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Marine Creatures Small and Great
| Article
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15676 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
2 / 1989 |
3,366 Words |
| Author
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William Li
William Li is a research scientist at the Bedford Institute of
Oceanography of the Canadian Department of Fisheries and
Oceans in Dartmouth, Nova Scotia. |
It is sometimes said that more may be known about the moon than about our oceans. Whether or not this is true, it is almost certain that there remains much more to be discovered about life in the sea. In the last decade, scientists have found dense colonies of creatures in the deep-ocean floor where hot gases are escaping from the earth's crust. The discovery of this unique food web, driven not by solar energy (as are all others) but by geothermal energy, has been well publicized. Perhaps less well known is the fact that scientists have also made intriguing discoveries about the microscopic, free-floating plants called phytoplankton in the overlying waters. In the last few years, oceanographers have greatly changed their perception of planktonic ecosystems. We now realize that throughout many parts of the vast oceans, especially far away from their coasts, the most numerous phytoplankters are those that are smallest. It has only been in the last decade that these very small phytoplankton--dubbed picoplankton--have been properly recognized. In the open oceans, the picoplankton often comprise the largest numerical component of the phytoplankton. They account for a significant proportion of the plant biomass and contribute substantially to the ecosystem's supply of energy.
Thus, it is not possible to consider processes of energy and material transformation in the ocean without due regard to this group of phytoplankton. Current discussions about the role of marine biota in the global problem of increasing levels of greenhouse gases, especially carbon dioxide, are enlightened by a greater understanding of phytoplankton in general and of picophytoplankton in particular.
Recent Recognition
In 1979, scientists at the University of Rhode Island and the Woods Hole Oceanographic Institution independently reported the widespread occurrence of small, unicellular cyanobacteria (blue-green algae) in marine plankton. (They were previously known to live only in colonies at the surface of tropical waters.) Cyanobacteria and other bacteria belong to the same kingdom of the living world: They are prokaryotes, lacking a nuclear membrane that divides the hereditary material of the chromosomes from the rest of the cell. (Kinds of life that possess this nuclear membrane--all other living things--are called eukaryotes.)
Once alerted to the large numbers of these prokaryotes, oceanographers soon established that many eukaryotic algae also fell into the same size class. In a general way, the existence of algae of this and slightly
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