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Wrack line

The Curious Beachcomber

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The Curious Beachcomber

Recently, while scanning the beach on Sanibel, we tend to see one particular ‘ocean debris’ that spikes curiosity in the minds of beach-goers. Is it some kind of snake? Is it man-made? Is it even a part of this planet? After big winds, mysterious capsules of all shapes and sizes wash up on our shores.  We'd like to share a little bit about these cases and what comes out of them!

Maybe you've made this face after coming across these long snake-like strings on the beach! 

Maybe you've made this face after coming across these long snake-like strings on the beach! 

Lightning Whelk 

The lightning whelk is a common sea snail here on Sanibel but has a shell that is not typical of most shells - it actually spirals and opens to the left side instead of the right, so we call it a left-handed shell. Covering its spiraled shell are vivid lightning-like markings that give this snail its name. Other than having a beautiful shell, it also lays the famous long snake-like egg clusters that we find washed ashore. The spiraled cluster of small disc-like pods can be over a couple feet long and it is the most common egg case washed up in the wrack line on Sanibel.  

Here's a lightning whelk egg case tangled among algae in the wrack line.

Here's a lightning whelk egg case tangled among algae in the wrack line.

Pear Whelk 

The pear whelk is a medium-sized shell and is not as common as the other snails we often see in this area. This smooth shell lacks horns like the lightning whelk and is not as colorful. These snails also lay long snake-like chains of egg capsules that are very similar to the lightning whelk. If you happen to be lucky enough to find these egg cases, compare the size with the lightning whelk egg cases - the pear whelk cases are much smaller in size, which includes the disc diameter and the length of the chain. The discs also have many projections along their margins - another key characteristic. 

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  Here you can see how similar these two egg cases are - the left is the pear whelk case and the right shows the lightning whelk egg case.

Here you can see how similar these two egg cases are - the left is the pear whelk case and the right shows the lightning whelk egg case.

Florida Horse Conch

The Florida horse conch is the state shell of Florida and one of the largest snails in the Gulf. Surprisingly, the massive shell often covered with algae, is not the first thing most people notice but rather, the bright orange soft body of the animal. Female conchs deposit egg cases that resemble a cluster of yellow flowers on hard objects on the ocean floor, such as rocks and shell debris. These egg cases can sometimes be confused with the banded tulip snail egg cases, but horse conch egg cases have 4-6 rings that run along the length of each individual capsule.

Banded Tulip Snail 

The banded tulip is a brightly colored, medium-sized shell that is named for its resemblance to a tulip flower blossoming.  Much like the horse conch, the female tulip snail lays its eggs on hard-submerged objects. The egg cases also resemble a bouquet of small yellow flowers but differ from the horse conch cases because they are smaller and lack the rings on each individual capsule. You might even find these eggs laid on other snail egg cases, which is another clue that they are tulip eggs!

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  If you observe the individual capsules in these two egg cases, you can easily tell them apart.  The horse conch is shown on the left (notice the rings) and the tulip is on the right (a smooth capsule). 

If you observe the individual capsules in these two egg cases, you can easily tell them apart.  The horse conch is shown on the left (notice the rings) and the tulip is on the right (a smooth capsule). 

Now it's time to get out to the beach and explore - next time you're at the beach, see if you can identify any egg cases that you find! Happy beachcombing! 

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Tunicates Take Over Sanibel Beaches

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Tunicates Take Over Sanibel Beaches

Imagine yourself enjoying a stroll down one of Sanibel’s beautiful beaches, taking in the fresh air and soaking up the sun, when all of a sudden you feel something squishy between your toes. When you look down and realize that a lumpy, brown blob is squeezing through your toes, your first reaction may be utter disgust. After taking a closer look at the wrack line, you realize that there is not just one of these strange blobs – the whole beach is littered with them!
 

The wrack line inundated in sea squirts - a common sight on Sanibel lately. 


The brown, wrinkly blobs in question are actually sea squirts, referred to as tunicates in the marine biology world. Tunicates are animals that house their tiny body in a thick covering that resembles a tunic – that’s how they get their name. Individuals have the ability to form dense colonies, which often end up looking like the irregular blobs we are now familiar with. These animals attach to docks, mangrove roots, and live shells, and spend their days filter-feeding plankton. The species you may have encountered recently (if you're on Sanibel) is the sandy-skinned tunicate (Molgula occidentalis), which is often covered in sand and bits of shell.

