Vol. 54, 2015
Seasonal dynamics of the copepod community in a tropical monsoonal estuary and the role of sex ratio in their abundance pattern
G. Vineetha*, N. V. Madhu, K. K. Kusum and P. M. Sooria
CSIR-National Institute of Oceanography, Regional Centre, Dr. Salim Ali Road, Kochi, India
As salinity is considered the prime “ecological master factor”
governing the zooplankton distribution and abundance in estuaries, a
spatio-temporal interactive approach was followed to assess whether the
responses of the estuarine copepod community towards the salinity are
always direct with a strong positive affinity or whether there exist
any complexities in their interrelationship. The study, also for the
first time, addressed the roleof sex ratio in governing the abundance and the population structure of copepods in the tropical monsoonal estuarine system.
ecological scenario in the Cochin estuary revealed that irrespective of
the season, higher zooplankton abundance occurred in the mesohaline
zone (MSZ; salinity 5–18) of the estuary, despite the pronounced
spatial shift of the MSZ from the lower reaches of the estuary to
upstream locations, in conjunction with the varying seasonal fluvial
influx and marine water intrusion. In the case of the sex ratio of
copepods, the seasonal scenario revealed that the dominant copepods had
a lower sex ratio during the period of higher abundance, and a negative
relation was observed between the abundance and the sex ratio of
copepod species during most of the seasons.
preponderance of the mesohaline and euryhaline species of the copepod
community formed the key contributing factor towards the maintenance of
higher abundance in the MSZ of the estuary. The bias in the sex ratio
towards females favored higher reproductive output, resulting in the
higher abundance during the favorable pre-monsoon period.
Key words: Zooplankton; Monsoonal estuary; Mesohaline; Copepod; Sex ratio.
*Correspondence: E-mail: email@example.com