Seagrass populations are in decline worldwide. California’s native seagrass, Zostera marina (eelgrass) is no exception to this trend. In the last 8 years, Morro Bay, California has lost 95% of its eelgrass. Eelgrass is an ecosystem engineer, providing important ecosystem services such as sediment stabilization, nutrient cycling, and nursery habitats for fish. The loss of eelgrass is likely to have rippling community effects. Expensive, large scale restoration efforts were conducted from 2012-2014 and have been unsuccessful in Morro Bay. The failure of these restoration efforts necessitates a better understanding of the causes of eelgrass decline in this particular estuary. Previous research on eelgrass in California has demonstrated a link between population genetic diversity and eelgrass bed health, ecosystem functioning, resilience to climate change, and tolerance of disease and grazing pressure. The genetic diversity of Morro Bay eelgrass populations has not been assessed until now. We characterize the genetic diversity of Morro Bay eelgrass by conducting fragment length analysis of 11 microsatellite loci. Additionally, we place Morro Bay eelgrass in the genetic context of other eelgrass populations on the west coast of North America.
Results/Conclusions
Despite the precipitous loss of eelgrass in Morro Bay between 2007 and 2017, genetic diversity remains comparable to other populations on the west coast. Allelic richness (AR) is 3.49 and is similar to values published for San Francisco Bay (4.29 AR for entire bay; Ort et al. 2012), lower than values published for southern California and Northern Mexico populations (4.78 and 4.83 average AR respectively; Olsen et al. 2014), and much lower than Bodega bay (5.49 AR; Kamel et al. 2012). We found no population differentiation within the bay, with all sampled populations demonstrating admixture indicative of consistently high gene flow throughout the bay. Comparison with other nearby populations revealed that Morro Bay eelgrass is considerably genetically differentiated, indicating little gene flow from populations to the north and south. Our results show that while genetic diversity in Morro Bay may be lower than before the large population bottlenecks of the recent past, diversity is still relatively high. Future restoration efforts in the bay could, therefore, use source material from any bed (or beds) within Morro Bay. Additionally, the isolation of the bay could mean there is local adaptation occurring, such that bringing in source materials from other populations could cause inbreeding depression.