ABSTRACT
This study presents the development of an optical fiber pH sensor based on evanescent wave absorbance for continuous pH measurements in marine microenvironments. The sensing layer consists of an optimized sol-gel matrix of tetraethoxysilane and dimethyldiethoxysilane, which substantially improves the entrapment efficiency of the pH indicator meta-cresol purple, leading to a long useable lifetime. The optical fiber pH sensor conforms to the Global Ocean Acidification Observing Network "weather" measurement quality guideline with precision of approximately 0.02 pH units, has a dynamic pHT range of 7.4-9.7 in seawater, a response time of 2.5-6.5 min and a useable lifetime of 7 days. The optical fiber pH sensor has additional advantages of being self-referencing, without the need of an external sensor reference, having a simple fabrication method and basic spectrometer instrumentation. The suitability of the optical fiber pH sensor was demonstrated in real-time measurements of the ecologically significant green seaweed Ulva sp. The optical fiber pH sensor monitored pH variations due to metabolic activity over 7 days within the seaweed canopy and 4 days within the diffusion boundary layer interface, demonstrating the suitability for measurements in marine microenvironments.
ABSTRACT
"It takes a village to finish (marine) science these days" Paraphrased from Curtis Huttenhower (the Human Microbiome project) The rapidity and complexity of climate change and its potential effects on ocean biota are challenging how ocean scientists conduct research. One way in which we can begin to better tackle these challenges is to conduct community-wide scientific studies. This study provides physiological datasets fundamental to understanding functional responses of phytoplankton growth rates to temperature. While physiological experiments are not new, our experiments were conducted in many laboratories using agreed upon protocols and 25 strains of eukaryotic and prokaryotic phytoplankton isolated across a wide range of marine environments from polar to tropical, and from nearshore waters to the open ocean. This community-wide approach provides both comprehensive and internally consistent datasets produced over considerably shorter time scales than conventional individual and often uncoordinated lab efforts. Such datasets can be used to parameterise global ocean model projections of environmental change and to provide initial insights into the magnitude of regional biogeographic change in ocean biota in the coming decades. Here, we compare our datasets with a compilation of literature data on phytoplankton growth responses to temperature. A comparison with prior published data suggests that the optimal temperatures of individual species and, to a lesser degree, thermal niches were similar across studies. However, a comparison of the maximum growth rate across studies revealed significant departures between this and previously collected datasets, which may be due to differences in the cultured isolates, temporal changes in the clonal isolates in cultures, and/or differences in culture conditions. Such methodological differences mean that using particular trait measurements from the prior literature might introduce unknown errors and bias into modelling projections. Using our community-wide approach we can reduce such protocol-driven variability in culture studies, and can begin to address more complex issues such as the effect of multiple environmental drivers on ocean biota.
