1
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Cannon SE, Donner SD, Liu A, González Espinosa PC, Baird AH, Baum JK, Bauman AG, Beger M, Benkwitt CE, Birt MJ, Chancerelle Y, Cinner JE, Crane NL, Denis V, Depczynski M, Fadli N, Fenner D, Fulton CJ, Golbuu Y, Graham NAJ, Guest J, Harrison HB, Hobbs JPA, Hoey AS, Holmes TH, Houk P, Januchowski-Hartley FA, Jompa J, Kuo CY, Limmon GV, Lin YV, McClanahan TR, Muenzel D, Paddack MJ, Planes S, Pratchett MS, Radford B, Reimer JD, Richards ZT, Ross CL, Rulmal J, Sommer B, Williams GJ, Wilson SK. Macroalgae exhibit diverse responses to human disturbances on coral reefs. GLOBAL CHANGE BIOLOGY 2023; 29:3318-3330. [PMID: 37020174 DOI: 10.1111/gcb.16694] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 03/01/2023] [Accepted: 03/01/2023] [Indexed: 05/16/2023]
Abstract
Scientists and managers rely on indicator taxa such as coral and macroalgal cover to evaluate the effects of human disturbance on coral reefs, often assuming a universally positive relationship between local human disturbance and macroalgae. Despite evidence that macroalgae respond to local stressors in diverse ways, there have been few efforts to evaluate relationships between specific macroalgae taxa and local human-driven disturbance. Using genus-level monitoring data from 1205 sites in the Indian and Pacific Oceans, we assess whether macroalgae percent cover correlates with local human disturbance while accounting for factors that could obscure or confound relationships. Assessing macroalgae at genus level revealed that no genera were positively correlated with all human disturbance metrics. Instead, we found relationships between the division or genera of algae and specific human disturbances that were not detectable when pooling taxa into a single functional category, which is common to many analyses. The convention to use percent cover of macroalgae as an indication of local human disturbance therefore likely obscures signatures of local anthropogenic threats to reefs. Our limited understanding of relationships between human disturbance, macroalgae taxa, and their responses to human disturbances impedes the ability to diagnose and respond appropriately to these threats.
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Affiliation(s)
- Sara E Cannon
- Department of Geography, University of British Columbia, British Columbia, Vancouver, Canada
| | - Simon D Donner
- Department of Geography, University of British Columbia, British Columbia, Vancouver, Canada
| | - Angela Liu
- Department of Geography, University of British Columbia, British Columbia, Vancouver, Canada
- School of Geography and the Environment, University of Oxford, Oxford, UK
| | - Pedro C González Espinosa
- Department of Geography, University of British Columbia, British Columbia, Vancouver, Canada
- Institute for the Oceans and Fisheries, University of British Columbia, British Columbia, Vancouver, Canada
| | - Andrew H Baird
- Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Queensland, Townsville, Australia
| | - Julia K Baum
- Department of Biology, University of Victoria, British Columbia, Victoria, Canada
| | - Andrew G Bauman
- Department of Marine and Environmental Science, Nova Southeastern University, Florida, Dania Beach, USA
| | - Maria Beger
- School of Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK
- Department of Aquatic Resources Management, Faculty of Fisheries and Marine Science, Pattimura University, Ambon, Indonesia
- Centre for Biodiversity and Conservation Science, University of Queensland, Queensland, St Lucia, Australia
| | | | - Matthew J Birt
- Australian Institute of Marine Science, Western Australia, Perth, Australia
| | - Yannick Chancerelle
- CRIOBE, UAR 3278 CNRS-EPHE-UPVD, Moorea French Polynesia and the French Center for Excellence for Coral Reefs (LabEx Corail), PSL Research University, Paris, France
| | - Joshua E Cinner
- Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Queensland, Townsville, Australia
| | - Nicole L Crane
- One People One Reef, California, Santa Cruz, USA
- Department of Biology, Cabrillo College, California, Aptos, USA
| | - Vianney Denis
- Institute of Oceanography, National Taiwan University, Taipei, Taiwan
| | - Martial Depczynski
- Australian Institute of Marine Science, Western Australia, Perth, Australia
| | - Nur Fadli
- Faculty of Marine and Fisheries, Universitas Syiah Kuala, Banda Aceh, Indonesia
| | | | | | | | | | - James Guest
- School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, UK
| | - Hugo B Harrison
- Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Queensland, Townsville, Australia
- School of Biological Sciences, University of Bristol, Bristol, UK
| | - Jean-Paul A Hobbs
- School of Biological Sciences, The University of Queensland, Queensland, Brisbane, Australia
