Phytobenthos comprises the plants belonging to the benthos, mainly benthic diatoms and macroalgae (seaweed). Benthopelagic fish inhabit the water just above the bottom, feeding on benthos and benthopelagic zooplankton. The MPA contains sandy beaches and subtidal sandy benthos, rocky platforms, and subtidal rocky reefs. They are covered with sediment but largely devoid of benthic life (benthos). Fauna include zooplankton, benthos and a number of fish species such as "Acanthobrama terraesanctae". Round whitefish are considered benthivores, feeding on benthos and plankton. Zoobenthos are the invertebrates that occupy the benthos of the riverbeds and lakebeds. The polychaetes are most elected component of benthos. Other areas have had sediments covered with concrete to prevent the fish eating the benthos. Nutrient fluxes in the profundal zone are primarily driven by release from the benthos. The main food sources for the benthos are algae and organic runoff from land. They thus ate benthos from the floor of shallow seas. These species strobilate in summer, but maintain polyps in the benthos year round. They feed by extending their syphon-like mouths to suck food from the benthos. The stiff necks would have been used to plough the sea bottom, eating the benthos.