Nearshore Periphyton

Deploying growth surfaces for periphyton at different depths and distances from the shore. The periphyton colonized and grew on the surfaces during two months of spring, their peak growing season. At the end of the experiment, the taxonomy and quantity of algae was assessed from nearly 80 substrate surfaces.

The outcome of a visual growth assessment is shown below. A rating of 5 indicates that the algae colonizing the substrate grew to a large mass that included filamentous strands. By contrast, surfaces exhibiting a rating of 1 had no visible algae and did not feel slick with a biofilm.

The results showed that periphyton growth is highest at the surface, toward the nearshore. The growth toward the surface was not unexpected, as the periphyton require light to photosynthesize. What was surprising was the Level 3 growth at depths down to 40 m (130 feet). Also surprising was the observation that conditions favoring
high growth (Level 3 and 4) extend to over 500 m (1,650 feet) from the shore,
corresponding to a depth at this west shore site of about 100 m (330 feet).

These findings help researchers better understand the sources of nutrients that are driving excess periphyton growth in the nearshore. With this information we can better advise agencies about the best strategies for managing the nearshore environment.