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Harmful Algae Blooms: A Short Introduction
ITEM: 19
SOURCE/AUTHOR: Julian Robbins
DATE: October 16, 1998
This article is for people who may have heard words like "red-tide" or
"harmful algae" in the news and thought to themselves that they would like to
know a little more. By "harmful algae" we mean microplankton which causes
problems one way or another. Harmful algae is a societal term, not a scientific one.
Firstly, algae is an ingredient in many common foods and household items. Some of these
items may be obvious such as yogurt, orange and yellow cheese and salad dressing. Others
are not so obvious (toothpaste, pet food and brownie mix). Many kinds of seaweeds (large
forms of marine algae growing in the coastal ocean waters of many countries) are edible
and rich in vitamins and iodine, but this is not, at least in all cases, why algae exists
in so many household products. Algae derivatives act as stabilizers, colorants and
thickeners in many of our household stock.
The three important groups of algae referred to as brown, red and green algae each provide
important ingredients for our foods, cosmetics and pharmaceuticals. If algae is so
much used, and even nutritious, in our everyday patterns of consumption, how then can it,
in some cases be harmful?
It is indeed the case that most species of algae (phytoplankton) are not harmful and,
quite alternatively, serve as the energy producers at the base of the food web.
Occasionally however, the harmful algae grow unusually fast (bloom) physically
accumulating into dense, visible patches near the water surface. Microplankton often, and
with increasing frequency, cause health problems, harm fisheries, sabotage aquaculture and
damage ecosystems due to either their production of potent toxins or their rapid
accumulation into large amounts of biomass. "Red Tide" is a common name for such
a phenomenon in which certain phytoplankton contain reddish pigments. Occasionally a small
number of phytoplankton species produce potent neurotoxins that can be transferred through
the food web where they might affect and even kill higher forms of life that feed either
directly or indirectly on them.
Only a few dozen of the many thousands of species of microscopic and macroscopic algae are
repeatedly associated with toxic or harmful blooms. Red tides are caused by dinoflagellates,
green films are cyanobacteria and brown tides are formed by still another type of
cell (marine plankton called chrysophytes, also known as golden-brown algae).
Some species, such as the dinoflagellate Alexandrium tamarense
and the diatom Pseudo-nitzschia australis produce potent toxins
which are liberated when the algae are eaten. Other species kill without toxins, like the Chaetoceros
species which has spines with serrated edges that can lodge in fish gill tissues, causing
irritation, over production of mucous, and eventual death. At least 300 species of marine
microplankton are known to cause harm (toxic and non-toxic combined).
Fluorescently-labeled Alexandrium cell
Since algae is a necessity or, at the very least merit significant use, in all levels
of the food web (including ourselves), it is thus extremely important to improve methods
of monitoring the occurrence of the harmful species. For instance, scientists need to know
more about questions like, "What are the conditions for development of such harmful
algal blooms?" In any case, each of these species, and many others, need careful
study at the organismal level if we are to understand the population dynamics and trophic
impacts of HAB's.
You can read more about efforts to understand and manage HAB's through contacting the
Intergovernmental Oceanographic Commissions (IOC) website. The site contains information
concerning IOC's Science and Communication Centre on Harmful Algae, the HARMFUL ALGAE
NEWS, the HAB Directory of Experts and IOC HAB Training Courses. IOC's home-page is
located at: http://ioc.unesco.org/iocweb/ .
You can also contact the IOC HAB Secretariat at hab.ioc@unesco.org.
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