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Preliminary impressions
Coral Reef Nutrient Monitoring Bonaire and Curaçao
First round successfully concluded.
March
28, 2006. Last week the first round of nutrient monitoring on the reefs of
Bonaire and Curaçao was concluded with a last dive at Watamula Reef in Curaçao.
A total of twenty sites, ten in Bonaire and ten in Curaçao, were visited over a
nineteen day period. On each site video transects were recorded, water samples
taken, and various algae samples collected, both at 60 ft and at 20 ft depths. A
total of eighty water samples and more than 220 algae samples were subsequently
processed and carried to the US by Brian Lapointe to be analyzed in specialized
labs. The results of this analysis are expected in about a month time, when a
start can be made with interpreting the data.
Meanwhile, some general preliminary impressions were formed with regard to
nutrient impact on the reefs of Bonaire and Curaçao. First of all it became
clear that there definitely is an impact of nutrient pollution on some of the
reefs on both islands. Compared to many other places in the Caribbean, the
reefs of Curacao and Bonaire still generally look to be in good condition, but
signs of nutrient pollution were seen on both islands. On average the reefs in
Bonaire were less impacted than those of Curacao, but both islands had some
sites that are a cause for serious concern. One particular site in Bonaire
showed blooms of various species of cyanobacteria (blue-green algae) including
the toxic Lyngbia (implicated in the development of disfiguring fibropapillomas
in sea turtles), and elevated incidence of coral diseases and corals killed
over the past few years. In Curaçao several sites such as Caracas Bay and
Piscadera had many dead corals and presented luxurious growth of various
macro-algae such as Lobophora, Halimeda, and Dictyota. Some sites in the
vicinity of resort areas showed alarmingly luxurious growth of Dictyota and
relatively high incidence of Black Band disease. Sites within the town area
both in Bonaire and Curacao had clear nutrient indicator macro-algae growing on
the rocks in the surf zone, and there is no question that they are being
impacted by nutrient pollution, but the other sites will have to await the lab
results before any clear conclusions can be drawn.
The specialized laboratory analysis will test for very low levels of dissolved
inorganic nitrogen and phosphorus, and will provide a measure of the amount of
phytoplankton (floating one-celled algae) in the water. The collected algae
samples will yield ratios of nitrogen isotopes in the algae tissues, indicating
the source(s) of the nitrogen. Natural sources of nitrogen, fertilizer
nitrogen, and sewage nitrogen all have different signatures. When luxurious
algae growth coincides with a signature of fertilizer or sewage nitrogen there
is clear cause for concern.
Any conclusions, even after the lab results come in, must also take into the
account the possible seasonality of nutrient sources, e.g. increased run-off or
mixing of ground water with sea water because of the rainy season. That is why
this is only the first round of monitoring. It will be repeated quarterly for a
year. Over the past couple of weeks volunteers in Bonaire and Curaçao had the
opportunity to observe how the sampling is done, how the water samples must be
carefully filtered after the dive, avoiding any contamination, and how to
distinguish various species of algae. They will now continue the monitoring
every three months to produce a complete picture of the nutrient situation of
the reefs from which clear conclusions and recommendations can be drawn.
To learn more about nutrients, macro algae and correefs you can
download the following:
Presentation
given by Dr. Brian Lapointe in Bonaire and Curacao (Powerpoint 8 MB)
Articles:
Lapointe,
Brian E. and Katie Thacker: “Community based Water Quality and Coral Reef
Monitoring in the Negril Marine Park, Jamaica: Land-based nutrient inputs and
their ecological consequences” (PDF, 5 MB)
Lapointe,
Brian E. 1997: Nutrient thresholds for bottom-up control of macroalgal blooms
on coral reefs in Jamaica and Southeast Florida (PDF, 1.3 MB)
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