[Coral-List] Diadema and sea level rise

[William Precht]

Gene,

I think these are important observations. When I started grad school at the
University of Miami in 1987, the Diadema was still fresh in everyone’s
memories. This is the same time I started hanging out with you and Harold.
One story I remember someone told me was that the hog fish in the upper
Keys especially off of Key Largo moved around and fairly large schools like
bonefish; not just as individuals or pairs.

In the fall of 1987 I went down to Belize with Bob Ginsburg and we were
being transported around the reef by local fish captains and guides. I
remember having a conversation with one of the older fisherman , and he
also told stories of large schools of Hogfish that were abundant before
1984, and by the fall of 87 had essentially disappeared. He thought it was
because all the Diadema were gone and now all the hog fish had to forage on
other stuff. Again, while this may be anecdotal , there may be more reality
to the story than fiction. It would be nice to know if others who were
working in the Caribbean at the same time made similar observations.

Bill

PS. In 1978 on one of my first reef dives at discovery Bay marine
laboratory in Jamaica. There was a queen triggerfish that was swimming
around with black urchin spines sticking out from around its face. It
reminded me of a dog that I just got into a fight with a porcupine.

On Mon, May 15, 2023 at 8:51 AM Eugene Shinn via Coral-List <
coral-list at coral.aoml.noaa.gov> wrote:

>   Dear readers, Here are some observations that may relate to the
> Diadema situation. When I began spearfishing in the Florida Keys in the
> late 1950s (I was a biology  student at University of Miami) One of my
> prime targets was Hog Fish, sold in markets as Hog Snapper. All the
> large Hog Fish had a dozen or more purple dots on their forehead and
> around mouth area. When I gutted them before selling to markets and
> restaurants their most common stomach content were bits of urchin tests.
> One day I came upon a Hog fish carefully removing the spines from a
> Diadema. I just watched and it became clear what caused the purple dots
> on the fishes head area. When almost all the spines had been removed the
> fish, known for its large expandable mouth swallowed the test in one
> gulp. After the Caribbean-wide Diadema die-off in 1983, the purple dots
> on the fish disappeared. It became obvious why the dots were missing.
> Their favorite meals were gone. Curiously I have never seen this noted
> in any publications.
>        Another observation that Harold Hudson and I noted back then was
> that the largest fattest Hog fish were located off the upper Keys,
> especially off Elliot Key and Key largo. These were the areas of most
> abundant live coral and lush Turtle grass. He had noted that off the
> middle keys in the vicinity of Grassy Key, Long Key, and opposite the 7
> mile bridge area, the Hog Fish were generally smaller and thinner and
> few had the purple dots.  The areas off the middle keys also had less
> live coral, large sandy areas and noticeably less Turtle grass. and also
> fewer Diadema. Farther southward, including off Key West, the Hog fish
> were a little larger but seldom as large as those off the upper Keys. In
> later years working with Robert N. Ginsburg we attributed the lack of
> lush reefs and sparse Turtle grass off the middle keys to runoff from
> Florida Bay (especially off 7 mile bridge area) during low tide. We also
> noted that the water depth in the middle and lower keys is deeper than
> off the upper keys. We were not the first to notice this. During the
> Holocene sea level rise the middle and lower keys were the first to to
> be affected by the more saline bay water than areas off Key largo were
> there are fewer tidal channels. We determined that outflow of bay water
> retarded or prevented development of coral growth. We published these
> observation several times in the past and attributed the deeper depth to
> the south to subsidence. Subsidence is suggested by several
> observations. The Pleistocene oolite limestone under Miami is 20 or more
> feet above sea level while the same age oolite under Key West is only
> about 10 ft above sea level. There are other evidences of differential
> subsidence toward the south as well. Evidences of subsidence and
> distribution of coral reefs are detailed in,  "Geology of the Florida
> Keys" 2018, Shinn and Lidz, University press of Florida. The book is
> available on Amazon and at Fossil Reef State Park on Windley Key.
> Whether the observations have significance to the recent Diadema die-off
> I do not know. Gene
>
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