Abstract
Animals can act as important vectors of nutrients throughout ecosystems, driving patterns in vegetation and animal biomass. However, introduced species, hunting, and man-made barriers have greatly reduced the prevalence and magnitude of these ecological linkages. Seabirds foraging at sea deliver and concentrate large quantities of nutrients onto the islands on which they roost and breed through guano, feathers, and carcasses. These seabird-derived nutrient subsidies can bolster plant and invertebrate biomass on islands, and leach into nearshore marine environments to enhance fish biomass and functions. With introduced rats and other pests decimating seabird populations across 90% of the world’s island archipelagos, the importance of restoring seabird-derived nutrient subsidies is raising interest in rat eradication efforts. This offers a conservation strategy that could benefit both terrestrial and marine ecosystems. Rat eradication may also benefit low-lying reef islands if seabird nutrients enhance reef growth and sediment supply, and thus help mitigate the impacts of sea-level rise. There is currently limited understanding of the role of seabirds on tropical island nutrient cycling; the spatial and trophic extent of nutrient export across the surrounding coral reef seascape; and the benefits of these nutrient flows to reef growth and sediment generation. Further, knowledge of the effects and timescales of subsidy returns following rat eradication, and how rapidly adjacent marine ecosystems respond, is central to planning effective conservation efforts. This project will study islands with long-term rat populations, islands that have never had rats, and islands where rats have been eradicated, spanning the Indian and Pacific Oceans (Tetiaroa, Chagos, Seychelles, Reunion). In summary, this project seeks to quantify the importance of seabird nutrient subsidies to nutrient cycling and understand wider effects on island ecosystems and coral reef ecology, and associated feedback loops. Such understanding will support tropical island conservation and restoration efforts.
Scientific Description
Technical Means Used On Site (Detailed description of environmental manipulations). Include links to Protocols like Protocols.io if you have them
Removal of organisms or materials from the reserve.
Objective 1 - Map and identify nutrient hotspots and key land-sea nutrient connectivity pathways - Our aim is to map and quantify, for the first time, how nutrients flow across a coupled island-reef system and highlight nutrient hotspots. Using high-resolution remote sensing techniques, we will classify and map nutrient signatures to track the magnitude and spatial distribution of nutrients flowing between land and sea across multiple islands, with varying densities of seabirds present. Using deep learning, we will link in situ water quality data with remotely sensed spectral data. We will also conduct hyperspectral measurements of the benthos and water column in situ using small portable radiometers (TriOS RAMSES Hyperspectral Radiance and Irradiance Sensors). The water quality measurements in situ will be done across Moorea and Tetiaroa using digital probes (EasyProbe for the measurement of water turbidity and FluoroProbe for the measurement of water column chlorophyll-a concentration) and no equipment will be left on the reef or in the field stations. All the methods used for this work are non-intrusive and no samples will be collected. All drone data has been collected for our project, and we will only use satellite data for upcoming fieldwork.
Objective 2—Determine what drives the spatial patterns of nutrient dynamics - We will evaluate the relative roles of coral reef habitat complexity, patch heterogeneity, depth, water flow, island vegetation type, and island geomorphology in mediating nutrient spatial patterns. We expect to see context-dependent effects of land-sea nutrient connectivity on seascape primary productivity driven primarily by the identity of the nutrients being transported, resulting in considerable variation among sampling sites. We will collect samples of Turbinaria and/or Halimeda macroalgae at sites distributed across Moorea and Tetiaroa for stable isotope analysis. Turbinaria and/or Halimeda samples will be shipped back to the United Kingdom where they will be analysed for total phosphorus (%P), total nitrogen (%N), N:P ratios, and nitrogen stable isotope ratios (15N:14N), these analyses will provide evidence of land-sea nutrient connectivity and assimilation of various nutrients in nearshore primary producers. In addition, we will conduct visual and video transect surveys to collect data on coral reef benthic and fish assemblage structure (e.g., fish length to the nearest 5 cm, feeding rates, etc.). Fish data will be estimated visually in situ and will not require the collection of any fish specimens or tissues. No equipment will be left on reefs or in field stations.
Areas of the reserve to visit or conduct manipulations in.
Island | Land Owner |
Tetiaroa | |
Moorea | |
Interest for French Polynesia
How does this research fit into past and current research in the region (especially Moorea, Tahiti, and elsewhere in French Polynesia, South Pacific, etc.)?
