3-2 Soft Sediment Communities

3-2 Soft Sediment Communities - SOFT-SEDIMENTS Topic 15...

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Unformatted text preview: SOFT-SEDIMENTS Topic 15 Chapters 5, pages 199-214 and 6, pages 308-330 from Nybakken and Bertness Non-vegetated bottoms BENTHIC COMMUNITIES Most of the seafloor is muddy Benthic communities are good indicators of human impact What controls the distribution and abundance of benthos on non-vegetated bottoms? Compare with rocky substrates: 1) Space not limiting to infauna: Sediments are 3-D and vertical segregation among species may lessen competition May migrate in response to crowding Exploitative competition for food, not by overgrowth, and monopolies are rare Figure 5.11 2) Predation is important too: Surface predators Siphon or tail nipping Burrowing predators Digging predators (blue crabs) Infaunal predators Most studies examine epifaunal predators only Figure 5.8 Predation effects differ: Density of most soft-sediment benthos increases without predators but with no change in species diversity monopolies are rare No single keystone predator but a suite Woodin study Diopatra cuprea lives in dense groups on sand flats A polychaete worm that lives head up, and builds a tough, ornamented tube cap about 2-3 cm high Diopatra affects infauna: Under dense Diopatra aggregations, the abundance of infaunal clams and worms is high Blue crabs dig to prey on infauna Is larval settlement, predation or other biotic interactions responsible for the increase? Baffling by tube caps may effect larval settlement Increased settlement of larvae may lead to increased adult abundance Woodin study Full and partial exclusion experiments were conducted Infaunal abundance increased in full cages (that reduce predation and enhance larval settlement), but not in 2-sided cages (that enhance larval settlement without interfering with predators) Suggests that predation from blue crabs is important Without predators, no change in richness/diversity no monopoly all infauna increased Soft-sediment communities do not follow the rocky shore paradigm 3)...
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3-2 Soft Sediment Communities - SOFT-SEDIMENTS Topic 15...

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