Oceanography | Vol. 37, No. 3
late summer declines were preceded by
spring shifs in deep-water conditions
(Record et al., 2019). Tere is no guar-
antee that a return to pre-heatwave con-
ditions will resupply C. fnmarchicus to
the eastern Gulf of Maine, as the rela-
tive importance of supply versus local
dynamics is still uncertain (Pershing and
Kemberling, 2024). However, in either
case, it is a shif that we should be look-
ing out for, given the sensitive state of
this management issue. Targeted whale
or zooplankton surveys would be help-
ful, as well as coordinated communica-
tion among those with eyes on the water
for opportunistic sightings.
AMERICAN LOBSTERS. Deep-water con-
ditions in spring strongly infuence the
timing of molt and inshore migration and
rates of post-settlement survival (Goode
et al., 2019) of the American lobster—
a species that supports a nearly billion-
dollar fshery. Changes in this phenol-
ogy can drive big swings in prices, and
because of the strong dependence on
temperature, deep waters in spring are
predictive of molt timing (Mills et al.,
2017). Based on the predictive power of
spring bottom temperatures, a success-
ful forecasting strategy was developed,
but operational forecasts were stopped
at the request of the industry (Pershing
et al., 2018). Deep-water temperatures
in the coastal zone have not yet cooled
to pre-heatwave conditions, but they are
getting close. Such a signifcant shif in
deep-water dynamics should be moni-
tored for its efects on stock dynamics. In
addition to ongoing buoy observations,
opportunistic water column profles
or bottom-moored thermistors would
fll gaps and give a more detailed map
of these dynamics.
KELP FORESTS. Deep-water conditions
also infuence the thermodynamics of
coastal waters where kelp forests prevail.
Such forests—which foster biodiversity,
fuel nearshore food webs, and underpin an
aquaculture industry—were widespread
at the turn of the twenty-frst century.
However, in response to unusually warm
springs and summers, forests in the
southwestern Gulf have since collapsed,
and forests in the northeast have become
less lush, with a loss of subarctic taxa
(Suskiewicz et al., 2024). A tempo-
rary return to pre-heatwave conditions
is unlikely to foster recovery of south-
ern forests because they have shifed to a
novel, alternative stable state, but cooler
conditions may bring a banner year for
kelp recruitment in the north, given the
positive efects of “cold-priming” on kelp
reproduction and recruitment (Liesner
et al., 2020; Gauci et al., 2022). Te poten-
tial efects of cooling on kelp abundance
may take one or more years to manifest, so
continual ecosystem monitoring will be
necessary for understanding the impacts
of deep-water cooling on forest resilience.
Learning how to use oceanographic
conditions as early warnings is a multi-
decadal learning process. Ocean and cli-
mate surprises, generally defned as mis-
matches between the expectations and
the realities of changing conditions, have
the potential to drive changes in human
and natural systems (Pershing et al.,
2019), and they have played a particu-
larly important role in the Gulf of Maine
(Record et al., 2023). If we hope to use
real-time oceanographic measurements
to prepare for future events, as some have
suggested (Link et al., 2023), we are obli-
gated to report signifcant events as they
unfold. We don’t mean to imply that this
oceanographic shif will return the Gulf of
Maine to a pre-heatwave ecosystem—that
is probably impossible in a world with
426 ppm CO2 concentrations (and ris-
ing). However, this type of oceanographic
change has had major efects in the past,
and we should be paying close attention
this summer and fall as events unfold.
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