Ecological potential of giant clams in Ambon Island waters, Eastern Indonesia

Giant clams are protected marine organisms universally, thus information on giant clams is important for management purposes. This research was conducted in July to August 2021 in Morella and Suli, Ambon Island Maluku Province to get information on ecological potential which consist of species composition, density, occurrence frequency and diversity of giant clams. Sample was collected by using linear quadrat transect line. As many as 25 quadrants (10x10m) were used in both locations. Every individual of giant clams found in the quadrant was identified, photographed and counted. There were three species of giant clams found in Morella namely Tridacna crocea, T. maxima, and T. squamosa while four species were found in Suli i.e. those three species mentions earlier and Hippopus Hippopus. Totally, T. crocea had more individuals followed by T. squamosa and then T. maxima while the lesser belonged to H. Hippopus with one individual. Density of giant clams in Morella (428 ind./ha) was much higher than density of giant clams in Suli (48 ind./ha). Giant clams in Morella can be found in 16 - 19 quadrants of 25 quadrants used while in Suli only found in 1 - 6 quadrants. Ecological indexes for diversity, evenness and dominance showed that giant clams in Morella and Suli had moderate diversity, high evenness and low dominance.

Giant clams are the international trade commodities with high economic value as a food, building and handicraft material.In fact, live clam fry has also become a commodity in the seawater ornamental aquarium trade (2,3).The high sales value and market demand from all over of the world result in exploitation that tends to be excessive (over exploitation) and has led to population decrease of giant clams.
Giant clam are species of biota that are protected nationally and internationally that have been included in the Convention on International Trade in Endangered Species (CITES) appendix II.Except for T. noae which is considered as Data Deficient (8), all giant clams that found in Indonesian waters are in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species [9,10].Similar regulations have been issued by the Indonesian Government through the Decree of the Minister of Forestry No.12/Kpts-II/1987 and Government Regulation No.8/1999 which states that giant clams are protected biota [3].All species of giant clams that have been included in appendix II of CITES since 1983 are protected based on Government Regulation No. 8 /1999 concerning the preservation of plants and wild animals which includes seven species of giant clams that live in Indonesian waters as animals with protected status.Based on this regulation, all forms of use of which are highly exploitative (catching and trading) and currently have not allowed unless they are the result of captive breeding and after being given status as a sport animal [3].
Ambon Island is included in Island Group VII in Maluku Province, Indonesia has potential as a habitat for giant clams.However, scientific information on the ecological aspects of giant clams on Ambon Island is still very limited even though information regarding giant clams which are protected species of mollusc is necessary for the purposes of sustainable management.Therefore, the research on ecological aspects of giant clams which consist of species composition, density, occurrence frequency and diversity was conducted in Morela waters and Suli waters, Ambon Island Maluku Province.

Time and location
This research was carried out from July to August 2021 in Ambon Island at the waters of Morella, Leihitu District and the waters of Suli, Salahutu District, Central Maluku Regency, Maluku Province Indonesia (Figure 1)

Data collection
Sampling of giant clams was done by using line transect method [1]) in which the number of transect used in each location is 5 transects with 25 plots/quadrants (size 10x10m).Every individual of giant clams found in each plot was counted and then photographed for identification purposes.Identification was based on standard reference [12].Interview was carried out to get the information of utilization of giant clams by using key informant.Hydrology parameters (temperature, salinity and pH) were measured in situ.

Data analysis 2.3.1. Density
Density of giant clams was calculated using the following formula [13]: Where: Di : Density of i th species Ni : Number of individual of i th species a : Sampling area

Occurrence frequency
Occurrence frequency of every species of giant clam was determined based on the number of plot/quadrant giant clam was found [13].

Diversity, evenness and dominance
Diversity of giant clam was determined based on Shannon -Wienner (H`) index [14]:

=
Shannon evenness or equality index (J') of giant clams was calculated based on [15]: ′ = ′ ‫ܖܔ‬ Dominance (D) index of giant clams was determined based on [15]: where: ln : Natural logaritm ni : Number of individual of i th species N : total individual of all species S : total number of species

