Jellyfish blooms: Are populations increasing globally in response to changing
ocean conditions?

Claudia Mills
University of Washington

Wednesday, March 15, 2000
3:00 p.m.—Pacific Forum

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In light of the growing awareness of man’s increasing influence on biological, chemical and even physical events in the oceans, there is reason to think that in some regions, new blooms of jellyfish are occurring in response to some of the cumulative affects of these impacts. I will review what is known about changes in jellyfish populations. The issue is not simple, and both increases and decreases have been documented in response to a wide range of situations. Examples of increasing populations include several cases of unpredicted increases of jellyfish species native to an ecosystem. A different phenomenon is demonstrated by species whose populations regularly fluctuate, apparently with climate, causing periodic blooms. Another type of jellyfish increase has occurred in recent decades, with introduced nonindigenous species in some places gradually building up to "bloom" levels. Lest one conclude that the next millennium will feature only increases in jellyfish numbers worldwide, I will also give examples in which their populations are decreasing in heavily impacted coastal areas, demonstrating potential losses of biodiversity in response to declining environmental conditions.

Knowledge about the ecology of both the medusa and the polyp phases of each life cycle is needed if we are to understand the true causes of these increases and decreases, but in most cases where changes in medusa populations have been recognized, we know nothing about the field ecology of its polyp.

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 Last updated: December 19, 2000