Atlanta lesueurii

Diel vertical distribution patterns of Atlanta lesueurii (among the 13 species of heteropods in the study) were investigated off leeward Oahu, Hawaii in waters overlying a bottom depth of 2,000 m (between 9 and 11 km off the coast) by Seapy (1990).[5] Heteropods were collected during day and night periods using paired, opening-closing BONGO nets at 50-m depth intervals between the surface and 200 m and at 200–300 m and 300–400 m.[5] Three or four replicated tows were taken in each depth interval.[5] Atlanta lesueurii was found to be the most abundant species, with a maximal density of 59 individuals per 1,000 m³ in a daytime 0–45 m depth interval.[5] The species ranged from the surface to 140 m during both day and night periods.[5] There was an apparent partial populational migration from a depth interval of 45–90 m during the day to 0–45 m at night.[5] However, high variability in densities between the replicated tows in each of the depth intervals resulted in statistically non-significant differences between day and night periods for each of the depth intervals.[5]

In a subsequent study off leeward Oahu (Seapy, 2008), duplicate tows were taken with a MOCNESS multiple, opening-closing net system during day and night periods at three stations located 1, 5 and 15 nm off the island in fall and spring sampling periods.[5] Mean densities were computed (as numbers of individuals beneath 100 m² of ocean surface) during day and night periods at each station.[5] As in the 1990 study, Atlanta lesueurii was the most abundant species in the fall, although it was a close second to Atlanta plana in the spring.[5] Comparisons were made using the nighttime density data to avoid issues such as daytime net avoidance and to include increased nighttime abundances resulting from possible nocturnal vertical migrator species.[5] Atlanta lesueurii was found to be most abundant at the offshore (15 nm) station during both seasons.[5] Offshore to inshore abundance decreased most dramatically in the fall; from mean nighttime densities of 480 (15 nm) to 124 (5 nm) to 37 (1 nm) individuals beneath 100 m² of ocean surface.[5] At the 15 nm station the species ranged downward to the greatest depths; to the 120–160 m depth interval in the spring and to the 80–120 m depth interval in the fall.[5] Clear evidence for nocturnal vertical migration was only seen in the spring at the 1-nm station (10-m depth interval tows were taken in the upper 100 m at this shallow-water station).[5] Highest abundances were recorded between 60 and 30 m during the day to 30 m to the surface at night.[5]