Changing restoration rules: Exotic bivalves interact with residence time and depth to control phytoplankton productivity

Abstract

Citation: Lucas, L. V., and J. K. Thompson. 2012. Changing restoration rules: Exotic bivalves interact with residence time and depth to control phytoplankton productivity. Ecosphere 3(12):117. http://dx.doi.org/10.1890/ES12-00251.1Abstract. Non-native species are a prevalent ecosystem stressor that can interact with other stressors to confound resource management and restoration. We examine how interactions between physical habitat attributes and a particular category of non-native species (invasive bivalves) influence primary production in aquatic ecosystems. Using mathematical models, we show how intuitive relationships between phytoplankton productivity and controllable physical factors (water depth, hydraulic transport time) that hold in the absence of bivalves can be complicated-and even reversed-by rapid bivalve grazing. In lightlimited environments without bivalves, shallow, hydrodynamically ''slow'' habitats should generally have greater phytoplankton biomass and productivity than deeper, ''faster'' habitats. But shallower, slower environments can be less productive than deeper, faster ones if benthic grazing is strong. Moreover, shallower and slower waters exhibit a particularly broad range of possible productivity outcomes that can depend on whether bivalves are present. Since it is difficult to predict the response of non-native bivalves to habitat restoration, outcomes for new shallow, slow environments can be highly uncertain. Habitat depth and transport time should therefore not be used as indicators of phytoplankton biomass and production where bivalve colonization is possible. This study provides for ecosystem management a particular example of a broad lesson: abiotic ecosystem stressors should be managed with explicit consideration of interactions with other major (including biotic) stressors. We discuss the applicability and management implications of our models and results for a range of aquatic system types, with a case study focused on the Sacramento-San Joaquin Delta (California, USA). Simple mathematical models like those used here can illuminate interactions between ecosystem stressors and provide process-based guidance for resource managers as they develop strategies to augment valued populations, restore habitats, and manipulate ecosystem functions.

Bivalve Grazing Can Shape Phytoplankton Communities

“…This finding applies to deep and shallow environments. However, the range of potential D:ND is broader for shallower habitats (Figure 9), likely due to the potentially short time scales for growth, benthic grazing, and diatom sinking in shallow water, the combination of which can result in a particularly broad range of outcomes (Lucas and Thompson, 2012). 2.…”

“…The rationale of conducting this generic study in 1D was to first analyze interactions between sinking, grazing, light-limited growth, and vertical transport, isolated from the effects of horizontal transport between deep and shallow habitats. Both channel and shoal environments were examined because previous work (Lucas et al, 2009;Lucas and Thompson, 2012) has revealed that they can function differently. Biological model parameters for the generic runs were guided by values representative of the broader San Francisco Bay but chosen to be relevant to other estuaries as well ( Table 1, Appendix in Supplementary Material).…”

Evaluating the Aquatic Habitat Potential of Flooded Polders in the Sacramento–San Joaquin River Delta

“…Complete (high) exchange is unlikely to support sufficient residence time to build up blooms of plankton. Low exchange may support blooms, but will cause drawdown of nutrients without replenishment, and limit distribution of food to other regions (i.e., open habitat) where it can be used by grazers and predators (Lucas et al 1999a(Lucas et al , 1999b(Lucas et al , 2002Ahearn et al 2006;Doyle 2010;Lucas and Thompson 2012). Polders that support exchange which varies on a lunar tidal scale are likely to support pelagic production and fishes.…”

Recent Advances in Understanding Flow Dynamics and Transport of Water-Quality Constituents in the Sacramento–San Joaquin River Delta

“…Turbulence affects whether particles will remain suspended and susceptible to transport. Thus, turbulence affects the time plankton remain productive in the photic zone and whether this material will be intercepted by benthic grazers such as clams (Lehman et al 2009;Lucas and Thompson 2012 Sediment supply decreased about 50% since the 19th century, and the fraction of sediment delivered during winter has increased while the fraction delivered during spring has decreased, mimicking discharge patterns.…”

“…Similarly, the relationship between flow characteristics such as velocity and turbulence and the production and sedimentation of organicrich particles (phytoplankton, phytodetritus, and detritus) has not been well characterized for Delta environments; a mismatch between production and transport may lead to significant attenuation of this carbon supply to lower Delta food webs (Lucas and Thompson 2012).…”