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Fish Kills in Etang de St Jean: Commentary

1/28/2012

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Fish Kills in Etang de St Jean

Recently we got news of a large fish-kill” in Etang de St Jean.  “A mass mortality of fish in the salt pond is sadly not new; these events have been a regular occurrence for well over a decade. An important difference today is that we are seeing a widening awareness of this ecological problem. 

Fish kills are a symptom of an ecosystem in trouble.  Fish die because the oxygen they need to survive has been depleted. In other words, they suffocate. Oxygen depletion is associated with high nutrient levels (usually nitrogen and phosphorous), which trigger the growth of microscopic plants. It is the same response you get when you add fertilizer to your garden i.e. more roses and veggies. 

In salt ponds, higher salinity and water temperatures exacerbate the effect of oxygen depletion; hotter, saltier water has less available oxygen.  Microscopic plant blooms in the salt pond (responsible for the dark green color) use up the oxygen, and animals like fish die.  Fish are often only one of many species affected but, because they float to the surface in large groups and smell, they tend to be the most visible.

Where do these nutrients come from?

The St Jean Salt pond is part of a 418 acre drainage system or watershed. Rainwater brings soil nutrients from the hillsides and carries runoff from roads directly into the pond. Human activities have increased the supply of nutrients. Septic tanks and garden fertilizers add extra loads to the system, as does cutting down vegetation and mangrove buffers that absorb nutrients. Strong winds can set up circulation patterns in shallow ponds and lakes which draw nutrients from the bottom to the surface, and in effect add “fuel to the fire”.  In combination all these events can create a perfect storm that “overdoses” the system with nutrients, and results in fish kills.   In the St Jean salt pond the lack of “flushing” i.e. an exchange of water from the pond to the bay makes the system stagnant and more prone to oxygen depletion, and accompanying fish kills.

In the past, it was often possible to identify a single point source of pollution, but not anymore. Today, sources of pollution are harder to pinpoint and tend to come from a wide array of diffuse activities and places.  

What can be done?

There have been several suggestions, including rapidly opening the pond to the bay. A “quick fix” of flushing the nutrient-rich stagnant water into the bay would have disastrous consequences for the reefs, turtles, fish and water in the bay itself, and would not solve the problem long term.

Ultimately the solution lies in restoring the ecosystem to health which includes re-establishing the link between the sea and pond (which will help with flushing and water movement), reducing nutrient overload, restoring the mangrove and plant buffer around the sides of the pond, and creating habitats for invertebrates, fish and birds that are the biological components which keep the system healthy.  But this has to be done carefully. Such an effort needs to be science-based, and take into account that the ecological system is more fragile today than before and that human activities are and will continue to be more pronounced.  We can’t go back to past times but we can build a future which includes resilient and healthy ecosystems.

Are there any scientific studies available?

In 2010, we (some of my grad students and I) participated in a hydrodynamic and geophysical study of the salt pond and that included work in St Jean Bay. Engineers and hydrologists from Ocean Earth Technologies conducted the study on sediments bathymetry, bay currents, sea surface waves, watershed delineation and more.  Their data were then used to develop models of the system and explore ways to re-link the bay and pond. Several models looked at water-flow in the pond; one looked at how restoring the reef would change the speed and force of the water in St Jean and help sand stay on the beach. The models were used to forecast exchange of water between the bay and pond under many different environmental conditions. The study included options for biological restoration of fish and bird habitats, and recovering the mangroves around the pond.  The study was a scientific and engineering framework for restoring the pond and as part of the larger St Jean Bay ecosystem.  This study like others awaits full discussion on implementation.  But it offers another part to the overall ecological and technical solutions for the troubled ecosystem of St. Jean bay and salt pond.

Science and the Environment

The fish kills, which have catalyzed the concern for the salt pond, highlight the importance of science and the environment.   On St Barths, as we continue to discuss the challenges facing our natural world, it is useful to look at both. Science is a rigorous process; it is a formal and unbiased way of getting to the truth. It distinguishes fact from belief, truth from opinion. It teaches us how our ecosystems work when at times we may believe or want to believe that they work differently.  It is a unique human endeavor and a powerful way of knowing.  Studies show that when science and scientists are involved in environmental decisions that the results are better for the ecosystem and the goals of the people involved.  We would never go into surgery without first having consulted trained doctors and surgeons, and doing surgery on our environment should also be science-based.  Scientific studies are a vital part how we understand and make decisions.  But science itself has no independent values or judgments. Only humans have those.