| | - Andrew S Hoey
- Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Queensland, Townsville, Australia
| | - Thomas H Holmes
- Marine Science Program, Biodiversity and Conservation Science, Department of Biodiversity Conservation and Attractions, Western Australia, Kensington, Australia
| | - Peter Houk
- University of Guam Marine Laboratory, UOG Station, Mangilao, Guam
| | | | - Jamaluddin Jompa
- Department of Marine Science and Fisheries, Hasanuddin University, South Sulawesi, Makassar, Indonesia
| | - Chao-Yang Kuo
- Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Queensland, Townsville, Australia
- Biodiversity Research Center, Academia Sinica, Taipei, Taiwan
| | - Gino Valentino Limmon
- Department of Marine Biology, Pattimura University, Ambon, Indonesia
- Maritime and Marine Science Centre of Excellence, Pattimura University, Ambon, Indonesia
| | - Yuting V Lin
- Institute of Oceanography, National Taiwan University, Taipei, Taiwan
| | | | - Dominic Muenzel
- School of Biology, Faculty of Biological Sciences, University of Leeds, Leeds, UK
| | - Michelle J Paddack
- One People One Reef, California, Santa Cruz, USA
- Santa Barbara City College, California, Santa Barbara, USA
| | - Serge Planes
- CRIOBE, UAR 3278 CNRS-EPHE-UPVD, Moorea French Polynesia and the French Center for Excellence for Coral Reefs (LabEx Corail), PSL Research University, Paris, France
| | - Morgan S Pratchett
- Australian Research Council Centre of Excellence for Coral Reef Studies, James Cook University, Queensland, Townsville, Australia
| | - Ben Radford
- Australian Institute of Marine Science, Western Australia, Perth, Australia
- Oceans Institute, University of Western Australia, Western Australia, Perth, Australia
| | - James Davis Reimer
- Department of Marine Science, Chemistry and Biology, Faculty of Science, University of the Ryukyus, Okinawa, Japan
- Tropical Biosphere Research Center, University of the Ryukyus, Okinawa, Japan
| | - Zoe T Richards
- Coral Conservation and Research Group, School of Molecular and Life Sciences, Curtin University, Western Australia, Bently, Australia
- Collections and Research, Western Australian Museum, Western Australia, Perth, Australia
| | - Claire L Ross
- Marine Science Program, Biodiversity and Conservation Science, Department of Biodiversity Conservation and Attractions, Western Australia, Kensington, Australia
- Oceans Institute, University of Western Australia, Western Australia, Perth, Australia
| | - John Rulmal
- One People One Reef, California, Santa Cruz, USA
- Ulithi Falalop Community Action Program, Yap, Micronesia
| | - Brigitte Sommer
- School of Life and Environmental Sciences, The University of Sydney, New South Wales, Sydney, Australia
- School of Life Sciences, University of Technology Sydney, 2007, New South Wales, Sydney, Australia
| | | | - Shaun K Wilson
- Marine Science Program, Biodiversity and Conservation Science, Department of Biodiversity Conservation and Attractions, Western Australia, Kensington, Australia
- Oceans Institute, University of Western Australia, Western Australia, Perth, Australia
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2
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Betancourt AM, Fenwick IF, Howard HB, Long AE, Fong P, Barber PH, Fong CR. Ontogenetic Variation in Blade Toughness May Contribute to the Spread of Turbinaria ornata Across the South Pacific. JOURNAL OF PHYCOLOGY 2023; 59:277-280. [PMID: 36308024 DOI: 10.1111/jpy.13292] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Accepted: 09/20/2022] [Indexed: 06/16/2023]
Abstract
Coral reefs are shifting from coral to algal-dominated ecosystems worldwide. Recently, Turbinaria ornata, a marine alga native to coral reefs of the South Pacific, has spread in both range and habitat usage. Given dense stands of T. ornata can function as an alternative stable state on coral reefs, it is imperative to understand the factors that underlie its success. We tested the hypothesis that T. ornata demonstrates ontogenetic variation in allocation to anti-herbivore defense, specifically that blade toughness varied nonlinearly with thallus size. We quantified the relationship between T. ornata blade toughness and thallus size for individual thalli within algal stands (N = 345) on seven fringing reefs along the north shore of Moorea, French Polynesia. We found that blade toughness was greatest at intermediate sizes that typically form canopies, with overall reduced toughness in both smaller individuals that refuge within the understory and older reproductive individuals that ultimately detach and form floating rafts. We posit this variation in blade toughness reduces herbivory on the thalli that are most exposed to herbivores and may facilitate reproduction in dispersing stages, both of which may aid the proliferation of T. ornata.
