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Fishery Bulletin 95( 1 ), 1997 
winter approaches until only small aggregations of 
cold-adapted individuals overwinter in the far east- 
ern waters along the SNE coast, on the central shoals 
of GBK, and within inshore waters in the GOM. 
Abundance in these areas increase as temperatures 
rise in spring. 
The life cycle of many marine copepods involves 
the production of resting eggs that allow the species 
to repopulate areas when environmental conditions 
again become favorable (Uye, 1985). Evidence that 
Centropages hamatus produce resting eggs has been 
found in the western North Atlantic (Lindley, 1990), 
the Gulf coast of Florida (Marcus, 1989), and in the 
MARMAP survey area on GBK (Davis, 1987). Al- 
though this report provides no direct evidence that 
C. hamatus produces resting eggs, it seems unlikely 
that the small pelagic population that overwinters, 
or oversummers, could produce the great abundance 
of the next generation without recruitment from 
benthic resting eggs. Marcus (1989) found that a C. 
hamatus population residing in a subtropical 
embayment area produces diapause eggs that allow 
the species to survive warm summer temperatures. 
This also likely occurs in the MAB when the popula- 
tion rapidly declines to a few individuals, or disap- 
pears entirely during summer, and begins to increase 
as temperatures decline in winter. Lower maximum 
temperatures observed on GBK are apparently not 
sufficiently high to impact populations there dramati- 
cally; abundance declines slowly during autumn af- 
ter peak abundance is reached in summer and does 
not increase until temperatures rise in early spring. 
This slow decline in abundance may occur because 
success of egg hatching decreases as females gradu- 
ally switch from subitaneous egg production to rest- 
ing egg production owing to decreasing temperatures 
and daylengths, as was found for the copepod 
Labidocera aestiva in nearby waters (Marcus, 1982). 
The resting eggs hatch in the spring to supplement the 
production of overwintering late-stage copepodites and 
to ensure the success of the population. Such variation 
in egg production between well-separated populations 
has been reported for other species (Marcus, 1984; Uye, 
1985). Somewhere in the SNE subarea there is prob- 
ably a transition zone between adults that are “tem- 
perature shocked” to release quiescent eggs and those 
that slowly change their egg-laying strategy as autumn 
progresses. Egg-production strategy in the GOM is 
probably similar to that found in the GBK. 
The strongly negative correlation of Centropages 
hamatus abundance to depth and its well-defined 
inshore-offshore abundance gradient confirm the 
importance of resting eggs in the life history of this 
species. Environmental conditions probably do not 
trigger the release of diapause eggs until after the 
population constricts inshore after peak abundance 
is reached. Evidence for this was found by Lindley 
(1990) in southern waters of Great Britain where C. 
hamatus eggs were found to be abundant only in 
depths of less than 50 m. When the eggs hatch, the 
prevailing westerly winds in the northwest Atlantic 
slowly spread the pelagic population and the new 
recruits offshore to establish the characteristic abun- 
dance gradient of this species. 
Abundance of Centropages hamatus appears to be 
related strongly to the availability of phytoplankton. 
The copepod’s abundance was highest at stations 
where chlorophyll values were high, and its distri- 
bution is similar to phytoplankton gradients in the 
study area (O’Reilly and Busch, 1984). However, cor- 
relation coefficients between variables were weak 
and inconsistent among subareas, indicating that the 
species is not particularly sensitive to phytoplank- 
ton availability. The low correlation may be because 
average water-column chlorophyll measurements are 
static measures that may not reflect the actual food 
concentrations that are, or were, available to the 
copepod over the previous 24 hours. Furthermore, it 
is also possible that late-stage copepodites of this om- 
nivorous species may be more sensitive to zooplank- 
ton prey concentrations. Nonetheless, food availabil- 
ity is a key limiting factor throughout nature and 
certainly has a major role in shaping the life history 
of this copepod. The maximum mean abundance of C. 
hamatus is greatest on GBK, the ecosystem subarea 
with the largest estimate of annual primary produc- 
tion (O’Reilly et al., 1987). Conversely, population den- 
sity is lowest in the GOM where average chlorophyll 
concentrations are also lowest. 
Monthly correlation coefficients between salinity 
and abundance of Centropages hamatus were also 
weak even though both variables have a strong off- 
shore gradient. Unlike chlorophyll correlations, these 
coefficients portray accurately the relationship be- 
tween variables. Centropages hamatus is a coastal 
species with a wide latitudinal range and must tol- 
erate wide environmental fluctuations. It has been 
reported in areas with salinity as low as 6 psu 
(Hernroth and Ackefors, 1977), as well as in Medi- 
terranean waters where salinity exceeds 36 psu 
(Gaudy, 1971). The large numbers of C. hamatus as- 
sociated with low salinity found in this study is prob- 
ably an artifact of the high phytoplankton concen- 
trations found in a narrow inshore band along the 
MAB and SNE coasts (O’Reilly et al., 1987). The an- 
nual spring increase in precipitation and subsequent 
river runoff that leads to lowered salinity in the MAB 
and SNE subareas (Manning, 1991) also introduces 
nutrient-enriched water that stimulates phytoplank- 
ton growth and zooplankton production. Further- 
