The effects of physiology and behaviour on the near-bottom distributions of <i>Karenia brevis</i> on the West Florida shelf: a numerical study

Abstract

The distribution of near-bottom populations of Karenia brevis depends on both cell physiology and behaviour. The migration distance of cells, and the subsequent exposure to light, may vary as a result of the nocturnal
uptake of nitrate. The adaptive advantage of higher nocturnal uptake rates and upward migration is evident in clear deep (90m) water columns as well as in shallower (30m), more turbid water columns. In deeper offshore environments, migrating cells with high nocturnal uptake rates are able to access light levels needed to compensate growth, whereas migrating cells
with slow nocturnal uptake rates or non-migrating cells cannot access the minimum light levels needed for growth. In shallow, more turbid environments, migrating cells access between 35% and 67% of the light
needed to saturate growth, whereas cells that do not migrate are only exposed to 6% of the light needed to saturate growth. Vertical migration may not only extend the depth distribution of K. brevis but also provide an
adaptation to persist in more turbid nearshore waters.