Although invasive species often resemble their native counterparts, diVerences in their foraging and antipredator strategies may disrupt native food webs. In a California estuary, we showed that regions dominated by native crabs and native whelks have low mortality of native oysters (the basal prey), while regions dominated by invasive crabs and invasive whelks have high oyster mortality and are consequently losing a biologically diverse habitat.Using Weld experiments, we demonstrated that the invasive whelk's distribution is causally related to a large-scale pattern of oyster mortality. To determine whether predatorprey interactions between crabs (top predators) and whelks (intermediate consumers) indirectly control the pattern of oyster mortality, we manipulated the presence and invasion status of the intermediate and top trophic levels in laboratory mesocosms. Our results show that native crabs indirectly maintain a portion of the estuary's oyster habitat by both consuming native whelks (density-mediated trophic cascade) and altering their foraging behavior (trait-mediated trophic cascade). In contrast, invasive whelks are naive to crab predators and fail to avoid them, thereby inhibiting trait-mediated cascades and their invasion into areas with native crabs. Similarly, when native crabs are replaced with invasive crabs, the naive foraging strategy and smaller size of invasive crabs prevents them from eYciently consuming adult whelks, thereby inhibiting strong density-mediated cascades. Thus, while trophic cascades allow native crabs, whelks, and oysters to locally co-exist, the replacement of native crabs and whelks by functionally similar invasive species results in severe depletion of native oysters. As 123 coastal systems become increasingly invaded, the mismatch of evolutionarily based strategies among predators and prey may lead to further losses of critical habitat that support marine biodiversity and ecosystem function.

Small offshore banks may be sites of intense feeding by upper trophic level predators. We studied the distribution of cetaceans, seabirds, pelagic fish, euphausiids and zooplankton over a 9 × 15 km bank to determine the conditions and processes that concentrated prey there and to examine the relative importance of bottom-up or top-down controls. Euphausiids were the primary prey during most foraging activity. While these were widespread in subsurface waters, foraging was concentrated on dense surface swarms that formed during daylight hours over 2 small crests. Internal wave passage resulted in upward movement and concentration of euphausiids in these areas through a coupling of physical processes and euphausiid behavior, resulting in surface swarms. Thus, internal waves appear to provide a critical mechanism enhancing trophic energy transfer. The formation of dense, localized and accessible prey concentrations was more important to foraging than was the overall available prey biomass. The estimated maximum daily consumption of euphausiids by cetaceans, seabirds and herring combined was < 0.4% of the estimated instantaneous euphausiid biomass, and top-down control was unlikely to have substantially influenced euphausiid biomass at this site. Some predator species that do not prey extensively on euphausiids or herring were more prevalent in off-bank waters. The scales of predictability and the temporal dynamics of such features determine the manner in which populations of upper trophic level organisms utilize a variable environment.KEY WORDS: Foraging ecology · Euphausiid · Internal wave · Consumption · Cetacean · SeabirdResale or republication not permitted without written consent of the publisher

BackgroundEcologists, fisheries scientists, and coastal managers have all called for an ecosystem approach to fisheries management, yet many species such as the American lobster (Homarus americanus) are still largely managed individually. One hypothesis that has yet to be tested suggests that human augmentation of lobster diets via the use of Atlantic herring (Clupea harengus) as bait may contribute to recent increases in lobster landings. Currently 70% of Atlantic herring landings in the Gulf of Maine are used as bait to catch lobsters in traps throughout coastal New England.Methodology/Principal FindingsWe examined the effects of this herring bait on the diet composition and growth rate of lobsters at heavily baited vs. seasonally closed (i.e., bait free) sites in coastal Maine. Our results suggest that human use of herring bait may be subsidizing juvenile lobster diets, thereby enhancing lobster growth and the overall economic value and yield of one of the most valuable fisheries in the U.S.Conclusions/SignificanceOur study illustrates that shifting to an ecosystem approach to fisheries management should require consideration of cross-fishery interactions.

Coastal marine habitats continue to be degraded, thereby compelling largescale restoration in many parts of the world. Whether restored habitats function similarly to natural habitats and fully recover lost ecosystem services is unclear. In estuaries, oyster reefs have been degraded by multiple anthropogenic activities including destructive fishing practices and reduced water quality, motivating restoration to maintain oyster fisheries and other ecosystem services, often at relatively high cost. We compared fish and invertebrate communities on recently restored (0-1 year post-restoration), older restored (3-4 years post-restoration), and natural oyster reefs to determine if and when restored reefs support functionally similar faunal communities. To test the influence of landscape setting on the faunal communities, the restored and natural reefs, as well as a control without reef present, were distributed among three landscapes (on the edge of salt marsh away from seagrass [salt marsh landscape], on mudflats [mudflat landscape], and near to seagrass and salt marsh [seagrass landscape]). Oyster density and biomass were greatest on restored reef habitat, as were those of non-oyster bivalve species. Total abundance of invertebrates was much greater on oyster reefs than in control plots, regardless of reef or landscape type, yet were frequently highest on older restored reefs. Meanwhile, juvenile fish densities were greatest on natural reefs, at intermediate densities on older restored reefs, and least abundant on controls. When comparing the effects of reef age and landscape setting, juvenile fish densities were greatest on younger reefs within the mudflat landscape. Collectively, these results indicate that oyster reefs harbor higher densities of resident invertebrate prey, which may explain why reef habitat is also important for juvenile fish. Laboratory and field experiments supported the notion that gag grouper (a predatory demersal fish) forage more effectively on oyster reefs than on unstructured mud bottom, whereas our experiments suggest that

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