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Affiliation(s)
- Austin M Betancourt
- Department of Biological Sciences, San José State University, 1 Washington Square, San Jose, California, 95192, USA
| | - Ileana F Fenwick
- Department of Marine and Environmental Science, Hampton University, Hampton, Virginia, 23668, USA
| | - Hunter B Howard
- University of Maryland Eastern Shore, Living Marine Resources Cooperative Science Center, Henry O. Tanner Airway Science Building, Building #915, 30806 University Boulevard South, Princess Anne, Maryland, 21853, USA
| | - Alexys E Long
- Biology Department, Norfolk State University, Suite 115 Woods Science Building, Norfolk State University 700 Park Avenue, Norfolk, Virginia, 23504, USA
| | - Peggy Fong
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 621 Charles E. Young Drive South, Los Angeles, California, 90095, USA
| | - Paul H Barber
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, 621 Charles E. Young Drive South, Los Angeles, California, 90095, USA
| | - Caitlin R Fong
- National Center of Ecological Analysis and Synthesis, University of California, Santa Barbara, 1021 Anacapa St, Santa Barbara, California, 93101, USA
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3
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Srednick G, Cohen A, Diehl O, Tyler K, Swearer SE. Habitat attributes mediate herbivory and influence community development in algal metacommunities. Ecology 2023; 104:e3976. [PMID: 36691779 DOI: 10.1002/ecy.3976] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 11/24/2022] [Accepted: 12/07/2022] [Indexed: 01/25/2023]
Abstract
Understanding the drivers and impacts of spatiotemporal variation in species abundance on community trajectories is key to understanding the factors contributing to ecosystem resilience. Temporal variation in species trajectories across patches can provide compensation for species loss and can influence successional patterns. However, little is known about the underlying mechanisms that lead to patterns of species or spatial compensation and how those patterns may be mediated by consumer-resource relationships. Here we describe an experiment testing whether habitat attributes (e.g., structural complexity and spatial heterogeneity) mediate the effects of herbivory on tropical marine macroalgal communities by reducing accessibility and detectability, respectively, leading to variable trajectories among algal species at community (within patch) and metacommunity (i.e., among patch) scales. Reduced accessibility (greater habitat complexity) decreased the effects of herbivory (i.e., depressed consumption rate, increased algal species richness), and both accessibility and detectability (spatial heterogeneity) influenced algal community structure. Moreover, decreased accessibility at the community scale and a mosaic of accessibility at the metacommunity scale led to variation in community assembly. We suggest that habitat attributes can be important influencers of consumer-resource interactions on coral reefs, which in turn can increase species diversity, promote species succession, and enhance stability in algal metacommunities.
