FIGURE 7.

Schematic illustration of the mechanism of phytoplankton presence in the aphotic layer. The shown process/phenomenon marked within the solid-lined box indicate they have been identified; the marks within the dotted box indicate they were hypothesized. (1) Phytoplankton cells sank from aphotic layers into the aphotic layers of the sea; they could sink alone or within the aggregates/fecal pellets; (2)the physical process and/or biological process might be involved in the sinking process to accelerate cell sink; (3) the phytoplankton cells might be ultimately degraded into phytodetritus, or the cells might become resting cells or cysts; the cells also might live in the dark sea as heterotroph; and (4) the phytoplankton cells as heterotroph might prey on bacteria and/or large particulate matter to survive.