Got Microbes?

Sophia Kruger measures canopy cover over a pool of the San Miguel River

Study by Sophia Kruger, Logan Goettl, Madison Deile.

With climate change continuing to produce heavy rainfalls and extreme weather events that alter the composition of water sources, water contamination concerns remain. Within the Cabo Blanco Nature Reserve exists a freshwater to saltwater gradient as the San Miguel River flows into the Pacific Ocean, providing an ideal environment for a controlled study on water quality through the analysis of microhabitat bacterial content. Stemming from interest as to how salinity may influence bacterial count, this study questioned how environmental factors affect the bacterial count of eight microhabitats ranging in distance from shore. We hypothesized that microhabitats with greater leaf litter coverage would produce higher bacterial richness and abundance due to additional micronutrients available from decaying organic matter, whereas a higher algal content would produce the opposite in response to competition for sunlight. Also, we anticipated microhabitats of higher salinity would produce lower bacterial richness overall. Across these microhabitats, three BioPaddle samples were taken from water sources and other aquatic surfaces (rocks, alga, and submerged leaves). Percent leaf litter cover, canopy density, algal count, temperature, pH, and salinity were measured across freshwater and marine standing water pools. All samples from the river and tide pools had microbial growth, including Staphylococcus and E. coli. After analyzing the relative bacterial species richness and bacterial abundance on the agar samples in relation to percent leaf litter and percent algal area of the pools, we found that neither richness nor abundance was significantly correlated with either leaf litter coverage or algal cover. Additionally, the relationship between bacterial richness and salinity and richness and canopy density were not statistically significant. However, microbial richness was significantly higher in river habitats compared to tide pools. Also, the amount of microbial growth was higher on the surfaces of rocks and leaves than it was in open water. Further analysis considering other water composition factors and species interactions beyond those of the hypotheses tested has the potential to further explain our findings.

Biopaddles showing growth of Staphylococcus (top) and Pseudomonas (bottom) bacteria from a river sample.