Thesis subject

MSc thesis topic: Using Sentinel-2 to assess the damage of Sargassum brown tides to mangroves

The massive arrival and decomposition of Sargassum on tropical shores leads to anoxia and the release of toxic compounds. These conditions have a detrimental effect to coastal ecosystems. Some local studies have already proven the negative impacts that these large amounts of Sargassum seaweed have on the fringes of mangrove forests (e.g., Bonaire’s protected mangroves). The decline or disappearance of a fraction of a mangrove forest commonly triggers the decline of the remaining part, as they are more vulnerable to disturbance.

Other factors such as coastal morphology (e.g. presence of tidal channels) could facilitate Sargassum deeper into the mangrove forest. In other words, the influence of Sargassum on the fringing mangroves could trigger a cascading effect with negative implications also for the fraction of the forest not directly exposed to Sargassum.

Open source satellite Sentinel-2 provides now new opportunities for mapping and monitoring effects of Sargassum on mangroves, see also Hedley et al. (2018).

In recent years, large amounts of Sargassum have been washing up on many tropical shores. This floating seaweed drifts on ocean currents while growing. Patches of Sargassum can be viewed by satellites. With Sentinel-2 passing on average once every week it may be possible to predict its impact on beaches and the neighbouring mangrove forests. Can patches of Sargassum be detected on the coast with Sentinel-2, and can it be distinguished from the mangrove forest or do we only see the impact on the mangrove forest?

Objectives

  • Is the quality and health of mangrove forests influenced by Sargassum events and how?
  • Can satellite information provide information on the spatial extent of a possible damage?
  • Does coastal morphology influence the degree to which mangrove health is affected by Sargassum?
  • What is the time-span until the mangroves show signs of decline? and until death/recovery of the affected fraction?

Literature

  • Brooks MT, Coles VJ, Hood RR, Gower JFR (2018). Factors controlling the seasonal distribution of pelagic Sargassum. Mar Ecol Prog Ser 599:1-18
  • Hedley et al. (2018). Coral reef applications of Sentinel-2: Coverage, characteristics, bathymetry and benthic mapping with comparison to Landsat 8. Remote Sensing of Environment 216: 598–614
  • Hernandez, W. J., Morell, J. M., & Armstrong, R. A. (2020). High-Resolution Satellite Imagery to Assess Sargassum Inundation Impacts to Coastal Areas. bioRxiv.

Requirements

  • Remote sensing (GRS-20306)
  • Advanced Earth Observation (GRS-32306)
  • Basic knowledge of tropical marine ecology

Theme(s): Sensing & measuring; Integrated Land Monitoring