The aquaculture industry lacks near-real time (NRT) support for their daily management decisions and for monitoring environmental parameters that may impact its activities. For that purpose, satellite remote sensing can be an effective tool as it can provide the necessary time and spatial resolution at reasonable costs.
Management actions (e.g. lowering cages, harvest, feed) change according to type of aquaculture (e.g. mussel, fish, seaweed), but, when considering monitoring purposes, there is a set of parameters that is common to the needs of the majority of aquaculture managers. All are interested in having information on weather and sea state conditions, as well as water temperature and chlorophyll-a (Chl-a) concentration data. The latter is seen as a relevant parameter to monitor as it can be used as a biomass proxy (i.e. food availability for mussels) or as an indicator of water quality. For weather and sea state conditions, instant information may be sufficient for real time management, however, temperature and Chl-a data have to be considered in the context of gradients and fluctuations in the environmental conditions for effective evaluation and decision making. It is therefore crucial to evaluate the natural variability of these parameters. For that purpose, within the AQUA-USERS project, 10 years of satellite data were processed for all the sites of interest and regional-specific time-series were determined. Threshold values were established based on deviations from the calculated baselines and should provide alert conditions to site managers.
Daily temporal series of Chl-a concentrations derived from MERIS full resolution (300 m × 300 m) observations, from 19 July 2002 to 8 April 2012, were isolated for each region. After quality control, for each time-series the 10th, 50th, and, 90th percentiles, the average and the standard deviation, were computed for each 7 days of the year. Each of these statistics was further filtered using a harmonic fitting (using 50 harmonics, i.e., an approximation to the 52 weeks that compose the year). An example is presented for the Danish site.
Information on marine environmental parameters like Chl-a is essential to monitor water quality, not only for aquaculture managing, but also to comply with environmental directives and to evaluate aquaculture impact in the surrounding media. The Chl-a 90 percentile (P90) has been recommended as an indicator of eutrophication in European coastal waters and different studies have highlighted the effectiveness of using ocean-colour remote sensing data with that purpose. The monitoring of areas relative to their natural variability should alert to abnormal conditions, eventually undesirable noxious blooms. The figure below exemplifies the applicability of the thresholds derived based on climatology in the detection of HABs. Two historical bloom occurrences were analysed, to check if the corresponding Chl-a records would be identified as an anomaly. A bloom of the toxic dinoflagellate Lingulodinium polyedrum that occurred in the coast of Algarve, on the 17 of August 2004, which attained 1x106 cells/L. Although no Chl-a measurements were taken in situ, according to pigment results obtained in cultures, this cell concentration would correspond to a Chl-a range of 12-20 mg m-3, which should be added to an unknown value for the rest of phytoplankton community (Brotas et al. 2014). The second, a Karenia mikimotoi bloom occurring off Cornwall in June 2010, with a cell abundance of 1x106 cells/L (Kurekin et al. 2014). In both cases, pronounced Chl-a anomalies were found.
The climatological data with respective statistics information and thresholds will be implemented in the AQUA-USERs app and users will be able to compare NRT Chl-a measurements with climatological data to support their management decisions.
Brotas V., Couto A.B., Sá C., Amorim A., Brito A., Laanen M., Peters S., Poser K., Eleveld M., Miller P., Kurekin A., Groom S., Åtland Å, Dale T., Sørensen K., Ledang A.B., Boye-Hansen L., Huber S., Kaas H., Andersson H., Icely J., Fragoso B. (2014) Deriving Aquaculture indicators from Earth Observation in the AQUA-USERS project (AQUAculture USEr driven operational Remote Sensing information Services), Ocean Optics, Portland, Maine, Oct-2014.