Abstract
East Harbor (Truro, Massachusetts, U.S.A.) is a tidally-restricted salt marsh lagoon that has undergone partial restoration since 2002. After reintroducing seawater to the system following nearly 140 years of impoundment, remarkable transformations in plant and animal communities have occurred. But while a host of marine fish, crustaceans, and benthic invertebrates have become established throughout the system, an important herbivore, common periwinkle (Littorina littorea) has not. This gastropod is absent throughout the open lagoon where in the past several years macroalgae (mainly Enteromorpha intestinalis) has proliferated to nuisance levels. Grazing experiments with common periwinkles suggest that this species could significantly reduce the extent of macroalgae biomass there. The inability of this organism to colonize the lagoon may be related to high water temperatures. Laboratory experiments suggest that 4 days of constant water temperatures ≥ 28°C or 6+ daily hours of 30°C for several days result in high mortality. Data from in situ temperature loggers show that such conditions occur in the lagoon during July–August. Increased tidal flushing could lower water temperatures throughout East Harbor and allow this species to expand its range. This, in turn, could limit the development of macroalgae through herbivory. This study highlights the role of keystone species and the importance of restoring suitable temperature regimes for the functional recovery of hydrologically-impaired systems.
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