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Affiliation(s)
- Griffin Srednick
- National Centre for Coasts and Climate, School of BioSciences, The University of Melbourne, Parkville, VIC, Australia
| | - Alyssa Cohen
- Department of Biology, California State University, Northridge, Northridge, California, USA
| | - Olivia Diehl
- Department of Biology, California State University, Northridge, Northridge, California, USA
| | - Kaela Tyler
- Department of Biology, California State University, Northridge, Northridge, California, USA
| | - Stephen E Swearer
- National Centre for Coasts and Climate, School of BioSciences, The University of Melbourne, Parkville, VIC, Australia
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4
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Ryznar ER, Smith LL, Fong P. Open space, not reduced herbivory, facilitates invasion of a marine macroalga, implying it is a disturbance-mediated "passenger" of change. MARINE ENVIRONMENTAL RESEARCH 2021; 170:105435. [PMID: 34385137 DOI: 10.1016/j.marenvres.2021.105435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 06/18/2021] [Accepted: 07/23/2021] [Indexed: 06/13/2023]
Abstract
Sargassum horneri, a brown macroalga, recently invaded the California coast, including into critical foundational communities such as kelp (Macrocystis pyrifera) forests. Despite its rapid spread, empirical tests that evaluate mechanisms underlying S. horneri's invasion success are lacking. To fill this knowledge gap, we conducted three field experiments on temperate rocky reefs in southern California using growth as a proxy for invasion success. We first tested whether S. horneri success differed with herbivory strength and native diversity by conducting a 2-factor experiment varying site (with different baseline levels of urchin densities and native algal diversity) and urchin access. We found S. horneri growth only differed among urchin treatments and not sites. We then evaluated whether S. horneri could successfully invade established algal canopies as a driver or whether it required open space as a passenger via a 2-factor experiment varying S. horneri size (small, medium, large) and canopy type (S. horneri, kelp, -canopy). We found that all S. horneri sizes grew fastest when canopy was lacking and light was high and slower in both canopy habitats with lower light; overall, small S. horneri grew slowest. Finally, we evaluated whether herbivore consumption for native species could facilitate S. horneri's invasion by conducting a 2-factor experiment varying species (M. pyrifera, S. horneri) and herbivore access. We found uncaged algae were consumed and caged algae grew, but there was no difference between species. Taken together, our results suggest that S. horneri is a "passenger" invader that will take advantage of points in time and space where light is plentiful, such as when M. pyrifera is removed via disturbance. Further, our results suggest that herbivory and native algal diversity are likely not key determining factors of the invasion success of S. horneri.
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Affiliation(s)
- E R Ryznar
- University of California Los Angeles, Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Los Angeles, CA, 90095-1606, USA.
| | - L L Smith
- University of California Los Angeles, Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Los Angeles, CA, 90095-1606, USA
| | - P Fong
- University of California Los Angeles, Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Los Angeles, CA, 90095-1606, USA
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5
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Sura SA, Molina NE, Blumstein DT, Fong P. Selective consumption of macroalgal species by herbivorous fishes suggests reduced functional complementarity on a fringing reef in Moorea, French Polynesia. JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY 2021; 536:151508. [PMID: 35530638 PMCID: PMC9075691 DOI: 10.1016/j.jembe.2020.151508] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Worldwide, many coral reefs are at risk of shifting to degraded algal-dominated states, due to compromised ecological conditions. Functional diversity of herbivorous fishes maintains coral reef health and promotes reef resilience to disturbances. Given previous evidence, it appears the functional roles of herbivorous fishes differ across geographical locations, indicating a need for further assessment of macroalgal consumption by herbivorous fishes. We assessed functional diversity by examining foraging behavior of herbivorous fish species on macroalgae on a fringing reef in Moorea, French Polynesia. We video-recorded choice experiments containing seven common macroalgae and used Strauss' linear resource selection index to determine macroalgal selectivities. We used cluster analysis to identify any distinct groups within herbivorous fish species, given the macroalgal species they targeted, and fitted generalized linear mixed-effects models to identify factors that best predicted the number of bites taken on macroalgae. Seven species from 3 fish families/tribes took a total of 956 bites. Fish species differed in their selectivity with some species (Naso lituratus, N. unicornis, Calatomus carolinus) strongly preferring one or two macroalgal species, while other fish species (Acanthurus nigrofuscus, Ctenochaetus striatus, Chlorurus sordidus, Balistapus undulatus) were less selective. This resulted in fish species forming two clusters. Only 3 of 7 macroalgae were preferred by any fish species, with two fish species both preferring the same two macroalgae. The limited differences in fish species' preferences for different macroalgae suggests limited functional complementarity. Two models (macroalgal species identity+fish functional group, macroalgal species identity+fish species) best predicted the number of bites taken on macroalgae compared to models incorporating only a single explanatory factor or fish family. In the context of this Moorean fringing reef, there is greater functional redundancy than complementarity of herbivorous fishes consuming macroalgae, and the fishes grouped together according to their relative selectivity. We observed fish species that are not classified as browsers consuming macroalgae, suggesting diets of herbivorous fishes may be broader than previously thought. Finally, we observed macroalgal selectivities and consumption that differed from previous studies for the same fish species. Our results contribute to the understanding of functional diversity of herbivorous fishes across coral reefs, and also highlight the need for additional research to further elucidate the role of context and functional diversity of herbivorous fishes consuming macroalgae on coral reefs.
