Inorganic Nutrient Fluxes in Anemone-dominated Tide Pools

Abstract

Physical and chemical characteristics of seawater in two natural tide pools on Rosario Beach, Fidalgo Island, Washington, were compared during midday low tides in July 1991. One pool contained a mixed assemblage of macroalgae (40% cover) and invertebrates (50% cover). The second pool was dominated (75% cover) by the sea anemone Anthopleura elegantissima (Brandt, 1835), which contains symbiotic algae (zooxanthellae). Temperature, salinity, dissolved oxygen, and pH levels increased in both pools with irradiance and length of emersion. The resident organisms caused changes in the inorganic nutrient levels of the tide-pool seawater. Anthopleura elegantissima released substantial amounts of ammonium; NH4 + in the anemone-dominated pool increased by 33% whereas NH4 + declined in the mixed assemblage pool by an average of 28%. Nitrate and nitrite declined in both pools, whereas phosphate remained constant during the 6-hr sampling periods. NH4 + release by A. elegantissima was confirmed in studies of artificial tide pools, where NH4 + levels increased by an average of 71% over an 8-hr period. Release of ammonium by A. elegantissima under natural conditions in the field provides a contrast to nutrient fluxes observed for tropical symbiotic associations.