Alternatieve stortstrategie voor de Westerschelde : Voortzetting monitoringsprogramma proefstorting walsoorden LOT 2: Ecologische monitoring

Contains fulltext : 35149.pdf (publisher's version ) (Open Access)148 p

Tropical biogeomorphic seagrass landscapes for coastal protection:Persistence and wave attenuation during major storms events

The intensity of major storm events generated within the Atlantic Basin is projected to rise with the warming of the oceans, which is likely to exacerbate coastal erosion. Nature-based flood defence has been proposed as a sustainable and effective solution to protect coastlines. However, the ability of natural ecosystems to withstand major storms like tropical hurricanes has yet to be thoroughly tested. Seagrass meadows both stabilise sediment and attenuate waves, providing effective coastal protection services for sandy beaches. To examine the tolerance of Caribbean seagrass meadows to extreme storm events, and to investigate the extent of protection they deliver to beaches, we employed a combination of field surveys, biomechanical measurements and wave modelling simulations. Field surveys of sea- grass meadows before and after a direct hit by the category 5 Hurricane Irma documented that estab- lished seagrass meadows of Thalassia testudinum re- mained unaltered after the extreme storm event. The flexible leaves and thalli of seagrass and calci- fying macroalgae inhabiting the meadows were shown to sustain the wave forces that they are likely to experience during hurricanes. In addition, the seagrass canopy and the complex biogeomorphic landscape built by the seagrass meadows combine to significantly dissipate extreme wave forces, ensuring that erosion is minimised within sandy beach fore- shores. The persistence of the Caribbean seagrass meadows and their coastal protection services dur- ing extreme storm events ensures that a stable coastal ecosystem and beach foreshore is maintained in tropical regions

Subsidence reveals potential impacts of future sea level rise on inhabited mangrove coasts

Human-induced land subsidence causes many coastal areas to sink centimetres per year, exacerbating relative sea level rise (RSLR). While cities combat this problem through investment in coastal infrastructure, rural areas are highly dependent on the persistence of protective coastal ecosystems, such as mangroves and marshes. To shed light on the future of low-lying rural areas in the face of RSLR, we here studied a 20-km-long rural coastline neighbouring a sinking city in Indonesia, reportedly sinking with 8–20 cm per year. By measuring water levels in mangroves and quantifying floor raisings of village houses, we show that, while villages experienced rapidly rising water levels, their protective mangroves experience less rapid changes in RSLR. Individual trees were able to cope with RSLR rates of 4.3 (95% confidence interval 2.3–6.3) cm per year through various root adaptations when sediment was available locally. However, lateral retreat of the forest proved inevitable, with RSLR rates up to four times higher than foreshore accretion, forcing people from coastal communities to migrate as the shoreline retreated. Whereas local RSLR may be effectively reduced by better management of groundwater resources, the effects of RSLR described here predict a gloomy prospect for rural communities that are facing globally induced sea level rise beyond the control of local or regional government

Sampling, separation, and quantification of N-acyl homoserine lactones from marine intertidal sediments

N-acyl homoserine lactones (AHLs) are molecules produced by many Gram-negative bacteria as mediators of cell-cell signaling in a mechanism known as quorum sensing (QS). QS is widespread in marine bacteria regulating diverse processes, such as virulence or excretion of polymers that mediate biofilm formation. Associated eukaryotes, such as microalgae, respond to these cues as well, leading to an intricate signaling network. To date, only very few studies attempted to measure AHL concentrations in phototrophic microbial communities, which are hot spots for bacteria-bacteria as well as microalgae-bacteria interactions. AHL quantification in environmental samples is challenging and requires a robust and reproducible sampling strategy. However, knowing about AHL concentrations opens up multiple perspectives from answering fundamental ecological questions to deriving guidelines for manipulation and control of biofilms. Here, we present a method for sampling and AHL identification and quantification from marine intertidal sediments. The use of contact cores for sediment sampling ensures reproducible sample surface area and volume at each location. Flash-freezing of the samples with liquid nitrogen prevents enzymatic AHL degradation between sampling and extraction. After solvent extraction, samples were analyzed with an ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) method that allows to baseline-separate 16 different AHLs in less than 10 min. The sensitivity of the method is sufficient for detection and quantification of AHLs in environmental samples of less than 16 cm(3)