Mapping and sampling the subtidal habitat of Sabellaria vulgaris in Delaware Bay
Date
2006
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Publisher
University of Delaware
Abstract
Sabellaria vulgaris (S. vulgaris) is a tube-building annelid polychaete found in dense aggregations throughout Delaware Bay. The worms build reefs on geologic hard bottom such as gravel, cobbles, or shells by cementing sand grains together to form masses of tubes. These structures provide habitat for a variety of organisms, which increases local species diversity. ☐ Although intertidal communities of S. vulgaris in Delaware Bay have been studied extensively, aggregation size, worm abundance, and specific sediment requirements are not well constrained for subtidal colonies. In order to better understand this habitat, an intensive mapping and sampling project was undertaken. During the summer of 2004, a suspected location of subtidal Sabellaria vulgaris 3.5 kilometers offshore of Slaughter Beach was mapped and sampled. The site had previously been identified as an area of high S. vulgaris abundance during a pilot study by Madsen (2004). ☐ Roughness (E1) and hardness (E2) values for the site were first mapped with the RoxAnnTM seabed classification system. The site was then grab sampled to determine worm abundance, to determine the preferred sediment type for subtidal S. vulgaris, and to determine if the system is capable of differentiating between bottom sediment and worm colony characteristics. In total, 78 samples were collected; of these, 72 samples were analyzed using standard dry sieving methods and the total number of S. vulgaris in each grab sample was tallied. Results were then statistically analyzed to understand the correlations between worm abundance, E1 and E2 values, and sediment size. ☐ Based on the RoxAnnTM data and sediment analysis, it was determined that the Slaughter Beach site was an area of high S. vulgaris abundance and that the colonies were patchy rather than continuous. The site was comprised of poorly sorted sediment with abundant gravel and medium sand, and very little fine sand and mud. Using Spearman and Kendall rank correlation coefficients, it was found that S. vulgaris was positively associated with larger grain size, specifically gravel, and negatively associated with fine sand and mud. Additionally, statistical correlation showed that S. vulgaris prefers a mixed sediment population, which is most likely a result of the sediment needs of the organism. Given the high positive correlation between gravel and abundance, it was inferred that abundant gravel sources dictate S. vulgaris settling locations. ☐ Study results also indicated that RoxAnnTM worked best at classifying areas of high E1 and E2 or low E1 and E2 values. Furthermore, it was determined that the system is an effective tool for identifying S. vulgaris habitat, but was less effective at identifying locations with little to no worm abundance.