steve_reynolds's Identifications

This is a living hammer oyster which is being used by the purple urchin as a form of defense against predators. (I've commented on this *behavior by purple urchins at some length in earlier submissions using 'Purple Urchin' as the header species)
Via snorkel in depth ~3-4 m.
*[I'm not sure if I included anything about whether this is symbiotic.Perhaps the live bivalves benefit as filter feeders by being higher in the water column, and/or gain some protection from their own predators through being so close to the urchin's formidable array of spines?]

I've tried what I'd believed was the old taxonomic label Electroma georgiana but no go.
Growing rapidly on cork-weed Scaberia aghardii.

NOTE:
ALSO in image are a few Zyzzyzus spongicolus (Hydrozoa). These small polyps to 10mm height are "Found always on sponge, on jetty piles and shaded reef..."( Karen Gowlett-Holmes' A field guide to the marine invertebrates of South Australia 2008 p30).

On scuba @ Dunny Block reef site. Most ledges and caves there have these little blue balls on their floors, generally towards the rear or in the shadiest sections.
I think they are sponges with symbiotic cyanobacteria but I'm not sure.They can look almost black from afar but look deep blue up close even in ambient light. (I have not noticed them on deeper reefs but that may be simply because everything looks green-blue at depths beyond about 10m)

Not a major component of the algae for this jetty, with some modest amounts at the shoreward end between entry steps and shoreline, then minimal presence further out except near the top of some piles. FWIW I saw very few larger wrasse eg male Brownspotted and Bluethroat, no Western Blue Groper of any age (not even any small juveniles), but nor did I notice large numbers of Western Pacific Purple Urchins or similar kelp eating spiny Urchin species. Unsurprisingly I saw no Southern Rock Lobster either. No Australasian Snapper either, which are currently bordering on being functionally extinct in GSV and Spencer Gulf, as is well documented by Pirsa Sardi and Fisheries management heads in SA. Urchin barrens already exist not far from this jetty on each side, and I bet they are anthropogenic, while acknowledging the dismal lack of scientific evidence for this claim. Personally I have dived the jetty (and much less often surrounding benthic habitat) for more than 50 years, and I am certain the kelp was much denser, healthier and ubiquitous 5 decades ago.

Adult to L of an adult Magpie Perch in 1st photo, and the other photos (which are not in temporal order) are all of the same individual, I'm fairly sure. Seen near end of this MLSSA dive .
Poor visibility hampered imaging but more importantly this fish was fast and flighty, surprisingly so given it's relatively low-risk location ie outgoing weak ('dodge') tide, and the relaxed generally approachable behaviour of many of the more common reef fishes at this site.
It zoomed about in depths from ~4m to ~7.5m, stopping quite often but only briefly (perhaps seeking a clean from the many WCCs and other host cleaner fish observed there).

Medium size adult, at a Western Cleaner Clingfish (WCC) cleaning station. Hosts not obvious in image 1 but @ least 3 are present on zooming per my later comment below, and image 2 (added later) more clearly shows the WCC on client's R flank.

[**IMPORTANT NOTE: The many small red tadpole-shaped critters on head are almost certainly parasites, not juvenile clingfish. I've photographic records of at least one other Harlequin Fish with a similar number of little red tadpole-like animals clinging to the opercula, and would love to know what they are. If they're parasites, they're possibly too large for WCCs to eat thus remove (*Although in image 2 one might postulate that the adult WCC on the operculum is showing interest in the wee red critters; it is close, and facing forwards looking at them. Its even possible that all those little red critters normally live out of our sight inside the gills but have been chased out onto the Harlequin's head by the WCCs...unlikely, but who knows?! ).
Which begs more questions: are they some sort of equivalent to remoras on rays and sharks, and what phylum are they in? Unfortunately the 2 other photo records I've located at time of this edit (01-07-2021) are both old slide scans. I've no other dSLR pics of Harlequins with these 'red tadpoles' on their heads, so I can't zoom in enough to determine even major group taxonomy eg phylum]

Might be same one submitted earlier this morning but hard to say and there were lots of females throughout the dive.
Opinion piece:- Again worth noting however that males were few and far between, despite this reef having been protected from spearfishing for many decades, and being protected from recreational (and occupational) fishing since circa 2013, perhaps earlier. One wonders if even the permitted recreational line fishing from the jetty (except for the outermost few metres which is reserved for diving snorkelling and swimming access) continues to deplete the male population.Being a haremic territorial species, even though most jetty based fishers' baited hooks don't reach more than about 20 or 30 metres along either side of the outer jetty, SOME DO.

