[Coral-List] Diadema and sea level rise
Eugene Shinn
eugeneshinn at mail.usf.edu
Sat May 20 21:37:50 UTC 2023
Thanks Mark, I could have said more. I can say I probably sold several
hundreds of pounds of those fish back when I was a poor hungry student
father of 3 young boys back when I had most of the keys reefs to myself.
Hog fish were often in schools of 25 o30 in those days. Some of it was
before polyethylene line and Styrofoam floats. Boy did that change. Gene
On 5/17/23 1:59 AM, Mark Tupper wrote:
> Hi Gene, Bill, and list,
>
> These are some fascinating observations on hogfish, and they match
> very well with what I observed living in the Exuma Cays in the late
> 1980s. Within the Exuma Cays Land & Sea Park, hogfish were numerous
> and large. Outside the park, they were less abundant and smaller.
>
> The largest fish were more colourful, with yellow pectoral fins and
> intense purple and yellow vermicular markings on their face that are
> reminiscent of the "Maori tattoo" markings on large humphead wrasse.
> Those more colourful fish were males. Hogfish are protogynous
> hermaphrodites, meaning they are all born female, and some proportion
> of the population will change to male, usually when they reach a
> certain length. However, the sex change can occur at a smaller size if
> there are insufficient males in the population, i.e. if the sex ratio
> is skewed towards females.
>
> There are typically two reasons that hogfish sex ratio could be skewed
> towards female. First, large males could be preferentially targeted by
> fisheries (almost certainly the case throughout the hogfish's range).
> Second, a slow growth rate, perhaps caused by suboptimal nutrition,
> would mean that fewer fish are reaching the size at which sex change
> normally occurs.
>
> The population response to both of these pressures is early maturation
> and sex change at a smaller size, to ensure that sufficient males are
> available to fertilise eggs and keep the population viable. I think
> this is what Gene witnessed in the Keys - a double hit of fishing
> pressure and the loss of a major food item (Diadema) causing hogfish
> to mature and change sex at smaller sizes. That would explain the
> small, skinny males with colourful faces.
>
> Cheers,
> Mark
>
>
> On Tue, 16 May 2023, 23:41 Eugene Shinn via Coral-List,
> <coral-list at coral.aoml.noaa.gov> wrote:
>
> Bill, Thanks for the conformation. I suspect there are few who
> made the
> same observation that Harold and I made. There is a little more
> that we
> also noticed. When a Hog fish is mature coloration around the head
> changes. It is very noticeable. Many of the skinny Hog fish in the
> middle keys also had the color change indicating maturity but they
> were
> noticeably smaller. I assume it was diet and reduced population of
> Diadema even before the 1983 Caribbean-Wide die-off.
>
> And yes, the schools of these fish off Key largo etc were larger than
> elsewhere in the Keys. In addition Studies of the composition of reef
> sand showed middle keys carbonate reef sand was different than
> elsewhere. Most noticeable was reduced numbers of coral fragments. in
> the sand samples. Bob Ginsburg had noted the change in his
> dissertation
> work in the early 1950s, Using a larger number of samples Barbara
> Lidz,
> confirmed his observation in the early 1980s. Gene
>
>
> On 5/15/23 9:29 AM, William Precht wrote:
>
> > 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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