Abstract
The extensive loss of natural wetlands and temporary ponds worldwide has led to their creation and restoration for biodiversity and functional objectives. The assessment of various restoration approaches of these habitats can promote the persistence of their inhabitants, including aquatic invertebrate communities. While aquatic invertebrate communities within restored perennial waterbodies are well studied, few studies have occurred in seasonal wetlands, especially in California where over 90% of all vernal pool habitats have been destroyed. Due to this habitat destruction, several California vernal pool invertebrate species (e.g., vernal pool fairy shrimp) have been listed as threatened or endangered and are referred to as the “listed branchiopods”. The few studies which have compared aquatic invertebrate communities, including listed branchiopods, between constructed and natural vernal pools have found mixed results. I compared 90 natural and 90 human-constructed vernal pools of different ages across 10 sites throughout California. An underutilized method, dry-season sampling, was used to compare natural and restored vernal pools. This method entailed the collection of topsoil (known to contain aquatic invertebrate resting eggs) from each vernal pool using a soil core, followed by culturing of resting eggs using mesocosms (i.e., adding collected soil and water to a container). An aquarium net was used to sample mesocosms at two-week intervals for ten weeks during which all emerging aquatic invertebrates were identified and enumerated. Constructed and natural pools were statistically compared in terms of listed branchiopod abundance, total invertebrate abundance, species richness, and community composition. The influence of environmental variables (e.g., pool depth, surface area, age of constructed pool, latitude, and elevation) on community composition was assessed. Listed branchiopod and total invertebrate abundance were higher in natural pools, but species richness was not different, consistent with the results of prior worldwide meta-analysis studies. Community differences were driven by greater abundances of both specialists (e.g., listed branchiopods) as well as generalists (e.g., Ostracoda, Cladocera, Copepoda) in natural pools. Environmental variables influenced richness and abundances but did not influence community similarity between constructed and natural pools. The observed similarity in species richness between constructed and natural pools is in part due to the use of inoculum (i.e., soil containing plant and aquatic invertebrate propagules) in vernal pool construction, which allows passively dispersing vernal pool invertebrates to rapidly colonize constructed vernal pools. The observed differences in listed branchiopod and total invertebrate abundance between constructed and natural vernal pools were likely due to unmeasured effects (e.g., hydroregime, construction techniques), which future studies should investigate. Vernal pool construction has a pivotal role in conservation efforts to help combat the negative impacts of historical and ongoing habitat destruction. However, vernal pool construction, such as mitigation efforts to offset the loss of natural vernal pools, must be mindful of their limitations. Constructed vernal pools may not be fully replacing the aquatic invertebrate communities lost.