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An assessment of a tropical urban stream using benthic macroinvertebrates as a bio-indicator in Muara Angke, Jakarta, Indonesia

Kelly C, Mitrasetia T, Sugardjito J. 2017. An assessment of a tropical urban stream using benthic macroinvertebrates as a bio-indicator in Muara Angke, Jakarta, Indonesia. Bonorowo Wetlands 1: 65-73. A preliminary study was conducted on the populations, density and distributions of benthic macroinvertebrate species along the course of the Ciliwung/Angke River, Jakarta. The selected river section is highly urbanized and heavily polluted, and five study sites were selected along its course to assess the health of the river ecosystem. Benthic macroinvertebrates are used as a bio-indicator for evaluation of ecosystem health. Their different pollution sensitivities, wide distribution and relatively sedentary lives make them useful candidates for this role. The focal point of the study is the MuaraAngke mangrove forest and wetland, a small remnant wetland at the mouth of the river in Jakarta Metropolitan. A comparison is drawn between the different study sites to assess the health and potential utility of this unique habitat. Despite several intense pressures resulting from the highly urbanized surroundings, and the mangrove's position at the mouth of the river where pollution accumulation would be highest, the data collected from this site showed a macroinvertebrate population dominated by pollution -sensitive taxa, suggesting the mangrove itself continues to provide significant ecosystem services in water -purification.


INTRODUCTION
At the margins of the land, mangrove habitat has long been recognized as a key component of nutrient transfer and species movement across large eco-regions. They have been identified as cornerstone ecosystems, supporting healthy functioning in other habitats through the food web (Mastaller 1997). It has been demonstrated in numerous simulation studies that coastal wetland plants are capable of absorbing excess phosphates, nitrates, and other organic materials, helping to prevent eutrophication of water courses and the asphyxiation of downstream biotic communities (Wong et al. 1997;Chu et al. 1998;Tilley et al. 2002). This is crucial for rivers receiving high levels of organic waste, particularly downstream from large scale agriculture operations which are known to use excessive nitrate and phosphate loading to increase yields. However, the nutrient load entering mangroves is often found to exceed wetland plant growth requirements, and other biological filtering mechanisms are also important factors (Ye et al. 2001).
It is not only sedentary mangrove species which depend on coastal wetlands. Studies have demonstrated a huge number of fish species rely on mangroves to provide nursery habitat for their juveniles (Sasekumar et al. 1992), and many migratory birds visit these rich environments for food and shelter (Giesen et al. 2007). This makes coastal wetlands vital ecosystems in the regional context, and yet the application of this knowledge to coastal development in the Jakarta Metropolitan area is worryingly underdeveloped. In recent years extreme degradations in the marine and coastal habitats of the Jakarta bay have been observed, an ecologically and commercially significant area. Reductions in size and health of coastal wetlands have already begun to undermine a number of key processes outlined above, and precipitated the decline of numerous species which rely on the mangrove. Perhaps most critical for this study is the ongoing reduction in commercial marine stocks. Not only do a number of key fish, shrimp and mollusc species depend on mangrove habitat for at least one part of their life cycle (Burhanuddin 1993), they also depend on nutrients carried downstream from Java's fertile volcanic highlands passing through coastal wetlands (Ligtvoet et al. 1996). A robust coastal wetland has the potential to support several commercial operations for Indonesia's citizens but this potential remains unrealized (Supartono et al. 2016).
This preliminary study investigates the influence of a unique urban wetland on regulating the water quality of a highly degraded urban stream, and terrestrial-marine interactions more generally in one of the world's largest coastal metropolitan areas. Diversity, abundance and community composition of benthic macroinvertebrates relative to wetland proximity was used as an indicator of overall ecosystem health and vigor in the Ciliwung-/Angke river. The ultimate purpose of this study is to appraise the immense value of one of Jakarta's remaining natural habitats in the hope of preserving its critical function in the 66 face of otherwise unmitigated developmental pressures. The focus of this study will be the MuaraAngke wetland, 170 hectares of remnant mangrove and wetlands which once dominated the Jakarta Bay, now serving as the city's last line of defense against coastal flooding and providing a home for a number of rare species (Palupi 2007). The role of coastal wetlands in mitigating Jakarta's Perennial flood crises has been well documented (Aerts et al. 2009;Firdaus 2013), in particular as a vital hydrological sink for the city's many rivers. Despite this, the size of the protected wetland area has continually been reduced from more than 1300 hectares due to population and developmental pressures (Nur et al. 2001).

