Diversity persists while function shifts: post-heatwave reorganization of reef fish communities in Baja California
Abstract
Background Marine heatwaves are increasing in frequency and intensity, driving persistent changes in kelp forests worldwide. Along the Pacific coast of Baja California, the 2014–2016 marine heatwave produced contrasting post-disturbance states, from persistent urchin barrens to understory-dominated reefs and declining canopy kelp. Kelp forests support reef-fish assemblages that sustain key ecosystem functions, yet how these functions track habitat reorganization after extreme warming remains unclear. Because no pre-heatwave baseline exists for the region, we examined post-disturbance trajectories from 2017 onward without assuming a common starting state across subregions. Methods We analyzed underwater visual census data from 2017 to 2024 across 12 sites spanning three biogeographic subregions (North, Middle, South) along ∼600 km of coastline. We quantified temporal changes in algae, invertebrates, and reef fishes, and assessed fish assemblages using a trait-based framework built on nine ecological traits, including body size, trophic group, growth performance, and maximum fecundity. Taxonomic and functional α-diversity were estimated as biomass-weighted Hill numbers, and β-diversity as temporal β-decay (dissimilarity over time since 2017). Species and traits driving compositional change were identified via SIMPER. Fish secondary productivity and biomass turnover (P/B) were calculated using a temperature-dependent growth model with species-specific life-history parameters and local sea surface temperature. Temporal trends were evaluated with generalized linear mixed models. Results Reefs followed divergent post-heatwave trajectories across subregions. Fish species richness and functional α-diversity remained stable everywhere, yet this stability masked contrasting regional dynamics in composition. In the North, assemblages showed minimal temporal change, consistent with a persistent urchin-barren configuration. In the Middle, functional β-decay increased over time, driven by shifts in trophic, growth, and body-size traits. The South showed the broadest reorganization, with significant increases in both taxonomic and functional β-decay and the strongest trait signal in maximum fecundity. Macroinvertivore biomass declined significantly in the North and showed a pronounced, though non-significant, decline in the South, with no compensatory increase in P/B among other functional groups. Our findings reveal a decoupling between biodiversity and ecosystem functioning in post-heatwave kelp-forest fish assemblages. Stable diversity metrics can conceal substantial reorganization in how assemblages produce and sustain biomass, and the biomass-dominant groups that underpin ecosystem processes are declining without compensation. Safeguarding these processes will require shifting from tracking diversity alone to directly monitoring and managing functional groups and biomass dynamics.
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BibTeX
@article{filz2026diversity,
title = {{Diversity persists while function shifts: post-heatwave reorganization of reef fish communities in Baja California}},
author = {Paulina Filz and Rodrigo Beas-Luna and Nicolas Loiseau and Julio Lorda and Jan Freiwald and Jeremie Bauer and Luis Malpica-Cruz},
journal = {PeerJ},
year = {2026},
month = jul,
doi = {10.7717/peerj.21452},
url = {https://hal.science/hal-05766779v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Diversity persists while function shifts: post-heatwave reorganization of reef fish communities in Baja California
AU - Paulina Filz
AU - Rodrigo Beas-Luna
AU - Nicolas Loiseau
AU - Julio Lorda
AU - Jan Freiwald
AU - Jeremie Bauer
AU - Luis Malpica-Cruz
PY - 2026
DA - 2026/07/08
JO - PeerJ
DO - 10.7717/peerj.21452
UR - https://hal.science/hal-05766779v1
AB - Background Marine heatwaves are increasing in frequency and intensity, driving persistent changes in kelp forests worldwide. Along the Pacific coast of Baja California, the 2014–2016 marine heatwave produced contrasting post-disturbance states, from persistent urchin barrens to understory-dominated reefs and declining canopy kelp. Kelp forests support reef-fish assemblages that sustain key ecosystem functions, yet how these functions track habitat reorganization after extreme warming remains unclear. Because no pre-heatwave baseline exists for the region, we examined post-disturbance trajectories from 2017 onward without assuming a common starting state across subregions. Methods We analyzed underwater visual census data from 2017 to 2024 across 12 sites spanning three biogeographic subregions (North, Middle, South) along ∼600 km of coastline. We quantified temporal changes in algae, invertebrates, and reef fishes, and assessed fish assemblages using a trait-based framework built on nine ecological traits, including body size, trophic group, growth performance, and maximum fecundity. Taxonomic and functional α-diversity were estimated as biomass-weighted Hill numbers, and β-diversity as temporal β-decay (dissimilarity over time since 2017). Species and traits driving compositional change were identified via SIMPER. Fish secondary productivity and biomass turnover (P/B) were calculated using a temperature-dependent growth model with species-specific life-history parameters and local sea surface temperature. Temporal trends were evaluated with generalized linear mixed models. Results Reefs followed divergent post-heatwave trajectories across subregions. Fish species richness and functional α-diversity remained stable everywhere, yet this stability masked contrasting regional dynamics in composition. In the North, assemblages showed minimal temporal change, consistent with a persistent urchin-barren configuration. In the Middle, functional β-decay increased over time, driven by shifts in trophic, growth, and body-size traits. The South showed the broadest reorganization, with significant increases in both taxonomic and functional β-decay and the strongest trait signal in maximum fecundity. Macroinvertivore biomass declined significantly in the North and showed a pronounced, though non-significant, decline in the South, with no compensatory increase in P/B among other functional groups. Our findings reveal a decoupling between biodiversity and ecosystem functioning in post-heatwave kelp-forest fish assemblages. Stable diversity metrics can conceal substantial reorganization in how assemblages produce and sustain biomass, and the biomass-dominant groups that underpin ecosystem processes are declining without compensation. Safeguarding these processes will require shifting from tracking diversity alone to directly monitoring and managing functional groups and biomass dynamics.
SN - 2167-8359
ER -