Composition and Spatial Relationships of Algal Wrack on a Mixed Substrate Beach Exposed to Moderate Wave Action: Cattle Point, WA

Abstract

Algal wrack serves as an integral component of the high intertidal zone. As a primary producer it contributes organic matter that may be utilized as a habitat and/or food source for a variety of wildlife. A vital resource in marine environments, it connects marine and terrestrial ecosystems and serves a variety of anthropological usages. Much of the research that investigates the ecological significance of algal wrack focuses on its prominence on sandy beaches, however there is little inquiry regarding other substrate categories. Moreover, composition and spatial distribution of the wrack have rarely been described. To address these deficits, we conducted a survey at Cattle Point, WA, on a small sand-and-gravel beach exposed to moderate wave action. Our aim was to gain a better understanding of the composition and spatial relationships of composition and individual blade size. We employed two sampling methods and then compared them in order to determine which method was most effective in describing characteristics of the wrack. Our results indicated that composition was consistent between sampling methods. Kelps were the most frequent algal group in the wrack, followed in descending abundance by filamentous reds, red blades, sea grasses, and greens. Additionally, we found no significant relationship between algal type or algal scrap size and position on the beach. When comparing sampling methods, we found that the two methods returned fairly consistent results regarding algal composition as well as similarly variable results regarding spatial relationships attributed to algal type/scrap size. We believe that more data and broader sample areas may address these shortcomings and give a more comprehensive picture as to algal wrack and its ecological significance on underrepresented sand-and-gravel beaches with moderate wave exposure. Nevertheless, our survey provides context for ecological relationships on the San Juan Islands.