Up close and personal with Molgula occidentalis - the sandy-skinned tunicate.


It’s hard to believe that tunicates are animals, but they are fully equipped with siphons for feeding, a stomach, and even a small brain. What is really interesting to us is that tunicates are closely related to vertebrates because they begin their life with a notochord, a row of specialized cells found in all animals with a backbone. But unlike vertebrates, the tunicate’s notochord disintegrates as it matures into an adult. 

When the tunicates wash ashore, they often die off shortly after being stranded on the beach. 

 
Last month, Sanibel Island was getting high winds from the North and West, which resulted in the tunicates becoming dislodged from the substrate and pushed up on our beaches en masse. Even though these creatures are quite unsightly, they aren’t harmful – they might just squirt out a little water if you handle them, which we encourage!

More windy weather this week deposited a fresh batch of tunicates near the lighthouse. 

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What’s washing up in the wrack?

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What’s washing up in the wrack?

The ever-changing wrack line can be a very dynamic environment. Originating from the Middle Dutch word “wrak”, meaning something damaged, this place may look damaged but is far from it! Technically, the wrack line is the place on the beach where marine debris is washed up and left behind by the most recent high tide. The wrack line may be teeming with life, full of stinky algae, or a treasure trove of seashells – it just depends on the day! Today, let's explore some of the more curious items we often find in Sanibel's wrack line. 

Sea pork

Is it a plant? An animal? A fungus? This mysterious blob is actually a colony of animals called tunicates. These teeny-tiny animals protect themselves with a sac made of cellulose and spend their days filter-feeding. Sea pork can be found in various colony sizes and be colored pink, purple, black, and even orange.

Purple variation of sea pork. 

Purple variation of sea pork. 

 Gastropod egg cases

Like sea pork, these paper-thin structures can come in all different shapes and sizes. Gastropods (live shells including whelks and conchs) are responsible for creating these elaborate structures to house their eggs in until they are ready to hatch as young shells. We often find these washed up on the beach after many of the eggs have hatched, but sometimes if you tear open one of the capsules, you can find some of the tiny shells that didn’t hatch. Give it a try next time you happen upon one at the beach. 

Lightning whelk egg case entangled in red drift algae. 

Lightning whelk egg case entangled in red drift algae. 

Parchment worm cases   

These hollow straw-like structures were once home to a marine polychaete worm that looks somewhat like a centipede. The worms build these housing tubes and attach themselves to various substrates or burrow beneath the sandy sea floor. These creepy tubes also provide a home to a couple different species of commensal crabs. Next time you find one on the beach, tear it open and you might discover these crabs!

Empty parchment worm housing tubes washed up on the beach.  Photo: iloveshelling.com 

Empty parchment worm housing tubes washed up on the beach. Photo: iloveshelling.com 

Sea anemones

Sea anemones are cnidarians that often resemble flowering plants, but beware of their beauty – they are armed with capsules of stinging cells called nematocysts for protection. Most of the anemones found around Sanibel don't have potent nematocysts and aren't dangerous to humans, but they do have an additional defense mechanism that makes you wonder if they might be a creature from outer space. When sufficiently irritated, they will release defensive threads called acontia that are neon orange and packed with powerful stinging cells.

Here is a sea anemone attached to a gastropod shell. Those vibrant acontia are hard to miss!

Here is a sea anemone attached to a gastropod shell. Those vibrant acontia are hard to miss!

 Pig bones

At first glance, you may think these are human artifacts or remains of a large marine mammal, but they are in fact just pig bones. Unfortunately, these don’t come from a rare species of marine swine but rather, pig parts that are used in crab traps as bait.  Crabs are attracted to the pungent aroma of the meat and enter the trap to chow down. After the bones have been picked clean, many of them wash out of the traps and end up on our beaches.

A pig bone found washed ashore.  Photo: iloveshelling.com 

A pig bone found washed ashore. Photo: iloveshelling.com 

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