Loss of a globally unique kelp forest from Oman

Abstract

Kelp forests are declining in many regions globally with climatic perturbations causing shifts to alternate communities and significant ecological and economic loss. Range edge populations are often at most risk and are often only sustained through localised areas of upwelling or on deeper reefs. Here we document the loss of kelp forests (Ecklonia radiata) from the Sultanate of Oman, the only confirmed northern hemisphere population of this species. Contemporary surveys failed to find any kelp in its only known historical northern hemisphere location, Sadah on the Dhofar coast. Genetic analyses of historical herbarium specimens from Oman confirmed the species to be E. radiata and revealed the lost population contained a common CO1 haplotype found across South Africa, Australia and New Zealand suggesting it once established through rapid colonisation throughout its range. However, the Omani population also contained a haplotype that is found nowhere else in the extant southern hemisphere distribution of E. radiata. The loss of the Oman population could be due to significant increases in the Arabian Sea temperature over the past 40 years punctuated by suppression of coastal upwelling. Climate-mediated warming is threatening the persistence of temperate species and precipitating loss of unique genetic diversity at lower latitudes.

First mesophotic Ecklonia radiata (Laminariales) records within the iSimangaliso Wetland Park marine-protected area, east coast, South Africa

“…Other risks, in addition to climate change, include coastal expansion, pollution, and increased human activity within the park, all of which can alter the natural balance of the environment. These combined stresses endanger not just the kelp forests but also the diverse species they support, emphasizing the critical need for comprehensive conservation measures (Wernberg et al, 2019a(Wernberg et al, , 2019bColeman et al, 2022).…”

“…Our observations represent the first verified report of this species occurring at mesophotic depths in the iSimangaliso MPA, and for the first time it has been documented in subtropical and tropical South Africa, north of its previously recorded range (Rothman, 2015; Rothman et al ., 2015; Coleman et al ., 2022).…”

“…E. radiata has also been documented in the subtropical waters of the south-western Indian Ocean (SWIO) region, in Madagascar (Silva et al, 1996;Tronchin and De Clerck, 2005;Vieira et al, 2021;Guiry and Guiry, 2022) and in southern Mozambique, off the coast of Zavora, at a depth of 34 m (Wernberg et al, 2019a;Coleman et al, 2022), and in the Northern Hemisphere from Oman (Rothman, 2015;Wynne, 2018). Anderson et al (2005), Wernberg et al (2019a), andColeman et al (2022) noted an anecdotal report (from Sink, pers.…”

“…Kelp forests are also recognized as critical ecological habitats that provide several direct and indirect ecosystem services (Smale et al ., 2013; Vásquez et al ., 2014; Filbee-Dexter and Wernberg, 2020). These globally significant, highly productive ecosystems are however under threat from climate change, habitat destruction, and over-fishing (Harley et al ., 2012; Spalding et al ., 2019; Wernberg et al ., 2019a; Buglass et al ., 2022; Coleman et al ., 2022; Pessarrodona et al ., 2023), and require ongoing research to better understand and communicate their socio-ecological value, and to improve their conservation and management.…”

“…E. radiata is the prevailing and extensively distributed kelp species in the Southern Hemisphere. Notably, it is one of the kelps that exhibit a high level of tolerance to temperatures, thriving in warm-temperate and subtropical waters (Wernberg et al ., 2019a; Coleman et al ., 2022). E. radiata is typically found within the temperature range of about 8–25°C (Bolton and Anderson, 1994), and temperature plays a crucial role in determining its regional distribution.…”