Macroalgae (Seaweeds) Blooms
Macroalgae, recognized by most citizens as seaweeds found along the intertidal shores and just below the low tide mark of the waters of Narragansett Bay, are an important component of a healthy Bay ecosystem. They provide both food and vital habitat / shelter to many marine animal species in the Bay. However, when nutrients become excessive (especially nitrogen), certain species of seaweeds, often called "nuisance" seaweeds, begin an explosive growth phase in summer months, often coating shallow areas with a carpet of sometimes rotting seaweed. These are often green seaweeds (from the phylum Chlorophyta), with the most common culprit being Ulva sp., known as "sea lettuce", although other species groups can and do occur in significant amounts. The complaints of foul odors (due to hydrogen sulfide coming from bacterial decay) at low tide in the upper Bay are often linked to carpets of this and other species of algae rotting in extreme hot summer temperatures.

One survey of macroalgae in the Bay was completed in 1988, but no one has been tracking baywide distributions since that single survey. In 2002, the NBEP began photographing the macroalgae cover along the URI Bay campus shoreline, and in 2004, we initiated underwater video transect surveys of various areas of the upper Bay and Greenwich Bay to better track the distribution of nuisance (and other) dominant macroalgae because they are linked to high nutrients. Video footage over the summers of 2004 and 2005 indicated that such underwater transects provided a very limited perspective on the large-scale distribution of nuisance macroalgae.

In 2006, NBEP scientists began utilizing the state helicopter to conduct photographic surveys of summer month macroalgae cover along the Providence and Seekonk tidal Rivers and the western shore of Narragansett Bay to the mouth of the Narrow River, Narragansett, RI .  This project is a collaboration with Dr. Giancarlo Cicchetti of the USEPA AED laboratory of Narragansett RI and the R.I. Airport Corporation.  The USEPA provides oblique (angled) 12 mega pixel digital pictures taken every 10 seconds from a height of 400-500 feet as we follow the shoreline contour during these flights. The results to-date have been fabulous photos which are analyzed for relative density of green, red and brown macroalgae (photo interpretation conducted by the NBEP staff) between June and September in these areas.  This data is then used to develop GIS maps of relative density for the 3 seaweed groups (click here to view maps). We expect these data will be useful to track changes to nuisance macroalgae populations in the future as nutrient levels are better controlled.

The results to-date have been fabulous photos and have also become the basis for a dataset categorizing density of green, red and brown macroalgae (photo interpretation conducted by the NBEP staff). We expect these data will be useful to track changes to nuisance macroalgae populations in the future as nutrient levels are better controlled.