Three decades of variability in California's giant kelp forests from the Landsat satellites
Abstract
Global, repeat satellite imagery serves as an essential tool to understand ecological patterns and processes over diverse temporal and spatial scales. Recently, the use of spaceborne imagery has become indispensable for monitoring giant kelp, a globally distributed foundation species that displays variable seasonal and interannual dynamics. In order to develop and maintain a continuous and spatially expansive time series, we describe a fully automated protocol to classify giant kelp canopy biomass across three Landsat sensors. This required correcting kelp canopy estimates to account for changes in the spectral response functions between the three sensors by simulating data using hyperspectral imagery. Combining multiple sensors also necessitated the use of an extended (15 year) time series of diver estimated kelp biomass to validate each sensor. We also describe a novel gap filling technique using known spatial scales of kelp biomass synchrony to correct for missing data due to the Enhanced Thematic Mapper Plus scan line corrector failure. These developments have led to a publicly available 34-year, seasonal time series of kelp canopy biomass across 1500 km of California coastline.
We used this time series to examine long-term trends in kelp canopy biomass and the response of kelp ecosystems to major El Niño-Southern Oscillation (ENSO) events, which are characterized by dramatic increases in sea surface temperatures. We found that kelp canopy biomass trends are associated with trends in low frequency marine climate oscillations, such as the North Pacific Gyre Oscillation. The cyclical nature of these low frequency marine climate oscillations complicates the detection of trends that may be associated with anthropogenic climate change. On shorter timescales, major ENSO events are associated with large-scale declines in kelp abundance across California. However, the recovery of kelp from these disturbance events was highly variable in space. This spatial variability provides important insight into the environmental drivers of kelp forest resilience, which are important to understand in the face of climate change.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.B31L2645C
- Keywords:
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- 0434 Data sets;
- BIOGEOSCIENCESDE: 0480 Remote sensing;
- BIOGEOSCIENCESDE: 1632 Land cover change;
- GLOBAL CHANGEDE: 1640 Remote sensing;
- GLOBAL CHANGE