Mangrove forests are found in tropical and subtropical saline coastal environments Myint

Mangrove forests are found in tropical and subtropical saline coastal environments (Myint et al., 2008). These ecosystems are among the most diverse in the world and provide many important ecological and societal goods and services (Day et al., 1989). Fishing operations, which support recreational and commercial activities as well as coastal community subsistence, are often dependent on mangrove forests and an important management concern (Rönnbäck, 1999). Mangroves serve as breeding and nursing grounds, protect juvenile fish from predators, and provide refuges for many marine and pelagic species (Day et al., 1989; Giri & Muhlhausen, 2008). Within mangroves, fish play important roles in nutrient fluxes across trophic levels and through space (Henderson et al., 2019). The world’s mangrove forests, however, have been reduced significantly over the last two decades (Valiela et al., 2001). These ecosystems continue to face threats from several anthropogenic disturbances, including the overharvesting of mangrove trees and clearing for urban and industrial development, agriculture, and aquaculture, which can lead to habitat fragmentation and resulting spatiotemporal changes (Giri & Mulhausen, 2008; Manson, Loneragan, & Phinn, 2003; Valiela et al., 2001). Forest fragmentation caused by changes in human land use activities is of primary concern for sustainability (Abdullah & Nakagoshi, 2007). Mangroves are often found in highly developed coastal landscapes and experience strong direct and indirect influences from human populations that can lead to habitat fragmentation (Friess et al., 2012). It is important for conservation efforts to not only consider the quality of the whole mangrove landscape, the number of different mangrove habitats, and their spatial arrangement, but also mangroves as a part of the anthropogenic landscape (Martin et al., 2014; Steiner & Kohler, 2003). The intensity of human effects on these ecosystems has been shown to be influenced by surrounding land uses and tenures. Blanco-Libreros and Estrada-Urrea (2015) examined mangrove ecosystems along an urban to wild gradient of human-transformed biomes (i.e. anthromes) in a deforestation hotspot of the Urabá Gulf of the Southern Caribbean near Turbo Municipality. Differences in deforestation rates, land use and tenure, and proximity to the municipality observed in each anthrome (peri-urban, rural, military-protected, or wild) led to significant differences in habitat fragmentation, in which protection and remoteness were effective in reducing anthropogenic edges and fragmentation (Blanco-Libereros & Estrada-Urrea, 2015). Fragmentation, which breaks the contiguous landscape into smaller patches, is considered one of the greatest threats to biodiversity and is a major cause of species extinction (Wilcox et al. 1985). Major effects from habitat fragmentation include decreasing patch size, increased edge effects, and increased patch isolation (Haila, 1999). A large majority of studies examining these effects have been limited to forest ecosystems. For example, Matlack (1993) showed that in forests, fragmentation increases edge habitat (i.e. the transition zone between two different habitats), which can lead to microclimatic changes along the fragment’s edge and an alteration of vegetation and animal communities. Harper et al. (2005) concluded that increasing forest edge can cause biological changes, such as in species composition, abundance, distribution, and interactions. Decreased size in and isolation of patches can also result in less connectivity between sink and source populations, reduce dispersal opportunities for resources or mates, and increase chances for invasions by generalist species (Harper et al., 2005; King & Chapman, 1983). This, in turn, can lead to reductions in populations or even extinctions for certain species and a possible reduction in diversity. With the advancements in remote sensing techniques, which has made it possible to study large geographical areas, several studies have used measurements of landscape metrics, such as patch size, patch number, edge density, and mean patch edge to investigate and quantify habitat fragmentation of mangrove ecosystems (Li et al., 2013; McGarigal & Marks, 1995). For example, Seto and Fragkias (2007) used these landscape metrics to investigate mangrove fragmentation of Ramsar sites in Northern Vietnam before and after the Ramsar Convention to monitor compliance for mangrove protection. Although these studies offer insights into changes in mangrove fragmentation patterns over time and/or due to anthropogenic effects, the effects of mangrove fragmentation on habitat characteristics related to important management issues, such as the sustainability of fisheries, remain to be elucidated. There is a close relationship between mangrove presence, high fish diversity, and increased fisheries stock (Hamilton et al., 1989). Mangrove fragmentation due to anthropogenic activities are likely to affect fish assemblages in these ecosystems. Variation in habitat extent, isolation, and connectivity has been shown to modify the composition of fish assemblages in other aquatic ecosystems, such as estuaries (Nagekerken et al., 2015). Mangrove fragmentation could reduce protection from predators by increasing light penetration, visibility, and proximity to open water (Li et al., 2013). Important habitats, such as fish nurseries, could also be reduced or eliminated. In addition, isolation can occur when the mangrove landscape is highly fragmented, which could affect biological exchanges throughout the mangroves (Li et al., 2013). Previous studies have examined relationships between mangrove forests and fish abundance and diversity. De Graaf and Xuan (1999) showed a positive relationship between mangrove area and marine fisheries catches for mangroves in Vietnam. Singkran and Sudara (2005) demonstrated that abundance and species richness of fish were reduced due to degraded water quality and fish habitats related to mangrove degradation, shrimp farming, and agricultural development. More recently, results from a study investigating mangrove degradation and restoration (Adite et al., 2013) found that fish species richness, species diversity, and dominant species abundance were higher for less and restored mangrove sites in West Africa. Although previous studies suggest important relationships between mangrove presence and habitat quality on fish communities, these studies do not specifically relate effects of fragmentation using landscape measures to fish distribution and abundance. The aim of this study is to identify the impacts of anthrome-dependent fragmentation of mangrove forests on fish assemblages. Specifically, the question of how distinctive fragmentation patterns, which are influenced by changes in land use and tenure, affect species richness, relative abundance, and diversity, will be addressed. The former study site of Blanco-Libereros and Estrada-Urrea (2015) containing mangroves along the Southeast coast of the Urabá Gulf with differences in fragmentation landscape metrics due to anthropogenic disturbance across an urban-rural gradient will be used as a case study. Results from this study will provide insights as to how mangrove landscape metrics contribute to fish abundance and diversity. An increased understanding of these landscape variables can contribute to improved mangrove restoration and fisheries management programs.

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