Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)

Coral reef ecosystems harbor a high biodiversity around the world, supporting a large amount of ecosystem services. Rapa Nui is a remote oceanic island situated in the Central South Pacific Ocean, and its coral reefs represent the eastern limit of their distribution. This island is considered a “hot...

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Autor: Zapata-Hernández, Germán
Tipo de recurso: tesis doctoral
Estado:Versión publicada
Fecha de publicación:2020
País:Chile
OAI Identifier:oai:repositorio.anid.cl:10533/253079
Acceso en línea:https://hdl.handle.net/10533/253079
Access Level:acceso abierto
Palabra clave:Ciencias Naturales
Ciencias de la Tierra y del Medio Ambiente
Biología Marina, Limnología
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dc.title.es_CL.fl_str_mv Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
title Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
spellingShingle Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
Zapata-Hernández, Germán
Ciencias Naturales
Ciencias de la Tierra y del Medio Ambiente
Biología Marina, Limnología
title_short Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
title_full Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
title_fullStr Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
title_full_unstemmed Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
title_sort Biodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)
dc.creator.none.fl_str_mv Zapata-Hernández, Germán
author Zapata-Hernández, Germán
author_facet Zapata-Hernández, Germán
author_role author
dc.contributor.advisor.none.fl_str_mv Sellanes, Javier
dc.contributor.institution.es_CL.fl_str_mv UNIVERSIDAD CATOLICA DEL NORTE
dc.subject.oecd1n.es_CL.fl_str_mv Ciencias Naturales
topic Ciencias Naturales
Ciencias de la Tierra y del Medio Ambiente
Biología Marina, Limnología
dc.subject.oecd2n.es_CL.fl_str_mv Ciencias de la Tierra y del Medio Ambiente
dc.subject.oecd3n.es_CL.fl_str_mv Biología Marina, Limnología
description Coral reef ecosystems harbor a high biodiversity around the world, supporting a large amount of ecosystem services. Rapa Nui is a remote oceanic island situated in the Central South Pacific Ocean, and its coral reefs represent the eastern limit of their distribution. This island is considered a “hot spot” of biodiversity, where a high level of endemism has been reported for invertebrates and coastal fishes. However, although it marine biodiversity is threatened by different anthropic factors (e.g., overfishing, pollution, plastic, alien species), it remains under-studied in biological and ecological terms. In order to characterize the temporal patterns (day-night) of community organization, their effects on trophic functioning and the main organic matter sources supporting marine communities on Rapa Nui, this study aimed to: assess diel changes in the composition, richness, density and biomass of mobile benthic invertebrates and reef fishes, ii) determine how community structure changes could impact in the trophic functioning of coral reef communities on Rapa Nui, and iii) estimate the trophic position of consumers and the relative importance of different sources of organic matter (e.g., phytoplankton, macroalgae and corals) supporting marine assemblages found on Rapa Nui. Using SCUBA, a series of visual censuses were conducted (replicated during day and night) at six sites around Rapa Nui to assess variation in community structure (composition, richness, density and biomass) of coral reefs, and how these differences could impact the trophic structure of invertebrate and fish assemblages, and hence the functioning of coral reefs. Additionaly, employing stable isotope analyses (SIA), the trophic position (TP) of different coastal species and trophic diversity in different marine assemblages (i.e., mesozooplankton, reef invertebrates and fishes and pelagic fishes) were estimated, and the relative importance of different organic matter sources (OM; corals, macroalgae and phytoplankton) in different taxa was inferred using Bayesian mixing models. Results suggest marked differences in the structure of invertebrates and fishes assemblages during the day and night. An inverse pattern was detected between assemblages, where higher values of richness, density and biomass were estimated for fishes during day, in contrast with invertebrates, which were predominant during night. In functional terms, during the day fishes were dominated by herbivore, carnivore