Persistence of tropical herbivores in temperate reefs constrains kelp resilience to cryptic habitats

Global warming is facilitating the range expansion of tropical herbivores, causing a tropicalization of temperate marine ecosystems, where tropical herbivores can suppress habitat‐forming macrophytes, supporting the resilience of canopy‐free ecosystem states. However, currently we lack a thorough un...

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Bibliographic Details
Published in:The Journal of ecology 2021-05, Vol.109 (5), p.2081-2094
Main Authors: Zarco‐Perello, Salvador, Bosch, Nestor E., Bennett, Scott, Vanderklift, Mat A., Wernberg, Thomas, Randall Hughes, A.
Format: Article
Language:English
Subjects:
Algae
Aquatic plants
Browsing
Canopies
Canopy
Climate change
Ecosystems
Global warming
Habitats
Herbivores
Herbivory
Juveniles
Kelp
kelp forest
Lagoons
Macrophytes
Marine ecosystems
Marine fishes
Nursery grounds
Open spaces
Populations
Propagules
Range extension
Recovery
Recruitment
Recruitment (fisheries)
Reefs
refuge
Refuges
Refugia
Resilience
Restoration
Sea grasses
seagrass
Seaweeds
Substrata
Survival
temperate reefs
Tropical climate
Tropical forests
tropicalization
Turf
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Summary:Global warming is facilitating the range expansion of tropical herbivores, causing a tropicalization of temperate marine ecosystems, where tropical herbivores can suppress habitat‐forming macrophytes, supporting the resilience of canopy‐free ecosystem states. However, currently we lack a thorough understanding of the mechanisms that, on one hand, support the persistence of tropical herbivores and on the other support the recovery of temperate foundation species in tropicalized ecosystems, a required knowledge to predict potential regime shifts and reversals to the baseline state of the ecosystem. This study tested processes behind the persistence of the tropicalization of temperate reefs which experienced a complete loss of their kelp forests and an influx of tropical herbivores following a marine heatwave in 2011. For this, we assessed the feedback mechanisms that maintain turf‐dominated states (recruitment of tropical herbivores, browsing and grazing rates and turf cover) and those that resist it (kelp recruitment, survival and reproductiveness). We found that the reefs remained tropicalized with high abundances of turf and tropical herbivores after 9 years from the regime shift. The rabbitfish Siganus fuscescens and the chub Kyphosus bigibbus were the most important herbivores whose persistence was supported by the adjacent reef lagoon, where seagrass meadows and the backreef habitats hosted juveniles of both species, particularly rabbitfish. Tropical herbivores exerted a strong top–down control on turf seaweed and kelp during herbivory assays, rapidly consuming kelp individuals in open areas. However, in topographical refuges in the reefs, herbivory was low and kelp individuals survived, with some having reproductive tissue. Synthesis. Our findings incorporate the importance of nursery grounds for tropical herbivores and herbivory refugia for kelp individuals into the tropicalization model, where the former increases the resilience of canopy‐free states and the latter might facilitate recovering kelp populations. The restoration of abundant warm‐resistant kelp populations in shelters could provide local sources of propagules to recolonize open spaces; however, our results suggest that the reduction of herbivory and the provision of turf‐free substratum would be necessary to boost the recovery of kelp forests. Our findings incorporate the importance of nursery grounds for range‐expanding tropical herbivores and herbivory refugia for kelp individuals int
ISSN:0022-0477
1365-2745
DOI:10.1111/1365-2745.13621