Solar panels cut light by 80% in sea cucumber ponds, but what happened to sea cucumbers surprised scientists

Solar panels installed over sea cucumber ponds in China may do more than generate renewable electricity. A study published in ScienceDirect found that photovoltaic panels significantly reduced sunlight reaching the water and lowered pond temperatures, creating cooler conditions during summer. The changes were associated with a predicted shorter aestivation period among sub-adult sea cucumbers, although researchers stressed that the 12-day difference was calculated from temperature thresholds rather than directly observed.

The research, titled “Integrating photovoltaic with sea cucumber aquaculture: Environmental impacts and holothurian digestion and aestivation”, examined whether combining photovoltaic generation with aquaculture could influence both farming conditions and the wider pond ecosystem.

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Solar panels cut light and lower pond temperatures

Researchers studied sea cucumber ponds in China’s Yellow River Delta where photovoltaic systems had been integrated into the farming setup.

The solar installation had a capacity of 200 MWp and covered 40% of the pond surface. Three ponds equipped with photovoltaic panels were compared with three ponds without them. Each pond covered about 6.7 hectares and had an average depth of 1.5 metres.

Environmental conditions were monitored monthly from March 2023 through February 2024, allowing the researchers to compare conditions across different seasons.

The panels produced substantial shading over the water. According to the study, light intensity in shaded areas fell by an average of 80.5%, while water temperature was 1.20°C lower than in ponds without photovoltaic systems.

Researchers then examined whether those physical changes were reflected in the physiology and summer behaviour of the farmed sea cucumbers.

Younger sea cucumbers showed a larger predicted change

The study focused on Apostichopus japonicus, a species that is sensitive to elevated temperatures and can enter aestivation during summer.

During aestivation, sea cucumbers become less active and reduce feeding as they respond to heat. Researchers estimated how long this period could last by applying temperature thresholds to the pond data.

For adult sea cucumbers, temperatures above 25°C were used in the calculation. For sub-adults, the threshold was 29°C.

The resulting estimates were relatively similar for adults. Their predicted aestivation period was 114 days in ponds without photovoltaic panels and 113 days in ponds with them.

The difference was more pronounced among sub-adults. Their predicted aestivation period fell from 62 days in non-photovoltaic ponds to 50 days in photovoltaic ponds.

That represents a 12-day reduction in the predicted period for younger sea cucumbers. However, the researchers did not directly observe sub-adult sea cucumbers ending aestivation 12 days earlier. The difference was derived from temperature-based calculations.

The researchers suggested that spending less time in aestivation could potentially create more favourable conditions for growth.

Solar panels also changed parts of the pond ecosystem

The effects were not limited to temperature and light. Researchers also examined plankton, sediment and digestive enzyme activity in the sea cucumbers.

The study found no significant change in the types of plankton present and no effect on the digestive enzyme activity of the animals.

However, some differences emerged in the shaded photovoltaic ponds. Zooplankton abundance declined, while Pyrrophyta, a type of phytoplankton, became more prevalent during spring.

In the photovoltaic ponds, Pyrrophyta accounted for an average of 57.9% of the phytoplankton during that period.

The researchers also recorded lower levels of organic matter in sediment beneath the panels.

These changes indicate that photovoltaic installations can alter more than the amount of heat and light entering the ponds. Changes in plankton and sediment conditions could also influence food availability and other parts of the aquaculture ecosystem, which is why the researchers emphasised the need for continued monitoring.

Could aquavoltaics help sea cucumber farming?

The findings point to a possible dual benefit from integrating solar generation with aquaculture.

According to the study, photovoltaic panels can produce renewable electricity while simultaneously creating a darker and cooler environment underneath. That could be relevant for sea cucumbers, which prefer low-light conditions and can seek shelter from heat.

By reducing the amount of solar radiation reaching the water and lowering temperatures, the panels may help reduce heat exposure during the hotter months.

At the same time, the researchers cautioned that modifying the pond environment could have longer-term consequences. Changes in plankton communities, zooplankton abundance and sediment organic matter need to be monitored to determine how the system develops over time.

The study therefore presents aquavoltaics as a potential way to combine energy generation with changes in aquaculture conditions, while highlighting that the ecological effects require further observation.