Local adaptation of juvenile giant kelp, Macrocystis pyrifera, from their southern limit in the northern hemisphere explored using reciprocal transplantation

ABSTRACT

The Pacific coast of the Baja California peninsula (Mexico) is a unique biogeographic transition zone, where many kelp species encounter their southern subtropical limits and have experienced a range contraction in the northern hemisphere. Using reciprocal transplant experiments with giant kelp populations from their southern limit and a northern temperate site on the Baja California peninsula, we hypothesized that juveniles from the southern site would grow longer, have more fronds (an individual stipe with its blades), and have higher photosynthetic efficiency (α) and blade tissue nitrogen, especially under warmer nitrate-limited field conditions experienced in their habitat. At the southern-limit transplant site, local juveniles had more fronds compared with those from the north after 90 days in field conditions (warm waters). At the northern transplant site, blade tissue nitrogen of juveniles from both populations was low after 23 days in field conditions (not significantly different during a warm water period), however, after a further 56 day cooling period and shortly after a strong upwelling event, juveniles from the southern population had greater blade tissue nitrogen concentrations than those from the north, which showed little change. Respiration and a were both greater at higher temperatures in juveniles from the southern population, and this pattern was maintained under warm water field conditions. These physiological differences in conspecific juveniles from different populations may be driven by population-level adaptation to frequently occurring thermal and nutrient stress in southern Baja California, which is the southern distribution limit for giant kelp. Further exploration of population level differences in ecophysiology should be applied to kelp forest restoration efforts as oceans warm.

KEYWORDS:

• Baja California
• common garden experiment
• distributional limits
• ecotype
• reciprocal transplants

Acknowledgments

Diving was conducted by LBL and JAZ. Facilities were provided by the Universidad Autónoma de Baja California, Instituto de Investigaciones Oceanológicas. Field assistance was provided by the Sociedad Cooperativo de Producción Pesquera de Bahía Tortugas. Assistance at all stages of this research was graciously provided by M.C. José M. Guzmán.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary information

The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2021.2007543

Supplementary table S1. Repeated measures ANOVA results comparing variables measured for the juvenile reciprocal transplants in (a) the southern-limit transplant experiment (time = initial and final evaluations) and (b) the Northern Baja California transplant experiment (time = initial, middle and final evaluations), with (c) comparisons of photosynthetic parameters from oxygen evolution tests at 15°C initially and after both transplant periods (time = initial, middle and final evaluations) in the Northern Baja California transplant experiment (23 days and 56 days), and (d) comparisons of photosynthetic parameters from oxygen evolution tests at 15°C and 25°C initially and only after the first transplant period (time = initial and middle evaluations) in the Northern Baja California common garden experiment (23 days). Significant p values lower than 0.05 are highlighted in red. When ANOVA assumptions were violated (see Levene’s test p values for homogeneity of variances results for each time period, last column), transformed results are shown below original results.

Author contributions

L.B. Ladah: experimental design, the collection of data, the analysis of the results, and the writing and reviewing of the manuscript; J.A. Zertuche-González: experimental design, the collection of data, the analysis of the results, and the writing and reviewing of the manuscript.

Additional information

Funding

This research was funded by SIMAC 970106007 and by the UABC segunda convocatoria interna to JAZ.