Reproductive output and consistency of source populations in the sea star Pisaster ochraceus

Abstract

Although a common goal of marine reserves is to protect areas of high reproductive output, few studies have tested whether these source populations are spatially and temporally consistent. For 6 years between 1995 and 2005, we examined nutrient storage and gonad production in the sea star Pisaster ochraceus at 2 sites on the central coast of Oregon, USA. Sea stars accumulated energy in the pyloric caeca during a short season of intensive feeding (May to September). Within a site, the size of the pyloric caeca in the fall accurately predicted reproductive output during the following spring. In accord with hypotheses regarding bottom-up effects, the pyloric caeca were generally larger at the site where mussels were more abundant in the diet, indicating a greater accumulation of surplus energy. However, gonad indices were consistently ∼50% lower at this site, suggesting striking differences in allocation to reproduction. This difference between populations was maintained despite marked variation among years in oceanographic conditions and reproductive output. These results suggest that (1) source populations may be consistent spatially, but (2) identifying those sources may be more complex than simply targeting areas with high quality resources and strong bottom-up influences. Rather, predicting patterns of per capita reproductive output may require a more detailed understanding of the causes of spatial variation in allocation to maintenance, growth, and reproduction. © Inter-Research 2007.