AMPHIPOD DISTRIBUTION IN THE SOFT-BOTTOM SUBTIDAL ZONES OF JAVA ISLAND IN RELATION TO SEDIMENT TYPES

Amphipods inhabit many marine benthic habitats and have an important ecological role. However, there is a lack of information about Indonesian amphipod diversity and distribution, especially in the shallow subtidal sediments of Probolinggo and Tangerang. During the transition to the monsoon season in September 2014, eight subtidal stations were sampled in Bayeman (Probolinggo) on East Java and seven subtidal stations were sampled in Kramat Kebo (Tangerang) in West Java. A total of 7346 amphipods individuals were collected, comprising five genera. Genus Photis was the most abundant group, followed by Grandidierella and Synchelidium. Multivariate analyses of these data indicated that sampling location and sediment granulometry were major determinants of distribution and composition of amphipods in Probolinggo and Tangerang.


INTRODUCTION
Some studies have reported on the global patterns of the macrobenthic communities (Rodil et al., 2006), but globally, only a small portion of marine habitats have been sampled for macrofauna including amphipods (Snelgrove, 1998).To date, Lowry (2013) stated that more than 10,000 amphipod species have been described.Amphipods (Peracarida, Crustacea) represent one of the most diverse taxa of Crustacea (Marques & Bellan-Santini, 1990) and are among the most diverse and numerically dominant organisms of soft-bottom benthic faunas (Prato & Biandiolino, 2005).Amphipods play an important role in the structuring of benthic assemblages (Duffy & Hay, 2000).Amphipods also function as an important source of food for other benthic animals and important commercial fishes (Beare & Moore, 1996).The distribution and abundance of amphipods inhabiting marine sediments are influenced by a number of abiotic factors, such as waves, primary productivity (Snelgrove & Butman, 1994), sediment composition (De Grave, 1999), sediment type and depth (Hoey et. al., 2004).
Probolinggo and Tangerang are special and complex estuarine systems, comprised of varied sedimentary habitats and inhabited by rich benthic fauna.Both areas also hold great economic and social importance.Amphipod fauna of the Probolinggo and Tangerang are little known, and few studies have been done to describe the diversity, distribution and composition of amphipods there.Thus, the main objectives of this paper were : (1) to characterize the composition and distribution of the amphipods fauna in  the sub tidal soft-bottom ecosystems of Probolinggo and Tangerang; and (2) to study the influence of sediment types on the distribution patterns of amphipods.This study will not only provide baseline data and update existing information on benthic amphipods, but also increase our knowledge on the biodiversity of Indonesian amphipods.

Study Area
The study area comprised two locations, namely Probolinggo and Tangerang.Samples were collected in eight stations in Probolinggo (coded Amp 1 to Amp 8), and seven stations (coded Amp 9 to Amp 15) in the Tangerang region (Fig. 1).

Sample Collection and Processing
Quantitative sampling was carried out during September 2014 at Bayeman in Probolinggo and Kramat Kebo in Tangerang by using a Smith McIntyre grab with a sampling area of 0.25 m 2 per grab.Three replicates were taken at each station, over a total area of 0.75 m 2 .These samples were sieved through a 0.5 mm sieve, and the fauna was preserved in 10% neutral buffered formalin (i.e.3.7%-4.0%formaldehyde in phosphate buffered saline), containing a Rose Bengal solution as a staining agent to facilitate sortation and identification of the fauna later at the laboratory.Amphipods were sorted under a binocular microscope (NIKON, SMZ 1500), then preserved in 70% ethanol, and then identified to genus level and counted.The system of classification proposed by Bellan-Santini et al. (1998) was followed in the identification process.An additional sediment sample was taken by using a Smith McIntyre grab at each station for determining granulometric composition.Sediment characteristics were analysed and grouped following Wentworth (1922).
The structure of the amphipod community was investigated using multivariate techniques provided by PRIMER software v5 (Clarke & Warwick, 2001).The Bray-Curtis coefficient is more accurate compared to others (Bloom, 1981) and was hence used to calculate the resemblance matrix.The log (X+1) transformation was applied to the raw data prior to analysis in order to minimise the contribution of the most abundant species (Ysebaert et al., 2002).
From the resemblance matrix, classification and ordination of sampling stations were performed.The classification of sampling stations was performed by cluster analysis based on the Unweighted Pair-Group Method using Arithmethic Averages (UPGMA), while the ordination was calculated based on Non-metric Multi-Dimensional Scaling (nMDS).
In addition, One-way Analysis of Similarities (ANOSIM) was applied for location, grain type and salinity factors.On ANOSIM, sampling stations were grouped into two locations, namely Tangerang (T) and Probolinggo (P), while for the salinity factor, sampling stations were assembled to Saline (S) if the salinity was bigger than 30 psu, and Brackish (B) if the salinity was equal or less than 30 psu.The grain factor represented sediment characteristics, sampling stations were convened to two groups, the first was the Silt-clay (SC) group if the the sediment had more than 70% Silt-clay, and the second was Sand (S) group if the sediment contained less than 70% Silt-clay.

Sediments
Sediments were dominated mainly by silt clay in most stations from the Probolinggo region, and sand was dominant in most of the Tangerang sampling stations (Table 1 & Table 2).

