Abstract. Hilmi E, Sari LK, Cahyo TN, Dewi R, Winanto T. 2022. The structure communities of gastropods in the permanently inundated mangrove forest on the north coast of Jakarta, Indonesia. Biodiversitas 23: 2699-2710. The permanently inundated mangrove ecosystem support gastropods communities to live and grow. The gastropods communities require a mangrove ecosystem for feeding, spawning, nursing, distributing, and breading. The distribution of gastropod communities is shown by the number, association, and clustering of gastropods and is influenced by the potential of permanent water inundation. This research used association, clustering, and correlation methods to describe the distribution of gastropod communities. The results of this research showed that the mangrove ecosystem on the north coast of Jakarta was dominated by Avicennia marina, Bruguiera gymnorrhiza, Calophyllum inophyllum, Cerbera manghas, Excoecaria agallocha, Nypa fruticans, Rhizophora apiculata, Rhizophora mucronata, Rhizophora stylosa, Sonneratia caseolaris, Terminalia catappa, and Thespesia populnea with density between 20-2800 trees/ha. However, the gastropods communities in the mangrove ecosystem were dominated by Cassidula angulifera, Cassidula aurisfelis, Cassidula plecotrematoides, Cassidula rugata, Ellobium aurisjudae, Ellobium gangeticum, Pythia plicata, Cerithidea obtusa, Cerithidea quoyii, and Melanoidessarius tuberculata with abundance between 0.36 to 6.68 ind/m2, 12 pairs positive association from 78 pairs, had uniform distribution (Moroshita index 0-0.87), and two clusters.

Segara Anakan Lagoon (SAL), located along side of soutern coast on western part of Central Java 108°46'–109 ° 05'E; 7 ° 34'–7 ° 48'S. SAL is necessasrily ecosistem as nursery ground. This has been becoming important research relating to primary productivity. The existance of antropogenical activities around the area, is changing inrush input into lagoon. This is going to be worried about giving influences in physical, chemistry, and biological factors of the water and causing deflation in rate value of primer productivity. Rainy and dry season's variability with important impacts on the phytoplankton community structure, abundance and dynamics. Furthermore, the number of coastal ecosystems with identified eutrophication symptoms is increasing worldwide due to the increasing anthropogenic pressures. One of 1the first symptoms of eutrophication is enhanced phytoplankton biomass. Generally, Fitoplanton is important biological indicators in the process. However, high abundance of biomass phytoplankton could give harmful effect toward lagoon, they could produce toxic substances that will be accumulated, it can be endangering .The aim of the research is to determine and calculate potential species of Harmful Algal Blooms (HABs) in SAL with spastial and temporal approach. The spatial approach is done at seven different stations of ecological characteristics SAL, with representations: natural factors and the presence of anthropogenic activities. On the temporal approach (time series) for a year, it refers to the monsoon wind pattern, which are called season (western, the transitional season 1, eastern, and the transitional season 2).The results of laboratory tests are discussed descriptively. Phytoplankton sample were taken vertically using plankton nets, meshsize 25 μm. The result showed that SAL have been found and consisted of 82 species from 5 division phytoplankton: Chrysophyta, Chlorophyta, Cyanophyta, Pyrophyta, and Euglenophyta. 20 species from 9 genus were identified potential as HABs, with four genus of them were known having toxin and endangering for human (Nitzschia, Oscillatoria, Anabaena dan Protoperidinium).Whether, five genus do not produce toxins but giving deflation Oxygen of waters with anoxia condition (Chaetoceros, Coscinodiscus, Rhizosolenia, Thalassiosira, Thalassiotrix).The highest of HABS abundance is dominated during the transitional season II. On the spatial approach, antropoegenic characteristics station contribute to the whole height of HABs. Influence of rainfall, spatially, antropogenical pressure, and hydrodinamical watres causing enhancement of HABs potency.

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