Angels and sponges are key indicators of reef health

March 28, 2014 

A Rock Beauty finds both protection and food in the prolific sponge community on Molasses Reef.

TIM GROLLIMUND

Sometimes I have no clue what I’m going to write about. Some folks might say I have no clue when I do know what I am going to write about.  

Either way, there are times when things fall right in my lap, seemingly at the right time to be examined in the context of the larger picture. And of course to me, that larger picture is the health, vitality and sustainability of our reef tract.

I subscribe to an email distribution list composed primarily of scientists, educators and marine biology practitioners. I am in the deep end of the pool most of the time, with weights on, when I am wading through the entries in these emails.  

The other day I saw a post by one of our established Keys scientists, Dr. Joe Pawlik, the “sponge doctor.” You may recall a column I wrote a while back when he and his able graduate student crew conducted a mission in Aquarius Reef Base. You can see an ebook based on the column here: http://timgimages.com/PDF/ARB_Sponges.pdf

Dr. Pawlik has taken his sponge studies to a new level by examining how sponges are establishing themselves as the primary habitat-forming organisms on Caribbean coral reefs. Last week, I read an article about the sponge die-off in the bay from the blue-green algae bloom. It sparked my curiosity. On one end, we had a tremendous event that killed sponges by the thousands, and on the other side, and Caribbean-wide, we have a proliferation of sponges taking over reefs.  

One is short term — the algae bloom event, one is long term — the sponge encroachment at the expense of coral growth.

As for the reef, Dr. Pawlik’s study looked at two broad classifications of sponges. Some sponges have chemical defenses, and some do not. Species that do not have chemical defenses grow and reproduce at a faster rate than species with chemical defenses. These are termed “palatable” because they are subject to predation by angelfishes and some parrotfishes.  

The slower growing varieties taste bad due to the chemical defenses. You can read the article here: http://people.uncw.edu/pawlikj/2014PNASLoh.pdf

So what? Well, if the right balance in the reef ecosystem does not exist, and the predatory species are present in low numbers, there are not enough fish eating the fast growing sponges.  

These sponges reproduce, grow and recruit at an unchecked rate. That overgrowth in sponges is displacing coral recruitment and growth. The long term effects on the reef are being seen now. SpongeBob SquarePants is gobbling up more than his fair share reef real estate. To see Dr. Pawlik explain this, check out this award-winning video designed for school kids here: https://www.youtube.com/watch?v=ObpHfasn7_k&feature=youtu.be

In various places around the Caribbean, Dr. Pawlik and his team measured the effects of defended and non-defended sponges in marine parks protected from fishing and unprotected areas open to fishing, especially some that use fish-traps, which are illegal in the Keys. The results are very clear.

Their theory of greater proportions of palatable, faster-growing sponge species on overfished reefs was clearly supported. When the predators disappear, the fast-growing species overgrow a reef, to the detriment of the remaining coral.

In his study, chemically-defended sponges comprised up to 90 percent of sponge community where many predators were present. Alternatively, on overfished reefs, more than 50 percent of the sponge community was comprised of palatable sponges.  

The definition of overfished is a bit different from the way I view it here in the Keys.  Their overfished areas included the heavy use of fish traps, which indiscriminately take a wide variety of species, leaving only very small fish behind.

The bottom line is the presence, or non-presence, of sponge predators explained about one-third of the variation of sponge species composition in the study areas, and up to 95 percent when you compare specific places, like Martinique (overfished) with Bonaire and Curacao (protected). That is a large effect.

This has important implications for the health and vitality of coral reefs. While not all of the factors in Dr. Pawlik’s study are appropriate for the Keys, such as the use of fish traps in certain areas that decimated sponge predator species, it is important to see this in a context of the critical balance of marine ecosystems in general.

It truly is all connected, and unintended consequences of various pressures are real.

Will our reefs survive the pressures from all the different uses, natural occurrences and man-made interventions? I do not know the answer to that. I do believe that unless we change some of the things we do, the tipping point is near.  

Some argue the tipping point is passed, and it is a matter of incrementally slowing the decline where we can, with little chance of complete recovery.

It will be very interesting to see, later this year, how the Sanctuary Advisory Council moves forward once the Ecosystem Protection Working Group is finished. There is a lot riding on that horse. 

In fact, all of us are in the saddle, and I believe that if inappropriate spurs are chosen, we will head down the wrong trail at an accelerating pace. The last part of the ride will be the gallop over the cliff.

You have a say in this, and you can contribute to the process. Please do so.

Tim Grollimund is a freelance photographer and PADI divemaster based in Key Largo.  He can be reached at tim@timgimages.com. Tim is a member of the Florida Keys National Marine Sanctuary Advisory Council.  Opinions expressed by Tim are not the official views of the FKNMS.

 

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