Sabellaria vulgaris, the sandbuilder worm, builds unique worm reef habitats only in Delaware Bay. While the basic population biology, larval biology, and aspects of the species tube building properties have been investigated, more information is needed to verify the role of these habitats in ecosystem functioning and their importance to resource managers. The purpose of this dissertation is to explore spatial and temporal variations in recruitment, post-settlement mortality, distribution of intertidal colonies, larval substrate selectivity, and larval availability using field and laboratory methods.
In field experiments with artificial settling plates, I observed settlement of Sabellaria vulgaris and co-occurring species at three sites, each with an intertidal and subtidal location, between 2005 and 2006. Settlement of S. vulgaris was greater at intertidal locations, greater in 2006 than 2005, and greater at the two sites that contained large reefs. I documented 56 species in the S. vulgaris settling communities and the community composition was also different at the two reef sites.
In the laboratory, I experimentally determined the lower lethal temperature of Sabellaria vulgaris in order to assess the inter-annual variability in winter mortality events. S. vulgaris dies at temperatures below -4.5°C, with decreasing exposure times required at decreasing temperatures. Meteorological observations, including air temperature, calculated wind chill, and tidal level, were used to assess winter mortality between years, and predicted that winter mortality differed among years, and was verified with field observations.
The distribution of intertidal colonies and reefs was documented along the Delaware shoreline between 2001 and 2008 using ground-based surveys and two aerial methods. The ground-based surveys documented the regular occurrence of intertidal colonies at Port Mahon and North Bowers Beach, and reef formations at Slaughter Beach, Fowler Beach, Prime Hook Beach, and Broadkill Beach. The extent of reefs at each site varied between years due to natural and anthropogenic events. Storm events had relatively short-term effects of less than a year, while beach nourishment required 2-3 years for reefs to return to pre-nourishment extents.
In laboratory experiments, I found that settling larvae of Sabellaria vulgaris exhibited a preference for large grain sizes, greater than 0.5-mm size fractions. Additionally, no preference for adults, adult tubes, or tube material was detected. The presence of large grain sizes at the beaches where reefs are found partially explains the distribution of S. vulgaris reefs in Delaware Bay.
To understand the pattern of reef formation in relation to dispersal of larval stages, I used a hydrodynamic model coupled with a particle advection model that included behavior of Sabellaria vulgaris larvae. Larvae are readily distributed everywhere in Delaware Bay, with larvae better retained on early season and spring tidal releases. Larval exchange occurs between New Jersey and Delaware populations, with early season releases providing more larvae to New Jersey habitats, and late season releases providing more larvae to Delaware habitats.
Superimposed upon settlement and tube growth patterns determined by small-scale, site-specific factors, I have demonstrated that both natural forces, such as extended exposure to cold during low tides and nor’easter storms, as well as anthropogenic disturbances, primarily beach nourishment, affect the distribution of sandbuilder reefs on the Delaware shoreline. Combined, these observations suggest that the distribution of Sabellaria vulgaris is determined by site-specific factors, including wave action for sediment resuspension and substratum stability.