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Dive Report

01-02-2022 Trench

Feb 2, 2022

DAY/DATE

Tuesday

01/02/2022

SITE/S

Trench
Inner Gneerings

 

PARTICIPANTS

Terry, David

 

TYPE

Subtidal

 

MODE

Boat Dives

 

VESSEL

Rebel II

 

DIVE

1

2

SITE/S

Trench

Trench

SPECIES #

11

10

DURATION

71 Min

66 Min

DEPTH/RANGE

15-20 m

15-20 m

TEMP.

27 C

27 C

VIS.

5 m

5 m

SURGE

Heavy

Heavy

CURRENT

Nil

Nil

COMMENTS & OBSERVATIONS

We knew the surge on the bottom would be heavy out on the Gneering Shoals but it had been over a month since the delights of offshore diving were sampled and we were itching to go. We chose the Trench for this excursion – plenty of depth to try and ameliorate the strength of the surge but close enough to permit a quick trip home should the predicted increase in wind strength arrive early. Due to that surge, combined with recent run-off, the close proximity of the Trench reduced visibility to 5 metres. Nevertheless we were keen and even went back in for a second round of punishment. Although the species count was expected to be low we were compensated by finding a pair of Thuridilla cf. splendens mating and an unusual colour form of Sagaminopteron ornatum for the records.

Taxonomic Diversity:
13 of the 15 species sighted were nudibranchs, with 11 being dorids (3/4 the overall total) comprising 1 x phanerobranch (non-retractile gill), 5 x porostomes (suctorial feeders and all Phyllidiidae family) and 5 x cryptobranchs (retractable gill) (all belonging to the Chromodorididae family). The balance of the nudibranchs were made up of: 2 x dendronotids. The other 2 non-nudibranch sea slug species comprised 1 x sacoglossan and 1 x cephalaspidean. If diet is considered then 11 of the 15 species sighted are spongivores.

Our Historical Data:
-This excursion brings the survey number to 21 at this site since we commenced fully recording data here on 27/06/2011.
– 105 species have been recorded at this site.
– All of the species recorded on these two dives have been recorded at this site previously, and included our most regularly recorded species.
– Our most commonly recorded species are: Chromodoris elisabethina (95%), Doriprismatica atromarginata (95%), Phyllidia pustulosa (95%) and Thuridilla cf. splendens (81%).
Sagaminopteron ornatum has only been recorded once previously on surveys at this site – Tritoniopsis elegans was recorded twice previously but the previous records come from back to back dives on the same day.
– Both the number of species, and number of opisthobranch organisms recorded on each survey have been dropping since a high in October, 2018, but the numbers of Chromodoris elisabethina, Phyllidiella pustulosa and Doriprismatica atromarginata recorded on each survey have been increasing. The graph in the image gallery demonstrates this phenomenon for Chromodoris elisabethina.
– This site last surveyed on 30/08/2021

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

TOTAL SPECIES SIGHTED: 15

 

SPECIES LIST – ALPHABETICAL

Bornella anguilla -/1
Chromodoris elisabethina 9/3 #95%
Doriprismatica atromarginata 7/14 #95%
Glossodoris vespa -/1
Goniobranchus splendidus 1/-
Hypselodoris bullockii 1/2
Phyllidia elegans 1/-
Phyllidia picta -/2
Phyllidia varicosa 1/-
Phyllidiella lizae 1/1
Phyllidiella pustulosa 11/5 #95%
Roboastra luteolineata 1/-
Sagaminopteron ornatum -/1
Thuridilla cf. splendens 2/2 #81%
Tritoniopsis elegans 1/-

SPECIES GROUPED BY ORDER

Nudibranchia
Bornella anguilla -/1
Chromodoris elisabethina 9/3 
Doriprismatica atromarginata 7/14 
Glossodoris vespa -/1
Goniobranchus splendidus 1/-
Hypselodoris bullockii 1/2
Phyllidia elegans 1/-
Phyllidia picta -/2
Phyllidia varicosa 1/-
Phyllidiella lizae 1/1
Phyllidiella pustulosa 11/5 
Roboastra luteolineata 1/-
Tritoniopsis elegans 1/-

Cephalaspidea
Sagaminopteron ornatum -/1

Sacoglossa
Thuridilla cf. splendens 2/2 

Umbraculoidea

Pleurobranchoidea

Anaspidea

DIVE IMAGES GALLERY

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