Deep Reef Discovery

Transcribed by Lucaya Luckey-Bethany.
Based on the interview with Dr. Albert Hine.


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Al Hine: While taking a group of students out on a boat, we had free ship time to do other things.  We said, “Let’s just over there.  The map shows some ‘funny bumps’ on the sea floor.  Let’s check out these ‘funny bumps’”.  And that’s all it was – no great revelation.  It was just “Let’s go look, let’s go look at these ‘funny bumps’”.  Its discovery was pretty much fortuitous and serendipitous.  We really did not know what was there.

I became curious about what was out there, and through time, discovered a very deep reef that was healthy, alive, and in deep water.  It was in 200 ft (between 60-70 meters) of water.  That’s an attention grabber!!  Most coral reefs are in shallow water because they require light.  But here is an extremely deep reef; we think the “deepest reef in the United States”.

These “funny bumps” were actually a paleo-shoreline, a shoreline that formed when the sea level was much lower and became lithified (turned to rock).  These shorelines were made of carbonate sand.  Carbonate sand grains cement together forming sedimentary rock (limestone), which means it is resistant to erosion.  These rocks are more resistant to beach erosion than the sand grains are.  Most shorelines in the U.S. are composed of quartz sand grains, which do not cement and thus are easily eroded by waves and sea-level rise.

So, here we had a situation where a shoreline could be preserved even when the sea level continued to rise and overtop it.  We had a preserved barrier island shoreline underwater.  You also had a hard substrate, which is a primary ingredient for coral reef development.

Corals generally don’t form in mud or sand.  They form on a hard substrate.  After settling on a hard substrate, coral larvae start to calcify and form coral skeletons.  This hard substrate is needed for this process.  Hard substrate is ingredient #1.

The second ingredients are clear water and warm water.  They were not present immediately after drowning – the sea level continued to rise as we came out of the last glaciation, so water got deeper and deeper.  But as it got deeper and deeper, the Gulf of Mexico was warming up.  That produced the warm water.

The corals are animals that depend on sunlight.  They grow algae, called zooxanthellae, on which they feed.  In other words, they basically farm their own food.  These zooxanthellae are light dependent.  They are also filter feeders.  There are light independent corals, too, but most coral reefs that people scuba dive on are light dependent.

So how do you get this light at depth?  Well, the light came in where you had a filament of very clear water called the Loop Current.  It’s called oligotrophic water.  This water is nutrient-free.  Now nutrient-rich water is not good for reefs because the nutrients stimulate competing organisms and also diminish the light.  Nutrients are good for other things, but not for coral reefs.  In summary, the Loop Current came in, thus providing the clear water needed for the sunlight to get through and causing it to grow.

The coral started to grow late in the development.  That’s a different wrinkle.  As soon as the barrier island was flooded, why didn’t the coral reef community come right in and occupy the substrate?  We don’t know the exact answer, but the working hypothesis is that the water was too cool.  I would say it was more temperature related and it really couldn’t produce coral reefs.  Corals, themselves, are temperature sensitive, so that didn’t happen until (I’m just guessing) 8 or 10 thousand years ago.  I guess that the reef started to form when the water was relatively deep – not when it was shallow – and it persists today.

INTERVIEWER:  When you say “relatively deep”, what range…

AH:  Oh, I would guess 30 meters or something like that.  As a matter of fact, pictures show that the morphological features of the barrier island are distinct.  You can see old beach ridges and old tidal inlets.  These are morphological features you can see on today’s barrier islands.

INTERVIEWER:  And when you found it, it was 200…?

AH:  200 feet down, yeah.

If a healthy reef had come in and built up, it would have buried all those features and you never would have seen them.  It would have covered them up.

Here’s a question you can ask:  “If this is a reef, how come you can still see the barrier island features?”  See if the students can figure that one out.  That’s a little tough one because you have to know something about reefs.

If the reefs grew up, they would become thick and would completely mask the beach ridges.  It would be like going to a line of barrier islands and covering it with 10 to 20 feet of cement.  You would bury all the morphological features.  If it were a thick, healthy, young reef, it would appear quite differently than it does now.  Here the reef is very thin.  It’s just a veneer on top of this old barrier island.

INTERVIEWER:  So if it’s thin, it is relatively young in terms of reef growth?

AH:  Yeah, young or slow growing, either one of the two.  Probably slow growing.  We really don’t know for sure.  This is a form of ongoing research.  You can start by answering this question:

“When did the reef come in?”

I’m guessing about 10,000 years ago, 12,000 years ago, but that’s just a guess.  We don’t know.  It’s a working hypothesis.  If the reef is about 10,000 years old and only about a meter thick, that’s pretty slow growth.  So it’s a living reef, but slow-growing because it is in deeper water.  The light is now about 1% of what it is on the surface.  You can see down there, but it’s dark.  However, there’s enough light for the corals to grow.  So it could be in its terminal stages.

It doesn’t look that way, but it could be just “holding on by its fingernails” right now, or, it could be perfectly well adjusted.  But if sea level cam up another 10 meters, there’d be enough water to put it into enough darkness and that would be the end of it.  A few things came together to create this thing:  (1) you have the hard substrate; (2) you have to have the right water column and parameters, temperature and light, lack of turbidity and lack of nutrients.  Those things can change and that reef, in time, would go away.  But what we think is interesting is that you can go down to the shallow reefs in 5 meters of water and they’re dying.  They’re unhealthy.

The reefs in the Florida Keys, for example, are stressed.  No question about it.  This reef, on the other hand, doesn’t seem to be stressed.  It is deep and that alone should stress, but it doesn’t seem to be stressed.  It’s perfectly “happy” in 200 feet of water.  But the corals in 15 feet of water (5 m of water) are definitely stresses.  Why is that?

It seems like a person who smoked and drank all his life yet is perfectly healthy, and a person who took vitamins and exercised all his life is dying.

INTERVIEWER:  Has there been any way of taking a sample of the reef?

AH:  All that has been done.  The reef is important because it supports a very healthy fish community of 86 different species of fish that live there.

The pelagic fishing is really good.  We’ve gone out there to do work and we see that the fishermen are on top of this.  They know it’s there.  Fishermen aren’t stupid.  Why is the fishing so good there?  We don’t know, but the fishing has always been good right there.

The fishermen are parked up there.  We go out there, parked with a camera over the side, and they tell us to get out of the way.  We’ve had a couple of little altercations with fishermen, but that’s a side story.

The point is that the reef is supporting a fisheries community, some of which is of economic value.  It’s an environment that is a “Habitat of Concern”.  It’s now on its way to becoming a sanctuary.  We’ll protect it so people won’t dredge up the corals.  It’s pretty deep, so it’s away from the normal recreation activity, but the commercial interest could have access to it.  The idea is to protect it from people dredging it, so it’s on its way to becoming a sanctuary.  It’s in a pre-sanctuary designation.  It’s a habitat of concern, an environmental concern.  It’s been designated that as a result of my work.

I should point out that this work has been done by graduate students, faculty, and government scientists (USGS).  It’s been a partnership.  That’s how science is done.  Just one person doesn’t do it.  It’s a team of people.  We’ve had biologists out there and we’ve used a variety of research tools.

We use high resolution seismic reflection profiling, side-scan sonar, multi-beam imagery, bottom cameras, and various sampling devices and expensive technological equipment.

Discussion Questions:

  1. What features of the nature of science are evident in this story?
  2. What basic science concepts does a learner need to know to appreciate the events in this story?
  3. What career opportunities may be implied from this story?
  4. What is the interaction of science, technology, and society implicit in this story?
  5. What might you do to enhance a class you teach now that you have an understanding of this episode?