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Affiliation(s)
- Shayna A. Sura
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA
- corresponding author:
| | - Nury E. Molina
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA
| | - Daniel T. Blumstein
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA
| | - Peggy Fong
- Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095, USA
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6
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Adam TC, Burkepile DE, Holbrook SJ, Carpenter RC, Claudet J, Loiseau C, Thiault L, Brooks AJ, Washburn L, Schmitt RJ. Landscape-scale patterns of nutrient enrichment in a coral reef ecosystem: implications for coral to algae phase shifts. ECOLOGICAL APPLICATIONS : A PUBLICATION OF THE ECOLOGICAL SOCIETY OF AMERICA 2021; 31:e2227. [PMID: 32918509 DOI: 10.1002/eap.2227] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 05/01/2020] [Accepted: 06/15/2020] [Indexed: 06/11/2023]
Abstract
Nutrient pollution is altering coastal ecosystems worldwide. On coral reefs, excess nutrients can favor the production of algae at the expense of reef-building corals, yet the role of nutrients in driving community changes such as shifts from coral to macroalgae is not well understood. Here we investigate the potential role of anthropogenic nutrient loading in driving recent coral-to-macroalgae phase shifts on reefs in the lagoons surrounding the Pacific island of Moorea, French Polynesia. We use nitrogen (N) tissue content and stable isotopes (δ15 N) in an abundant macroalga (Turbinaria ornata) together with empirical models of nutrient discharge to describe spatial and temporal patterns of nutrient enrichment in the lagoons. We then employ time series data to test whether recent increases in macroalgae are associated with nutrients. Our results revealed that patterns of N enrichment were linked to several factors, including rainfall, wave-driven circulation, and distance from anthropogenic nutrient sources, especially human sewage. Reefs near large watersheds, where inputs of N from sewage and agriculture are high, have been consistently enriched in N for at least the last decade. In many of these areas, corals have decreased and macroalgae have increased, while reefs with lower levels of N input have maintained high cover of coral and low cover of macroalgae. Importantly, these patchy phase shifts to macroalgae have occurred despite substantial island-wide increases in the density and biomass of herbivorous fishes over the time period. Together, these results indicate that nutrient loading may be an important driver of coral-to-macroalgae phase shifts in the lagoons of Moorea even though the reefs harbor an abundant and diverse herbivore assemblage. These results emphasize the important role that bottom-up factors can play in driving coral-to-macroalgae phase shifts and underscore the critical importance of watershed management for reducing inputs of nutrients and other land-based pollutants to coral reef ecosystems.
