COMMENTS & OBSERVATIONS

We headed off to Holbourne Island to give the boat a run, check out the conditions and see if the sea slug numbers have increased. The boat ran well, the water was still green but visibility was somewhat better than our last dive here. Things started off a bit slow but at least we were finding slugs. Tiny slugs. We found quite a few different species but nothing in large numbers.

We headed in the opposite direction for the second dive and again found scattered slugs until we reached one nondescript patch of rubble that looked no different to the other rubble patches but there must have been something good here as we kept finding slugs, mostly still tiny. When you stopped to photograph one that had caught your eye, you suddenly spotted others of more cryptic coloration. Terry found a decent sized Hypselodoris tryoni on this patch of rubble with a hitchhiking Emperor Shrimp, which whilst we have seen this overseas, this is the first time we have found one ourselves and the first time we have observed these shrimp here. On checking the photos, it turns out there were 2 shrimp. Julie’ s camera battery went flat on the second dive much to her disgust so the numbers of Plakobranchus is actually higher than reported below but without photos, it is hard to differentiate between the species we were recording.

We were very pleased with the resulting tally and the new finds. As mostly everything was so tiny we wonder now if they are slowly making a comeback – let’s hope so.

Taxonomic Diversity:
Twenty-six of the thirty-two species sighted were nudibranchs, twenty being dorids comprising 9 x porostome (suctorial feeders), 2 x phanerobranchs (non-retractile gill), 9 x cryptobranch (retractable gill); and six cladobranchs comprising 2 x aeolid, 4 x arminid and 0 x dendronotinids.  Five sacoglossans and one cephalspidean round out the species count. A total of 79 specimens were recorded. Eighteen of the thirty-two species are spongivores.

Our Historical Data:
– We have now completed 17 surveys at Manta Reef since our first survey here on 13/03/2023.
– We have recorded 79 species at this site.
– Our most frequently recorded species here are Phyllidia varicosa (53%), Phyllidiella sp. a (53%), Plakobranchus sp. 01 (47%), and Elysia marginata (41%).
– The most abundant species recorded by us at this site are Phyllidiella sp. a (1.5/dive), Plakobranchus sp. 04 (1.3/dive), Plakobranchus sp. 01 (1.2/dive), and Elysia marginata (0.9/dive).
 – This is the first occasion on which we have recorded:
* Hallaxa hileenae on any of our dives;
* Dermatobranchus oculus, Goniobranchus geometricus, Gymnodoris sp. 07, and Thorunna daniellae in the Whitsundays;
* Jorunna sp. 03, Phyllidiella sp. c2 and Verconia simplex at this site.
 – Our last survey at this site was on 1/02/2026.

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

TOTAL SPECIES SIGHTED: 32

DIVE IMAGES GALLERY

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