Recent Jellyfish Trends in the Northern
Gulf of Mexico
Over the past several years, we have documented a dramatic increase in the
abundance of jellyfish in the northern Gulf of Mexico. Many of you may have read about
some of these observations in local and national newspapers over the past year.
We have seen significantly increased numbers of two common local species, such as
moon jellies and sea nettles (Aurelia aurita and Chrysaora quinquecirrha),
in the past couple of years. We then saw the arrival of two uncommon tropical species in
summer and fall of 2000: the so-called Australian spotted jellyfish (Phyllorhiza punctata) and “the
big pink jellyfish” (Drymonema dalmatinum).
These occurrences have raised the obvious questions:
Why are we seeing such an increase? And, what impact can such blooms have on the
ecosystem? (Here, a bloom is the relatively sudden appearance of a large number of a
particular species of jellyfish.)
Why Are We Seeing More Jellyfish?
Scientists are not yet sure why there has been such an increase in jellyfish
abundance, or why we are seeing exotic (non-native) species in high numbers. Moon jellies
and sea nettles are natural members of our local ecosystem and are not considered
"nuisance species" until their numbers are extraordinarily high, as in blooms.
Long-term changes in jellyfish abundance may be a response to the effects of
intense fishing along the coast, nutrient enrichment of local waters
(‘eutrophication’), or a combination of the two. This sequence of events has
occurred in other bodies of water, such as the Black Sea. There are several major rivers
carrying nutrients from land run-off to the northern Gulf of Mexico. This
nutrient-enrichment of coastal waters could be favorable for increases in jellyfish
numbers. If jellyfish abundance is correlated to intense fishing and/or eutrophication, it
could be viewed as an indicator for changes in the local ecosystem. In this case, some
predictions could be made about what could occur in local waters in regard to future
abundances of jellyfish, local fish species, crabs, and shrimp, and the overall functional
ecology of the northern Gulf of Mexico.
Although
scientists understand the long-term effects these potentially nuisance species have on the
ecosystem, they know little about bloom development and movement. What short-term effects
can such large numbers of jellyfish have on food availability and reproductive success of
local fish, crab, and shrimp populations. What changes in the ecosystem could result from
the feeding and reproduction strategies of exotic species?
Another
distinction scientist are trying to make is whether blooms of jellyfish occur in one place
then move with the currents, thus giving the illusion of multiple blooms in different
locations; or if multiple blooms are actually occurring in several places. Is it multiple
bloom development or single bloom movement? If a bloom is being transported by water
movement, then the estimated number of jellyfish will be much less than if multiple blooms
are occurring.
Why are We Seeing 'Exotic' Species?
Scientists
are not sure how exotic, tropical species arrived in the northern Gulf of Mexico or how
they proliferate in coastal Gulf waters. In 2000, two exotic species bloomed and
flourished in the northern Gulf: Australian spotted jellyfish (Phyllorhiza punctata) and “the
big pink jellyfish” (Drymonema dalmatinum).
One idea is
that the Gulf Stream 'Loop Current', which extends from the Caribbean Sea into the
Gulf of Mexico, entrains these tropical species and carries them north. Eddies (mini
bodies of water) are known to spin-off from the tropical Loop Current and transport
jellies into the northern Gulf. This Loop Current does not form the same pattern every
year, so in some years it may extend further north than in other years, thus providing a
greater potential of delivering exotic species to our coastal waters.
Exactly how
they are getting here remains to be determined. As does whether or not they will become a
part of our local ecosystem for years to come.
What is 'DockWatch'?
The biggest
problem with studying jellyfish bloom development, movement, and propagation in the
northern Gulf of Mexico is the extensive resources required for a few scientists to
continuously survey jellies in the Gulf for months on end. For the public at
large, jellyfish are often a nuisance that is not well understood. DockWatch unites
scientists and the public in a joint effort to meet the demands of this type of study and
to provide answers to the public.
Dr. Monty
Graham and Ms. Lisa Young of Dauphin Island Sea Lab (Dauphin Island, AL) have developed a
protocol for a 1-year pilot study (DockWatch) to evaluate the effectiveness of this union.
Mississippi-Alabama Sea Grant Consortium (MASGC) and the Environmental
Protection Agency's (EPA) "Gulf of Mexico Program" are funding this study.
Volunteers along the coasts of Alabama and Mississippi will collect environmental data and
visual observations of jellyfish species and numbers. Dr. Graham will analyze the data to
determine the seasonality and distribution of the observed species in local waters, if
blooms are developing and where, and if blooms are local or transported.
All of
these data will be available on this project-dedicated web site, allowing the volunteers
immediate reward for their effort. This web site will help explain why nuisance species
like jellyfish are important to both the ecology and economy. It will also emphasize that
ecological impacts occur at the ecosystem level rather than simply at the species or
population level. Upon completion of the study, the results will be made available to the
general public and the program will be evaluated for continuation. Besides accomplishing
Dr. Graham's and Ms. Young's objectives, the volunteers will learn about the different
species of jellyfish and will better understand their roles in the local ecosystem.
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