Beagle kelp maps from: One of the least disturbed marine coastal ecosystems on Earth: Spatial and temporal persistence of Darwin’s sub-Antarctic giant kelp forests

Aim: Marine habitats and their dynamics are difficult to systematically
monitor, particularly those in remote locations. This is the case with the
sub-Antarctic ecosystem of the giant kelp Macrocystis pyrifera,
which was already noted by Charles Darwin in his accounts on
the Voyage of the Beagle and recorded on the nautical
charts made during that expedition. We combined these and other nautical
charts from the 19th and early 20th centuries with surveys conducted in
the 1970s and 1980s and satellite detection algorithms from 1984 to 2019,
to analyse kelp distribution through time and the factors that correlate
with it. Location: Marine ecoregions of Channels and Fjords of Southern
Chile, Falkland Islands (Malvinas), and the island of South Georgia.
Taxon: Macrocystis pyrifera. Methods: We characterised
309 giant kelp forests by their coastal geospatial attributes.
Statistically significant variables were included in a conditional
inference tree to predict kelp forest size. Sea surface temperature (SST)
records were analysed to confirm temperature ranges over the last four
decades. Nautical charts, historical surveys, aerial photogrammetry,
unmanned aerial vehicle (UAV) surveys and satellite imagery were overlaid
to assess spatial distribution of kelp forest canopies, spanning the
period 1829–2020. Results: Considering the extensive natural and human
caused changes over the last two centuries, this diverse kelp ecosystem is
remarkably persistent. We found that the ocean currents and wave exposure,
combined with the geomorphological settings of the coastline are the most
critical factors predicting the extent of the kelp forests. Main
conclusions: We have described the long-term ecological persistence of the
kelp forests in this vastly under-studied region that offers a conceptual
biogeographical model supporting the global importance proposed by Charles
Darwin 200 years ago (Darwin, 1845). In the current context of
global change, the need for conservation of this persistent and
well-preserved marine ecosystem has never been more important.