MODERN HARD SUBSTRATES IN AN ESTUARINE SETTING: MAPPING AND SAMPLING THE SUBTIDAL HABITAT OF SABELLARIA VULGARIS IN DELAWARE BAY

Sabellaria vulgaris is a tube-building sedentary polychaete common to the Mid-Atlantic United States from Cape Cod to Georgia. They typically inhabit low intertidal to shallow subtidal waters. In terms of benthic habitat, one of the distinct aspects of Sabellaria is that they can be found in dense aggregations sometimes forming what have been termed “worm reefs”. These reefs, composed primarily of sand particles and formed preferentially on pebbles to cobbles, form a hard substrate that occurs within the overall finer-grained, softer, sediments that are common of estuarine settings. The reefs are more physically stable and ecologically diverse than surrounding sediments and as such, they, and their associated invertebrates, function as an abundant food source and represent a productive nearshore habitat that may be of great importance to local fisheries.

This project is using three acoustic instruments, a RoxAnn seabed classification system, a chirp sub-bottom profiler, and a multi-beam bathymetric mapping system, integrated with bottom grab samples and underwater video imaging to map and sample the subtidal habitat of Sabellaria vulgaris in the lower-to-middle portions of Delaware Bay. The grabs are analyzed to determine the distribution of grain-size and to constrain the type and abundance of macroinvertebrates and other organisms associated with this habitat. This research is part of a larger effort to identify and map the various benthic habitats and bottom and sub-bottom sediments of Delaware Bay.

Preliminary results indicate that Sabellaria will begin to colonize and construct hard substrate reef environments on larger grain-size particles (e.g., cobbles and pebbles) when sufficient sand- to silt-sized particles are also present to construct their tubes. This rather unique requirement, given the estuarine setting of Delaware Bay, appears to be created where higher energy events (e.g., storms, scour due to bottom currents) have concentrated larger grain-size particles. An example of this environment has been mapped approximately 1 km offshore in shallow (3-4 m) water in an area of steeper slope that is aligned to prevailing bottom currents. This 850 m x 450 m area contains abundant Sabellaria reefs. Further mapping and sampling of the hard substrates associated with the presence of Sabellaria is on-going.