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1.
A number of studies have suggested that mangrove forests and their faunal components may be pre-adapted to the impact of organic waste discharge, making them possible natural wastewater treatment wetlands. However, the results from recent research are contradictory. Some studies have shown that negative effects, sometimes subtle and difficult to observe, can be detected on specific biotic components of forests subjected to organic pollution. Therefore, the aim of the present study was to investigate possible alterations in the ecosystem engineering activities of a fiddler crab community dominating the landward belts of Kenyan mangrove forests. The total processed sediment produced by burrowing and foraging activities in a population from a peri-urban mangrove area receiving untreated domestic sewage was compared with that from a forest not affected by urban wastewater. The results showed how the peri-urban site hosted a higher biomass of crabs, which produced a significantly lower amount of processed sediment compared with the pristine site, resulting in a lower total top sediment mixing activity of the crabs. Thus, the present study showed a link between sewage exposure and top sediment reworking by crabs, which is potentially beneficial for mangrove growth and ecosystem functioning. This represents a possible example of cryptic ecological degradation in mangal systems.  相似文献   

2.
Mangrove ecosystems are sites with high biodiversity of benthic fauna, and fiddler crabs (genus Uca) are common benthic fauna in mangroves. The North Sulawesi in Indonesia has a good condition of mangrove while the information of the fiddler crabs is still limited. Manual samplings were conducted in wet, dry and transient seasons at a mangrove in Kema, North Sulawesi to investigate the species composition, density and distribution pattern of fiddler crabs. A total of 168 individuals, subjected to eight species of genus Uca crabs were collected at the mangrove, with U. triangularis having the highest abundance and U. annulipes having the lowest abundance. The densities of fiddle crabs were 27.56 ind./m2, 32.89 ind./m2 and 14.22 ind./m2 at the seaward, middle and landward zones, respectively, and the density was higher in dry and wet seasons than in transient season.  相似文献   

3.
Constructed wetlands, especially mangroves, have been studied for their usefulness in sewage treatment but the effects of mangrove vegetation and a sewage load on mangrove macrofauna have been given little attention. Ocypodid crabs are important components of mangrove forests and constitute good bioindicators of the functioning of the ecosystem as a whole. In constructed mangrove mesocosms, three vegetation treatments (bare substratum, and Avicennia marina and Rhizophora mucronata seedlings) were subjected to 0, 20, 60 and 100% sewage loads from a nearby hotel. The physiological condition of introduced Uca annulipes and Uca inversa was evaluated in terms of their RNA/DNA ratio after one, five and twelve months, and used as an indicator of ecological function in the system. Crab condition in 0% sewage load was similar to that of wild crabs throughout, suggesting no significant effects of the mesocosms on their RNA/DNA ratio. Overall, both species coped well with the administered sewage loads, suggesting good ecological function in the system. Both species manifested similar patterns in RNA/DNA ratio, being more affected by seasonal fluctuations than by sewage load and vegetation presence and type. Higher RNA/DNA ratios were recorded in the long compared to the short rainy season. Sewage enhanced crab condition in the bare substratum and R. mucronata treatments, especially after one year, probably as a result of enhanced food availability. Uca inversa may be more sensitive to sewage pollution than U. annulipes. In A. marina, no difference in crab condition was observed between sewage loads, and this mangrove yielded the best reduction in sewage impacts. Our results support the usefulness of constructed mangrove areas in sewage treatment, especially if planted with A. marina and inhabited by physiologically healthy ocypodid crabs to enhance the system's performance.  相似文献   

