Meeting Abstract
In Echinodermata, aboral spines have many different functions. Certain spines in Ophiuroidea have been modified to function as lenses, whereas urchin spines may be used for protection and even locomotion. Previous work on fossil echinoderms suggests that aboral spines can function as a second test to combat wave forces and to create a boundary layer for respiration. These morphological assumptions are presumed of echinoid-like anatomy. To date, there has been little research on asteroid spine morphology and within-species variation across environmental gradients. Pisaster ochraceus is a forcipulate sea star that resides in a variety of habitats from wave-exposed rocky intertidal zones of the open coast to wave-protected embayments. Here I describe distinct variation in aboral spine density and morphology in P. ochraceus across developmental, seasonal, and spatial environmental gradients using scanning electron microscopy. P. ochraceus aboral spine density was significantly higher in stars at wave-exposed sites and during winter, when wave force is maximal. Results also indicate that aboral spine microstructural variation also varies according to habitat type. Spines from stars in wave-protected habitats were often larger with spine heads lacking lateral protrusions and contained smaller spinelets than those in wave-exposed counterparts. Laboratory studies are being conducted to determine whether the observed variation in aboral spines reflects phenotypic plasticity in star body shape via the uptake or discharge of seawater in response to short-term variation in flow conditions, or a longer-term developmental response by juveniles to varying flow conditions.
