Biological Oceanography

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and they rise to the mixed layer as they develop. Arriving, they may or may not find
sufficient food for copepodite development. However, those arriving when the
seasonal peak of production is in progress grow and produce the following year’s
resting stock. Mackas et al. (2007) have shown that the date of peak biomass and
prevalence of the late copepodite stages ready for diapause varies with the rate of
warming of the upper water column from a baseline (6°C) reached every year (Fig.
16.24). Early warming can produce an early April peak; late warming delays
development success into July. The prevalence of similarly effective bet-hedging
strategies among marine fauna is unknown.


Fig. 16.24 Date of the seasonal maximum of the Neocalanus plumchrus population in
the northeast Pacific vs. cumulative warmth of the upper ocean during the March–
May growing season as “degree days” between when spring warming passes 6°C and
the peak. Cumulative degree days depend mostly upon the starting date for spring
warming. Peak dates have varied between early April and early July (by 3 months).
Stage ratio is the number of fifth copepodites relative to the total of all stages; it
corresponds closely to the peak of stock biomass. “Alaska gyre” includes samples
from 50°N, 145°W and to the east but well offshore.
(After Mackas et al. 2007.)


Lessons from El Niño


(^) Similar help with predicting the responses of ocean biota to climate change comes
from the response to shorter events than NAO or PDO shifts, events that are part of
normal climate variability. Among the most informative are responses to the El Niño–
Southern Oscillation cycle, already considered briefly in regard to its effects on

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