MATERIALS AND METHODS
The study took place across five main sites along the course of the Ciliwung river, with varying degrees of proximity to the coastal wetland (Figure1). Since we are concerned with the impact of the MuaraAngke Wetland on water quality being discharged into the Jakarta Bay and in the lower reaches of the river, and not with the impact of urbanized spaces on less contaminated upstream flows, the first samples will be collected from sites in densely urbanized areas representing the most significant anthropogenic influences on faunal community abundance and composition. From here, our five study sites will be divided into three groups based on their proximity to the wetland and surrounding land -use types to allow for both inter and intra-group comparisons where relevant.
This study uses sampled measurements of benthic macroinvertebrate community composition and density to indicate water quality and establish the significance of the remaining wetland area's bio-filter effect. This method has been employed in a number of previous studies worldwide (Rosenberg and Resh 1993;Adakole and Annune 2003;Diaz et al. 2013).
Benthic macroinvertebrates make excellent study specimens, being numerically abundant, readily collected and surveyed, comparatively easy to identify and taxonomically rich (Dodson 2001). Most benthic macroinvertebrates, particularly in their larval stages, are also relatively sedentary, unable to easily relocate and displaying any effects of localized environmental conditions (Cairns and Prall 1993). In addition, bio-indication using benthic macro-invertebrates gives a clearer picture of water quality over the course of time, particularly but by no means limited to the life-cycles of identified species, which is reflected in the distribution and diversity of pollution sensitive versus pollution tolerant communities (Warwick 1993).
A total of 435 samples were taken across all study sites over four weeks period June -July 2015. Initially it had been planned to take three samples per day at each site, but this was increased to six to reduce overall study length when little daily variation in results was observed during the first weeks of collecting data. Instead the six daily samples would be taken at a number of different specific locations surrounding each study site in an attempt to capture any spatial variation in benthic species distribution within a given area. Sampling methods involved basic disturbance sampling of river bed substrate and collection using a standard kick net. It is important to note that, due to unstable or otherwise hazardous conditions of river banks, including the build up of extremely soft and deep sediment at the waters' edge, samples were almost universally collected within two meters of the bank with deeper water samples collected where possible. Given the spatial distribution of different species throughout the benthic habitat it is recognized that this may affect the validity of results. Therefore, future studies may wish to employ boats or floating platforms in order to gather samples over a wider area.
The substrate was disturbed for thirty seconds at various points within each study site, with net contents emptied into a sample tray, spread evenly and analyzed on site in the field using a magnifying glass. In order to account for human error in species identification and counting, scrutiny of any given sample was limited to five minutes, or until satisfied that there were no further specimens to identify in that sample. It is also important to note that due to issues with attempting to accurately count large numbers of individuals, counts for a single species were capped at 50 in a given sample. Species were identified as precisely as possible, including taking into account of the specific life stage (i.e, larvae, pupae, adult). For the purposes of analysis the taxonomic group of collected specimens was considered sufficient to draw conclusions from bio-indication given the large number of different groups monitored, and the practical difficulties of precise species identification in the field (Hodkinson and Jackson 2005).

Study areas
The main factor dictating the selection of specific sample sites was ease of access. Large stretches of the river have artificial concrete banks which make access to the river bed extremely difficult, and in the interests of safety these areas were avoided in favor of sites where water access was possible on foot. In order to include a range of different circumstances influencing water quality and species community composition, sites were also selected to incorporate a variety of nearby human activities and land uses. These sites were then grouped together to reflect similarities in habitat conditions as follows: (i) Group 1 -'Highly Urbanized' (sites 1 and 2); (ii) Group 2 -'Transition Areas' (sites 3 and 4); (iii) Group 3 -'Wetland Influenced' (site 5).
A brief description of each group and specific study sites is given below.
Group 1 -Highly Urbanized, representing habitats extremely affected by surrounding urban activities. This group experiences little or no influence from natural ecosystems.
