Kelpwatch: A new visualization and analysis tool to explore kelp canopy dynamics reveals variable response to and recovery from marine heatwaves

Abstract

Giant kelp and bull kelp forests are increasingly at risk from marine heatwave events, herbivore outbreaks, and the loss or alterations in the behavior of key herbivore predators. The dynamic floating canopy of these kelps is well-suited to study via satellite imagery, which provides high temporal and spatial resolution data of floating kelp canopy across the western United States and Mexico. However, the size and complexity of the satellite image dataset has made ecological analysis difficult for scientists and managers. To increase accessibility of this rich dataset, we created Kelpwatch, a web-based visualization and analysis tool. This tool allows researchers and managers to quantify kelp forest change in response to disturbances, assess historical trends, and allow for effective and actionable kelp forest management. Here, we demonstrate how Kelpwatch can be used to analyze long-term trends in kelp canopy across regions, quantify spatial variability in the response to and recovery from the 2014 to 2016 marine heatwave events, and provide a local analysis of kelp canopy status around the Monterey Peninsula, California. We found that 18.6% of regional sites displayed a significant trend in kelp canopy area over the past 38 years and that there was a latitudinal response to heatwave events for each kelp species. The recovery from heatwave events was more variable across space, with some local areas like Bahía Tortugas in Baja California Sur showing high recovery while kelp canopies around the Monterey Peninsula continued a slow decline and patchy recovery compared to the rest of the Central California region. Kelpwatch provides near real time spatial data and analysis support and makes complex earth observation data actionable for scientists and managers, which can help identify areas for research, monitoring, and management efforts.

How environmental drivers of spatial synchrony interact

“…But how, specifically, might improved understanding of Moran effects from this study aid kelp conservation or restoration? Scientists and managers are currently developing a stability model that informs when, where, and how to restore kelp forests following recent large‐scale declines (Bell et al 2023). Specifically, these efforts inform kelp restoration by modelling the dynamics of kelp abundance (measured by diver surveys) as a function of environmental and bathymetric variables.…”

“…Resulting maps of kelp stability are then compared to maps of recent canopy declines to identify sites where restoration activities are needed and would lead to stable future forests (Giraldo‐Ospino et al In prep.). It is well known that stability of regional populations is influenced by synchrony, both generally (Wilcox et al 2017) and for kelp specifically (Walter et al 2022); and the first step in the emerging kelp restoration decision tree of Bell et al (2023) and Giraldo‐Ospino et al (In prep.) involves predicting kelp stability across all suitable habitat in California.…”

A tool for detecting giant kelp canopy biomass decline in the Californias

“…A recently created webpage (http://kelpwatch.org) provides an interface to visualize, select, and download parts of this data. A companion publication to http://kelpwatch.org demonstrates how it can be used to analyze long‐term trends in a kelp canopy across variable temporal and spatial scales (Bell et al, 2023). Here we describe the R (R core team, 2022) package kelpdecline that generates ready‐to‐interpret kelp decline statistics extracted from the SBC‐LTER kelp canopy data.…”

Marine protected areas promote resilience of kelp forests to marine heatwaves by preserving trophic cascades

“…(Bell et al, 2023), and an outbreak of sea urchins that are eroding kelp forest resilience. Additionally, California has a network of MPAs that cover 16% of state waters (Saarman & Carr, 2013), decades of satellite-derived estimates of kelp cover (Bell et al, 2023), and underwater surveys of kelp forest communities (Malone et al, 2022). With the rich ecological monitoring data that exist in this ecosystem, we can evaluate for the first time the resilience to and the underlying mechanisms of kelp forest ecosystems to MHWs within MPAs at a regional scale.…”

“…During 2014–2016, the California coast was subject to one of the largest and longest MHW regime ever documented on Earth (Cavole et al, 2016; Di Lorenzo & Mantua, 2016; Frölicher & Laufkötter, 2018), providing a unique opportunity to investigate the dynamics of MPAs and ecosystem resilience. The combination of the 2014 warm-water anomaly and the 2015–2016 El Niño Southern Oscillation led to extremely warm waters (Cavole et al, 2016; Frölicher et al, 2018) that caused species range shifts (Favoretto et al, 2022; Sanford et al, 2019; J. G. Smith et al, 2023), a widespread loss of kelp forests from Northern California to Baja California Sur, Mexico (Bell et al, 2023), and an outbreak of sea urchins that are eroding kelp forest resilience. Additionally, California has a network of MPAs that cover 16% of state waters (Saarman & Carr, 2013), decades of satellite-derived estimates of kelp cover (Bell et al, 2023), and underwater surveys of kelp forest communities (Malone et al, 2022).…”