Learn About Feather Stars: Predators & defenses

Little work has been done on predators and defenses of west-coast feather stars. Defenses include autotomy, swimming, a highly calcified body that is poor in nutritional content, and possibly the presence of unpalatable chemicals. Studies on the first 3 topics are considered in this section.

NOTE no work on chemical defenses appears to have been done on west-coast crinoids. However ,in this regard, certain Indo-Pacific comatulid crinoids possess sulphated polyketides (e.g., anthraquinoine-2-suphonate and sodium 2-hydroxy-anthraquinone sulphate) that deter feeding of fishes at physiological concentrations. Rideout et al. 1979 Experientia 35: 1273.

Autotomy

Research study 1: Autotomy

photograph of sunflower star Pycnopodia helianthoides...a predator of feather stars?Arm loss through autotomy is common in west-coast Florometra serratissima, but what causes it? Reports on European species list wave action, moving debris including seaweeds, high temperatures and other physiological stressors (including UV light), and disturbance by animals.As Florometra is rarely found in waters shallower than 20m, none of the physical factors listed are likely to influence them. Potential predators are more likely to be the cause. The author describes attacks on Florometra by predatory sea stars Pycnopodia helianthoides resulting in arm loss, and a single encounter with a spider crab Oregonia gracilis in the field that may have resulted in arm loss. Mladenov 1983 Can J Zool 61: 2873.

NOTE the process of autotomy can be found elsewhere in this section of the ODYSSEY: FEATHER STAR: REGENERATION

Sunflower star Pycnopodia helianthoides...a predator of feather stars? 0.4X

Research study 2: Autotomy

photograph of feather star Florometra serratissima showing broken arm facing into cameradrawing of autotomy location in cirrus of feather star Florometra serratissima courtesy Holland & Grimmer 1981 Zoomorph 98: 169

Autotomy in Florometra serratissima can occur at several specific breakage locations along the arms and cirri. The arms and cirri are comprised of skeletal ossicles joined by ligaments and other connective-tissue fastenings (see drawing above Right). Each ligament consists of thousands of fibers running parallel to the long axis of the cirrus. Each fiber is a bundle of collagen fibrils along with associated interfibrillar material including cells known as fibroblasts. A large nerve travels the length of each cirrus and arm, penetrating each ossicle at its centre and sending branches into the ossicles. The special autotomy locations are characterised by ligament fibers of collagen and nerve axons filled with presumed neurosecretory granules. Fibers vary in length depending upon the diameter at the autotomy site, but are in the range of 50-75┬Ám.

drawings of autotomy locations in cirrus of feather star Florometra serratissima courtesy Holland & Grimmer 1981 Zoomorph 98: 169Studies on specimens of Florometra collected at La Jolla, California and Bamfield, British Columbia indicate that the process of autotomy involves a massive exocytosis of granules at the site stimulated by neural transmission (see drawing below Right). The released neurosecretions, which could contain chelating agents, strong acids, and proteolytic enzymes or enzyme activators, is thought to liquify the ligament fibers, fibroblasts, and other connective tissues, leading to loss of the cirrus or arm. The calcareous ossicles on either side of autotomy site show signs of erosion. On stimulation of an arm tip in an intact specimen, such as by crushing or cutting with scissors, the proximally closest autotomy site breaks after about 1sec. Holland & Grimmer 1981 Zoomorph 98: 169.

NOTE the authors term these zyzygies ("yoked together" G.), defined in astronomy as 3 celestial bodies, such as sun, earth, and moon in a straight-line configuration, and here as ordinarily strong joints that lose tensile strength by an intrinsic mechanism acting suddenly and causing autotomy

NOTE in the arm this is known as the brachial nerve

Research study 3: Autotomy

Another less well-known predator of Florometra serratissima is the pink/crested sea star Lophaster furcilliger. Although generally uncommon in B.C., as shown in the accompanying photographs it can be quite abundant in deeper, currenty areas where prey feather stars aggregate. Lophaster is a typical slow-moving sea star, but this may be an advantage as it creeps onto a feather-star's arm lying on the substratum and begins to feed. If the feather star then responds by swimming, the arm would likely be autotomised. The following photographs and in situ observations are contributed by Neil McDaniel. McDaniel 2019 pers. comm. Photographs courtesy the author. neilmcdaniel.com

view of deep reef on the BC coast with aggregation of feather stars Florometra serratissima and predatory pink-crested stars Lophaster furcilliger photograph of pink-crested sea star Lophaster furcilliger photograph of pink-crested star Lophaster furcilliger eating a prey feather star Florometra serratissima
25m-depth reef in Sechelt Inlet, BC with dense aggregation of feather stars Florometra serratissima along with several predatory pink-crested sea stars Lophaster furcilliger. Note the strong current flow Close view of Lophaster presumably eating a detached
arm of a feather star Florometra. Note the white, reticulated skeleton visible past the outer calcareous extensions, or "crest", that bear tufts of smaller spines

In strong currents Florometra's arms lie on the substratum, allowing predatory sea stars Lophaster
easy access to their arms. It is not known whether
this arm is detached, or still attached to its owner

NOTE Neil McDaniel is arguably one of the best SCUBA-diving marine photographers on the west coast. He combines fine imagery with extremely useful scientific observations, such as those provided here

Swimming

Research study 1: Swimming

photograph of swimming feather star Florometra serratissima

The only information on specific defenses in west-coast crinoid Florometra serratissima s comes from anecdotal references to swimming on contact with sunflower stars Pycnopodia helianthoides or crabs that wander through an aggregation.Contact with Pycnopodia, for example, is followed by about a 5-sec delay, after which several power strokes carry the stimulated individual 1-2m distance. This cycle can be repeated several times and capture by a sea star is actually thought to be rare. Mladenov 1983 Can J Zool, Lond 61: 2873.

A swimming feather star Florometra serratissima 0.5X

Nutritional value

Research study 1: Nutritional value

A crinoid really is just "skin and bones", yet no studies have been done directly on the poor nutritional return that a predator would get from a meal of crinoid. Yet, a species like Florometra serratissima will swim from contact with various animals including ones that attempt to capture them, so it seems that at least some predators find them to be tasty.

NOTE for information pertinent to this subject see LEARN ABOUT NUDIBRANCHS:DEFENSES: NUTRITIONAL CONTENT