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Dive Reports

26-06-2024 East Boulders – OWI

DAY/DATE

Wednesday

26/06/2024

SITE/S

East Boulders
Mudjimba Is 

 

PARTICIPANTS

David

 

TYPE

Subtidal

 

MODE

Boat Dives

 

VESSEL

Li’l Mischief

 

DIVE

1

2

SITE/S

East Boulders

East Boulders

SPECIES #

10

13

DURATION

71 Min

69 Min

DEPTH/RANGE

10-13 m

10-13 m

TEMP.

21 C

21 C

VIS.

15+ m

15+ m

SURGE

Slight

Slight

CURRENT

Nil

Nil

COMMENTS & OBSERVATIONS

Li’l Mischief has been sitting on its trailer for 10 weeks. Weather, illness and other commitments have all conspired to prevent a launch. Finally, “all the planets aligned” and I headed up to Mudjimba Island for another pair of Sea Slug Surveys. East Boulders was selected as it is an exposed shallow site only suitable when the swell is slight. Surface conditions were almost perfect. I had the feeling I should have seen more species but perhaps the site’s shallow and exposed position has been affected by the larger swells of the past month thus impacting on the species diversity currently in residence. Mostly only the usual subjects to record but I was most fortunate in documenting the feeding process of Hypselodoris zephyra whereby it repeatedly extended its colourful buccal mass in order to place the radula upon the sponge it was eating.

Taxonomic Diversity:
Sixteen of the sighted species were nudibranchs, with 14 being dorids comprising 2 x phanerobranchs (non-retractile gill), 4 x porostomes (suctorial feeders – all of the Phyllidiidae family), 8 x cryptobranchs (retractable gill – all 8 belonging to the Chromodorididae family) and 2 were cladobranchs comprising 2 x aeolids, 0 x arminids and 0 x dendronotinids. A single sacoglossan (sap-suckers) and a single cephalaspidean (headshield slugs) complete the species count. If diet is considered then 14 of the 18 species sighted are spongivores. 36 specimens in total were recorded.

Our Historical Data:
– This excursion brings the number of survey dives to 15 at East Boulders since we commenced fully recording data here on 18/11/2011.
– 101 species have been recorded at this site.
– Our most commonly recorded species at East Boulders are Doriprismatica atromarginata (93%), Goniobranchus splendidus (97%) Hypselodoris jacksoni (87%) and Phyllidiella pustulosa (87%).
– We are regularly seeing species here that we have not recorded here previously and on these dives, leaving aside the phyllidiids which we still have under review, Bulbaeolidia alba and Glossodoris vespa were recorded by us for the first time.
– For anyone looking closely enough at the historical data who notices that the total species count at this site increased from 97 to 101 on these dives, the other two species potentially recorded for the first time were the Phyllidiella cf. pustulosa and the juvenile Phyllidiella granulata.
– Although there is some fluctuation, the decrease in the abundance and diversity of nudibranchs  recorded by us at this site appears to be trending downward. Other than an actual drop in numbers, there are a number of variables that could be impacting on this observation, including the number of surveyors, weather leading up to the survey, and length of the dives. We will keep an eye on the trend to try to determine whether it continues, which would suggest that there is a drop in numbers for some reason. See graph below in image gallery, plotting species against actual total specimens across all the surveys.
– Our last survey at East Boulders was on 01/04/2023
(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: 18

 

SPECIES LIST – ALPHABETICAL

Aegires citrinus 1/-
Bulbaeolidia alba 1/1 +
Chromodoris kuiteri -/1
Doriprismatica atromarginata -/4 #93%
Glossodoris rufomarginata 1/-
Glossodoris vespa 1/- +
Goniobranchus splendidus 3/1 #97%
Gymnodoris sp. 30 -/1
Hypselodoris jacksoni 2/- #87%
Hypselodoris obscura 1/1
Hypselodoris zephyra -/2
Phyllidiella cf. pustulosa 1/- +
Phyllidiella granulata (Juv) -/1 +
Phyllidiella lizae 1/1
Phyllidiella pustulosa -/2 #87%
Pteraeolidia semperi -/2
Sagaminopteron ornatum -/4
Thuridilla cf. splendens 1/2

SPECIES GROUPED BY ORDER

Nudibranchia
Dorids
Phanerobranchs
Aegires citrinus -/1
Gymnodoris sp. 30 -/1
Cryptobranchs
Chromodoris kuiteri -/1
Doriprismatica atromarginata -/4
Glossodoris rufomarginata 1/-
Glossodoris vespa 1/-
Goniobranchus splendidus 3/1
Hypselodoris jacksoni 2/-
Hypselodoris obscura 1/1
Hypselodoris zephyra -/2
Porostomes
Phyllidiella cf. pustulosa 1/-
Phyllidiella granulata (Juv) -/1
Phyllidiella lizae 1/1
Phyllidiella pustulosa -/2

Cladobranchs
Aeolids
Bulbaeolidia alba 1/1
Pteraeolidia semperi -/2

Arminids

Dendronotinids

Cephalaspidea
Sagaminopteron ornatum -/4

Pteropoda

Sacoglossa
Thuridilla cf. splendens 1/2

Umbraculoidea

Pleurobranchoidea

Anaspidea

DIVE IMAGES GALLERY

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