TRACKING
The most direct way of measuring marine
movement is to record observations of
ocean-dwelling organisms in situ. Those
data can be collected through photographs,
videos, or visual surveys or by using tags
that store or remotely transmit location
information to researchers. Tracking is
particularly effective for large, migratory
animals, but is practically infeasible for
smaller species and larvae.
GENETICS
Tissue samples from marine organisms allow
researchers to quantify genetic diversity
within populations and gene flow between
them. One particularly resource-intensive
and time-consuming approach known as
parentage analysis even allows researchers
to identify which adults spawned a particular
larva. For species that move relatively little in
adulthood, such as many species of reef fish,
researchers can then extrapolate to figure
out where that larva was spawned.