The Effects of Habitat Loss, Fragmentation, and Community Homogenization on Resilience in Estuaries

Abstract

When changes in the frequency and extent of disturbance outstrip the recovery potential of resident communities, the selective removal of species contributes to habitat loss and fragmentation across landscapes. The degree to which habitat change is likely to influence community resilience will depend on metacommunity structure and connectivity. Thus ecological connectivity is central to understanding the potential for cumulative effects to impact upon diversity. The importance of these issues to coastal marine communities, where the prevailing concept of open communities composed of highly dispersive species is being challenged, indicates that these systems may be more sensitive to cumulative impacts than previously thought. We conducted a disturbance-recovery experiment across gradients of community type and environmental conditions to assess the roles of ecological connectivity and regional variations in community structure on the recovery of species richness, total abundance, and community composition in Mahurangi Harbour, New Zealand. After 394 days, significant differences in recovery between sites were apparent. Statistical models explaining a high proportion of the variability (R2 > 0.92) suggested that community recovery rates were controlled by a combination of physical and ecological features operating across spatial scales, affecting successional processes. The dynamic and complex interplay of ecological and environmental processes we observed driving patch recovery across the estuarine landscape are integral to recovery from disturbances in heterogeneous environments. This link between succession/recovery, disturbance, and heterogeneity confirms the utility of disturbance-recovery experiments as assays for cumulative change due to fragmentation and habitat change in estuaries.

Form, function and physics: the ecology of biogenic stabilisation

“…Nevertheless, the cost and logistical efforts behind much of this work are immense and so unlikely to be widely repeated; therefore, efficient use of resources and cooperative work are important. The aim of laboratory experiments is usually to reduce or control the number of variables that might influence an outcome, whereas in natural mesocosms or in the field, the number of variables increases and the interactions become extremely complex (Thrush et al 2008;Tolhurst et al 2009). As a consequence, the nature of the relationships between factors is increasingly multifaceted in the latter scenarios.…”

“…While the effects of multiple stressors on communities have received greater attention in recent years (Alsterberg et al 2014), assessing multiple stressor effects on various functions and processes the communities perform has received little attention (Thrush et al 2008;Kenworthy et al 2016). As an example, sediment stabilisation is a factor of critical importance to the ecology of marine and freshwater systems.…”

Towards a meaningful assessment of marine ecological impacts in life cycle assessment (LCA)

“…The overall impact of physical disturbances on benthic communities is a function of three interacting processes: disturbance characteristics (scale and intensity), initial benthic response and recovery time (Thrush et al, 1996;Thrush et al, 2008;Bolam and Rees, 2003;Kaiser et al, 2006). The primary response of benthic organisms to a physical disturbance is often severe damage or mortality (Bolam and Rees, 2003;Kaiser et al, 2006;Collie et al, 2000).…”

“…These environmentspecific differences in recovery time are well-documented in metaanalyses of benthic ecosystem recovery from several physical pressures, including fishing, aggregate extraction, and dredged material deposition (Bolam and Rees, 2003;Kaiser et al, 2006;Foden et al, 2009). The recovery time furthermore depends on the scale of disturbance (Thrush et al, 2008) and the number of successional stages required regaining the original community composition (Bolam and Rees, 2003).…”

“…Physical disturbances of the seabed can result in permanent community changes when the frequency and extent of disturbance outstrips the recovery potential (Thrush et al, 2008). Permanent community shifts from dominance by high biomass organisms, including bioturbating macrofauna, towards small-bodied opportunistic species, such as polychaetes, have been documented for heavily trawled areas, such as the Gulf of Mexico and the North Sea (Crowder et al, 2008;Jennings et al, 2001a;Jennings et al, 2001b).…”