Retraction Retraction: Co-existence of Epiphytes on Eucheuma Denticulatum (Rhodophyceae) in Varying Depths Cultivated with Verti Net Method ( IOP Conf. Ser.: Earth Environ. Sci.

. The existence of macroepiphytes is one of the issues seaweed farmers often face. This research aimed to explore the co-existence of macroepiphytes with seaweed Eucheuma denticulatum at varying depths using verti net method. Results showed that the highest and the lowest density of macroepiphyte were obtained on day -10 in the depth of 50 cm and 200 cm at 248,4 and 121,28 ind/m 2 /day, respectively. On day-20, in the depth of 100 cm and 200 cm the densities were 333,54 and 270,01 ind/m 2 /day, respectively. The most dominant macroepiphyte y is Chatomorpha crasa . Physical and chemical parameters showed a temperature of 29 o -30 o C, current velocity of 0,050-0,067 m/sec, brightness 92%, salinity 30-33‰, nitrate 0,237-0,0416 mg/L, phosphate 0,0015-0,0036 mg/L and dissolved oxygen 5,7-6,2 mg/L. The obtained optimum environmental parameters and the type of the macroepiphytes did not show any significant negative effect on the growth of E. denticulatum .


Introduction
Euchema denticulatum is one of the seaweeds that serve as an important commodity that is abundant in Indonesian waters. An epiphyte is an organism that clings into living flora or fauna and lifeless things such as rock. Epiphyte grows by attaching to the bark of trunks and branches, leaves, and to the surface of a sinking rock. Epiphyte communities that have clinging nature tend to stay in one location. Hence, this fact is deemed as bio-indicator of the quality of the flowing water area [1] Macroepiphyte is an epiphyte that owns larger size of leaves than other varieties. The parts such as (root, branch, and leaf) can be differentiated clearly with the size of 1>mm and microepiphyte has <1mm smaller with no vessels [2]. Macroepiphyte is a group of lower microorganisms that has no vessels and is included in Thallophyta group or widely known as a plant with thallus [3].
Macroepiphyte is morphologically enriched with a root-like part (holdfast) functioning as an attaching organ in their water habitat. The growth of mosses and epiphyte will block sunlight which later result in the decreasing process of photosynthesis. This will make the cultivated seaweed thin, and the growing pace will decrease [4]. Epiphyte clinging to thallus algae does not give negative impacts directly. However, the very existence of them serves as the competitors for the host in resources gathering. Hence this competition will affect E. denticulatum. The absorption of nutrients and sunlight is one of which. Their existence can also invite harmful organism [5]. The rise of macroepiphyte that is deemed as a primary problem and how far they attack often depends on the cultivated seaweed quality, environmental parameters, and extreme weather fluctuation [6]. Epiphyte is a disturbing pest that decrease the seaweed production [7].
In cultivating activity, one of the factors is the existence of epiphyte. Seaweed is a potential host to be attached by macroepiphyte so that the production will be affected. The existence of epiphyte on thallus algae gives direct negative impacts, but it can also serve as a competitor for the host. Epiphyte and the host have the same purpose in absorbing the nutrients as well as the sunlight. Thus, the  [5]. The existence of macroepiphyte can create a competition of absorbing the sunlight, this will render the production rate plunging down [8]. The growth of mosses and epiphyte will block sunlight which later result in the decreasing process of photosynthesis. This will make the cultivated seaweed thin, and the growing pace will decrease [4]. Seaweed can benefit from the sunlight to optimize the photosynthesis process as well as the process of growing and absorbing nutrients [9]. Macroepiphytes that attach to the thallus of seaweeds can hinder the growth and absorption of nutrients, block the sunlight for photosynthesis, hence, competing for food and space [10]. The important factor that influences seaweed growth is the amount of sunlight received by the seaweed growing in the different depths. It can influence the growth of new cells such that these cells exhibit slow growth in portions that receive little amount of sunlight [11]. The co-existence of macroepiphyte with seaweeds is evident in seaweed farms that are not well-managed. Vertinet is a rectangular seaweed cultivation tool that is deployed at different depths of the waters. This structure is used to protect seaweeds from predation by herbivorous fish and turtles. Vertinet method is one of the solutions to fix the cultivation management in most of these seaweed farms [12], [13].

