Relative importance of vascular plants and algal production in the food web of a Spartina-invaded salt marsh in the Yangtze River estuary

Abstract

The trophic importance of microphytobenthos (MPB), phytoplankton, C 3 vascular plants and invasive Spartina alterniflora in benthic and pelagic food webs was studied in Jiuduansha, a newly formed salt marsh in the Yangtze River estuary, using natural stable carbon and nitrogen isotopic analyses and IsoSource evaluation. MPB was found to be the major food source of meiofauna and important in the diets of macrofaunal consumers. Carbon derived from C 3 vascular plants significantly contributed to the nutrition of all planktonic copepods and supported planktivorous nekton, but played a minor role in the benthic food web. Although phytoplankton could be utilized by all the consumers, low production in this highly turbid estuary might restrict its relative importance. High trophic-level consumers could get carbon from 13 C-enriched MPB and 13 C-depleted C 3 plants via zoobenthos and zooplankton, respectively. Neither benthic nor pelagic animals fed exclusively on S. alterniflora except for a gastropod species in the present study, indicating a minor contribution of this invasive C 4 plant to the food web of the Jiuduansha salt marsh. In light of the degradation of salt marshes in the Yangtze River estuary, the rapid expansion of this invasive C 4 plant may alter the nutrient foundation of resident and migratory consumers and thus significantly impact the ecosystem there.KEY WORDS: Salt marsh · Food web · Microphytobenthos · Spartina alterniflora · Invasion · Trophic shift Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 367: [93][94][95][96][97][98][99][100][101][102][103][104][105][106][107] 2008 and are seldom found in predators' stomachs (Gee 1989). Stable isotope analysis provides a powerful tool to measure assimilated, and therefore nutritionally important, materials among diets; hence the relative contribution of different food sources can be identified (Peterson et al. 1985, Vander Zanden & Rasmussen 2001. In general, stable carbon isotope ratios (δ 13 C) exhibit little or no enrichment (within 1 ‰) relative to diet and are thus useful for determining the food sources of consumers (DeNiro & Epstein 1978, Peterson & Fry 1987. Stable nitrogen isotope ratios become enriched by 3 to 4 ‰ between prey and predator tissues, thereby providing a measure of consumer trophic position (DeNiro & Epstein 1981, Peterson & Fry 1987.According to distinct carbon isotope signatures between C 3 and C 4 salt marsh vascular plants (Smith & Epstein 1971), and consistent within-site differences between planktonic and benthic algae (France 1995), stable carbon isotope ratios are widely used to distinguish the relative contribution of salt marsh primary producers. In spite of the visible large amount of biomass represented as vascular plants in salt marshes, carbon isotope signatures of consumers are frequently consistent with an algal-based food web (Sullivan & Moncreiff 1990, Riera et al. 1999. In particular, microphytobenthos (MPB) has been shown to be a major source of nutr...

The effect of water management on extensive aquaculture food webs in the reconstructed wetlands of the Doñana Natural Park, Southern Spain

“…Following the methods of (Shang et al (2008)) and Al-Maslamani et al (2012), the trophic position of the consumers in each lagoon was estimated as the difference between the δ 15 N value of the consumer and the mean δ 15 N value of primary producers using the previous discrimination factors of 2.2 ‰ for the initial trophic step and 2.9 ‰ for subsequent steps . The contribution of the primary producers to the food webs supporting the consumers was estimated using these discrimination factors to correct for the diet:tissue discrimination across the difference in trophic level.…”

“…Early studies used isotopic similarity to infer consumption of a prey by consumer, more recently isotopic mixing models such as IsoSource (Phillips and Gregg 2003), SIAR (Parnell et al 2008) and mixSIAR (Stock and Semmens 2013) have enabled the calculation of the most likely proportional contribution of multiple food sources to the tissue of a consumer, and hence, dietary composition. The effect of nonnative species on food webs has been studied using stable isotope mixing models to examine both the impact of introducing non-native fish species on other species (Cucherousset et al 2007) and non-native primary producers on both primary consumers (Levin et al 2006) and higher trophic species (Currin et al 2003;Shang et al 2008). Isotopic analysis has advantages over stomach contents analysis in providing dietary information as it provides a more integrated longer term dietary signal reflecting assimilated not merely ingested material (Al-Maslamani et al 2009).…”

Trophic interaction among organisms in a seagrass meadow ecosystem as revealed by bulk δ13C and amino acid δ15N analyses

“…At present, several approaches, such as gut content analysis, lab culture analysis, and stable isotope analysis (SIA) of carbon and nitrogen within bulk tissues, are available to identify the trophic position (TP) of organisms of interest in the food webs of seagrass meadow ecosystems (Lugendo et al ; Shang et al ; Olsen et al ; Unabia ; Ouisse et al ). In gut content analysis, although it is highly useful to directly identify the species on which the investigated consumers actually feed, the remaining materials in the gut do not always correspond to the major diet sources adopted by consumers because heavily digested materials prevent identification of the resource species.…”

Fate of Organic Carbon Burial in Modern Sediment Within Yangtze River Estuary

“…Therefore, it is expected that increased contributions of vascular plant debris in coarse particles to sediments during erosion and transport may result in changing in δ 13 C org and δ 15 N with the alterations of terrestrial C org loading and/or sedimentary grain size (Bouchez et al, ). In addition to sediment composition, the alteration of vegetation types in the Yangtze River drainage basin and coastal areas will also change the isotopic δ 13 C org and δ 15 N. For example, C4 plants (i.e., Spartina alterniflora ) in the coastal marsh of the YRE are characterized by positively δ 13 C org (13.1 ± 0.1‰ on average; Shang et al, ). Coastal marshes appear to act as particle sinks, thus, C org derived from the marsh particles export could be largely limited due to subsidence (Gordon & Goñi, ; Nyman et al, ).…”

“…Coastal marshes appear to act as particle sinks, thus, C org derived from the marsh particles export could be largely limited due to subsidence (Gordon & Goñi, ; Nyman et al, ). However, marsh‐derived C org to the YRE seems inconspicuous but cannot be ruled out with the rapid expansion of this invading Spartina alterniflora (Shang et al, ). It should be noted that it may be difficult to differentiate among possible sources with these data alone, but it is clear that enhanced inputs of eroded particles containing a different mixture of OM may influence the C org compositions.…”