Multivariate Analysis
Cluster analysis was carried out by applying the Bray Curtis Similarity Index with group average.The analysis showed at least three major clusters, namely group I, II and III (Fig. 2).
Group I contained all stations from Kramat Kebo-Tangereang with 60.37% similarity, while the stations on group II mostly comprised samples sites from the Bayemen-Probolinggo region with 46.35% similarity, however two stations in the Probolinggo region, namely Amp 1 and Amp 5 belonged to Group III and had 66.84% similarity.
The nMDS ordination showed similar results with cluster analysis (Fig. 3).The ANOSIM test of amphipod abundance based on factors: grain size and sampling location, showed significant differences (p < 0.01).ANOSIM on the location factor resulted in higher global R than the grain factor, where the values were 0.763 and 0.506 for location and grain size respectively (Fig. 3).However, ANOSIM on the salinity factor did not show significant different between the Saline and Brackish water group (p > 0.05, data not shown).

Distribution of amphipods in relation to sediment type
Significant relationships between the density/diversity of amphipods and sediment types were detected.Based on the average value of the Shanon-Wiener diversity index, the Probolinggo region had higher diversity than the Tangerang region.This condition was concordant to what had been previously reported for the Portuguese coast (Marques and Bellan-Santini, 1990).
These results can be attributed to higher organic matter in silt clay sediments (Carvalho et al., 2006;Sousa et al., 2007), which is an important food resource for benthic communities (Rodríguez-Graña et al., 2008).Furthermore, the finer sediments also reflect low levels of physical disturbance (Nicholls et al., 1998).Therefore, both food availability and reduced disturbance may allow for the existence of an abundant amphipod community.
Conversely, our findings on amphipod fauna in the Tangerang region showed higher density despite a predominantly sandy sediment type.This finding related to the domination of Photis spp.(7231 individuals) compared to five individuals for other genera (Melita and Synchelidium).Photis domination at Tangerang region could be attributed to the high amount of decaying algae that was available on this subtidal substrate.The fact that most Photidae species prefer to live in tubes constructed using sand or organisms, such as macroalgae, explained this finding (Souza-Filho & Serejo, 2010;Myers & Lowry, 2003).In addition, high density Photis spp. in sandy bottoms was also reported in the southern Portugese coast (Carvalho et al., 2012).
To our knowledge, this is the first description of amphipod communities of Bayeman (Probolinggo) and Kramat Kebo (Tangerang).This is particularly important since these two locations have similar substrata characteristics as Segara Anakan Lagoon (Cilacap) where benthic organisms became important living natural resources, and hence had economical potential for its local population (Nordhaus et al., 2009).Besides fishing, dredging, eutrophication and aquaculture are known to threaten these highly diverse habitats (Hall-Spencer et al., 2006).There have been no previous publications regarding the amphipod communities associated with the sediment type in these locations, thus we could not compare our data findings with previous data.However Sanders (1969) stated that there have been several attempts to examine diversity in different habitats and, in general, estuaries tend to have relatively low diversity and tropical environments are thought to be generally species rich.It has also been suggested that higher biological diversity maybe associated with higher sediment grain diversity (Etter & Grassle, 1992).Thus, it is reasonable to expect that the habitat for sedimentary fauna is defined largely by the surface sediment (Grange, 1977) and sediment grain size (Connell, 1978).Gray (1968) also found low species diversity in areas with high current action and coarse sediments, where the sediment was too loose and unstable for construction of permanent burrows.Furthermore, habitat diversity tends to promote biological diversity as well (Connell, 1978).

Ecological patterns of dominant taxa:
Photis spp.
In the present study, the most abundant genus (Photis spp.) accounted for 98.7% of the total density.There is a variety of Photis spp.found in oceans all around the world (Barnard, 1962) from cold to tropical waters.They usually inhabit shallow waters less than 200 m in depth (Barnard & Karaman 1991).The dominance of Photis spp.might be biased due to genus level identification employed in this study.However, according to McKinney (1980) the dominance of Photids was common in softbottom communities.Myers & Lowry (2003) said that most species of Photidae live in tubes constructed using sand, mud or organisms such as macroalgae, coral rubble and sponges.Some of them also inhabit mollusc shells, and Snelgrove (1998) suggested that they have a key role as food for many secondary consumers.

Biogeographic notes of Major Genus:
Photis spp.
Regional biogeographical syntheses of amphipods have been assembled for different areas of the world, but global syntheses are hindered by several problems.Firstly, the huge areas of the oceans necessitate very limited and uneven coverage, and most areas are poorly sampled.Secondly, another problem is the lack amount of funds and expertise needed to process available samples.Thirdly, some species that had been previously assumed to be cosmopolitan were in fact species complexes (Snelgrove, 1998).
Despite a lack of species-by-species syntheses over broad scales, several generalizations can be made about amphipod distribution.Amphipods are often expected to have an endemic tendency due to their limited dispersal capacity, resulting both from the direct development and from reduced swimming capacity (Marques and Bellan-Santini, 1990).There were only two records on the genus Photis from Indonesian waters.Pirlot (1938) reported Photis spp.from Dongala, Celebes and Photis dolichommata from Siboga.The latest finding on Indonesian photis were Photis cavimana and Photis longicaudata at Bunaken, 18 years ago by Ortiz & Lalana (1997).After those findings, there are no recent publications/information/reports on this genus from Indonesian waters.

CONCLUSION
There were 7346 amphipods individuals comprising five genera found at Bayeman (Probolinggo) and Kramat Kebo (Tangerang), collected during the transition to the monsoon in September 2014.Overall, this study revealed that their distribution was affected by grain size and sampling location.
The methods of linking community patterns to environmental variables used in this study were developed mainly to assess the effects of pollution on benthic community structure.In the present context, it was shown that these methods are useful in showing the importance of environmental factors in regulating community structures.

Fig 2 .
Fig 2. Amphipods in Probolinggo and Tangerang as determined by cluster analysis based on Bray-Curtis similarity coefficient