4.
The abundance and distribution of mud crabs were studied in a replanted mangrove forest in Buswang, Aklan, Philippines. Two fishing gears, lift nets and bamboo traps, were used to monitor relative abundance of Scylla spp. populations from March 2002 to December 2003 inside the mangrove forest. A third gear, a stakenet set across a creek, was used to monitor crabs migrating out of the mangroves during the ebb tide. Scylla olivacea formed 99.3% and 70.3% of the catch in the mangrove and the stakenet, respectively. The percentage of Scylla tranquebarica increased from <1% in the mangrove catches to 29% in the stakenet. Scylla serrata was present at very low levels in both catches. The lack of modal progression in the size–frequency plots and the year-round catch rate of gravid females suggested that recruitment was constant throughout the year. Even though relative abundance decreased over the study period indicating that the stock is being over-exploited, mud crab production is more than equivalent to that of most natural mangroves.  相似文献   

5.
The fish communities of mangrove and cleared sites were investigated in Gazi Bay, Kenya. Five forested sites were compared with paired sites that had been cleared of mangroves by human activity. Forested sites included plantations and natural stands of Sonneratia alba and natural Rhizophora mucronata stands. Two methods of stake netting were used to take quantitative samples; method one used a single 100-m-long, 18-mm mesh net, method two used paired 24-m-long, 1-mm mesh nets—samples were taken during seven different months in 2002. Mean abundances of fish found in mangrove and cleared sites, respectively, were 0.004 m−2 and 0.014 m−2 (method 1) and 0.21 m−2 and 0.25 m−2 (method 2). Thirty species were sampled, 12 of which were found exclusively in mangrove habitats and 10 of which were limited to cleared sites. The most abundant species in mangrove plots was Atherina afra (although it was only found in two, large catches); the most abundant in cleared plots was Gerres oyena (found frequently). Mean abundance (using data pooled for all sites) was significantly higher in cleared, compared with forested, sites, and multivariate analysis showed significantly different community structures in the two habitat types. There was large variation in catch rates between dates and sites, with one forested site recording no catches at all. These results do not support the predator refuge hypothesis (which predicts higher abundance of juvenile fish inside mangroves). The low abundance of fish recorded in the mangrove sites may have been due to site-specific factors determining fish abundance within mangrove forests, to the sampling techniques used or to relatively high turbidities at these sites.  相似文献   

6.
The study aims to compare the differences of macrofauna communities of wetlands at 3-year-forest- age, 5-year-forest-age Sonneratia apetala artificial mangroves, 5-year-forest-age Kandelia candel ar- tificial mangroves with the same restoration background, and the naked tidal flat in the Qi’ao Island Mangrove Nature Reserve of Zhuhai, Guangdong Province. The results show that there were signif- icant structural differences in macrofauna communities among four kinds of habitats. The increase of biomass and species diversity of macrofauna at 3-year-forest-age S. apetala artificial mangroves was obviously faster than that at 5-year-forest-age K. candel artificial mangroves whose average tree height was close to that of 3-year-forest-age S. apetala artificial mangroves. The BIOENV analysis shows that it was related to the rapid growth of S. apetala, which rapidly changed the light level and shading conditions in the forests. The 5-year-forest-age S. apetala artificial mangroves had lower macrofauna species diversity but higher density and biomass than K. candel artificial mangroves with the same forest age. This was due to the rapid changes of physical and chemical properties of habitat soil by the ecological restoration of S. apetala artificial mangroves as well as the changed food sources possibly caused by the leaf-litter of such non-indigenous mangrove species S. apetala. However, further survey should be conducted on whether there are any negative ecological impacts of large-scale cultivation of S. apetala on macrofauna communities, so as to evaluate correctly S. apetala’s role in the restoration of coastal mangrove ecosystems.  相似文献   

