Landscape ecology and the functions of marine soft-sediment habitats: How seagrass landscapes influence growth and survival of a marine invertebrate

Seagrass beds occur in a variety of spatial configurations at both high-energy shoals and low-energy quiescent bays. I investigated the effects of seagrass presence and seagrass patch size under high- and low-energy regimes on growth and survival of small (22.3 mm) and large (41.9 mm) hard clams, Mercenaria mercenaria, and the effect of spatial patterning of the vegetation (i.e., percent cover) on survival and siphon cropping of small hard clams.; There was no effect of presence of vegetation, seagrass patch size, or ambient energy regime on the growth of large clams. Growth of small clams was also independent of seagrass patch size; but was significantly less in unvegetated sediments under both high- and low-energy conditions, and the effect was more pronounced at high-energy sites.; Survivorship of large clams in the fall was independent of presence of seagrass and seagrass patch size, but approximately three times as many live clams were recovered from low-energy than from high-energy sites. In the spring an opposite pattern occurred for small clams with significantly fewer live clams recovered from low-energy sites. For small clams, twice as many were recovered live from large patches of seagrass than from small, and 18 times more were recovered from large patches than from unvegetated sediments.; The spatial patterning of the vegetation influenced siphon cropping and survival of small clams. Nearly twice as many animals were recovered live from the sand and the seagrass in 100-m{dollar}sp2{dollar} plots with 99% seagrass cover than with 23% cover, while survivorship was intermediate with 70% cover. Adjusted siphon weights were also significantly heavier with 99% seagrass cover than with 70% or 23% cover. Survivorship of clams placed within an equal area of seagrass in very patchy, patchy, and continuous cover was 40% higher in the continuous treatment than in either of the two patchy treatments.; This study clearly demonstrates that habitat patch size and energy regime in a soft-sediment marine ecosystem can affect growth rates and survival of an infaunal bivalve. Predation and cropping also is altered as the amount and spatial patterning of vegetation in the landscape changes.