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Structural changes in Aruba’s reef islands between 2002 - 2022

MSc. Christie Mettes

Metabolic Foundation

Aruba

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Surfside Science is a project by Metabolic Foundation to develop low cost and replicable methods to start monitoring key environmental parameters where these are currently lacking.

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Started in 2019 with support from UNESCO and has been supported since last summer by RESEMBID, an EU grant

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Reef Islands

  • Physical barrier between Aruba and the open ocean
  • Support important ecosystems
  • Provide natural protection against the impacts of climate change including sea level rise, and storm events
  • Perceived as vulnerable to climate change, due to their low-lying nature, small size and mobile sediments

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Plan van het Eyland Aruba, opgenomen met de planchet, door Engelbertus Horst, Capitain Lieutenant en Ingenieur (1773) : Horst, Engelbertus : Free Download, Borrow, and Streaming : Internet Archive

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Measuring Changes

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  • Area

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  • Compactness

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  • Fracturing�

Looking at all 46 reef Islands along the leeward coast of Aruba during the period 2002 - 2022

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Methods

  • Satellite images were accessed freely through Google Earth Pro (GEP)
  • High resolution: 0.64m (2002) and 0.3m (2022) pixel sizes
  • Reef Islands traced by hand using the GEP polygon tool
  • Area and perimeter were calculated by GEP based on polygons

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Change in Size graph

Changes in area

Change in Size Graph 1

*Disappearing islands were verified to be consistently visibly underwater for several dates

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Locations and changes in area

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Methods

  • Compactness ratio used to measure changes in shape relative to a circle, which is the “roundest” shape

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  • Where islands fractured, calculations were based on totals of previously connected parts

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Changes in compactness

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Reef Island fracturing

2002 2022

  • 4 reef islands fractured into 2 parts
  • 1 reef island fractured into 3

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Summary

  • We see most reef islands decreasing in size
  • We see most reef islands becoming rounder (increasing compactness ratio)
  • Where islands fracture this tends to happen at the outends
  • A large number of reef islands seem to have completely disappeared

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1940-1945

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Oranjestad Key

2002 2022

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Old image of rodger’s beach

1958

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San Nicolas Bay Keys

2002 2022

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Discussion

  • This is in contrast with other research on reef islands indicating they stabilize or often grow even in the face of sea-level rise
  • Future research directions:
    • More measurements
    • Possible causes of observed changes
    • impacts of on coastal protection
    • Working on an automated version using Google Earth Engine
  • Additional measurements can add to this research:
    • Island position changes
    • Width and length
    • Surrounding bathymetry
    • Elevation
    • Vegetative cover

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Thank you!

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science.brenchies.com

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Check out our poster presentation on Friday!

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Christie Mettes

christie@metaboli.ca

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References

  • Biribo, N., & Woodroffe, C. D. (2013). Historical area and shoreline change of reef islands around Tarawa Atoll, Kiribati. Sustainability Science, 8, 345-362.
  • Ma, Y., Xu, N., Liu, Z., Yang, B., Yang, F., Wang, X. H., & Li, S. (2020). Satellite-derived bathymetry using the ICESat-2 lidar and Sentinel-2 imagery datasets. Remote Sensing of Environment, 250, 112047.
  • Mann, T., Bayliss-Smith, T., & Westphal, H. (2016). A geomorphic interpretation of shoreline change rates on reef islands. Journal of Coastal Research, 32(3), 500-507.
  • Webb, A. P., & Kench, P. S. (2010). The dynamic response of reef islands to sea-level rise: Evidence from multi-decadal analysis of island change in the Central Pacific. Global and Planetary Change, 72(3), 234-246.
  • Yates, M. L., Le Cozannet, G., Garcin, M., Salaï, E., & Walker, P. (2013). Multidecadal atoll shoreline change on Manihi and Manuae, French Polynesia. Journal of Coastal Research, 29(4), 870-882.
  • Kench, P.S. & Mann, T. (2017). Reef Island Evolution and Dynamics: Insights from the Indian and Pacific Oceans and Perspectives for the Spermonde Archipelago. Frontiers in Marine Science, 4.

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