By Kim Smiley

Jellyfish are some of nature’s most impressive survivors.  They have been around since long before the dinosaurs roamed the earth and continue to thrive.  In some cases, they may even be thriving a little too successfully.  Massive jellyfish blooms can flourish in the right environment and can decimate other species and cause significant damage.

Naturally occurring jellyfish blooms have been around for ages and while they may be inconvenient at times, they aren’t particularly alarming.  The real concern is that manmade conditions may lead to the growth of jellyfish blooms at times or regions that wouldn’t normally see them.  Large numbers of jellyfish can cause a number of serious issues.  Safety is a concern because jellyfish stings are painful and can even be deadly.  Regions that depend on tourism can also be impacted because travelers may avoid areas with large numbers of jellyfish.  Jellyfish have caused damage to ships and buildings when they clog intake lines.  Populations of other species have also been decimated in some areas by jellyfish blooms which can affect commercial fishing operations.

What causes these jellyfish blooms can be explored by building a Cause Map or visual root cause analysis.  A Cause Map intuitively lays out causes that contribute to an issue and shows the cause-and-effect relationships between them.  In this example, the jellyfish blooms grow because jellyfish are well suited for life in low oxygen “dead zones” that are being created in the ocean.

It all starts with fertilizer containing nutrients running into the ocean.  An algae bloom forms as algae feed on the nutrients.  Eventually the nutrients are depleted and the algae dies off leading to the growth of a bacterial bloom as bacteria feed on the dead algae.  The bacterial bloom depletes the oxygen making the region unsuitable for most species.  However, the opportunistic jellyfish can survive and even thrive in low oxygen levels.  Jellyfish are able to rapidly grow and reproduce quickly so the population surges upward in an environment with few predators and little competition.

A few facts so that the reproductive abilities of jellyfish can be fully appreciated: a single female jellyfish can release tens of thousands of eggs per day, and jellyfish are able to double their weight in a single day if food is abundant.

Eating habits of jellyfish also make it very difficult for other species to move back into the region even if oxygen levels increase.  Jellyfish not only compete for the same food as larvae of other species, plankton, they are fond of eating larvae and eggs.  It’s difficult to compete with a species that is both a predator and competitor.

Before anyone has nightmares of huge jellyfish causing wide scale destruction, I should note that researchers have not found evidence that jellyfish are in danger of overrunning the oceans.  But many scientists do believe that human activities have contributed to jellyfish blooms growing in localized areas.  It’s always worth trying to understand how human activities are impacting our environment, especially when a species so well equipped for survival is involved.

To view a high level Cause Map of this issue, click on “Download PDF” above.