A new study from Stellenbosch University (SU) has confirmed that the mussel worm is a native species that has populated our shores for at least the past 6.4 million years.
Previously known as Pseudonerei variegata, a species originally described from Chile in 1857, it will forthwith be known as Pseudonerei podocirra.
Prof Carol Simon, a polychaete specialist based in the Department of Botany and Zoology at SU, says their findings indicate that there are far higher levels of diversity among our own marine worms than previously thought.
But reaching this conclusion required the passion and dedication of postgraduate student Jyothi Kara, who, starting in 2015, had to unravel a highly confusing taxonomic record that has not been interrogated for the past 150 years.
She explains: “The mussel worm was first described in 1857 in Chile and named Pseudonereis variegata. In South Africa, two different species of mussel worms were described in 1861 and 1866. But in the 1900s taxonomists decided that these two species actually look alike, and that they are similar to the Chilean mussel worm, so according to the rules of taxonomy they were all renamed P. variegata, because it was the first one to be described."
Until the 1990s, all similar looking marine worms found all over the world were also named P. variegata, giving rise to the (now erroneous) belief that marine worms such as mussel worms are essentially cosmopolitan species, i.e. occurring in most of the major ocean basins.
Polychaetes, or bristle worms, are considered to be the most primitive of all segmented animals, with fossil records going back as far as 505 million years. They are highly diverse, and occur in all ocean basins, from the shallow intertidal to sea vents kilometers deep. Today Prof Simon is one of the few polychaete taxonomists in the world trying to unravel the family tree of these fascinating creatures.
For this project, Jyothi sampled mussel worms all the way from Lamberts Bay in the West Coast to Kidds Beach on the East Coast. The mussel worm, so called because it occurs among mussel beds on the rocky shores of South Africa, is a popular bait species among fishermen, even though its collection has been banned because of destructive harvesting methods.
She then compared their physical features and DNA to specimens of P. variegata from Chile in order to confirm whether they are the same species or not.
“I loved it! I felt like a detective who had to unravel all these linkages and how they fit in," this former Durbanite laughs.
Some of her findings, published in the journal Invertebrate Systematics recently, include:
- The species found in South Africa is not Pseudonereis variegata as was commonly believed. It represents Pseudonereis podocirra that was initially described from South Africa in 1861. This indicates that the South African species was confused with the species from Chile for almost 150 years.
- Results from the DNA analyzing process indicate that P. podocirra forms a single meta population along the South African coast and that there is a high level of gene flow. In population genetics, gene flow (or gene migration) is the transfer of genetic variation from one population to another, which means that the species is not prone to local extinction.
- Finally, the South African mussel worm P. podocirra evolved on these shores around 6.4 million years ago.
Prof Simon and her team suspects that approximately 50% of the 600 to 700 species of polychaete worms reported along South Africa's shores may be like P. podocirra: indigenous species that have been perceived as cosmopolitan. So for now they are concentrating on the ecologically and economically important ones.
“Apart from serving as bait for local fishermen, many polycheate worms are regarded as keystone species and ecosystem engineers in the marine environment. They build extensive tubes forming reefs which then provide a habitat for many other marine invertebrates. Other polychaete worms burrow into the sand, thereby aerating the sediments and making it more habitable for other marine animals. This also results in the redistribution of organic matter trapped in the sediment, making it more available for other marine animals to consume," Dr Kara explains.
She plans to continue in this field, working as a postdoctoral fellow under Prof Simon, and will next tackle the genetic history and taxonomy of wonder worms, another popular bait species.
All in all, understanding the true diversity of indigenous species in South Africa will help us to better conserve our resources, they conclude.
Dr Kara, originally from Durban in KwaZulu-Natal, was awarded her doctoral degree from Stellenbosch University during the April 2019 graduation ceremony.
Did you know?
- Polychaetes are commonly known as bristle worms because of the many spiny bristles that stick out from each body segment. Polychaete is Greek for “with much hair".
- Bioturbation (the reworking of soils and sediments by living organisms such as burrowing) is known to act as the primary driver of marine biodiversity.
- Pseudonereis podocirra belongs to the family Nereididae. Nereids refer to sea nymphs in Greek mythology.
Dr Jyothi Kara, a marine biologist from Stellenbosch University, collecting mussel worms from a rocky beach in Mossel Bay for her doctoral research into the genetic and evolutionary history of this species. Photo: Safiyya Seddick
A blue-grey variant of the indigenous mussel worm, Pseudonereis podocirra. Image: Jyothi Kara
Prof Carol Simon
Tel: 021 808 3068
Dr Jyothi Kara
Tel: 021 808 3068
Mobile: 083 625 7419