Our study originally demonstrates biodiversity spatial distribution of the largest Brazilian coastal MPA Costa dos Corais and the importance of zoning as a major coral reef conservation strategy at SWA. Additionally, we have shown how depth influence fish and coral biodiversity within the MPA. No take zones and visiting zones presented higher coral cover and richness as well as higher fish abundance and biomass. Hence, management and zoning strategies have influenced the structure of coral reef communities with a series of different ecological effects highlighting the importance of management strategies for Southwestern Atlantic Ocean MPAs.
Spatial variation on reef biodiversity has been observed whitin MPA Costa dos Corais being the NAL region (Maragogi and Japaratinga) the area with higher coral cover and richness with up to 80% of coral cover in some sites highlighting the importance of Brazil waters on SWA coral reef communities. In contrast, highest fish community (abundance, richness, and biomass) have been recorded for SAL region. Interesting, the region with higher coral attributes such as cover and richness (NAL) had no positive effect on fish community. Russ et al., (2021) recently suggested that benthic community is often a stronger driver of fish biomass than fishing. However, additional attributes such as local environmental factors and global warming could interact on this relationship (McClure et al., 2020; Hall et al., 2021).
“No fishing effect” on both no-take zones and visiting zones seems to similarly influence reef fish abundance, richness, and biomass. In contrast, areas without fishing restrictions (sustainable use zone - SUZ) demonstrated a significant reduction on reef fish communities. Fishing is one of the most important activities for coastal local communities in many countries including Brazil (Freire and Pauly 2010) and unfortunately the lack of surveillance and compliance seems to directly impact reef fish communities. MPA Costa dos Corais has one of the richness fish communities in the SWA with 327 species and up to 50% of the fish diversity in the SWA (Pereira et al., 2021a). However, many different species have demonstrated signs of fishing presume (Benevides et al., 2018), and overexploitation such as parrotfishes (Pereira et al., 2021b). Hence, together with zoning strategies a fishing management strategy including quotas, seasoning catch periods and fish banning must be urgently implemented in Brazilian waters (Pereira et al., 2021b; Pinheiro et al., 2021). Roos et al., (2020) recently demonstrated that protected areas without a fisheries management plan is not enough to conserve fish populations.
Fishing activities are prohibited on both VZ and NTZ and therefore some fish trophic groups responded similarly to this effect, demonstrating high values of biomass in NTZ (379.85 ± 74.21 g/100 m²) and lowest values registered for SUZ (237.32 ± 71.98 g/100 m²). Evans & Russ (2004) observed that Plectropomus spp., a carnivorous species targeted by fisheries in the GBR, presented a biomass 3.9 times higher in protected areas than in fishing zones and they also noticed that, even considering the control of fish size for the (> 35cm TL), this species had 3.8 times more individuals compared to the fishing zones featuring a combination of protected areas regulations and an implemented fisheries management plan.
No difference on coral abundance was recorded according to depth on the present study. However, coral richness significatively differed on a depth gradient with only two dominant species (Montastraea cavernosa and Siderastrea stellata) representing almost 90% of coral communities on reefs below 20 m. Previous studies have demonstrated a similar trend with coral dominance reducing according to depth in the SWA (Matheus et al., 2019. Soares et al., 2021) likely due to due to light attenuation, changes in water temperature and resource availability. For instance, Matheus et al., (2019) observed a cross-shelf pattern with high turf and macroalgae abundance in shallow inner-shelf reefs, and high abundance of reef building organisms (particularly crustose calcareous algae and the scleractinian coral Montastraea cavernosa) in deeper outer-shelf reefs.
Conversely, our findings demonstrate a sharp increase on fish abundance, species richness and biomass according to depth as previous observed by Pereira et al., (2018) in the study area. In addition, Bridge et al., (2016) found that mesophotic reefs offer a lower risk of local extinction for reef fish when compared to shallow reefs, because fishing pressure decreases proportionally with increasing depth. For instance, reefs below 20 m had an average biomass of 945 ± 550 g/m² inside the MPA. In contract, Morais et al., (2017) observed that the total mean biomass of coastal localities in Brazil was only 232 g/m². These findings emphases the importance of deeper reefs on species life phase and ontogenetic migration and behavior (Slattery et al., 2011; Pereira et al., 2020; Appeldoorn and Bouwmeeste, 2022). However, despite the general idea that deeper reefs are potentially intact and under reduced anthropogenic influence, Rocha et al., (2019) recently demonstrated that deeper reefs are distinct, impacted and in much need of protection as shallow coral reefs. Deeper reefs on MPA Costa dos Corais are currently with little protection and no-take zones were only recently established on deeper reefs (> 10m). Our findings emphasis the importance of conservation of connectivity including shallow and deeper reefs and a cross-shelf patters of habitat use for several fish species that must be under full protection.
Recent evidence suggested that Brazilian marginal reefs could be more tolerant to short-term water heat events given that most corals that inhabit Brazilian coastal areas are adapted to moderate turbidity (Teixeira et al., 2019; Sully and Woesik, 2020; Mies et al., 2020). Yet, a recent unprecedented coral mortality on Southwestern Atlantic (SWA) coral reefs following major thermal stress could suggest that we are crossing the threshold for thermal tolerance on those environments (Pereira et al., 2022). Therefore, a combination of local human impacts together with global threats on marginal reefs such as Brazilian ecosystems could jeopardize those ecosystems. Consequently, proper zoning strategies could be vital for safeguarding the unique Southwestern Atlantic coral reef. A combination of zoning strategies, co-management efforts (Pereira et al., 2020) and fishing regulation (Pinheiro et al., 2020) would be the preferable strategy.