Littoraria spp. Snail (Mollusca: Gastropoda) as a Bioindicator in The Mangrove Ecosystem

Coastal environmental damage often occurs in various regions, especially around the mangrove forest area. Generally caused by anthropogenic which is increasingly high and causes mangrove habitat to change and gives great pressure on the biological community that inhabits it. One of the main objectives of bioindicators is to identify species or groups of species that can indicate environmental disturbances, so this study aims to determine or assess how suitable species or groups of Littoraria species as bioindicators in monitoring programs in coastal environments, especially mangrove ecosystems. The results of the study concluded that Littoraria spp. can be used as a species or group of bioindicator species. This is because they have fulfilled the requirements that must be fulfilled by an organism to be used in the biomonitoring program. However, the criteria for Littoraria’s spp. relationship with other species is still unclear, so they must be used with caution.


Introduction
Littoraria spp. is one of the genus of the gastropod class with its family taxa is Littorinidae which has taenioglossate type radula which is seven teeth in each row (a common feature of most caenogastropods) [1], able to survive when exposed to seawater splashes [2], are opportunistic feeders [3] and also eat small invertebrates [4,5]. Availability of food, competition, and predation is a limiting factor for survival and distribution [6,7], while wave heights [8] and currents [9] are limiting factors for density. In addition, the movement of Littoraria spp. was greatly influenced by the tidal period of the sea and the size of the shell [10].
One of the most widely used approaches to monitoring environmental quality is the use of indicator species (bioindicators), both animals [11,12,13,14] and plants [15,16,17,18,19,20,21,22,23]. Bioindicators are very useful in measuring biological and non-biological changes [24] with their application depending on the conditions of reference that define the biological conditions or habitat to be achieved [25]. In simple terms, bioindicators are defined as species or groups of species that reflect the biotic or abiotic state of the environment, representing the effects of environmental changes in a habitat, community or ecosystem, and can show diversity in other species [26], so that using bioindicators is very possible assess the impact caused by human activities on surrounding organisms [27].

Categories and Selection of Bioindicator Standards
Biological indicators are used to supplement toxicity [86], chemical valuation methods [25] and serve as evaluations of environmental quality [25,27]. The most important reason for using bioindicators is cost effectiveness [27] and is a technique that is fast in estimating several groups or the overall diversity of a species [87], so that someone (such as experts) can predict or predict and prepare future [24]. [26] divides indicators into three parts, namely environmental, ecological and biodiverity indicators. Environmental indicators detect changes and or monitor environmental conditions, while ecological indicators show the effects of stressors on biota and monitor changes that cause long-term stress, while biodiversity indicators identify the diversity of taxa in certain areas and monitor changes in biodiversity. To detect environmental changes, environmental and ecological indicators are used, while to detect the diversity of living things, biodiversity indicators are generally used [24].
The abundance of species on earth, there is at least one that fulfills it as an indicator criterion [27], although its selection is very complicated and difficult [24,88,89]. This is because species responses to environmental changes may be contradictory [90,91], the activity and abundance of each species vary throughout the year [92], each species has different ecological requirements [90,91,93], and some species that are general in various habitats and some are special [27]. In addition, the most difficult problem in selecting bioindicators is the generalization of results [27] namely how well species or groups of species represent other species in the event of environmental changes [90,91], so as to make as species or groups of indicators of environmental change species must have several standards or criteria, namely: 1) taxonomy, ecology and habitat characteristics must be clear, 2) spread over a wide geographical area, 3) can provide early warning of a change, 4) easy and cost-effective when surveyed, 5) have many groups of individuals who are independent and not too affected by the size of individual groups, 6) represent responses of other species, 7) represent ecological changes caused by the influence of human (anthropogenic) pressure, and 8) very important socially, economically and culturally [24,88,89,94]. Furthermore, species or groups of species to be used as environmental indicators must also have been carried out studies of climate change, easily observed and emerged for a long time and formed groups with many individuals [24].

Testing Littoraria spp. as a Bioindicator
Studies of marine and coastal biota have been numerous and have been used successfully in various types of indicator studies [95,96,97 (Table 3). In addition, Littorina species are also used to understand the spatial and temporal effects of hydrocarbon oil spills and the evaluation of biomonitoring tributyltin (TBT).

Has a clear taxonomy
Littoraria's taxonomy has been revised and explained by Bandel and Kadolsky [119] and Reid [117,120,121], where previously Littoraria species were included in the genus Littorina [121] whose grouping was based on shell characters [122,123,124,125]. In the family level monograph proposed by Rosewater [122], the group 'scabra' in the Indo-Pacific consists of three species, namely L. scabra (widespread and highly variable), L. melanostoma and L. carinifera (both spread only in Indo-Malaya). Furthermore, after switching to soft anatomical characters [126], the 'scabra' group consists of 20 species, so it must be referred to in the genus Littoraria and recently the number of species from the genus Littoraria has reached 39 species [118].

