Plankton refers to any organism, plant or animal, which does not swim strongly enough to overcome the ocean currents and therefore drifts with them. They may be microscopic or very large in size. Recent oceanographic studies have shown serious declines in plankton communities throughout the globe. Plant plankton in the North Pacific have declined by more than 30% in the past 20 years. In the waters off southern California, animal plankton have declined 70% since 1951. Why should we, as terrestrial mammals (or amphibious in my case), care about these declines? Read on...

Many scientists attribute these declines to global warming. Although warming (and cooling) periods are not unusual in Earth's long geologic history, the rapid rate at which the oceans and atmosphere are currently warming suggests that human activities are at least a major part of the cause. Increases in "greenhouse gasses" like carbon dioxide (CO2) from burning fossil fuel are believed to be the reason. However plant plankton (known as phytoplankton), like all photosynthetic organisms, use CO2 and produce oxygen (O2) when sunlight is available. Shouldn't an increase in CO2 actually favor an increase in phytoplankton?

Plant plankton can only photosynthesis when their essential needs are met: sunlight, CO2 and nutrients. Warming of the ocean surface over the past few hundred years has created an increased barrier to obtaining nutrients which are found largely in deeper, colder waters. Warmer waters at the surface create thermoclines (rapid changes in temperature with depth) that prevent deeper, nutrient rich water from reaching the surface. In addition, warmer waters have lower nutrient levels than cooler waters so the warming itself causes a decline directly. It is the drop in surface nutrient levels that causes the decline in phytoplankton despite increased CO2 in surface waters.

We are all aware that plants produce much of the oxygen that we and other animals breathe. How many realize that marine plants produce more than half (perhaps up to 70%) of the world's oxygen, and that phytoplankton produce most of this? Without healthy plant plankton populations, oxygen in our atmosphere will most likely decline. This should catch your attention as you slowly start gasping from oxygen starvation over the next few decades! Okay, perhaps I exaggerate a bit? Besides most of the mainland population already gasps from air pollution, so they may not notice the difference. But we island residents may!

Plant plankton also perform a vital service in trapping CO2 and thereby carbon created within ecosystems. They absorb CO2 and incorporate it in their tissues and hard parts. When the plankton die, they settle to the bottom and trap the excess carbon and CO2 there. By trapping carbon and CO2, atmospheric levels of this gas are decreased and accumulation of this greenhouse gas is lowered. However when phytoplankton decline, the increasing levels of atmospheric CO2 due to human activity are not countered. Therefore declines in phytoplankton due to global warming may actually accelerate the rate of the warming process. I know most of us would enjoy warmer winters in southern California, but think of the other consequences of these declines in plankton.

Plant plankton are one of several starting points in the complicated food webs of the marine world. Through photosynthesis they provide food for many species that feed directly on the plant plankton, or upon those animals that feed on them! If plant and animal plankton decline, there is less food for the filter feeders that abound in the kelp forests... or for many fish and birds in the nearshore waters. The decline in certain commercial fish species like anchovy, jack mackerel and rockfish may be related to the decline in plankton as well as to fishing activity. Fish-eating sea birds like the sooty shearwater, which has declined by 90% recently, may also have been affected. Even our mammalian relatives the great whales, as well as dolphins and porpoises could be impacted.

While many plankton, plants and animals, live permanently in these drifting communities, some are only temporary. Organisms which live only part-time in the plankton are called "meroplankton." These include the eggs, larvae and young stages of many marine invertebrates and fish. By drifting in the current, these species obtain an easy way to disperse to new marine habitats (like Catalina!) and to increase population numbers and gene flow at sites already established. In addition the meroplankton often gain added benefits such as increased warmth in the surface waters to accelerate growth, and an abundant food supply- other plankton! Declines in permanent members of the plankton could affect these larvae and young, and thereby affect their adult populations which may not rely directly on plankton for food.

Here on Catalina we have additional reasons to consider plankton important. How many of you have awakened in the middle of the night, crawled into the bathroom without turning on the light and accomplished your basic biological functions. If you happened to look at the toilet bowl after pulling the lever, you may have noticed the sparkling bioluminescence of tiny planktonic organisms disturbed by the turbulent water. These flashes of light were caused by plankton known as dinoflagellates in our salt water toilets (and the open ocean). Although common here, while on the Lindblad Expeditions cruise ships I referred to them as the "green flush" when talking to our mainly landlocked, fresh-water toilet using passengers. This was to distinguish this phenomenon from the "green flash" that other naturalists emphasized at sunrise and sunset.

When I was on board the ship, our passengers and many of the naturalists were totally enthralled by the great whales we saw. I felt it my responsibility to point out that Earth's marine ecosystems functioned quite nicely before the whale's "recent" appearance about 50 million years ago. Of course whales often serve as "marquee species" in conservation. Being fellow mammals, they are easier for us to relate to. Yet we could all survive without whales (albeit less wondrously). However, without plankton Earth's marine ecosystems would crash... no oxygen and no food for uncounted species, including one very important to us... Homo sapiens.

There are plenty of conservation groups dedicated to whales, sea otters and other marquee species. Based on the information above, I think you all should consider an old tradition here in America- to look out for the "little guy." I think I will start an organization dedicated to the conservation of perhaps the most important group of organisms on Earth, the plankton. Let's see... Save Our Plankton (SOP)? Just send your donations to me, Dr. Bill! Then we can really make a difference (especially to my empty wallet).

© 2003 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Image captions: Top (L to R) Permanent members of the plankton including phytoplanktonic diatoms;
diatom and dinoflagellate; dinoflagellates like those causing the "green flush"; zooplanktonic copepod
Bottom (L to R): Temporary planktonic eggs and larvae: young octopus still in egg; larval brittle
star; larval sea urchin with spines and tube feet; larval fish still in egg

(Images extracted from video provided courtesy of Sally Bartel)

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia