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Smithsonian National Museum of Natural History

Human activities are having a profound global impact on the earth's oceans, from declining fish populations and reduced coral reef health to changes in the physical nature of the ocean environment. Observations of the ocean's physical parameters are proving to be vital to our understanding of these changes and their impacts on the creatures that live there. As the home of the Caribbean Coral Reef Ecosystems (CCRE) program, the Smithsonian's Carrie Bow Cay research station in Belize has been the site of extensive biological, ecological, and geological study for four decades. In 1993 the program began participating in an ocean observation network known as CARICOMP (Caribbean Coastal Marine Productivity) in order to enhance our understanding of physical factors that influence the coral reef environment. Participating marine labs throughout the Caribbean take water quality measurements twice a week, and the resulting 19-year-long dataset is among the most comprehensive in the Caribbean and certainly the longest in Belize. In 1997, the CCRE program also installed a permanent environmental conditions monitoring station. This assembly of sensors records meteorological (wind speed/direction, solar radiation, rainfall, barometric, temperature and humidity) and oceanographic (water level, temperature, salinity, pH, and turbidity) conditions every ten minutes, providing real-time data to anyone with access to the internet. The information is available on the CCRE website ( and has contributed to new and existing research studies, publications, and management programs.

Station managers conduct Secchi measurements
Carrie Bow Cay station managers take bi-weekly Secchi measurements in front of the "drop-off".

Among the more striking trends these records have revealed is the steady decline in water transparency. "Cloudy" water reduces the amount of light available to bottom-dwelling plants and animals, which can drastically affect the health of photosynthetic organisms, such as seagrasses and corals. Research station staff and volunteers measure water transparency twice a week with a simple tool called a Secchi disk. The small black-and-white disk is lowered into the water on a cable until the researcher can no longer see the disk and that distance is recorded. Since these regular measurements started in 1993, the annual mean vertical Secchi-distance in front of Carrie Bow Cay has dropped by 8.2 meters (27 feet).

Graph depicting the decline in water clarity over the reef since 1993
Annual mean of Secchi disk distance (vertical) over the "drop-off" seaward of Carrie Bow Cay. (Koltes & Opishinski 2009)






The dramatic decrease in water transparency over the past 15 years suggests that coastal development and inland agricultural practices in Belize and neighboring countries have increased the sediment and nutrient input to the Mesoamerican Reef, the latter resulting in increased algal blooms. Changes in water quality such as these have been shown to have profound impacts on the health of coral reefs around the world, and underscores the importance of long-term water quality measurements for informing sustainable coastal management policy throughout the Caribbean.

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