HISTORIC CHANGES IN THE ABUNDANCE AND DISTRIBUTION OF SEAGRASS BEDS IN THE CARTAGENA BAY AND NEIGHBORING AREAS (COLOMBIA)

Abstract

The spatial distribution of seagrass beds within the Cartagena Bay and neighboring areas was reconstructed through comparative analyses of maps, aerial photographs and satellite imagery, as well as observations in the field for five time periods within the last six decades. From slightly more than 1,000 hectares of seagrass beds existing in 1935-45, only 76 remained in 2001, which is less than 8%. The loss rate of seagrass within the bay showed an inverse exponential pattern, whereas outside of the bay the tendency was linear. The almost disappearance of this community was probably raged by the reopening of the Canal del Dique early in the thirties, causing the introduction of important amounts of turbid freshwater and sediments into the bay, and subsequently accelerated by the rapid development of the industrial zone, spilling of polluted industrial and domestic waters, dredging and coastal development. The reduction of seagrass areas has been seemingly accompanied by changes in the structure of the animal community, becomig apparent through the evident disappearance of suspension feeding invertebrates which were so far dominant elements three decades earlier. The loss of seagrass beds in the bay during the 20th century seems likely to be part of the long lasting human transformation process of this ecosystem, which started three centuries before.