COMMENTS & OBSERVATIONS

Finally the winds, the boat and time off work aligned and we headed off to Holbourne Island. The trip up was a bit lumpy but we just travelled a bit slower which gave more time for some whale watching. Conditions at the island were superb with the bottom visible from the boat. We anchored in 7m of water and dropped down onto a rubble patch where we spent 45 mins of the first dive, scouring the substrate for critters other than phyllidiids. Eventually we headed off to some other bommies and continued our searching and were pleased with the results from this dive. The water is starting to warm up meaning we are now able to dive that bit longer.

For the second dive we chose to head deeper to the ledge and veered off in an easterly direction. As with previous dives in this area we did not find as many critters but did find a few we had not seen on the first dive. The Coryphellina flamma was only found as Julie spent a long time searching in a small area for the Plakobranchus she sighted and then subsequently lost; yes she found the Plakobranchus again after the Coryphellina! This area has lots of phyllidiids and Terry even managed to find a flatworm that looks like a phyllidiid, Pseudoceros imitatus.

Taxonomic Diversity:
16 of the 24 species sighted were nudibranchs, of which 12 were dorids comprising 7 x porostome, (suctorial feeders – all of the Phyllidiidae family), 2 x phanerobranchs (non-retractile gill), 3 x cryptobranch, (retractable gill) and 4 were cladobranchs comprising 1 x aeolid, 3 x arminids and 0 x dendronotinids. A single cephalaspidean (headshield slug) and 7 x sacoglossans (more than half being Thuridilla) complete the species count. If diet is considered 10, of the total of 24 species, were spongivores dominated by the phyllidiids. 46 specimens in total were recorded.

Our Historical Data:
– We have now completed 8 surveys at Manta Reef since our first survey here on 13/03/2023.
– We have now recorded 57 species at this site.
– This is the first occasion on which we have sighted Dermatobranchus fasciatus, Niparaya sp. 02 or Thuridilla bayeri in the Whitsundays.
– This is the first occasion on which we have sighted Dermatobranchus rodmani, Dermatobranchus sp. 07, Phyllidia elegans, Gymnodoris sp. 10, Thuridilla carlsoni or Thuridilla ratna at this site.
– A relatively rare sighting was the flatworm Pseudoceros imitiatus, reported here because it is a phyllidiid mimic. Probably not a bad defence mechanism given the toxicity of these nudibranchs and the numbers of them we record at this site.
– Our last survey at this site was on 12/06/2024.

Note: The large number of phyllidiid species in the lists below reflects the work that has identified taxonomic-cryptic species delineated in the paper: Papu, A., Bogdanov, A., Bara, R., Kehraus, S., Konig, G., Yonow, N. & Wagele, H. (2022). Phyllidiidae (Nudibranchia, Heterobranchia, Gastropoda): an integrative taxonomic approach including chemical analyses. Organisms Diversity & Evolution. https://doi.org/10.1007/s13127-021-00535-7 At the time of publishing this report we are in the process of reviewing all of our Phyllidiella records to align them with the findings of the above paper.

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

TOTAL SPECIES SIGHTED: 24

DIVE IMAGES GALLERY

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