MEPS 537:121-135 (2015)  -  DOI: https://doi.org/10.3354/meps11412

ABSTRACT: The abundance of submerged aquatic vegetation (SAV) fluctuates from year to year, and these fluctuations differ among the tributary embayments within estuaries. Quantifying the causes and spatial patterns of interannual variability in SAV abundance is critical to understanding the dynamics of SAV in complex estuaries. We applied empirical orthogonal function (EOF) analysis to quantify the temporal synchronicity among embayments within each of 3 salinity zones (oligohaline, mesohaline, and polyhaline) of Chesapeake Bay. EOF analysis extracts shared modes of variation among the embayments in each zone. The amount of synchronicity differed among zones, and embayments were most synchronous within the polyhaline zone. The extracted modes of variation showed that fluctuations in SAV abundance are not synchronized among the salinity zones. We detrended the modes of common variation in SAV abundance for each salinity zone and then used cross-correlation analysis to compare the detrended modes to detrended water quality variables (dissolved organic carbon, suspended solids, chlorophyll a, Secchi depth, river nitrogen load, temperature, and salinity). The water quality variables that were significantly related to SAV abundance differed among salinity zones. Chlorophyll a levels in months when seed germination and shoot production rates are high were important negative predictors in the oligohaline and polyhaline zones, possibly because young SAV plants are especially sensitive to even short-term disturbances. As the SAV communities in the 3 salinity zones have different year-to-year dynamics and different responses to stressors, conservation, restoration, and management plans should be tailored to each community.

KEY WORDS: Empirical orthogonal function · Aquatic plants · Water clarity · Multiple stressors · Community identity · Time series analysis