Recruitment tolerance to increased temperature present across multiple kelp clades

Abstract

Kelp systems dominate nearshore marine environments in upwelling zones characterized by cold temperatures and high nutrients. Worldwide, kelp population persistence and recruitment success generally decreases with rising water temperatures coupled with low nutrients, making kelp populations vulnerable to impending warming of the oceans. This response to climate change at a global scale, however, may vary due to regional differences in temperature variability, acclimation, and differential responses of kelp species to changing conditions. Culture experiments were conducted on 12 eastern Pacific kelp taxa across geographic regions (British Columbia, central California, and southern California) under three nitrate levels (1, 5, and 10 μmol/L) and two temperatures (12°C and 18°C) to determine sporophyte production (i.e., recruitment success). For all taxa from all locations, sporophytes were always present in the 12°C treatment and when recruitment failure was observed, it always occurred at 18°C, regardless of nitrate level, indicating that temperature is the driving factor limiting recruitment, not nitrate. Rising ocean temperatures will undoubtedly cause recruitment failure for many kelp species; however, the ability of species to acclimatize or adapt to increased temperatures at the warmer edge of their species range may promote a resiliency of kelp systems to climate change at a global scale.

Resistance, Extinction, and Everything in Between – The Diverse Responses of Seaweeds to Marine Heatwaves

“…Reproduction potential and early life-history stages of many seaweeds are temperature-sensitive (Bartsch et al, 2013;Andrews et al, 2014), and increased temperatures can both suppress or enhance reproduction and recruitment success (de Bettignies et al, 2018;Muth et al, 2019). Following the 1982/83 El Niño, the turf-forming Pelvetia fastigiata and the canopy-forming fucoid Sargassum muticum showed increased recruitment success at La Jolla, California (Gunnill, 1985), which led to elevated abundances and likely shifted competitiveness News articles were only included if results were not yet published in peer-reviewed journals.…”

Ecological feedbacks stabilize a turf-dominated ecosystem at the southern extent of kelp forests in the Northwest Atlantic

“…However, despite localized kelp declines, there is no unifying global pattern of kelp change, with some populations remaining unchanged and others expanding over the past half century 6 . Based on studies at early life-history stages, it is predicted that warm-adapted kelp populations existing at the equatorial range limits of species distributions may be the most resilient to climate change and most likely to persist into the future 7 . Longitudinal field observations at the range limits of kelp species are required to test this hypothesis.…”

Long-term changes in kelp forests in an inner basin of the Salish Sea

“…The familiar sporophyte phase of Nereocystis is primarily an annual, with a holdfast that attaches to coarse substrates, a long stipe connected to a terminal buoyant bulb, and blades that proliferate on the water surface. The sporophyte has an obligatory alternate phase, a microscopic gametophyte, whose ecology is poorly understood and may be vulnerable to different environmental factors than the macroscopic sporophyte [12,35,36]. Limited research has shown that Nereocystis populations within Puget Sound are genetically distinct from populations on the exposed coast [37], and they host a distinct microbiome [38].…”

“…In field studies, concentrations of 10 µM were associated with thicker blade tissues and a lower rate of blade erosion in Macrocystis sporophytes[132]. Laboratory studies showed increased performance in microscopic stages of Nereocystis associated with DIN increases from 1 to 15 µM[36]. Nitrogen requirements may be greater during periods of rapid growth or elevated temperatures[133].…”

“…In contrast, summer temperatures at nearshore stations in the West and Central sub-basins consistently exceeded this threshold, and additional sampling within the Squaxin Island kelp forest documented even higher temperatures than at the nearshore stations, ranging from 17 °C to 20 °C[103]. These temperature maxima approached or exceeded thresholds for decreased resilience of sporophytes and increased zoospore mortality[36,130,131].Nitrogen requirements for Nereocystis are not defined, yet data suggest that low summer concentrations in recent decades may be impacting Nereocystis performance in portions of SPS.The authors observed that the Nereocystis blades at Squaxin Island were thin, relatively short and shredded. In field studies, concentrations of 10 µM were associated with thicker blade tissues and a lower rate of blade erosion in Macrocystis sporophytes[132].…”