and planktivore taxa, while for invertebrates, herbivore and carnivore species prevailed. However, at night, fishes were dominated by only one carnivorous species and other planktivorous, and invertebrates were largely dominated by detritivore species (e.g., ophiuroids and holothuroids). Therefore, due to this decrease in the density of carnivore fishes and an important increase of cryptic invertebrates during night, it is hypothesized that a reduction in the predation risk could be an important factor determining these daily changes in the community structure. Conversely, the macroinvertebrate assemblage showed a shift in composition, an increase in richness, density and biomass during night. Furthermore, estimates of isotopic functional diversity indexes reveal significant differences in the Isotopic Uniqueness (IUni) values, suggesting that despite an increase in the biodiversity during night, nocturnal assemblages tend to be trophically more redundant, as a response to the activity patterns of detritivore taxa. Therefore, due to these important differences in the structure and functional roles of species between day and night, it is necessary to include nocturnal communities in the monitoring, management and conservation plans of coral reefs of Rapa Nui, and likely elsewhere. In addition, endemic invertebrates had low densities and biomass exercising limited influence in the trophic functioning of coral reefs and are thus potentially vulnerable to environmental changes or disturbances. SIA showed a clear pattern of 13C and 15N enrichment from invertebrates (mesozooplankton, emergent fauna, macrobenthos and reef invertebrates), towards reef fishes, pelagic fishes and seabirds. TP estimations of species indicate that most invertebrates are primary consumers and some taxa secondary consumers (TPrange=2.0-3.6); reef fishes had a wide trophic position ranges (TPrange=2.3-4.5), together with pelagic fishes (TPrange=3.6-5.4) and seabirds TP overlapped with that of pelagic predators (TPrange=4.0-5.1). Measures of trophic diversity (SEA: standard ellipse area) indicated that invertebrate and reef fish assemblages have wider trophic diversity (13.1 and 10.6 ‰2, respectively), in contrast to mesozooplankton and pelagic fishes (1.6 and 4.2 ‰2, respectively). Bayesian mixing model estimations indicated that coral-derived organic matter (e.g., coral polips and mucus) could be an important nutritional sources used by a diverse range of coastal species (e.g., macrobenthos: 58 %, reef invertebrates: 67 %, reef fishes: 62 %, and some pelagic fish predators: 41 %). Macroalgae could be important mainly for herbivore species such as sea urchins (51 %). Conversely, in some pelagic fishes (e.g., Mahi-mahi and flying fish) phytoplankton-derived energy dominated (44-40 %). Therefore, due to the importance of corals as an OM source and refuge for marine biodiversity in Rapa Nui, conservation efforts need to be focused on coral reefs and their cryptic biodiversity.
publishDate 2020
dc.date.issued.es_CL.fl_str_mv 2020
dc.date.accessioned.none.fl_str_mv 2021-12-30T13:07:21Z
2022-08-23T12:56:27Z
dc.date.available.none.fl_str_mv 2021-12-30T13:07:21Z
2022-08-23T12:56:27Z
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spelling UNIVERSIDAD CATOLICA DEL NORTEZapata-Hernández, Germán2020https://hdl.handle.net/10533/253079http://purl.org/coar/access_right/c_abf2Biología Marina, LimnologíaCiencias de la Tierra y del Medio AmbienteCiencias NaturalesBiodiversity, structure and trophic functioning of marine communities in Rapa Nui (Easter Island)Sellanes, JavierUNIVERSIDAD CATOLICA DEL NORTEChileZapata-Hernández, Germán2021-12-30T13:07:21Z2022-08-23T12:56:27Z2021-12-30T13:07:21Z2022-08-23T12:56:27Z2020Coral reef ecosystems harbor a high biodiversity around the world, supporting a large amount of ecosystem services. Rapa Nui is a remote oceanic island situated in the Central South Pacific Ocean, and its coral reefs represent the eastern limit of their distribution. This island is considered a “hot spot” of biodiversity, where a high level of endemism has been reported for invertebrates and coastal fishes. However, although it marine biodiversity is threatened by different anthropic factors (e.g., overfishing, pollution, plastic, alien species), it remains under-studied in biological and ecological terms. In order to characterize the temporal patterns (day-night) of community organization, their effects on trophic functioning and the main organic matter sources supporting marine communities