Effects of shoreline modification on a Northern Puget Sound beach: Microclimate and embryo mortality in surt smelt (Hypomesus pretiosus)

Abstract

Human alteration of Puget Sound shorelines is extensive yet its ecological consequences are largely undocumented. This study evaluates differences between natural and heavily modified beaches in terms of microclimate and one aspect of biological condition. Electronic data laggers were placed at a tidal height of approximately 3.7 m (12 ft) above mean lower low water during July 16–20, 2001, to monitor light intensity, substrate and air temperatures, and humidity. Substrate samples were collected at the end of the monitoring period to evaluate condition and density of eggs from surf smelt (Hypomesus pretiosus), a forage fish species that spawns on gravel-sand beaches in the upper intertidal zone. The modified beach had significantly higher daily mean light intensity, air temperature and substrate temperature, and significantly lower daily mean relative humidity. Particularly striking were the differences in substrate temperature which, on the natural beach, ranged from 12.1°C to 18.2°C (mean=14.1°C) and on the modified beach ranged from 14.4°C to 29.4°C (mean=18.8°C). In addition to these different means and more extreme values, microclimate conditions on the modified beach were more variable, indicative of a less buffered environment. The proportion of smelt eggs containing live embryos on the altered beach was approximately half that of the natural beach.