This blog is one in a variety of pollution posts designed to provide readers with insight into the work being done by NCCOS in the area of pollution.
Coral reefs are ecosystems vital for fish habitat, offer distinct recreational opportunities, and have cultural significance for many coastal communities. Although corals may not look like it, they are animals. They get their food from tiny photosynthetic algae (algae that use sunlight for energy) that live inside them. Being good stewards of our coral reefs means that we need to understand what types of stress a reef is under, keep track of how stressors change over time, and provide that information to coastal managers who maintain and oversee the health of those resources.
Reefs worldwide are experiencing a decline in health due to a variety of factors, including pollution. The types of pollution impacting coral reefs include: nutrients, sediments, chemicals related to oil and gas, pesticides, and heavy metals.
NOAA scientists from NCCOS’ Center for Coastal Monitoring and Assessment and the University of Puerto Rico, Mayaguez (UPRM) have been working together for the past three years to establish a baseline of environmental data in and around the reefs near Guanica Bay, Puerto Rico to answer some key ecological questions posed by region’s coastal managers.
The baseline serves two purposes. One is that it allows us to determine how healthy this reef is today. The second is that is serves as a benchmark against which we can measure change over time by comparing future data against what we are measuring today. Once we know what factors might be impacting the reef’s health, we provide that information to regional coastal managers who then determine the best way to manage and protect our coastal resources based on that baseline data.
Nitrogen and phosphorus are two nutrients required by all living things, but can cause environmental problems in high concentrations. In coral reef ecosystems, excess nutrients can cause increases in algal growth which can lead to the algae outcompeting and overgrowing corals. Also, nitrogen and phosphorus can directly impact corals by lowering reproductive success and by reducing photosynthesis and growth rates.
Nutrients that end up in coastal waters can come from different sources, including fertilizers, septic systems, waste treatment plants, and natural sources. If excess nutrients are a problem in the ecosystem, a variety of management strategies can be implemented. For example, improvements in waste water treatment technology to remove more nitrogen from human waste. Or, farmers can improve the methods and timing of fertilizer applications to maximize the benefit to their crops and minimize the amount of nutrients leaving their fields.
Our efforts to determine the impacts of pollution on the reefs near Guanica Bay include study of the Rio Loco. The Rio Loco delivers the majority of the water containing nutrients and sediments to Guanica Bay. Pollutants are also being washed directly into the Bay by surface runoff. No coral reefs exist within Guanica Bay itself, but there is an extensive reef system in the adjacent areas that receives significant water flow from the Bay, and could be impacted by pollution, nutrient and sediment runoff.
Our field team, led by Dr. Clark Sherman, a professor at UPRM, is making monthly trips into the field to collect samples of surface waters and to measure the amount and composition of sediment being deposited on the reefs. Both of these parameters need to be measured monthly because they can change over relatively short periods of time, such as after storms when rainfall quickly washes sediments and nutrients into the waters.
In order to determine the levels of nutrients in the coastal waters, our field teams visit 20 sites in Guanica Bay and three river sites in the watershed. At each site, a sample bottle is filled with surface water which is sent to the lab for nutrient analysis. This type of water sampling is pretty easy to do, but we have to be careful to avoid contaminating the samples. Touching a sample with bare skin, or even breathing on a sample can contaminate it, so our field personnel wear disposable gloves.
Once back in the lab, nutrient samples are frozen before being shipped to our analytical contract lab for analysis. Once processed, the lab sends us back the data that we can use to understand how nutrient levels change throughout the year and over time.
Sediments wash into rivers and subsequently coastal systems when it rains. While this is a natural process, it can be accelerated by human activities such as construction and agriculture that disturb the soil. In areas where there are coral reefs, sediment deposition can damage the reefs by smothering and killing coral tissue or by reducing light levels. Reduced light level in turn reduces the ability of the algae that live inside the coral to photosynthesize. Sediment can be especially problematic because once it reaches a reef system, it may take years to leave, and may be re-suspended, reducing light levels each time.
In order to measure the flux of sediments to the reefs, our research teams installed sediment traps at 11 sites: 9 on the reefs and two in Guanica Bay. Each month, SCUBA divers carefully bring each trap to the surface and the contents of the trap are analyzed in the lab to determine the characteristics of the sediment, such as grain size and composition. Based on these characteristics, we can tell how much of the material in the traps is coming from land, as opposed to sands or silts that originate in the ocean.
This type of assessment is the only way we can detect improvements in environmental quality and help insure healthy coral reefs for future generations.This monitoring effort is part of a larger environmental assessment being conducted by NCCOS’ Center for Coastal Monitoring and Assessment. In addition to monitoring nutrients and sediment traps, the project also measures pollution in sediment and coral tissues, and assesses the biological health of the coral reefs outside the Bay. We plan to repeat this study in five years in order to detect changes to the health of the ecosystem. Once available, the data will support regional resource manager decision making and best practices pertaining to this region of Puerto Rico.