Giant Kelp Canopy Cover and Biomass from High Resolution SPOT Imagery for the Santa Barbara Channel

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Giant Kelp Canopy Cover and Biomass from High
Resolution SPOT Imagery for the Santa Barbara
Channel

• Kyle C Cavanaugh, David A Siegel, Brian P Kinlan,
  Dan C Reed

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Macrocystis pyrifera

• High economic and ecologic importance
• ecosystem engineer
• Kelp abundance highly dynamic
• Avg. frond life 3-5 months
• Ave. plant life 2-3 years
• Growth rates up to 0.5 m/day

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Macrocystis growth and mortality

• Growth and mortality regulated by water temp,
  nutrients, depth, bottom type, predation, wave
  action
• Nice model system for the study of a number of
  interesting ecological theories

Kelp biomass data from Kelco visual estimates
Fish observations from Brooks et al 2002
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Previous surveys

• Aerial visual canopy biomass estimates by ISP
  Alginates (monthly from 1958 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

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Research goals

• Expand spatial and temporal resolution of kelp
  canopy cover and biomass datasets using high
  resolution satellite imagery
• Use this data to model kelp population dynamics
  in relation to patch size, connectivity, and
  biophysical forcing

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Research Area
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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)

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SPOT Imagery

• Well suited to differentiate kelp
• Spectral bands in the green, red, NIR, SWIR
• 10 m resolution

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SPOT Imagery Datasets

1. Canopy Cover
2. Biomass

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Methods Canopy Cover

• Principal components analysis calculated for kelp
  habitat (0-60 m depths)

PC band 1

• Positive contribution from all 3 bands
• Glint, sediment loads, atmosphere variations,
  etc.

False color SPOT image (8/15/2006)
PC band 2

• High NIR, low green and red reflectance
• Kelp

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Methods Canopy Cover Classification

• Minimum kelp threshold value selected from
  99.9th-tile value of offshore (35-60 m) pixels

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Validation Canopy Cover

• Cover measurements compared with high resolution
  2004 CDFG aerial kelp survey

SPOT Oct 29, 2004
CDFG Sept-Nov 2004
r2 0.98 p lt 110-7
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Kelp Occupation Frequency Jan 2006- May 2007

• 8 image dates
• 39 of occupied pixels were present in at least
  half the scenes
• 4 of pixels were present across all dates

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Previous metapopulation analyses (Reed et al 2006)

• Kelp is highly dynamic
• Patch isolation positively correlated with
  extinction rates, negatively correlated with
  colonization rates

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Biomass Data

• More useful for understanding and modeling
  ecosystem interactions
• Turnover rates, export, NPP, etc.
• Difficult to measure directly
• Time and effort intensive

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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

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Seasonal kelp biomass changes along 3 LTER
transects

• Maximums in late 2002
• Wave driven seasonality apparent

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Role of Biomass in NPP

• Reed et al (in press) initial biomass explains
  63 of inter-annual variation in net primary
  production (NPP)
• Surprisingly, growth rate was insignificant in
  explaining variation in NPP
• Remote measures of biomass would be valuable for
  making regional estimates of NPP

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Methods Biomass

• Normalized Difference Vegetation Index (NDVI)
• (NIR-RED)
• (NIRRED)
• Calculated for areas of kelp cover

NDVI Transform
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Validation Biomass
r2 0.71 p lt 110-7 y 14.33x - 0.13
r2 0.54 p lt 110-7
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Regional Kelp Biomass

• Created from biomass-NDVI relationship for areas
  of kelp cover

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Seasonal kelp biomass changes at Mohawk
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Comparison of SPOT vs. Kelco Biomass Data
r2 0.73 p lt 110-7
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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

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Assessing the role of forcing processes