Community structure and trophic interactions in restored and natural estuarine mudflats: Complex trophic cascades and positive and negative effects of nutrients (California)

Habitat restoration can partially compensate for the extensive loss of coastal wetlands, but creation of habitat with intact ecological functions remains a challenging task. To evaluate structural features of restored coastal wetlands, I monitored gastropod and shorebird populations in restored sites within Mugu Lagoon, southern California. To compare ecological functions between natural and restored sites, I examined trophic relationships in a mudflat community under varying levels of nutrient enrichment. A four-year study of horn snail Cerithidea californica colonization into a newly restored site revealed lower densities than in a natural area throughout the study period. Snails were not evenly distributed throughout the restored site due to habitat quality and limited snail dispersal ability. Monitoring shorebird assemblages over one winter revealed that densities and species diversity were frequently as high or higher in restored as in natural areas, though each species preferred specific sites based on habitat heterogeneity and the amount of tidal flat available. To compare trophic relationships between natural and restored mudflat communities, I crossed presence of the herbivorous snail C. californica and nutrient (N and P) addition within enclosures on tidal mudflats. A strong upward trophic cascade was observed, as nutrient enrichment caused benthic cyanobacterial blooms, particularly in the restored site, which were consumed by C. californica and resulted in increased snail mortality. A second experiment crossed the presence of a predatory crab (Pachygrapsus crassipes) and nutrient enrichment on benthic microalgal and C. californica assemblages in natural and restored mudflats. In addition to direct predation on the snails, P. crassipes lowered C. californica growth rates through sediment disturbance, which reduced benthic microalgal biomass, particularly in the sandy sediments of the restored site. Nutrient enrichment decreased P. crassipes consumption of C. californica. These studies suggested that although restored sites provided adequate habitat for some wetland species, complex trophic dynamics often differed from those in natural areas. Experimental manipulations allow evaluation of ecological functions and can supplement structural assessments of restoration success.