Research Study 1

Fig. 1.  Luidia foliata showing its sucker-less tube feet

The sea star Luidia foliata commonly inhabits sand/mud habitats over which it can crawl quite quickly, possibly relating to the lack of suckers on the tube feet (Fig. 1). Thus, it moves tippy-toe fashion.  Interestingly, its diet includes a range of invertebrates, including bivalves, but how it catches and manipulates its prey without suckers is not known.  This might make a good a good student project at a summer marine station, if enough specimens could be found.

Research Study 2

Fig. 1.  A sunflower star Pycnopodia helianthoides escapes from a pursuing sun starSolaster dawsoni by fast crawling

Fig. 2.  This leather star Dermasterias imbricata is unable to outrun its predator Solaster dawsoni 

Subtidally, the most aggressive predator of west-coast sea stars is the sun star Solaster dawsoni. Responses of prospective prey species as observed at Friday Harbor Laboratories, Washington is to crawl away, and the ones listed below can often out-run the predator:

• Pycnopodia helianthoides (Fig. 1)
• Dermasterias imbricata (Fig. 2)
• Evasterias troschelii
• Mediaster aequalis
• Crossaster papposus

One species, Solaster stimpsoni even pushes back against the predator when attacked. A similar pushing defense is also used by S. stimpsoni to repel attacks by conspecifics. 

Research Study 3

Fig. 1. This large sunflower star Pycnopodia helianthoides is photographed crawling directly towards the camera. Within a few moments it transits completely over the camera and the SCUBA diver, and departs on the other side

Subtidal measurements of Solaster dawsoni’s locomotory rate show a top chase speed of about 10cm • min^-1.  Interestingly, when touched by one of Solaster’s rays, even some sluggish-seeming species can outrun the predator.  At crawling speeds of 120 - 160cm • min^-1 the sunflower star Pycnopodia helianthoides is, of course, in a class by itself (Fig. 1), but even the normally quiescent Mediaster aequalis (33cm • min^-1) and Crossaster papposus (65cm • min^-1) easily outrun the predator. Of asteroids whose crawling speeds are recorded, the bat star Patiria miniata may be one of the slowest, at 6cm • min^-1. It does not appear to be eaten by Solaster, however, perhaps for reasons of distastefulness or by living in habitats not frequented by the predator. 

NOTE locomotory rates are for adult-sized individuals for all sea stars save Pycnopodia and Patiria, which are about half maximum size (46 and 5cm diameter, respectively)

Research Study 4

Fig. 1.  The exception that proves the rule?  A sun star Solaster dawsoni with its half-digested meal of leather star Dermasterias imbricata, suggests that we may need to revise our previous estimates of its lack of vulnerability to the predator

Courtesy Brooke Reiswig and Dave Cowles, Walla Walla University, Washington

Much the same kind of data for behavioural responses of asteroids to contact with Solaster dawsoni is presented in a study at the Bodega Marine Laboratory, California.  Here, strong escape responses are displayed by Patiria miniata, Henricia leviuscula, Leptasterias hexactis, Pycnopodia helianthoides, and small Pisaster ochraceus.  However, all the slow-moving species are subsequently captured and eaten.  Only P. helianthoides crawls quickly enough to escape. Although large-sized Pisaster ochraceus can defend itself from the predator with its pedicellariae, small-sized individuals, as noted, are generally eaten.  Of the species tested, only the leather star Dermasterias imbricata is immune to predation (but see Fig. 1). The authors use the presence or absence of an escape response to predict whether a species is susceptible to predation from Solaster dawsoni.