Persistence and Distribution of Temperate Intertidal Worm Reefs in Delaware Bay: A Comparison of Biological and Physical Factors

The sandbuilder worm Sabellaria vulgaris is widely found along the Mid-Atlantic region of the USA, but occurs in dense, reef-like structures in only one estuary. Reef formation and persistence was monitored in lower Delaware Bay along the western shoreline between 2001 and 2009 using ground surveys and aerial photography. These observations were combined with field larval settlement studies, laboratory low temperature susceptibility experiments, and an examination of the physical properties of the individual beaches to attempt to explain the location and persistence of the reefs. Neither exposure to temperature minima during spring low tides nor yearly variations in recruitment accounted for the observed reef distribution patterns. This study suggests that two physical factors, the distance from the beach to the 2-m isobath and the presence of coarse substratum >2 mm explain the greatest amount of variation in the observed distribution of intertidal S. vulgaris reefs and small aggregations.