The insidious effect of diatoms on copepod reproduction

The productive regions of the ocean are characterized by seasonal blooms of phytoplankton which are generally dominated by diatoms, This algal class h as, therefore, traditionally been regarded as providing the bulk of the foo d that sustains the marine food chain to top consumers and important fisher ies. However, this beneficial role has recently been questioned on the basi s of laboratory studies showing that although dominant zooplankton gazers s uch as copepods feed extensively on diatoms, the hatching success of eggs t hus produced is seriously impaired(1). Here we present evidence from the fi eld showing that the hatching success of wild copepods feeding on a diatom- dominated bloom is also heavily compromised, with only 12% of the eggs hatc hing compared with 90% in post-bloom conditions. We report on the structure of the three aldehydes isolated from diatoms that are responsible for this biological activity, and show that these compounds arrest embryonic develo pment in copepod and sea urchin bioassays and have antiproliferative and ap optotic effects on human carcinoma cells.