PHOTO 4 Each year since 1990, scientists studying shoreline recovery following the Exxon Valdez spill in Prince William Sound have taken photos of a prominent boulder, know commonly referred to as Mearns Rock. The photo series, available at http://response.restoration.noaa.gov/photos/mearns/mearns.html, demonstrates the complex changes that can take place year to year in the nature and abundance of marine organisms. (A) 1991 The entire boulder is covered with Fucus sp., a gold-brown algae. Notice the darker species of seaweed forming an apron around the base of the boulder. The beach area surrounding the boulder (the “beach face”) is also completely covered with other seaweed species. In the water behind the boulder, healthy eelgrass (Zostera marina) bed is visible. The boulder’s condition appears to be improving, shown by the heavier covering of seaweed. (B) 1993 Fucus now covers about 20 percent of the boulder’s surface. Large, older plants are gone apparently replaced by young plants. Mussels are growing on the front face of the boulder (black regions). (C) 1995 About half of the mussels have disappeared, leaving smaller dark regions on the right side of the boulder. Fucus is making a comeback on the left side and top surface of the boulder. Also visible is an apparent resurgence of algal growth on the beach face. The disappearance of the mussels may be the result of predation (perhaps by sea otters) or natural mortality. Regardless of whatever caused the boulder’s plant life to die back in 1993-94, the boulder now seems to be supporting new plant and animal life. (D) 1997 The boulder is once again covered (about 80 percent) with the seaweed Fucus. There are several age groups of Fucus on the boulder. Young Fucus is growing over the top section of the boulder and adult Fucus is growing around the mid-portion. The beach face is again rich with seaweed. No mussels are visible and the areas occupied by the barnacles have shrunk. Starfish and sea otters may have been preying on the mussels, and a predatory snail, Nucella, has likely been eating the barnacles.