiella sp. a (50%).
– The most abundant species recorded by us at this site are Phyllidiella sp. a (1.2/dive), Elysia marginata (1.1 per dive), Phyllidiella pustulosa (1.1 per dive), Plakobranchus sp. 04 (1.18 per dive).
– This is the first occasion on which we have sighted Gymnodoris sp. 36 in Australia – we previously photographed the species in the Philippines.
– This is the first occasion on which we have recorded Dermatobranchus sp. 16 and Phyllidiella sp. 07 on any of our dives.
– Our last survey at this site was on 14/12/2025.

Key to symbols
+++ New Species
+ First time sighted at Whitsundays
# Most commonly sighted at this site with %

TOTAL SPECIES SIGHTED: 19

DIVE IMAGES GALLERY

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