Ecology of Glacial Till Substrate in Massachusetts Bay

Ann E. Pembroke 1, Michael Tyrrell 2, Paul D. Martin 2, and George A. McLachlan 3

1 Normandeau Associates, Inc., Bedford, New Hampshire
2 TRC Environmental, Inc., Lowell, Massachusetts
3 Duke Energy, Inc., Boston, Massachusetts

Benthic resources were monitored for the purpose of siting and permitting a 30-mile long gas pipeline in Massachusetts Bay and Boston Harbor. The pipeline crosses several substrate types, including silt, sand, glacial till, and boulder/ledge. The biological monitoring program incorporates a "Before-After Control-Impact" (BACI) design for each of these substrate types so that recovery of the benthic resources following construction could be documented. Two preconstruction surveys (winter and summer) were completed and results of the surveys of the glacial till substrate are discussed herein.

Glacial till is a complex substrate consisting of various mixtures of sediments that run the entire range of the Wentworth classification system. This complexity provides habitat for numerous invertebrate species exhibiting different life history strategies, including early benthic phase (EBP) lobsters, but also makes it a difficult habitat to sample quantitatively. Air-lift methods developed to inventory EBP lobster populations were successfully adapted to sample the entire benthic community.

Species richness was high (up to 189 taxa/1.5m2) regardless of season and numerical dominance by a single species was rare. Numerical classification indicated that stations were most closely associated by depth and season. Species composition was similar to rocky communities but the presence of cobble-to-gravel sized rocks and granular sediments created interstitial spaces that enabled recruitment of infaunal and cryptic species as well.

Keywords: glacial till, marine benthos, EBP lobsters, BACI design