Site 1 is called Roxy. It is located near the center of Jakarta's most densely populated area, is named after the adjacent Roxy Mall, and demonstrates a variety of surrounding urban land use types including major roadways, a large mall parking area, a ground level train route, a relatively small, informal food market and a mixture of established residential neighborhoods and kampung (Informal, low income housing). High volumes of plastic waste are evident on the river banks as well as in the water itself, and this site represents the most extensive influence of various urban activities on the local benthic ecosystem. It is clearly a highly degraded habitat.
Site 2 is called 'Season City,' is also located near a major roadway which passes directly over the watercourse, and is surrounded by a number of different settlement types. The urban density in the immediate vicinity is significantly less than further upstream and the road itself is also considerably smaller. There is reduced land use pressure on the banks of the river at this point, as evidenced by more extensive embankments, and there are several clusters of trees growing adjacent to the watercourse Group 2 -Transition Areas, representing habitats with an increased natural component. Whilst these sites cannot be labelled wetlands in the true sense, they are influenced by significantly more natural areas and may begin to experience a mild bio-filter effect.
Site 3 was named after Jakarta's airport toll road which passes over the study site, responsible for the conversion of previous wetland and the inundation of numerous surrounding areas. At ground level there is almost a total lack of paved or otherwise wholly impermeable surfaces, instead the throughfares are largely dirt tracks connecting small pockets of informal settlement. The river banks themselves are less crowded with refuse than the sites in group 1. We can expect the numerous pockets of largely inundated green spaces surrounding the river at this stage to absorb some surface contamination, initiating a mild bio-filter effect.
Site 4, named 'Pluit,' lies at the upstream edge of the MuaraAngke protected wildlife area. Despite its proximity to the largest intact area of near-pristine wetland its position on the upstream fringe of this area limits the potential for wetland derived improvements to local water quality. Furthermore, Site 4 is under greater pressure from local development projects and associated land use changes than Site 3, is surrounded by a network of fully paved roads and far more extensive human settlement including the neighborhood of MuaraAngke.
Group 3 -Wetland Influenced. These sites are sufficiently proximate to remnant or naturalised areas of wetland that we would expect to see a significant influence of the aforementioned bio-filter effect on the local benthic community. This group is comprised only of site 5.
Site 5 is positioned just beyond the downstream edge of the MuaraAngke Wildlife Protection Area from which it derives its name. While this site is not within the conservation area itself, where the naturalized state of the wetland would doubtless deliver higher biodiversity, it was selected to provide an insight into the downstream bio-filter effect impact on water having passed through the mangrove area. While this group contains only one site, it was also selected because it contains both a naturalized and artificially planted wetland area in close proximity from which samples can be collected.
We have divided the individuals collected into 3 groups representing those species capable of tolerating high levels of pollution (group 3), somewhat pollution tolerant species (group 2) and those species highly sensitive to pollution and degradation of aquatic habitats (group 1), according to a number of field guides and previous studies (Swari et al. 2014;Emere and Nasiru 2008;Azrina et al. 2006). This is to highlight the importance of exactly which species comprise a given ecological community when using bio-indication, in addition to basic abundance and biodiversity analyses. The purpose is to demonstrate visually a difference in community composition in addition to abundance. For the calculations we use the same primary data, and multiply the number of individuals by their pollution weighting to give our weighted abundances.
The Shannon Diversity Index (BDI) was calculated for the samples taken each day at all study sites, following Ogbeibu and Oribhabor's study. 2002). A number of statistical tests such as Kruskal-Wallis and Mann Whitney U test were performed on the data collected from the study to determine the significance of differences between study sites and to prove or disprove the stated hypotheses.

Macroinvertebrate abundance and community composition
The overall macroinvertebrate abundance and community composition are summarized in table 1, with different taxa organized by their sensitivity to pollution. A total of 19 taxa were identified from a total sample of 7168 individuals collected. The number of taxa identified at each site range from just 4 at site 1 (Roxy) to a total of 11 at site 5 (MuaraAngke), with a steady increase from each site further downstream, as anticipated from the increasing influence of more natural environments at each location. From group 3, we can assume a higher local water quality, perhaps attributed in part to the bio-filter effect, even if overall biodiversity of species is found to be equal or lower than other sites dominated by pollution tolerant species.
