Habitat fragmentation differentially affects trophic levels and alters behavior in a multi-trophic marine system

Abstract

Seagrass, an important subtidal marine ecosystem, is being lost at a rate of 110 km year, leading to fragmented seagrass seascapes. Habitat fragmentation is predicted to affect trophic levels differently, with higher trophic levels being more sensitive, stressing the importance of a multi-trophic perspective. Utilizing the trophic relationship between the blue crab (Callinectes sapidus) and hard clam (Mercenaria mercenaria), where adult blue crabs prey on juvenile blue crabs, and juvenile blue crabs prey on small hard clams, we examined whether predation rates, abundance, and behavior of predators and prey differed between continuous and fragmented seagrass in a multi-trophic context at two sites in Barnegat Bay, NJ. We tested the hypothesis that fragmented habitats would differentially affect trophic levels within a tri-trophic system, and our results supported this hypothesis. Densities of adult blue crabs were higher in fragmented than continuous habitats. Densities of juvenile blue crabs, the primary predator of hard clams, were lower in fragmented habitats than continuous, potentially due to increased predation by adult blue crabs. Clams experienced lower predation and burrowed to a shallower depth in fragmented habitats than in continuous habitat, likely due in part to the low densities of juvenile blue crabs, their primary predator. Our results suggest that while trophic levels are differentially affected, the impact of habitat fragmentation may be stronger on intermediate rather than top trophic levels in some marine systems.

Facilitating foundation species: The potential for plant–bivalve interactions to improve habitat restoration success

“…Seagrasses can facilitate clams by providing shelter from predators (Irlandi, 1994) and increased food availability (Irlandi & Peterson, 1991). However, seagrass can also hinder clam growth at high densities (Heck, Coen, & Wilson, 2002) and provide shelter for predators (Rielly‐Carroll & Freestone, 2017). Results likely vary due to differences in predator identity and abundance, and seagrass density.…”

Do species display characteristic intraspecific levels of patchiness in a given habitat type? The case of intertidal seagrass macrobenthos

“…It also occurs at all spatial scales such that patches are themselves patchy (Kotliar and Wiens 1990;Morrisey et al 1992). These spatial patterns have been much studied in seagrass systems, particularly in relation to anthropogenicallyinduced habitat fragmentation (Bell et al 2001;Rielly-Carroll and Freestone 2017). Some seagrass faunal characteristics do seem resistant to the effects of mosaic habitats, in some areas at least (Lefcheck et al 2016), but even continuous and apparently uniform beds may support patchy macrofaunal assemblages both in terms of their occupancy and abundance (Kraan et al 2009; Barnes and Hamylton 2019).…”

The World of Edges in Submerged Vegetated Marine Canopies: From Patch to Canopy Scale

“…If this elevated secondary production leads to increases in trophic transfer, then edges may serve as a significant trophic conduit to higher-level consumers within patches [144]. While trophic levels are differentially affected, the impact of habitat fragmentation may be greater on intermediate rather than top trophic levels in fragmented seagrass seascapes [182]. Predators increase their success by searching patch edges, and this results in the greatest predation risk being for prey in isolated intermediatesized patches rather than larger ones [149].…”