Contrasting impacts of light reduction on sediment biogeochemistry in deep- and shallow-water tropical seagrass assemblages (Green Island, Great Barrier Reef)

Schrameyer, Verena, York, Paul H., Chartrand, Katie, Ralph, Peter J., Kuhl, Michael, Brodersen, Kasper Elgetti, and Rasheed, Michael A. (2018) Contrasting impacts of light reduction on sediment biogeochemistry in deep- and shallow-water tropical seagrass assemblages (Green Island, Great Barrier Reef). Marine Environmental Research, 136. pp. 38-47.

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Abstract

Seagrass meadows increasingly face reduced light availability as a consequence of coastal development, eutrophication, and climate-driven increases in rainfall leading to turbidity plumes. We examined the impact of reduced light on above-ground seagrass biomass and sediment biogeochemistry in tropical shallow- (~2m) and deep-water (~17m) seagrass meadows (Green Island, Australia). Artificial shading (transmitting ~10-25% of incident solar irradiance) was applied to the shallow- and deep-water sites for up to two weeks. While above-ground biomass was unchanged, higher diffusive O2 uptake (DOU) rates, lower O2 penetration depths, and higher volume-specific O2 consumption (R) rates were found in seagrass-vegetated sediments as compared to adjacent bare sand (control) areas at the shallow-water sites. In contrast, deep-water sediment characteristics did not differ between bare sand and vegetated sites. At the vegetated shallow-water site, shading resulted in significantly lower hydrogen sulphide (H2S) levels in the sediment. No shading effects were found on sediment biogeochemistry at the deep-water site. Overall, our results show that the sediment biogeochemistry of shallow-water (Halodule uninervis, Syringodium isoetifolium, Cymodocea rotundata and C. serrulata) and deep-water (Halophila decipiens) seagrass meadows with different species differ in response to reduced light. The light-driven dynamics of the sediment biogeochemistry at the shallowwater site could suggest the presence of a microbial consortium, which might be stimulated by photosynthetically produced exudates from the seagrass, which becomes limited due to lower seagrass photosynthesis under shaded conditions.

Item ID: 52505
Item Type: Article (Refereed Research - C1)
Keywords: carbonate sediment, hydrogen sulphide, light, O2 demand, seagrass, shading, tropical
ISSN: 1879-0291
Funders: Augustinus Foundation of Denmark, P.A. Fiskers Fund, Jorck and Wife's Fund, Carlsberg Foundation (CF), Danish Council for Independent Research (DCIR) Technical and Production Sciences, Australian Research Council (ARC)
Projects and Grants: CF 16-0899, DCIR 4184-00515, ARC LP110200454
Date Deposited: 02 Mar 2018 01:39
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0503 Soil Sciences > 050304 Soil Chemistry (excl Carbon Sequestration Science) @ 40%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 30%
06 BIOLOGICAL SCIENCES > 0605 Microbiology > 060504 Microbial Ecology @ 30%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960507 Ecosystem Assessment and Management of Marine Environments @ 100%
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