7.
The gastropod Terebralia palustris often dominates the surface of muddy to sandy substrates of intertidal mudflats and mangrove forests, where they clearly destabilize the sediment. In the present study, it was investigated whether and to what extent the behaviour of juvenile and adult snails differs among habitats (mudflat vs. mangrove stand) in a Sonneratia alba mangal at Gazi Bay, Kenya. For this purpose we: (1) examined their distribution along three land–sea transects; and (2) applied stable isotope analysis to determine the feeding patterns of different-sized snails from the mangrove and mudflat habitats. Additionally, we investigated if these gastropods exert an impact on microphytobenthic (diatom) biomass, and whether this is size-dependent. The latter objective was met by either enclosing or excluding different-sized snails from experimental cages on the intertidal mudflat and the subsequent assessment of a change in pigment concentration of the sediment surface. In agreement with several previous studies conducted in other mangroves and geographical locations, a spatial segregation was demonstrated between juveniles (more common on the mudflat) and adults (more common in the mangrove forest). On the intertidal mudflat juveniles avoided sediment patches characterized by highly saline water in intertidal pools and a high mud content, while adults tended to dwell on substrates covered by a high amount of leaf litter. Stable carbon isotope analysis of the foot tissue of snails sampled from the S. alba stand and the mudflat indicated a transition in food source when a shell length of 51 mm is reached. Considering the δ13C value of juveniles, it seems they might be selecting for microphytobenthos, which might explain their preference for the mudflat. The diet of size classes found in both habitats did not differ significantly, although juveniles inhabiting the mangrove forest were slightly more depleted in 13C compared to those residing on the mudflat. Assuming juveniles feed on benthic microalgae and considering the lower microalgal biomass inside the mangrove forest, this may be a consequence of a higher contribution of other, more 13C depleted organic carbon sources, like phytoplankton, to their diet. Experimental results indicate a negative, but insignificant, impact on benthic diatom biomass by juveniles (due to grazing) and adults (due to physical disturbance). This finding seems to be in agreement with the results of the stable carbon isotope analysis, strongly suggesting the selective feeding of juvenile T. palustris on benthic diatoms.  相似文献   

8.
The demand for mud crab Scylla serrata (Forsskål 1775) in the global market has increased, hence there is growing momentum to farm the species in Africa. Aquaculture production in Kenya and elsewhere in East Africa currently relies on juvenile seeds sourced from the wild. Wild-seed collection calls for management of the juvenile crab industry founded on knowledge of the species’ ecology, so as to achieve a sustainable seed supply and recruitment to the capture fishery. This study investigated the tidal, diurnal and seasonal occurrence of juvenile crabs in three habitats (intertidal-flat boundary zones, inside the mangroves, and in channels) in small creeks (Mida, Kilifi and Mtwapa) and Gazi Bay, on the coast of Kenya. Sampling was done with scoop nets and seining at receding tides and via burrow searches at low spring tides (day and night). Juveniles in the mangrove/intertidal-flat boundary zone were found sheltered under mangrove leaves or debris, or in shallow burrows during low spring tides, whereas at receding tides they could be seen moving out with the tide or searching for sheltering substrate or burrows. Catch per unit effort at high-abundance sites varied between 59 and 68 crabs fisher?1 day?1. More juvenile crabs, sized 10–80 mm internal carapace width (ICW), occurred at night during the receding tide. Net-seining was effective in the collection of juvenile mud crabs <30 mm ICW, whereas burrow sampling was effective for gathering larger crabs. However, collection of juveniles by seining reduced the quality of the crabs caught due to frequent loss of chelipeds, as compared with retrieving individual crabs by searching burrows. Some juveniles collected in the intertidal-flat boundary-zone habitat were either in the process of moulting or had just moulted, indicating the significance of this habitat for mud crabs at this physically delicate life stage.  相似文献   

