Conditional Outcomes of Facilitation by a Habitat‐modifying Subtidal Bivalve

Abstract

Facilitation by habitat modifiers is common in ecological communities, but the potential for temporal and spatial variations in environmental conditions to modify the outcome of these interactions and influence the strength of feedbacks is poorly understood. Suspension-feeding bivalves are important habitat modifiers that can facilitate surrounding communities by providing refuge from predation and changing boundary flows and through the production of organically enriched biodeposits. However, numerous studies have highlighted the problem of finding generalizable patterns. We tested the strength and generality of the relationship between the large suspension-feeding bivalve Atrina zelandica and surrounding macrofauna and hypothesized that facilitation by Atrina is conditional and modulated by site-specific suspended sediment concentration (SSC), which influences the quantity and quality of biodeposit production. We found temporally consistent patterns of higher rates of biodeposition and increased abundance and species richness in close proximity to Atrina under low SSC conditions. Facilitation strength decreased with increasing SSC, suggesting that the facilitation effect of Atrina is reduced and reversed along this environmental stress gradient.

Role of two contrasting ecosystem engineers (Zostera noltii and Cymodocea nodosa) on the food intake rate of Cerastoderma edule

“…In areas with relative strong hydrodynamics, as was the case in our study, food refreshment is high enough to prevent food depletion, whereas in more sheltered area this need not be the case. This would suggest that outcomes of ecosystem engineering by seagrass meadows on Wlter feeder performance has a conditional outcome, as has also been shown for other ecosystems (Norkko et al 2006). Flume studies would oVer an interesting approach for future studies to resolve these questions, since the use of a Xume allows the manipulation of individual factors (e.g.…”

Comparing biodiversity effects among ecosystem engineers of contrasting strength: macrofauna diversity in Zostera noltii and Spartina anglica vegetations

“…The contrasting influence of Spartina species on macrobenthos composition may be due to conditional outcomes of ecosystem engineering. For other systems, it has been demonstrated that depending on the physical forcing, effects of ecosystem engineers on biodiversity may be quite different (Norkko et al 2006). Another explanation for variable outcomes of increased structural complexity might be that in some systems, predators themselves may also benefit from protection against predation, thereby increasing predation rates on other smallest infaunal species (Bowden et al 2001).…”

Comparative physiological, biochemical, and molecular thermal stress response profiles for two Unionid freshwater mussel species

“…Ecosystem-level functional alteration may be especially pronounced within the state of Alabama, a renowned biodiversity hotspot for freshwater fauna, particularly fishes, crayfish and mollusks (Lydeard and Mayden, 1995). Mussels provide fundamental services such as nutrient cycling (Christian et al, 2008;Jost and Helmuth, 2007), habitat modification (Norkko et al, 2006) and water filtration (Budd et al, 2001). This functional diversity thus supports increased biodiversity within aquatic systems (Donadi et al, 2013;Vaughn et al, 2008).…”