Visitors walking along North Broulee Beach recently may have been shocked by the huge amount of reddish, stringy algae washed ashore. However, locals recognize it as a regular natural occurrence in the cooler months.
The alga appears to be a type of Gracilaria. There are over 150 species of this seaweed worldwide. Some are cultivated for agar production, others are used in Asian food and some are poisonous to humans.
Blooms of a related species have been studied in Jervis Bay along with other drifting algae. Gracilaria appears to be attached loosely in soft sediment for part of its complex life cycle. However, when detached by waves or currents it drifts in the clear, sheltered water of the Bay and continues to grow where it can get enough light and not be too broken up by waves. Sometimes nutrients in the water increase allowing the seaweed to grow rapidly. The most likely explanations for the blooms were groundwater entering the Bay or upwelling of richer ocean water.
The blooms are a natural event and not a form of pollution. In Jervis Bay a red alga, now thought to be Gracilaria, clogged the nets of an experimental trawl done in 1898, long before much human impact on the Bay.
As in other years, the seaweed masses stranded at North Broulee will gradually be mixed into the sand, decompose and help feed and shelter the myriad of shore creatures.