Current Research: The objective of this ongoing section of my research (funded as a portion of Levin Lab SeaGrant) is to 1) test the hypothesis that benthic diversity and soil food web in a Spartina foliosa marsh vary by presence or absence of aboveground vegetation and 2) to evaluate the mechanistic effects of light and aboveground structure. I used field manipulation of light levels and aboveground plant structure to determine whether vascular plant interactions with the benthic microalgal and invertebrate communities were associated with shading effects or with structural effects. Three treatments were established. These treatments were (1) Clipped - Unshaded, 2) Clipped - Shaded, 3) Control - Unshaded. Clipping and shading treatments isolate the effect of reduced light condition from the effect of aboveground plant structure on both the microalgal and infaunal communities.

The clipping and shading manipulations revealed that Spartina foliosa exerts strong influence on abiotic environmental factors (salinity, water content, and temperature at the soil surface) that mediate changes in the biotic community. The infaunal community in unshaded treatments resemble communities seen in a newly restored marsh; unshaded treatments had lower species richness, a larger proportion of insect larvae and a smaller proportion of annelids than when plants remain (control) or their shading effects were mimicked (shaded). This experiment demonstrates the dramatic effect of light reduction by the vascular plant canopy on the abiotic environment as well as on the infaunal community.

Abstracts:

Response of benthic communities to changing flushing regimes in a Southern California lagoon
The Southern California coast is dotted with coastal lagoons and embayments. Typically, geographically small with episodic freshwater input linked to rain events, these lagoons also receive significant inputs of energy, nutrients and organisms from the sea. Occasionally, lagoons close for extended periods or during specific reproductive seasons, possibly causing key species with life cycles dependent on ocean flushing and transport to disappear. Because plant cover is a main source of spatial heterogeneity in Pacific coast wetlands, changes in plant community can influence the abundance and diversity of benthic invertebrates. The objective of this research was to determine responses of the seagrass, Ruppia maritima L. and associated benthic communities to changing ocean flushing conditions in San Dieguito Lagoon.
San Dieguito Lagoon contains approximately 260 acres of wetland habitat that forms the lower part of the San Dieguito River valley. This lagoon opens and closes regularly based on rainfall amounts and flood scour. In October of 2002, San Dieguito River inlet was breached after an extended 8-month closure. The lower salinity, higher temperature water that resulted post-breach coincided with changes in abiotic sediment properties, with changes in plant distribution, and with changes in the benthic invertebrate community. Pre-breach, tidal flats were dominated by R. maritima but were largely unvegetated after opening the inlet. With the significant decrease in R. maritima cover, porewater salinity increased, porewater temperature decreased, and sediment redox values became more positive. Multivariate analysis indicates differences between pre- and post-breach seagrass fauna composition, partially due to increases in opportunistic species, such as Capitella capitata complex. After breaching the inlet, the seagrass infauna communities also exhibited an increase in diversity and evenness. Understanding the benthic community alterations due to changes in plant cover and in flushing regime will increase knowledge of complex wetland interactions and aid conservation of Southern California lagoon ecosystems.

Salt marsh vascular plant regulation of microalgal and infaunal community structure
Changes in plant cover are a feature of many disturbed wetland habitats (i.e. through wrack deposition, invasion, creation or flushing changes). This work is designed to identify the role of plant cover in wetland trophic functions. Previous studies of animal gut content analysis and isotope analysis suggest that the microalgae are the primary food source of macrobenthos in early successional stages of Pacific salt marshes, while Spartina foliosa detritus is used in later stages. In this experiment, we manipulate light and plant cover to determine how vascular plants interact with the benthic microalgae and invertebrate communities. Clipping and shading manipulations, designed to mimic the effects of vascular plant presence and absence and their shading effects, revealed that plants exert strong influence on abiotic environmental factors (salinity, water content, and temperature at the soil surface) that mediate changes in the biotic community. In the absence of plants, soils exhibited higher temperature and salinity, and lower water content than those in unclipped controls or shaded patches. The algal mats experienced greater mortality in the unshaded treatment and increased thickness in the shaded plots whose plants were removed. Early successional stage infaunal communities resembled communities seen in an early stage marshes; they had lower species richness, a larger proportion of insect larvae and a smaller proportion of annelids than when plants remain (control) or their shading effects are removed. This experiment demonstrates the dramatic effect of light reduction by the vascular plant canopy on the abiotic environment as well as on the infaunal community. This research will help elucidate the trophic ecology of salt marsh animal communities in general and the implications of changing plant cover associated with marsh restoration or plant invasion.