Abstract
The kelp forests of southern South America are some of the least disturbed on the planet. The remoteness of this region has, until recently, spared it from many of the direct anthropogenic stressors that have negatively affected these ecosystems elsewhere. Re-surveys of 11 locations at the easternmost extent of Tierra del Fuego originally conducted in 1973 showed no significant differences in the densities of adult and juvenile Macrocystis pyrifera kelp or kelp holdfast diameter between the two survey periods. Additionally, sea urchin assemblage structure at the same sites were not significantly different between the two time periods, with the dominant species Loxechinus albus accounting for 66.3% of total sea urchin abundance in 2018 and 61.1% in 1973. Time series of Landsat imagery of the region from 1998 to 2018 showed no long-term trends in kelp canopy over the past 20 years. However, ~ 4-year oscillations in canopy fraction were observed and were strongly and negatively correlated with the NOAA Multivariate ENSO index and sea surface temperature. More extensive surveying in 2018 showed significant differences in benthic community structure between exposed and sheltered locations. Fish species endemic to the Magellanic Province accounted for 73% of all nearshore species observed and from 98–100% of the numerical abundance enumerated at sites. Fish assemblage structure varied significantly among locations and wave exposures. The recent creation of the Yaganes Marine Park is an important step in protecting this unique and biologically rich region; however, the nearshore waters of the region are currently not included in this protection. There is a general lack of information on changes in kelp forests over long time periods, making a global assessment difficult. A complete picture of how these ecosystems are responding to human pressures must also include remote locations and locations with little to no impact.
Highlights
Giant kelp (Macrocystis pyrifera) forests are the foundation of marine communities on many shallow rocky coasts of the world’s cold-water marine habitats and constitute one of the most diverse and productive ecosystems on the planet [1,2,3,4,5]
The Mitre Peninsula (MP) and Isla de los Estados (IE) are the terminus of the South American continent and the 7,200 km long Andes mountain range [27,28]
We found a remarkable degree of similarity in relative abundance of kelp, sea urchins, and seastars from the in-situ surveys conducted during the two time periods
Summary
Giant kelp (Macrocystis pyrifera) forests are the foundation of marine communities on many shallow rocky coasts of the world’s cold-water marine habitats and constitute one of the most diverse and productive ecosystems on the planet [1,2,3,4,5]. There is concern for the future of kelps (Laminariales) as temperate nearshore systems are increasingly impacted by both local stressors such as sedimentation, pollution, overfishing and direct harvest as well as global stressors related to climate change such as marine heatwaves [5,6,7,8,9,10,11]. Despite a plethora of recent scientific studies and popular media headlines showing dramatic losses of kelp forests, often marked by sharp transitions to low diversity urchin barrens or turf algae, a comprehensive global analysis showed that kelp loss is not uniform, but rather highly spatially variable in both magnitude and direction of change [10]. That global study concluded that local and regional-scale drivers can dominate kelp forest dynamics and noted that many regions of the world suffer a dearth of data on kelps, precluding our ability to understand changes that might occur in a rapidly warming ocean. The most thorough and longest time series come from very few regions of the world [10,11], which limited our understanding of how these ecosystems functions and how best to conserve them
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