The fate of our environment is a reflection of the values that we citizens place on it.  Government policies, laws, and actions such as creating reserves as well as individual activities mirror societal opinions on a healthy environment and the ecosystem services it provides.  Environmental values are based a wide range of factors and priorities.  Citizens‘ access to and understanding of science helps to shape those values. The old idea was that we had to choose between prosperity and environment, and that false dichotomy polarized communities.   What is true is that all of us share the environment.  We all have a role to play in shaping the type of environment we want for ourselves, our children and into the future. Participating is a gift and a responsibility.
Deborah Brosnan
email: mailto:brosnan@deborahbrosnan.com
Main Lab Page   http://brosnancenter.com

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Seawalls

1/21/2011

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St Barths has been nature's playground for the past few months. Summer hurricanes, rain and floods, and even a mild earthquake last night, all remind us that nature can have as much fun on St Barths as we humans do. Lately, thanks to vigorous seas, several of the island's beaches have been particularly dynamic with sand movement. In our projects on St Jean Bay and at Gouverneur, we're asked what about seawalls and beaches. The topic came up again in the Association meeting with President Magras. In response to the question, here's a short overview on why seawalls only contribute to erosion on beaches.  
What do to with existing seawalls?- Perhaps reconnect the dunes and the sea by restoring the sand dunes and feed a starving beach. 
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Seawalls
People build seawalls to stop "land erosion" into the sea. But these walls only refocus erosion onto the beach and result "beach loss".
25% of Oahu (Hawaii)'s sandy beaches have either disappeared or narrowed significantly due to the construction of seawalls (U. Hawaii studies). For a tourism island like Oahu this has been "bad news". Seawalls starve the beach of sand, and a starved beach erodes and eventually disappears.
How does it work?
A dune shares it sand with the sea. Like a game of beach-frisbee the sand is tossed back and forth between the ocean and dune. In storms, when the "waves are up", the sea takes the sand and there is less "beach".  Depending on the bay, you can often find where the sea is storing that sand- for instance, when you wade out and suddenly come across a shallow bank of sand a few meters offshore about knee depth. ( E.g. St Jean bay, especially the Nikki Beach side).  When the sea calms down, the lapping waves gently toss the sand back onto the beach and dune. There is more beach. This game of sand-frisbee never ends.  It's why even on a retreating coastline the beach shape is maintained- In other words even eroding beaches have a "beach".  
However seawalls change the equation. They stop the beach-frisbee. When we build sea walls ( technically called "hardening the beach") the dune can no longer share its sand with the sea. In a retreating beach, when the sea meets a seawall it has no sand to draw on and so it erodes. Wave meets wall. As the waves continue to pound against the seawall there is little or no opportunity for the sand to return to the beach.  
Anything that starves a beach of its sand supply, will lead to beach loss.

(Image courtesy U. Hawaii- thanks to my scientific partners here, Ralph Clarke, Joan Oltman-Shaye, and to Chip at U. Hawaii)


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Reef Monitoring

7/28/2010

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Reef surveys have begun! 

Yesterday scientists at the Brosnan Center began to establish permanent monitoring sites on the back reef of St. Jean Bay. They plunged into the sea, science gear in hand. Diving for science is very different than diving for pleasure, there’s much to do and to keep track of. For instance, there is alot of gear that we must bring down with us to establish a site: transect tapes, quadrat, clipboards with datasheets, video camera, still camera, hammer, pins, underwater epoxy...the list goes on. 

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Reef Clearing

7/26/2010

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Members of the Brosnan Center have been hard at work this week on Eden Rock pulling and scraping to remove the algal growth. By physically clearing as much algae as possible, we are paving the way for coral recruits to settle and grow. We are also providing areas to transplant adult corals onto. We want to make the site as habitable as possible to ensure successful transplantation. By removing algae, we remove competition for the limited space on the rock. Both on snorkel and on SCUBA we go out and pull off macroalgae and scrub off turfy algae. 

