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What is missing?

By Staff | Apr 16, 2019

SANIBEL SEA SCHOOL Beachcombers gather around a lightning whelk egg case in March 2017.

If this was your first spring on our islands, or if you are not an observant, seasoned beachcomber, you might not notice that something on our islands is amiss. This spring is not like the others. The beaches are not the same as in the past. The difference is not a subtle one.

Many of us mark the seasons along our shores, and this year, the bastion of beach spring is missing – lightning whelk egg cases. Those two-feet long, “snake-like” helical structures laid by female lightning whelks to house and protect her thousands of offspring, until the young snails are a millimeter or two in diameter and crawl from their natal egg case into the sand to begin their new life. Originally, they are anchored in the sandy bottom, but many become detached during storms and wash ashore to either puzzle, horrify, or delight beach goers.

I say snake-like because that’s how they are commonly described by beach goers who are curious of their origin. They really don’t look much like snakes, but we humans are enthralled by snakes – whether in a good, or a not-so-good way. And somehow that large helical structure, at least in our minds, looks like a snake.

By now, our beaches should be littered with them. Over the years, I have created a private game with one player – me – to see how early I encounter my first lightning whelk egg case. My record is early February. But as of this third week of March, I had yet to find a single, glorious egg case. Maybe, just maybe, lightning whelk reproduction is late this year, and soon we will return to normal spring beaches festooned with egg cases. But sadly, a more likely explanation is that there will be no accumulation of egg cases this year, or perhaps maybe the next.

This likely loss is a lingering result of the red tide algal blooms of last summer and early fall. One of the phases of an intense and prolonged algal bloom is a separate but related biological process of mass decomposition; the decomposition of animals killed by the red tide toxins, and the decomposition of the billions of algal cells that bloomed and caused the red tide.

Dr. Bruce Neill

Decomposition is a process in which free-living bacteria consume organic matter. These bacteria undergo respiration (i.e., they breathe), consuming oxygen and giving off carbon dioxide. When an algal bloom is so intense, and produces so much organic matter, the bacteria reproduce very rapidly (they also bloom) and ultimately consume all of the oxygen in the water and upper layers of the sandy bottom. This portion of the ocean stripped of oxygen is called an hypoxic zone.

Hypoxic areas are also known as dead zones. They are areas not life-supporting for the animals that normally occupy the sandy ocean bottom habitats. The good news is that we no longer have hypoxic zones just off our shores. Most of the organic matter is gone, as storms have mixed the water and returned oxygen levels to normal.

The bad news is that seemingly most of the lightning whelks of reproductive age were killed during the hypoxic event. Now we wait, to see how many years it will take until our spring beaches are again decorated with lightning whelk egg cases.

Dr. Bruce Neill is the executive director and co-founder of the Sanibel Sea School. It is a non-profit organization whose mission is to improve the ocean’s future, one person at a time. For more information, visit sanibelseaschool.org.