Nutrient-limited growth of the coral reef macroalga Sargassum baccularia and experimental growth enhancement by nutrient addition in continuous flow culture

Abstract

ABSTRACT-The observed high biomass of Sargassum species and other fleshy macroalgae on nearshore coral reefs in the Great Barner Reef (Australia) raises the concern that this may be a sign of a phase shift from hard coral to dominance by algae, thus indicating the degradation of these reefs. Nearshore reefs are, due to their geographical position, exposed to inputs of nutnents and particles from mainland run-off. This study estimated the limiting and optimum nutrient concentrations for the growth of Sargassum baccularia under continuous supply of ammonium and phosphate. To assess the nutrient situation in the field, critical and subsistence levels of tlssue nutrients as determined in cultures were compared with field tissue nutrient levels, and a 'mlnl budget' was estimated that compares nutnent requirements with nutrient supply. The growth rates of S, baccularia almost doubled within the narrow window of substrate concentrations from 3 pM ammonium plus 0.3 pM phosphate to 5 pM ammonium plus 0.5 pM phosphate. Lower and, unexpectedly, higher nutrient concentrations resulted in reduced growth rates. Field thalli of S. baccularia were always sufficiently supplied with N and P to show positive growth rates. However, field growth was both N-and P-limited, particularly in austral summer, when fast growth of S. baccularia occurs. Thls was indicated by tissue N and P concentrations that fell below the respective critical nutrient values, and estimated nutrient demands that exceeded the nutrients available from the water column. We suggest that if land-derived nutrient inputs increased. S. baccularia would become nutrient-sufficient, especially during the summer wet season. This may increase the competitive potential of this species to colonise larger areas on the nearshore reefs.

Supply- and demand-driven phosphate uptake and tissue phosphorus in temperate seaweeds

“…Wheeler & Björn -säter 1992), and comparable to some seaweeds from coral reefs (e.g. Schaffelke & Klumpp 1998, Lapointe et al 2005, Tsai et al 2005. These ranges of tissue phosphorus values are smaller than the ranges in seawater phosphate concentrations (3.43-fold) and phosphate uptake rates at 5 μM, which varied from 2.88-fold in P. lucida to 10.94-fold in Melanthalia abscissa.…”

“…Some brown seaweeds have very low K m values for phosphate uptake: Laminaria japonica (Ozaki et al 2001) and Sargassum baccularia (Schaffelke & Klumpp 1998) have K m values of 0.14 and 0.26 μM, respectively. However, red and green seaweeds in general have lower K m values for phosphate uptake (4 μM or less) than brown seaweeds (Rees 2003).…”

Nutrient and growth dynamics of Halimeda tuna on Conch Reef, Florida Keys: Possible influence of internal tides on nutrient status and physiology

“…Some studies have shown a rapid uptake response by tropical algae when they are exposed to short-duration pulses of enhanced nutrients in controlled experiments (Lapointe 1985;Schaffelke and Klumpp 1998a,b;Schaffelke 1999). After uptake, some species store excess nutrients, whereas others have limited storage capacity (e.g., Ulva spp.)…”

Offshore and Multi-Use Aquaculture with Extractive Species: Seaweeds and Bivalves

“…Considering a 10:1 DW:FW ratio and average values of nitrogen (Pyropia/Porphyra: 5.5%, Gracilaria: 3.0%, Kappaphycus/Eucheuma: 1.7%, kelp: 2.0% and Sargassum: 4.1%) and carbon (Pyropia/Porphyra: 38%, Gracilaria: 28%, Kappaphycus/Eucheuma: 29%, kelp: 30% and Sargassum: 34%), the total nitrogen and carbon removal by these five major aquaculture groups is approximately 54 million t of nitrogen per year and 700 million t of carbon per year (equivalent to 2600 million t of CO 2 ), respectively (Asare and Harlin 1983;Gerard 1997;Schaffelke and Klumpp 1998;Gevaert et al 2001;Schaffelke 2001;Chung et al 2002;Rawson et al 2002;Sahoo and Ohno 2003;Dean and Hurd 2007;Kim et al 2007Kim et al , 2014aKim et al , 2015aBuschmann et al 2008;Abreu et al 2009;Robertson-Andersson et al 2009;Levine and Sahoo 2010;Broch et al 2013). This is, in fact, a significant amount of carbon and nitrogen removal.…”