Data from: From kelp forests to turf reefs: patterns, drivers, and impacts on functional diversity

Kelp forests are declining in many regions due to ocean warming, predator
loss, and other anthropogenic stressors. In areas of rapid ocean warming,
including the southern Gulf of Maine, these ecosystems have transitioned
to a novel state dominated by low-lying mats of turf algae. However, the
pace, drivers, and ecological consequences of this transition remain
unclear. Here, we used field surveys from 32 sites over five years
(2018–2023) to reveal a continuation of kelp forest collapse and northward
expansion of turf algae across Maine’s coast. Next, we united data on
benthic cover with key environmental variables in a structural equation
model to show that turf algae were directly enhanced by higher ocean
temperatures and decreased wave disturbance and indirectly enhanced by a
warming-induced loss of kelp cover. Lastly, the shift from kelp to turf
yielded a seaweed assemblage dominated by traits associated with rapid
growth, high surface-area-to-volume ratios, and markedly reduced canopy
height, indicating declines in habitat provisioning and carbon storage
with kelp forest loss. Our findings highlight the accelerating impacts of
climate change on temperate reef ecosystems and the vital services they
provide. Further, we provide insights into a new state shift that is now
occurring globally and underscore the need for urgent actions to mitigate
further loss of foundational kelp forests.