If you’re a regular reader, you probably know this blog started as a way to address the many emails and texts I receive, asking, “What IS this?” On a semi-regular basis, these questions also come from professional colleagues. All of us curious outdoorsy folk, the natural resource Extension Agents in the Panhandle have decades of combined field and academic experience. But sometimes a photo leaves us all pretty stumped.
Earlier this week, I was included in an email thread from our Sea Grant Agent in Walton County. She’d been sent a photo by several county colleagues, originating from a beach visitor. The photos were of rows and rows of tiny brown/black specks along the beach sand. No one knew exactly what they were looking at as it was passed up the chain.
Upon seeing the photos, my first question was, “Did anybody pick it up?” Basic science rests first on observation. While we had an idea of the size, shape, and color of these little beach tidbits, we had no appreciation for texture. If these small black specks were solid, they might be plastic. If they crumbled into pieces, they might be seeds or other plant material. And if they were squishy, they might be fish poop. As disgusting as it sounds, animal feces, or scat, is a really common way to identify wildlife in the field. Most animals are secretive and disappear when humans come nearby, so interpreting tracks and scat can be really helpful.
Turns out, fish poop was the closest guess. Another astute colleague in south Florida suggested ghost shrimp feces, and I think they nailed it. A quick photo search identified the mystery bits as the waste of burrowing invertebrates. Not being satisfied until I could confirm them in person, I visited the beaches of south Walton County yesterday. I happened to be giving presentation to a group just a mile away, so I walked down to the beach to feel and see for myself. The ghost shrimp of 30A did not disappoint; within a few minutes, I was greeted with littered strands and piles of tiny fecal pellets. As predicted, they were quite squishy when pressed. Most of the pellets clustered where the sand was indented from footprints, or along the edge of the small wrack lines formed by waves washing up. Seeing these pellets is somewhat unusual (hence our unfamiliarity with them), but a local state park ranger explained that the recent calmer waves likely account for the large amount of material present. In heavier surf, the pellets are quickly washed out to sea.
Ghost shrimp (Callichirus islagrande, most likely in our area–but there are hundreds of species) are small, (3-4” long), skinny, cryptic organisms that build deep (3-4 feet) individual burrows underwater and in the swash zone of the beach. These burrows serve as hiding places from would-be predators. The shrimp themselves use small abdominal paddles to move water through their burrows, picking up algae and small bits of detritus to eat. The name ghost shrimp comes from their light pigmentation and minimal shell calcification–both features they can dispense with when living deep underground. These invertebrates play an important role in nutrient provision and movement on beaches, bringing organic material deep under the sand, transforming it, and moving it to the surface.
While it’s rare to see a ghost shrimp on the beach or in the water, the tops of their burrows are evident all along the beach as open holes that bubble up as the waves wash in. Underwater, they look like tiny open-topped volcanoes. As you can imagine, if you lived alone in a deep, narrow underground shaft, you wouldn’t want to be surrounded by your own waste. So, ghost shrimp package up their poo and expel these mucus-covered “fecal pellets” from their holes daily—averaging up to 500 per shrimp!
Ghost shrimp are often used as bait, and can be pulled up from their burrows using yabby pumps (vacuum suction tools made of PVC) in the sand. Trying to dig them out by hand is generally a fruitless endeavor, as they burrow quite deeply and can move horizontally. Their burrows are interconnected with other shrimp, creating an entire underground network.
So—mystery solved—and some new information you can use to gross out your friends and family on your next beach walk!
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