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- Title
Effects of short-term low irradiance on health status and biomechanics of Zostera marina.
- Authors
Vettori, Davide; Middelboe, Anne Lise; Rice, Stephen
- Abstract
Marine dredging activities may increase turbidity of the water and thereby potentially impactthe health status of benthic vegetation. The Fehmarn Belt Fixed Link is a planned tunnel thatwill connect Denmark and Germany providing a direct railway and road link between the twocountries. The tunnel construction will require intense dredging activities that will increasethe concentration of suspended particles in the water and reduce underwater light availability.It is anticipated that this may impact the benthic macrophyte Zostera marina, which is a keyseagrass species in the benthic communities of the Fehmarn Belt (FEMA, 2013). Here weinvestigated the effects of short-term low irradiance conditions on the health status andbiomechanical properties of Z. marina via laboratory experiments. Ninety (90) plants werecollected from Rødsand Lagoon, next to the Fehmarn Belt, Denmark in April 2018and arrived at Loughborough University, UK within 36 hours of collection. Theywere distributed in two mesocosms consisting of 1000 l aerated tanks filled withsaltwater. A control mesocosm was designed to replicate the natural environmentalconditions (salinity, temperature, irradiance); the treatment mesocosm was designedto reproduce the highest reduction of irradiance due to dredging activities. 110μmol m−2 s−1 was used to represent 70% of the natural irradiance (e.g. predictedmaximum reduction in Rødsand Lagoon, FEMA, 2013). The health status, morphologyand flexural rigidity of five plants from each mesocosm were investigated dailyfor nine days. Seagrass health status was assessed by chlorophyll fluorescence,specifically by measuring the maximum quantum yield of photosystem II (Fv∕Fm)on the second youngest leaf. The flexural rigidity and bending Young’s modulusof leaves was measured with cantilever tests conducted using a Peirce’s testingapparatus (Henry, 2014). Results indicate that Fv∕Fm was not significantly affectedby the low irradiance to which plants were exposed, likely because the level ofirradiance was well above the light compensation points for leaves of Z. marina reportedin the literature (22 μmol m−2 s−1). We did not report any significant effect oflow irradiance on mass density, flexural rigidity or bending Young’s modulus ofseagrass leaves. Our results indicate that a short-term reduction of irradiance abovethe compensation point does not affect the health status of Z. marina nor inducesvariation in the biomechanical properties of its blades. Considering that longerperiods of exposure to reduced light or periods that occur at different points of thegrowing cycle can have different effects, these findings can provide guidance forthe planning of dredging activities so that environmental impact on seagrass isminimized. FEMA (2013). Fehmarnbelt Fixed Link EIA. Marine Fauna and Flora – ImpactAssessment Benthic Flora of the Fehmarnbelt Area. Report No. E2TR0021 - Volume I.Available from: https://vvmdocumentation.femern.com/ Henry, P. Y. T. (2014). Bending properties of a macroalga: Adaptation of Peirce’scantilever test for in situ measurements of Laminaria digitata (Laminariaceae). Americanjournal of botany, 101(6), 1050-1055.
- Subjects
DENMARK; ZOSTERA marina; UNITED States. Federal Emergency Management Agency; BENTHIC plants; MARINE plants; BIOMECHANICS; TUNNEL design &; construction; PHOTOSYSTEMS
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article