on Rapa Nui, this study aimed to: assess diel changes in the composition, richness, density and biomass of mobile benthic invertebrates and reef fishes, ii) determine how community structure changes could impact in the trophic functioning of coral reef communities on Rapa Nui, and iii) estimate the trophic position of consumers and the relative importance of different sources of organic matter (e.g., phytoplankton, macroalgae and corals) supporting marine assemblages found on Rapa Nui. Using SCUBA, a series of visual censuses were conducted (replicated during day and night) at six sites around Rapa Nui to assess variation in community structure (composition, richness, density and biomass) of coral reefs, and how these differences could impact the trophic structure of invertebrate and fish assemblages, and hence the functioning of coral reefs. Additionaly, employing stable isotope analyses (SIA), the trophic position (TP) of different coastal species and trophic diversity in different marine assemblages (i.e., mesozooplankton, reef invertebrates and fishes and pelagic fishes) were estimated, and the relative importance of different organic matter sources (OM; corals, macroalgae and phytoplankton) in different taxa was inferred using Bayesian mixing models. Results suggest marked differences in the structure of invertebrates and fishes assemblages during the day and night. An inverse pattern was detected between assemblages, where higher values of richness, density and biomass were estimated for fishes during day, in contrast with invertebrates, which were predominant during night. In functional terms, during the day fishes were dominated by herbivore, carnivore and planktivore taxa, while for invertebrates, herbivore and carnivore species prevailed. However, at night, fishes were dominated by only one carnivorous species and other planktivorous, and invertebrates were largely dominated by detritivore species (e.g., ophiuroids and holothuroids). Therefore, due to this decrease in the density of carnivore fishes and an important increase of cryptic invertebrates during night, it is hypothesized that a reduction in the predation risk could be an important factor determining these daily changes in the community structure. Conversely, the macroinvertebrate assemblage showed a shift in composition, an increase in richness, density and biomass during night. Furthermore, estimates of isotopic functional diversity indexes reveal significant differences in the Isotopic Uniqueness (IUni) values, suggesting that despite an increase in the biodiversity during night, nocturnal assemblages tend to be trophically more redundant, as a response to the activity patterns of detritivore taxa. Therefore, due to these important differences in the structure and functional roles of species between day and night, it is necessary to include nocturnal communities in the monitoring, management and conservation plans of coral reefs of Rapa Nui, and likely elsewhere. In addition, endemic invertebrates had low densities and biomass exercising limited influence in the trophic functioning of coral reefs and are thus potentially vulnerable to environmental changes or disturbances. SIA showed a clear pattern of 13C and 15N enrichment from invertebrates (mesozooplankton, emergent fauna, macrobenthos and reef invertebrates), towards reef fishes, pelagic fishes and seabirds. TP estimations of species indicate that most invertebrates are primary consumers and some taxa secondary consumers (TPrange=2.0-3.6); reef fishes had a wide trophic position ranges (TPrange=2.3-4.5), together with pelagic fishes (TPrange=3.6-5.4) and seabirds TP overlapped with that of pelagic predators (TPrange=4.0-5.1). Measures of trophic diversity (SEA: standard ellipse area) indicated that invertebrate and reef fish assemblages have wider trophic diversity (13.1 and 10.6 ‰2, respectively), in contrast to mesozooplankton and pelagic fishes (1.6 and 4.2 ‰2, respectively). Bayesian mixing model estimations indicated that coral-derived organic matter (e.g., coral polips and mucus) could be an important nutritional sources used by a diverse range of coastal species (e.g., macrobenthos: 58 %, reef invertebrates: 67 %, reef fishes: 62 %, and some pelagic fish predators: 41 %). Macroalgae could be important mainly for herbivore species such as sea urchins (51 %). Conversely, in some pelagic fishes (e.g., Mahi-mahi and flying fish) phytoplankton-derived energy dominated (44-40 %). 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