August 30, 2014

While the idea that a waterspout could lift sharks out of the ocean and rain them down on land is utterly absurd (albeit entertaining), there is one event involving marine life and weather that is veryreal--jellyfish swarms.

A range of weather conditions can lead jellyfish to invade coastlines, putting them in a prime position to "attack" beach-goers with stings. The  jellyfish-carrying weather includes:  

Ocean/Coastal Currents. Strong winds blowing across the ocean surface can actually sweep jellyfish away from their homes out to sea and congregate them into large swarms, or "blooms," of hundreds or thousands near the shore. As these winds blow, they push water away from an area, causing water from beneath the surface to rise up and replace the water that was blown away. (This process is known as "upwelling.") While jellyfish are able to swim, their motion is very limited (they propel forward by opening and closing their bell-like bodies--much like you open and close an umbrella) which leaves them helpless against these currents.

Several consecutive days of sea breezes (light winds that develop over the ocean and blow towards land) can have a similar effect. 

After winds die down, the jellyfish eventually retreat offshore.

Abnormally Warm Ocean Temperatures. Higher water temperatures are also known to cause explosive blooms, as they both speed reproduction and extend the reproductive season.

 "Jellyfish season," the time of year when jellies are naturally more abundant, occurs in late summer (mid-July into August). 

Drought.  Drought conditions cause jellyfish populations to spike in two ways: by raising salinity (water's salt content) and speeding water warm-up.

Without significant rainfall, coastal waters and estuaries receive very little freshwater; the less freshwater there is to dilute nutrients, the higher the salinity. In general, jellyfish favor high salinity as it means reduced competition for resources (many species of fish and invertebrates are unable to rid their bodies of excess salt). 

In addition, reduced rainfall also causes low water levels. This means that however much water is contained in lakebeds and estuaries warms up at a faster rate than it would if at normal levels. In August, Lake Oroville, one of California's largest reservoirs, noticed a spike in freshwater jellyfish for this very reason. Its water levels were reportedly at 32% of reservoir capacity.

Jellyfish Swarms of Summer 2014

This summer, jellyfish have been washing onto beaches and crowding the shorelines of the Pacific Northwest, the East Coast, and the U.K. In late August, more than 400 swimmers were stung by jellyfish at Florida Beaches alone.

According to scientists, year-to-year differences in jellyfish blooms are normal, but there's a concern that the increase in jellyfish populations seen in recent years is linked to the effects of global warming.