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

Abstract

Extensive aquaculture in coastal and estuarine wetlands can support both increased food production and wider ecosystem services when underpinned by effective management to promote productivity and hence food webs that support both commercial species and biodiversity. Changing hydrology, specifically water movement, within wetlands significantly impacts the physico-chemical properties of the water body and hence can be employed to manipulate productivity and alter patterns of recruitment of commercial species and may also transfer non-native species from the supplying water bodies. The reconstructed wetlands of Veta la Palma in the Doñana Natural Park are subjected to either a 1 % or 5 % d -1 water exchange with water drawn from the adjacent Guadalquivir estuary. This site provides an excellent opportunity for examining the effect of water management on the food webs that support both the birdlife and aquaculture activities for which this habitat is managed. Stable isotopes were used to examine food webs in three replicate lagoons under each water management scheme. In lagoons receiving higher water exchange, phytoplankton productivity appeared to be more important than benthic production in supporting food webs. Increased water exchange also changed the shape of the food webs, facilitated the colonisation of at least one non-native species and increased the importance of non-native species in the diets of large commercially harvested fish (> 60 % of seabass diet). Lagoons with high water flows also had between three and four times greater shrimp biomass than those of low flow lagoons. Non-native fauna were opportunistic omnivores, eating marginally more non-natives in lagoons with greater water exchange. Overall non-native cordgrass Spartina densiflora contributed only slightly more to food webs compared with the native reed Phragmites australis, despite the lagoon edge occupancy ratio of 9:1, respectively. Nonnatives also appear to enhance food provision for large predators and wetland birds, by increasing biomass, without competing for resources with native species, supporting the dual management objectives of aquaculture and waterbird conservation.

Identifying management actions to increase foraging opportunities for shorebirds at semi‐intensive shrimp farms

“…Thousands of shorebirds feed on the intertidal mudflats of the coastal lagoon during the non-breeding season (Navedo, Sauma-Castillo & Fern andez 2012;Navedo et al 2015b). Although some aquaculture ponds have high densities of benthic invertebrates (Arias & Drake 1994;Walton et al 2015a), this food source is unavailable to shorebirds because the ponds are too deep and steep-sided. However, drainage of the ponds to harvest the shrimp allows shorebirds to forage on these invertebrates (Navedo et al 2015b).…”

“…Caudill, de Clerck & Husband 2015). However, although aquaculture is the fastest expanding global animal food production sector (Jones et al 2015), the potential of these habitats has been largely ignored (but see Green et al 2015;Walton et al 2015a). There is a need, therefore, to further explore aquaculture management practices that improve quality as habitats for wildlife.…”

“…Extensive shrimp aquaculture entails an important reduction of tidal processes at coastal wetlands where they are built, while semi-intensive aquaculture represents a mid-point where some natural processes can still occur in a modified environment. The appropriate management of semi-intensive shrimp aquaculture systems can help to mitigate their impacts on natural systems and may result in trophic subsidies to wildlife (Walton et al 2015a), mimicking other agroecosystems (e.g. Navedo et al 2015a).…”

“…Coastal aquaculture ponds, including shrimp farms, can provide foraging habitats for declining shorebird populations in south-western Europe, Asia and America. Extensive aquaculture ponds in south-western Europe (Kloskowski et al 2009;Marquez-Ferrando et al 2015;Walton et al 2015a) or Mexico (Navedo et al 2015b) are used by large numbers of shorebirds and waterbirds. In contrast, despite currently supplying 89% of global aquaculture production (FAO 2012), aquaculture ponds in Asia do not appear to provide relevant foraging opportunities for shorebirds (Yasu e & Dearden 2009;Sripanomyom et al 2011;Li et al 2013;Green et al 2015).…”

Phylogenetic relatedness of co‐occurring waterbird communities: a test of Darwin's competition‐relatedness hypothesis

“…All the studied ponds had similar water quality and plant communities (water circulates through the ponds, homogenizing the water quality; see Walton et al for details), but differed somewhat in water level. Thus, we tested if water level had an influence on the phylogenetic relatedness of the pond community present.…”