Effect of sampling time on the heavy metal concentrations of brown algae: A bioindicator study on the Arabian Gulf coast.

Macroalgae have often been studied as bioindicators for heavy metal pollution on sea coasts including the Arabian Gulf. On the Arabian Gulf coasts, heavy metals are continuously being released by industrial activities and therefore, pollution monitoring is needed. Biomonitoring studies using macroalgae has given highly different assessments due to the variability in algal species and sampling time points. We carried out a systematic monthly sampling of brown algae (Phaeophyta) from three locations on the western coast of the Arabian Gulf between September and February 2018. One urban area (Uqair) and two oil refining areas (Ras Tanura and Jubail) were monitored due to they have a common brown macroalgae species composition. The incidence of Cystoseira myrica, C. trinodis C. osmundacea, Hormophysa cuneiformis, Sargassum aquifolium, S. latifolium, S. filipendula and Padina boryana varied among the sites and with the time of year within the sites. The concentrations of Co, Cd and Pb varied among the sampling sites, the algal species and the sampling time points remarkably. A tentative time-trend increasing towards February was observed for some species. However, it appeared that neither optimum sampling time point, nor superior brown algae species could be recommended. The highest heavy metal accumulation was observed in Padina boryana. However, this species grew only on the two oil polluted sites. We concluded that some brown algae species can be used for biomonitoring heavy metal pollution on the western coast of the Arabian Gulf. The species incidence should be monitored systematically and the species used should be chosen locally and sampled at the same time of the year.