<Emphasis Type="Italic">Oithona similis</Emphasis> in a high latitude ecosystem: abundance,distribution and temperature limitation of fecundity rates in a sac spawning copepod |
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Authors: | P Ward A G Hirst |
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Institution: | (1) British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge, CB3 0ET, UK |
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Abstract: | In this study we report the abundance, fecundity and an index of the relative survival of Oithona similis (nauplii to copepodites) across a large latitudinal and temperature range within the Southern Ocean. The abundance of O. similis was strongly related to temperature and to depth-integrated (0–100 m) chlorophyll a, abundance increasing with increasing temperature (and therefore decreasing latitude) and Chl a. In situ egg production rates and fecundity per female were also significantly and positively related to temperature and
Chl a. Egg hatch times rapidly lengthen as temperature decreases and in sac spawning species the next batch of eggs cannot be produced
until the previous clutch hatch. Consequently, we predict that in O. similis, fecundity must decline rapidly at low temperatures, especially below 5°C. A model comparing maximum rates of fecundity with
in situ data suggested production rates were strongly food limited across our study region. However, the relationship of in
situ and maximum rates to temperature were similar, confirming the importance of temperature. Further, as time taken to develop
from egg to adult also rapidly extends with declining temperature, it is increasingly unlikely that O. similis will be able to maintain its population against mortality. Our findings have broad implications for the cold temperature
(and hence geographic) limits of O. similis, but also for the distribution of other sac spawning copepods and planktonic species generally. |
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