Macrocystis pyrifera before (2008) and after (2018-19) microsatellite data in Structure format

Given the impacts of climate change and other anthropogenic stressors on
marine systems, there is a need to accurately predict how species respond
to changing environments and disturbance regimes. The use of genetic tools
to monitor temporal trends in populations gives ecologists the ability to
estimate changes in genetic diversity and effective population size that
may be undetectable by traditional census methods. Although multiple
studies have used temporal genetic analysis, they usually involve
commercially important species, and rarely sample before and after
disturbance. In this study, we run a temporal analysis of giant kelp,
Macrocystis pyrifera, genetic diversity over the scope of 10 years
(2008-2018) using the same microsatellite marker panel to assess the
genetic consequences of disturbance in several populations of giant kelp
(Macrocystis pyrifera) in the Southern California Bight. The study is a
rare pre- and post-disturbance microsatellite analysis that included
declines to giant kelp caused by the 2015/16 El Nino Southern Oscillation
event. We used canopy biomass estimated by remote sensing (Landsat) to
quantify the extent of disturbance to kelp beds, and sea surface
temperature data to understand how kelp was pushed towards its temperature
limits during this period. Despite prolonged periods with decreased canopy
at several sites, no changes in genetic structure and allelic richness
were observed. We argue that giant kelp in the region is best described as
a “patchy population” system where true extinctions are rare. We discuss
how deep refugia of subsurface sporophytes and cryptic microscopic life
stages could have kept genetic diversity through disturbance. Given the
increasing effects of climate change and uncertainty in modeling impacts
of species with cryptic life history stages, we suggest further
investigation to reveal the role such stages play in species resilience.
Genetic monitoring studies of sites selected by remote census demographic
and climate surveys should be continued in the future given the predicted
impacts of climate change.