The fundamental role of ecological feedback mechanisms for the adaptive management of seagrass ecosystems – a review

Abstract

Seagrass meadows are vital ecosystems in coastal zones worldwide, but are also under global threat. One of the major hurdles restricting the success of seagrass conservation and restoration is our limited understanding of ecological feedback mechanisms. In these ecosystems, multiple, self-reinforcing feedbacks can undermine conservation efforts by masking environmental impacts until the decline is precipitous, or alternatively they can inhibit seagrass recovery in spite of restoration efforts. However, no clear framework yet exists for identifying or dealing with feedbacks to improve the management of seagrass ecosystems. Here we review the causes and consequences of multiple feedbacks between seagrass and biotic and/or abiotic processes. We demonstrate how feedbacks have the potential to impose or reinforce regimes of either seagrass dominance or unvegetated substrate, and how the strength and importance of these feedbacks vary across environmental gradients. Although a myriad of feedbacks have now been identified, the co-occurrence and likely interaction among feedbacks has largely been overlooked to date due to difficulties in analysis and detection. Here we take a fundamental step forward by modelling the interactions among two distinct above- and belowground feedbacks to demonstrate that interacting feedbacks are likely to be important for ecosystem resilience. On this basis, we propose a five-step adaptive management plan to address feedback dynamics for effective conservation and restoration strategies. The management plan provides guidance to aid in the identification and prioritisation of likely feedbacks in different seagrass ecosystems.

Rocking the Boat: Damage to Eelgrass by Swinging Boat Moorings

“…This loss of United Kingdom seagrass from boat moorings is small but significant at a local scale. This is because it fragments existing meadows and ultimately reduces their resilience to other stressors such as eutrophication (Unsworth et al, 2015; Maxwell et al, 2016). …”

Long-term Patterns of Eelgrass (Zostera marina) Occurrence and Associated Herbivorous Waterbirds in a Danish Coastal Inlet

“…Eelgrass meadows at 0-1 m are also more affected than those at 1-2 m by physical disturbances from ice scour in winter, wave action (Krause-Jensen et al, 2003) and possibly also from drifting macroalgae and burrowing fauna which may hamper the establishment of seedlings (Valdemarsen et al, 2010). As eelgrass meadows become sparse they also loose resilience, and feed-back mechanisms may act to maintain the state of reduced cover, e.g., through increased sediment resuspension (Maxwell et al, 2016). The temporal mismatch between the measure of eelgrass cover (generally monitored in August-September) and the grazing pressure, which peaks later in the season, may further reduce the chance of identifying potential relationships between the two factors.…”

“…Seagrass meadows are important features of coastal ecosystems (Hemminga and Duarte, 2000) and are increasingly recognized for their vital role as ecosystem engineers, because their structure and biomass reduce hydrodynamic energy (e.g., Bouma et al, 2005), increase sedimentation (e.g., Gacia et al, 2003;Bos et al, 2007) and stabilize sediments (Fonseca, 1989), preventing coastal erosion (e.g., Adriano et al, 2005) and increasing water clarity (Maxwell et al, 2016). Moreover, seagrass meadows constitute significant carbon stocks (Duarte et al, 2013), serve as habitats and hatching/nursery areas for a wealth of organisms, and are an important source of food for herbivores such as nonbreeding herbivorous waterbirds (Baldwin and Lovvorn, 1994;Ganter, 2000;Heck and Valentine, 2006).…”

Eelgrass Leaf Surface Microbiomes Are Locally Variable and Highly Correlated with Epibiotic Eukaryotes

“…Recent research suggests that relative success of eelgrass and associated algae is determined by complex interactions between biotic processes such as grazing on both algae and eelgrass by invertebrates, and environmental factors such as nutrient concentrations and temperature (Eklöf et al, 2012; Alsterberg et al, 2013). However, these mechanisms are not well understood and their complexity necessitates a holistic ecosystem approach taking into account several organism groups that inhabit seagrass meadows and their interactions to be resolved (Boström et al, 2014; Maxwell et al, 2016). …”