University of California Institute of Marine Science - San Clemente State Beach

Restoration Project

University of California Institute of Marine Science - San Clemente State Beach

Restoration Objective:

To gain insight into the processes most likely to limit its recovery from catastrophic disturbances, which is highly relevant to kelp forest restoration. Specifically, we sought to determine: (1) how spatial patterns of giant kelp colonization varied in relation to distance from the nearest source population, (2) the extent to which density dependence during early stages of colonization influenced patterns of adult kelp abundance and biomass, and (3) the amount of time for the standing biomass of giant kelp at the artificial reef to approach levels comparable to that at nearby natural reefs. In addition, we evaluated the efficacy of outplanting laboratory-reared kelp embryos to the artificial reef as a useful and necessary tool for accelerating the establishment of giant kelp. Our results improve understanding of the ecological processes underlying kelp forest dynamics, particularly with respect to recovery from disturbance, which is needed for designing cost-effective restoration programs aimed at re-establishing kelps on natural reefs where they have declined.

Site Selection Criteria:

A site located near, but outside the influence of, the San Onofre Nuclear Generating Station discharge plume, intended to compensate for loss of giant kelp forest caused by station operations.

Cause Of Decline:

Wheeler North Reef (hereafter “artificial reef”) is a large artificial reef complex in southern California that was built to mitigate the loss of giant kelp forest habitat caused by the turbid discharge plume of the San Onofre Nuclear Generating Station (SONGS). It is located ~1 km offshore of San Clemente, California, USA (33.40210, −117.62420) at 13–16 m depth in an expansive area of sandy habitat that is near, but outside, the influence of the SONGS discharge plume.

Scientific Paper

The ecology of giant kelp colonization and its implications for kelp forest restoration

Reed, D. C., Schroeter, S. C., Huang, D., Weisman, D., Beheshti, K. M., & Smith, R. S. (2024).https://pubmed.ncbi.nlm.nih.gov/39072751/

Organisation:

University of California Institute of Marine Science

Site Observations:

Observation Date

1st Aug 1999 – 1st Aug 2003

Action Summary:

Construction of an artificial reef complex in three stages near a natural reef, with limited outplanting of laboratory-reared giant kelp to supplement natural colonisation. The reef was monitored for 3–4 years following construction of each phase.

In part 1 of Phase 1, approximately 7 hectares of a low-relief (<1 m tall) artificial reef at 13–16 m depth were constructed, with half built from quarried rock boulders and half from concrete rubble. The reef was divided into seven blocks of six reef modules (40 m × 40 m), with equal representation of each material within each block.

Lessons Learned:

Following physical habitat creation, natural kelp colonization and succession can be rapid and effective when stressors are alleviated, often outperforming seeding and transplanting, which are costly and uncertain.

Project Outcomes:

The rate of kelp biomass increase on the newly constructed artificial reef was relatively rapid and the average biomass of giant kelp for all phases of the artificial reef exceeded that at San Mateo and Barn within 2 or 3 years after reef construction. The low biomass of giant kelp at San Mateo from 2021 to 2023 is particularly noteworthy since the size of a spore source is directly related to the standing biomass of giant kelp (Castorani et al., 2017). The smaller source population at San Mateo during this period may have contributed to the lower recruitment observed on the Phase 3 modules compared to that observed following the construction of Phases 1 (Figure 3a) and 2 (Figure 4a) when the standing biomass of giant kelp at San Mateo was much larger.

Area of Restoration (Ha)

7

Distance to nearest kelp forest (in metres)

500

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Dry Weight Kelp

1.3500
g DW/m2
0.0000
g DW/m2

Observation Date

1st Jul 2000 – 1st Jun 2001

Action Summary:

Construction of an artificial reef complex in three stages near a natural reef, with limited outplanting of laboratory-reared giant kelp to supplement natural colonisation. The reef was monitored for 3–4 years following construction of each phase.

Giant kelp spores were cultured on braided nylon lines under laboratory conditions until embryonic sporophytes (~1 mm) developed. The seeded line segments were attached to polyvinyl chloride plates and outplanted to 14 additional Phase 1 modules in June–July 2000 (778 units total). In Phase 1, approximately 2 ha of low-relief (<1 m tall) artificial reef at 13–16 m depth were constructed as 14 additional modules (two per block across seven blocks), using quarried rock boulders and concrete rubble, with equal representation of each substrate type within each block.

Lessons Learned:

Following physical habitat creation, natural kelp colonization and succession can be rapid and effective when stressors are alleviated, often outperforming seeding and transplanting, which are costly and uncertain.

Project Outcomes:

The method used for outplanting embryonic giant kelp to the ar tificial reef in this study was relatively successful in that kelp survived for at least 11 months on 66% of the outplant units installed. Despite this level of success, outplanting proved unnecessary due to the wide spread natural colonization by giant kelp the first year after the artificial reef was constructed. This finding is important from a restoration context because the ef fort and expense involved in culturing kelp in the lab oratory and in fabricating and installing the outplant units in the field were substantial. That this effort in volved only 14 of 56 modules covering ~20% of 10 ha of the Phase 1 reef and produced an average plant density (0.02 · m−2) that was ~75 times lower than the average density of natural recruits.

