Giant Kelp Canopy Cover and Biomass from High Resolution Multispectral Imagery for the
Santa Barbara Channel
Kyle C Cavanaugh, David A Siegel, Brian P Kinlan, Dan C Reed
Macrocystis pyrifera
• High economic and ecologic importance– “ecosystem engineer”
• Kelp abundance highly dynamic– Growth rates up to 0.5 m/day– Avg. frond life: 3-5 months– Ave. plant life: 2-3 years
Macrocystis growth and mortality
• Growth and mortality regulated by water temp, nutrients, depth, bottom type, predation, wave action
• Nice model system for studying the role of disturbance in regulating ecosystems
Kelp biomass data from Kelco visual estimates; Fish observations from Brooks et al 2002
Previous SB Channel surveys
• Aerial visual canopy biomass estimates by ISP Alginates (monthly from 1958-2005; entire coast)
• CDFG 2m resolution aerial surveys using NIR imagery (annual from 2002-present; entire coast)
• LTER SCUBA transects (monthly for 3 SBC kelp beds from 2002-present)
• Scale issues…
Research goals
1. Expand spatial and temporal resolution of kelp canopy cover and biomass datasets using high resolution satellite imagery
2. Use this data to model kelp population dynamics in relation to patch size, connectivity, and biophysical forcing
Research Area
Remote Sensing of Macrocystis
• Surface canopy of giant kelp exhibits typical vegetation spectral signature (red-edge)– Low red reflectance– high near infrared (NIR) reflectance
• Canopy biomass well correlated to entire forest biomass (r2 = 0.92)
SPOT Imagery• Well suited to differentiate kelp
– Spectral bands in the green, red, NIR, SWIR– 10 m resolution
SPOT Imagery Datasets
1. Canopy Cover
2. Biomass
Methods: Canopy Cover
• Principal components analysis calculated for kelp habitat (0-60 m depths)
PC band 1
PC band 2
False color SPOT image(8/15/2006)
• Positive contribution from all 3 bands• Glint, sediment loads, atmosphere variations, etc.
• High NIR, low green and red reflectance• Kelp
Methods: Canopy Cover Classification
• Minimum kelp threshold value selected from 99.9th%-tile value of offshore (35-60 m) pixels
Validation: Canopy Cover
• Cover measurements compared with high resolution 2004 CDFG aerial kelp survey
SPOT: Oct 29, 2004
CDFG: Sept-Nov 2004
r2 = 0.98p < 1*10-7
Biomass Data
• More useful for understanding and modeling ecosystem interactions– Turnover rates, export, NPP, etc.
• Difficult to measure directly– Time and effort intensive
SBC-LTER SCUBA Measurements of Frond Density and Biomass
• Monthly SCUBA measurements of frond density and biomass made at Arroyo Quemado (AQUE), Arroyo Burro (ABUR), and Mohawk (MOHK) kelp beds.
• Limited spatial scale
Seasonal kelp biomass changes along 3 LTER transects
• Maximums in late 2002• Wave driven seasonality apparent
Methods: Biomass• Normalized Difference Vegetation Index (NDVI)
(NIR-RED)(NIR+RED)
• Calculated for areas of kelp cover
NDVITransform
Validation: Biomass
r2 = 0.71p < 1*10-7
y = 14.33x - 0.13
r2 = 0.54p < 1*10-7
Seasonal kelp biomass changes at Mohawk
Comparison of SPOT vs. Kelco Biomass Data
r2 = 0.73p < 1*10-7
Population Dynamics Modeling
• Persistence, extinction, and biomass changes of kelp patches as a function of size, connectivity, and biophysical factors– High spatial resolution kelp maps will allow us
to include effects of sea temperature, nutrients, wave energy, substrate, light attenuation, spore production and dispersal
Data RequirementsKelp Ecological Process Forcing Factor Method of Assessment Spatial Scale Temporal Scale
Kelp cover and biomass change
- multispectral imagery (SPOT from 2006-2008; Landsat/IKONOS/QB before and after)
<30 m seasonally
Extinction swell wave stress buoy data/ CDIP models 100 m hourly-daily
Spore dispersal currents HF radar. Bottom mounted ADCP observations
~ 100 m hourly-daily
Colonization substrate sidescan mapped substrate ~ 100 m annual-decadal
Colonization bathymetry hi-res gridded bathymetry ~ 100 m decadal
Productivity background light limitation
MODIS incident PAR & Kd490 imagery
500-1000 m daily
Productivity nutrient limitation MODIS/AVHRR SST/nutrient relationships
500-1000 m daily