Precision and cost-effectiveness of bioindicators to estimate nutrient regimes on coral reefs

Sentinels for future coral reef conditions: assessment of environmental variability and water quality in semi-enclosed inland bays in the southern Caribbean

“…The water samples, however, confirmed significantly higher nitrate, phosphate and ammonium levels during the wet than dry season across the mangrove-seagrass-coral reef continuum, but only ammonium was 13.4% higher in the bays than on reefs. Future research should consider the use of macroalgal bioindicators (Vaughan et al, 2021) because, in contrast to seagrass, macroalgae are present in all habitats along this continuum (Figure 2). Overall, elevated nutrient concentrations can have a wide range of effects on marine taxa (Nalley et al, 2023) and may make them more susceptible to co-occurring stressors such as coastal acidification (Silbiger et al, 2018), but this may not be the case for moderate nutrient concentrations in corals (Dobson et al, 2021).…”

“…The water samples, however, confirmed significantly higher nitrate, phosphate and ammonium levels during the wet than dry season across the mangrove-seagrass-coral reef continuum, but only ammonium was 13.4% higher in the bays than on reefs. Future research should consider the use of macroalgal bioindicators (Vaughan et al, 2021) because, in contrast to seagrass, macroalgae are present in all habitats along this continuum (Figure 2).…”

Nitrogen stable isotopes (δ15N) and tissue nitrogen in shallow‐water and mesophotic macroalgae differ between the Main Hawaiian Islands and the Northwestern Hawaiian Islands

“…Nutrient regimes in coral reefs across the world have been successfully described using macroalgal stable isotopes and tissue nutrients (Dailer et al 2010; Adam et al 2021; Lapointe et al 2021b; Vaughn et al 2021). Knowledge of the nutrient regimes from shallow to mesophotic reefs throughout the Hawaiian Archipelago, informed by known land‐use practices and their recent changes, could be used to identify areas that are likely to be influenced by point and nonpoint pollution around the Main Hawaiian Islands via increased nitrogen loading in macroalgal tissue (Lapointe and Bedford 2011; Dailer et al 2012a,b; Amato et al 2016).…”

“…Species or genus‐specific differences in δ 15 N fractionation may exist depending on an alga's physiological mechanisms for nitrogen processing (Vaughn et al 2021) or biological uptake of nitrate (Mariotti et al 1982), requiring caution when interpreting results across different species or genera. However, most macroalgae have heterogeneous, patchy distributions (Pyle et al 2016; Spalding et al 2019b) that make collecting replicates of the same genera or species at every site difficult, especially when examining trends across broad scales, such as the Hawaiian Archipelago.…”