Research Method
This research was conducted in February -July 2019 within a water area in Tanjung Tiram village, Konawe Selatan District, Southeast Sulawesi. The assays for water quality were done in the Laboratory of Marine and Fishery Faculty, Halu Oleo University, Kendari. The research location was divided into two observational points with a distance of 100 meters between sampling points. The specific point locations aim to enrich the data due to the homogeneity of the research location. Point 1 was at the coordinate 04° 01' 59" LS dan 122° 40'25" BT. Point 2 was at the coordinate 04° 01' 57" LS dan 122° 40'29" BT. The arranged verti nets are placed in two different locations with the distance around ± 100 m. Each verti net has different depths: 50 cm, 100 cm, and 200 cm which later be identified as Verti net A and verti net B. 15 (fifteen) E. Denticulatum seed is placed on each verti net at the different depths. The thallus net is attached to the net. Each thallus weighs 50 g. To differentiate, each verti net is labelled with different ties as verti net A and verti net B. The ties will also serve as a tool for observation.

Sampling Method
Samples were taken three times with the interval of 10 days. Twenty thallus (27) in total samples were taken at the depths of 50 cm, 100 cm and 200 cm. Thallus were taken by cutting the tie. Each sample was put into labelled plastic which later would be identified the existence of the macroepiphyte within.

Water Quality Parameter
Physical and chemical parameter were used together with macroepiphyte samples. Thermometer was used to scale physical parameter, Secchi disk for the brightness, the current velocity was scaled by a special tool, salinity by Hendrafraktometer. The scaling of DO and Nitrate was conducted in the Laboratory. The examination was done in the Laboratory of Marine and Fishery Faculty, Halu Oleo University. The researcher used brucin method (SNI 06-2480-1991) for scaling nitrate and spektrofotometer (APHA 4500-PD-1998) for phosphate.

Statistical Analysis
Scaling the density value of macroepiphyte was done to determine attachment rate of macroepiphyte in this research. The macroepiphyte attachment rate was calculated using relevant patterns. The analysis of attachment rate and water quality parameter was processed statistically with the assistance of SPSS software ver. 16

Macroepiphyte Species
The results showed that there are 9 varieties of macroepiphyte attaching to thallus E. denticulatum in Study site (Table 1): Rhodophyceae

Macroepiphyte Density
Based on the density observation on day-10, the researcher found 3 species of macroepiphyte attaching to thallus E. denticulatum which were C. crassa, unidentified species 1, and unidentified species 2. The highest density in the depth of 50 cm, 75 and 200 ind/m 2 were C. Crassa type and unidentified species 2. (Figure 2).

Macroepiphyte Attachment Rate
The result of the attachment rate of macroepiphyte to seaweed E. denticulatum in total is shown on Table 2.  Table 3. Correlation analysis between attachment rate and water quality parameter showed that the ones that had real correlation to attachment rate were temperature and salinity which can be seen on Table 4.

