Mangrove or mudflat: Prioritising fish habitat for conservation in a turbid tropical estuary

Mangrove habitats are typically the focus of conservation efforts in tropical estuaries because their structural complexity is thought to support greater biodiversity and nursery function than unvegetated habitats. However, evidence for this paradigm has been equivocal in turbid tropical estuaries where unvegetated mudflats are also highly productive. The present study compared the community composition, biodiversity, nursery-role and commercial fish biomass in two mangrove habitats and one mudflat habitat in the Gulf of Paria, Trinidad. A total of 12 705 fishes, comprising 63 species from 26 families, were sampled in mangrove creeks, seaward mangrove fringe and the subtidal margin of an intertidal mudflat from June 2014 to June 2015. The composition of the creek and mudflat communities were distinct, while the community of the mangrove fringe more closely resembled the mudflat than the mangrove creeks. Mean species richness (MSR), total species richness (TSR) extrapolated from species accumulation curves, and juvenile species richness (JSR) were significantly greater in the mudflat (MSR = 11.4 +/- 1.0; TSR = 75 +/- 14; JSR = 9.1 +/- 0.8) than mangrove creeks (MSR = 9.0 +/- 0.5; TSR = 49 +/- 3; JSR = 6.1 +/- 0.4) and the seaward mangrove fringe (MSR = 6.4 +/- 0.7; TSR = 58 +/- 14; JSR = 5.2 +/- 0.4). Meanwhile, Shannon Weiner diversity, juvenile fish abundance and commercial fish biomass were comparable between habitats. These findings caution against the generalisation that mangroves are the most important habitat for fishes in turbid tropical estuaries. There is now a growing body of evidence that mudflats warrant consideration as important repositories of biodiversity and nursery function for juvenile fishes.