Eutrophication and macroalgal blooms in temperate and tropical coastal waters: nutrient enrichment experiments with Ulva spp.

Abstract

Receiving coastal waters and estuaries are among the most nutrient-enriched environments on earth, and one of the symptoms of the resulting eutrophication is the proliferation of opportunistic, fast-growing marine seaweeds. Here, we used a widespread macroalga often involved in blooms, Ulva spp., to investigate how supply of nitrogen (N) and phosphorus (P), the two main potential growth-limiting nutrients, influence macroalgal growth in temperate and tropical coastal waters ranging from low- to high-nutrient supplies. We carried out N and P enrichment field experiments on Ulva spp. in seven coastal systems, with one of these systems represented by three different subestuaries, for a total of nine sites. We showed that rate of growth of Ulva spp. was directly correlated to annual dissolved inorganic nitrogen (DIN) concentrations, where growth increased with increasing DIN concentration. Internal N pools of macroalgal fronds were also linked to increased DIN supply, and algal growth rates were tightly coupled to these internal N pools. The increases in DIN appeared to be related to greater inputs of wastewater to these coastal waters as indicated by high δ15N signatures of the algae as DIN increased. N and P enrichment experiments showed that rate of macroalgal growth was controlled by supply of DIN where ambient DIN concentrations were low, and by P where DIN concentrations were higher, regardless of latitude or geographic setting. These results suggest that understanding the basis for macroalgal blooms, and management of these harmful phenomena, will require information as to nutrient sources, and actions to reduce supply of N and P in coastal waters concerned.

Selection of effective macroalgal species and tracing nitrogen sources on the different part of Yantai coast, China indicated by macroalgal δ15N values

“…and Ceramium Japonicum which showed lower tissue TN at S2 and S3 compared to S4 as a result of P limitation, the tissue TN and C:N ratios of U. pertusa, however, seemed mainly consistent with the seawater DIN concentrations (Fig. 2), indicating the high nitrogen uptake and demand (Pedersen and Borum, 1996;Raven and Taylor, 2003;Teichberg et al, 2008Teichberg et al, , 2010. C. pilulifera, Scytosiphon lomentaria and Petalonia fascia all showed lower TN values and higher C:N ratios compared to other macroalgal species, might be related to the low ability of DIN absorption and/or quick nitrogen release (Tyler et al, 2005;Tyler and McGlathery, 2006).…”

Abiotic factors influencing biomass accumulation of green tide causing Ulva spp. on Pyropia culture rafts in the Yellow Sea, China

“…Teichberg et al (2010) suggested that other factors are important especially under luxuriant nutrient conditions. This could explain why the abiotic factors determining Ulva biomass in this study are temperature and tidal effects rather than nutrient concentrations.…”

Green and golden seaweed tides on the rise

“…The Sargassum thallus is leathery, tough and differentiated into features that resemble leaves and a stem, and has well-developed gas bladders for flotation. Both Ulva and Sargassum are cosmopolitan, exceptionally speciesrich genera and increase their growth rate in response to nutrients 10,11 . Whereas most species will only grow when attached to a hard substrate, a few can substantially increase their biomass in a free-floating state, either by increasing the size of the thalli and their fragments, or by making new floating thalli.…”