11.2019 | THE SCIENTIST 37Carr, along with a large group of col-
leagues, graduate students, and volunteers,
recently carried out a parentage analysis
for kelp rockfish (Sebastes atrovirens), an
abundant species in temperate ecosystems.
The team sampled 6,000 fish—clipping a
bit of fin tissue from individuals caught
with a hook and line, or nicking the skin
of freely swimming fish with a custom-
ized pole spear while scuba diving—along
25 kilometers of California’s coastline that
included multiple MPAs. Analyzing nearly
100 different genetic markers in the sam-
ples, the researchers identified eight par-
ent-offspring pairs. At least two of those
offspring had moved out of the M PA where
their parents lived into areas where fishing
is allowed. Four other offspring had also
dispersed out of their parents’ M PA , but
subsequently found their way into another.^5
Unfortunately, such projects are expen-
sive and time-consuming, notes Simon Thor-
rold, an ocean ecologist at the Woods Hole
Oceanographic Institution whose group
used parentage analysis a couple of years agoto reveal high levels of connectivity among
clownfish (Amphiprion percula) and but-
terflyfish (Chaetodon vagabundus) popula-
tions around Papua New Guinea.^6 “[Mak-
ing] direct measurements of dispersal in the
ocean is a hugely intensive effort,” Thorrold
says. Because researchers can’t study every
species in the ocean using these methods, he
adds, “we’re always going to be extrapolating
from the few species we know considerably
more about.”Models of the sea
To aid in making such inferences, research-
ers turn to computer models. Simulations
based on a species’ distribution and life his-
tory, combined with physical data such as
ocean current measurements, can help labs
predict the movements of marine organ-
isms. Metaxas and colleagues, for example,
recently modeled larval dispersal to assess
connectivity between populations of deep-
water corals, ecologically important but dif-
ficult-to-study organisms, in canyons in
the ocean floor off the coast of Nova Sco-
tia. Using physical data on ocean currents
as well as the distribution of corals—which
the team visually assessed using a remotely
operated vehicle—the researchers estimated
the movement of larvae from one population
to another and found evidence for frequent
exchange between Canadian and US waters.^7When possible, researchers complement
physical data on ocean currents with biologi-
cal data on larval behavior. Larvae of many
species can swim up and down in the water
column, for example, or toward or away from
stimuli such as light, noise, and certain envi-
ronmental chemicals. Nandini Ramesh, a
postdoc in atmospheric scientist William
Boos’s lab at the University of California,
Berkeley, and colleagues recently developed
one such biophysical model to estimate the
larval movement of more than 700 commer-
cially important fish species around the globe.
Results generated by the model suggested
that the world’s fisheries are highly intercon-
nected, with many fish spawned in one coun-
try’s waters going on to be caught in another’s.
Accounting for the species’ economic value to
the fishing industry, the team estimated that
this international connectivity helps generate
more than $10 billion a year.^8
Such biophysical models can predict,
on a large scale, both where individual ani-
mals might end up and how they get there.
But the findings are difficult to validate,
says Thorrold. “While [simulations] can
produce quite compelling visuals, there
really has been no way of determining how
accurate those biophysical models are,” he
says. “It’s going to come down to combining
[them] with other methods.”
Back in Portugal, Queiroga and his col-
leagues have been working on just such a
combined approach for their mussel popula-
tions. Last year, the researchers published a
biophysical model of larval dispersal based on
ocean currents along the coast and compared
it to observations from their geochemical
analyses. The results of the two approaches,
the team found, were highly correlated.^9 “If
the different methods converge, [and their]
estimates are similar to each other,” says
Queiroga, “then we begin to be more confi-
dent about the description of the process.”A protective net
As researchers continue to demonstrate the
practical importance of marine connectivity,
the concept is slowly being incorporated into
conservation planning. Metaxas, who acts
as an advisor to the Canadian government’s
Department of Fisheries and Oceans, notes
ASIA ARMSTRONG that policymakers around the world increas-
TRACKING GIANTS:With the help of citizen
scientists, researchers such as University of
Queensland PhD student Chris Lawson have
been photographing reef mantas for an online
database that notes when and where the mas-
sive rays have been spotted.