Large‐scale one‐off sea urchin removal promotes rapid kelp recovery in urchin barrens

Miller, Kelsey I.; Balemi, Celia A.; Bell, Daria R.; Blain, Caitlin O.; Caiger, Paul E.; Hanns, Benn J.; Kulins, Sara E.; Peleg, Ohad; Spyksma, Arie J. P.; Shears, Nick T.

doi:10.1111/rec.14060

Cited by 8 publications

(4 citation statements)

References 72 publications

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“…Removal areas and barren control habitats were not significantly different prior to removal (Figure 3A; Appendix S1: Table S3). The increase in macroalgal density in removal areas corresponded to an increase in total canopy cover from ~5% to ~43%, with E. radiata as the dominant canopy cover (Miller, Balemi, et al, 2024).…”

Section: Resultsmentioning

confidence: 99%

“…The study sites were predominantly sloping rocky reefs dominated by urchin barrens. A large‐scale sea urchin removal was conducted from four 1.6‐ to 2‐ha areas of urchin barrens at these sites to evaluate this method as a potential tool for macroalgal restoration (Miller, Balemi, et al, 2024). Urchin barren and kelp control areas were selected as close together as practical, while ensuring these habitats could be represented at the same depth (Figure 1).…”

Section: Methodsmentioning

confidence: 99%

“…Four large (1.6–2 ha) semi‐discrete areas of urchin barrens were cleared of almost all (~90%) adult sea urchins (≥40 mm), predominantly by manual culling with remains left in the marine system (Miller & Shears, 2023), between 2 September 2020 and 25 March 2021. For further details, see Miller and Shears (2023) on removal methods and Miller, Balemi, et al (2024) for monitoring methods and further details on kelp recovery. The density of forest‐forming macroalgae (kelp and fucoids, including E. radiata , Carpophyllum maschalocarpum , C. flexuosum , C. plumosum , C. angustifolium , Sargassum sinclairii , Cystophora retroflexa , C. torulosa , and Xiphophora chondrophylla ) was assessed pre‐removal, and at 6, 12, and 24 months post‐removal by counting all thalli within 1‐m 2 quadrats placed along semipermanent transects (Miller, Balemi, et al, 2024).…”

Section: Methodsmentioning

confidence: 99%

“…With growing recognition of the widespread existence of urchin barrens, there has been increased interest in accelerating kelp forest restoration through active kina removal (i.e., culling or harvest; Fisheries New Zealand, 2023; Miller et al, 2022; Miller & Shears, 2023). Sea urchin removal studies in New Zealand have demonstrated macroalgal recovery (Andrew & Choat, 1982; Ayling, 1981; Miller, Balemi, et al, 2024; Villouta et al, 2001), which increases the availability and quality of food for sea urchins and can ultimately improve their roe condition.…”

Section: Introductionmentioning

confidence: 99%

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Sea urchin roe quality within urchin barrens and improvement through kelp restoration

Miller,

Balemi,

Blain

et al. 2024

Ecosphere

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Sea urchin overgrazing is a major cause of kelp loss and consequently sea urchin removal is frequently promoted as a tool for restoring kelp in urchin barrens. While many sea urchin species support high‐end roe fisheries, roe condition is generally lower in barrens than in kelp forests due to reduced food availability. Understanding how roe condition varies between kelp and barren habitats, and in response to kelp restoration, is key to developing effective, culturally and socially acceptable approaches to sea urchin removal and for assessing the potential benefits of kelp restoration. We assessed whether sea urchin roe quality within urchin barrens in northeastern Aotearoa New Zealand can be sufficient for harvest, and whether sea urchin removal can ultimately enhance urchin roe condition (by increasing food quality and quantity). We monitored roe condition (roe weight and gonadosomatic index [GSI]) in kelp forest and urchin barrens monthly for one year at two sites, and quarterly over two years at four sites following large‐scale (1.6–2 ha) sea urchin removal from urchin barrens. While roe condition was generally lower in barrens, the magnitude of this difference varied seasonally and among sites. Sea urchin roe quality within barrens was sufficient for commercial harvest (GSI ≥ 6%) during spring–summer at three sites. Following large‐scale sea urchin removal, kelp and fucoid density increased over two years (~9–58 plants m−2), but remained low in barren control areas. Although variable, sea urchins from removal areas (restored kelp) typically showed increased GSI, roe weight, and improved roe color within nine months following removal. These results suggest that, at some locations, harvest may provide a viable method for removing urchins from urchin barrens for kelp restoration purposes. However, to ensure sea urchin densities are reduced and maintained below the critical levels needed to achieve restoration outcomes, strategic approaches with critical evaluation of methods are required. Furthermore, we demonstrate that effectively removing urchins and promoting kelp recovery can ultimately improve urchin roe quality.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sea urchin roe quality within urchin barrens and improvement through kelp restoration

