RECOVERY AND GENETIC DIVERSITY OF THE INTERTIDAL KELP LESSONIA NIGRESCENS (PHAEOPHYCEAE) 20 YEARS AFTER EL NIÑO 1982/83¹

Abstract

Massive mortality in kelp beds of the Pacific coasts of North and South America was caused by the rise in surface seawater temperature during the El Niño Southern Oscillation (ENSO) event of 1982/83, the strongest in the four and half previous centuries. In northern Chile a stretch of 600 km of coastline showed massive mortality of the intertidal kelp species Lessonia nigrescens Bory, of which only a few individuals managed to survive. Kelps and their associated biodiversity recovered but kelp beds re‐colonization in general was variable in time and space seemingly very slow along northern Chilean coasts. Here we show, effectively, that northward re‐colonization advanced less than 60 km in 20 years. Conversely, kelp beds of the Northern Hemisphere recovered 300 km in only six months after the same ENSO event. Genetic diversity in the two most affected populations of L. nigrescens shows half of the heterozygosity and polymorphism with respect to that observed in six non affected populations. In addition, geographically separated populations seem highly isolated as evidenced by high and significant fixation indices (all FST values over 0.4).

Genetic structure of the giant kelp Macrocystis pyrifera along the southeastern Pacific

“…Such sharp population declines, or bottlenecks, such as those seen during recent ENSO events, may translate into losses of genetic variation of marine organisms (Steinfartz et al 2007). Martínez et al (2003) found that, in sites in northern and central Chile impacted by the 1982-83 ENSO, genetic diversity of Lessonia nigrescens was lower than in non-impacted sites. For sampling locations details, see Fig.…”

“…A similar low genetic variation has been shown in several marine species along the Chilean coast, both invertebrates (Gallardo & Carrasco 1996, Toro & Aguila 1996, Gallardo et al 2003, GomezUchida et al 2003, Toro et al 2006) and fish (Galleguillos et al 2000), presumably associated with the high dispersal potential of these taxa, which have long-lived larvae. Along the SEP, few studies have analyzed the genetic structure of macroalgae (Martínez et al 2003, Faugeron et al 2005, Vidal et al 2008, Tellier et al 2009, and most of them have found high genetic differentiation among populations. In contrast, we provide evidence for low genetic variation in a macroalga over a wide area of the SEP and throughout the subantarctic region.…”

“…To date, only 1 study has addressed concordance between phylogeographic patterns and the 2 main biogeographic transitions along the SEP. Tellier et al (2009) found a major phylogeographic break at 30°S in the intertidal kelp Lessonia nigrescens, a brown alga with reduced gene flow (Martínez et al 2003, Faugeron et al 2005 and no floating structures that could facilitate dispersal of adult thalli. We may expect a different result in kelps with high dispersal potential, such as Macrocystis pyrifera.…”

Production and fate of kelp detritus

“…Fishing high-level predators releases sea urchin populations and leads to the destructive grazing of kelp beds and forests (Steneck et al 2002). Climate change is expected to cause large-scale losses in kelp biomass and decrease the resilience of kelp beds and forests due to warming sea surface temperatures, changes in the nutrient dynamics of the water column, and increases in storm frequency and intensity (Steneck et al 2002, Martinez et al 2003, Springer et al 2010. Large-scale kelp canopy loss is linked to warm water temperatures associated with the disruption of upwelling cycles during El Niño years (Gunnill 1985, Steneck et al 2002, Martinez et al 2003, Vasquez et al 2006, Foster & Schiel 2010, Springer et al 2010.…”

“…Climate change is expected to cause large-scale losses in kelp biomass and decrease the resilience of kelp beds and forests due to warming sea surface temperatures, changes in the nutrient dynamics of the water column, and increases in storm frequency and intensity (Steneck et al 2002, Martinez et al 2003, Springer et al 2010. Large-scale kelp canopy loss is linked to warm water temperatures associated with the disruption of upwelling cycles during El Niño years (Gunnill 1985, Steneck et al 2002, Martinez et al 2003, Vasquez et al 2006, Foster & Schiel 2010, Springer et al 2010. Storms that cause large wave events and reduce kelp biomass (Gerard 1976, Luning 1979, Gunnill 1985, Seymour et al 1989, Reed et al 2008) are likely to have greater long-term effects as the incidence of severe storm events increases (Easterling et al 2000, Byrnes et al 2011.…”