Differing temporal patterns of Chara hornemannii cover correlate to alternate regimes of phytoplankton and submerged aquatic-vegetation dominance

Abstract

Cover of the alga Chara hornemannii Wallman and water-quality parameters were measured over a 3-year period in adjacent mangrove subestuaries in Florida Bay, so as to describe temporal variability and infer relationships between Chara cover and water quality that will assist resource managers to restore Chara abundance to historically higher levels. A seasonal pattern of Chara cover was observed in the Alligator Creek subestuary that coincided with seasonal changes in water transparency in a relatively high-nutrient and phytoplankton environment. In contrast, higher Chara cover in the relatively low-nutrient and phytoplankton-abundance McCormick Creek subestuary did not exhibit a repeatable seasonal pattern, but was temporally negatively correlated with salinity and water depth. These observations suggest that water transparency may determine the importance of the salinity driver in these Chara communities. The present study demonstrates the differential importance of water quality and environmental drivers in estuaries distinguished by alternate regimes of phytoplankton and submerged aquatic-vegetation (SAV) dominance, and explains how differences in local estuarine geography may filter the response of SAV communities to environmental stressors.