Ascophyllum nodosum is a phaeophycean, or brown alga. Since it is a photosynthetic organism, it has light harvesting pigments. In addition to chlorophyll a, it also possesses the accessory pigments chlorophyll c and fucoxanthin. Fucoxanthin not only gives the alga its olive green color, but also absorbs green and yellow light, allowing brown algae to be found in slightly deeper waters than green alga (Bertness, p.43). It is a slow growing, long lived alga that accumulates gas bladders annually, which allows for it to be aged easily. A. nodosum is found in protected open-coastal areas of the rocky intertidal, found as far south as Long Island Sound (Keser, 2005) and as far north as Nova Scotia, Canada.

Ecology of Atlantic Shores students conducting field research at Northeastern University's Marine Research Center in Nahant,Massachusetts

Due to its large size and the canopy it creates, it is an important protector of sessile intertidal organisms. Barnacles and mussels, as well as other algae, live in close proximity with A. nodosum. It provides them protection from predation and environmental stresses, like desiccation by holding in moisture (Bertness, p. 229). In addition to providing refuge for intertidal organisms, A. nodosum adds to the shallow water’s oxygen budget (Stengel, 1997).

Clearly Ascophyllum is an important contributor to the intertidal community, but what makes this alga unique is its ability to live throughout the different zones of the intertidal, and thus, experience a wide range of environmental factors. Organisms that span the intertidal must be able to deal with conitions associated with both low and high tides. Low tide includes aerial exposure which can lead to drastic temperature fluctuations and desiccation and during high tide they are fully submerged. This study examines morphological and physiological differences of between Ascophyllum nodosum from three different intertidal zones: upper, middle, and lower. The parameters of this study include: total height, annual growth, age, and pigment concentrations of the algae. The purpose is to determine if there are differences in these parameters depending on intertidal zone.