Lanternfish - Ecology

Ecology

Lanternfish are well known for their diel vertical migrations: during daylight hours most species remain within the gloomy bathypelagic zone, between 300 metres (980 ft) and 1,500 metres (4,900 ft) in depth, but towards sundown the fish begin to rise into the epipelagic zone, between 10–100 metres (33–330 feet) deep. The lanternfish are thought to do this to avoid predation, and because they are following the diel vertical migrations of zooplankton, upon which the lanternfish feed. After a night spent feeding in the surface layers of the water column, the lanternfish begin to descend back into the lightless depths and are gone by daybreak.

Most species remain near to the coast, schooling over the continental slope. Different species are known to segregate themselves by depth, forming dense, discrete conspecific layers, probably to avoid competition between different species. Due to the lanternfishes' gas bladders, these layers are visible on sonar scans and give the impression of a "false bottom": this is the so-called deep-scattering layer that so perplexed early oceanographers.

There is great variability in migration patterns within the family. Some deeper-living species may not migrate at all, while others may do so only sporadically. Migration patterns may also be dependent on life history stage, sex, latitude, and season.

The arrangements of lanternfish photophores are different for each species, so it is assumed that their bioluminescence plays a role in communication, specifically in shoaling and courtship behaviour. The concentration of the photophores on the flanks of the fish also indicate the light's use as camouflage; in a strategy termed counterillumination, the lanternfish regulate the brightness of the bluish light emitted by their photophores to match the ambient light level above, effectively masking the lanternfishes' silhouette when viewed from below.

A major source of food for many marine animals, lanternfish are an important link in the food chain of many local ecosystems, being heavily preyed upon by whales and dolphins; large pelagic fish such as salmon, tuna and sharks; grenadiers and other deep-sea fish (including other lanternfish); pinnipeds; sea birds, notably penguins; and large squid such as the jumbo squid, Dosidicus gigas. Lantern fish themselves have been found to feed on bits of plastic debris accumulating in the oceans. At least one lantern fish was found with over 80 pieces of plastic chips in its gut, according to scientists monitoring ocean plastic in the Pacific Ocean's Eastern Garbage Patch.