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.
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.
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.
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!
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.
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.