Area of Restoration (Ha)

2

Distance to nearest kelp forest (in metres)

500

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Percent Survival

75.3800
%
100.0000
%

Observation Date

1st Aug 2008 – 1st Aug 2012

Action Summary:

Construction of an artificial reef complex in three stages near a natural reef, with limited outplanting of laboratory-reared giant kelp to supplement natural colonisation. The reef was monitored for 3–4 years following construction of each phase.

Phase 2 comprised 18 irregularly shaped modules (0.6–16 ha each) interspersed among the Phase 1 modules. Phase 2 encompassed ~61 ha of low-relief (<1 m tall) artificial reef at 13–16 m depth, constructed entirely of quarried rock boulders with ~45% bottom coverage.

Lessons Learned:

Following physical habitat creation, natural kelp colonization and succession can be rapid and effective when stressors are alleviated, often outperforming seeding and transplanting, which are costly and uncertain.

Project Outcomes:

The rate of kelp biomass increase on the newly constructed artificial reef was relatively rapid and the average biomass of giant kelp for all phases of the artificial reef exceeded that at San Mateo and Barn within 2 or 3 years after reef construction. The low biomass of giant kelp at San Mateo from 2021 to 2023 is particularly noteworthy since the size of a spore source is directly related to the standing biomass of giant kelp (Castorani et al., 2017). The smaller source population at San Mateo during this period may have contributed to the lower recruitment observed on the Phase 3 modules compared to that observed following the construction of Phases 1 (Figure 3a) and 2 (Figure 4a) when the standing biomass of giant kelp at San Mateo was much larger

Area of Restoration (Ha)

61

Distance to nearest kelp forest (in metres)

500

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Dry Weight Kelp

1.1800
g DW/m2
0.0000
g DW/m2

Observation Date

1st Aug 2019 – 1st Aug 2023

Action Summary:

Construction of an artificial reef complex in three stages near a natural reef, with limited outplanting of laboratory-reared giant kelp to supplement natural colonisation. The reef was monitored for 3–4 years following construction of each phase.

Phase 3a consisted of 11 irregularly shaped modules (0.6–12 ha each), encompassing ~50 ha of low-relief (<1 m tall) artificial reef at 13–16 m depth, constructed entirely of quarried rock boulders with ~45% bottom coverage.

Lessons Learned:

Following physical habitat creation, natural kelp colonization and succession can be rapid and effective when stressors are alleviated, often outperforming seeding and transplanting, which are costly and uncertain.

Project Outcomes:

The rate of kelp biomass increase on the newly constructed artificial reef was relatively rapid and the average biomass of giant kelp for all phases of the artificial reef exceeded that at San Mateo and Barn within 2 or 3 years after reef construction. The low biomass of giant kelp at San Mateo from 2021 to 2023 is particularly noteworthy since the size of a spore source is directly related to the standing biomass of giant kelp (Castorani et al., 2017). The smaller source population at San Mateo during this period may have contributed to the lower recruitment observed on the Phase 3 modules compared to that observed following the construction of Phases 1 (Figure 3a) and 2 (Figure 4a) when the standing biomass of giant kelp at San Mateo was much larger

Area of Restoration (Ha)

50

Distance to nearest kelp forest (in metres)

500

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Dry Weight Kelp

0.0600
g DW/m2
0.0000
g DW/m2

Observation Date

1st Aug 2020 – 1st Aug 2023

Action Summary:

Construction of an artificial reef complex in three stages near a natural reef, with limited outplanting of laboratory-reared giant kelp to supplement natural colonisation. The reef was monitored for 3–4 years following construction of each phase.

Phase 3b consisted of 9 irregularly shaped modules (0.6–12 ha each), encompassing ~30 ha of low-relief (<1 m tall) artificial reef at 13–16 m depth, constructed entirely of quarried rock boulders with ~45% bottom coverage.

Lessons Learned:

Following physical habitat creation, natural kelp colonization and succession can be rapid and effective when stressors are alleviated, often outperforming seeding and transplanting, which are costly and uncertain.

Project Outcomes:

The rate of kelp biomass increase on the newly constructed artificial reef was relatively rapid and the average biomass of giant kelp for all phases of the artificial reef exceeded that at San Mateo and Barn within 2 or 3 years after reef construction. The low biomass of giant kelp at San Mateo from 2021 to 2023 is particularly noteworthy since the size of a spore source is directly related to the standing biomass of giant kelp (Castorani et al., 2017). The smaller source population at San Mateo during this period may have contributed to the lower recruitment observed on the Phase 3 modules compared to that observed following the construction of Phases 1 (Figure 3a) and 2 (Figure 4a) when the standing biomass of giant kelp at San Mateo was much larger

Area of Restoration (Ha)

30

Distance to nearest kelp forest (in metres)

500

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Dry Weight Kelp

0.3300
g DW/m2
0.0000
g DW/m2
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