Restoration Objective:

This study used reciprocal transplants (though not precisely matched) to test the hypothesis that M. pyrifera sporophytes from the southern distribution limit in the northern hemisphere have developed local adaptations to a stressful thermal and nutrient regime (associated with ocean warming events) over recurrent exposure to these selective forces. The alternate hypothesis is no local adaptation has occurred in these southern populations, because strong genetic drift or high gene flow from the northern populations continue. he reason for currently revisiting the data is the recent documentation of continued resilience of the southern-limit populations after a marine heat wave (Cavanaugh et al., 2019) and the renewed interest in using them as a propagule source for restoration efforts to protect against kelp forest loss due to accelerating climate change.

Site Selection Criteria:

The Campo Kennedy site in northern Baja California (Fig. 1) was the northern juvenile source and transplant site, representing the northern distribution for Mexico and the middle of the northern hemisphere distribution. M. pyrifera populations survived the 1997–98 El Niño mass-mortality event, and generally experience less thermal stress than the southern site in this location with strong upwelling

Cause Of Decline:

The giant kelp forests at their southern distributional limit in the northern hemisphere in Mexico have been negatively affected by warming events over the past decades (Ladah et al., 1999; Edwards, 2004), like other trailing edge kelp populations globally, however, they have also shown resilience (Ladah et al., 1999; Cavanaugh et al., 2019), which is surprising considering the limited spore dispersal (Gaylord et al., 2006) and thermal sensitivity of the species (Schiel & Foster, 2015). After one of the largest extirpation events measured to date on this coast in situ, recovery at the southern limit most likely occurred from microscopic stage survival in a seed bank analogue (Ladah et al., 1999; Ladah & Zertuche-González, 2007), which would have allowed for population and genetic continuity in the absence of spore availability from other populations, and potentially preserved any local adaptation to the thermal and nutrient environment of the region.

Key Reasons For Decline:

Ocean Warming

Scientific Paper

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

Ladah, L. B., & Zertuche-González, J. A. (2022).https://www.tandfonline.com/d...0.1080/09670262.2021.2007543

Organisation:

Universidad Autónoma de Baja California

Site Observations:

Observation Date

20th Sep 1999 – 7th Dec 1999

Action Summary:

Juvenile Macrocystis pyrifera were collected from both warm and cool origin sites and transplanted either back to their site of origin or to the contrasting temperature site, so that both warm and cool locations contained individuals from each origin. Transplants were monitored for 79 days.

Ten juvenile kelp (~1 m tall, bearing one or two fronds) from the cool origin population were collected from 10 m depth and replanted at the same site. Individuals were packed and left overnight to imitate transport treatment before being threaded onto polypropylene rope, labelled, secured to weighted lines, and deployed at ~5 m depth along the inshore edge of the existing kelp forest.

Lessons Learned:

Populations from the warmer range edge may be valuable propagule sources for restoration in regions experiencing nutrient limitation, thermal stress, or increased competition from warm-tolerant macroalgae. Although changes in frond length did not differ significantly between origins, juveniles from the warmer range edge exhibited greater frond addition and increased tissue nitrogen more rapidly.

Project Outcomes:

There were no population-level differences found for frond lengths after in situ experiments, although there was a difference for frond addition. Juveniles from the south may divert energy into adding fronds rather than elongating the stipe. Overall, this study suggests that under some common field conditions, the southern-limit juveniles of giant kelp in the northern hemisphere can increase their frond numbers and their tissue nitrogen faster than those from a more northern temperate population, with higher respiration and higher photosynthetic efficiency at higher temperatures. These patterns could be the result of local adaptations and may explain how populations have been resilient at the southern limit in the northern hemisphere and merit further exploration.

Indicator Data:

Indicator:	Ending Value:	Starting Value:
Length	2.6200 m	0.7630 m

Transplant Info:
Life Stage:	Juveniles
Source:	Wild

Observation Date

20th Sep 1999 – 7th Dec 1999

Action Summary:

Ten juvenile kelp (~1 m tall, bearing one or two fronds) from the warm origin population were collected at 10 m depth and transplanted the following day to the northern (cooler) site. Individuals were threaded onto polypropylene rope through the holdfast, labelled, secured to weighted lines, and deployed at ~5 m depth along the inshore edge of the existing kelp forest.

Lessons Learned:

Project Outcomes:

Indicator Data:

Indicator:	Ending Value:	Starting Value:
Length	2.9170 m	0.9250 m

Transplant Info:
Life Stage:	Juveniles
Source:	Wild

Universidad Autónoma de Baja California - Campo Kennedy

Universidad Autónoma de Baja California - Campo Kennedy

Restoration Project

Universidad Autónoma de Baja California - Campo Kennedy

Restoration Objective:

Site Selection Criteria:

Cause Of Decline:

Ocean Warming

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

Organisation:

Universidad Autónoma de Baja California

Site Observations:

20th Sep 1999 – 7th Dec 1999

Action Summary:

Lessons Learned:

Project Outcomes:

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Length

20th Sep 1999 – 7th Dec 1999

Action Summary:

Lessons Learned:

Project Outcomes:

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Length