Impacts of docks on seagrass and effects of management practices to ameliorate these impacts

Abstract

Seagrasses have high conservation and human-use values, but around the world they are being damaged by human activities. Compared to the larger spatial scale at which some human activities affect estuaries and their seagrasses (e.g. catchment disturbance, dredging, pollution, trawling), recreational boating and infrastructure of moorings and docks act at smaller scales. However, the cumulative effects contribute to stresses acting on seagrass beds. This study assessed the effects of docks on the native seagrass Zostera muelleri subsp. capricorni in an estuary in south-east Australia and of current management practices designed to reduce dock impacts on this seagrass. A field survey found that seagrass biomass was significantly reduced below docks, and the effects were not influenced by dock orientation. Management practices requiring the use of a mesh decking to provide greater light penetration reduced, but did not eliminate, the reduction in seagrass biomass caused by docks. A modified beyond BACI experiment provided evidence for a causal link between the installation of wooden or mesh docks and reductions in biomass of seagrass. The reduction in biomass was apparent 6 mo after dock installation, and by 26 mo seagrass biomass had declined by at least 90%.Faced with increasing coastal populations, increases in recreational use, and continued pressures from other human activities, alternative management practices that further minimize the effects of docks are needed.

Fish conservation in freshwater and marine realms: status, threats and management

“…New approaches, involving the use of artificial substratum to facilitate seagrass seedling establishment, have led to recovery (Tanner, ) and their associated biodiversity (McSkimming et al, ). Seagrass damage at smaller scales is reduced or eliminated through modifications to the designs of docks (eliminating the shading impacts of traditional docks) (Gladstone and Courtenay, ) and by replacing traditional boat moorings with seagrass‐friendly moorings (Demers et al, ). Habitat enhancement, involving the addition of complexity to artificial structures or the addition of biotic habitat elements to shoreline protection measures, has increased the abundance of seahorses and their prey (Hellyer et al, ), established fish assemblages that still differed from natural undisturbed habitats (Peters et al, ), and provided food for fish (Ng et al, ).…”

Effects of small‐scale, shading‐induced seagrass loss on blue carbon storage: Implications for management of degraded seagrass ecosystems

“…With the increased interest in blue carbon management and restoration research, we are only beginning to understand the impact of human-induced disturbances on seagrass C org stocks and subsequent recovery of C org sequestration during restoration (Bourque, Kenworthy, & Fourqurean, 2015;Dahl et al, 2016;Macreadie, Trevathan-Tackett, et al, 2014;Macreadie et al, 2015;Serrano et al, 2016). In an effort to reduce the effects of shading disturbances on seagrass ecosystems, studies have highlighted the challenges and limited success in increasing incident light underneath dock structures using alternative materials, for example increased grating, aluminium mesh or prism materials (Fresh, Wyllie-Echeverria, Wyllie-Echeverria, & Williams, 2006;Gladstone & Courtenay, 2014;Steinmetz, Jeansonne, Gordon, & Burns, 2004). Rather, it is possible that both timeframe of shading and increased incident light availability strongly influence survival of seagrass under and around dock structures.…”

Dragging the chain: Quantifying continued losses of seagrasses from boat moorings

“…This is particularly so for small-scale disturbances caused by boating, provided that the distribution of seagrasses is well known. Boating-related damage to seagrasses can be attributed to propellers (Dawes, Andorfer, Rose, Uranowski, & Ehringer, 1997;Zieman, 1976), anchors (Creed & Amado Filho, 1999;Williams, 1988), moorings (Demers, Davis, & Knott, 2013;Hastings, Hesp, & Kendrick, 1995;Unsworth, Williams, Jones, & Cullen-Unsworth, 2017;Walker, Lukatelich, Bastyan, & McComb, 1989;Williams & Meehan, 2004), the construction of marinas, and the shading from jetties or floating docks (Burdick & Short, 1999;Gladstone & Courtenay, 2014;West, 2011). Anchor or propeller damage is a short-term (pulse) disturbance that is often not spatially restricted, meaning that damage can occur anywhere in an estuary.…”