Site 1 displayed significantly lower species abundance and taxonomic diversity than the other sites (54 individuals, 0.75% of total), whilst recorded species were dominated by segmented worms of the orders Oligochaetaeand Hirudinae, both species known to be extremely tolerant to pollution, abundance remained low throughout the time period of this study. The presence of fly larva (Muscidae), normally less tolerant of pollution, may be explained by the presence of discarded rotting meat and other organic material from nearby human settlements.
Site 2 saw a marked increase in the abundance and diversity of recorded taxa (239 individuals, 3.33% of total). Oligochaetaeremained the most abundant taxa, however a number of similarly pollution tolerant species not present at site 1 including Physidaeand Chironomidae (bloodworm) were recorded in significant numbers, increasing the recorded diversity at this site.
The increase in both species abundance and recorded taxa between sites 1 and 2 is perhaps a result of the larger surrounding earthen embankments, which may absorb some volume of contaminated run-off and provide a more suitable habitat for colonization. Furthermore, an increase in surrounding vegetation provides a greater organic nutrient input, particularly for Physidaewhich are known to graze on decaying leaves (Magee 1993). The lower number of urban pollution sources identified in the immediate area is also likely to result in less degraded habitat. It is worth noting that the presence of a single larva from the family Tipulidaerecorded at this site would appear to be anomalous, perhaps indicating that this individual had been dislodged from further upstream. Nevertheless, its impact on the overall trend in this study is minimal, and as such it has been included in the final data set. Site 3, the first of the identified 'transition sites' demonstrated a significant increase in invertebrate abundance (1624 individuals, 22.66% of total) and a less significant but notable increase in the identified taxa from a total of 7 for Sites 1 and 2 (Group 1) to 9 for Site 3 alone.
A key factor which may explain this incremental increase in diversity is a similar increase in the diversity of available micro-habitats along this stretch of the river, including variations in substrate, light and temperature conditions and flow velocity. This may allow colonization of different points by new species combinations, and indeed significant spatial heterogeneity was recorded for this study site.
There was an increase in abundance for all taxa recorded at upstream study sites excepting Hirudinaeat site 3, and in particular a dramatic increase in the abundance of Oligochaetaeby a factor of more than 7, clearly dominating this habitat. Physidaenumbers also increased, and for the first time Ciroxidaeand Noteridaewere recorded, indicating a significant increase in digestable organic material present. This composition is clearly related to the presence of extensive riparian vegetation as compared sites further upstream, given that each of these taxa is known to consume decaying plant matter (Anderson and Sedell 1979), as well as a build up of organic and chemical pollutants tolerable to segmented worms in particular.
Unlike Site 3, the recorded abundances for many groups actually dropped at study site 4, perhaps attributed to a combination of heavy siltation generating warm, shallow, slow moving water and the accumulation of upstream pollution sources allowing the particularly tolerant Oligochaetaeto out-compete other species for deposited organic nutrients. The two exceptions include Notonectidae, for which the slow moving water likely provides a more suitable hunting ground than upstream river stretches, and the earthworms of Lumbricidae, for which the marshy banks and variable watermark permit the easy transition between riparian and newly flooded habitat.
Site 4 also saw a further increase in abundance (2429 individuals, 33.89% of total), with the Oligochaetaeworms cementing their near total domination of the invertebrate faunal community (over 96% of recorded individuals). The worm population was very dense at this site, and since many samples contained individuals too numerous to accurately count by hand, they were allocated a count of 50+, and total population numbers are certainly under-represented.
As expected, site 5 contributed the largest number of individuals (2822; 39.37% of total), and the greatest number of taxa (57.89% of total). Crucially, the taxonomic composition recorded at this location was dominated, overwhelmingly, by species identified as being sensitive to pollution, and was unique amongst the 5 study sites in this regard. All other sites were dominated by taxa from the 'pollution tolerant' group, as identified below. Particularly important is the almost total absence of Oligochaetaeworms, the dominant taxa at all other study sites, and their replacement as the dominant taxa by Pachychilidae, gilled snails known to be highly sensitive to pollution (Allen et al. 2012). Atydaecomprise the other significant pollution sensitive taxa at this site, and are almost entirely absent from upstream locations. Finally, the presence of predatory larvae, both dragonfly and damselfly from the order Odanata, at site 5 indicate the presence of a more complex food web than was identified at Site 1-4, where the majority of species documented were simply detritus feeders.
