FACTORS RELATED TO JELLYFISH OCCURANCE

A)Zooplankton

Plankton is defined as all those organisms suspended in free water (Barnes, 1980). The plankton comprises of aquatic organisms which drift passively and have limited ability to move contrary to the movement of the water mass. Zooplankton is the animal portion of the plankton (Ismail, 1998). Zooplanktons are referred as microscopic aquatic organisms that have less or no resistance towards water current. Majority of them are microscopic, unicellular or multi-cellular forms with size ranging from a few microns to a millimeter or more (Barnes, 1980).

Therefore, zooplanktons play an important role in the study of fauna biodiversity of aquatic ecosystems. They include representatives of almost every taxon of the animal kingdom and occur in the pelagic environment either as adults (holoplankton) or eggs and larvae (meroplankton) (Raymont, 1983). Holoplanktons are plankton that spent their entire life drifting about in water as plankton, while meroplankton spent only part of their life as plankton (Ismail, 1998). Holoplanktons include the pelagic copepods, chaetognaths, some medusae and pteropods. Larval stages of many starfish, worms, bottom-living fish, crabs, and prawns are include as mesoplankton.
Zooplanktons provide a major role in the marine food web from primary producer to higher levels of trophic links. Many zooplanktons eat phytoplankton, and are in turn preyed upon by fish larvae and many adult planktivorous fish (Ismail, 1998). Conversely, certain zooplankton groups (e.g. medusae) also prey on fish eggs and larvae. Due to their intermediate position in the food web between primary producers and predators, zooplankton serves as a link between bottom-up climate-related control of phytoplankton and fish.

The distributions of zooplankton are usually influenced by the environmental factors, availability of food source and the interaction between them. Some of the species of zooplankton are found differently according to latitude variation. The presence of available food supply plays a great influence on its distribution. The composition of zooplankton is high with the presence of phytoplankton or small zooplankton that is fed by larger sizes of predatory zooplankton. Competitions for food, space, and breeding partner between zooplankton which occupied the same habitat also affect its distribution.

B)Phytoplankton

Marine phytoplankton is a microscopic single-cell plants which are the most abundant planktonic plant in the sea. It is able to absorb water and captures light energy from the sun, thus converting it into oxygen and nutrients through photosynthesis (Zeitzschel, 1970). In addition to light and oxygen (O2), they require basic simple inorganic chemical nutrients, such as phosphate (PO4) and nitrate (NO3). They also require carbon in the form of carbon dioxide (CO2). They obtain the nutrients which are released after the decomposition of waste and dead tissue by bacteria. Phytoplankton creates materials such as carbohydrates, fats, and proteins from carbon dioxide, water and inorganic chemical nutrients through photosynthesis.

Phytoplankton belongs to the groups of non-flowering plants such as Cyanochloronta (blue-green algae), Rhodophycophyta (red algae), Chlorophycophyta (green algae), Euglenophycophyta (euglenoid), Phaeophycophyta (brown algae), Chrysophycophyta (golden and yellow-green algae including diatoms), and Pyrrophycophyta (dinoflagellates), Cryptophycophyta (cryptomonads). Dinoflagellates are more diverse in the marine environment whereas green and blue-green algae constitutes greater in freshwater environment. On the other hand, diatoms are more common in both environments (Harris, 1986).

According to Lund (1954-55), various factors affect the distribution of phytoplankton such as the concentration of major ions (C, N, P, S, and Si) and weather condition. Alongi (1998) verifies that nutrient availability depends on physical force such as monsoons. After monsoon season, a maximum mixing occurs between seawater and freshwater, thus producing high concentration of nutrients. Therefore, the situation promotes higher production of phytoplankton. During pre-monsoon season, nutrient depletion occurs due to less intensity of mixing between freshwater and seawater, therefore causing low productivity. The productivity is much lower during monsoon season because of the effect of water turbulence that cause greater turbidity and low level of light penetration.

Phytoplankton analysis is important for this project because it helps researchers to correlate the phytoplankton and jellyfish indirectly based on its biomass and composition. We will not be able to identify the primary cause (instead of zooplankton abundance) of sudden jellyfish bloom if the analysis is not done. As a result, the analysis will provide one of the important evidences responding to the unpredictable bloom of jellyfish or other aquatic organisms.

C) Water Quality

According to Purcell et al., 2007 and Mills, 2001, the jellyfish blooms may be triggered by the warming of sea temperature due to global climate change or power plant effluent. In temperate area, the jellyfish usually increased their asexual production of polyps bud and new jellyfish during warm temperature while in tropical area, the jellyfish production may occur all year (Lucas, 2001). Thus, the jellyfish blooms may occur all the time at the tropic area despite of the season.

Eutrophication may also increase the abundance of jellyfish in that area. The eutrophication occurs as a result of increased mineral nutrients concentration (primarily nitrogen and phosphorus), change in nutrients ratios and increase in turbidity, where there are human activities at the coastal area (Howarth, 2002; Arai, 2001). Eutrophication can occur because of natural processes such as river inflow and upwelling, but anthropogenic cause has become the present concern (Arai, 2001). Nutrients are increasing in water bodies as the result from addition of sewage, deforestation, fertilizer usage on adjacent land and reactive nitrogen emitted to the atmosphere during fossil fuel combustion. The increasing of nutrients in water column may lead to greater biomass at all trophic levels and increasing the food source for jellyfish polyps (Daskalov, 2002; Purcell et. al., 1999). Besides that, the jellyfish will also increase their asexual production as well as sexual production (Stibor & Tokle, 2003; Lucas, 2001 see Purcell et. al., 2007). Eutrophication also can caused complex changes in the food web. It may change the food path of an ecosystem towards a flagellate-based path that ends with ‘low energy’ consumers, which favors the jellyfish. This condition may occur when N:P ratios is high and could shift the phytoplankton community away from diatoms towards flagellates and jellyfish (Nagai, 2003). Furthermore, nutrient enrichment may reduce the size of zooplankton community which is detrimental to fish. This is because they are visual predators that prefer large zooplanktons. Therefore, this will benefits the jellyfish that are not visual and they can consume small or large prey.