LAGUNA MADRE - SEAGRASS CHANGES CONTINUE DECADES AFTER SALINITY REDUCTION

Vegetation maps of the lower Laguna Madre prepared from surveys conducted in 1965-1967, 1974-1976, and 1988 document a > 330 km2 decrease in cover by Halodule wrightii, an increase of almost 190 km2 in other seagrass species, and an increase of 140 km2 in bare bottom. Loss in seagrass cover is confined to deeper parts of the laguna; turbidity caused by maintenance dredging is the suspected cause. The species shifts are consistent with observed reductions in salinity maxima. Although the hydrological alterations and climatic shift responsible for moderating the salinity regime occurred between 1948 and 1965, the biological changes continue. Establishment of patches away from source meadows appears to be the process for displacing species that limits their rate of expansion into suitable habitat in this elongate embayment.