Additionally, Cheryl is collecting coral samples in St. Jean Bay to identify the species that are present. She gently chips off small sections of coral and brings them back to the lab. They are then bleached and dried in the sun to isolate the skeleton for taxonomy. Then the coral skeletons are photographed under the microscope and their unique features are identified. For example, Cheryl has identified three species of the coral Siderastrea. 
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Dengue Developments

7/23/2010

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Research on Dengue is well underway. Data from the Pan American Health Organization (PAHO) show that Saint Barthelemy had the highest incidence rate for Dengue infection in the entire Caribbean in 2009. Preliminary data from 2010 report roughly the same number of cases of Dengue on St. Barth in the first 6 months of 2010 as for the entire year of 2009. These frightening numbers suggest not only that Dengue has a strong presence on the island, but that infections are increasing. 

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Taking on Dengue

7/14/2010

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Monday marked the beginning of a new initiative to fight Dengue fever on St. Barths. Claire Simeone joined the team at the Brosnan Center to investigate the impact Dengue is having on the island. Claire is a veterinary student in her final clinical year at the Virginia-Maryland Regional College of Veterinary Medicine. She has an interest in international wildlife management and ecosystem health.  Claire met Deborah in 2008, during a program called Envirovet, which brings veterinary students and veterinarians from around the world together to learn about terrestrial and marine wildlife conservation. 

After learning about the re-emerging problem of Dengue fever on the island, Claire decided that she wanted to help to implement a community program of mosquito control and disease eradication. She will be visiting the Brosnan lab for 3 weeks, as she works with Deborah, Cheryl, Meghan, and doctors around the island to get a better idea of the magnitude of the problem, and the best way to encourage control measures. 

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Eden Rock Reef

7/8/2010

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Cheryl and Meghan did some snorkel reconnaissance today to check out the status of the reef off Eden Rock. Happily donning snorkel and fins, they set out across Pelican Bay and waved to a few turtles on the way. Unfortunately, as with much of the bay, Eden Rock is overgrown with macroalgae. The high nutrient input in the bay makes conditions ripe for the growth of many species of algae. However, that leaves less room for the corals. While this may seem disheartening, it is, in fact, why we are here; to assess how to change the state of the system back to coral dominance. On a positive note, we found some marked areas that Deborah cleared of algae last year, and they are still clear. This is a promising sign as it suggests that if we continue clearing the algae, it may stay away. We’ll keep you posted on our progress and tactics as we persevere in the name of science and conservation. 
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Tropical Science

7/5/2010

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23.00 hours on St Barths. Winds from Africa are blowing over the island. The palm trees outside the lab are rustling to the rhythm, as though they can hear the drum beats from a distant continent. 

Tonight is cooler and we welcome a pleasant break from the intense heat of the past few days. We are all a little pink - not from dye but because we’ve spent many hours in the water in the intense tropical sun- sunscreen can only do so much. But we’re so excited and driven by the work that we don’t want to come out, so we are a rosy hue.

Today’s rain brought us inside for an afternoon meeting. Using the data and insights we’ve gathered over the past week we were ready to really refine our goals and activities in the weeks ahead. Our new white board was invaluable in drawing and sketching our ideas and equations.  This was the kind of lab meeting that you live for, when everyone is contributing and learning at once, and where you get something done.  We’ll be sharing it all with you soon. But now it’s late and I’ve been up since 05.00. 

This is Deborah, signing off from the lab tonight. 

Bonne Nuit!
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La Vie en Rose

7/3/2010

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Yes, the water is pink- do not adjust your glasses. 

We invited an engineering team from Florida (here to evaluate the salt pond) to work with us on St Jean Bay. This morning we cruised the bay in a small boat dropping tablets of pink dye to study currents and water flow in the bay. Why?  We need to know the speed and direction of currents to estimate sand and coral transport in the water. This will help us to identify where corals are spawning and likely to settle, and will help us know where to put our transplant corals. Early results are interesting.  

Last night we invited the coastal engineering and geology team over to brainstorm with us and share information on St Jean Bay. And, great news! They are now working in partnership with us and will be doing some seriously sophisticated mathematical modeling to look at how raising the height of the reef is likely to affect beach retention in the bay. We have several key questions that we want answered and they will be running the models to answer them. 
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