A response surface investigation of the larval tolerances of three spionid polychaetes to temperature, salinity and food concentration

Response surface techniques were used to investigate the tolerances of the planktonic larvae of three spionid polychaetes to a variety of temperature and salinity combinations. Two of the spionids were morphologically very similar members of the genus Boccar.dia., B. proboscidea and B. columbiana which occupy nearly identical geographic ranges. The other was Polydora giardi a common coinhabitant with B. columbiana. In addition a third independent parameter, food concentration, was added to the study of B. columbiana and P. giardi. The larvae of the two Boccardia species were extremely euryhaline, in marked contrast to those of Polydora giardi which were confined to an extremely narrow salinity range. They were distinctly sepArated by their temperature tolerances, however; B. proboscidea exhibiting maximum growth and survival at the upper temperature extremes of the design , while B. columbiana preferred a moderate to low temperature regime. The larvae of P. giardi are extremely eurythermal and are only slightly affected by temperature variations. It is suggested that the reproductive schedule of the three spionids can be explained, at least in part, in terms of the information generated by the response surfaces. The long duration of the reproductive season of P. giardi is a reflection of the larvae\u27s eurythermal nature. The inability of the larvae of P. giardi to cope with osmotic stress and the lack of an abundance of food items in the plankton during the winter months are probably of greater consequence in dictating the cessation of the reproductive season, than the minimum water temperatures that occur at t.his time. The Boccardia larvae are in contrast less subject to the above considerations but are very dependent on the ambient water temperature to promote larval survival and growth