Moon jellies are washing up on SLO County beaches. Are they harmful to humans?

When I was on active duty with the U.S. Navy in the early 1980s, I took a swim off the coast of Naval Air Station Mayport in Jacksonville, Florida, on a hot and humid summer day.

The Atlantic Ocean water was a balmy 80 degrees Fahrenheit.

About 500 yards from the beach, I felt intense pain, like a white-hot sharp piece of barbed wire had wrapped around my right shoulder and arm.

The excruciating discomfort took my breath away as I swam toward the shore with only one arm functioning.

It turns out that I was stung by a venomous Portuguese man-of-war. It left visible marks along my torso for months afterward.

Thank goodness we don’t have these tiny gas-filled bladder monsters along the California coastline. They resemble a 16th-century warship at full sail with 100-foot-long tentacles loaded with thousands of skin-piercing, stinging nematocysts used to paralyze and kill fish.

Nevertheless, beachgoers in San Luis Obispo County have been reporting seeing moon jellies and by-the-wind-sailors washed up on the sand.

What are these sea creatures and can they harm humans?

The short answer is: Not really. With that said, if you handle moon jellies, don’t touch your face or eyes since irritation may result.

Jellyfish are not fish, but invertebrates, meaning they have no backbones. The cnidarians also don’t have brains, instead relying on so-called “nerve nets,” and are comprised 95% of seawater.

Moon jellies are found throughout the world’s oceans and are about the size of a coffee saucer. The jelly, whose scientific name is Aurelia aurita, is named after its translucent, moonlike bell.

Visitors to local beaches have also spotted vast hordes of almost transparent rubbery electric blue sea creatures called Velella velella, or, by-the-wind-sailors.

The marine animal, also known as a sea raft, purple sail or little sail, was once believed to be a siphonophore — an animal made up of a colony of specialized zooids, working together. However, the latest research indicates that the Velella velella is a single animal and not a colony.

Much like the man-of-war, these cnidarians resemble small sailboats.

On average, the flattened oval creatures are two inches long with a relatively large and stiff translucent, angled sail.

Not a lot is known about the details of their life cycle. They seem to live less than a year and can reproduce quickly.

Billions of these creatures live where the sea meets the sky in the warm or temperate waters of the world’s oceans.

By-the-wind-sailors glide along the surface of the ocean and feed generally on tiny fish larvae and zooplankton that they capture with their dangling stinging tentacles below their gas-filled bodies.

But that’s not their only source of nutrition. If you look closely, you can see brown microalgae that exist in a symbiotic relationship inside their bodies, providing an additional food source.

If you’ve spent any time out at sea, you can sometimes see millions of these creatures clustered closely in mile-long rows that resemble oil slicks.

Some marine biologists believe two forms of Velella velella exist in the north Pacific Ocean.

The velella found along California’s Central Coast has a sail that is angled 45 degrees along the creature’s centerline to take advantage of winds that predominantly blow from the north to the south along the west coast of North America. Therefore, the angle of the sail, much like a sailboat, helps to steer these critters out to sea.

On the other side of the Pacific Ocean, the winds often blow from the south to the north.

The sail of the velella that lives in the western Pacific is angled in the opposite direction of its eastern cousin — functioning to keep these animals offshore and off the coast of Korea and Japan.

Why have we been seeing increased numbers of jellies on our local beaches?

Over the past month, we have seen cycles of gale-force northwesterly (blowing out of the northwest to the southeast) winds along the coastline. These winds produced a southwesterly (out to sea) flowing ocean current.

However, these gale-force northwesterly winds have been followed by periods of gentle southerly winds and consequently a northeasterly (onshore) flowing current, bringing these creatures to our coastline.

PG&E promotes safe digging

Wednesday, Aug. 11, is National Safe Digging Day.

The day serves as a reminder to PG&E customers, contractors and anyone digging to call 811 a minimum of two business days prior to starting any digging project, no matter how large or small. 811 is a free service for anyone planning to dig.

This story was originally published August 10, 2021 at 5:05 AM.