If there is a significant silt component in the sediment, the interstitial spaces are filled by the silt particles, impacting the interstitial fauna. While most sand beaches have a strong enough wave regime to remove silt, there can be significant fine-sediment components near river mouths, at the base of landslides, and in relatively sheltered areas around sloughs and estuaries, reducing the abundance and variety of interstitial fauna. Meiofauna are also influenced by tidal level. They exhibit pronounced vertical migrations within the sand, closely following the tidal curve. Near river mouths and other freshwater sources, the abundance of meiofauna can be impacted by sub-surface freshwater flows.
Few studies exist on meiofauna in central California.
Polychaetes, oligochaetes, and nematodes are dominant, with oligochaetes generally found in the higher intertidal. There are also seasonal pulses of harpacticoid copepods and archiannelid worms. Despite the barren appearance of sand beaches, they harbor a diverse and abundant assemblage of macrofauna. These animals generally live buried in the sand, and are highly mobile, so are somewhat more difficult to study than, for instance, the more sessile organisms of rocky intertidal zones. Because the beach is a physically rigorous environment, physical factors often limit the distribution of these organisms.