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TITLE:  BEST Calanus marshallae/glacialis Egg Production Rates
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Principal Investigators: 

Dr. Carin J. Ashjian
508-289-3457
Woods Hole Oceanographic Institute
cashjian@whoi.edu

Dr. Robert G. Campbell
401-874-6692
University of Rhode Island
campbell@gso.uri.edu

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Data Set Overview:
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Egg production was determined for Calanus marshallae/glacialis. The two 
species were not differentiated as they are almost impossible to identify 
visually during sorting of live animals because of their overlapping body size 
and very similar morphology and pigmentation (Frost, 1974). 

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Data Format:
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The data are in a spreadsheet. For each egg production experiment, the date 
and location for the collection of the animals used are listed.  The 
experiment number is internal to the project. The station number corresponds 
to station numbers in the hly0802 event log.  Listed for each experiment are 
the numbers of females used, the spawning frequency (the proportion of the 
total females that laid eggs each day), the average clutch size (total number 
of eggs laid/number of females that laid eggs), the egg production rate 
(total number of eggs laid/total number of females), and the mean hatching 
(the mean proportion of eggs that hatched in each of three sets of 100 eggs 
that were incubated for up to 8 days).

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Methods:
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The following was adapted from Plourde et al. (2005).  The same methods were 
used for the egg production measurements on HLY0802. In the data, egg hatching 
success is available only when the cruise had sufficient days left to permit 
an 8-day hatching period; eggs collected within 10 days of the end of the 
cruise could not be retained to determine hatching success.  

Animals for egg production (EP) were collected with a 1-m^2 mouth area, 153 
micrometer net equipped with a non-filtering cod-end towed obliquely or 
vertically from 100 m or 10 m above bottom to surface at 30 m min-1. Depending 
on plankton density, one to three net hauls were performed at each station to 
collect enough animals for the experiments and other measurements. The 
plankton catch was immediately diluted in 4-L jars filled with surface water 
and stored in coolers until work began in the laboratory.

Animal sorting and incubations were conducted in a walk-in cold room 
maintained at a temperature close to the ambient conditions (-1 degrees C). As 
quickly as possible after collection, 30-40 adult females were sorted randomly 
from the plankton catch with a large bore pipette and incubated individually 
in 45-ml dishes filled with 0.2 micrometer filtered sea water (FSW) for 24 h 
in dim light. Care was taken to select only animals in good condition, i.e. 
bearing intact setae on the antennules and on the furca. Incubation of 
individuals during 24 h immediately after capture allowed the measurement of 
in situ EP, clutch size, and spawning frequency (Runge and Roff, 2000). 
Cannibalism was assumed negligible as feeding of females on their eggs has 
been observed only on few occasions, females generally swam on their back when 
they were in contact with the bottom on the dishes, and comparison of the 
Petri dish method with the egg separator method for C. finmarchicus has 
demonstrated that cannibalism is negligible (Plourde and Joly, 2008; Plourde 
et al. pers. observation). At the end of the 24 h incubation, eggs were 
counted and gently transferred to a large dish with a pipette. 

Hatching success was determined at most stations. Eggs were randomly sorted 
with a pipette from the single batch and incubated in three replicates of 50 
eggs in 45-ml dishes filled with 0.2 micrometer FSW in dim light at -1  
degrees C. Eggs were checked daily until hatching. Non-hatched eggs and 
abnormal nauplii (either showing malformations or non-swimming on the bottom 
of the dish) were first enumerated. After the addition of 2-3 ml of 5% acetic 
acid, the total number of nauplii was determined and the percentage of viable 
nauplii calculated after subtraction of the number of abnormal ones.

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References:
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Frost, B.W. 1974. Calanus marshallae, a new species of calanoid copepod 
closely allied to the sibling species C. finmarchicus and C. glacialis. Marine 
Biology 26, 77-99.

Plourde, S., Campbell, R.G., Ashjian, C.J., Stockwell, D. 2005. Seasonal and 
Regional Patterns in Egg Production of Calanus glacialis/marshallae in the 
Chukchi and Beaufort Seas during Spring and Summer, 2002. Deep-Sea Research II 
52: 3411-3426.

Plourde, S., and P. Joly.  2009.  Comparison of in situ eg production rate in 
Calanus finmarchicus and Metridia longa:  discriminating between 
methodological and species-specific effects.  Mar. Ecol. Prog. Ser. 353: 
165-175.