Establishment of Seagrass Decline and Causative Mechanisms in Pearl Lagoon, Nicaragua through use of Traditional Ecological Knowledge, Sediment Coring and Direct Visual Census

Seagrass beds are declining in all ecosystem types around the world. Members of a community-based resource management project in Pearl Lagoon (RAAS, Nicaragua) initiated interest into the loss of seagrass in Pearl Lagoon. The desire was to know if and why seagrass beds have been disappearing from the shallow littoral zone throughout the entire 60 km long lagoon. The loss, in a region where human population is rapidly increasing, could have drastic affects for the local shrimp and fish industry as well as a loss of major feeding grounds for the West Indian manatee. The use of Traditional Ecological Knowledge (TEK) to inform the development and execution of this project allowed the expansion from a high resolution study of a small area to include a low resolution study of the entire lagoon. Direct visual census via collaborative field work established the present distribution of seagrass beds. Visual census of seagrass beds obtained significant baseline information: (a) identification of the two species Ruppia maritima and Najas guadalupensis, (b) present locations of patches throughout the lagoon and (c) a rough measure of seagrass abundance. The results of semi-directive interviews were expected to provide a 30 year time course of seagrass abundance. Sediment coring for shells of a seagrass habitat-specialist gastropod species provided an empirical indicator of historical seagrass presence and enabled the determination of confidence limits around TEK responses. TEK definitively established that significant seagrass coverage has disappeared, perhaps to the extent of 75% over the last three decades. Interview responses and empirical evidence suggested that loss of seagrass patches is mainly in response to hurricane disturbances coupled with point (dredging) and non-point source (sedimentation) anthropogenic changes. While the grass might have been able to recover from each of these disturbances individually, the cumulative effect may have been fatal. The incorporation of TEK into an ecological study is essential in information poor areas which are often impoverished regions. The use of TEK provides otherwise unavailable information and through participation empowers local people.