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Affiliation(s)
- Thomas C Adam
- Marine Science Institute, University of California, Santa Barbara, California, 93106, USA
| | - Deron E Burkepile
- Marine Science Institute, University of California, Santa Barbara, California, 93106, USA
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California, 93106, USA
| | - Sally J Holbrook
- Marine Science Institute, University of California, Santa Barbara, California, 93106, USA
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California, 93106, USA
| | - Robert C Carpenter
- Department of Biology, California State University Northridge, Northridge, California, 91330, USA
| | - Joachim Claudet
- National Center for Scientific Research, PSL Université Paris, CRIOBE, USR 3278 CNRS-EPHE-UPVD, Maison des Océans, 195 rue Saint-Jacques, Paris, 75005, France
- Laboratoire d'Excellence CORAIL, Moorea, French Polynesia
| | - Charles Loiseau
- National Center for Scientific Research, PSL Université Paris, CRIOBE, USR 3278 CNRS-EPHE-UPVD, Maison des Océans, 195 rue Saint-Jacques, Paris, 75005, France
- Laboratoire d'Excellence CORAIL, Moorea, French Polynesia
| | - Lauric Thiault
- National Center for Scientific Research, PSL Université Paris, CRIOBE, USR 3278 CNRS-EPHE-UPVD, Maison des Océans, 195 rue Saint-Jacques, Paris, 75005, France
- Laboratoire d'Excellence CORAIL, Moorea, French Polynesia
| | - Andrew J Brooks
- Marine Science Institute, University of California, Santa Barbara, California, 93106, USA
| | - Libe Washburn
- Marine Science Institute, University of California, Santa Barbara, California, 93106, USA
- Department of Geography, University of California, Santa Barbara, California, 93106, USA
| | - Russell J Schmitt
- Marine Science Institute, University of California, Santa Barbara, California, 93106, USA
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California, 93106, USA
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7
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Abstract
Ecological theory predicts that under the same environmental conditions, an ecosystem could have more than one community state that is maintained by reinforcing feedbacks. If so, a sufficiently large disturbance can flip the system to a less desired community that is difficult to reverse. Here, we demonstrate that a coral reef can become trapped in a seaweed-dominated state in the same conditions under which corals thrive. The implications are profound, particularly in light of the increasing occurrence of shifts to seaweed on coral reefs worldwide. Our results indicate that anticipatory management strategies that lessen the chance of a switch to seaweeds will be more effective than those aimed at restoring the coral community after a shift. Ecological theory predicts that ecosystems with multiple basins of attraction can get locked in an undesired state, which has profound ecological and management implications. Despite their significance, alternative attractors have proven to be challenging to detect and characterize in natural communities. On coral reefs, it has been hypothesized that persistent coral-to-macroalgae “phase shifts” that can result from overfishing of herbivores and/or nutrient enrichment may reflect a regime shift to an alternate attractor, but, to date, the evidence has been equivocal. Our field experiments in Moorea, French Polynesia, revealed the following: (i) hysteresis existed in the herbivory–macroalgae relationship, creating the potential for coral–macroalgae bistability at some levels of herbivory, and (ii) macroalgae were an alternative attractor under prevailing conditions in the lagoon but not on the fore reef, where ambient herbivory fell outside the experimentally delineated region of hysteresis. These findings help explain the different community responses to disturbances between lagoon and fore reef habitats of Moorea over the past several decades and reinforce the idea that reversing an undesired shift on coral reefs can be difficult. Our experimental framework represents a powerful diagnostic tool to probe for multiple attractors in ecological systems and, as such, can inform management strategies needed to maintain critical ecosystem functions in the face of escalating stresses.