Miller,

Balemi,

Blain

et al. 2024

Ecosphere

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Vulnerability of kelp, Ecklonia radiata, to persistent nitrogen pollution and coastal darkening

Mason,

Blain

2024

Mar Biol

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Coastal darkening is expected to have pervasive impacts on benthic primary producers. However, the effects of nitrogen enrichment, an often-co-occurring stressor, on benthic primary producers and their functions is less clear. This study investigates the interactive effects of coastal darkening and nitrogenous eutrophication, including nitrogen source (NH4+ vs. NO3−), on the function of the kelp Ecklonia radiata. First, an in-situ experiment was used to assess the differential impacts of NH4+ and NO3− pulse enrichment on the photosynthetic performance and pH modulation capacity of E. radiata. Second, a laboratory experiment was used to assess the longer-term impacts of nitrogen enrichment under low-light conditions mimicking coastal darkening on service provisioning, including photosynthetic performance, pH modulation, nutrient uptake and growth. While pulse nitrogen enrichment had no impacts on the photosynthetic performance of E. radiata in-situ, persistent exposure to either NH4+ or NO3− acted as a stressor to sporophytes as indicated by elevated rates of dark respiration and lamina erosion and reduced photosynthetic efficiency and growth rates. Furthermore, low-light conditions elicited reduced photosynthetic capacity at saturating irradiance, which extended to a reduction in the extent of pH modulation, and significantly increased lamina erosion. While the two stressors appeared to act on distinct parameters, ultimately, both darkening and eutrophication directly reduced net primary production, especially when in combination. These results demonstrate the negative interactive effects of coastal darkening and eutrophication on E. radiata function, while suggesting a vulnerability of E. radiata to even moderate levels of persistent nitrogen enrichment. This vulnerability highlights the need to consider environmental conditions during kelp conservation and restoration, and when attempting to valorise kelp ecophysiology for nature-based solutions.

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Marine heatwave promotes population expansion of the invasive ascidian Symplegma brakenhielmi

Spyksma,

Miller,

Shears

2024

Biol Invasions

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The global increase in frequency and severity of marine heatwaves (MHWs) is highlighting the impact these extreme climatic events can have on marine ecosystems. Throughout the summer of 2021/2022 northeastern Aotearoa/New Zealand suffered an unprecedented MHW. Worst impacted areas, such as the semi-enclosed Te Moananui-ā-Toi/Tīkapa Moana/Hauraki Gulf, experienced more than three continual months of temperatures at or above the climatological mean maximum (20.7 °C). During this period, we observed a rapid increase in the abundance and cover of the invasive, warm-affinity colonial ascidian Symplegma brakenhielmi on temperate rocky reefs. Population expansion of this species has not previously been linked to MHW events. Benthic monitoring as water temperatures cooled showed a sharp decrease in S. brakenhielmi abundance, but not complete disappearance, and the coverage of individually monitored colonies also declined. There was no observed increase in abundance or cover throughout the summer of 2022/2023, a potential consequence of cooler water temperatures and multiple cyclones. Observed impacts included the growth of S. brakenhielmi over other sessile invertebrate and macroalgal species, as well as on highly mobile spiny lobster, suggesting that this species can have a variety of impacts on temperate rocky reefs. In the future, as ocean temperatures continue to warm, these findings provide insight into what we can expect and highlight how MHW can facilitate the rapid expansion and integration of non-native, warm-affinity species into temperate reef ecosystems.

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Large‐scale one‐off sea urchin removal promotes rapid kelp recovery in urchin barrens

Cited by 8 publications

References 72 publications

Sea urchin roe quality within urchin barrens and improvement through kelp restoration

Sea urchin roe quality within urchin barrens and improvement through kelp restoration

Vulnerability of kelp, Ecklonia radiata, to persistent nitrogen pollution and coastal darkening

Marine heatwave promotes population expansion of the invasive ascidian Symplegma brakenhielmi

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