We usually hear about lost kelp forests in hectares and satellite images. A new study from Tasmania measures the loss differently: in dive trips. Researchers at the University of Tasmania’s Institute for Marine and Antarctic Studies teamed up with Eaglehawk Dive Centre on the Tasman Peninsula, in the island’s south-east, and went through the operator’s trip logs and business records from 1991 to 2021. The result, published in Annals of Botany in September, is what the authors call one of the first quantitative assessments of kelp forest dive tourism. It reads a little like an obituary.
The logbooks cover 49,908 dives by 14,280 divers at 243 dive sites. Between 1993 and 2017, 4,690 of those dives were in giant kelp (Macrocystis pyrifera) forests. That’s about 11 per cent of the total, and it made kelp the third most-dived attraction after shallow reefs and sea caves. The team matched every site to its habitat type, then compared the dive numbers with satellite sea-temperature records and remote-sensing data on kelp cover. Kelp diving rose steadily from 1991 to 2010. Then marine heatwaves in 2010 and 2016 caused sudden kelp losses, and from 2017 there were no kelp forest dives left to log.
The money side is where it gets stark. According to the study, led jointly by Scott Bennett and Nicole Currie, the sharp drop in kelp dives in 2011 all but erased the local operator’s gross margin: on the study’s relative measure, it fell from a peak of 2.59 to 0.03. And the business was paying for the slow retreat even before the final collapse. As giant kelp disappeared from sites close to the boat launch, reaching it meant travelling further. Munro Bight, the most distant of the main kelp sites, is a 44 km round trip, compared with 5.4 km for Lufra, and the study estimates the gross margin per trip there was about 15 per cent lower. Two of the co-authors, Mick Baron and Karen Gowlett-Holmes, work at the dive centre itself. That gives the paper an unusual inside view of a business watching its main attraction drift out of reach.
Why does one dive shop’s ledger matter? Kelp forests are usually valued for things that are hard to see, like carbon storage, fisheries and coastal protection. The authors’ point is that climate extremes are wearing these benefits away, often before anyone has measured them. Dive tourism is one of the few that leaves a paper trail. The limits are worth keeping in mind, though. This is one operator’s records from one stretch of coast. The gross-margin figures are the researchers’ calculations from those records, not audited accounts. And dive numbers are an indirect measure of the forest itself, because they also reflect where people chose to dive.
For now, the study adds a human-scale number to a story usually told in square kilometres. When a kelp forest goes, it takes local livelihoods with it, and the evidence is often sitting in someone’s logbook. The obvious open question is how many other coastal businesses have similar records that nobody has thought to look at yet.
Further reading: Bennett, S., Currie, N.E. et al., “Impacts of climate-driven loss of giant kelp forests on local dive tourism,” Annals of Botany (2026).