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8
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Fong CR, Chancellor KS, Renzi JJ, Robinson DR, Barber PH, Habtes SY, Fong P. Epibionts on Turbinaria ornata, a secondary foundational macroalga on coral reefs, provide diverse trophic support to fishes. MARINE ENVIRONMENTAL RESEARCH 2018; 141:39-43. [PMID: 30093235 DOI: 10.1016/j.marenvres.2018.08.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Revised: 07/31/2018] [Accepted: 08/02/2018] [Indexed: 06/08/2023]
Abstract
Worldwide, many coral reef ecosystems have shifted from coral to algal dominance, yet the ecological function of these emergent communities remains relatively unknown. Turbinaria ornata, a macroalga with a rapidly expanding range in the South Pacific, forms dense stands on hard substrate, likely providing ecological services unique from corals. While generally unpalatable, T. ornata can function as a secondary foundation species and hosts an epibiont community that may provide overlooked trophic resources in phase shifted reef ecosystems. Results from video recorded field experiments designed to quantify consumer pressure on T. ornata epibionts showed that both consumer pressure and epibiont cover increased with thallus size. Additionally, most fish species, including herbivores, omnivores, and detritivores, exhibited higher bite rates on thalli with epibionts compared to thali with epibionts experimentally removed. Juvenile parrotfishes were responsible for 50% of total bites recorded and also had the highest bite rates. Results indicate that epibionts, particularly on large T. ornata, are a food resource for a diversity of fishes, representing a previously undescribed function of this macroalga in coral reef ecosystems. Exploring the functions of macroalgal dominated reef communities will be increasingly important as reefs continue to phase shift toward macroalgal dominance in the Anthropocene.
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Affiliation(s)
- Caitlin R Fong
- University of California, Santa Barbara, Department of Ecology, Evolution, and Marine Biology, Santa Barbara, CA, 93106, USA.
| | - Kendall S Chancellor
- Hampton University, Department of Marine and Environmental Science, Hampton, VA, 23668, USA
| | - Julianna J Renzi
- University of Arizona, School of Soil, Water, and Environmental Science, Tucson, AZ, 85719, USA
| | - De'Marcus R Robinson
- Florida A&M University, School of the Environment, 1601 S Martin Luther King Jr Blvd, Tallahassee, FL, 32307, USA
| | - Paul H Barber
- University of California Los Angeles, Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Los Angeles, CA, 90095, USA
| | - Sennai Y Habtes
- University of the Virgin Islands, Center for Marine and Environmental Studies, #2 John Brewers Bay, St. Thomas, USA
| | - Peggy Fong
- University of California Los Angeles, Department of Ecology and Evolutionary Biology, 621 Charles E. Young Drive South, Los Angeles, CA, 90095, USA
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9
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Briggs CJ, Adam TC, Holbrook SJ, Schmitt RJ. Macroalgae size refuge from herbivory promotes alternative stable states on coral reefs. PLoS One 2018; 13:e0202273. [PMID: 30226879 PMCID: PMC6143192 DOI: 10.1371/journal.pone.0202273] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Accepted: 07/03/2018] [Indexed: 11/20/2022] Open
Abstract
Coral reef systems can undergo rapid transitions from coral-dominated to macroalgae-dominated states following disturbances, and models indicate that these may sometimes represent shifts between alternative stable states. While several mechanisms may lead to alternate stable states on coral reefs, only a few have been investigated theoretically. We explore a model that illustrates that reduced vulnerability of macroalgae to herbivory as macroalgae grow and mature could be an important mechanism: when macroalgae are palatable to herbivores as juveniles, but resistant as adults, coral-dominated and algae-dominated states are bistable across a wide range of parameter space. We compare two approaches to global sensitivity analysis to rank the relative importance of the model parameters in determining the presence and magnitude of alternative stable states, and find that the two most influential parameters are the death rate of coral and the rate of maturation of algae out of the vulnerable stage. The Random Forest approach for global sensitivity analysis, recently adopted by ecologists, provides a more efficient method for ranking the relative importance of parameters than a variance-based approach that has been used frequently by computer scientists and engineers. Our results suggest that managing reefs to reduce chronic stressors that cause coral mortality and/or enhance the growth rates of algae can help prevent reefs from becoming locked in a macroalgae-dominated state.
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Affiliation(s)
- Cheryl J. Briggs
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, United States of America
- * E-mail:
| | - Thomas C. Adam
- Marine Science Institute, University of California, Santa Barbara, CA, United States of America
| | - Sally J. Holbrook
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, United States of America
- Marine Science Institute, University of California, Santa Barbara, CA, United States of America
| | - Russell J. Schmitt
- Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA, United States of America
- Marine Science Institute, University of California, Santa Barbara, CA, United States of America
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