JOURNAL OF PLANKTON RESEARCH | VOLUME 8 | NUMBER 5 | PAGES 927-937 | 1986
© Oxford University Press
research-article |
Individual variability in lipid content of bivalve larvae quantified histochemically by absorption photometry
1Woods Hole Oceanographic Institution Woods Hole, MA 02543 2Virginia Institute of Marine Science Gloucester Point, VA 23062, USA
Received on August 1, 1985; accepted on June 1, 1986
Lipid energy reserves in individual larvae of the Teredinid bivalve, Bankia gouldi (Bartsch), were quantified photodensitometrically after staining whole larvae with the lipid-specific stain, Oil Red O. A modification of the two-wavelength densitometric technique of Mendelsohn (1966) was used to document variability in stored lipid in healthy larvae and larvae under imposed nutritional Stress. The results were compared with analytically derived total lipid values for the same larval groups. A third wavelength was added to the two-wavelength technique to allow direct background subtraction of tissue and shell absorbance on individual larvae. Lipid conent in individual larvae was estimated photodensitometrically to range from a mean of 7 ng in 3-day-old straight hinge larvae, to 175 ng in pediveliger larvae which were competent to metamorphose. During starvation, pediveliger larvae lost lipid at a rate of about 20 ng/day while a loss of 1–2 ng/day/larva was evident in 6-day-old early umbo larvae. Variability in lipid content between individuals of the population was analyzed by frequency histogram and by the product of the third moment to detect abnormal distribution about the mean, i.e. skewness. Although the variability was high in healthy larvae (e.g. for 18-day-old larvae: mean, 
ng lipid/larva, coefficient of variation, CV = 61%) it increased substantially during starvation (e.g. for 18 + 6 days starvation: 
, CV = 197%). Starvation caused the lipid content of individuals to become highly skewed with respect to the population mean (i.e. more individuals fell below rather than above the mean). The magnitude and direction of skewness away from the mean proved to be a more timely and sensitive indicator of physiological stress than considering mean or standard deviation parameters alone. It is suggested that analysis of lipid energy stores of individuals within zooplankton populations may provide valuable insight into the capacity of natural assemblages to cope with stress, be it chemical, thermal, physical or biological in nature.