EFFECTS OF MEDIA WITH LOW SILICIC ACID CONCENTRATIONS ON TOOTH FORMATION IN ACARTIA TONSA DANA (COPEPODA, CALANOIDA)

¹ School of Oceanography, Oregon State University, Corvallis, Oregon 97331
² Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543

Acartia tonsa Dana can extract sufficient silicon for formation of siliceous teeth from media with concentrations of silicic acid as low as 0.2 µM. Low silicate media were produced by growing diatoms in seawater collected from oligotrophic habitats and enriched with nutrients other than silicic acid, then removing them by filtration when they reached a silicic acid-limited stationary phase. Most teeth formed by A. tonsa in 0.2 µM medium were greatly reduced in profile, probably by increased effects of wear on insufficiently mineralized teeth. Teeth formed at silicic acid levels comparable to those in the field habitat of the copepod (1.5 µM) were normal. The extent of this ability to remove silicon from dilute media is comparable to that of diatoms. It is unlikely that low silicate levels in the field are an important limiting factor for A. tonsa or other copepods normally found in oligotrophic, pelagic habitats in the sea.