Abstract
We report on patterns of abundance, recruitment, and predation on the blue mussel (Mytilus edulis) in three human‐dominated estuaries in the northeastern United States. Through replicate field experiments and observational studies at multiple sites nested within each of the three estuaries, we investigated the relative influences of local and regional scale variation in select bottom‐up and top‐down factors on blue mussel populations on wave‐protected rocky shores. The most striking result was the decoupling between adult abundance and recruitment: mussel recruitment rates were highest in the most northern estuary, Casco Bay, while adult abundances were highest in the most southern estuary, Long Island Sound. We detected evidence of top‐down forcing on adult abundance by consumers in the two more southern estuaries, Narragansett Bay and Long Island Sound, but not in Casco Bay. Finally, we observed some indications of bottom‐up forcing on mussel abundance and recruitment at the within‐estuary scale, but these signals were not consistent among estuaries or across the responses measured (e.g., adult abundances and recruitment rates). Our results support previous work demonstrating the importance of both top‐down and bottom‐up influences on rocky shore populations, and also highlight how future research—particularly integrating studies of the different ontogenetic stages of mussels—could further advance understanding of biological population dynamics in this and other systems.
Highlights
Rocky shore communities—shaped by strong environmental gradients and dominated by manipulated and often slow moving organisms—have served as important development and testing grounds for ecological theory (Paine 1994, Menge and Branch 2001)
Environmental data As expected, summer air and water temperatures were higher in the southerly estuaries, Narragansett Bay (NB) and Long Island Sound (LI), in comparison to Casco Bay (Table 1)
In summary, M. edulis populations varied in ways consistent with some but not all of the hypotheses presented in this paper
Summary
Rocky shore communities—shaped by strong environmental gradients and dominated by manipulated and often slow moving organisms—have served as important development and testing grounds for ecological theory (Paine 1994, Menge and Branch 2001). Mussels are one of several organisms that have given significant insights into rocky shore community dynamics worldwide. Observations and experiments of predator-prey dynamics involving mussels have yielded important insights, including understanding of how spatial and temporal variation in predation strength and predator identity can shape benthic community structure and functioning (Paine 1966, Robles et al 1995, Navarrete and Menge 1996, Menge et al 2004, Navarrete and Manzur 2008, Boudreau and Hamilton 2012). Ecological processes may be shaped by latitudinal clines in environmental conditions and concomitant biogeographic and oceanographic variation. Understanding if and how ecological processes may vary across biogeographic and oceanographic clines is critical for our broader understanding of community functioning in rocky shores, as well as other marine systems. Understanding processes in wave-protected estuarine settings is critical, given the ecosystem’s vulnerability to human impacts, rising temperatures, and other environmental stressors due to climate change (Helmuth et al 2006, Gedan et al 2011, Bernhardt and Leslie 2013)
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