Ship Tracking Data Pinpoints Pathways of Invasive Caulerpa Seaweed in New Zealand
Marine scientists from the Australian Institute of Marine Science (AIMS) have mapped the spread of two invasive Caulerpa seaweed species—C. brachypus and C. parvifolia—across New Zealand’s coastline by analysing vessel movement records. The study, published in Marine Ecology Progress Series, correlates high‑traffic shipping routes with newly documented seaweed infestations between 2015 and 2024.
Caulerpa species, native to the Indo‑Pacific, can outcompete local algae, alter habitats, and damage fisheries, representing a significant ecological and economic threat. New Zealand’s marine biosecurity agency has long struggled to pinpoint how the algae cross ocean basins, prompting the novel use of Automatic Identification System (AIS) data to trace possible vectors.
Researchers examined over 4 million AIS entries for vessels that docked at New Zealand ports and later visited coastal sites where Caulerpa was first observed. They identified a strong association between ballast‑water discharge from cargo ships arriving from Australian ports and subsequent seaweed outbreaks. “Our model suggests that 78 % of new infestations can be linked to specific vessel routes,” said Dr. Rebecca Liu, the study’s lead author in a Phys.org interview. AP reported a complementary finding that recreational yachts contribute a smaller, yet non‑negligible, pathway for local spread.
Biosecurity experts welcomed the quantitative evidence, noting that targeted ballast‑water management could dramatically reduce future introductions. Professor James O’Connor of the University of Auckland warned, “Even with strict regulations, compliance monitoring must be rigorous; otherwise, we risk repeated introductions.” The study also sparked discussion about the feasibility of real‑time AIS‑based alerts for port authorities.
AIMS intends to work with New Zealand’s Ministry for Primary Industries to pilot an early‑warning system that flags high‑risk vessels for inspection. Upcoming legislative reviews on ballast‑water treatment standards and international cooperation agreements will likely shape the next steps in curbing the Caulerpa invasion.