Photovoltaics for sea cucumber aquaculture

Scientists in China have conducted a year-long study on six "aquavoltaics" farms hosting sea cucumber aquacultures under the solar panels. Due to the lower water temperature, the hibernation period of the animal was reduced, as was mortality, compared to the previous year.

Researchers from China have conducted a year-long investigation into the impact of PV farms on sea cucumber aquaculture.

Using the structural equation modeling (SEM) statistical technique, the group collected information from six similar ponds used for the commercial growth of the Apostichopus Japonicus sea cucumber species. Three of them, called PVP, were partly covered with PV panels (PVP), while the other three were not covered at all and were labeled nPVP.

“As an important economic species in the world, sea cucumbers have high nutritional and medicinal values, which are often in short supply in the consumer market,” the researchers explained. “By installing PV arrays above and cultured sea cucumbers below, this integration may address some of the issues in sea cucumbers pond aquaculture: the shading effect from the PV panels will reduce the water temperature in the ponds, potentially preventing sea cucumbers summer high-temperature mortality; and the cooling from shade may shorten the aestivation duration of sea cucumbers.”

The integration of solar power with aquaculture is often called “aquavoltaics.” The aquavoltaic station where the research was done is located in the east of China, in the Yellow River Delta. It spanned approximately 4.28 km², with 40.0% of the pond area covered by PV. The station has a total capacity of 200 MW, with the PV modules being placed with an azimuth angle of 0◦, and a tilt angle is 37◦. The panel height relative to the water changes with the season, but at no point is it less than 1.5 meters.

Each of the six studied ponds had an area of about 6.7 hm2, with an average water depth of 1.5 m. Monitoring took place between March 2023 and February 2024, using different sensors. In addition, water samples were taken from three random sites established along the diagonal of each pond. A sample of three to five individuals of sea cucumbers was randomly selected from each pond, weighed, dissected, and preserved at -80 C.

“SEMs were constructed using the piecewise SEM package in R. Initially, correlations between all parameters were analyzed to hypothesize the pathways of interaction between parameters for model design and optimization,” the academics explained. “The final optimized model, which included the most variables and significant paths (p<0.05), with the lowest akaike information criterion (AIC) scores, was assessed for goodness-of-fit using chi-square statistics.

Per the research results, the PV coverage had significantly reduced light intensity and water temperature. Compared with the nPVPa, light intensity in shaded areas of the PVPs was reduced by 80.5%, resulting in a drop of 1.20 C in water temperature. The duration of aestivation – a state of hibernation the sea cucumbers undergo when water temperatures become too high – was also reduced in the PVP. In sub-adult sea cucumbers, it was reduced by 12 days and in adults by one day.

“Sea cucumbers yield data from 2023 indicated a higher productivity in the PVP group (900kg/hm²) compared to the nPVP group (750kg/hm²), based on farmer-record,” the academics added. “However, the data were sourced from external records and were not directly monitored by us, thus their accuracy and validity cannot be fully guaranteed.”

Additionally, the analysis found that PV integration did not negatively impact other physical and chemical parameters, plankton composition, or sea cucumber digestive physiology. “However, the seasonal increase in Pyrrophyta, and the reduced in zooplankton abundance, emphasize the need for continued ecological monitoring to avoid potential cascading effects on ecosystem stability and aquaculture productivity,” they emphasized.

Their findings were presented in “Integrating photovoltaic with sea cucumber aquaculture: Environmental impacts and holothurian digestion and aestivation,” published in Aquaculture Reports. Researchers from China’s Chinese Academy of Sciences, the Qingdao Marine Science and Technology Center, Ludong University and Yantai University have conducted the study.