Chemical camouflage

 

View from the southern end of Bodega Head, with Bodega Rock offshore and Tomales Point in the far background.  Note the bright green surfgrass (Phyllospadix scouleri) in the foreground.

 

The Surfgrass Limpet (Lottia paleacea) (= Notoacmaea paleacea) is one of the smallest of the West Coast limpets.  They are tall and narrow, up to 10 mm long and about 3 mm wide (no wider than a surfgrass blade).  

Surfgrass Limpets only live on these slender seagrass blades.  They feed on the plant's outer tissue — look for the grazing scars in the photo below (paler section to the right of the limpet).

 

Surfgrass Limpets appear to be chemically defended against predation by seastars.  Debby Carlton studied this relationship on Bodega Head.  Three small gastropods are common in surfgrass beds — Surfgrass Limpet, Chink Snail (Lacuna marmorata), and Carinated Dove Snail (see yesterday's post).

The two snails react strongly to Six-armed Seastars (Leptasterias sp.).  When contacted by a seastar, the Chink Snail waves its tentacles, twists its shell, and drops off the surfgrass blade, all defensive behaviors to avoid the seastar's grasp.  The Carinated Dove Snail flees, but may also bite the seastar.  In contrast, the Surfgrass Limpet clamps down and remains motionless.  Sometimes the seastar even crawls over the limpet and continues on, without capturing it.

Debby proposed that this was an example of chemical camouflage.  She found evidence that the same chemicals (flavonoids) were present in both the surfgrass tissues and in the limpet's shell.  It's possible the non-visual seastar predator does not detect this likeable limpet because it smells like surfgrass!