Robotic glider reveals giant phytoplankton chains in Mediterranean Sea

Scientists from Scripps Institution of Oceanography at UC San Diego and the Mediterranean Institute of Oceanography in Marseille have documented giant chains of phytoplankton in the Mediterranean Sea using a robotic glider called the Zooglider. The instrument, invented at Scripps in 2019, carries a high-resolution camera, sonar, and an underwater microphone, allowing it to glide silently and photograph marine life without disturbing the water column.

The study, published in Limnology and Oceanography Letters, found chains of diatoms such as Guinardia and Proboscia exceeding 10 millimeters in length — far larger than specimens captured by conventional nets and water bottles. Researchers determined that traditional sampling tools break these fragile structures, leading to systematic underestimation of their true size.

Because the chains are too large for most zooplankton to consume, they may bypass the usual grazing pathway and sink directly to the deep ocean floor. This mechanism could alter the transport of carbon and nutrients through the marine food web and affect estimates of the ocean's biological carbon pump.

Lead author Mark Ohman of Scripps said the finding challenges historical perspectives on phytoplankton size structure and trophic dynamics. The team believes similar giant chains likely exist throughout the global ocean but have remained undetected due to methodological limitations.

The Zooglider's noninvasive imaging capability provides a new way to observe delicate planktonic organisms in their natural state. The researchers suggest that in situ imaging will be essential for revising models of ocean productivity and carbon cycling.