Connecting polarized light and water turbidity with feeding rates in Octopus americanus paralarvae

Abstract

This study aimed to evaluate whether polarized light or water turbidity enhances Octopus americanus paralarvae daily feeding rates (FRs) when fed on natural prey (Acartia lilljeborgi copepods) and estimate their daily energy consumption. Paralarva individual FR was obtained using a density of 80 copepods L−1. The polarized light experiment had a control (regular light) and two polarized light treatments (electronic vectors at 90° and 45°) for newly-hatched and 15-day-old paralarvae. The water turbidity experiment had a control (0.09 NTU [nephelometric turbidity unit]), and three other treatments (3.80, 19.44, and 45.82 NTU) obtained with different Isochrysis galbana densities for newly-hatched and 8-day-old paralarvae. Five experimental units were used for each treatment and the experiments lasted 24 hr. No significant differences in the FRs were found for polarized light and water turbidity. The general FR was 3.9 ± 2.3, 7.7 ± 2.9, and 15.9 ± 6.5 copepods paralarva−1 day−1 for newly-hatched, 8-day-old, and 15-day-old paralarvae, respectively. Water turbidity at the higher NTU might have impacted swimming performance of paralarvae, reducing their FRs. Our methodological errors for quantifying FRs of paralarvae were <3%, providing reliable results for understanding the daily feeding requirements of Octopus paralarvae under rearing conditions and their feeding ecology in the wild.