Our confidence in the state of polychaete taxonomy in southern Africa is unfounded: Setting taxonomic priorities for polychaete worms in the region

Polychaetes (marine annelids) occupy nearly all marine habitats from the intertidal and estuaries to the deep sea, and many occupy extreme habitats such as heated hydrothermal vents and whale carcasses.  It is therefore not surprising that this is a very diverse group, with more than 11,500 species described to date. These worms are super abundant and can contribute to more than 60% of the species, and more than 70% of the animals, in benthic samples. Consequently, polychaetes fulfil many important ecological roles.

Figure 1. A clew/clat/bed/ bunch of worms. The diversity of polychaetes is reflected in the diversity of collective nouns for worms

The first step in exploring the many ecological functions of polychaetes is to identify them. In this regard, marine biologists globally have relied on A monograph on the Polychaeta of southern Africa, written by John Day while employed as a professor of Zoology at the University of Cape Town. Since its publication in 1967, the monograph has been the go-to identification key because it provides clear, simple, and easy to follow illustrations, keys and descriptions of more than 700 species of polychaetes in more than 40 families that were reported in southern Africa. Because of this, researchers have for a long time considered the state of our knowledge of local polychaetes to be high, thus implying that polychaete taxonomic research is not a high priority in the region. However, our review of the taxa contained in the monograph suggest that this is far from true, and that more than half the species contained in it have probably been misidentified and should be revised.

 

Figure 2. Polychaetes fulfil many ecological roles. On the left is Gunnarea gaimardi, an ecosystem engineer that builds conspicuous sandy tubes on rocks in the intertidal, creating environments for other organisms.  On the right is an abalone shell damaged by spionid polychaetes that bore into the shells of farmed molluscs, stimulating the formation of these characteristic blisters.

The biggest factor contributing to the misidentification of so many species is the age of their descriptions. About 70% of the species reported here were described before 1900, including many that were first described outside of southern Africa. These early descriptions are usually brief, poorly illustrated and most defining characters are not described. Consequently, it is easy to match specimens collected all over the world to these descriptions, fueling the misconception that many polychaete species have cosmopolitan distributions. We now know that few polychaete species are truly cosmopolitan and we therefore predict that most cosmopolitan species reported in southern Africa (>60% of species recorded in the monograph) are actually undescribed indigenous taxa. The continued indiscriminate use of the monograph would therefore perpetuate old identification errors, leading to inaccurate distribution and diversity records, not only in southern Africa, but globally.

The consequences of misidentifying species can be dire. An alien species mistaken for an indigenous one will flourish until eradication becomes impossible. When confidence in the identities of species is low, comparisons between studies become almost meaningless, and studies themselves are not repeatable. We cannot begin to measure the rate of species extinctions in the face of global change or select biodiversity hotspots for conservation when we don’t know what species are present. Management of harvested species can also be impacted if multiple species occupying discreet ranges are mistaken for a single widespread species.

My coauthors and I generated lists of taxa at the family, genus and species level that should be prioritised for taxonomic revision. The four top priority families are the Syllidae, Nereididae, Eunicidae and Spionidae. Together they comprise ~25% of species in the monograph, and 53% to 85% of the species in each family are unresolved cosmopolitan (i.e., species supposedly with cosmopolitan distributions but without supporting evidence). Taxa in these families are also ecologically and economically important: Syllidae are numerically abundant and species rich; many species of Spionidae are pests of aquaculture, globally distributed aliens and or indicators of environmental health; and Nereididae and Eunicidae include many species that are harvested as bait. These four families also include many of the genera that have been prioritised for revision. The top sedentary species that are prioritised for revision include the indigenous, widespread and conspicuous Gunnarea gaimardi, commonly known as the Coral- or Cape Reefworm and a popular bait species, which is really at least two species, and the unresolved cosmopolitan ‘Capitella capitata’, which is widely used as an indicator of environmental health, and part of a well-known complex of multiple, morphologically similar species.

Clearly identifying polychaetes using the monograph is just the first step. The identifications should then be checked against the lists generated in our study to gauge confidence in identification; the higher the priority, the lower the confidence. When confidence in identification is low, specimens should be compared to original descriptions, recent revisions, type material or specimens from the natural distribution ranges of the species, and where appropriate, the new species should be described. This last activity is the most time consuming, and undoubtedly, the one that will be skipped when identifying taxa to species level is not the primary goal of the study. It is therefore essential that ecologists and other scientists for whom species identifications is an essential part of data collection should collaborate with taxonomists. We recommend that large studies include student projects focused on describing species found, and that reference material that can be reliability linked to DNA sequences and taxa reported in publications be deposited in museums. This is the only way that we can tackle the enormous task of resolving the taxonomy of this very important group of animals.

All photographs taken by C. Simon

Selected further reading

  1. Hutchings P, Kupriyanova E. 2018. Cosmopolitan polychaetes–fact or fiction? Personal and historical perspectives. Invertebrate Systematics 32 (1): 1‒9. https://doi.org/10.1071/IS17035
  2. Kara J, Santos C, Macdonald A, Simon C. (2020). Resolving taxonomic identities and genetic structure of two cryptic Platynereis Kinberg species from South Africa. Invertebrate Systematics, 34(6), 618-636. https://doi.org/10.1071/IS19072
  3. Kara J, Molina-Acevedo I, Zanol J, Simon C, Idris I. (2020). Morphological and molecular systematic review of Marphysa Quatrefages, 1865 (Annelida: Eunicidae) species from South Africa. 8: e10076. https://doi.org/10.7717/peerj.10076
  4. Kara J, Macdonald AHH, Simon C. (2018). Integrative taxonomic methods reveal an incorrect synonymisation of the South African Pseudonereis podocirra (Schmarda) as the widespread Pseudonereis variegata (Grube) from Chile. Invertebrates Systematics, 32(6), 1282-1297. https://doi.org/10.1071/IS18016
  5. Simon C, Kara J, du Toit A, van Rensburg H, Naidoo C, Matthee C. (2021). Reeling them in: taxonomy of marine annelids used as bait by anglers in the Western Cape province, South Africa. PeerJ, 9:e11847 DOI 10.7717/peerj.11847
  6. Simon CA, van Niekerk HH, Burghardt I, ten Hove HA, Kupriyanova E. 2019c. Not out of Africa: Spirobranchus kraussii (Baird, 1865) is not a global fouling and invasive serpulid of Indo-Pacific origin. Aquatic Invasions 14(2): 221–249. https://doi.org/10.3391/ai.2019.14.2.05
  7. Sivadas S, Carvalho R. 2020. Marine Annelida of India: taxonomy and status evaluation and an updated checklist. Journal of Threatened Taxa 12(12): 16647–16714 DOI: https://doi.org/10.11609/jott.5357.12.12.16647-16714
  8. Villalobos-Guerrero TF, Kara J, Simon C, Idris I (2022). Systematic review of Neanthes Kinberg, 1865 (Annelida: Errantia: Nereididae) from southern Africa, including a preliminary molecular phylogeny of the genus. Marine Biodiversity, 52(2), 1-30. https://doi.org/10.1007/s12526-021-01244-2