Accumulation of epiphytes on Halodule Wrightii in response to nutrient enrichment in East Flats, Corpus Christi Bay and Nighthawk Bay, Upper Laguna Madre, Texas

Increased epiphyte abundance on seagrasses is often associated with anthropogenic eutrophication of estuarine ecosystems, but the quantitative relationships are complex and not fully understood. A nutrient enrichment experiment was conducted at two sites during three seasons to measure epiphyte accumulation on Halodule wrightii and artificial seagrass substrates. A novel fluorescence imaging technique, based on excitation of phycobilin and fucoxanthin accessory pigments, was used to quantify epiphyte abundance. For natural seagrasses, significant dose-dependent increases in epiphyte accumulation occurred due to the introduction of nutrients at East Flats, during early summer and fall sampling seasons. Significant nutrient responses were also detected during late summer at East Flats, and during early summer and fall only at a hypersaline lagoon site, Nighthawk Bay. Additionally, nutrient enrichment caused significant decreases in combined seagrass and epiphyte biomass across all seasons at Nighthawk Bay, and during late summer at East Flats. At East Flats, biomass increased with increasing nutrient treatments during early summer and fall seasons. Artificial substrates failed to corroborate results of the natural seagrass experiment; however, a change in species composition was evident, but results were inconsistent across seasons and sites. These findings imply that epiphyte abundance is sensitive to nutrient enrichment under a wide range of ambient conditions, including different predominant grazer abundances, and is likely to increase with eutrophication.