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The Possible Link between the Declining Superorder Batoidea Population and Mangroves Degradation


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Image by Timothy K
Mangroves | Unsplash/Şahin Sezer Dinçer

Often known as rays, the superorder Batoidea are found across the ocean floor and the coastal region. Approximately 200 occurring species are verified to roam the Indonesian Exclusive Economic Zone (EEZ) territory. The majority of the ray populations have been declining for the past few years. The causes of the declining population are very diverse in a lot of different contexts and are correlated. Of course rays' natural behaviour and their habitat are taken into accountability with regards to their declining population. This suggests that rays that live in the coastal and short depth ocean territory are more prone to either incidental or targeted fisheries. Due to rays' economical value, rays are heavily targeted both by unregulated fishery activities and fishing industry companies in Indonesia. Along with the mass fishery, rays in a certain ecological niche could also face struggles when it comes to food competition and larger predators. These reasons leave young and newly born rays in danger. This is because rays eggs are fertilised and hatched inside the mother’s womb, thus a live mature birth is given by their mother. This makes young rays not fully dependent on maternal help. Although they will stay by their mother’ side, young rays do fetch their own food and protect themselves from danger. These young rays are in need of a complimentary habitat that is able to protect young rays. One of these habitats is the mangrove forest, where recorded active movements of rays are found.

Mangrove forests play an essential role in why young coastal rays favour the mangrove environment. Mangrove grows in heavily salinated water (salt water) and anaerobic mud that contains little to no oxygen. This extreme condition, whereas other vegetation will not survive, allows the mangroves to row a complex root system to adapt to their environment. Mangrove forests are able to provide protection and shelter to young rays and other coastal inhabitants among mangrove specialised roots to flourish. With a sealed environment, young rays are able to avoid food competitors, predators and overfishing. However the degradation of the mangrove forests could pose a potential danger to the future generations of rays. The habitat of this coastal ecosystem has been under the threat of degradation for the past few years in Indonesia. As in data, Landsat-8 satellite has been used to detect the decreasing of mangrove forests distribution and density. In 2016 the total mangrove area in Indonesia was 5,3 million ha and the total mangrove area has decreased down to 2,1 million ha by 2020.

Mangrove degradation in Indonesia is mainly caused by the conversion of land use, which is claimed to provide economical goods to the nation. One of the biggest and well known conversion terms is the ‘Blue Revolution’. The term was first introduced in 1985 by Dr. Hiralal Chaudhuri and Dr. Arun Krishnsnan, referring to the sudden and exponential growth of the production and domestication of aquaculture, striving for economical ambitions. This term could later on be applied to Indonesia’s mass aquaculture farming. Indonesia's potential aquaculture farming in 2020 is 5,6 million ton per year at the Maximum Sustainable Yield (MSY). This relatively big number puts the farming of aquaculture at an important position to economical and food security development. One of the biggest contributors to this sudden explosion of aquaculture production is the conversion of mangrove forests into shrimp farms. According to data provided by the Indonesian Ministry of Marine Affairs and Fisheries approximately 239 million kilograms of shrimp are exported in 2020 alone and approximately to be groced at 2 billion dollars bruto. The data also acts as an indicator that the income from shrimp and other aquaculture exports will continue to outgrow the previous year’s number. Seeing how the numbers exponentially grow, this naturally leads to more conversion of mangrove forests and other coastal regions into aquaculture land uses.

As mentioned earlier, young rays seek protection in between the specialised roots of mangrove forests. Which makes the deforestation and degradation of mangrove forests a crucial obstacle for their survival. Mangrove forests provide a protection extended to the fishing industry in Indonesia, predatory behaviours against young rays and at the same time providing food. This means young rays are no longer fully protected by their ecological habitat, leaving them exposed to overexploitation, competition for food with other adult rays and predators. In terms of the ability to repopulate, rays are categorized as having a slow cycle of reproduction. This natural element plays a big part as to why the population is declining. Rays reach their sexual maturity between 10-15 years depending on the
species, making the regeneration process happen at a much slower pace than the degrading process of their habitat. Less and less rays are barely surviving into adulthood. The total amount of rays population decreases around 2 percent each year. In sync with the decimated mangrove habitat, 40 percent of species of the superclass are now declared as highly threatened or almost extinct.


In attempt to reduce deforestation, in 1984, the Minister for Agriculture and The Minister for Forestry adopted a joint decision Concerning Regulations on Making Available Forest Areas for the Development of Agricultural Cultivations. This joint decision aims to provide a cultivation area for agriculture which also includes the development of aquaculture cultivation in mangrove forests (Article 3). However, this article is very exclusive and only applies to certain coastal conservation zones that are nationally recognised. Whereas there are mangrove forests that are located outside the nationally recognised conservation zones that also need to be protected. This limited applicability raises issues regarding the high mangrove deforestation percentage which further affect the declining population of young rays that unfortunately depend on mangrove forests. As the survival of rays is dependent on their habitat, therefore, an immediate action needs to be taken by the government, particularly to adopt new legislation related to mangrove conservation. Such action is crucial, aiming to provide better protection of mangrove forest and the ecological lives in it.