Isotopic niche size variability in an ecosystem engineer along a disturbance gradient in a South African lagoon. (January 2022)

• Record Type: Journal Article
• Authors: Källberg Normark, Lydia; Liénart, Camilla; Pillay, Deena; Garbaras, Andrius; Savage, Candida; Karlson, Agnes ML.
• Is Part Of: Marine environmental research. Volume 173(2022)
• Publication Date: 2022-01
• Subjects: Environmental status assessment -- Nutrient gradient -- Stable isotopes -- Trophic niche -- Body condition -- Marine invertebrates; Marine pollution -- Environmental aspects -- Periodicals; Marine ecology -- Periodicals; Mer -- Pollution -- Aspect de l'environnement -- Périodiques; Écologie marine -- Périodiques; Electronic journals; 577.705
• DOI: 10.1016/j.marenvres.2021.105541
• Languages: English
• ISSNs: 0141-1136

Abstract

Abstract: A key challenge for natural resource management is how to detect effects of environmental stress on individuals and populations before declines in abundance occur. Variability in carbon and nitrogen isotope composition (δ 13 C and δ 15 N) among consumers can provide information on the population trophic niche and how it may change in response to environmental stress. We measured δ 13 C and δ 15 N values in primary producers and in an ecosystem engineer, the bioturbating sandprawn Kraussillichirus kraussi, in Langebaan Lagoon, South Africa, along a human disturbance gradient. Diet partitioning mixing models were coupled with isotope niche analyses and individual body condition data to investigate shifts in resource utilisation and diet plasticity from minimally to highly disturbed sites. The δ 15 N values of seagrass, Zostera capensis indicated a nutrient gradient, with the highest δ 15 N values at highly disturbed sites indicating either anthropogenic or marine nitrogen inputs. A decreasing δ 15 N signal with distance from human disturbance/mouth of lagoon was however not evident for sandprawns nor their presumed dietary sources (phytoplankton, microphytobenthos or sediment organic matter), likely because of faster isotope turnover time compared to seagrass and/or differential fractionation for sandprawns among the sites. Sandprawn isotope niche sizes varied among sites, with no trend along the disturbance gradient. The smallest niche coincided with uniform feeding on microphytobenthos according to mixing models. On an individual level, deviating isotope values from population means were correlated to better body condition, suggesting that a divergent feeding strategy is beneficial. Our results support a generalist feeding behavior of the sandprawns with no evidence of reduced physiological status at the site with most human disturbance. Highlights: Sandprawn isotope niche size linked to diet models along a disturbance gradient. Generalist feeding behavior correlated to better body condition. No indication of deteriorated body condition at the most disturbed site.