Are Scyphozoan Blooms Increasing? Causes and Consequences

Defense Date


Document Type


Degree Name

M.S. Coastal Zone Management

First Advisor

Charles Messing

Second Advisor

Tamara Frank


Scyphozoan medusae exhibit important population fluctuations over a variety of time scales. Populations of many species bloom, that is, exhibit a rapid localized population increase, as a natural part of their life cycles; however, blooming events are being reported more frequently. Anthropogenic impacts that are altering the physical and chemical processes of the ocean, such as overfishing and pollution, are creating environments that favor medusae and may cause increases in their abundance. These trends have been most observed in the Adriatic Sea, Bering Sea, Mediterranean, North Sea, Gulf of Mexico and Sea of Japan. The reports examined in this paper show that scyphozoan species are able to take advantage of conditions created by anthropogenic influences. However, more information about global and long-term trends is needed to clarify whether scyphozoan blooms are truly increasing or not. Limited top-down control of medusae populations has led many to assume that medusae are trophic dead ends. However, medusae have been recognized as important contributors to pelagic food webs, providing inorganic nutrients to primary producers via excretion and serving as prey for turtles, mammals, birds and some fish. It is important to understand scyphozoan life cycles and how they are affected by anthropogenic impacts that may play a role in bloom formation. In order to understand blooms better, more research is needed for: understanding the benthic phase and its role in recruitment, roles of phenotype and genotype in influencing responses to environmental cues, and the reproductive strategies of medusae relative to changing environmental conditions. Medusa blooms are considered by some as warning signs of a degrading ocean, and research into these phenomena is needed to better monitor and manage conditions influencing blooms for future conservation decisions.

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