Understanding Habitat Fragmentation Between a Full Tidal Bay and a Tidally Restricted Urban Lagoon

Structures installed to modify hydrology in waterways such as culverts can cause fragmentation across intertidal and subtidal areas, leading to increased habitat patchiness of previous interconnected habitats. This study aimed to understand the potential impacts of a 268-m culvert on habitat parameters in a large tidal bay and a coastal lagoon in Southern California. We analyzed key habitat characteristics of both sites including water conditions and sediment characteristics as well as biotic communities including zooplankton, benthic macroinvertebrate, and fish communities. As compared to the tidal bay, the lagoon had more extreme temperature differences, decreased dissolved oxygen and salinity, and lower zooplankton abundance. The composition of zooplankton, benthic macroinvertebrates, and small fish communities also differed between the two habitats, suggesting higher habitat heterogeneity than might be expected given their proximity. Removing the culvert that connects these habitats and returning it to an earth-lined open channel would decrease fragmentation between the two habitats and improve trophic quality while retaining the estuarine characteristics of the overall system.