Kelp forests at the end of the earth: 45 years later

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.

Multi-decadal decline in cover of giant kelp Macrocystis pyrifera at the southern limit of its Australian range

“…comm.). Strong positive relationships (r 2 > 0.994) in kelp cover fractions derived from the different sensors have also been demonstrated using the MESMA technique (Bell et al 2020). Considering that the focus of this work is on detecting presence or absence of surface canopy cover, and not a quantitative analysis of NDVI, no correction to the NDVI was required.…”

“…These results are echoed in ongoing research using the same Landsat archive in this and the broader Californian region (e.g. Bell et al 2020), but whether these longterm trends and links between biomass and climate signals are similar in other locations around the world is unknown.…”

“…Under-standing how these changes manifest, however, is difficult. Species' responses are the re sult of complex biotic and abiotic interactions, and long-term datasets are required to separate anthropogenically driven changes from natural variability (Reed et al 2016, Bell et al 2020. Data collection in the marine environment is costly and often labour intensive, so despite recognition of the value of long-term data sets, few studies are able to assess long-term change.…”

Marine communities of the newly created Kawésqar National Reserve, Chile: From glaciers to the Pacific Ocean

“…The kelp forests of Southern Chile are some of the healthiest on earth [ 2 , 3 , 42 ] and much of the coastline of the KNR is dominated by this important habitat. The kelp forests of the KNR are an important nursery habitat for the Chilean king crab ( Lithodes santolla ), which is one of the most important fisheries in the region.…”

Ocean temperature controls kelp decomposition and carbon sink potential

“…Many kelp forests are declining globally, particularly in regions with high seawater temperatures and rapid warming [22][23][24][25] . In contrast, kelp forests in cooler regions are relatively stable, and in some cases kelp is even increasing in abundance 24,[26][27][28][29] . Changes in the abundance of kelp, and the environmental conditions they experience, may have consequences for the global carbon cycle.…”