Nitrogen excretion by the surf zone bivalves Donax serra and D. sordidus

Abstract

Nitrogen excretion by 2 surf zone bivalves, Donax serra and D. sordidus , was determined under laboratory and field conditions. Comparison of the forms of nitrogen excreted revealed only slight differences between species, with ammonia and amino acids constituting 70 to 78% and 21 to 30% of total dissolved nitrogen (TDN) respectively. During exposure at low tide, ammonia accumulated in D. serra mantle cavity fluid at 1 to 10% of the immersed excretion rates. On re-immersion, an initial uptake of ammonia was recorded with subsequent recovery to peak excretion rates within 2 h. Mass significantly influenced rate of ammonia excretion in both species. The effect of temperature on ammonia excretion rates is reflected in Q sub(10) values of 2.2 (D. serra ) and 2.3 (D. sordidus ) for starved sand-mussels over the temperature range 15 to 25 degree C.