ANNUAL REPORT 2011 - University of Namibia

Title: CO 2 emission from the Benquela Upwelling System.
Authors: Pillay, K. (Rhodes University), Schickenberg N. (University of Bremen), Steigüber, C.
(University of Bremen), Mokanya, E. (University of Namibia and Chiquequela, J. (Augustinho Neto
University)
Introduction
It has become increasingly important to understand the ocean carbon cycle as it is a major
contributor in controlling atmospheric CO 2 (a greenhouse gas contributing to climate change). A
characteristic of upwelling areas is that cold, nutrient-rich and CO 2 rich waters are brought to the
surface. The pCO 2 of the shelf waters of the Northern Benguela has not been measured. This
study was a first in understanding the carbon cycling within the Northern Benguela. Continuous
underway pCO 2 , sea surface temperature (SST), bathymetry measurements are presented.
Results
Preliminary analysis shows pCO 2 variability between inshore and offshore waters. Inshore
measurements indicate cells of high pCO 2 concentration which can be representative of
upwelling cells. This elevated pCO 2 appears to be correlated to low SST and shows a possible
link to coastal bathymetry.
Conclusion
The identified upwelling cells (high pCO 2 ) show the expected trend of low SST. These factors
appear to be klinked to coastal bathymetry. The coastal bottom topography could be a
contributing factor to the permanent upwelling in the Northern Benguela. This links needs to be
further investigated.
Mariculture Research
Silver Kob, Argyrosomus inodorus, juvenile feeding trials
This experiment was aimed at investigating the optimum feeding rate of the Silver Kob under
laboratory conditions. The juvenile system was stocked with the cohort of the 2009 spawned fish
which was divided into eight experimental tanks with 10 fish per tank. Each tank was fed a fixed
amount of scientifically formulated feed at 2, 4, 8 and 10% fish body mass per day for a period of 6
months. Each feeding rate had a replicate. The experimental feed was obtained from Marifeed®
company, based on a diet developed by Rhodes University specifically for Kob.
All the fish were weighed & measured every two weeks, amount of feed over the following 2 weeks
were adjusted accordingly. Growth (mass & length), condition factor and food conversion ratio
(FCR) were calculated. At the end of the feeding trial, growth trend was suggesting a positive
growth projected by fish fed 8% body weight, with the specific growth rate (SGR) of 2.3, 2.2, 4.4
and 1.2 g/day obtained for fish fed 2, 4, 8 and 10% body weight per day, respectively.
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