Blooms of bryozoans and epibenthic diatoms in an urbanized sandy Beach (Balneário Camboriú - SC - Brazil): dynamics, possible causes and biomass characterization

Abstract

Balneário Camboriu (SC - Brazil) is a touristic city where the disordered growth of the urban population and the implementation of coastal works without proper evaluation generated environmental impacts and affected the sanitary quality of water and sediment of Camboriu River and marine adjacent area. One of the most recent and alarming phenomena observed are the blooms of invasive bryozoans (Arboscuspis bellula and Membraniporopsis tubigera) associated with epibenthic diatoms (Amphitetras antediluviana and Biddulphia biddulphiana). Several clues associate these phenomena, started in 2003, with the excess of nutrients and organic matter in the Camboriú cove and large coastal works such as dredging, landfills and construction of jetties, leading to changes in benthic ecological structure. Being an aesthetic and environmental health problem, the concern of the scientific community and government agencies intensified as the occurrences become more frequent and persistent. This research addresses this issue through environmental and experimental studies. Samplings of the benthic material collected by boat and diving, and blooms monitoring were the environmental approach. The laboratory work included the algal isolation and culture, in addition to growth conditions assessment and chemical biomass analysis. Monitoring data showed a seasonal trend in the blooms, with more conspicuous events in warmer months. Diatoms increase in abundance in colder months and bryozoans in the warmer ones. The diatom A. antediluviana, predominant in the blooms, grew satisfactorily in laboratory cultivation, showing better growth in media with higher concentrations of silicate and phosphate. Bryozoans showed slow growth in laboratory conditions. The deposited material collected in the environment showed low concentrations of saturated fatty acids, but the high biomass suggest a possible use for biofuels production. Biomass samples dominated by bryozoans showed moderate antimicrobial activity against Klebsiella pneumoniae. The explanation for the occurrence of these blooms are still inconclusive, but there is considerable evidence that it is a synergistic effect between the high concentration of bacteria and organic debris in the water related to local pollution and the elimination of natural competitors by coastal works.