Browning, Thomas J. , Al-Hashem, Ali A., Achterberg, Eric Pieter , Carvalho, Paloma C., Catry, Paulo, Matthiopoulos, Jason, Miller, Julie A.O. and Wakefield, Ewan D. (2023) The role of seabird guano in maintaining North Atlantic summertime productivity. Science of The Total Environment, 897 . Art.Nr. 165309. DOI 10.1016/j.scitotenv.2023.165309.

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Abstract

Highlights

• Oceanic nutrient supply from seabird guano is poorly constrained by field observations.
• This was assessed for guano from caught-and-released North Atlantic seabirds.
• Guano released nutrients and relieved in situ phytoplankton nutrient limitation.
• Guano was modelled to potentially be a major nutrient supply term in summer.
• Declining pelagic seabird populations will impact this function.

Abstract

Nutrients supplied via seabird guano increase primary production in some coastal ecosystems. A similar process may occur in the open ocean. To investigate this directly, we first measured bulk and leachable nutrient concentrations in guano sampled in the North Atlantic. We found that guano was strongly enriched in phosphorus, which was released as phosphate in solution. Nitrogen release was dominated by reduced forms (ammonium and urea) whilst release of nitrate was relatively low. A range of trace elements, including the micronutrient iron, were released. Using in-situ bioassays, we then showed that supply of fresh guano to ambient seawater increases phytoplankton biomass and photochemical efficiencies. Based on these results, modelled seabird distributions, and known defecation rates, we estimate that on annual scales guano is a minor source of nutrients for the surface North Atlantic. However, on shorter timescales in late spring/summer it could be much more important: Estimates of upper-level depositions of phosphorus by seabirds were three orders of magnitude higher than modelled aerosol deposition and comparable to diffusion from deeper waters.

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