Knowing dispersal distances is important for managing fisheries, effectively designing marine reserves, and controlling invasive species.
[7] Though it has been generally disproved, the larval lottery hypothesis represents an important understanding of the difficulties faced by larvae during their time in the water column.
[8] Most planktivorous fishes are gape-limited predators, meaning their prey is determined by the width of their open mouths, making larger larvae difficult to ingest.
[12][13][14][15] An example of reverse tidal migration performed by crab species would begin with larvae being released on a nocturnal spring high tide to limit predation by planktivorous fishes.
[16] The most widely accepted theory explaining the evolution of a pelagic larval stage is the need for long-distance dispersal ability.
Many estuarine species exhibit swimming rhythms of reverse tidal vertical migration to aid in their transport away from their hatching site.
One study observed crab postlarvae and found that they would swim vigorously until they encountered a floating object, which they would cling to for the remainder of the experiment.
Settlers must be wary of adult filter feeders, which cover substrate at settlement sites and eat particles the size of larvae.
Therefore, they have evolved many sensory systems: Far from shore, larvae are able to use magnetic fields to orient themselves towards the coast over large spatial scales.
[30][31] There is additional evidence that species can recognize anomalies in the magnetic field to return to the same location multiple times throughout their life.
[30] Though the mechanisms that these species use is poorly understood, it appears that magnetic fields play an important role in larval orientation offshore, where other cues such as sound and chemicals may be difficult to detect.
The larvae of the annelid Platynereis dumerilii do not only show positive[34] and negative phototaxis[35] over a broad range of the light spectrum,[36] but swim down to the center of gravity when they are exposed to non-directional UV-light.
[37] Species that produce more complex larvae, such as fish, can use full vision[30] to find a suitable habitat on small spatial scales.
[42] Many families of coral reef fish are particularly attracted to high-frequency sounds produced by invertebrates,[43] which larvae use as an indicator of food availability and complex habitat where they may be protected from predators.
It is thought that larvae avoid low frequency sounds because they may be associated with transient fish or predators[43] and is therefore not a reliable indicator of safe habitat.
[44] There is concern that changes in community structure in nursery habitats, such as seagrass beds, kelp forests, and mangroves, could lead to a collapse in larval recruitment[45] due to a decrease in sound-producing invertebrates.
[46] Many marine organisms use olfaction (chemical cues in the form of scent) to locate a safe area to metamorphose at the end of their larval stage.
Although several behaviours of coral reef fish, including larvae, has been found to be detrimentally affected from projected end-of-21st-century ocean acidification in previous experiments, a 2020 replication study found that "end-of-century ocean acidification levels have negligible effects on [three] important behaviours of coral reef fishes" and with "data simulations, [showed] that the large effect sizes and small within-group variances that have been reported in several previous studies are highly improbable".
Though the mechanism for this process is still not fully understood, some studies indicate that this breakdown may be due to a decrease in size or density of their otoliths.
Evidence also suggests that larval ability to process olfactory cues was also affected when tested under future pH conditions.
[59] Red color cues that coral larvae use to find crustose coralline algae, with which they have a commensal relationship, may also be in danger due to algal bleaching.
[60] Sediment runoff, from natural storm events or human development, can also impact larval sensory systems and survival.
One study focusing on red soil found that increased turbidity due to runoff negatively influenced the ability of fish larvae to interpret visual cues.
Recent work has shown that many populations are self-recruiting, and that larvae and juveniles are capable of purposefully returning to their natal sites.
[65] It is proposed that this mortality rate is related to food supply as well as an inability to move through the water effectively at this stage of development, leading to starvation.
Species with shorter dispersal patterns are more likely to be affected by local changes and require higher priority for conservation because of the separation of subpopulations.
Successful fisheries management relies heavily on understanding population connectivity and dispersal distances, which are driven by larvae.