Morphological Features and Hatching Patterns of Eggs in Acartia Steueri (Crustacea, Copepoda) from Sagami Bay, Japan

Abstract

Morphology, production rate and hatching success of the eggs spawned by Acartia steueri from Sagami Bay, Japan were examined from November 2000 to December 2001. A. steueri produced two morphological types of egg. One with a smooth surface (smooth egg) and the other with branched spines on the envelope (spiny egg). Abundance of adult A. steueri increased from April to June 2001, and then decreased from July 2001. Adult A. steueri were low in abundance between August and October 2001, then increased in November 2001. Smooth eggs were produced through out the study period, while spiny eggs were produced during restricted periods from March to July 2001. Six of thirteen females produced both smooth and spiny eggs within 24 h. All the smooth eggs hatched within 48 h, like the so-called subitaneous eggs. Spiny eggs that did not hatch within the time determined by the Bělehradek's temperature function of egg development time plus 24 h were categorized as diapausing eggs. In the present study, A. steueri seems to survive by utilizing egg dormancy during the period of environmental adversity, and produced two physiologically different types of eggs. This may be why A. steueri dominants in temperate coastal waters where environmental conditions vary drastically.