• Effects of a no-take reserve on mangrove fish assemblages: incorporating seascape 2 connectivity

      Marley, Guy; Deacon, Amy; Phillip, Dawn; Lawrence, Andrew; University of the West Indies; Trinidad & Tobago; University of Chester
      No-take reserves (NTRs) have been effective at conserving fish assemblages in tropical systems such as coral reefs, but have rarely been evaluated in turbid tropical estuaries. The present study evaluated the effect of a mangrove NTR on the conservation of juvenile fish abundance, commercial fish biomass and biodiversity at the assemblage level, and the abundance of juveniles, target and non-target adults at the family level. The evaluation incorporated one aspect of seascape connectivity, namely proximity to the sea, or in this case, the Gulf of Paria. Linear mixed models showed that the NTR had a positive effect only on species richness at the assemblage level. However, juvenile fish abundance, commercial fish biomass, taxonomic distinctness and functional diversity were not enhanced in the NTR. The inclusion of connectivity in these models still failed to identify any positive effects of the NTR at the assemblage level. Yet, there were significant benefits to juvenile fish abundance for 5 of 7 families, and for 1 family of non-target adults. Possible explanations for the limited success of the NTR for fish assemblages include failing to account for the ecology of fish species in NTR design, the drawbacks of ‘inside−outside’ (of the NTR) experimental designs and the fact that fishing does not always impact non-target species. It is important to recognise that mangrove NTRs do not necessarily benefit fish assemblages as a whole, but that finer-scale assessments of specific families may reveal some of the proclaimed benefits of NTRs in tropical estuaries.
    • Mangrove and mudflat food webs are segregated across four trophic levels, yet connected by highly mobile top predators

      Marley, Guy; Lawrence, Andrew; Phillip, Dawn; Hayden, Brian; Canadian Rivers Institute
      Seascape connectivity is crucial for healthy, resilient ecosystems and fisheries. Yet, our understanding of connectivity in turbid mangrove-lined estuaries—some of the world’s most productive ecosystems—is limited to macrotidal systems, and rarely incorporates highly mobile top predators. We analysed δ13C and δ15N isotope values of 7 primary producers, 24 invertebrate taxa, 13 fishes, 4 birds and 1 reptile to reveal trophic interactions within and between a mangrove and adjacent mudflat in a microtidal system of the Gulf of Paria, Orinoco River estuary. Primary producers, invertebrates and fishes collected within the mangrove were significantly depleted in 13C and 15N compared to those collected on the mudflat. Stable isotope mixing models showed that mangrove-derived carbon was predominantly assimilated by invertebrates (78 ± 5% SE) and fishes (88 ± 11%) sampled in the mangrove. In contrast, invertebrates and fishes sampled in the mudflat derived <21% of their carbon from mangrove sources. Instead, microphytobenthos and phytoplankton underpinned the mudflat food web. Scarlet ibis Eudocimus ruber and yellow-crowned night heron Nyctanassa violacea were also highly associated with mangrove carbon sources. However, osprey Pandion haliaetus, snowy egret Egretta thula and spectacled caiman Caiman crocodilus obtained carbon from both mangrove and mudflat sources, effectively integrating the food webs. The present study demonstrates simultaneous aspects of food web segregation and connectivity, as well as the importance of surveying the entire food web across a range of tidal systems when investigating seascape connectivity.