Study unravels how ocean warming impacts early development of Giant Kelp, can aid conservation

Ocean warming disrupts early-stage development of Giant Kelp, the largest marine algae that are intrinsic to sea life, leading to rapid decline in kelp forests across the world, a new study found. 

The world has lost much of its kelp forests in the last century to rising sea temperatures, but the mechanism of deterioration was not fully understood by scientists. 

The new report by researchers at the University of Otago, New Zealand sheds light on the process of thermal impact and can help devise efforts to conserve the seaweed, the authors noted. It was published in the PLOS One journal December 8, 2022. 

The Giant Kelps reproduce by releasing single-cell units called spores that grow into ‘germ tubes’ that gather nutrients and develop into adults. 

At higher temperatures, spore release increased but “spore settlement, germination and germ-tube length” were negatively impacted, the researchers found. The decline of each part was significant at temperatures above 23.8 degrees Celsius, 21.7˚C, and 19.8˚C respectively, the authors noted in the report. 

To arrive at the findings, the scientists measured spore release, survivorship, germination and growth over five days “across 10 temperature treatments ranging from 9.5 to 26.2 ± 0.2°C”. 

They observed the following outcomes: 

• Spore production at 26.2°C was significantly greater than at temperatures 21.7°C and below
• Spore settlement was the lowest at 26.2°C and highest at 21.7°C
• Germination of spores reduced significantly above 19.8°C and was around 1 per cent above 23.8°C
• Around 98 per cent of viable cells had not germinated under the 23.8°C treatment and remained at the spore stage; complete mortality of cells occurred at 26.2°C

There was a significant interaction effect between temperature and time on germ-tube growth. No germ-tube growth was recorded in the 26.2°C treatment as all cells had perished. But below 21.7°C, average germ-tube diameter at day five was significantly greater than that at day one 

In the last 30 years, sea surface temperatures have gone up by 0.13°C per decade and oceans are expected to heat up by 1-3°C by the turn of the century, the scientists wrote. This condition threatens existing kelp forests as well, they warned.

These large, fleshy brown algae are found along much of the world’s coastline. They nourish and shelter thousands of marine species. In the healthy state, they act as carbon sinks. 

But as they are damaged, they release much of the sequestered carbon into the atmosphere. 

Understanding the thermal threshold of spore and germling life stages of giant kelp is key for making predictions of how such a valuable ecosystem engineer will perform in decades to come, said Matthew Desmond from the department of marine science of the University of Otago.