Transcript Giant Kelp Canopy Cover and Biomass from High Resolution

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
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
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
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…
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
• 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
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 = 0.98
p < 1*10-7
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
Previous metapopulation analyses
(Reed et al 2006)
• Kelp is highly dynamic
• Patch isolation positively correlated with
extinction rates, negatively correlated with
colonization rates
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
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
Methods: Biomass
• Normalized Difference Vegetation Index (NDVI)
(NIR-RED)
(NIR+RED)
• Calculated for areas of kelp cover
NDVI
Transform
Validation: Biomass
r2 = 0.71
p < 1*10-7
y = 14.33x - 0.13
r2 = 0.54
p < 1*10-7
Regional Kelp Biomass
• Created from biomass-NDVI relationship for
areas of kelp cover
Biomass Along SB Coastline
Nov. 2004: 15000 tonnes
Nov. 2006: 7800 tonnes
Kelp Biomass (metric tonnes)
25000
20000
15000
10000
5000
0
Dec-05
April 2007: 22350 tonnes
Mar-06
Jun-06
Sep-06
Dec-06
Mar-07
Jun-07
Seasonal kelp biomass changes
at Mohawk
Comparison of SPOT vs. Kelco
Biomass Data
r2 = 0.73
p < 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
Assessing the role of forcing
processes
Kelp Ecological Process
Kelp cover & biomass
change
Extinction
Forcing Factor
-
Method of Assessment
SPOT & Landsat imagery
Swell wave stress
Spore dispersal
Currents
Colonization
Substrate suitability
Colonization
Bathymetry
Productivity
Background light limitation
Productivity
Nutrient limitation
Productivity & colonization
Sediment variability
Kelp extinction
Wind stress
Hourly observations of swell wave height along the
10 m isobath from CDIP
HF radar data from PISCO & SBC-LTER. Bottom
mounted ADCP observations (SBC-LTER)
Sidescan mapped fields of substrate type available
from CDFG – also collaboration w/ USGS
CDFG-high resolution gridded bathymetry (200m
horizontal, 1m vertical) & Sidescan fields (2m horiz)
MODIS incident PAR & Kd490 imagery tuned using
SBC-LTER & PnB observations
MODIS/AVHRR SST imagery & SST/Nutrient
relationships from SBC-LTER & PnB observations
SPOT & MODIS (250 m) imagery of total
suspended solids (also collaboration w/ USGS)
Winds from NDBC buoys 46053, 46054, 46069 &
46063 (ndbc.noaa.gov)