9.
Changes in biotic and abiotic processes following mangrove clearing   总被引：1，自引：0，他引：1  
Mangrove forests, important tropical coastal habitats, are in decline worldwide primarily due to removal by humans. Changes to mangrove systems can alter ecosystem properties through direct effects on abiotic factors such as temperature, light and nutrient supply or through changes in biotic factors such as primary productivity or species composition. Despite the importance of mangroves as transitional habitats between land and sea, little research has examined changes that occur when they are cleared. We examined changes in a number of biotic and abiotic factors following the anthropogenic removal of red mangroves (Rhizophora mangle) in the Panamanian Caribbean, including algal biomass, algal diversity, algal grazing rates, light penetration, temperature, sedimentation rates and sediment organic content. In this first study examining multiple ecosystem-level effects of mangrove disturbance, we found that areas cleared of mangroves had higher algal biomass and richness than intact mangrove areas. This increase in algal biomass and richness was likely due to changes in abiotic factors (e.g. light intensity, temperature), but not biotic factors (fish herbivory). Additionally the algal and cyanobacterial genera dominating mangrove-cleared areas were rare in intact mangroves and included a number of genera that compete with coral for space on reefs. Interestingly, sedimentation rates did not differ between intact and cleared areas, but the sediments that accumulated in intact mangroves had higher organic content. These findings are the first to demonstrate that anthropogenic clearing of mangroves changes multiple biotic and abiotic processes in mangrove forests and that some of these changes may influence adjacent habitats such as coral reefs and seagrass beds. Additional research is needed to further explore the community and ecosystem-level effects of mangrove clearing and their influence on adjacent habitats, but it is clear that mangrove conservation is an important aspect of managing tropical coastal systems.  相似文献   

10.
汕头3种人工红树林湿地大型底栖动物群落的比较   总被引：1，自引：1，他引：0  
对广东省汕头市莲阳河口区恢复背景相同的拉关木(Laguncularia racemosa)、无瓣海桑(Sonneratia apetala)、海桑(Sonneratia caseolaris)3种人工林和光滩湿地中大型底栖动物群落进行比较研究。结果显示,4种生境中大型底栖动物优势种(Y0.02)存在差异;相似性分析检验(One-Way ANOSIM)表明4种生境间大型底栖动物群落结构差异显著。等级聚类和非参数多变量标序也显示4种生境间的大型底栖动物群落结构差异显著。3种人工林中,无瓣海桑、海桑人工林中大型底栖动物群落结构较为相似;3种人工林中大型底栖动物物种多样性和生物量从大到小的排列次序为:拉关木海桑无瓣海桑。BIOENV分析表明大型底栖动物分布与林地土壤p H、有机质、砂粒和粉粒含量、红树植物平均株高、平均胸径、平均基径和冠幅(南北×东西)这些理化因子显著相关,这进一步证实了红树植物种类对林地大型底栖动物多样性和分布的影响。  相似文献   

11.
广东省红树林资源变化遥感监测   总被引：1，自引：0，他引：1  
利用1990年的Landsat-5TM、2000年的Landsat-7ETM+和2008年的CBERS-02BCCD 3期遥感影像对广东省近18a来的红树林湿地资源进行监测,并对其时空变化情况进行分析。结果表明:广东省红树林呈现不断增加的趋势,1990年、2000年和2008年的面积分别为7 733.2,8 722.0和9 593.3hm2;红树林由沿岸分散分布趋于集中分布;天然林减少,人工林增加。  相似文献   

12.
A programme of mangrove planting has been undertaken around the island of Rodrigues (SW Indian Ocean) since the mid-1980’s involving the introduction of the species Rhizophora mucronata. We examined three coastal embayment sites (Baie Diamant, Anse Goeland and Anse Pansia) in which planting has been undertaken over different time periods within the past 20 years. Planting has met with variable success in the different sites, probably due to variations in fluvial and groundwater influence. At two sites (Baie Diamant – first planted in 1990, and Anse Pansia – first planted in 1995) ecological data indicates that the mangroves are becoming well-established, and sedimentary evidence suggests that relatively rapid modification of intertidal substrates has occurred. This is evident in the form of significant increases in sediment organic-matter content (especially fibrous organic-matter) and an increase in the accumulation of sediment fines inside the mangroves. A strong correlation exists between the magnitude and depth of substrate modification and mangrove forest density, especially root and sapling density. At the third site, Anse Goeland (first planted in 2001), mangrove establishment has not been successful, many of the seedlings have died and no secondary colonisation has occurred. Sediment substrates show no deviation from background levels in terms of organic content or weight % fines content, and we find no evidence for mangrove planting influencing sediment substrates. Despite evidence for the development of a distinctive mangrove facies at Baie Diamant and Anse Pansia there is, however, no evidence as yet for a marked change in substrate geochemistry such as would be demonstrated by evidence of active bioclast dissolution – a common process in many natural (mature) mangrove substrates. We infer this to be a function of the present relative immaturity of the still developing mangrove substrates, but may also be a function of the apparent paucity of burrowing crabs which play an important role in nutrient cycling and sediment geochemistry. Thus whilst the mangroves in some of the study sites are reaching a stage where they are producing distinctive sedimentary facies, the systems appear to be in a state of progressive sedimentary and diagenetic modification as the floral and infaunal components of the mangroves continue to develop.  相似文献   

