Ecopol Project - Portland State University

Jellyfish and dead zones 

Jellyfish could play an important role in determining the overall health of our oceans, including the impact of dead zones. Oceanographers have been noticing an increase in jellyfish abundance, known as a bloom, in specific regions. It is hypothesized that there are multiple factors increasing bloom prevalence such as drought, increase water temperatures, reduction in predators, increased water salinity, overfishing, eutrophication and low oxygen levels. Scientists take these blooms as a sign that unhealthy areas of our oceans may be returning to a more pre-historic composition where jellyfish prevailed. In relation to ocean dead zones, their relative abundance acts as an indicator to help identify sites of existing or future dead zones. Because dead zones are characterized by regions of low vertebrate populations, it opens a niche for the jellyfish to exploit without worry of being preyed upon. They are known to feed primarily on small fish, plankton and zooplankton, and with the eutrophication (increased nutrient content) of dead zone waters, they can thrive upon the resultant increased concentration of their prey. Jellyfish are able to survive in these hypoxic (low oxygen concentration) areas because they have large amounts of dissolved oxygen stored within their tissues. Their body mass is comprised of 95 percent water, much more than in humans. Another problem that relates to these blooms is the increased harassment of beach goers and scuba divers by jellyfish. This concerns the tourism industry, as people are choosing to go elsewhere to avoid being stung as well as the scientific world. It will be even more difficult to study these areas if we are unable to send divers into the water to collect data.