Contents lists available at ScienceDirect Journal of Sea Research journal homepage: www.elsevier.com/locate/seares Ecological impact of salt farming in mangroves on the habitat and food sources of Austruca occidentalis and Littoraria subvittata Alex Nehemia a,b, ⁎ , Margaret Chen d , Marc Kochzius a , Frank Dehairs c , Natacha Brion c a Marine Biology, VrijeUniversiteit Brussel (VUB), Pleinlaan 2, Brussels 1050, Belgium b Department of Biosciences, Sokoine University of Agriculture, P.O. Box 3038, Morogoro, Tanzania c Analytical, Environmental and Geo-Chemistry, Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels 1050, Belgium d Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel (VUB), Pleinlaan 2, Brussels 1050, Belgium ARTICLE INFO Keywords: Isotope ratios Mangrove deforestation Salt production Western Indian Ocean ABSTRACT The impact of salt farming on the habitats and food sources of Austruca occidentalis and Littoraria subvittata was studied in mangroves along the coast of Tanzania using stable isotopes ( 13 C and 15 N) and sediment particle size analysis. The 13 C and 15 N stable isotope composition in mangrove leaves, sediments and invertebrate tissues, were used to evaluate whether there are diferences in feeding ecology of the crab Austruca occidentalis and the snail Littoraria subvittata collected from natural mangroves and mangroves around the salt ponds. Organic C, total N content and particle size distribution in sediments were used to assess if there are diferences in habitat characteristics of mangroves around the salt ponds. Mangrove leaves and sediments were found to be 13 C en- riched around salt ponds compared to those from natural mangroves. Likewise the macroinvertebrates collected from mangroves around salt ponds were found be enriched in 13 C relative to undisturbed mangroves. In addition, mangrove sediments around salt ponds were poorer in organic carbon and nitrogen and had more sand content compared to sediments from natural mangroves. These results indicate that salt pond activities have contributed to the modifcation of the habitats of macroinvertebrates by causing δ 13 C stable isotopes enrichment and al- teration of sediment characteristics in the ecosystem. 1. Introduction High population pressures in tropical coastal zones resulting from increased human activities are prime cause of mangrove loss and de- gradation. Salt farming in mangroves is among the major factors that contribute to global loss of forested areas (Walters et al., 2008). For example, in Brazil it has been estimated that about 50,000 ha of forest have disappeared over the last 25 years and salt farming is one of the factors driving this loss (Ferreira and Lacerda, 2016). Moreover, in Kenya, about 10,000 ha of mangroves have been cleared between Ngomeni and Karawa due to salt farming (Abuodha and Kairo, 2001). Salt production has been taking place for many years in Tanzania, in some places since 1920 (Mmochi et al., 2001; Liingilie et al., 2015). Several studies have highlighted threats on the ecosystem due to clearing of mangroves for salt ponds (Mwandya et al., 2009; Nehemia et al., 2017; Nehemia and Kochzius, 2017; Ocholla et al., 2013; Liingilie et al., 2015). Logging of trees from the mangrove forest can be detri- mental to ecosystem functions because it can alter the microbial pro- cesses that are highly sensitive to the chemical quality and quantity of litter entering the soil. These processes include non-symbiotic N fxa- tion, denitrifcation, net N mineralisation and nitrifcation (Pérez et al., 2009). Logging of mangrove trees during salt production can also cause changes in chemical, physical and biological parameters of the sedi- ments (Ellegaard et al., 2014). A study on fsh assemblages in Tanza- nian mangrove creek systems revealed reduced abundances caused by the change in the hydrodynamics and sediment characteristics due to salt pond activities (Mwandya et al., 2009). The dykes (Fig. 1) con- structed around the salt ponds become obstacles to the free movement of water, which are essential for dispersal of larvae of many in- vertebrates. Mangrove deforestation due to salt farming and other human activities has also been observed to cause unsteady tidal force, thereby increasing soil erosion and foods (Mazda et al., 2002; Ocholla et al., 2013). Physical disturbances in mangrove sediments have shown to have a signifcant efect on grain size distribution and sediment or- ganic carbon content (Mazda et al., 2002; Balke et al., 2013). Salt production in mangroves therefore has a major infuence on the distribution and diet of macroinvertebrates. Faunal communities tend to utilise more mangrove carbon as their food source in systems with https://doi.org/10.1016/j.seares.2019.01.004 Received 8 December 2017; Received in revised form 4 January 2019; Accepted 16 January 2019 ⁎ Corresponding author at: Department of Biosciences, Sokoine University of Agriculture, P.O. Box 3038, Morogoro, Tanzania. E-mail address: nehemiah@sua.ac.tz (A. Nehemia). Journal of Sea Research 146 (2019) 24–32 Available online 21 January 2019 1385-1101/ © 2019 Elsevier B.V. All rights reserved. T