Some sea slugs use sunlight for energy, just like plants

Casual observers often overlook sea slugs, yet some species hide astonishing traits that challenge our expectations. One remarkable example is Elysia chlorotica, a small sea slug that produces energy from sunlight.

“It’s unique; it’s controversial; it’s elusive; it never eats,” said Dr. Patrick Krug of California State University in Los Angeles (CSU). This slinky slug steals tiny green structures from inside algal cells and uses them to produce energy from sunlight. 

Sea slugs living on sunlight

All plants contain chloroplasts that convert sunlight into energy. Most animals depend on regular meals to survive. However, by retaining chloroplasts from algal cells, Elysia chlorotica can photosynthesize for months without typical feeding.

“We demonstrated that a nuclear gene of oxygenic photosynthesis, psbO, is expressed in the sea slug,” wrote Mary E. Rumpho, a biochemist involved in a 2008 study.

Researchers have shown that these stolen chloroplasts keep running inside the slug, even though vital genes usually reside in the original algal cells. 

Probing deeper into this bizarre fusion of plant-like capabilities and animal physiology may help experts see how genes could move between species. That possibility intrigues many in the scientific community because it suggests a hidden path for adaptation.

Shrinking sea slug habitats

Although these slugs captivate researchers, actually finding them is tricky. Shifting coastlines, development, and habitat changes might be shrinking their marshy homes.

Some specialists note that high tide fluctuations and coastal erosion can wipe out the algae on which these creatures depend. Others point out that a combination of warming waters and pollution could intensify threats to their survival.

Only a handful of scientists have tried to unravel these secrets, and many have since retired or pivoted to other projects. As the number of experts declines, so does the knowledge pipeline for these unusual mollusks.

Mysteries of photosynthesis in sea slugs

The biggest mystery is how the sea slug’s own cells refrain from attacking foreign chloroplasts. Animals typically react to invaders, yet this species tolerates them in ways not fully understood.

Another question concerns the slug’s ability to deal with the free oxygen radicals generated through photosynthesis. Normally, this process is toxic to animal tissue, but these leaf-like wanderers seem to sidestep the damage.

Experiments have hinted that certain immunological tweaks may help the slugs coexist with these solar components. Some researchers suspect molecular signals borrowed from algae might give the slug an edge.

Dwindling population makes research difficult

Some who once pursued this slug have turned their attention to more readily available species. Collecting enough specimens for robust studies has become increasingly difficult, which limits progress.

The researchers note that raising these sea slugs in the lab is challenging. The adults, which usually live less than a year, require attentive care to reproduce. Their eggs hatch into free-swimming larvae that feed on various types of algae.

As they mature, however, the young slugs switch to eating Vaucheria litorea – a slow-growing and difficult-to-culture alga.

“They’ll eat it literally faster than we could ever grow it,” said researcher Sidney Pierce, who has studied these animals for decades.

As younger generations of scientists seek research topics, many avoid elusive organisms. Without fresh talent, answers to fundamental questions may never materialize.

DNA reveals genetic surprises

Genomic research is uncovering interesting details about the slug’s DNA. One draft genome assembly found over 24,000 protein-coding genes, suggesting that the genome is larger than expected.

Scientists are investigating whether the slug has captured additional algal genes that help maintain stolen chloroplasts. If confirmed, these conclusions would offer a template for understanding genetic transfers across species.

Such discoveries might even point to new approaches in biotechnology, where harnessing photosynthesis in novel settings could be a game-changer. But these sampling efforts hinge on keeping the slug’s population stable.

Viable solutions going forward

In addition to yielding biological insights, the slug’s weird synergy with algae may inform ecological restoration. If we comprehend how this animal adapts to shifting coastal conditions, we might refine habitat protection strategies.

Some suggest that mapping the slug’s distribution and monitoring water quality could reveal its true population status. Others envision citizen science programs that inspire local communities to document sightings.

Secrets of sun-loving sea slugs

Many experts see the value in this sea slug’s rare talent to convert sunlight into energy. They believe that more comprehensive studies could spark exciting breakthroughs.

If scientists persevere, the synergy between animals and plants might reveal more about life’s creative potential.

Even though the path ahead looks challenging, there is hope that future teams will unlock more secrets about this sun-loving creature. Each fresh observation could demonstrate how life can seemingly bend the rules.

Future research directions

Environmental groups may collaborate with academic institutions to fund targeted surveys. This would ensure that these elusive sea slugs are not overlooked in shifting habitats.

Support from diverse disciplines, including molecular biology, marine ecology, and conservation policy, might unite to keep Elysia chlorotica alive for generations.

Scientists remain optimistic about new fieldwork opportunities. Additional synergy and collaboration across scientific networks could generate crucial momentum.

The study was published in the journal Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–