Drifting macroalgae is of concern in the lower Laguna Madre due to its inferred negative impact on the seagrass beds. Field sampling was conducted during late winter (February-March) and late summer (August-September) in 2001 to characterize the drifting macroalgal flora of the lower Laguna Madre, Texas at three sites: South, Arroyo and North. The Arroyo site was closest to the mouth of the Arroyo Colorado, the most eutrophied waterway in Texas. Due to persistent northerly currents, the North site is less impacted by the Arroyo Colorado than the Arroyo site with the South site being the least impacted. Two sample collection protocols (netting vs. quadrat) are compared. The quadrat method resulted in higher average algal biomass than the seining method (112 vs. 24 wet g/sq. m., p=0.008). Using the quadrat method data, the three sites did not differ in algal biomass in summer (p=0.47) but did differ in winter (p=0.03) with the Arroyo site having the highest algal biomass (0.96 dry g/sq.m.) and the South site having the least (0.06 g/sq. m.). Winter and summer mean algal biomass (in dry g/sq.m.) did not differ for the Arroyo (2.88 vs. 0.95) and North (5.59 vs. 0.74) sites but did at the South site (4.31 vs. 0.06, p=0.0004) due almost entirely to the summer growth of Laurencia poiteaui. The North and Arroyo sites were dominated by Jania capillacea and Cladophora heteronema (tentative identification). In addition to macroalgae, dead seagrass was a consistently large component of drifting vegetation and may be equally important stressor of seagrass beds.

Key words: Cladophora, lagoon, Laurencia poiteaui, macroalgae, marine, seasonality