13.
The Caeté Estuary lies within the world's second largest mangrove region, 200 km south-east of the Amazon delta. It has an extension of about 220 km2and is subjected to a considerable human impact through intensive harvest of mangrove crabs (Ucides cordatus) and logging of mangroves. In order to integrate available information on biomass, catches, food spectrum and dynamics of the main species populations of the system, a trophic steady state model of 19 compartments was constructed using the ECOPATH II software (Christensen & Pauly, 1992). Ninety-nine percent of total system biomass is made up by mangroves (Rhizophora mangle, Avicennia germinans andLaguncularia racemosa ), which are assumed to cover about 45% of the total area and contribute about 60% to the system's primary production. The remaining biomass (132 g m−2) is distributed between the pelagic and benthic domains in proportions of 10% and 90% respectively. Through litter fall, mangroves inject the main primary food source into the system, which is either consumed directly by herbivores (principally land crabs, Ucides cordatus) or, when already metabolized by bacteria, by detritivors (principally fiddler crabs, Uca spp.). These two groups are prominent in terms of biomass (80 g and 14·5 g m−2), and food intake (1120 g m−2 yr−1and 1378 g m−2 yr−1respectively). According to the model estimates, energy flow through the fish and shrimp compartments is of relatively low importance for the energy cycling within the system, a finding which is contrary to the situation in other mangrove estuaries reported in the literature. The dominance of mangrove epibenthos is attributed to the fact that a large part of the system's production remains within the mangrove forest as material export to the estuary is restricted to spring tides, when the forest is completely indundated. This is also the reason for the low abundance of suspension feeders, which are restricted to a small belt along the Caeté River and the small creeks which are watered daily. Phytoplankton, temporarily refloating benthic diatoms, neritic zooplankton and small pelagic fish dominate the (low) pelagic biomass. Total system throughput (10 559 g m−2 yr−1) and mean transfer efficiency between trophic levels (9·8%) calculated by the model fit well into the range reported for other tropical coastal ecosystems. The very high gross efficiency of the fishery (catch/net primary production) of 8·6% and its low trophic level (2·1) is explained by a high harvesting rate of mangroves and the fact that the main animal resource in the system are the mangrove crabs (Ucides cordatus), which feed at the first trophic level. The model was balanced asuming a turnover rate for the land crabs of P/B=0·25 (P/B: production per unit of biomass) which is possibly too high. If this value was replaced by a (possibly more realistic) lower value, the model would not balance, suggesting a situation in which more biomass is being harvested than produced, which hints to an overexploitation of this resource A ranking of the various system components in terms of their contribution to the system function (ascendency sensu Ulanowicz, 1997) revealed that detritus and associated bacteria contribute 34%, mangroves 19%, fiddler crabs 13%, phytoplankton and microphytobenthos 10%, mangrove crabs 10%, and the remaining 14 groups 14% to the total ascendency. Summary statistics of the model are given and compared with those of other coastal ecosystems.  相似文献   

