Can We Estimate the True Weight of Zooplankton Samples after Chemical Preservation?

Abstract

Zooplankton are collected and sorted into two size fractions from which samples are randomly alloted to a battery of commonly used preservation techniques. We determine dry weight, ash content, and caloric content. We compute organic and inorganic losses of the samples to examine potential causes of variation in dry weight estimates. Treatments are: no preservation, preservation with one of three chemicals (75% ethanol, 5% or 10% buffered formaldehyde), preservation for 1 or 66 wk, and oven- or freeze-drying. Overall dry weight losses are independent of preservation methods. Chemical preservation reduces dry weight by 37 to 43%. Organic and inorganic losses range from 25 to 33% and 73 to 82%, respectively. Because inorganic losses are large, chemical preservation increases the caloric content of samples by 13 – 27%. Dry weight losses are somewhat size-dependent (37 versus 43% for the large and small size fraction respectively, after 66 wk of preservation). A regression of percent dry weight losses on body length (in millimetres) is obtained for our data, and published reports where formaldehyde is used as a preservative. It is: In[dry weight loss] = 4.149 − 0.576 length0.333. This relationship can be used to adjust the weight of zooplankton samples which have been preserved chemically. A survey of studies published in 1983 indicates that most authors did not adjust for dry weight losses due to preservation.

standing stocks

“…4). Mesozooplankton carbon was estimated from dry weight, corrected for preservation effects after Giguere et al (1989), and converted to carbon using conversion factors for Neocalanus plumchrus after Miller (1993a, b) and for all other species after Omori (1969). …”

Estimating larval fish ingestion rates: can laboratory derived values be reliably extrapolated to the wild?

“…Sixty percent of all larvae contained in our data set were preserved in formalin before dry weight determinations were performed. Losses in dry weight are known to occur in larval fishes as a consequence of preservation but the magnitude of this loss has not been thoroughly evaluated (Delafontaine & Leggett 1989, Giguere et al 1989. Available estimates of preservation-induced dry weight loss range from 9 to 30 % (Theilacker & Dorsey 1980, Bailey 1982, Hay 1984.…”

“…(g 6 Artem~a nauplius = 1.85 pg 2 Brachionus (mixed sizes) = 0.16 pg 17 C'alanus finmarchicus (nauplius) = 1.5 pg 4 Euryternora affinjs (naupl~us) = 0.28 pg 3, 10 E. affinls (copepodite) = 2.2 pg 3 E. affinis (adult) = 10.4 {(g (April-May in Chesapeake estuary) 9 Pseudocalanus (nauplius) = 0.26 ~cg 13 1, BBmstedt (1986); 2, Benijts et al (1975);3, Burkhili & Kendall (1982;see also Chesney 1989);4, Davis (1984);5, Delafontaine & Leggett (1989);6, Durbin & Durbin (1981); 7, Giguere et al (1989);8, Hay (1984) proportions of all prey; (3) in cases where only 1 size of prey was offered per experimental treatment (N = 7), we multiplied the numerical density of prey by the dry weight equivalent of an individual prey comprising the diet. All 11 studies used in our analysis reported ingestion rate estimates for larvae of several sizes.…”

Distribution of Engraulis encrasicolus eggs and larvae in relation to coastal oceanographic conditions (the South-western Adriatic Sea case study)

“…After subtracting anchovy eggs and larvae, samples were dried in an oven for 24 h at 60° C and weighed; the procedure was repeated until a constant weight was reached (Postel et al, 2000). Possible loss of material due to formalin fixation was corrected by applying a conversion factor obtained by averaging several conversion factors used for different zooplankton taxa (Giguère et al, 1989). The mass loss after drying was estimated to be 31.32% of the total original mass.…”