Abstract In 1974, Braun suggested that environmental changes influenced prehistoric shellfish utilization along the southern New England coast. This was based principally on an evaluation of mollusk data from midden horizons around Boston Harbor, Massachusetts, and secondarily on literature derived from a variety of sources relevant to Northeast coastal environments. From his analysis, Braun (1974) concludes that utilization of particular shellfish species in New England coastal waters changed with the climate and was not directly related to cultural preference, as implied by Ritchie (1969). As a result of the cooling climate, the warmer water mollusk assemblage (oysterquahog) became a less viable food resource by the middle Woodland period (ca. 1,800 to 1,600 yr BP). After this, there was a marked increase in the utilization of the cooler water mollusk species (soft shell clam-blue mussel). Snow (1980, 1981) also supports the concept that cultural adaptation in a coastal environment occurs when physical factors change. He notes that the availability of shellfish species is determined by environmental conditions in a particular area, which in turn limit human exploitation of certain shellfish assemblages (Snow, 1980, 1981). Although controversy exists regarding the direct causal relationship between climate and cultural subsistence change (Dincause, 1981), Wendland and Bryson (1974) demonstrated a strong correlation between inferred climatic variation and worldwide cultural adaptation. Lightfoot (1985) and Erlandson (1988) recently elaborated on the relationship between shellfish utilization and coastal site strategies. Both also suggest that adaptation and site selection appears to be, in part, related to changing environmental conditions rather

Abstract Occurrences of algal mats at Plum Island along the northeastern coast of Massachusetts at 43°N latitude consist of laminated quartz silt and sand bound by mucous-secreting, filamentous blue-green algae (Cyanophyta). Recent discoveries of modern algal mats in quartz sands along cool, temperate coasts further confirms the fact that algal mat-forming organisms have wide temperature and salinity as well as substrate tolerances. At Plum Island, algal mats occur along the high intertidal to low supratidal margins of a metahaline pond in a swale on a recurved spit at the southern end of the island. They are also found along the margin of the marsh next to the edge of the backdune area of the island's dune field. The algal mats on Plum Island are vertically stratified into three major zones. The upper 1 mm of the mat in the spit area is dark brownish green due to filaments of Lyngbya, Microcoleous, and other smaller filamentous blue-green (?) algae. Coccoid cyanophytes (including Enthophysalisl), diatoms, Euglena, and nematode worms also are present. Below this upper green layer, there is a thinner, pinkish layer containing anaerobic, photosynthetic purple sulfur bacteria. Underlying the pinkish layer, there usually is a third layer composed of organic-rich black sand, 1-10 cm thick, indicating anaerobic conditions. This black layer contains the remains of buried older surface mats whose laminae can be recognized as alternating layers of decaying organic matter and layers of water-laid sands and wind-blown silts. Gelatinous material aiding filament-binding of sediment extends 1-7 mm below the upper surface. No carbonate cementation was found. The larger structures associated with these algal mats include gas domes, desiccation ploygons, elongated ridges, rolled mats, mounds, and distorted mats redeposited after flotation. Algal mat growth affects physical sedimentation in part of the interdune area of the spit by stabilizing silt and sand after erosion and/or sediment deposition. By stabilizing each new sediment surface, these mats aid upward growth of low, ponded areas of the spit. Overturned and rolled mats produce mounds that become colonized by vascular plants and thus initiate dune development on low, flat areas. Ancient quartzose algal mats may be difficult to recognize in the stratigraphic record, but occurrences are known. Preservation potential is low because of the lack of carbonate cementation. Possible criteria for recognition include fine sand and silt laminae, desiccation cracks, elongated ridges, mounds, and overturned mats.