Biofilm diatom community structure: Influence of temporal and substratum variability

Abstract

Diatoms, which are early autotrophic colonisers, are an important constituent of the biofouling community in the marine environment. The effects of substratum and temporal variations on the fouling diatom community structure in a monsoon-influenced tropical estuary were studied. Fibreglass and glass coupons were exposed every month for a period of 4 days and the diatom population sampled at 24 h intervals, over a period of 14 months. The planktonic diatom community structure differed from the biofilm community. Pennate diatoms dominated the biofilms whilst centric diatoms were dominant in the water column. Among the biofilm diatoms, species belonging to the genera Navicula, Amphora, Nitzschia, Pleurosigma and Thalassionema were dominant. On certain occasions, the influence of planktonic blooms was also seen on the biofilm community. A comparative study of biofilms formed on the two substrata revealed significant differences in density and diversity. However species composition was almost constant. In addition to substratum variations, the biofilm diatom community structure also showed significant seasonal variations, which were attributed to physico-chemical and biological changes in both the water and substratum. Temporal variations in the tychopelagic diatoms of the water were also observed to exert an influence on the biofilm diatom community. Variations in diatom communities may determine the functional ecosystem of the benthic environment.     

Quantification of diatoms in biofilms: Standardisation of methods

Abstract

Benthic diatoms, which often dominate marine biofilms are mostly pennate along with a few centric species that have an attached mode of life. Even though the range of diatoms in biofilms is diverse, their ecology is poorly understood because of the difficulty in sampling and enumeration. Scraping or brushing are the traditional methods used for removal of diatoms from biofilms developed on solid substrata. The method of removal is the most critical step in enumerating the biofilm diatom community structure. In this study, a nylon brush and ceramic scraper were used as tools for the removal of diatoms from 1 – 4-day-old biofilms developed on fibreglass coupons and glass microscope slides. Standardisation of methods showed that the sample volume used in the analyses had the least influence on the quantification, whereas the method of removal was critical. The nylon brush was more efficient at recovering diatoms compared to a ceramic scraper. Direct microscopic enumeration of the community in the case of glass slides indicated that scraping resulted in between 30–50% underestimation. Heterogeneity in diatom community structure between replicate samples is one possible reason for such underestimation.