14.
Terebralia palustris is a common mud-whelk present at a particularly high density in all Indo-West Pacific mangroves. Young snails feed on nothing but mud while larger specimens are able to feed on fallen leaves too. In Kenya (Mida Creek) under the canopy, competition for mangrove leaves can be very high due to the high density of Sesarmidae crabs. On open exposed muddy platforms, no Sesarmidae occur but the leaf density is very low because the leaves are only randomly present as they are deposited and removed twice a day by the tide. However, the snail density is always very high, raising the question as to whether the snails use a special searching strategy to optimize their resource finding rather than a purely random movement. By analyzing the snails' movements on a uniform area at different levels and comparing them with simulated random paths, we could show that the snails' movements are not purely random. The distribution of different size classes of T. palustris in Mida Creek was known to be quite odd: the same simulation approach suggests that the zonation asymmetry could reasonably be due to the stochastic recruitment of juveniles in space and time and maintained by a substantial long-lasting spatial inertia.  相似文献   

15.
Mud crab (Scylla serrata) is a delicacy for subsistence consumption in fisher communities and tourist hotels in the coast of Kenya while export demand to markets in China and Japan is expanding and provides competitively higher prices. Crab exploitation and degradation of the mangrove forests have increased over the last decades therefore threatening the capture fishery. The preferred market size crab has consistently decreased from more than 1 kg two decades ago to the current size of 0.5 kg therefore posing both management and livelihood threat to the critical ecosystem (mangrove) and coastal populations. To meet the increased tourist and export demand and provide surplus for the local community while conserving the critical crab ecosystem, small-scale aquaculture has been initiated in the concept of silvofisheries. Initial culture methods have targeted sub-adult crabs of 150–350 g for culture to market size (>0.5 kg) in drive-in cages and pens (mud crab fattening). These technology attained survival of between 50 and 70% and a market price of 5 dollars per kilogram. However, research is ongoing to assess viability of stocking juvenile seed crabs directly in ponds as practised in South East Asia (SEA) as opposed to stocking of sub-adults in drive-in cages. In comparison with other areas, crab capture fisheries in East Africa have limited management and enforcement frameworks/capabilities within the wider regional fisheries policies. Also there is limited understanding of wild mud crab resources and suitable management options to avoid over-exploitation as observed in SEA. The double-edged demand (wild market size capture and juvenile capture for aquaculture) for mud crabs in addition to mangrove degradation are likely to cause great challenges to stock exploitation and livelihoods of the coastal people dependent on the resource. This review paper provides an inside onto the tradition, trends and options for development of mud crab capture and culture in Kenya.  相似文献   

16.
This article contributes to the understanding of the changes in distribution and total area of mangrove forests along the mainland Tanzania coast over the past decade. Mangroves are recognized as critical coastal habitat requiring protection and special attention. The Tanzania coastline forms a suitable habitat for establishment of mangrove forests. Mangrove forests are distributed from Tanga in the north to Mtwara in the south covering approximately 109,593 hectares from 1988-1990 and about 108,138 hectares in 2000. The largest continuous mangrove stands are found in the districts of Rufiji, Kilwa, Tanga-Muheza, and Mtwara. Comparison of data between these two time periods shows that the geographic coverage of mangroves has no dramatic change in the past decade. The Tanzania Mangrove Management Project and other closely related programs and efforts pertaining to mangrove conservation contribute to direct restoration and natural regeneration of mangroves. This study documents the changes of mangroves and demonstrates that remote sensing and GIS offer important data and tools in the advancement of coastal resource management and ecosystem monitoring. Application of geographic information technologies is critical for improved coastal resources management and decision making for sustainable development in Tanzania.  相似文献   

