Seasonal changes in the abundance and distribution of submerged aquatic vegetation in a highly managed coastal lagoon

Abstract

The inflow of fresh water into coastal lagoons is a key factor influencing the structure and function of these ecosystems. Biscayne Bay, a coastal lagoon adjacent to the city of Miami, is located downstream of the Everglades ecosystem where the extensive water management system now in place has modified the historical hydrology, replacing groundwater and overland flows with pulsed releases from canals. In areas where canals discharge directly into littoral habitats, an environment with low-mean salinity and high-salinity variability is created. In this study, we characterize the salinity patterns of nearshore habitats (<500 m from shore) and document patterns of seasonal abundance and distribution of submerged aquatic vegetation (SAV) to evaluate the impacts of water management practices. Seagrasses were the principal component of the SAV community during the 2005 dry season (mean cover = 25.5%), while macroalgae dominated during the wet season (mean cover = 33.4%). The distribution and abundance of SAV were directly related to the tolerance of each taxon to salinity patterns. Seagrass species with high tolerance to low and variable salinity such as Halodule wrightii and Ruppia maritima were found only in canal-influenced areas and increased in abundance and spatial distribution in the wet season when freshwater inflow is highest. The dominance of rhizophytic macroalgae during the wet season was determined by the appearance and high abundance of Chara, a taxon commonly associated with freshwater environments. Thalassia testudinum, the most abundant seagrass species, was found throughout the study region, but decreased in abundance in the canalinfluenced areas during the wet season when lower, more variable salinity resulted in lowered productivity. The data presented here showed a significant relationship between salinity patterns and the seasonal abundance and distribution of SAV. These findings support the use of SAV as appropriate indicators of changes in water quality resulting from future restoration projects associated with the Everglades Restoration Plan, which will once again modify the delivery of fresh water into littoral habitats with unknown ecological consequences.Handling editor: S. M. Thomaz

Quantifying freshwater-induced fragmentation of submerged aquatic vegetation communities using a multi-scale landscape ecology approach

“…In a preliminary analysis, 100 m extraction buffers were used (100 m is the extension of the buffers used as strata in the benthic surveys conducted by Lirman et al 2008b). The 2 buffers (100 and 200 m) closest to shore were identified using an analysis of similarities (ANOSIM) analysis as the buffers that differed significantly from all other buffers.…”

Spatio-temporal patterns and nutrient status of macroalgae in a heavily managed region of Biscayne Bay, Florida, USA

“…The presence of this taxon is a clear sign of low mean salinity and changes in its spatial distribution can be expected as lower salinity conditions are expanded in the Bay. While it was initially believed that the presence of Chara at Black Point was only a seasonal occurrence (Lirman et al 2008b), the collections conducted here show a consistent background presence of this taxon in the areas closest to shore (-100 m from shore) with the lowest mean salinity. Another assemblage characteristic of the freshwater group is the category labeled here as puff, comprised of a mix of diatoms, green filamentous algae, and Cyanobacteria, which was present in low-salinity habitats of Black Point.…”

“…The latter species is a dominant taxon in South Florida coast- al lagoons commonly associated with marine conditions (Davis andFourqurean 2001, Collado-Vides et al 2007). The freshwater group, found only in low-salinity habitats, was characterized by Chara hornemanii, a freshwater-estuarine species that is common in inland lakes and marshes in the Everglades (Montague andLey 1993, Frankovich et al 2011) and has been increasing in abundance and range in central Biscayne Bay and mangrove lakes in western Florida Bay (Lirman et al 2008b, Frankovich et al 2009) in the past few years. The presence of this taxon is a clear sign of low mean salinity and changes in its spatial distribution can be expected as lower salinity conditions are expanded in the Bay.…”

“…Another assemblage characteristic of the freshwater group is the category labeled here as puff, comprised of a mix of diatoms, green filamentous algae, and Cyanobacteria, which was present in low-salinity habitats of Black Point. Puff is highly dependent on the presence of seagrasses, specifically the low-salinity tolerant species Halodule wrightii (Lirman et al 2008b, Lirman and Cropper 2003, Koch et al 2007), for attachment and has been shown to respond quickly to changes in nutrient availability, especially phosphate (Frankovich et al 2009). The rest of the taxa comprise the estuarine group, in which two groups were evident.…”

Temporal variability in potential connectivity of Vallisneria americana in the Chesapeake Bay

“…We are unsurprised to find turnover in patch occupancy because substantial yearly changes in the local and regional distribution of submersed aquatic species are common (Cristofor et al 2003;Demars and Harper 2005;Lirman et al 2008), reflecting the dynamic nature of aquatic environments (van der Nat et al 2003;Orth et al 2010b;Santos et al 2011;O'hare et al 2012). Nonetheless, the magnitude of turnover and the number of patches persisting for less than 2 years is surprising.…”