Macroalgal responses to experimental nutrient enrichment in shallow coastal waters: growth, internal nutrient pools, and isotopic signatures

Abstract

Increased nutrient inputs to temperate coastal waters have led to increased occurrences of macroalgal blooms worldwide. To identify nutrients that are limiting to macroalgae and to determine whether different forms of these nutrients and long-term ambient nutrient conditions affect macroalgal response, we used in situ enrichment methods and tested the response of 2 bloom-forming species of macroalgae, Ulva lactuca and Gracilaria tikvahiae, from shallow estuaries of Waquoit Bay, Massachusetts, USA, that receive different land-derived N inputs. We enriched caged macroalgal fronds with nitrate, ammonium, phosphate, and N + P combinations, and measured growth, nutrient content, and δ 15 N signatures of fronds after 2 wk of incubation. In these estuaries, P did not limit growth, however, the 2 species differed in growth response to N additions. Growth of U. lactuca was greater in Childs River (CR), the estuary with higher nitrate inputs, than in Sage Lot Pond (SLP); growth in SLP increased with nitrate and ammonium enrichment. In contrast, growth of G. tikvahiae was greater in SLP than in CR, but had no growth response to N enrichment in either site. C and N contents differed initially between species and sites, and after nutrient enrichment. Final tissue % N increased and C:N decreased after nitrate and ammonium enrichment. δ 15 N values of the macroalgae demonstrated uptake of the experimental fertilizers, and a higher affinity and faster turnover of internal N pools with ammonium than nitrate enrichment in both species. We suggest that U. lactuca blooms in areas with both high nitrate and ammonium water column concentrations, and is more N-limited in oligotrophic waters where DIN levels are too low to sustain high growth rates. G. tikvahiae has a greater N storage capacity than U. lactuca, which may allow it to grow in less nutrientrich waters.

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).…”

“…Several foliose and filamentous macroalgal species could more efficiently reflect the nitrogen sources in the water column as they were characterized by having faster nitrogen uptake and growth rates, and were more sensitive to changes in environmental conditions, chemical forms and isotopic composition of N in the water (Deutsch and Voss, 2006;Teichberg et al, 2008;Dailer et al, 2010;Ochoa-Izaguirre and Soto-Jiménez, 2015). However significant different tissue δ 15 N values were found for species of same functional groups or even same genus.…”

“…Macroalgal internal structure, attachment strategies, growing rates, reproduction strategies, preference assimilation for nitrogen chemical, uptake kinetics, storage capacity and individual condition of species (e.g., juvenile or adult) could cause the difference of δ 15 N values between macroalgal species (Ochoa-Izaguirre and Soto-Jiménez, 2015). For example, foliose and filamentous macroalgae such as Ulva intestinalis could more efficiently reflect the δ 15 N-DIN variations because their faster uptake and growth rates (Teichberg et al, 2008;Dailer et al, 2010;Ochoa-Izaguirre and Soto-Jiménez, 2015). Environmental factors such as seawater nutrient levels, temperature and light may also result in the difference of macroalgal δ 15 N values (Umezawa et al, 2002;Derse et al, 2007;Viana and Bode, 2015).…”

δ15N and δ13C reveal differences in carbon flow through estuarine benthic food webs in response to the relative availability of macroalgae and eelgrass

“…Herbivores are able to choose their food based on palatability using cues like tissue %N (Mattson 1980, Boyer et al 2004, plant morphology (Hay 1997), the presence of structural compounds like cellulose and lignin (Cebrián & Duarte, 1998), or grazing deterrents (Hay & Fenical 1988). Augmented nutrient supply has been shown to increase tissue %N of macrophytes in Waquoit Bay (Teichberg et al 2007(Teichberg et al , 2008, and we might expect to see differences in the nutrient content of primary producers across the gradient of N loads. Uptake and assimilation of the available nutrients reduces the C to nutrient ratio of seagrass or algal tissues, making producers a better quality food source for grazers (McGlathery 1995, Hemmi & Jormalainen 2002, Boyer et al 2004, Olsen & Valiela 2010).…”

Short-term ecophysiological and biochemical responses of Cystoseira tamariscifolia and Ellisolandia elongata to environmental changes

“…On one side, slow-growing perennial macroalgae, adapted to stable or seasonally variable N conditions, can develop large N and P storage pools (Martínez et al 2012). At the another extreme, fast-growing opportunistic algae are unable to store large amounts, but show remarkably high N-and Puptake rates to profit from unstable N-supply conditions (Teichberg et al 2008). Finally, nutrient enrichment increases the photoprotection capacity of sea weeds due to the increase in protein content, MAAs (Korbee-Peinado et al 2004, Huovinen et al 2006 or polyphenols (Arnold & Targett 2002).…”