COMMENTS & OBSERVATIONS

David has been out of the water for some time. Recovery from the skin bend in Bali, installation of a powered anchor gypsy on Li’l Mischief and an engine service all contributed to the hiatus. A welcome weather & swell window presented itself on Monday, so Harvey joined the excursion up to Mudjimba Island. We wanted to scope out the new Buoys for the No-Anchor Zone installed last July. There are 5 buoys in an arc from SW to W to NW. The no-anchor zone is located inside an imaginary line joining the 5 buoys and from the first and last buoy into the closest point on the island to those buoys. 

We chose to dive on the SE point of the island at a site we call Bornella Reef. 18 species were sighted on the first dive including a couple of interesting chromodorids: Thorunna florens, but this specimen lacks the usual orange band to the anterior edge of the mantle and a Goniobranchus that initially was thought to be Goniobranchus daphne but a review of the images revealed different coloured mantle margin bands and multi coloured spots and streaks on the notum. We are calling this Goniobranchus sp. 12 on the website for now. Please refer to the composite comparison image in the gallery below where it is shown along side a cropped image by Harvey Braun of a Goniobranchus daphne taken on the same dive. The second dive was not as productive. Four species of Dermatobranchus, all small specimens, were sighted over the two dives and more may have been present. Fewer phyllidiids than normal were recorded. Thuridilla cf. splemdens was present in significant numbers and had the highest count on both dives representing 20% of the total specimen count.

Taxonomic Diversity:
Twenty-four of the twenty-five sighted species were nudibranchs, with 15 being dorids comprising 2 x phanerobranchs (non-retractile gill), 2 x porostomes (suctorial feeders – all of the Phyllidiidae family), 11 x cryptobranchs (retractable gill – all 11 belonging to the Chromodorididae family) and 9 were cladobranchs comprising 4 x aeolids, 4 x arminids and 1 x dendronotinid. A single sacoglossan (sap-suckers) completes the species count. If diet is considered then 13 of the 25 species sighted are spongivores. More than 50 specimens in total were recorded.

Our Historical Data:
– This excursion brings the number of survey dives to 36 at Bornella Reef since we commenced fully recording data here on 19/07/2010.
– 146 species have been recorded at this site.
– Our most commonly recorded species at Bornella Reef are Goniobranchus splendidus (97%), Phyllidiella pustulosa (78%), Doriprismatica atromarginata (75%) and Hypselodoris jacksoni (69%).
– This is the first time we have recorded Goniobranchus sp. 12 in Australia;
– This is the first time we have recorded Cratena lineata, Gymnodoris sp. 14, Samla bicolor, Goniobranchus sp. 02 or Thorunna florens at this site;
– The graph, in the image gallery below, shows that the number of species observed in any survey dive has varied from 41 to 7 over our survey period and visual examination might be suggestive of a slight downwards trend. However, statistical analysis of the data revealed that any variation was not significant.
– Our last survey at Bornella Reef was on 06/12/2023.
(Historical data courtesy of Terry Farr, who extracts it from his comprehensive database.)

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

TOTAL SPECIES SIGHTED: 25

DIVE IMAGES GALLERY

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