Sacoglossan sea slugs have the unique ability to incorporate functional chloroplasts over weeks or months during starvation and thus are able to survive by maintaining photosynthetic activity. One of those so-called long-term retention forms is Plakobranchus ocellatus a common inhabitant of shallow coral reef pools and lagoons. It is seldom seen as it is well-camouflaged, half buried in the coral sand. It shows an exceptional ability to starve over months with a relatively slow loss of photosynthetic activity. For this reason, it is of high interest for our understanding of the mechanism of functional long-term photosynthesis in Sacoglossa. It is known that plastids from algae are sequestered by the sea slugs. The alga is eaten normally and partially digested, leaving the plastid intact. The plastids are maintained within the host, temporarily retaining functional photosynthesis for use by the predator. This phenomenon is called kleptoplasty.
Little is known regarding the taxonomy and food sources of Plakobranchus ocellatus, but it was suggested that it is a species complex and feeds on a broad variety of green algae of the family Ulvophyceae.
A group of researchers from Germany now identified the species of algal food sources depending on starvation time and light treatment by means of DNA-barcoding. They used for the first time the combination of two algal chloroplast markers, rbcL and tufA. Furthermore, they used COI and 16S sequences of specimens from various localities to show that Plakobranchus is indeed a species complex with likely four distinct clades. Food analyses do not indicate an ecological separation of the clades into differing foraging strategies. The combined results from both algal markers suggest that, in general, Plakobranchus ocellatus has a broad food spectrum.