Species richness was calculated for each study site using the Shannon-Wiener index, and a significant increase was recorded for each site (27, 90.3, 541.3, 768.1, 850.9 respectively). The recorded individuals are listed by species in table 1, visualised further in figure 2.

Benthic macroinvertebrate abundance
An initial Kruskal-Wallis H test demonstrated a clear statistically significant difference in the abundances of macroinvertebrates recorded at the different study sites (x2 (4) = 114.138, p<0.001). The mean rank scores for abundance for study sites 1-5 were 15.19, 44.41, 93.71, 115.66 and 96.03 respectively. In order to detect the differences in abundances recorded between pairs of study sites we applied Mann-Whitney U test. The results show a significant difference for all comparisons (p<0.001) except 3: 5 and 4: 5, where high counts of segmented worms at sites 3 and 4 approached the total individual count at site 5.  Table 1. List of individuals family taxa recorded at study site (in Muara Angke, Jakarta, Indonesia) arranged in accordance to pollution sensitivity These results, although clearly demonstrating a significant difference between the abundances recorded at upstream sites with the least influence by the wetland and those sites further downstream, the mean rank abundances recorded at sites 3 and 4 were higher than at site 5. Although these results were not found to be statistically significant, the similarities in higher abundances recorded at the 3 furthest downstream sites compared to those upstream suggests that wetland proximity and the presence of river-adjacent green spaces positively influences benthic biotic activity.

Weighted abundances by pollution grouping
As previously stated, in order to contextualize subsequent biodiversity analyses it is important to consider the different pollution sensitivities of recorded species. It is clear that a dramatic change in community composition favoring species sensitive to water-borne pollution was recorded at site 5,which is particularly influenced by the surrounding MuaraAngke wetland. A subsequent analysis will now be conducted to determine the statistical significance of this change. The weighted abundances show an exaggerated increase in species count at site 5 when compared with the abundances recorded in figure 3, which was expected given the dominance of pollution sensitive species in that area. These test results display a greater, more significant difference between each of the study sites (p<0.001 for all comparisons), and, crucially, exaggerate the differences between sites 3, 4 and 5 because of the different weightings assigned to the species found there. This is important for the purposes of this study because pollution sensitive species are more significant indicators of ecosystem health, and the distortion of our initial findings when pollution weightings are applied has increased our weighted abundances by a greater factor at each successive downstream study site when compared to the results before pollution sensitivity is accounted for.

Species diversity
As outlined in our preliminary analysis, the recorded species richness increased with each site in proximity to the MuaraAngke wetland, but due to the domination of certain taxonomic groups a subsequent biodiversity analysis will be conducted to give a more accurate picture of the relationship between wetland proximity and biotic diversity at each site. Initial Kruskal-Wallis H test analysis demonstrated a clearly significant difference in Shannon Biodiversity Index rating between the 5 study sites: x2 (4) = 31.04, p<0.001, with mean ranks of 58.03, 87.67, 61.02, 54.50 and 103.78 for sites 1-5, respectively.
To determine the significant differences between individual study sites and to enable a direct comparison, a Mann-Whitney U test was performed on the Shannon BDI results for paired site results. The results indicate the most significant differences in biodiversity can be found when comparing site 3 and 4 to study site 5, with lower counts of fewer species accountable for the statistical insignificance recorded between upstream sites.
The results of the BDI comparison support a number of points. First of all, the near -total dominance of aquatic worms from the Oligochaetaetaxa amongst the collected individuals, particularly at sites 3 and 4, has resulted in a lower BDI rating at these sites despite the higher number of total species recorded there when compared with site 2, for example. Similarly, the domination of recorded individuals at site 5 by the Pachychilidae gilled snails may explain the lack of significant difference in biodiversity between site 5 and site 2, where the domination by a single species, although present, was far less dramatic.

Biodiversity by site group
The five study sites from which samples were collected were placed in 3 groups to reflect similarities in local conditions, wetland proximity and other factors identified as affecting benthic faunal composition. No significant difference was calculated for the BDI between study site group 1 and study site group 2 (U=1477, p=0.254), consistent with the observation of low taxonomic diversity across all sites in the watercourse areas upstream of the wetland, where little variation in species was also recorded. The differences in diversity between study site group 1 and the heavily wetland influenced site in group 3 were more significant (mean ranks: 4.32, 51.36 respectively; U=627.5, p=0.05), and between group 2 and group 3 the divergence even more significant (mean ranks: 31.36, 65.48 respectively; U=160, p<0.001).

