Van Alstyne Laboratory Research
Marine Harmful Macroalgal Blooms in Washington State
Blooms of green macroalgae, which are often called "green tides", can be harmful to marine communities, fisheries, and aquaculture facilities. They occur regularly in shallow embayments throughout the Puget Sound/Northwest Straits region. Dr. Van Alstyne and her colleague, Dr. Tim Nelson of Seattle Pacific University, are undertaking a study of the causes and effects of green tides in Washington State. Funding for this research is being provided by the National Oceanic and Atmospheric Administration and the National Science Foundation.

The study will attempt to determine where green tides are occuring in the Puget Sound/Nothwest Straits area and why they occur in some locations and not others. A second component of the study will examine the effects of green tides on marine communites. Green tides can be detrimental to other marine life because they can overgrow and smother it or deprive it of oxygen when the green tide algae die and decompose. Dr. Van Alstyne and Dr. Nelson will also be working to identify toxins that are produced by green tide algae and will study their effects on local marine plants and animals. For more information about this project, please see the Harmful Macroalgal Bloom Website.

Activated Chemical Defenses in Ephemeral Green Algae

Green seaweeds are common in marine habitats around the world. In some locations, they become so abundant they can become a nuisance and choke out other plant and animal life. Members of Dr. Van Alstyne's research group have been studying how these seaweeds interact with herbivorous animals. Many herbivores readily consume green algae, while others actively avoid them.

To understand why some herbivores dislike green algae, Dr. Van Alstyne's laboratory has been studying some of the chemical constituents of the algae, particularly the compounds DMSP, acrylic acid, and DMS. DMSP is found in high concentrations in the algae, but is not distasteful to most herbivores. When the algae are physically damaged, such as when they are chewed upon by an herbivore, they use an enzyme called DMSP lyase to break DMSP into DMS and acrylic acid. This is referred to as an activated defense because the defensive compounds are immediately "turned on" when the alga is damaged.
Dr. Van Alstyne and her students have shown that acrylic acid is a potent feeding deterrent towards animals that dislike green algae but does not appear to affect feeding by those that prefer to eat green algae. Thus, the DMSP activated defense system appears to the reason why some herbivores avoid feeding on green algae. This may contribute to the ability of the algae to form large nuisance blooms in some locations.
Induced Phlorotannin Production in Marine Brown Algae

 Brown algae (division Phaeophyta), such as kelps and rockweeds, are also abundant in many habitats including rocky shores in temperate areas and coral reefs in the tropics. These algae can provide food and habitat for many other animals and plants, including commercially important species of fish and shellfish. Some species of brown algae are readily consumed by herbivorous fishes, sea urchins, and snails, whereas others are avoided. Phlorotannins are the compounds that are thought to be responsible for making some species of brown algae distasteful to herbivores.

Dr. Van Alstyne's research has shown that rockweeds (Fucus gardneri) in different locations can contain very different concentrations of phlorotannins. The reason why some brown algae have such variable concentrations of phlorotannins is that they can produce "inducible defenses", defenses that are produced in greater concentration after the alga is grazed. When rockweeds are artificially grazed, their phlorotannin concentrations increase by about 20% over two weeks. The algae that have been previously damaged and have higher concentrations of phlorotannins are eaten about half as much by snails (Littorina sitkana and L. scutulata) as undamaged plants. Snails sample previously damaged and undamaged algae at about the same rate, but leave the damaged algae with the higher phlorotannin levels more quickly, so they end up spending less time feeding on them.

Environmental and Geographical Variation in Chemical Defense Production
The importance of herbivores in controlling algal populations varies from place to place. For example, in the tropics, herbivorous fishes that travel rapidly and in large schools, can have a large imapct on seaweed populations. Along northeastern Pacific coasts, the major herbivores are slow-moving sea urchins, molluscs, and crustaceans. Because algae have historically been exposed to different amounts of grazing pressure, they should produce different levels of chemical defenses to protect themselves in different locations.

Dr. Van Alstyne has studied seaweed chemical defenses along the west coast of North America, in Australia and New Zealand, in the Caribbean, and in Micronesia to determine how defense levels differ across regions that historically have had different levels of herbivory. To conduct these studies she measures concentrations of DMSP in seaweeds found in each of these regions and measures the effects of DMS and acrylic acid on feeding by herbivores at each location. The results of these studies have provided insight into the evolution of chemical defenses around the world and may help predict the effects of herbivore removal (e.g., by overfishing) in different locations.

Seaweeds are also affected by changes in their environment. Environmental factors, such as nutrient availability, salinity, drying, temperature, light levels and human-generated pollution, can all affect the health of seaweeds and their ability to produce chemical defenses. Dr. Van Alstyne and her students have conducted experiments with green and brown algae to determine how changes in the environment affect the growth of seaweeds and their ability to protect themselves from herbivores. Most of these studies were conducted in the waters of Puget Sound.

Dr. Van Alstyne's research is currently funded by the National Science Foundation and the National Oceanic and Atmospheric Administration.

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