|Uptake and release of nitrogen by the macroalgae Gracilaria vermiculophylla (Rhodophyta)|
|Tyler, A.C.; McGlathery, K.J. (2006). Uptake and release of nitrogen by the macroalgae Gracilaria vermiculophylla (Rhodophyta). J. Phycol. 42(3): 515-525. hdl.handle.net/10.1111/j.1529-8817.2006.00224.x|
|In: Journal of Phycology. Blackwell Science: Malden. ISSN 0022-3646, more|
; ; dissolved organic compounds; invasive species; lagoons; macroalgae; nitrogen; organic matter; Virginia Coast
Macroalgae, often the dominant primary producers in shallow estuaries, can be important regulators of nitrogen (N) cycling. Like phytoplankton, actively growing macroalgae release N to the water column; yet little is known about the quantity or nature of this release. Using 15N labeling in laboratory and field experiments, we estimated the quantity of N released relative to assimilation and gross uptake by Gracilaria vermiculophylla (Ohmi) Papenfuss (Rhodophyta, Gracilariales), a non-native macroalgae. Field experiments were carried out in Hog Island Bay, a shallow back-barrier lagoon on the Virginia coast where G. vermiculophylla makes up 85%–90% of the biomass. There was good agreement between laboratory and field measurements of N uptake and release. Daily N assimilation in field experiments (32.3±7.2 µmol N·g dw-1·d-1) was correlated with seasonal and local N availability. The average rate of N release across all sites and dates (65.8±11.6 µmol N·g dw-1·d-1) was 67% of gross daily uptake, and also varied among sites and seasons (range=33%–99%). Release was highest when growth rates and nutrient availability were low, possibly due to senescence during these periods. During summer biomass peaks, estimated N release from macroalgal mats was as high as 17 mmol N·m-2·d-1. Our results suggest that most estimates of macroalgal N uptake severely underestimate gross N uptake and that N is taken up, transformed, and released to the water column on short time scales (minutes–hours).