Species and pollution in the Ciliwung River
Although the biodiversity analysis results do not fully support the hypothesis that proximity to the wetland correlates with a significantly higher biodiversity rating, they are nonetheless useful for drawing several important conclusions. Namely, it is important to note that the biodiversity ratings at site 5 were consistently higher than at other sites, and significantly higher than at sites 3 and 4, which rank second and third in our study for species richness and specimen abundance and share a similar dominance in recorded specimens by a single taxon. Secondly, this significant difference in BDI rating between sites 3 and 4 (group 2) and site 5 (group 3) was recorded despite only a single additional taxa being recorded at site 5, indicating that the benthic macroinvertebrate community itself is more diverse, and thus in better ecological health (Schläpfer et al. 1999).
What, then, does this specific composition of invertebrate species, and their abundances, reveal about the water quality of the Ciliwungriver system throughout its lower, urbanized reaches, and, importantly, about the role of the MuaraAngke Wetland therein? Firstly, it is clear that dividing the study sites into groups as stated in the methodology accurately reflects a degree of physical, chemical and faunal variation between these groups. The low abundance and diversity recorded at highly urbanized sites clearly indicates the negative impact of numerous urban pollution sources, as well as upstream contributors, on overall ecosystem health and functioning. It is important to note that dramatic differences in the size of individuals were also noted, with upstream study sites in group 1 displaying a tendency towards far smaller individuals of the same species than in group 2. This is likely related to the significant increase in riparian vegetation surrounding these sites, providing edible material for detrital feeders and potentially compensating somewhat for the accumulation of pollutants from upstream in supporting a food web based on periphytic algae (Sharma and Rawat 2009). Although this data was not recorded, adequate facilities and time being unavailable, it was nonetheless significant and should be taken into account when planning subsequent studies.
While differences between group 1 and group 2 study sites were significant, the radical changes in both composition and abundance at study site 5 compared to the other four study sites emphasize the strong influence exerted by the MuaraAngke Wetland system on polluted water, as expected from the results of previous studies included in the literature. Despite variations in specific composition, invertebrate communities at each of sites 1-4 were dominated by Oligochaetae, a taxon widely known to be particularly tolerant of high levels of pollution, both organic and anthropogenic, and low oxygen or anoxic stream conditions (Lin and Yo 2008;Azrina et al. 2006). Other groups common at these sites were also found in the 'pollution tolerant' grouping, including Chironomidae, Physidaeand both Ciroxidaeand Notonecidaefamilies of water boatman. Of the other taxa recorded at these sites the vast majority fell into this grouping, with a small number of moderately tolerant taxa also recorded. Many of these species are capable of surviving in stream conditions with very little oxygen, either because they are able to gather this from the surface or possess other physiological adaptations, suggesting a low dissolved oxygen content in the stream water. This may be a result primarily of organic pollution precipitating algal blooms, however the neartotal dominance of Oligochaetae, especially tolerant to various stressors even amongst this grouping, suggest that high levels of inorganic contamination were also present. It is important to note that upstream sites recorded almost no species from the 'pollution sensitive' grouping 3, with the sole exception of a single Atydaeshrimp at site 3, which would appear on all counts to be an anomalous result.

Biofiltration in and around the MuaraAngke Wetland
Site 5, identified in the study methodology as being heavily influenced by the ecology of the remnant MuaraAngke Wetland, possessed a very different taxonomic composition. As is clearly evidenced from even a brief overview of the data presented in Table 1, and is further visualized in figure 1, this study site was dominated almost entirely by taxonomic groups identified as being highly sensitive to pollution related stressors in surrounding water. Further analysis of the taxa recorded indicates that this is not simply a result of variations in habitat conditions. Gilled snails (both Pachychilidaeand Ampullariidae) identified previously as the dominant group at this site, unlike their cousins the Pouch Snails, breathe using an aquatic gill system, and depend on high levels of oxygen in the surrounding water, thus making them highly sensitive to both organic and inorganic contaminants (Voshel 2002). Individuals from at least two distinct species were identified at various points around study site 5, suggesting a number of different ecological niches are available for this pollution sensitive group of creatures, and decreases the likelihood that their abundance can be explained simply by an unusual surplus of a particular food source, for example. Similarly, the presence of crustacean taxa Atydaeand Parathelphusidae, both dependant on gill systems to breathe, indicates an improved water quality given the sensitivities of these species to pollutants, suspended particulates and oxygen (Harmon 2008).