Eg when salmon school inside the reef during rough weather; another example is the use of floating tackle, which must still capture the occasional wrasse, and I have occasionally seen baited float tackle, carried by wind and tide, dangling overhead very close to the reef platform, at distances of several hundred metres either side of the outer jetty.
As research has clearly shown, male wrasse get first bite, a privilege of haremic reproductive strategies. So wherever humans have fishing access (and the larger wrasse species are legitimate bycatch here, with bag limits but no requirement for return to water, the only exception being Western Blue Groper, the juveniles of which most recreational fishers struggle to identify anyway), wrasse populations are highly vulnerable and likely to be severely impacted.
Common Kelp is almost absent from some sections of the shallow subtidal parts of the platform reef, but thriving in others. And its patchily absent (in places replaced by fucoid canopy browns, but some virtually canopy free areas occur) from some sections of the deepest 1-2 metres, where rock meets sand/silt/rubble.
The mid to upper depth part of the inshore side of the platform reef (north of jetty),however, happily retains a quite good Common Kelp cover.
My above description is relevant because when we dived there 5 decades ago we saw dense Kelp entirely clothing the reef, from shallowest subtidal down to the reef/sand interface.
Many things have happened in the past 5 decades, some good and some bad for inshore reefs (eg improving the historically horrible sewerage outflows along the Adelaide coast was good, but uncontrolled coastal residential subdivision was bad),so I can't pretend to know which factors are most responsible for this Kelp loss.
But I have little doubt that Western Pacific Purple Urchins are one important current factor limiting regrowth of full Kelp cover.
This Urchin urgently needs rigorous local baseline surveillance, ongoing monitoring and serious research funding at a local level.
Wrasse need full protection regardless (it can be done very quickly and easily with the stroke of a Ministerial pen, but voters will retaliate).
Because of their key roles in keeping temperate reefs healthy, which includes their ability-as mature adults-to control Urchin population densities.
Much speculation and anecdote above, obviously, and I don't know why some of the shallowest subtidal Kelp is suffering.
Patchily only.
Perhaps seasonal eg storms together with nutrient related heavy epibiotic loads?
I doubt Urchins would be able to target the shallowest subtidal Kelp unless they get prolonged calm weather, because I gather that they avoid this zone due risk of repeated traumatic loss of spines via wave action.

The End

Small adult foraging but again very wary (perhaps because they have to pass through the heavily spearfished area separating the Rapid Head Green Sanctuary Zone from the jetties, in order to access the food associated with the old jetty's benthic habitat). If so, a good argument for extending the GSZ to include the jetties. Some spearos use the new jetty's outer platform for easy access to the area described above, which means that they are carrying spears and spearguns along the jetty, popular with recreational fishers and eco divers and snorkellers. On occasion these spearos will return to the new jetty platform with their speared catch, rather than using the more difficult exit via the rocky shoreline.
Declaration of conflict of interest:- I'm an eco diver who frequently uses the jetties.

NB: The kingfish is already subject in an earlier submission from same dive, and in image 2 the background luderick is probably the same individual also subject in an earlier submission from same dive.
FWIW the kingfish behaved as a client, loitering at this particular site under the T Junction, where WCCs regularly provide host services to a range of bony fish including old wife, magpie perch, silver trevally, and various leatherjackets and wrasses.
It appeared desperate for a clean, having separated from the main kingfish school, and virtually hanging motionless, repeatedly circling between 'stops ', above the WCC sponge stations that are below the main old wife aggregation.

One or two juveniles at about 6-7m depth under outer jetty and near inner reef wall.
There were dozens of these, all within a small area of roughly 6 by 6 m square.
This is one of a number of smaller inshore reef and surrounding habitat-associated bony fish species that appear to be becoming more common almost year by year here in SA - particularly in GSV but I think also in almost all parts of coastal SA .
( Anecdotally including various gobies, blennies, triple-fins, weed fishes, cowfishes, and some pipefishes, among others)

Adult pair, that were reluctant to leave this bit of jetty pile despite being about 2.5m above the base. I wonder if the small juvenile Western Talma to L of uppermost subject was the reason. There are old reports of SA divers seeing juvenile talmas cleaning bits off certain client fish species, but there seems to have been little if any enduring acceptance that juv Western Talmas really do -opportunistically- act as host cleaners to bigger reef fish clients.
This photo while suggestive is obviously not proof, but I'll include it in the relevant MLSSA project just in case.
I've been looking for confirmation of this role for juv Western Talmas for several decades, but still don't have contact images or video as proof. However, I've often seen small juveniles loitering and posing repeatedly at sites that appear as good makeshift stations. Locations that are safe but easily visible to potential clients. And whether relevant or coincidence, juveniles often inhabit the same ledges and nooks used by juvenile Moonlighters, which opportunistically host a wide range of demersal fish client taxa.
I could speculate further, by noting that a host's head, snout, mouth, dental morphologies and dietary preferences (ie not just size discrepancy cw clients, which are, AFAIK, always bigger than any given host) are critical determinants of what types of parasite, fungi, bacteria, skin mucus, indeed any edible external debris are accessible and targeted by the host.
WRT some of the better-known SA inshore marine cleaner host fishes (WCCs, juvenile Moonlighters, juvenile Blackspotted Wrasses are the 3 best examples) one can see clear differences in head/snout/mouth/dental morphology. Looking at juvenile Moonlighters and juvenile Western Talmas, the initial impression is that these 2 species have very similar front-end attributes. But there are potentially important, albeit more subtle differences. E.G. the more truncate, slender mouth of a juvenile Western Talma.

A large school of adults occupied most of the T-junction, from mid to upper water column, for the duration of my time spent there.
(There were a few similar-sized yellowtail kingfish among them, which were more difficult to image being more wary, but see next submission).