17.
Remote Sensing of Mangrove Change Along the Tanzania Coast   总被引：1，自引：1，他引：0  
This article contributes to the understanding of the changes in distribution and total area of mangrove forests along the mainland Tanzania coast over the past decade. Mangroves are recognized as critical coastal habitat requiring protection and special attention. The Tanzania coastline forms a suitable habitat for establishment of mangrove forests. Mangrove forests are distributed from Tanga in the north to Mtwara in the south covering approximately 109,593 hectares from 1988-1990 and about 108,138 hectares in 2000. The largest continuous mangrove stands are found in the districts of Rufiji, Kilwa, Tanga-Muheza, and Mtwara. Comparison of data between these two time periods shows that the geographic coverage of mangroves has no dramatic change in the past decade. The Tanzania Mangrove Management Project and other closely related programs and efforts pertaining to mangrove conservation contribute to direct restoration and natural regeneration of mangroves. This study documents the changes of mangroves and demonstrates that remote sensing and GIS offer important data and tools in the advancement of coastal resource management and ecosystem monitoring. Application of geographic information technologies is critical for improved coastal resources management and decision making for sustainable development in Tanzania.  相似文献   

18.
The increasing exploitation of mangrove forests, without any sustainable planning, has been seriously compromising the survival of this ecosystem and of its exclusive resources. Scylla serrata is one of the most commercially exploited crabs inhabiting mangroves and estuaries of the Indo-Pacific region. This species is extensively harvested, mainly for selling to the tourist market, and, as a consequence, its populations are in constant decline. The aim of the present study was to assess the level of genetic exchange of S. serrata within the Western Indian Ocean (WIO), using a population genetic structure approach. To achieve this goal, we reconstructed the intra-specific geographic pattern of genetic variation by partial sequencing the mitochondrial DNA cytochrome oxidase subunit I, in samples from seven mangrove sites of the WIO. Our data set then encompassed all the sequences for the same genetic marker deposited in Genbank and corresponding to samples from South East Asia, Australia and some Pacific Islands: this allowed us to estimate the level of connectivity among S. serrata populations within its distribution area.  相似文献   

19.
Seasonal variation in the distribution of mollusks in relation to environmental parameters was studied at four mangrove stations on the Pondicherry coast during September 2008–August 2009. A total of 37 species of molluscs were recorded, among them 16 species of bivalves belonging to 7 families and 12 Genera, and 21 species of gastropods belonging to 14 families and 19 Genera, with the Cereithedia cingulata being the dominant group. An increase of species density and diversity in the Post monsoon season was observed, with the highest values for both indexes at stations 1 and 2, and the lowest at stations 3 and 4 fine where the sand assemblage was dominated by a few gastropods. Pollution indicator species Cassidula nucleus, Melampus ceylonicus, Sphaerassiminea minuta were found only in highly polluted regions near stations 3 and 4; they were totally absent in moderately polluted areas near stations 1 and 2. From a stepwise multivariate analysis of the different environmental parameters regarding molluscan density, it was found that in all 10 parameters govern the density variation of benthic mollusks in Pondicherry mangroves and that the organic matter of sediment and sulphide, DO, and salinity were the highly significant ones.  相似文献   

20.
Mangroves occur in South African estuaries at their poleward distribution limits, extending into temperate habitats. In 1963, William Macnae published the first comprehensive assessment of mangrove swamps in South Africa and made firsthand observations of these mangrove ecosystems. This article reassesses South African mangrove habitats, highlighting changes since Macnae’s assessment, through a literature review of research done in the past 50 years and using the results of a dedicated mangrove survey spanning 2012–2017. Until now, changes have been recorded mostly for mangrove vegetation, including a change in mangrove cover and a poleward shift of mangrove species. While some mangrove-associated fauna have disappeared from most sites (e.g. the gastropod Terebralia palustris), others, such as fiddler crabs, have spread farther south. The effects of decreasing diversity with an increase in latitude were not observed along the South African coast. Instead, habitat quality and estuarine mouth state seem to exert greater influence on species diversity in the mangroves, and a poleward shift in species distribution is now evident not just for the mangrove flora but for the fauna as well. South African mangrove research needs to include a continuous monitoring plan, especially if we are to contribute to global knowledge on blue carbon, the effects of sea-level rise, and the resilience of the mangrove ecosystem.  相似文献   

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