Conservation of fish diversity in protected sites and adjacent fishing areas of the Southern Mexican Pacific Ocean

Abstract

The global decline in marine biodiversity is accelerating, prompting Mexico's government to establish marine protected areas to regulate human activities. The objective of this study was to test whether there were differences in fish taxonomic and functional diversity among protected reef sites within Parque Nacional Huatulco and adjacent non-protected (NP) zones, as well as whether the temporal trends in fish diversity, density, and biomass of commercial and non-commercial species differed in relation to these human use levels. It was hypothesized that fish functional diversity would be similar among protected and NP sites, given that fishing and tourism activities persist at protected sites. Concurrently, taxonomic and functional diversity decline was predicted, associated with decreasing commercial species due to increasing human activities in both zones. We collected data from underwater monitoring conducted by SCUBA divers (2006-2020) at 20 coral and rocky reef sites to calculate taxonomic and functional diversity metrics based on six biological traits. Functional diversity metrics were employed to analyze the resemblance among human use levels. Additionally, ecological indicators were incorporated as response variables in linear models to assess temporal changes. The results demonstrated functional diversity resemblance among human use levels, as well as temporal stability in Simpson's dominance index and significant increases in fish species richness and density at both zones. For protected sites, significant changes in fish functional diversity (increase in functional richness and decrease in divergence and originality), could indicate positive effects of protection, such as functional redundancy increases and the capacity to maintain reef functions over time. Commercial and non-commercial species exhibited stability or increase in density and biomass at both protected and NP sites.

Fig 1. a) Study area in the southern Mexican Pacific.

It includes two distinct groups of sites: b and d) ten non-protected sites (NP: 1-6 and 17-20), indicated by red dots, and c) ten protected sites within Parque Nacional Huatulco (MUMPA: 7-16), marked with blue dots. The protected area borderlines are outlined with a black line. The name of each site is included in Table A in S1 Text.

Fig 2. The functional structure of fish among protected (MUMPA: blue) and non-protected (NP: orange) sites of the Oaxaca coast are illustrated.

The first four axes of the PCoA are used to plot functional indices, which are defined as follows: a) Functional richness (FRic): volume occupied by functional entities; b) Functional divergence (FDiv): proportion of total density supported by functional entities with extreme traits; c) Functional originality (FOri): isolation of functional entities within the functional space.

Fig 3. The standardized coefficients (mean ±  95% confidence interval) of Linear Mixed Models for fish ecological indicators calculated for protected (MUMPA: blue) and non-protected (NP: orange) sites of the Oaxaca coast are presented.

The indicators are: species richness (S), density (d), Simpson’s dominance index (D), functional richness. (FRic), functional divergence (FDiv), and functional originality (FOri). The colored circles indicate statistically significant changes in the index, while the gray circles indicate non-significant changes over the study period (2006-2020).

Fig 4. The temporal trends for density (a and b) and biomass (c and d) of commercial and non-commercial fish species at protected (MUMPA: blue) and non-protected (NP: orange) sites of the Oaxaca coast are presented.

The linear model indicators, R² and P, are displayed alongside each graph.