Discussion
There were 9 species of macroepiphytes that attached to the thallus of E. denticulatum. The numbers of macroepiphytes attaching were caused by the thallus' form which was small and full of tiny thorns. This made macroepiphyte that were flowing with current be able to easily attach [14]. The most dominant macroepiphytes were C. crassa dan H. Cervicornis. C. crassa which is commonly found attaching to other macroalgae, thrived by spreading on the substrate of rocks and sand. It has cylinders thallus like hair resembling tangled thread [12,13]. In the previous research in Tanjung Tiram village, it was found 16 species of macroepiphyte at E. denticulatum. All of them consisted of 8 species from Rhodophyta class, 6 from Chlorophyta and 2 from Phaeophyta class [17].
The morphology of the thallus seaweed was very important to the placement of epiphyte attachment. The complex structure of the thallus was great to be colonized by numbers of epiphytes because of its capability to provide shelter [18]. Macroalgae were found the most on the substrate of lifeless corals than those of living corals. This happened because the living corals had saliva and empowering cells that initially had been habituated by tube macroalgae which later be followed by bigger ones [19]. In the water area in Tual, Southeast Maluku, found 8 species of macroepiphytes attaching to seaweed such as Codium sp., E. clatharata, A. dendroides, A. spicifera, D. dichotoma, Padina sp., and blue green algae [20].
The research in Lakeba found 8 species of macroepiphytes clinging to seaweed E. spinosum such as macroepiphytes A. spicifera, C. papilosa, C. crassa, J. longifurca, P. triquete, U. lactuca, T. ornata and unidentified species [21]. Six other species which were E. clatharata, C crassa, U. fasciata, J longifurca, Ps triquete and unidentified species [22]. One of the density factors which was influenced by physical-chemical of the water area was current velocity. The current velocity during research could be categorized as normal with the value of 0,097-0,473 m/s. The high velocity could break the thallus body and it tended to trigger macroepiphyte growth on thallus. The opposite would do no good to the thallus itself such as the thriving macroalgae can dominate the sunlight as well as nutrient absorption [23].
The varieties and numbers of macroepiphyte attached to thallus E. denticulatum on verti net could cause the failure of the seaweed harvest. Because of the body of the seaweed was so thin and fragile, harvesting them would mean more loss [12,24]. The researcher found the different in numbers and species of the macroepiphyte attaching. Epiphyte is one of the parasites that can cause harvest failure, the said one is Neosiphonia apiculata [10]. The attachment of macroepiphyte can harm thallus seaweed. The growth rate of the seaweed will remain stagnant day per day because of the competitive match over sunlight and nutrients [13,25]. The existence of macroepiphyte can be a new competitor due to its ability to cling to thallus seaweed [20]. Macroepiphyte and disease infection can make the seed quality bad to cultivate [14,26]. The inability to thrive in the deep water is caused by the small supply of sunlight and oxygen [11]. The sunlight absorption is a limiting factor to the growth of the seaweed thus the depth of the water must be paid attention to when it comes to seaweed cultivating [28].
Macroepiphyte at a specific species looks like a brownish hair, attaching to thallus, this renders the thallus' surface wavy. Macroepiphyte E. flaccida live by gathering at the wounded part or on the base of thallus. They slowly cover all the surface of the thallus. The macroepiphyte is included to the type that can be easily remove because of its weak adhesive power. This type also merges with water dirt. They can rot the thallus if left attaching for too long [27,29]. Each organism has different threshold towards several environmental parameters such as salinity including seaweed. Some has high threshold so that they can endure and thrive in the environment deemed not well for others. That condition indicates that macroepiphyte attachment rate does not have significant influence towards thallus as the media to attach [30]. If we put that into 5 species, the average effects caused by macroepiphyte can be put into type -3 in which the macroepiphyte attaches without destroying the metabolism cells that can help other cells to grow [31].
The high rate of macroepiphyte attachment can be caused by the optimum nitrate concentration which can support the growth of the macroepiphyte. The phosphate concentration found during research was so low around 0,0015-0,0036 mg/L. That value can be considered low for the the optimum value needed. One of the causes of the loss of the attaching algae which was found in the first week during the research in Bantaeng district was the low concentration of phosphate in the water area. The macroepiphyte attached was A. spicifera, Boergeseniella sp., C. crasa, C. papillosa, P. minor, P. pavonica, Un identified species 1 and unidentified species 2. That research gives us hints that there are different patterns to the species of macroepiphyte attaching [23]. There are changes in either the species and light intensity towards attaching biota with simpler morphology like thread. Enthermorpha and Chaetomorpha will attach in moderate number and will dissipate and be replaced by other species with more complex form. Macroepiphyte with strong adhesive power which can penetrate into cell wall and corticosteroids tend to cling strongly and to cause harms to the growth of seaweed. In the opposite, the weak adhesive type doesn't cause significant harm to the seaweed. The macroepiphyte's growth really depends on the physical and chemical parameters. If they are not fit living, then they will be replaced by those who fit [31].

Conclusion
Macroepiphytes that attached to the thallus of E. denticulatum are composed of 9 species; A. spicifera, Boergeseniella sp., C. crasa, C. papillosa, P. minor, P. pavonica, S. cristaefolium. The highest and lowest attachment rate was observed on day-10 in the depth of 50 cm and 200 cm which were 248,4 and 121,28 ind/m 2 /day, respectively. Temperature and salinity significantly influenced and resulted in positive effects on the attachment rate of the macroepiphytes.