The resurgent eastern oyster (Crassostrea virginica ) aquaculture industry in Delaware Bay , NJ may influence the relationship between horseshoe crabs (Limulus polyphemus ) and rufa red knots (Calidris canutus rufa ). Delaware Bay hosts the world’s largest spawning population of horseshoe crabs. Red knots are federally threatened shorebirds that feed on the abundant eggs to fuel their circumpolar migration. The overlap of aquaculture with spawning and foraging habitat may alter this trophic interaction. Research shows that oyster farms do not impact the ability of horseshoe crabs to access spawning beaches; however, it is unknown how they may impact the distribution of eggs or other prey available to the birds. The red knot distribution in Delaware Bay is associated with horseshoe crab egg abundance, and while foraging behavior is not impacted by the presence of farms, red knot abundance is reduced by 2-7% while farms are tended, so the relative abundance and distribution of eggs in relation to oyster farms may significantly impact this shorebird species.
This study examines the effect of oyster farms on the distribution of red knot foraging resource s. During the Spring 2021 spawning and migration season, benthic sediment surveys were conducted in four paired plots (90 m x 180 m) across a 3.5 km stretch of tidal flats that contain areas with and without oyster farms in Delaware Bay. Sediment cores determined the relative abundance of surfi cial eggs and other prey across each plot . Preliminary analysis suggests that the abundance of horseshoe crab eggs was highest on the beach slope and declined with increasing distance from the high tide line (Figure 1). Eggs were scarce farther than 300 ft from the high tide line, where farms were located. Other prey (e.g., bivalves, gastropods, and polychaetes ) were more abundant on the tidal flats than horseshoe crab eggs. This preliminary analysis indicates that eggs are not associated with red knot use or avoidance of oyster farms. Furthermore, across the tidal flats and within oyster farms , red knots likely forage primarily on alternative prey . Subsequent paired comparison analyses will examine whether oyster farms affect the distribution and abundance of horseshoe crab eggs or other prey.