Seagrass beds occur in a variety of spatial configurations at both high-energy shoals and low- energy quiescent bays. I applied a landscape-ecology approach to examine how habitat patch size under high- and low-energy conditions influenced growth and survival of large (41.9 mm) and small (22.3 mm) hard clams, Mercenaria mercenaria, and how the spatial configuration (i.e., percent coverage) of seagrass patches influenced survival and siphon cropping of small clams.

Large and small clams grew faster within vegetation than out at both high- and low-energy sites. Within the vegetation, growth of large clams was faster in medium sized patches of seagrass (2-3 m across) than in small patches (1 m across) and was intermediate in large patches (>4-5 m across). Growth of small clams was independent of the two seagrass patch sizes tested (large vs. small). Although small clams grew significantly more within seagrass under both high- and low- energy conditions, the effect was significantly more pronounced at high-energy sites than at low. The effect of seagrass cover on clam growth appears to be the result of a complex interaction among food supply, predation disturbance, and sediment stability with the relative importance of these processes varying with size of the clam, hydrographic regime, habitat patch size, and local site differences.

Survivorship of large clams was independent of presence of seagrass and seagrass patch size, but approximately three times as many clams were recovered live from low-energy than from high- energy sites. An opposite pattern occurred for small clams with significantly fewer clams being recovered live from two low-energy sites than from one high-energy site. Small clam survivorship also increased with the areal extent of seagrass cover. Twice as many clams were recovered live from large patches of seagrass than from small, and 18 times more were recovered from large patches than from unvegetated sediments. Survivorship patterns of small clams were positively correlated to changes in below-ground biomass and shoot densities among sites and seagrass treatments as well as to patterns in growth of clams.

When clams were placed in both the vegetated and unvegetated portions of a 100-m^2 area of seafloor nearly twice as many clams were recovered live with 99% seagrass cover than with 23% seagrass cover, while survivorship was intermediate with 70% cover. Mean adjusted siphon weights were also approximately 76% heavier from the 99% seagrass cover treatment than from the 70% or 23% cover treatments. Survivorship of clams placed within an equal area of seagrass (100-m^2) in very patchy, patchy, and continuous spatial configurations was 40% higher in the continuous seagrass treatment than in either of the two patchy treatments.

I applied a landscape-ecology approach to an aquatic environment and demonstrated that trophic transfer of energy in seagrass ecosystems changes with patch size and spatial configuration of the habitat. These results have direct application to restoration and management of seagrass beds.