Despite not being recorded in our dataset, as mentioned previously, it is important to note that each of these taxa at site 5 displayed considerable variations in size, and, by extension, age, with both the largest and some of the smallest individuals collected from any study site being identified within the same species. This was most pronounced amongst the Ampullariidaetaxon of gilled snails, but also amongst Atydaeand the other recorded Mesogastropoda. This clearly indicates a wide range of ages amongst individuals, and would suggest that significant pollution levels are not accumulating over time within their bodies, allowing them to reach greater ages than taxa at upstream sites, which are unlikely to survive in highly polluted conditions for as long (Mason 2002). Similarly, identifying predatory species from the taxa Odanatae, and even the more tolerant Nepidaegroup, gives a good indication that pollution from the surrounding water is not accumulating in sufficient concentrations in the bodies of prey species to be harmful. The increasing concentration of inorganic pollutants through higher levels of the food web has been well documented in a variety of aquatic and terrestrial environments (Farag et al 1998;Hsu et al. 2007), and such the presence of a more complex food web at this study site can be taken as clear evidence of improved ecosystem health and function.
Finally, it is worth noting that, although the same number of different taxa were identified within the natural wetland area and the adjacent constructed wetland, the abundances of those species were significantly higher at points where the water had also passed through the planted mangroves of the artificial wetland area. This suggests that a combination of natural and constructed wetlands may well offer the maximum potential for improving water quality, and thereby ecosystem functioning. Having established the positive influence of the MuaraAngke wetland on even the most degraded urban watercourses, follow up studies should be undertaken to establish the optimal system for wetland-based bio-filtration in this area using a combination of natural and managed or constructed wetland infrastructures.
To summarize, a number of important conclusions can be drawn from the results discussed above. First of all, despite the methodological limitations of this study, it is clear that the presence of wetland areas has a significant positive impact on the quality of water in the Ciliwung/Angke watershed, even after significant reductions in wetland area, and the significant degradation of river water from upstream activities and the urban habitat. All indicators identified in the study methodologies (diversity, abundance, size of individuals and pollution sensitivity) were found to support that the MuaraAngke wetland area continues to act as a biological filter for the surrounding megacity. It is therefore crucial that existing measures intended to ensure protection for the wetland be reinforced, and extended where possible, to ensure significant ecosystems services to the surrounding area and further afield are not lost. Whilst quantifying the reach and extent of these benefits is beyond the scope of this preliminary research, it is likely to include significant improvements to local soil and water quality, as well as benefits for the health of the Jakarta Bay ecosystem, and regulating the interaction between Jakarta's urban, terrestrial and marine environments more generally. Interestingly, and perhaps unexpectedly, the results recorded at Sites 3 and 4 suggest that the far less extensive green spaces in these areas may already be delivering some measure of ecosystems services to the Ciliwung river, at the very least increasing the input of biological materials.

ACKNOWLEDGEMENTS
The first author wishes to thank Dr. Robert Francis, project supervisor, whose insight and support was invaluable in undertaking a relatively risky research project in an unknown area, and whose guidance in transforming raw data into presentable statistics was particularly key in the realization of this research. We appreciate Cendriko Dimas Putra from Faculty of Biology, Universitas Nasional, Jakarta and the Jakarta Green Monster, who spent endless hours to arrange documents in government institutions, facilitating field work in an incredibly complex urban environment and to help us collect samples. RUJAK center for Urban Studies, Jakarta, whose ongoing support for all projects pertaining to the transformation of Jakarta into a sustainable metropolis remains one of the city's greatest hopes, and whose generosity in allowing the use of their office space and data was invaluable during this time. We acknowledge the government of the Republic of Indonesia, without which this research would not have been possible, particularly the Ministry of Environment and Forestry; Ministry of Research, Technology, and Higher Education, Government of Indonesia.