It has clear ecology and habitat characteristics
Thirty-nine (39) of Littoraria species are distributed in the tropics and subtropics, most (mainly) found in mangrove trees, although at least some are found on rocky beaches or protected rocks (Table 5) [1,118].

Spread over a wide geographical area
The geographical distribution of Littoraria is widespread in the Indo Pacific, Atlantic and Pacific Oceans [70,118,121,122,126,127,128,129], where Littoraria is almost exclusively found in tropical regions compared to subtropics, both spread and biodiversity [121] (Table 5).

Can provide an early warning of a change
The most well-known mangrove-related Littorinidae are L. scabra (Linne) in the Indo-Pacific and L. angulifera (Lamarck) in the Atlantic [126]. The destruction of mangrove forests caused by land conversion for residential settlements and agricultural land causes gastropod L.scabra not found in Ambon Bay mangrove forests [130]. Then the area that experienced physical pressure by aquaculture, industry, residential settlements and tourism, also caused gastropod L. scabra not to be found in the mangrove forest of Tugurejo Village, Semarang [131]. While in the mangrove rehabilitation program area, gastropod L. scabra was only found with a low attendance rate at some points [132].

Easy and economically inexpensive during the survey
In conducting surveys, Littoraria can be collected by hand (collected without using a tool). This is because his life tends to be relatively sedentary [133] and its movements are very slow [10].
3.6. Have many groups of individuals who are independent and not too affected by the size Littoraria is typically found on tropical and subtropical beaches [1,118,126] and has geographical variations in shell size. As many as 50 individuals of L. scabra have been collected by [70] on the Southwestern side of Nananu-i-Ra Island in the Fiji Islands and obtained the size of the shell between 13 ± 28 mm, while [10] measured 30 shell lengths of L. scabra on the beach Tawiri Ambon Island (Indonesia) ranges from 10 ± 24 mm. If the survey/study is carried out in several locations (replication), it will reduce the problem of inequality of a species, where the more number of locations carried out, the species will be evenly distributed and the results will be more accurate [134].

A represent the response of other species
Specifically, the response of other species due to changes in Littoraria (increased or lost) is still less studied. However, changes in L. littorea, the closest relative of Littoraria [108] have been studied and greatly influence algal cover [135,136,137] and barnacles Balanus balanoides [137]. This has similarities with Littoraria, where Littoraria is a herbivorous gastropod [5,129,138,139] with food types such as microalgae, macrophyte sheets, algal filaments and mangrove tissue [3,129].   [118] In addition, Littoraria contributes to the dynamics of food webs in mangroves [70] or rocky substrates, where the presence of Littoraria on the surface of mangrove mud and rocks can provide food for macro-organisms and microalgae and other small invertebrates [4]. IOP Conf. Series: Earth and Environmental Science 695 (2021) 012008 IOP Publishing doi:10.1088/1755-1315/695/1/012008 10 [140] study show that the presence of L. scabra in non-polluted areas has a greater total weight, length and width of the shell compared to the polluted area. Likewise, the density is lower in polluted areas when compared to non-polluted areas.

Representing ecological changes caused by the influence of human pressure
3.9. A study of climate change has been carried out [141] examined the variable environment temperature of L. scabra related to climate change and showed that the maximum limit of environmental temperature that could be tolerated by L. scabra only reached 33.40ºC, then they showed better-locating behavior if the temperature exceeded 33.40ºC.

Easy to observe, appear for a long time and form groups with many individuals
The Littoraria lifestyle tends to move up and down mangrove trees or perpendicular to the coastline [137]. To move down the mangrove tree, L. scabra requires a slower time than upward [70], so they are very easy to observe and appear for a long time. In addition, Littoraria is the only arboreal gastropod most abundant in the intertidal region [126] and its dispersal pattern forms groups with many individuals [142]. This statement is also supported by [143] that gastropods live in groups.

Important socially, economically and culturally
Littoraria can be considered economically important because it has the properties of grazers that affect the density of algae and barnacles. [144] states that Littorinidae density is a key factor in barnacle population dynamics, where barnacles are often a serious problem for a building that is affixed (eg dock/port pole) which can damage and shorten the life of a building [145].

Conclusion
Changes and sensitivities of Littoraria in coastal areas, especially mangrove ecosystems, can cause them to be used as species or groups of bioindicator species. This is because they have fulfilled the requirements that must be fulfilled by an organism to be used in biomonitoring programs, although their response to represent other species or groups of species is unclear.