Chondria tumulosa

Chondria tumulosa
Scientific classification
Domain:	Eukaryota
Clade:	Archaeplastida
Division:	Rhodophyta
Class:	Florideophyceae
Order:	Ceramiales
Family:	Rhodomelaceae
Genus:	Chondria
Species:	C. tumulosa
Binomial name
Chondria tumulosa A.R.Sherwood et J.M.Huisman

Chondria tumulosa is a species of red algae in the family Rhodomelacae. It was first discovered in 2016, growing in small patches in the Pearl and Hermes Atoll in the Northwestern Hawaiian Islands. By 2019, the species had spread to cover several thousand square meters, smothering and killing vast swathes of the atoll's coral reefs. C. tumulosa is unlike any other species in its genus, having a tumbleweed-like growth form that allows fragments to break off and spread, allowing it to colonize new areas. The true origin of C. tumulosa in the region remains unknown; it displays many characteristics of an invasive species and is not closely related to any other Hawaiian Chondria , but it would have been relatively difficult to colonize such a remote area. It has also been suggested that it is a native species that suddenly spread due to changes in the ecosystem. Control and mitigation strategies will have to be made to prevent the species' spread. ^{[1] [2] [3]}

Management and Monitoring

A novel environmental DNA (eDNA) assay has been developed to detect Chondria tumulosa in the Papahānaumokuākea Marine National Monument (PMNM), a significant marine reserve. This red alga, which is known for its invasive traits, forms dense mats that overgrow coral reefs, threatening native species and ecosystems. The eDNA assay uses quantitative polymerase chain reaction (qPCR) and high-throughput sequencing to detect C. tumulosa from seawater samples, even at low abundance levels (below 1%). The high sensitivity and reliability of this method support its use for early detection and management of C. tumulosa, providing valuable insights for conservation efforts and invasive species control. This tool helps mitigate the spread of C. tumulosa in PMNM and similar ecosystems, enhancing management strategies for invasive species containment and eradication. ^[4]

Passive eDNA sampling

Researchers have recently evaluated a passive eDNA sampling method known as Passive Environmental DNA Samplers (PEDS), which is a more accessible and cost-effective alternative to conventional active filtration for detecting Chondria tumulosa in Hawaiʻi. The study found that a 15-minute deployment of PEDS achieved detection sensitivity comparable to that of filtering 2 L of seawater in all cases where C. tumulosa was known to occur.

The researchers assessed three performance attributes of the species-specific eDNA assay: clinical sensitivity, DNA yield, and overall detection performance and deployed site-occupancy modeling to better evaluate trade-offs. Although PEDS yielded lower amounts of target eDNA compared to active methods, C. tumulosa was still detected at very low abundances (<1%).

In comparing different sampler types, absorbent cotton rounds outperformed research-grade mixed cellulose ester filters in capturing eDNA, demonstrating higher yields and more reliable detection. The study also observed that PEDS attached to stationary buoys and those carried by SCUBA operators delivered similar eDNA occupancy estimates, but the SCUBA-roving samplers showed reduced capture rates.

Overall, while acknowledging limitations related to lower eDNA yields and increased potential for false positives or negatives, the study demonstrates the effectiveness of PEDS (especially when combined with sufficient qPCR replication) as a scalable, low-cost tool for early detection and monitoring of Chondria tumulosa in remote reef systems. ^[5]

A detailed description of the passive eDNA sampling method has also been published as a formal laboratory and field protocol to support reproducibility and application in other aquatic ecosystems. ^[6]

References

1. Sherwood, Alison R.; Huisman, John M.; Paiano, Monica O.; Williams, Taylor M.; Kosaki, Randall K.; Smith, Celia M.; Giuseffi, Louise; Spalding, Heather L. (2020-07-07). "Taxonomic determination of the cryptogenic red alga, Chondria tumulosa sp. nov., (Rhodomelaceae, Rhodophyta) from Papahānaumokuākea Marine National Monument, Hawai'i, USA: A new species displaying invasive characteristics". PLOS ONE. 15 (7): e0234358. Bibcode:2020PLoSO..1534358S. doi: 10.1371/journal.pone.0234358 . ISSN   1932-6203. PMC   7340295 . PMID   32634147.
2. "Algae species discovered infesting NW Hawaiian waters has been identified". ScienceDaily. Retrieved 2020-07-09.
3. Fazio, Marie (2020-07-08). "New Red Algae Are Threatening Hawaii's Coral Reefs, Scientists Say". The New York Times. ISSN   0362-4331 . Retrieved 2020-07-09.
4. Nichols, Patrick; Fraiola, Kaʻuaʻoa; Sherwood, Alison; Hauk, Brian; Lopes Jr., Keolohilani; Davis, Colt; Fumo, James; Counsell, Chelsie; Williams, Taylor; Spalding, Heather; Marko, Peter (2024-03-31). "Early detection of Chondria tumulosa using environmental DNA assays for management of coral reef ecosystems". PLOS ONE. doi: 10.1371/journal.pone.0318414 . PMC   11793909 .
5. Nichols, Patrick; Marko, Peter (2025-08-25). "No pump, no problem: evaluating passive eDNA sampling for marine biomonitoring of a nuisance macroalga". PeerJ. doi: 10.7717/peerj.19939 .
6. Nichols, Patrick; Vimond, Cécile; Marko, Peter (2025-08-12). "Simple Passive Environmental DNA Samplers for Marine Biomonitoring in Resource-Limited Programs". Current Protocols. doi:10.1002/cpz1.70186.