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

Abstract

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.