Kelp Forest Capability Analysis
In addition to other vital ecosystem functions, kelp forests play a crucial role in carbon sequestration and provide significant economic and ecological value. Despite recent gains from urchin harvesting efforts, these ecosystems remain at risk due to warming oceans and the decline of key predator species. Off the coast of California, kelp cover has struggled to recover from a major collapse linked to both ecological imbalances and coastal development. My goal in this project was to identify areas along the California coast where conditions still support healthy kelp growth.
To accomplish this, I conducted a capability analysis identifying optimal habitats for kelp forest restoration and conservation off California's coastline using ArcGIS Pro. I integrated bathymetric data, sea surface temperature, and substrate composition from NOAA, NASA, and the Pacific Marine and Estuarine Fish Habitat Partnership (PMEP). I reclassified seafloor substrate data based on grain size categories and previous ecological research, including the Coastal and Marine Ecological Classification Standards, to accurately model kelp habitat suitability. I created a weighted raster overlay model to rank coastal areas by their capability to support kelp growth, identifying critical environmental factors like substrate stability, optimal temperature ranges, and suitable depths for sunlight penetration.
More About Substrate Type
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The seafloor substrate data was downloaded as a shapefile Both substrate classes and categories were used to reclassify substrates according to standards adopted from the results of the study by Rubin et al., (2011). Details from the CMECS document (Federal Geographic Data Committee, 2012), primarily regarding substrate grain size in millimeters, were used to designate either substrate class or substrate category into five groups. Notably, anthropogenic substrates with no further classifications were dubbed “Unclassified,” and woody debris both anthropogenic and organic were both put into the more general “Organic” category, in this case meaning organic substrates of any origin. Any substrate with grain size higher than 1,000 millimeters was classified as “Boulder/Bedrock”, including reef habitats that fit these conditions. Following reclassification of the substrate type polygon layer, it was converted using the Feature to Raster tool. This resulting raster layer was used as a mask when clipping the temperature and depth layers with Extract by Mask.
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Substrate type was given the highest priority in this model. Kelp holdfasts attach to rocks on the seafloor, and thus require a strong, sturdy substrate to grow and remain attached during storms. Rubin et al. (2011) found that boulder and bedrock reefs had the highest kelp density, mixed gravel and cobble substrates had a medium density, and sand had the lowest kelp density. Ratings for each substrate range follow the findings of the same study with the addition of organic substrates which were assigned a rating of 1, seeing as they can provide adequate support albeit not as long-term as bedrock.
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Data was downloaded from the Pacific Marine and Estuarine Fish Habitat Partnership and represents the Substrate Component of the Coastal and Ecological Classification Standard.
https://www.pacificfishhabitat.org/data/nearshore-cmecs-substrate-habitat/
https://www.fgdc.gov/standards/projects/cmecs-folder/cmecs-index-page
Rubin, S. P., Miller, I. M., Elder, N., Reisenbichler, R. R., & Duda, J. J. (2011). Nearshore biological communities prior to the removal of the Elwha River dams: Chapter 6 in Coastal habitats of the Elwha River, Washington--biological and physical patterns and processes prior to dam removal (No. 2011-5120-6, pp. 131-174). US Geological Survey. https://doi.org/10.3133/sir201151206
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To estimate seafloor depth, bathymetry data was downloaded at a 15 arc-second resolution that translated to a 432.76-meter cell size in the study area.
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To get enough sunlight kelp forests must grow in relatively shallow waters. While this depends on species and water clarity, it’s safe to assume that depths between 5 and 30 meters are optimal across varying species requirements and ancillary conditions (NOAA National Marine Sanctuaries). Giant kelp has been known to grow as low as 60 meters deep (Williams, 2007). Seafloor depth, and thus sunlight availability, was determined to be the next most important factor after substrate type and weighted accordingly (Smith et al., 2021).
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Seafloor depth was accessed using the ETOPO Global Relief Model courtesy of NOAA National Centers for Environmental Information.
https://www.ncei.noaa.gov/maps/bathymetry/
Smith, K. E., Moore, P. J., King, N. G., & Smale, D. A. (2022). Examining the influence of regional‐scale variability in temperature and light availability on the depth distribution of subtidal kelp forests. Limnology and Oceanography, 67(2), 314-328. https://doi.org/10.1002/lno.11994
Williams, N. (2007). Kelp surprise. Current Biology, 17(20), R862–R863. https://doi.org/10.1016/j.cub.2007.09.046
Input Factors
More About Seafloor Depth
More About Sea Surface Temperature
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Sea surface temperature data was downloaded as a netCDF at a 4km resolution representing the average temperature over the entirety of 2024. It was then resampled to match the resolution of the depth raster layer.
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Research suggests that the optimum temperatures for kelp growth are between 8 and 15 degrees Celsius with prime reproduction around 12 degrees (Augyte et al., 2019). Kelp forests are unlikely to survive temperatures above 22 degrees (Becheler et al., 2022). While high sea surface temperatures are a severe threat to kelp survival, their establishment in an ecosystem is not possible without a suitable substrate to attach to at a depth facilitating adequate sunlight (Randell et al., 2022), so this factor was not weighted.
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This data was collected by NASA’s Ocean Biology Processing group using Aqua MODIS (Moderate Resolution Imaging Spectroradiometer on the Aqua spacecraft).
https://oceandata.sci.gsfc.nasa.gov/l3/order/
Augyte, S., Yarish, C., Neefus, C. D., Augyte, S., Yarish, C., & Neefus, C. D. (2019). Thermal and light impacts on the early growth stages of the kelp <italic>Saccharina angustissima</italic> (Laminariales, Phaeophyceae). Algae, 34(2), 153–162. https://doi.org/10.4490/algae.2019.34.5.12
Becheler, R., Haverbeck, D., Clerc, C., Montecinos, G., Valero, M., Mansilla, A., & Faugeron, S. (2022). Variation in Thermal Tolerance of the Giant Kelp’s Gametophytes: Suitability of Habitat, Population Quality or Local Adaptation? Frontiers in Marine Science, 9. https://doi.org/10.3389/fmars.2022.802535
Randell, Z., Kenner, M., Tomoleoni, J., Yee, J., & Novak, M. (2022). Kelp-forest dynamics controlled by substrate complexity. Proceedings of the National Academy of Sciences, 119(8), e2103483119. https://doi.org/10.1073/pnas.2103483119
Final Result
This map shows areas with the highest capability scores after combining sea surface temperature, seafloor depth, and sea substrate type components.
