Hard to believe that this is my 350th "Dive Dry with Dr. Bill" column... it seems like just yesterday I started this series with the story of Gary Garibaldi guarding his nest. Of course at my advanced age, I can't remember yesterday... but then, back in the Woodstock era, I never expected to see my 30th birthday. I wanted people to trust me, and it would be impossible beyond that advanced age. Also hard to believe that August 24th will be the 40th anniversary of my move to Catalina. To mark these milestones, I thought I'd write about something critical to every one of us on Earth, yet that largely remains invisible to most. I'm talking about plankton... er, writing about it. This is a very timely topic since I'm also working on the 29th episode of my proposed "Munching and Mating in the Macrocystis (Giant Kelp)" cable TV show on this very subject.
There are about two billion planktonic organisms (plankters) in a gallon of seawater (Carl Sagan would have been overwhelmed if he were an oceanographer). Plankton are defined as organisms that drift or "wander" with ocean currents, unable to move against them horizontally. In this respect they are distinguished from the nekton, critters like fish and squid which can propel themselves through the water, or benthic species like barnacles and crabs which dwell either attached or moving about on the bottom. Plankters may be so tiny even my microscope can't reveal all their secrets... or large like the Nomura's jellyfish off Japan which reach over six feet in diameter. Humans love to categorize things, so plankton are commonly divided into different groups based on their size, ranging from tiny femtoplankton like viruses and picoplankton like bacteria up to the megaplankton ranging from about an inch upwards.
Keeping with the human need to group things together, which I call the "categorical imperative" (not the same as Immanuel Kant's), plankton can also be subdivided based on their ecological role in the ocean community. Plankters which are autotrophic, creating their own food through photosynthesis, are called phytoplankton. These include diatoms, cyanobacteria, coccolithophores and dinoflagellates. Organisms that are consumers and generally considered animal in nature, are called zooplankton. Some confuse the issue by being able to photosynthesize and munch on other organisms and are called mixotrophs. Finally there are the bacterioplankton which are the recyclers, breaking down organic matter back into nutrients.
Why would these ecological roles be important to my readers? I'm sure none of you go into Vons to purchase plankton for dinner or even breakfast (although you can find "health" food supplements made from plankton on the Internet). However, I'm sure a number of you buy fish there, or at Armstrongs, or catch it yourself from our island waters. Yes, they are active swimmers or nekton, not plankton. Nor are invertebrates like the benthic or bottom dwelling lobster and clams (or oysters... if you "need" them!) considered plankton. However, the food chains that support these tasty critters begin with the phytoplankton which capture energy from the sun and convert inorganic nutrients into carbohydrates that feed critters higher up in the food chains (no, not Vons this time).
Some of you may be strict vegetarians or vegans, and believe plankton are of no importance to you. You prefer to eat nuts, roots, berries and tubers... possibly supplemented with a little seaweed. However, like your carnivorous and omnivorous neighbors, you are intimately linked to plankton communities as well. All of us breathe oxygen, whether from the atmosphere... or a SCUBA tank. Many assume that the primary source of that oxygen is from trees and plants on land. Wrong answer! The ocean covers about 70% of our planet (so why is it called Earth?). NASA has stated that anywhere from 50 to 90% of our atmospheric oxygen comes from primary producers in the ocean, mostly phytoplankton.
Therefore the health of our plankton communities, the "drifters" or "wanderers," is very important to all of us. However, are these communities truly healthy, allowing us to breathe easier? Perhaps not. Long-term studies of the plankton off our West Coast show a 70% decline since 1950. Studies by Algalita have shown that tiny fragments of degraded plastics outnumber animal or zooplankton at a ratio of 6-to-1 in some regions of the globe, and about 2.5 times here off southern California. To the best of my knowledge, plastic neither photosynthesizes or serves as good food for fish. Major geographic shifts in plankton communities northward or southward (in the southern ocean) have been detected due to changes in ocean climate. In fact, global climate change may have far greater impact on the oceans than on land-based ecosystems. Some have suggested that other pollutants, primarily toxins originating from run-off and human wastewater streams near our coasts, have seriously impacted the health of phyto- and zoo-plankton species.
Plankton also play an important role in what is called the "biological pump," or carbon cycle critical to life on Earth. Through photosynthesis, phytoplankton "fix" carbon in the form of carbon dioxide into carbohydrates. Zooplankton then incorporate the carbon-based carbohydrates into their tissues when they munch on phytoplankton (and one another). When plankters die, their corpses fall towards the ocean floor carrying carbon with them to the bottom. This process is also referred to as a carbon sink (both biogeochemically and literally!).
Given the concern of most scientists about the increasing carbon dioxide levels in the atmosphere, whether due to human activity or not, this process is of great interest to them. More than 70 years ago oceanographers proposed that dust from wind storms on land can "seed" the oceans with nutrients that increase phytoplankton growth. Often these are micronutrients like iron that may be limiting plankton growth even when major nutrients like nitrogen and phosphorus were abundant. Thanks to satellite images, evidence has been obtained that dust storms coming off the Gobi Desert in China and the Sahara in northern Africa have indeed stimulated phytoplankton "blooms."
Back in the 1980s California scientist John Martin suggested the "Iron Hypothesis." It was his belief that "seeding" the ocean with iron would accelerate phytoplankton growth and enhance the biological pump to sink excess carbon dioxide to the bottom of the sea. Many scientists agreed with this, and experiments were undertaken to see if this process could reduce atmospheric levels and reverse "global warming." Results suggest that although iron seeding does enhance phytoplankton growth, a much smaller percentage of the carbon sinks than was previously assumed.
Oceanographers David Siegel at UCSB and Dierdre Toole at Woods Hole reported another interesting link between plant plankton and climate. Ultraviolet light from the sun can damage phytoplankton just as it burns our skin. These poor organisms don't have access to umbrellas or great sunscreens like Soleo for protection. These researchers found that under high levels of UV radiation, phytoplankton release a chemical known as dimethylsulfoniopropionate (DMSP) which is broken down by bacteria into dimethylsulfide (DMS), then released into the atmosphere. There it reacts with oxygen to form various sulfur compounds that collect dust particles. These promote the condensation of water vapor, resulting in cloud formation that shades and protects the phytoplankton!
To bring plankton even closer to home, I'll end this column with the story of "the green flush." I used this tale to wow passengers on the Lindblad Expeditions eco-cruise ships I worked on earlier this decade in the Sea of Cortez and off Belize and Honduras. Toilets that use ocean rather than fresh water, like those on many boats and here in Avalon, contain plankton. During periods when one type known as dinoflagellates are abundant, flushing the toilet may excite them to bioluminesce a blue-green light just like fireflies do in the Midwest (in the air, not the toilets). So, some night when you wake up and have to go... don't turn on the lights. Finish your "duty" and watch in the dark as your toilet bowl empties down the drain. You may discover plankton in your very own bathroom (or head)!
© 2009 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 and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!
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"Billions and billions..." an overview of a plankton sample I videotaped; a tiny jellyfish
and an even tinier dinoflagellate like those responsible for the "green flush."
This document maintained by
Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia