An investigation of methods for sampling microbial films on rocky shores

Abstract

Chlorophyll analysis and methods of direct observation of rock surfaces under the SEM were used to estimate composition and abundance of epilithic microbial taxa. Effectiveness of different chlorophyll extraction techniques was assessed. Extraction from ground and intact rock was compared using both hot methanol and acetone extraction methods. Hot methanol extraction from intact rock provided the most accurate and precise estimates of chlorophyll content. SEM preparation methods were compared. Microbial taxa were counted under the SEM from cryostage, critically point dried and air-dried material. It was concluded that air drying was the most appropriate preparation method for SEM observation. Air drying provides reasonable estimates of microbial composition and abundance and was less time consuming so allowing an adequate number of samples to be analysed. Cumulative species number with sampling effort curves were used to establish minimal sample sizes with respect to estimates of species number. Sequential estimates of mean abundance with increasing sample size were used to determine the effects of increasing sample size on estimates of abundance of the dominant taxa. These estimates were compared at different times of the year and for two different locations. Microbial communities were found to be extremely patchy in distribution. However, sample sizes required to give good estimates of taxa number and abundance were established. These estimates were found to be similar for the main taxa at different times of the year and at different locations.

Microspatial variation in marine biofilm abundance on intertidal rock surfaces

“…The present study suggests that the interaction between grazing by different molluscan species and rock surface roughness contributes to small-scale patchiness within rocky intertidal communities (Hill & Hawkins 1990) in Hong Kong. As such, grazers and their interaction with physical surface structures may be responsible for a larger amount of variation in distribution and abundance of species than is presently thought, and their accumulated impact may influence larger-scale community patterns on these shores.…”

Intertidal biofilms on rocky substratum can play a major role in estuarine carbon and nutrient dynamics

“…Extraction was performed in a mixed solution of acetone, methanol and water (45:45:10 ratio, respectively), according to Joye et al (1996). Also, Hill & Hawkins (1990) found that methanol extraction is a more accurate and precise method than acetone extraction to estimate chlorophyll content in intact rocks. Chl a concentration was determined spectrophotometrically, using standard equations (Parsons et al 1984).…”

Bioeconomics of foraging route selection by limpets

“…For example, in NE Atlantic benthic communities, where Patella vulgata predominates, patchiness seems to be a common feature at different spatial scales (review in Hawkins et al 1992), including a small scale comparable with that experienced by individual limpets while foraging (e.g. Hill & Hawkins 1990, 1991. The general environmental characteristics of these shores seem to be comparable with conditions promoting rule-based behaviour over random choice.…”