Invasive Submerged Aquatic Vegetation and Associated Macroinvertebrates in the Sacramento-San Joaquin Delta

The Sacramento-San Joaquin Delta is a highly modified, tidally-influenced network of sloughs and canals that drains into San Francisco Bay. It has been postulated that the Delta has recently undergone an ecological regime shift. Historically, the Delta was a dynamic estuarine environment with a seasonally variable hydrograph and salinity fluctuations; currently it is characterized by a more homogenous, freshwater environment dominated by invasive submerged aquatic vegetation (SAV) and warm-water fish species. It has been shown that SAV biomass is positively related to the abundance of largemouth bass (Micropterus salmoides), however little is understood about the mechanism of this relationship. This study seeks to determine the influence of invasive SAV on associated invertebrate communities and the invertebrate-mediated effect of vegetation on the growth and feeding of young-of-year largemouth bass. These effects of vegetation on invertebrate communities are driven by several factors, including habitat complexity, biomass, and species composition. Using a modified Marklund sampler, we extensively sampled SAV and associated invertebrates at nine sites across the Delta while concurrently collecting young-of year largemouth bass. Given that plant morphology is the main determinant of vegetative habitat complexity, fractal geometry was used to quantify morphological differences between different SAV species and as a proxy for overall habitat complexity. We then evaluated the influence of SAV on invertebrate community structure using multivariate statistics and examined the relationships between SAV, invertebrate abundances, and bass diet, condition and growth.