Thursday, 3 April 2014

Remote Sensing for Oceanic Microbes

Grimes et al. (2014) discuss methods of observing Vibrios’ and Cyanobacteria using remote sensing, discussing the environmental drivers associated with such monitoring. They also discuss its applications and significance with reference to multiple case studies.

Most data is recorded passively by satellites using the colour sensors (recording light/heat) to detect changes blooms (i.e. monitoring chlorophyll types/auxillajry pigments).

Remote sensing is ultimately easier, quicker, and cheaper way of gaining information than research vessels, though it’ findings currently need to be validated by such means.

A limitation of remote sensing is that about 90-95% of light detected by the sensor is light scattered by the atmosphere and not of oceanic origin, and must be extracted. This is considerably harder in coastal waters due to the heterogeneity of the water content, and the atmosphere surrounding it. This issue remains one of the biggest uncertainties surrounding remote sensing.

A further complication is that certain measurements are easier to make with remote sensing than others. For instance sea surface temperature (SST) is relatively easy to measure, while sea surface salinity cannot be measured closer than 200km to the coast. Developments in satellite technology i.e. the GEO-CAPE planned for US coastal waters, with higher spatial resolution will likely allow for coastal measurements, hopefully allowing more accurate predictions of blooms and vibrios proliferation.

A common and well known vibrio that remote sensing is used to detect is Vibrio cholorea. Most of the work concerning this organism has taken place in the Bay of Bengal but other promising research in east and South Africa has shown interesting results.  Research shows that just one environmental variable used to estimate blooms isn’t completely accurate and that it is only used as an indicator of blooms. However work in East Africa has shown sea surface temperatures to have less than a month lag when predicting V. cholerae blooms. Studies have shown that the occurrence of V. cholerae are associated with up welling of cold water and with increased run off from rivers containing terrestrial nutrients.

Combined with data for viewing Vibrio parahaemolyticus, for which SST is also a primary environmental driver the general conclusion for this kind of data is for use as an early warning system for outbreaks of such pathogens. In the case of V. parahaemolyticus studies have been undertaken combining remote sensing data with the continuous plankton recorder data (1961-1995), (amongst other such surveys) in order to give estimations for future levels of vibrio with rising sea temperatures. This is of particular importance for areas such as Northern Europe which has the some of fastest rising temperatures (studies concerning Vibrio vulnificus).

Other applications of remote sensing include the detection of ocean colour which can help understand the role of ocean picoplankton populations in the global carbon cycle. Achievement noted in this area include differentiation of Trichhodesmium from clouds, the characterisation of Nodularia (a cyanobacteria associated with two nasty toxins) and understanding of its formation and migration, and detecting Mycrocytis in lakes which has implications with drinking water safety.

In other cases Bioluminescence of Vibrio harveyi can be used for mapping chemical contamination on a coastal scale using a bioluminescent to total bacteria scale. There is no published literature on this but satellites exist are likely able to be applied to this type of work. Harmful algal blooms have also been detected for many years, helping to warn of harmful toxins produced by them for coastal communities.

Remote sensing can be a powerful tool in microbial ecology. Studies can be combined with it to give building region specific predictive models for HABs and pathogen out breaks, and the influence of climate change upon them. New technologies and cooperation of international institutions will hopefully  further enhance our understanding of oceanic diseases and improve public health.

Grimes, D. J., Ford, T. E., Colwell, R. R., Baker-Austin, C., Martinez-Urtaza, J., Subramaniam, A., & Capone, D. G. (2014). Viewing Marine Bacteria, Their Activity and Response to Environmental Drivers from Orbit. Microbial Ecology, 1-12.

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