Fish Diversity in Mangroves of São Tomé Island (Gulf of Guinea)

Tese de mestrado, Ecologia Marinha, Universidade de Lisboa, Faculdade de Ciências, 2021Mangroves are valued for their role in climate regulation, countering coastal erosion and providing raw materials. Mangroves have diverse fish communities, and the roots of mangrove trees provide shelter for fish species, especially juveniles. Little is known about Santomean mangroves, with 12 mangrove systems identified, from which four were included in this study. This thesis aims to comprehend how fish diversity varies between mangroves with different characteristics, using Santomean mangroves as case study. The environmental conditions found in the smaller systems were more homogeneous than those of the larger systems. Twenty-two species were sampled, with Malanza showing the highest richness and Praia das Conchas the lowest. The functional diversity results suggest that Malanza is more diverse and has a functionally richer community. This higher diversity is probably due to the heterogeneity of environmental conditions and their temporal stability. Angolares had low diversity, with an even but species poor community. Likely due to the environmental variability that only allows tolerant species to establish. The reduced size and depth of Diogo Nunes is probably stunting its diversity. Nevertheless, the fish community of Diogo Nunes is functionally more diverse than that of the larger Angolares system. Pelagic and marine species preferred larger and deeper mangroves, while benthic and estuarine species were predominant in Diogo Nunes. Species and functional diversity were positively correlated indicating complementarity between them and showing that functional diversity adds information about species-environment interactions. Functional and species evenness were not correlated showcasing the importance of the use of both metrics to acquire a more complete understanding of the communities. Taxonomic and functional diversity were negatively correlated indicating that species from different taxa may perform similar functions. From a management point of view this approach represents an advantage as it can identify which systems are more important for which groups, allowing the prioritizing of systems for conservation and management

Assessing Ecosystem Services in Mangroves: Insights from São Tomé Island (Central Africa)

Mangroves are some of the most productive coastal systems on the planet and provide valuable ecosystem services (ES). They are especially important in threatened ecosystems and developing countries, where they are likely to have direct impacts on local communities. An approach based on ES allows assessing ecosystems across the domains of ecology, sociology and economy. This study focused on the evaluation of ES in mangroves and started by creating a comprehensive global list of mangrove ES based on the Millennium Ecosystem Assessment. These services were then quantified using the best available indicators for mangrove systems. The mangroves of Diogo Nunes, São João dos Angolares and Malanza, located in the São Tomé Island, were used to illustrate the challenges in applying ES indicators in this type of ecosystems. The obtained results confirmed that mangroves can provide important and diverse services. However, the high variability among mangrove systems affects their ability to deliver ES, requiring caution for the extrapolation across regions. This assessment emphasizes how the ES framework can be used as a tool to develop management plans that integrate conservation goals and human wellbeing.info:eu-repo/semantics/publishedVersio

Community perceptions about mangrove ecosystem services and threats

The Ecosystem Service Framework discloses the ecosystem’s benefits to society and provides support to preserve threatened systems while considering the economic and social dimensions of the communities more dependent on its resources. Mangroves provide important and valuable goods and services to communities, at different spatial and temporal scales. Nevertheless, over-exploitation of these resources can generate poverty traps, where rural households can no longer use the ecosystem as a source of food security or income. This study uses three communities that live in surrounding areas of mangroves from São Tomé Island (Diogo Nunes, Angolares, and Malanza) as a case study. The main aim was to evaluate locals’ perspectives about ecosystem use, threats, and conservation. Questionnaires were conducted among local populations and provided valuable information to identify the major beneficiaries of mangrove resources. These results also indicated that the services and threats identified locally are different from those identified in the literature. The importance of considering the impact of local values and traditions in the use of ecosystem resources was also highlighted by the obtained results since São Tomé residents do not acknowledge the existence of services that do not bring a direct benefit. The absence of awareness about mangroves and their threats can cause severe damages to the ecosystem’s health, requiring the implementation of specific awareness-raising policies among populations that interact with mangrove ecosystems.info:eu-repo/semantics/publishedVersio

Comparison of the Efficiency of Different Eradication Treatments to Minimize the Impacts Caused by the Invasive Tunicate <i>Styela plicata</i> in Mussel Aquaculture

In 2017, aquaculture producers of the Albufeira lagoon, Portugal, reported an invasion of tunicates that was disrupting mussel production, particularly the tunicate Styela plicata (Lesueur, 1823). A totally effective eradication method still does not exist, particularly for S. plicata, and the effects of the eradication treatments on bivalves’ performance are also poorly understood. Our study examined the effectiveness of eradication treatments using three laboratory trials and five treatments (air exposure, freshwater immersion, sodium hypochlorite, hypersaline solution and acetic acid) for S. plicata, as well as their effects on survival and growth of blue mussel Mytilus edulis Linnaeus, 1758. While air exposure and freshwater immersion caused a 27% mortality rate in S. plicata, the acetic acid treatment was the most effective in eliminating this species (>90% mortality). However, a 33–40% mortality rate was registered in mussels. Both species were not affected by the hypersaline treatment in the last trial, but the sodium hypochlorite treatment led to a 57% mortality rate in mussels. Differences in mussels’ growth rates were not detected. These trials represent a step forward in responding to the needs of aquaculture producers. However, further studies are needed to investigate the susceptibility of tunicates to treatments according to sexual maturation, as well as to ensure minimum mussel mortality in the most effective treatments, and to better understand the effects on mussel physiological performance in the long-term