Little is currently known about the spatial-temporal patterns of nutrient flows and the effects of nutrient inputs on island ecology and coral reef systems in French Polynesia (Adam et al., 2020; Bambridge et al., 2019; James et al., 2020). In particular, there is a knowledge gap about the ecological significance of seabird-derived nutrient subsidies. This project aims to address this knowledge gap, and thereby build on and contribute to the existing body of knowledge on nutrient cycling in French Polynesian island systems. We will investigate how the biodiversity and species abundance of plant and animal communities on and around islands is influenced by the presence/absence of rats and the loss/return of seabirds. This will be supported by baseline data (e.g., nutrientscapes mapped by macroalgae sampling; isotopic analysis across coral reef food webs; visual censuses of coral reef benthic communities) from previous research expeditions, allowing for the comparative study of cross-ecosystem nutrient flows and their ecological consequences before and after rat eradication. Such understanding will support tropical island conservation and restoration, as knowledge of the effects and timescales of subsidy returns following rat eradication, and how rapidly adjacent marine ecosystems benefit, is central to effective conservation efforts. Regarding Tetiaroa and Moorea specifically, this research complements marine ecological work being conducted by researchers from Lancaster University (who are part of the same Bertarelli-funded project). For example, data on nutrient export from islands to the marine environment will be linked to data on fish and benthic communities and their nutrient compositions (baseline data collected by Dr Casey Benkwitt and Rosalie Wright in November 2021, in collaboration with Oregon State University researchers). This research has been designed to maximize spatial coverage and capture the unique geology and land-sea spatial positioning, nutrient sources (humans, rats, seabirds), and anthropogenic and cultural contexts of Moorea and Tetiaroa. This work would also complement previous and ongoing ornithological research on seabird colonies in Tetiaroa led by researchers from organisations such as Island Conservation, University of Washington, University of Auckland, and SOP Manu. We will work with these organisations and the Tetiaroa Society to obtain seabird census data. Additionally, we note that in its innovative application of drones and satellites to map nutrient flows across the land-sea interface, this project builds on recent research employing cutting-edge remote sensing technologies in Pacific island systems (Collin et al., 2018, 2019), such as the Moorea IDEA Project (Davies et al., 2016). With the proposed research, we hope to increase our understanding of what drives coral health, allowing us to better assess the current and future resilience of Tetiaroa’s and Moorea’s unique island and coral reef environments. Outcomes from this project may have the ability to inform environmental management initiatives on land that can improve both island and coral reef health together.
Why must this research be done in Tetiaroa [or Moorea], and how does it address the mission of the Tetiaroa Society/Gump Station?
Coastal ecosystems, such as coral reefs, are in rapid decline globally due to accelerated climate change and local human activities (GCRMN, 2021; Waycott et al., 2009). The resilience of these vulnerable ecosystems to climate change could be strengthened by restoring natural nutrient pathways across the land-sea interface (Benkwitt et al., 2020; D’Angelo & Wiedenmann, 2014; Mcleod et al., 2019; Perry et al. 2018). Seabirds play a critical role in maintaining healthy nutrient cycles in tropical island systems (Graham et al., 2018), and with introduced rats and other pests decimating seabird populations across 90% of the world’s island archipelagos (Jones et al. 2008), the restoration of seabird-derived nutrient subsidies through rat eradication is gaining increased interest. This represents a promising conservation strategy to benefit both terrestrial and marine ecosystems. Tetiaroa provides a unique opportunity to study the significance of seabird-derived nutrients, as rat eradication was recently conducted on the islands in 2022. Critically, the availability of baseline data from previous research expeditions will allow for the comparative study of cross-ecosystem nutrient flows and their ecological consequences before and after rat eradication. The outputs of this project are expected to significantly contribute to the science underlying island/reef conservation. An increased understanding of the spatial-temporal patterns and ecological effects of cross-ecosystem nutrient subsidies will be fundamental to the development of effective climate adaptation strategies in tropical island systems. Indeed, in striving to inform restoration efforts and resilience-based management in tropical island systems, this project is perfectly aligned with the mission of the Tetiaroa Society.
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Research Output Management
Output Management Plan Link(s):
GEOME Project Link
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XDrive Project Link
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OSF Project Link: https://osf.io/pdg8r/?view_only = b4e56cadafd048668f79f61346aa8af8
Acknowledgement
This work was supported by Bertarelli Foundation as part of the Bertarelli Programme in Marine Science.
Related Identifiers
Stuart, C. E. (2024, May 7). Peterson_seabird_island_reef. Retrieved from osf.io/pdg8r
Peterson, E.A., Stuart, C.E., Pittman, S.J., Benkwitt, C.E., Graham, N.A.J., Malhi, Y., Atger, T., Stoll, B., Purkis, S.J., & Wedding, L.M. (In Revision). Graph-theoretic modeling reveals connectivity hotspots for herbivorous reef fishes in a restored tropical island system. Landscape Ecology.