Species composition of giant clams
There were four species of giant clams belong to two genera and one family found during the research.Four species namely Tridacna crocea, T. maxima, T. squamosa and Hippopus Hippopus were found in Suli waters while three species i.e.T. crocea, T. maxima and T. squamosa were found in Morella waters (Table 1).The absence of H. Hippopus in Morella waters could be attributed to the substrate in this location which is predominantly by massive coral while in Suli waters predominant substrate is sand where H. Hippopus was found.Previous studies showed that H. Hippopus only found in the sand substrate [16,17].Species composition and the number of species found in this Ambon Island waters is similar to the giant clams found in Tanjung Bilik, Baluran National Park [17] but lesser than the number of species in Kei Island (5 species) [7] and Kei Kecil waters (6 species) [18].The species absence compared to Kei Island is T. noae while to Kei Kecil are T. derasa and T. gigas.12 individuals).The more individuals of giant clams in Morella compared to Suli because giant clams are protected in Morella but unprotected in Suli.Based on species, T. crocea has more individuals i.e. 40 individuals in Morella or 33.6% of the total giant clams found in both locations while the lesser individual of giant clams belongs to H. hippopus which was only found in Suli with one individual or 0.8% (Figure 2).The highest number of T. crocea was also reported from Kei Island [7], Kei Kecil waters [18] and Anambas Islands [19].Meanwhile, previous studies in Morella showed that T. squamosa has more individuals than other species of giant clams [16,20,21].

Density and occurrence frequency of giant clams
The result in this study shows that density of giant clams in Morella with three species (428 ind./ha) is much higher than those in Suli with four species (48 ind./ha).Based on species, density of giant clams in Morella ranging from 124 ind./ha (T.maxima) to 160 ind./ha (T.crocea) while in Suli density ranging from 4 ind./ha(T.maxima and H. Hippopus) to 24 ind./ha(T.squamosa) (Figure 3).The density of giant clams in Morella is comparable to the previous study in the same location [21] and density of those in Kei Island [7] but higher than giant clams in Kei Kecil [18] and lower than density of giant clams in Anambas [19].Of the 25 quadrants used in each location, the species of giant clams in Morella were found in 16 -19 quadrants while in Suli they were found in 1 -6 quadrants which means that 64 -76% chance to find each species of giant clams in one quadrant in Morella while the possibility in Suli only 4 -24% (Figure 4).Low occurrence frequency of giant clams in Suli could be due to high exploitation of them in this area.Local community in Suli usually exploit marine organisms such as fish, echinoderms (sea urchin and sea cucumber) mollusks including giant clams during low tide or locally called bameti.Based on Government Regulation No.8/1999, some species of giant clams are protected biota [3], however, based on interview with local community it is revealed that there is no socialization of this regulation to local community and there is no monitoring and controlling on utilization of giant clams in Suli.On the contrary, Government Regulation No.8/1999 has been socialized to the local community in Morella, thus exploitation of giant clams during bameti is prohibited.In addition, Morella is well known as marine tourism area and giant clams are one of the iconic attractions in coral reef ecosystem for tourists who like snorkelling and diving.Moderate diversity of giant clams in Morella and Suli is caused by low number of species.High evenness and low dominance means that giant clams communities are in stable condition [23].However, low number individuals of giant clams such as in Suli could affect their sustainability even lead to extinction.Giant clams are synchronized broadcast spawning among conspecific individuals [12], i.e. spawning of some individuals will induce others to spawn.Reducing number of individuals of giant clams could inhibit their reproductive success in nature.

Physical and chemical parameters
Measurement of physical and chemical parameters is showed in Table 2. Data environment parameters as shown in Table 2 are suitable for marine organisms including giant clams.Giant clams can live and grow well at temperature ranging from 25 -30°C, salinity 25 -40 ppt and pH 7 -9 [20].Even though giant clams can tolerate wide range of temperature, but high temperature can cause bleaching [24] and lead to mass mortality [25].Giant clams have some tolerance to a range of

Index value
Morella Suli salinities, thus small change in waters salinity has little impact [26].Low pH is one of the factors responsible for ocean acidification that leads to reduce survival and growth of giant clams [27].

Conclusion
It can be concluded from this study that giant clams in Ambon Islands waters consist of 4 species namely Tridacna crocea, T. maxima, T. squamosa and Hippopus Hippopus.T. crocea has more individuals than other giant clams while the lesser belongs to H. Hippopus.T. crocea also has highest occurrence frequency and the lowest is H. Hippopus.Giant clams community in Ambon Islands waters have moderate diversity, high evenness and low dominance.

Figure 2 .
Figure 2. Relative frequency of giant clams

Figure 4 .
Figure 4. Relative occurrence frequency of giant cla

Tabel 1 .
Species composition and the number of individuals of giant clams

Table 1
also shows the number of individuals of giant clams.The number of individuals of giant clams in Morella (107 individuals) is higher than those in Suli (

Table 2 .
Average physical and chemical parameters