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Dive Reports

21-12-2023 Trench

DAY/DATE

Thursday

21/12/2023

SITE/S

Trench
Inner Gneerings 

 

PARTICIPANTS

David

 

TYPE

Subtidal

 

MODE

Boat Dives

 

VESSEL

Li’l Mischief

 

DIVE

1

2

SITE/S

Trench

Trench

SPECIES #

9

8

DURATION

66 Min

66 Min

DEPTH/RANGE

13-18 m

13-18 m

TEMP.

23 C

23 C

VIS.

12 m

12 m

SURGE

Nil

Nil

CURRENT

Nil

Nil

COMMENTS & OBSERVATIONS

Fairly stable weather right through this week offered the opportunity to head out offshore again. This time the destination was the Trench on the Inner Gneerings. A forecast of variable 10 knot winds is not to be ignored and I was over the site before 07:00. The visibility was about 6 m on the surface but that opened up to 12 m on the bottom. There was a difference in the water temperature as well, with 26 C on the surface but only 23 C on the bottom, making for a “chilly” transition. The species count was not high and I put this down to the time I spent looking through the Caulpera algae that has made its substrate-covering, seasonal appearance. The hope was to find species of Oxyone and Lobiger that feed on it, but all the time and effort only turned up one small specimen of Oxyone jacksoni. Depths ranged from 13 m to 18 m with most of both dives spent at around 14 m, the deeper depths just for setting and retrieving the anchor. One other find of note was a single specimen of our Goniobranchus sp. 08 (Goniobranchus sp. 15 in NSS!-2).

Taxonomic Diversity:
Ten of the thirteen sighted species were nudibranchs, with 9 being dorids comprising 1 x phanerobranch (non-retractile gill), 1 x porostome (suctorial feeders  of the Phyllidiidae family), 7 x cryptobranchs (retractable gill – all belonging to the Chromodorididae family) and 1 was a cladobranch comprising 0 x aeolids, 0 x arminid and 1 x dendronotinid. A single head-shield slug, and 2 sacoglossans complete the species count. If diet is considered then 10 of the 13 species sighted are spongivores. 48 specimens in total were recorded.

Our Historical Data:
– This excursion brings the number of survey dives to 40 at this site since we commenced fully recording data here on 10/07/2010.
– 137 species have been recorded at this site.
– The most regularly recorded species at this site are: Doriprismatica atromarginata (98%), Phyllidiella pustulosa (96%), Thuridilla cf. splendens (83%) and Chromodoris elisabethina (78%).
– This is the first time we have recorded Goniobranchus sp. 08, Oxynoe jacksoni or Sagaminopteron psychedelicum at this site.
Aegires citrinus is a relatively rare sighting for us at this site; last seen by us here on 5th November 2010 (see Graph in Image Gallery below)
– In the report of our last survey at this site we reported on a possible seasonal pattern to the seasonal abundance of Doriprismatica atromarginata and Goniobranchus splendidus at this site, on this occasion you may note in the Graph below that there is a slight decline in the number of species and total organism count on these two dives. Not too much should be drawn from this as the decline is possibly explained by the amount of time spent searching the Caulpera looking for Oxynoe and Lobiger.
– This site last surveyed on 01/03/2023.
(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: 13

 

SPECIES LIST – ALPHABETICAL

Aegires citrinus 1/-
Bornella anguilla -/1
Cadlinella ornatissima -/1
Chromodoris elisabethina 8/- #78%
Chromodoris kuiteri 2/1
Doriprismatica atromarginata 4/8 #98%
Goniobranchus sp. 08 1/- +
Goniobranchus splendidus 1/-
Hypselodoris jacksoni -/5
Oxynoe jacksoni 1/- +
Phyllidiella pustulosa 4/3 #96%
Sagaminopteron psychedelicum -/1 +
Thuridilla cf. splendens 2/4 #83%

SPECIES GROUPED BY ORDER

Nudibranchia
Dorids
Phanerobranchs
Aegires citrinus 1/-
Cryptobranchs 
Cadlinella ornatissima -/1
Chromodoris elisabethina 8/-
Chromodoris kuiteri 2/1
Doriprismatica atromarginata 4/8
Goniobranchus sp. 08 1/-
Goniobranchus splendidus 1/-
Hypselodoris jacksoni -/5
Porostomes
Phyllidiella pustulosa 4/3

Cladobranchs
Aeolids

Arminids

Dendronotinids
Bornella anguilla -/1

Cephalaspidea
Sagaminopteron psychedelicum -/1 

Pteropoda

Sacoglossa
Oxynoe jacksoni 1/-
Thuridilla cf. splendens 2/4

Umbraculoidea

Pleurobranchoidea

Anaspidea

DIVE IMAGES GALLERY

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