Influence of macrofaunal assemblages and environmental heterogeneity on microphytobenthic production in experimental systems

Abstract

Despite the complexity of natural systems, heterogeneity caused by the fragmentation of habitats has seldom been considered when investigating ecosystem processes. Empirical approaches that have included the influence of heterogeneity tend to be biased towards terrestrial habitats; yet marine systems offer opportunities by virtue of their relative ease of manipulation, rapid response times and the well-understood effects of macrofauna on sediment processes. Here, the influence of heterogeneity on microphytobenthic production in synthetic estuarine assemblages is examined. Heterogeneity was created by enriching patches of sediment with detrital algae (Enteromorpha intestinalis) to provide a source of allochthonous organic matter. A gradient of species density for four numerically dominant intertidal macrofauna (Hediste diversicolor, Hydrobia ulvae, Corophium volutator, Macoma balthica) was constructed, and microphytobenthic biomass at the sediment surface was measured. Statistical analysis using generalized least squares regression indicated that heterogeneity within our system was a significant driving factor that interacted with macrofaunal density and species identity. Microphytobenthic biomass was highest in enriched patches, suggesting that nutrients were obtained locally from the sediment-water interface and not from the water column. Our findings demonstrate that organic enrichment can cause the development of heterogeneity which influences infaunal bioturbation and consequent nutrient generation, a driver of microphytobenthic production.

Habitat structure mediates biodiversity effects on ecosystem properties

“…Resource availability and distribution, in particular, are fundamental in influencing community structure and species behaviour [4,51], and may also strongly modify ecosystem properties [18,19]. In contrast to previous studies that have demonstrated clear effects of biodiversity on ecosystem function under largely homogeneous conditions (e.g.…”

“…To incorporate habitat heterogeneity, patches were either non-enriched (NE) or enriched (E) with dried, ground U. intestinalis [18,19]. We assembled two heterogeneity configurations (H A and H B ).…”

“…[16,17]) have subsequently been shown to be of much greater importance in equivalent heterogeneous systems [18]. Moreover, the way species interact with their environment has the potential to alter the nature of trophic interactions [19] and the fundamental form of the relationship between biodiversity and ecosystem properties [20,21], rekindling debate over the relevance and capacity of manipulative experiments to inform management, conservation and policy [22][23][24][25][26].…”

Functional effects of the hadal sea cucumber Elpidia atakama (Echinodermata: Holothuroidea, Elasipodida) reflect small-scale patterns of resource availability

“…In the present study, E. atakama spent 150 min relocating and 267 min feeding (a ratio of 1:1.8), suggesting that resource supply is indeed abundant and that the distance between patches is relatively short (20-40 min travel time, or approximately 10 body length distance). This pattern of movement suggests considerable sensitivity to food concentration (McClintic et al 2008) and implies that the dynamics and organisation of hadal communities are intimately linked to habitat structure and the distribution of resources in ways similar to those found in shallower benthic communities (Levinton and Kelaher 2004;Dyson et al 2007;Bulling et al 2008;Nogaro et al 2008;Godbold et al 2011). Thus, the cumulative response of hadal species to such small-scale variation is likely to influence species contributions to ecosystem properties at much larger scales (Godbold et al 2011).…”

Form, function and physics: the ecology of biogenic stabilisation

“…It is difficult for researchers to take full account of the complete environmental and biological context (Hewitt et al 2007); thus, the role these attributes play in mediating stressor impacts is not fully understood (Bishop and Kelaher 2013). Natural environments tend to be heterogeneous, whereas mesocosm or laboratory studies are generally controlled homogeneous environments (Dyson et al 2007). Natural heterogeneity has been observed to buffer against stressor effects (Godbold et al 2011) or negate patterns observed under laboratory conditions (Bulling et al 2008).…”