Contrasting patterns of amphipod dispersion in a seagrass meadow between day and night: consistency through a lunar cycle

Abstract

Changes in light intensity, typically over the course of a day, affect the dispersion of aquatic organisms at short temporal scales. Amphipods, for example, have strong behavioural responses to light conditions. In this study, we used amphipod assemblages inhabiting a Cymodocea nodosa seagrass meadow on the east coast of Gran Canaria Island (eastern Atlantic) to test whether short-term dispersion of seagrass-associated amphipods differed between day and night, testing the consistency throughout an entire lunar cycle. Replicated artificial seagrass units were deployed, and subsequently retrieved, during the day (from 8:00 am to 18:00 pm) and the night (from 18:00 pm to 8:00 am) on three consecutive days within each of the four moon phases of a complete lunar cycle. We collected 13,467 amphipods corresponding to 32 species and 17 families. Significantly larger abundances of amphipods were collected during the night through the entire moon cycle. The total abundance of amphipods was also affected by the moon phases; under full moon, larger abundances of amphipods dispersed into the artificial seagrass units followed by the third quarter, the new moon and the first quarter. The species density of amphipods per unit followed the same pattern. In conclusion, the short-term dispersion of amphipods living in a seagrass meadow was considerably greater during the night than the day, while dispersion of amphipods was more intense under full moon.