Final answer:
Seagulls are likely to be the relatively rare organisms on a rocky shore compared to algae, crabs, and barnacles which are well-adapted to this environment.
Step-by-step explanation:
Out of the given options which include algae, seagulls, crabs, and barnacles, the organisms expected to be relatively rare on a rocky shore would likely be seagulls. Algae, crabs, and barnacles are all well-suited to life on rocky shores. For instance, barnacles secrete a substance to anchor themselves to rocks, while certain algae are common in the intertidal zone and crabs are versatile crustaceans found in various environments, including rocky shores. Seagulls, on the other hand, are less dependent on the intertidal zone for survival and are often more mobile, searching for food over wider areas.