Mysid Photos from Second Valley Dive

February 11, 2016 | Posted in: Crustaceans, Marine invertebrates

During our recent dive at Second Valley, David Muirhead took a couple of photos of what he thought were late larval planktonic phase southern rock lobsters. Below is a cropped version (by David) of one of his photos: –

Juv.Rock Lobster,ready to settle out of water column,Second Valley 6-2-16( Sea Life camera)DSM(cropped++)i099

?“Juv. Rock Lobster, ready to settle out of water column, Second Valley 6-2-16”?

(with bullseye in background)

He thought that they had swum inshore to get ready to settle on a rock reef (such as at Second Valley).

He sent one photo titled “Juv. Rock Lobster, ready to settle out of water column, Second Valley 6-2-16” off to some colleagues, asking “Am I right in my presumptive ID of late larval planktonic phase southern rock lobsters? If so, this was my first ever observation, in my decades diving SA waters, of the species at such a tiny size, which probably simply reflects my earlier lack of awareness of their probably frequent presence at such sites at similar times of year. But it is nice to speculate that, just maybe, they’ve not usually been in sufficient densities for me to notice their presence, until the gazetting of the Rapid Head Marine Park sanctuary zone. Because I do know that, despite only being accessible by boat, increasing numbers of recreational divers (including me, albeit not for at least 2 decades now!) have annually harvested the legal-sized lobsters that once were common in a quite small, localised ‘best diving section’-both in scenic terms and for snaring lobster-of Rapid Head’s near-shore rocky reef benthos.”

Mysids near shaded ledge wall Second Valley MLSSA dive(Sea Life camera)6-2-16;DSM(cr++)i100

Mysids near shaded ledge wall Second Valley

(Cropped by David Muirhead)

Our Patron, Scoresby Shepherd replied to David, saying “An interesting pic. But it doesn’t seem the right time of the year for puerulus larvae to come into the shallows. The eggs are laid and hatch around October, and then the phyllosome larvae are carried west by the prevailing SE winds and current for ~4+ months, and then return when the currents change and the Leeuwin Current flowing east + the NW winds bring them back along the SA coast where they (now at the puerulus stage) settle inshore, usually July to around October. I’ll check the above with our lobster biologist, Adrian Linnane, who published a paper on this, and found that the NW winds played a strong part in returning the larvae to SA coasts.”

Society member, Andrea Crowther also responded by saying, “When I showed this photo to Rachael (crustacean expert Rachael King), she thought they looked like Mysid shrimp*. But it is a bit hard to tell!”

* (Order Mysidacea)

Scoresby Shepherd then added, “I agree. When I re-examined the pic, and enlarged it, a distinguishing feature of mysids are the two flattened appendages projecting from the tail. See pics in Edgar’s book on “Australian Marine Life” (p.213). They usually swim in swarms of varying size on sand or sand/reef (see Shepherd/Edgar 2013 “Ecology of Australian Temperate Reefs” p. 168.” (mlssa 1075).

Mysids near shaded ledge wall Second Valley MLSSA dive(Sea Life camera)6-2-16;DSM(sl.cr)i100

Mysids near shaded ledge wall Second Valley

(Cropped by Steve Reynolds)

David’s reply to both Scoresby & Andrea was, “My provisional ID, based on your collective advice (and noting the uppermost pictures on pages 182-183 of Edgar’s revised edition) is of a mysid of some sort! And feasibly, or if I’m explicit, as a guess only, either one of these two species [despite their (then) known distributions being limited to Victoria & Tasmania, and Tasmania, respectively] Paramesodopsis rufa: I take this punt largely because it is ‘..extremely abundant on sand at the edge of reef’, with ‘Habitat: Moderately exposed reef, sand; 0-12 m depth’, and has a stronger resemblance to, and better size range match with the ones in my pics (notably with regards to ‘forked’ tail and overt rostrum) and with a known distribution (then) that includes Victoria not just Tasmania, so it would seem very likely to occur in eastern SA also. Mysidetes halope: I take this punt largely because of the habitat given by Edgar as ‘Exposed reef: 5-30 m depth’, and ‘..deep in the back of seacaves..’. I’d favour P.rufa (but again, wild guessing . . . .).”

Mysids near shaded ledge wall Second Valley MLSSA dive(Sea Life camera)6-2-017

Mysids near shaded ledge wall Second Valley

 According to page 168 of “Ecology of Australian Temperate Reefs” edited by Scoresby Shepherd & Graham Edgar (2013), (mlssa 1075), “Mysids are highly mobile, shrimp-like crustaceans.” According to “Australian Marine Life” by Graham Edgar (revised edition 2000), (mlssa 1053), “Mysids are generally found in swarms living just above the seabed and are often mistaken by divers for schools of juvenile fish.”

According to the web page found at https://en.wikipedia.org/wiki/Crustacean_larvae#Decapoda , “The larvae of the Achelata (slipper lobsters and spiny lobsters) are unlike any other crustacean larvae. The larvae are known as phyllosoma, after the genus Phyllosoma erected by William Elford Leach in 1817. They are flattened and transparent, with long legs and eyes on long eyestalks. After passing through 8–10 phyllosoma stages, the larva undergoes “the most profound transformation at a single moult in the Decapoda”, when it develops into the so-called puerulus stage, which is an immature form resembling the adult animal.”

Scoresby Shepherd sent us this photo of a puerulus larva: –

Rock Lobster Puerulus

Steve Reynolds is the current President of MLSSA and is a long-standing member of the Society. Steve is a keen diver, underwater explorer, photographer and is chief author of the Society’s extensive back catalogue of newsletters and journals.

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