Biogeographic variation in temperature drives performance of kelp gametophytes during warming

Abstract

The capacity for thermal adjustment or adaptation is critical to population persistence in a warming ocean. Understanding such performance across a species' range can give insights into the extent of possible adjustment as well as spatial variation in vulnerability. This study tested the effects of temperature on the density and size of gametophytes of the habitatforming kelp Ecklonia radiata, across its Australian distribution (between ~9° and ~33°S). Gametophytes from warm, intermediate and cool biogeographic regions were cultured over a temperature gradient from 12 to 26°C, revealing optimum temperatures of ~18 to 23°C-well above current maximum temperatures in parts of the range-and a positive relationship between in situ temperature and thermal optima for performance. Optimum temperatures in warmer regions were more than 1°C higher than in cooler regions. Biogeographically, the thermal optima for gametophytes were more strongly linked to long-term temperature characteristics of a region (annual extremes, 3 yr range) than short-term variation (mean for the month prior) in sea temperature. These results document that present-day populations of E. radiata have adjusted their gametophyte thermal sensitivity according to their local environment, and further indicate that these differences are adaptive rather than phenotypic. Collectively, these findings suggest that the scope for thermal adaptation and gametophyte performance of E. radiata across most of its Australian distribution is within projected levels of future warming.

Assessing the ecosystem‐level consequences of a small‐scale artisanal kelp fishery within the context of climate‐change

“…However, these effects were generally observed over temperature ranges that span 2°-20°C over ambient (Fain and Murray 1982, Deysher and Dean 1986, Wernberg et al 2010, Brown et al 2014. Kelp populations are known to be locally adapted to the conditions they typically experience, with populations displaying different responses to changes in temperature throughout a latitudinal range (Buschmann et al 2004, Mohring et al 2014. However, the mean temperatures observed in this study (11.9°-12.7°C) are well within the thermal range known for M. pyrifera (8-23°C;Schiel and Foster 2015).…”

Interactions of daylength, temperature and nutrients affect thresholds for life stage transitions in the kelp Laminaria digitata (Phaeophyceae)

“…These assumptions do not take into account that local populations may have adapted to their respective conditions (e.g. Mohring et al 2014) and thus may show a different response to multifactorial changes than just one population. Furthermore the current investigation did not verify the situation in the field or consider spores taken throughout the season, but it clearly shows that responses of kelp life stages vary in time.…”

The importance of phenotypic plasticity and local adaptation in driving intraspecific variability in thermal niches of marine macrophytes

“…These studies reported both pronounced variability and little-to-no variability between populations. For example, Ecklonia radiata populations in Australia and New Zealand were found to have optimal performances reflective of those experienced by the environment in which they persist (Novaczek 1984, Mohring et al 2014 whereas no intraspecific variability in the gametophyte stage was reported for four kelp species in the northeast Atlantic (Bolton and Lüning 1982). Whether such differences will be important in the context of species redistributions will depend on the comparative vulnerability of the life stages.…”