TAKING A CLOSER LOOK: ROCK POOLS ON ABACO


Rock Pool, Abaco 2

TAKING A CLOSER LOOK: ROCK POOLS ON ABACO

Here’s a promising-looking rocky outcrop a short distance south of Crossing Rocks. The action of the sea over centuries has eroded and pitted it – ideal for the formation of pools in which marine life can thrive.Rock Pool, Abaco 1

Time to clamber up to see if the theory holds good… the prospects are encouraging. There are certainly plenty of sea urchins here.Rock Pool, Abaco 4

Let’s zoom in on the nearest pool. There are clearly 2 different-coloured sea urchins here, but I’m not sure if that’s an age thing or a species thing. Rock Pool, Abaco 6

Apart from the sea urchins, there are some shells and other things that need a closer look…Rock Pool, Abaco 5

At the bottom of these photos, you can see that a zebra-marked nerite is quite happy to share a hole with an urchin. There are two brownish accretions on or in the rock. My tentative suggestion is that these are the shells of some sort of worm, perhaps petaloconchus.

UPDATE Rick Guest helpfully comments “Yes, it’s quite the invertebrate hotel mostly due to the urchin’s talent for scouring out protective “rooms”. Of interest is the Magpie shell (Livona pica) in frames 4 and 5. The rather ubiquitous Livona’s very thick shell, (Up to 5″ diameter) and ability to withstand most attempts at removal by predators, including Homo sapiens, assures their continued presence on littoral shore lines. They are edible, but not particular tasty to my palet. All these “Condo” residents “party” at night and will even leave the rock in search of food and perhaps romance, so a flash pic of the condo at night would be an interesting contrast to a daylight shot”.ROCK POOLS, ABACO 11

In a snug little cave (top right) just above the water-level of the pool is a primitive-looking chiton, a species that has been around for millions of years. Below, there’s a clearer image of one from a different pool. These creatures always remind me of school projects on prehistoric trilobites.Rock Pool, Abaco 7Rock Pool, Abaco 10

The rough rocky surfaces close to the pool are covered in shells. The stripey nerites are small, the grey shells really are miniature.  They are mostly littorines/ periwinkles and perhaps ceriths, I think.Rock Pool, Abaco 9Rock Pool, Abaco 12

Close-up views of nerites showing their distinctive markings and spiralsRock Pool, Abaco 13Rock Pool, Abaco 14

ABACO BEACHCOMBING: KASIA IS BACK… WITH ANOTHER MYSTERY OBJECT


Kasia has returned to grace the blog with treasures from her Abaco beach-combing from the Delphi Club and further afield. Expect more shells, more sea glass… and more mystery objects. We have already had part of a RAY’S PALATE and a PACIFIC ANGARIA SHELL  that had somehow arrived on the shores of Abaco. There’s a long thin WHITE BONE, as yet unidentified (no suggestions yet). And now this extraordinary item… 

To which my answer is “not the faintest idea”. My guesses are (1) a fossilised vertebra of some medium-sized creature (2) a fossilised ‘soft’ rock that worms have been at (but why only on one side?) (3) a bread roll that went disastrously wrong in the baking…

All suggestions welcome, preferably via the COMMENT box (so others can view them); or to rollingharbour.delphiATgmail.com (spam guard: convert AT to @)

STOP PRESS Mystery quickly solved, thanks to Colin Redfern who says “This is part of the remains of a colony of Petaloconchus worm-shells (molluscs). They attach to rock or coral, and the colonies can be quite large.”  Colin’s website includes some examples from his archive, one chunk being very similar to Kasia’s 

And here’s another chunk, top and bottom view Photos courtesy of James St. John (Geology, Ohio State University at Newark)
…and here is the worm that makes the vermi-accretion or whatever the term is