Anchialine pool shrimp (Halocaridina rubra) as an indicator of sewage in coastal groundwater ecosystems on the island of Hawai'i.

Groundwater is a primary pathway for wastewater and other pollutants to enter coastal ecosystems worldwide. Sewage associated pathogens, pharmaceuticals, and other emerging contaminants pose potential risks to marine life and human health. Anchialine pool ecosystems and the endemic species they support are at risk and provide an opportunity to sample for presence of contaminants prior to diffusion in the marine environment. In this study, we tested the potential use of nitrogen isotopes in the tissues of a dominant anchialine pool grazing shrimp (Halocaridina rubra), as a bioindicator for sewage in groundwater flowing through their habitats. Water quality parameters and shrimp tissue isotopes (N and C) were collected from pools exposed to a range of sewage contamination along the West Hawai'i coastal corridor from 2015 to 2017. Data were used to test for spatial and temporal variability both within and among pools and to examine the relationship between stable isotopes and water quality parameters. Within 22 pools, mean δ15N from whole tissue samples ranged between 2.74‰ and 22.46‰. Variability of isotope values was low within individual pools and within pool clusters. However, δ15N differed significantly between areas and indicated that sewage is entering groundwater in some of the sampled locations. The significant positive relationship between δ15N and dissolved nitrogen (p<0.001, R2 = 0.84) and δ15N and phosphorus (p<0.001, R2 = 0.9) support this conclusion. In a mesocosm experiment, the nitrogen half-life for H. rubra tissue was estimated to be 20.4 days, demonstrating that the grazer provides a time-integrative sample compared to grab-sample measurements of dissolved nutrients. Ubiquitous grazers such as H. rubra may prove a useful and cost-effective method for δ15N detection of sewage in conjunction with standard monitoring methods, enabling sampling of a large number of pools to establish and refine monitoring programs, especially because anchialine habitats typically support no macroalgae.

Using oxygen and hydrogen stable isotopes to track the migratory movement of Sharp-shinned Hawks (Accipiter striatus) along Western Flyways of North America.

The large-scale patterns of movement for the Sharp-shinned Hawk (Accipiter striatus), a small forest hawk found throughout western North America, are largely unknown. However, based on field observations we set out to test the hypothesis that juvenile migratory A. striatus caught along two distinct migration routes on opposite sides of the Sierra Nevada Mountains of North America (Pacific Coast and Intermountain Migratory Flyways) come from geographically different natal populations. We applied stable isotope analysis of hydrogen (H) and oxygen (O) of feathers, and large scale models of spatial isotopic variation (isoscapes) to formulate spatially explicit predictions of the origin of the migrant birds. Novel relationships were assessed between the measured hydrogen and oxygen isotope values of feathers from A. striatus museum specimens of known origin and the isoscape modeled hydrogen and oxygen isotope values of precipitation at those known locations. We used these relationships to predict the origin regions for birds migrating along the two flyways from the measured isotope values of migrant's feathers and the associated hydrogen and oxygen isotopic composition of precipitation where these feathers were formed. The birds from the two migration routes had overlap in their natal/breeding origins and did not differentiate into fully separate migratory populations, with birds from the Pacific Coast Migratory Flyway showing broader natal geographic origins than those from the Intermountain Flyway. The methodology based on oxygen isotopes had, in general, less predictive power than the one based on hydrogen. There was broad agreement between the two isotope approaches in the geographic assignment of the origins of birds migrating along the Pacific Coast Flyway, but not for those migrating along the Intermountain Migratory Flyway. These results are discussed in terms of their implications for conservation efforts of A. striatus in western North America, and the use of combined hydrogen and oxygen stable isotope analysis to track the movement of birds of prey on continental scales.