## 1 Introduction  
Changes in the extent of mangrove cover has resulted in fragmentation that can greatly affect its functions and services to the environment and human kind [1]. Fragmentation of mangrove areas refers to the sub-division of a continuous landscape into smaller units,which can be characterized based on patch size, edge, and shape modification. Fragmentation analysis and monitoring are important indicators of how mangrove patches influence ecosystem habitats, species diversity, carbon storage capacity, etc. [2]. [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] [1] showed that Southeast Asia (SEA), which has the highest mangrove tree species diversity, is a hotspot for mangrove fragmentation. Among the SEA countries, Malaysia in particular has the highest reduction of mangrove mean patch size, ranked at first place in the nations of the world [1]. Fragmentation could impact habitat health and could cause species extinction, and the report of [PERSON] et al. [3] showed that Sungai Pulai and Johor Straits in the southern part of Peninsula Malaysia have lost many of their dugong species as a consequence of mangrove loss and fragmentation. Mangroves that provide important economic, social, and ecosystem functions and services [4; 5] warrant effective monitoring for appropriate management to avert further loss. The mangrove ecosystem is an essential component of nature-based solutions for climate change mitigation and adaptation [6; 7; 8]. While the prevention of deforestation and degradation of mangroves is the most effective strategy for climate change mitigation and adaptation, restoration can reverse the impacts of climate change after 25-30 years [9; 10; 11]. Mangroves can protect shorelines against storm surges, cyclones, and tsunami waves. [12; 13]. Although recent studies revealed that mangrove loss has been reduced in last decade [14], further and continuous monitoring can help to accelerate the restoration and conservation of mangroves [15]. A review of the literature shows that, in the past decade, although studies on habitat loss is well reported, research on habitat fragmentation has been poorly documented [16]. The limited studies catalogued on habitat fragmentation have focused on nutrient cycling, dung removal, pollination, and seed dispersal [17]. Studies emphasizing the impacts of forest fragmentation on biomass, productivity, predation, parasitism, infection rate, and aquatic functioning account for only 3% of forest fragmentation studies [18]. This gap of information on the impact of fragmentation on mangrove productivity must be addressed and is one of the objectives of the current study. Gross primary production (GPP) of any ecosystem is often used as an indicator of the total amount of CO\({}_{2}\) assimilated by the ecosystem, particularly by the vegetation [19]. Thus, analysis of GPP and its relation to mangrove cover loss and fragmentation can provide useful information pertaining to the dynamics of the mangrove's function to assimilate CO\({}_{2}\). GPP is affected by forest vegetation structure and stand parameters such as the diameter, tree height, canopy area, basal area, leaf area index, and mean tree weight and density [20]. Leaf Area Index (LAI) refers to the total leaf area per unit surface, and this index has been used for assessing the rate of carbon assimilation, primary productivity, and respiration and growth of vegetation, including that of mangroves since the 1990s [21; 22; 23; 24; 25] because it is relatively easy to measure in the field and also to derive using remotely sensed data [26]. It can be hypothesized that, due to mangrove forest changes, the LAI of mangroves will be significantly affected, and this will be reflected in the amount of GPP accumulated by mangrove trees. LAI and GPP can therefore be considered as simplified indices to monitor the carbon storage of mangroves. Previous studies have mapped the carbon stock and biomass of mangroves using various remote sensing technology and unmanned aerial vehicle systems [25].