The density of marine debris in seaweed farming sites in Kupang Bay, East Nusa Tenggara Province – Indonesia

Organic and inorganic debris in the seaweed farming areas in Kupang Bay and its surroundings is a serious problem, but until now there has been no accurate scientific data on this waste, both macro and micro. This study aimed to calculate and analyze macro debris wasted in seaweed farming areas. Sampling for macro debris consists of (1) sampling of debris deposited in the farming area, using Belt Transect, (2) sampling of debris at Sea Level and Water Column. The data obtained were analyzed for absolute density (weight of waste), absolute density (number of pieces of waste), relative density (weight of waste), and relative density (number of pieces of waste). The results of this research found that the dominant debris found at the seaweed farming site in Kupang Bay and its surroundings was plastics, with a details density of 24.33 amount/1000 m2 (37.83%) in Bolok; 13.67 amount/1000 m2 (35.57%) in Tablolong; 38.00 amount/1000 m2 (74.06%) in Tesabela; 37.67 amount/1000 m2 (58.55%) in Pasir Panjang, and 87.00 amount/1000 m2 (57.90%) in Sulamu, followed by wood waste and nylon rope waste. The most dominant source of waste was the activities of seaweed farming itself.


Introduction
Marine debris is defined as any persistent solid material that is produced or processed and directly or indirectly, intentionally or unintentionally, abandoned of or disposed in the marine environment [1].East Nusa Tenggara (NTT) is the second-largest producer of seaweed production in Indonesia.NTT's seaweed production gives a value-added of 4.3 trillion rupiahs [2].In fact, this marine aquaculture activity uses a lot of plastic as the main base material.In seaweed farming, for example, the plastic used is nylon rope and plastic rope (hanging ropes and binding seeds), plastic bottles (additional buoys), and plastic drums (transporting seeds and harvest).These plastic materials can enter the sea by (1) being released by themselves due to the influence of strong currents and waves or intentionally discarded by farmers, and (2) this plastic has a useful life, which when not used anymore tends to be thrown into the sea by seaweed farmers.The same problem was also stated by Msuya [3] on seaweed farming in Tanzania, in which floaters or buoys are made of recycled cooking oil cans and recycled plastic mineral water bottles, while anchors are made of plastic fertilizer bags filled with sand.According to Singh & Sharma [4], plastic waste found floating in the sea can be degraded by microbes, heat, ultraviolet light, and physical abrasion into plastic flakes, which then if enter the body or are consumed by marine life will be very dangerous.Zamroni and Yamao [5] also stated that very often, seaweed lines are detached by strong waves and currents, which carry floating debris that gets entangled in the lines causing significant crop losses.
Indonesia is listed as the largest contributor of plastic pollutants to the ocean in the world (0.48-1.29 million metric tons of plastic/year) [6].This value increases every year along with the increasing demand for plastic by business actors at sea.For the scope of Kupang Regency and City, with the rapid growth of aquaculture activities in the sea leading to aquaculture industrialization, this results in more and more plastic being used and wasted into the sea.Hiwari et al. [7] research in Kupang and Rote waters found that the size of the microplastics found ranged from 5 μm-2 mm.The microplastics found have undergone a long process of degradation.The sources of microplastics are thought to be plastic waste originating from tourism activities, fishermen, cultivators, anthropogenic activities, and industries in the Kupang and Rote areas which are fragmented and scattered in the sea.
From the description above, it is clear that plastic waste in the sea has become a serious problem in Kupang Bay and its surroundings, but until now there has been no accurate scientific data on plastic waste, both macro and micro in marine aquaculture areas.This study aimed to analyze the composition and density of macro-waste used and discarded in the seaweed farming areas in Kupang Bay.The benefits of this research will provide information about marine debris and negative effects on seaweed farming

Materials and methods
This research was carried out for 3 (three) months, August -October 2021, at several locations of seaweed farming around Kupang Bay (the waters of Sulamu, Pasir Panjang, Bolok, Tesabela, and Tablolong (Figure 1).A sampling of waste deposited in the farming areas was carried out using the "Belt Transect" method during low tide.Sampling was done by placing a transect line vertically from the coastline of 50-100 m, with data taking 5 m to the left and right of the transect line.The distance between transects is 100 m.The total number of transects depends on the size of the sampling area.For the sites of Bolok, Pasir Panjang, and Tesabela, 3 transects were used each; while for the Sulamu and Tablolong sites, 5 transects were used each.At each location, sampling was conducted once a month, meaning that there were three replicates in each for the duration of the study.
The data obtained were analyzed using the formula [8]: Relative Density (Weight of piece of waste) = Weight of pieces of waste in each category The total weight of waste in all categories ×100

Debris composition
The results found that the waste discharged at the seaweed farming sites in Kupang Bay and its surroundings varies and was dominated by plastic, wood, and nylon rope.Plastic waste referred to here is PETE (Polyethylene Terephthalate) which consists of bottles and glass packaging for mineral water, cooking oil bottles, juice, chili bottles, medicine bottles, and single-use plastic packaging.Most of the plastic waste found at the farming sites was waste from used aqua bottles that were no longer used in farming construction.The wood waste found was almost entirely wood that was no longer used in farming constructions in the Off-Bottom Method.Meanwhile, nylon rope waste found at the farming site was nylon rope with a diameter of 3-10 mm which was no longer used in the construction of seaweed farming.

