many habitat situations. Significant and separate issues are how many eggs hatch and
how many of the first nauplii (N1) are healthy. Poulet et al. (1994) discovered that, in
fact, there can be substantial rates of hatching failure that seem to correlate with the
prevalence of diatoms in the diet. They issued a challenge to everyone on Earth to
prove or disprove that diatoms eaten by copepod mothers are toxic to their eggs. Quite
a few folks took up the challenge. One of the better experiments was by Uye (1996),
working with C. pacificus collected off the Oregon coast. He alternately fed females
with several different diatoms and with several dinoflagellates. The results are striking
(Fig. 8.4). Females eating diatoms soon spawn eggs that don’t develop. When
switched to dinoflagellates, the viability of their eggs recovers. Nauplii that do hatch
from diatom-fed females are often teratogenized, with missing limbs or just bulbous
stumps. They are a sad sight. Uye showed the active principle is a chemical; he
soaked eggs produced by females eating a strictly dinoflagellate diet in diatom
extracts, producing high rates of teratogenesis.
Fig. 8.4 Egg production rate (bar height) and egg viability (black = healthy nauplii,
hatched = deformed nauplii, white = inviable, no hatching) of Calanus pacificus.
Females were initially fed Prorocentrum minimum, a dinoflagellate, then shifted to the
diatom Chaetoceros difficilis on day 2, then switched back to Prorocentrum on day 11
(as indicated by the bars along the top). Fecal pellet production (connected circles)
indicates feeding level.
(^) (After Uye 1996.)