Novel Species Interactions in a Highly Modified Estuary: Association of Largemouth Bass with Brazilian Waterweed Egeria densa

Abstract

Frequent invasions in coastal ecosystems result in novel species interactions that have unknown ecological consequences. Largemouth Bass Micropterus salmoides and Brazilian waterweed Egeria densa are introduced species in the Sacramento-San Joaquin River Delta (the Delta) of California, a highly modified estuary. In this system, Brazilian waterweed and Largemouth Bass have seen marked increases in distribution and abundance in recent decades, but their association has not been specifically studied until now. We conducted a 2-year, bimonthly electrofishing survey with simultaneous sampling of water quality and submerged aquatic vegetation (SAV) biomass at 33 locations throughout the Delta. We used generalized linear mixed models to assess the relative influences of water temperature, conductivity, Secchi depth, and SAV biomass density on the abundance of both juvenile-sized and larger Largemouth Bass. Water temperature had a positive relationship with the abundance of both size-classes, but only juvenile-sized fish had a positive association with SAV biomass density, with highest abundances at intermediate SAV densities. In contrast, larger fish were generally ubiquitous across all sampling

Evidence of a Shift in the Littoral Fish Community of the Sacramento-San Joaquin Delta

“…Introduced fishes showed the most consistent increases over time, though the key factors behind the increases likely differ between species. For example, previous studies in the Delta [33] and elsewhere [66,67,68,69] have shown a positive relationship between submerged aquatic macrophytes and fish species within the Centrarchidae family ( e . g .…”

“…Previous studies describing the POD shift in the upper San Francisco Estuary have generally focused on the declining pelagic fish species [16,18,20,29,30,31] that occupy open water habitat and exhibit relatively unique life histories [32]. The few analyses on Delta littoral fish species indicated that major shifts have also occurred in the littoral habitat [24,25,33]. However, such studies are scarce and lack a continuous time series dataset [24] or are more focused on the spatial variation in fish species composition [34,35].…”

Predation on Fishes in the Sacramento-San Joaquin Delta: Current Knowledge and Future Directions

“…Predation on Delta fishes also is affected by ecosystem-level effects of invasives, such as the shift in the food web produced by the non-predatory overbite clam (Corbula amurensis, Cloern and Jassby 2012, Brown et al, forthcoming) or changes in the structural complexity of littoral habitats produced by invasive submerged aquatic macrophytes such as Egeria (Brown et al 2016, forthcoming;Conrad et al 2016). The increase in littoral structural complexity favors invasive species that currently inhabit the Delta, although it may also provide refuge for some prey species.…”

Food Webs of the Delta, Suisun Bay, and Suisun Marsh: An Update on Current Understanding and Possibilities for Management

“…These studies have highlighted changes in the fish community (Brown and Michniuk 2007;Grimaldo et al 2012;Conrad et al 2016). This new habitat has also established new food webs (Grimaldo et al 2009b;Young 2016).…”

“…The invasion and spread of Brazilian waterweed established a new food web. Aquatic macrophytes provide structural complexity and surface area, expanding habitat for epiphytic algae, invertebrates (Schultz and Dibble 2012), and fishes (Brown and Michniuk 2007;Grimaldo et al 2009bGrimaldo et al , 2012Conrad et al 2016).…”