Absolute density and relative density (number of pieces of waste)
From the survey results in all sampling locations of seaweed farming in Kupang Bay and its surroundings, plastic waste dominated, with a total density ranging from the smallest 13.67 amount/1000 m 2 in Tablolong, to the largest 87.00 amount/1000 m 2 in Sulamu (Table 1A); while the relative density of the numbers ranged from the smallest 37.06% in Bolok, to the largest 81.56% in Sulamu (Table 1B).
The highest amount density of plastic waste in Sulamu was due to the higher farming intensity, which covers a larger area than other farming sites in Kupang Bay and its surroundings.So that more plastic was used and wasted as waste than other sites.The results of Paulus et al. [9] research conducted in a mangrove ecotourism area in Kupang Bay (Oesapa) found 9 types of marine debris, they were plastic waste, foamed plastic, cloth, glass and ceramics, metal, paper and cardboard, rubber, wood.as well as other types of waste with the highest average compositional value and total density found in plastic waste with an average composition value of 92.32% and a total density value of 9.622 amount/m 2 .2A and Table 2B).Study by Djohar et al. [11] in Tongkaina, North Sulawesi found that the density of plastic waste was the highest weight at 6348 grams/1200 m 2 (52,900 grams/Ha) followed by fabric type waste as much as 5 Plots/1200 m 2 (41,666 Plots/Ha) with a weight of 680 grams/Ha.1200 m 2 (5,666.6gram/Ha).Other types of waste found were metal with a weight of 130 grams/1200 m 2 (1,083.3grams/Ha) and followed by glass waste with a waste weight of 490 grams/1200 m 2 (4,083.3grams/Ha).
From the description there are some marine debris that was also found by Mariño et al. [10].They stated that seaweed farmers in Rote Island used nylon rope to tie the seeds, and use 2L mineral bottles every 6 meters as floats, to keep the seaweed on the surface of the water during high tide.Apart from that, they also used plastic sacks filled with sand to make anchors for seaweed cultivation.ropes, plastic sacks and mineral bottles that have been damaged and are no longer used will simply be thrown away thereby contributing to the high density of plastic waste.Debris at the farming sites was mostly generated from the seaweed farming activity itself.Many used aqua bottles that were no longer used in farming activities were scattered around the farming sites.This makes up the largest component of the amount of plastic waste in the farming sites.Debris in the form of nylon rope, including one that makes up the largest component of waste around the farming sites.This waste came from nylon rope used in the construction of off-bottom and longline farming methods which were no longer used by seaweed farmers but were not removed from the sea.Even though the nylon ropes are not too many, they are heavy, so they make up the density and relative density for the dominating waste weight.According to Huntington [12], Common causes of plastic loss from aquaculture activities into the marine environment can be caused by mis-management: including (a) poor plastic waste management, (b) poor placement, installation, and maintenance of plastic materials, (c) Inadequate recycling of plastics, (d) intentional disposal, and (d) lack of awareness and training.
Debris in the form of wood, which was produced from the activity of seaweed farming by the offbottom method, dominated the composition of waste in the waters.Most of the seaweed farming activities in Kupang Bay and its surroundings used the off-bottom method.In this method, a lot of wood is used as the main construction material.The wood used has a shelf life of about 3-4 years.From the survey results at the farming sites, a lot of wood that was no longer used in the seaweed farming area remains stuck and was in the farming sites.This constitutes a sizable composition of waste at seaweed farming sites in Kupang Bay and its surroundings.
For the sampling location in the farming site in Bolok marine waters, the location is close to Ferry Ship Port.This condition causes the discovery of garbage at the location of seaweed farming originating from activities at the port.From the survey results, it was found that plastic leftovers from packaging for food, drinks, cigarettes, and others that were sold at the port and on the ferry, were scattered and stuck at the seaweed farming location.
For the sampling location in Tablolong, the location of seaweed farming is around tourist sites.This has resulted in the discovery of quite a lot of waste, especially plastic waste from food and beverage packaging scattered around the farming site; also found paper, cloth, and other waste due to tourism activities.
For the sampling location in Sulamu, seaweed farmers build simple houses around the farming site.These houses are not equipped with toilets and trash cans, so farmers throw their garbage carelessly around the seaweed farming site.According to UNEP [12], The potential impact of chemical marine debris tends to increase as the particle size of the waste decreases, while the physical impact will increase as the size of the waste increases Purba et al [13], in their research at Savu Sea found marine debris collected from Kupang, Rote and Ndana weighed 52.14 kg with an average abundance of 4,447 ± 1,131 kg/m 2 and 215,417 ± 35,609 items/m 2 .It is strongly predicted that this debris was sourced from local residents through various activities.However, it is strongly suggested that beached debris in Ndana was transported from other places via ocean currents.The most dominant debris types were food wrappers and other plastic bags, which were found in every transect, and then it was said that marine debris would affect the balance of marine biodiversity, including seaweed farming.

Conclusion
1.The composition and density of the largest amount of waste in all seaweed farming sites in Kupang Bay and its surroundings was plastic waste.2. Based on weight, plastic waste, wood, and nylon rope were the dominant waste in all seaweed farming sites in Kupang Bay and its surroundings.3. The dominant source of waste found in seaweed farming sites in Kupang Bay and its surroundings came from the farming activity itself, followed by other activities such as tourism and ports.
Density (number of pieces of waste) = Number of pieces of waste in each category Total sampling area (m 2 ) Absolute Density (weight of waste) = Weight of waste in each category Total sampling area (m 2 ) Relative Density (Number of piece of waste) = Number of pieces of waste in each category The total number of waste in all categories ×100

Table 1 .
Average absolute density and relative density (number of pieces of waste) in farming sites in Kupang Bay.

Table 2 .
Average absolute density and relative density (weight of waste) in several farming sites in Kupang Bay.