Creatures small and smaller: the marine food chain

Studying the lives and threats to life of those at the bottom of the food chain
Bangkok Post 29 Dec 07;

"Deterioration of the water quality will stop only if land development in coastal areas stops," she added. "All that the developers and investors think about is how to make more money, they don't care about the quality of life of the people - and many of the investors who destroy our natural resources are not even Thais, but foreigners."

For 18 years, marine biologist Dr Suree Satapoomin has been studying organisms so tiny they cannot be seen with the naked eye. Her subjects? Plankton.

"If you take a glass of water from the sea, the water may look clear but it is certain to contain plankton, which are so tiny they can be seen only under a powerful microscope," she said.

Suree specialises in copepods, or microscopic crustaceans, a type of plankton that serve as food for aquatic animals. "Whether it's freshwater, brackish water or saltwater, you will find copepods," Suree said.

Plankton are waterbound animals or plants that possess such limited powers of movement that they drift about on currents. One characteristic that defines different types of plankton is whether they remain plankton all their life (holoplankton) or whether they grow into other animals (meroplankton). Many marine creatures, including types of coral, fish, prawns, crabs, molluscs, starfish, sea-urchins and worms, start their lives as meroplankton.

The copepods that Suree studies are holoplankton and are the most important type of plankton found in the surface waters of the sea.

Copepods are a form of zooplankton, which are generally larger than other forms of plankton, such as viruses, bacteria and phytoplankton (plankton capable of photosynthesis), which they tend to eat.

"Viruses, and especially bacteria in this case, do not cause disease but are the primary ring in the food chain," Suree explained.

"They turn inorganic matter into energy through chemosynthesis, or chemical elements, instead of light, while phytoplankton are microscopic plant life that absorb nutrient elements like phosphorous, nitrogen and silicon and process these into food with the help of light, or photosynthesis."

The survival of marine life depends on the survival of plankton. Different types of plankton live at different depths in the water where the animals that feed on them know to seek them out.

The sea is essentially divided into two layers, which represent totally different environments for life, the marine biologist explained. The surface waters constitute the warm and illuminated upper layer known as the troposphere, while the cold, dark recesses that extend to the ocean floor are called the stratosphere.

"People see the importance of the big fish, prawn and crab, which they can eat, but they don't look after water quality," said Suree, who is head of the Marine and Coastal Resource Assessment and Production Unit at the Phuket Marine Biological Centre (PMBC).

Suree's unit investigates the community structure of marine and coastal resources, does laboratory and field work on enhancing production and assesses the changes in various types of marine organisms, food chains and algal blooms, including "red tides".

When the water is polluted, light needed to develop food through photosynthesis cannot penetrate the water, Suree said. Even bacteria, which process food by chemosynthesis so do not need light, cannot survive because there are no nutrients in the water.

"Only if the water is of high quality, where viruses, bacteria and phytoplankton could exist, will there be bigger marine animals for man to eat. If the water is so polluted that the primary food producers could not exist, then there would be no food for the zooplankton, which in turn serve as food for bigger animals, so the link in the chain is broken and humans at the upper end will be affected."

However, Suree said that in her 18 years of research she hasn't observed any major changes in the sea.

"There's a great diversity of plankton in tropical waters, especially in the Andaman Sea where the tide rises and recedes twice a day. The only visible problem is in coastal areas that are heavily populated, such as popular tourist spots," she said.

"In Phuket, hotel and road construction, tourists getting in and out of the water and improperly treated wastewater that flows into the sea all have destroyed the water quality in Patong. This can be seen from the plankton bloom that occurs in Patong every year.

"The year before the tsunami was the worst I've ever seen, when algal bloom turned all the sea green."

Algal or plankton bloom, also known as green or red tides depending on the colour the algal pigment makes the water, is caused by an influx of nutrients from increased nitrogen and/or phosphorus in the water as a result of agricultural fertiliser or sewage draining into the sea, especially washing detergents. The bloom often results in bacterial decomposition, which may reduce the level of oxygen in the water thereby reducing its quality and making it unfit for marine life.

A more dangerous form of plankton bloom is the one caused by algae that spread poison, which is then passed up the food chain to humans. Mussels made toxic through such a bloom could cause diarrhoea or worse, Suree said.

The worst form of algal bloom is the red tide, as the plankton that cause it produce a deadly neurotoxic substance called saxitoxin, which depresses sodium transport in the human body and affects the nervous system. Within 12 hours of ingestion of mussels contaminated with saxitoxin, breathing becomes inhibited and cardiac arrest may follow. Luckily for Patong's tourism industry, no tourist has yet died from eating toxic mussels.

Japanese scientists have been collecting data for more than 50 years, but they still cannot predict when an algal bloom will occur, Suree said. "All they can do is warn people not to eat shellfish at the first sign of the bloom.

"Deterioration of the water quality will stop only if land development in coastal areas stops," she added. "All that the developers and investors think about is how to make more money, they don't care about the quality of life of the people - and many of the investors who destroy our natural resources are not even Thais, but foreigners."

As Suree spoke, a new resort was being built right by the beach at Cape Panwa in Phuket where the PMBC is located.

Global warming has started to melt polar ice caps, which scientists say will result in a gradual rise in sea levels and changes to global currents.

"The effects of warmer waters on plankton is not yet clear," Suree said, "but a sudden change in water temperature by 2C would certainly change the marine community. Marine life that can adapt to warmer waters will survive, and that which cannot will become extinct. Whether this will have a positive or negative effect on the ecosystem remains to be seen.

"That's why there's a need for research," she added, "so that we know what the marine community is like before and after the change, and what impact the change will have on the productivity of Thai waters. But in Thailand there's very little money for research, unlike in developed countries where they have been collecting data for the past 50 years or more."

A graduate of the University of Copenhagen, where she obtained her doctorate, Suree has participated in an international educational and scientific marine expedition financed by the Danish government. She has also observed the importance the Danish people place on research.

"There was a web site where teachers, students and journalists [from the expedition] wrote about their experiences during the day, and it was closely followed by the people of Denmark," she said.

Suree admits that when studying for her bachelor's and master's degrees at Chulalongkorn University, she "did not like the subject of plankton. Like other young people, I loved diving in coral reefs to observe coral, prawns and fish, as you could see them clearly and admire their beauty.

"But the seawater is not just about coral reefs or sea grass beds, which the dugong inhabit. We have to look at the whole ecosystem and understand where the dugong stands in that ecosystem. Without the microorganisms that are the primary producers of food, the link will be cut off, the whole ecosystem will collapse and man at the upper end of the food chain will suffer."