A Sea Cucumber that’s an Apple? - Observation of the Week 2018-08-17

Our Observation of the Week is this Violet Sea Apple, seen off of Taiwan by huang_shu_chen!

You might have noticed that the number observations from Taiwan have been growing quite a bit (see chart below), showing off the incredible biodiversity of the island and its surroundings. Much of this growth has has been spurred by a community of both researchers and citizen scientists, one of whom is Cheng-Tao Lin (@mutolisp), the current top observer in Taiwan and an Assistant Professor in the Department of Biological Resources at National Chiayi University. Prof. Lin has graciously translated the responses from this week’s observer, so I want to thank him and Shu-Chen for collaborating on this.

huang_shu_chen (whom I’ll refer to as Shu-Chen), is a diving volunteer for the National Museum of Marine Science and Technology in Keelung, Taiwan, and says “My partner and I (see below) do routine underwater work about coral reef restoration, patrol and investigation, and assist in recording species to create a marine diversity checklist. In addition to these routine tasks, I will also take photos of these beautiful marine creatures.”

The beautiful Violet Sea Apple you see above was taken by Shu-Chen during her first dive using an underwater camera with a flash, and she tells me

it is also the first time I saw such a fascinating and gorgeous sea cucumber, just the same as its name, “red apple”. It’s a pity that I did not meet its “flowering” state (when it stretches tentacles to catch plankton). If I had a chance to see its flower, I will upload it to iNat again!

As Shu-Chen says, these creatures are sea cucumbers, although we use a different vegetative term to describe them (apple) due to their more round shape than your standard sea cucumber. The “flowering” behavior she describes is how the creature catches plankton, by extending its frilly tentacles into the water. And like many other sea cucumbers, violet sea apples can expel parts of their sticky innards into the water when threatened, allowing a predator to concentrate on its entrails rather than the rest of its body. If that doesn’t work, they also have two tricks up their sleeves: they can release a toxin known as holothurin (a type of saponin) into the water, and they can also ingest water, allowing them to double in size and use currents and gravity to sweep them to a new home.

Shu-Chen (above) has recently joined iNaturalist, and says

my photos of nature were just silently stored in my own computer disks in the past, but since I learned about iNaturalist platform, and that observation data uploaded to iNaturalist would become part of GBIF data, I’m so glad that they could be used and studied by other people around the world...I also use iNaturalist to create species checklist at the place where I care and concern. It is really convenient to have iNaturalist to record nature observations, and it motivates me to collect more data.

- by Tony Iwane. 

- Why not take a gander at some of the great observations being made in Taiwan? Here are the faved ones. 

- Some Pearlfish will use the anus of a sea cucumber as a home and/or eat their gonads. This is true. 

- Sea cucumbers demonstrate some astonishing diversity, check out observations of them here!

Posted on August 28, 2020 10:31 AM by hannahsun99