Hypersalinity as a trigger of seagrass ( Thalassia testudinum ) die-off events in Florida Bay: Evidence based on shoot meristem O 2 and H 2 S dynamics

Johnson, Craig R.; Koch, Marguerite S.; Pedersen, Ole; Madden, C.J.

doi:10.1016/j.jembe.2018.03.007

Cited by 29 publications

(11 citation statements)

References 30 publications

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“…The seagrass die‐off we report is 30% greater than a previous decline of approximately 1,000 km 2 of colonizing seagrass meadows (~5% cover of Halophila spp.) after successive flooding and cyclone events in Hervey Bay, Australia (Preen, Long, & Coles, 1995), and is an order of magnitude greater than several documented seagrass die‐off events induced by extreme events such as 161 km 2 loss in Florida Bay (Johnson, Koch, Pedersen, & Madden, 2018) and 83 km 2 in Spencer Gulf (Seddon, Connolly, & Edyvane, 2000).…”

Section: Discussionmentioning

confidence: 96%

Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area

Strydom

Murray²,

Wilson

et al. 2020

Global Change Biology

192

133

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The increased occurrence of extreme climate events, such as marine heatwaves (MHWs), has resulted in substantial ecological impacts worldwide. To date, metrics of thermal stress within marine systems have focussed on coral communities, and less is known about measuring stress relevant to other primary producers, such as seagrasses. An extreme MHW occurred across the Western Australian coastline in the austral summer of 2010–2011, exposing marine communities to summer seawater temperatures 2–5°C warmer than average. Using a combination of satellite imagery and in situ assessments, we provide detailed maps of seagrass coverage across the entire Shark Bay World Heritage Area (ca. 13,000 km2) before (2002 and 2010) and after the MHW (2014 and 2016). Our temporal analysis of these maps documents the single largest loss in dense seagrass extent globally (1,310 km2) following an acute disturbance. Total change in seagrass extent was spatially heterogeneous, with the most extensive declines occurring in the Western Gulf, Wooramel Bank and Faure Sill. Spatial variation in seagrass loss was best explained by a model that included an interaction between two heat stress metrics, the most substantial loss occurring when degree heating weeks (DHWm) was ≥10 and the number of days exposed to extreme sea surface temperature during the MHW (DaysOver) was ≥94. Ground truthing at 622 points indicated that change in seagrass cover was predominantly due to loss of Amphibolis antarctica rather than Posidonia australis, the other prominent seagrass at Shark Bay. As seawater temperatures continue to rise and the incidence of MHWs increase globally, this work will provide a basis for identifying areas of meadow degradation, or stability and recovery, and potential areas of resilience.

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Section: Discussionmentioning

confidence: 96%

Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area

Strydom

Murray²,

Wilson

et al. 2020

Global Change Biology

192

133

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“…However, in some scenarios, the concentrations found in this study were close to reported phytotoxic levels that cause reduced aboveground production or death for VCHs (≥500 µmol L −1 for A. marina mangroves and Salicornia salt marsh species and >600 µmol L −1 for Zostera seagrass species; Lamers et al, 2013 and references herein). In naturally vegetated areas, the O 2 from the plant roots would help prevent sulfide intrusion into the plant, but this defense against phytotoxicity is regulated by the daylight hours, hypersalinity and the water-column O 2 availability (Pedersen et al, 2004;Brodersen et al, 2015bBrodersen et al, , 2017bKoren et al, 2015;Johnson et al, 2018). There was a pronounced reduction in the maximum total sulfide concentration in the deep sediment of mangrove and seagrass ecosystems by a factor of 4 to 24, respectively, which can be explained by less easily degradable carbon in the deeper sediment layers (Burdige, 2007;Costa et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

Oxygen Consumption and Sulfate Reduction in Vegetated Coastal Habitats: Effects of Physical Disturbance

et al. 2019

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Brodersen et al. Sediment Biogeochemistry in Vegetated Coastal Habitats anoxic conditions, especially in mangrove and seagrass sediments, as well as sediment acidification with depth, likely decreased microbial remineralisation rates of sedimentary carbon. However, physical disturbance of sediments and thereby exposure of deeper sediments to O 2 seemed to stimulate aerobic metabolism in the exposed surface layers, likely reducing carbon stocks in VCHs.

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“…Among other effects, reduced light availability hampers photosynthesis‐driven radial oxygen loss from seagrass roots (Frederiksen & Glud, 2006; Jovanovic, Pedersen, Larsen, Kristensen, & Glud, 2015) and thus hinders a major pathway by which seagrass can avoid excess sulphide intrusion (Hasler‐Sheetal & Holmer, 2015; Lamers et al., 2013). Excessive and prolonged sulphide exposure is thought to be a proximate, though not ultimate, cause of several observed T. testudinum die‐off events in Florida (Borum et al., 2005; Carlson et al., 1994; Johnson, Koch, Pedersen, & Madden, 2018; Koch, Schopmeyer, Nielsen, et al., 2007). We hypothesized that the presence of C. orbicularis would increase T. testudinum growth and survival even without added environmental stress, as in van der Heide et al.…”

Section: Introductionmentioning

confidence: 99%

Facilitation of a tropical seagrass by a chemosymbiotic bivalve increases with environmental stress

et al. 2020

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Facilitation of foundation species is critical to the structure, function and persistence of ecosystems. Understanding the dependence of the strength of this facilitation on environmental conditions is important for informed ecosystem management and for predicting the impacts of global change. In coastal seagrass habitats, chemosymbiotic lucinid bivalves can facilitate seagrasses by decreasing potentially toxic levels of sulphide in sediment porewater. However, variation in the strength of lucinid–seagrass facilitation with environmental context has not been experimentally investigated. We tested the hypothesis that the presence of the tiger lucine Codakia orbicularis becomes more important to the growth and survival of the seagrass Thalassia testudinum under decreased light availability and increased sulphide stress. In a mesocosm experiment, we reduced average ambient‐light to T. testudinum by 64% and/or increased sediment porewater sulphide concentrations by ~200% and compared growth and tissue chemistry of T. testudinum with and without C. orbicularis. We found that T. testudinum was better able to maintain growth under shading and sulphide stress when C. orbicularis was present. C. orbicularis strongly decreased sediment porewater sulphide, an effect that minimized sulphur build‐up in seagrass tissue and was likely achieved through bioirrigation as well as chemoautotrophy. The relative effects of C. orbicularis on T. testudinum growth were strongest in the presence of environmental stressors. Synthesis. The strength of lucinid–seagrass facilitation increases under environmental conditions that hinder the ability of seagrass to detoxify sulphide. Our results provide evidence of a potential mechanism by which the spatiotemporal association between lucinids and seagrasses is maintained and support the incorporation of interspecific facilitation into conservation and restoration strategies for foundation species in the face of increasing anthropogenic impact and global change.

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Hypersalinity as a trigger of seagrass ( Thalassia testudinum ) die-off events in Florida Bay: Evidence based on shoot meristem O 2 and H 2 S dynamics

Cited by 29 publications

References 30 publications

Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area

Too hot to handle: Unprecedented seagrass death driven by marine heatwave in a World Heritage Area

Oxygen Consumption and Sulfate Reduction in Vegetated Coastal Habitats: Effects of Physical Disturbance

Facilitation of a tropical seagrass by a chemosymbiotic bivalve increases with environmental stress

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