MAPPING AND ASSESSING ECOSYSTEM CONDITIONS OF SOUTH ...
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MAPPING AND ASSESSING ECOSYSTEM CONDITIONS OF SOUTH AFRICAN KELP
FORESTSBY
Loyiso Victor DungaUniversity of Cape TownDepartment of Biological Sciences
Under supervision of: Dr. Sink Kerry; Dr. Blamey Laura; Dr. Rothman Mark Dr. Lück-Vogel Melanie and Dr. Bolton John
Introduction: What are kelps?
• Group of large brown algae or seaweeds from the Orders Laminariales
• Dominating 25% of world’s coastlines
• Spanning across 43% of the world’s ecoregions.
KELPS:Phyletically diverse, structurally complex and highly productivecomponents of cold-water rocky marine coastlines
Steneck et al. 2002
How are Kelp Forests Ecosystems (KFE) significant?
• Kelp beds / kelp forests
Terrestrial forests Kelp forests
Associated phyla Chordata, Arthropoda and Annelida Chordata. Arthropoda, Annelida, Echinodermata, Bryozoa, Cnidaria, Mollusca, Platyhelminthes, Brachiopoda, Porifera
Height 10 – 30 m in 20 - 30 yrs. 1 – 15 m in 1 – 3 yrs.
Longevity Centuries to millennia 25 years
KFE (structure producing kelps + myriad of associated biota
KFE (key ecosystem services with Ecological, Social and Economic significance)
Comparison terrestrial – Kelp forests
Ecological Social Economic
Biogenic habitat Human dependence on the resource (direct or indirectly)
Harvesting and processing
Dampening effect and detritus Coastal rocky shore protection Important food source
Harbours important species(Nursery, Shelter and food source
Intrinsic beauty Fisheries
Ecologic, Economic and Social KFE Services
(a) A kelp forest (Ecklonia maxima) in South Africa. (b) A kelp trawler in Norway. (c) A scientific diver undertaking kelp research in Australia.. Photographs: From (Filbee-Dexter et al. 2018)
Problem statement & research aims and objectives
Aim:To produce a national kelp forest map for South Africa
Objectives:1. Develop a S2 based approach for extraction of kelp forests as baseline for future monitoring2. Produce a kelp map for South African coast as a status-quo information
South African kelp forests are well studied, yet it has been more than a decade since they were mapped using low spectral and spatial resolution techniques. These mid-2000s maps by (Tarr (1993; Rand 2006, Anderson et al. 2007) after analysis were found to have substantial kelp beds missing. As significant components of biodiversity Kelp forest were not included in the 2011 National Biodiversity Assessment and are listed under the priority research areas.
To serve as a decision support tool in the operational coastal vegetation management context
Study area
Methods and Material• Sentinel 2 A satellite remote sensing imagery• Sen2Cor: TOA to BOA conversions • Three classification methods : Visual analysis and interpretation, (angular training polygons) supervised and
(cluster 2 pixel groups) unsupervised• ArcGIS software and QGIS : Raster imagery Pre-processing and post processing
SENTINEL 2AAcquisition
SEN2CORConversion
ArcGIS/QGIS
Training data
NDVI
Classifications
Mosaic Validation data
Analysis
NDVI MAPPre-processing
Processing Post-processing
Kelp beds
NW SpainSPOT 43 classification methodsResolution compatibilityCasal et al. 2011
Japan IKONOSSpectral signature Acute results Sagawa et al. 2012
West of South AfricaLandsat 4Multi-methods Under-estimationAnderson et al. 2007
West of South AfricaSentinel 2A3 classificationprogressDunga, 2018
Comparison of RS derived kelp maps
Satellite Bands Temporal
Resolution
Principle Spatial Resolution (m)
Sentinel 2A 13 10 days Push broom 10; 20; 60
Landsat 3-7 7 16 days Scanner 30; 60
SPOT-5 4 26 days Push broom 2.5; 10; 60
RS for Mapping kelp: WHY S2A?
Tar, 1993 (Hand drawn) S2A: 2017 (Raw image) S2A derived Kelp map
NDVI range of kelp non-kelp areas
Normalized Difference Vegetation Index = (NIR reflectance – Red reflectance) / (NIR reflectance + Red reflectance)
y = -0.087ln(x) + 0.34R² = 0.053
y = -0.0117x + 0.1935R² = 0.0415
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Kommetjie y = 0.0587x - 0.2479R² = 0.3958
y = 0.0147x - 0.0351R² = 0.0541
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Cape Hangklip
y = 0.0297x - 0.283R² = 0.2357
y = 0.0042x - 0.237R² = 0.0071
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Robben Island
Kelp No Kelp Linear (Kelp) Linear (No Kelp)
y = -0.0009x + 0.3553R² = 0.004
y = -0.0002x - 0.3369R² = 0.0017
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Kelp No Kelp Linear (Kelp) Linear (No Kelp)
NDVI range of kelp non-kelp areas
Results
Drawn ConclusionsS2a capability to determine kelp is satisfactory (NDVI thresholds)
Objective 1:
• .Develop a S-2 based mapping system for kelp occurrence as baseline for future
monitoring
• Produce kelp map for the whole of South Africa coast as a status-quo information
• Kelp forest includes all surface emergent kelp and but excludes isolated beds that where
ground truth data is not available e.g. the case of the EC.
Three kelp ecosystem types (Namaqua, Cape and Agulhas) for the following chapter are
captured in the map
Where to from here?
• Pressure Mapping of three Kelp ecosystems (Namaqua; Southern Western Cape and Agulhas) Conditions.
• Based on identified Expert based pressures• Adopting Halpern et al 2008;2009 & Teck et al 2010
methods
ACKNOWLEDGEMENTS
Thank you all for listening!
Dr. Sink Kerry; Dr. Blamey Laura; Dr. Rothman Mark Dr. Lück-Vogel Melanie; Dr. Phil Desmet; Prof. Bolton John;