Marine broadcast spawners have two-phase life cycles, with pelagic larvae and benthic adults.
Larval supply and settlement link these two phases and are crucial for the persistence of marine
populations. Mainly due to the complexity in sampling larval supply accurately, many
researchers use settlement as a proxy for larval supply. Larval supply is a constraining variable
for settlement because, without larval supply, there is no settlement. Larval supply and
settlement may not be well correlated, however, and settlement may not consistently estimate
This paper explores the argument that larval supply (i.e., larval abundance near settlement sites)
may not relate linearly to settlement. We review the relationship between larval supply and
settlement, from estimates and biases in larval supply sampling, to non-behavioral and
behavioral components, including small-scale hydrodynamics, competency, gregarious behavior,
intensification of settlement, lunar periodicity, predation and cannibalism. Physical and structural
processes coupled with behavior, such as small-scale hydrodynamics and intensification of
settlement, sometimes result in under- or overestimation of larval supply, where it is predicted
from a linear relationship with settlement. Although settlement is a function of larval supply,
spatial and temporal processes interact with larval behavior to distort the relationship between
larval supply and settlement, and when these distortions act consistently in time and space, they
cause biased estimates of larval supply from settlement data.
Most of the examples discussed here suggest that behavior is the main source of the decoupling
between larval supply and settlement because larval behavior affects the vertical distribution of
larvae, the response of larvae to hydrodynamics, intensification of settlement, gregariousness,
predation and cannibalism. Thus, larval behavior seems to limit broad generalizations on the
regulation of settlement by larval supply. Knowledge of the relationship is further hindered by
the lack of a well founded theoretical relationship between the two variables.
The larval supply- settlement transition may have strong general consequences for population
connectivity, since larval supply is a result of larval transport, and settlement constrains
recruitment. Thus, measuring larval supply and settlement effectively allows more accurate
quantification and understanding of larval transport, recruitment and population connectivity.