Bioturbation of Intertidal Quartz-Rich Sands: A Modern Example and Its Sedimentologic and Paleoecologic Implications

Abstract

Callianassa californiensis is a deep burrowing deposit-feeding thalassinid shrimp which is abundant in intertidal areas of Mugu Lagoon, California. It occurs in greater densities ($170/m^{2}$) and is distributed more evenly to a depth of 50 cm below the sediment surface in quartz-rich sands than in muddy sands ($78/m^{2}$), where most individuals live 15 to 30 cm below the sediment-water interface. Callianassa californiensis produces extensive unlined burrow networks and deposits excavated material at the sediment surface. Given published excavation rates, the population of C. californiensis in the sandy area of Mugu Lagoon would deposit a layer 1 to 3 m thick each year; it is also capable of rapidly reestablishing burrow openings after burial by up to 16 cm of sediment. Burrows act as conduits for fresh seawater, and rapid overturn of sands inhibits compaction. This results in flushing of nutrient and oxygen-rich waters to considerable depth in the quartz-rich sands, as reflected by a depressed oxic-anox...