CULTURE BOTTLE EXPERIMENTS ON THE GROWTH OF PHYTOPLANKTON IN WATER SAMPLES TAKEN FROM SULU SEA

Updated: Mar 15

Increasing the carrying capacity of a body of water by adding the limiting nutrients has been demonstrated in several works, particularly in freshwater environments. This was demonstrated in very early studies (Swingle and Smith, 1938; Ball, 1948; Hall et al., 1970). More recent studies where phosphorus fertilization was carried out in the Kuparuk River, Alaska, during 1985–90 resulted in a 1.4- to 1.9-fold increase in the size of age 0+ fish and a 1.5- to 2.4-fold increase in the weight gain of adult grayling in some years (Deegan and Peterson, 1992). In another study in the same river, it was shown that fifty-six percent of the variance in adult grayling growth rate in said river was associated with nutrient level and mean summer discharge which suggested that river discharge and water temperature may influence long-term survival and population dynamics of grayling in Arctic tundra streams (Deegan et al., 1999). A long-term (16 years) of stream (Kuparuk River) fertilization (phosphorus, H3PO4) experiment was performed to evaluate the potential eutrophication of an arctic stream ecosystem. A positive response to fertilization was observed at all trophic levels with increases in epilithic algal stocks, some insect densities, and fish growth rates (Slavik et al., 2004).


In Toolik Lake, Alaska, it was demonstrated that the addition of inorganic nitrogen and phosphorus dramatically increased phytoplankton productivity. The phytoplankton biomass however was not sufficient to draw down all the nitrogen and phosphorus that was added and these nutrients reached high levels in the last half of the summer (O'Brien et al., 1992). In artificial lakes and fishponds, nutrient enrichments has 2 been undertaken and has been shown to increase biological productivity and fish production. This has been practiced for several years in China, Indonesia, Philippines and other parts of Asia.


In the sea, purposeful enrichment with nutrients is less common. Kyle Scotnish, a loch in Scotland, was fertilised during the Second World War with the aim of increasing the fish biomass. According to Gross (1950) the nourishment brought about an increase of four to five times the weight of first year plaice and an increases also in second year plaice. This experiment was not deemed to be an economic success but the experimenters noted they did not have the data to allow an assessment of the economic factors in optimised enrichment demonstrations. While this experiment can be criticised for the lack of a control and other problems like poor fertiliser distribution, it showed that nourishment led to “fatter fish”. The feed stock limitation to fish production had been removed. Heartened by these results Jones and Young (1997) proposed the concept of Ocean Nourishment to inject nutrients into the upper ocean both to store carbon to slow climate change and to increase the base of the marine food web to provide low cost protein for the world’s poor. Jones (2001) reported that the more fortunate have an ethical need to contribute to feeding these additional people. The extra food production will inevitably require further change of the environment but if done efficiently it might increase the standard of living to allow more education.


The above experiences indicate the positive effect of fertilization in general, on biological productivity and fish production in several types of water bodies. Several trials have been done by the Ocean Nourishment Corporation (macronutrients fertilization) and LOHAFEX (e.g. iron fertilization), among others. However, large–scale oceanic iron fertilization appears not a feasible strategy to sequester anthropogenic CO2 (Zeebe and Archer, 2005; Allsopp et al., 2007). It is along this vein that this experiment was embarked on with the aspiration of enriching the barren areas of the sea thus increasing biological productivity and fish production in the selected area and enhancing the protein source needed by the inhabitants of that locale. With proper protocols this can be repeated in other parts of the world.


With this as the concept, culture bottle experiments were carried out wherein samples of ocean water were collected from an area in the Sulu Sea. As earlier indicated, the proposed sampling site of this investigation (third in a series) was in a location of Sulu Sea as close as possible to where the first and second investigations (Latitude 100 19’58.54”N; Longitude 1220 5’28.83”E) were carried out.

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