Mangrove associates versus true mangroves: a comparative analysis of leaf litter decomposition in Sundarban

Mangrove species are broadly classified as ‘true mangroves’ and ‘mangrove associates’. We hypothesized that the leaf litter decomposition rates of true mangroves differ significantly from the mangrove associates under the same ecological and bio-climatic conditions. In order to test this hypothesis, the leaf litter decay rates of 24 true mangrove species and 10 mangrove associates along with the concomitant carbon and nitrogen dynamics of the litters were studied in the tropical mangrove forest of Sundarban by means of litter bags. The decomposition was monitored for six consecutive weeks in the pre-monsoon, monsoon and post-monsoon season. All the species in general went through a rapid decay phase in the first 2 weeks, however, the rate substantially decreased in the following 4 weeks. Most of the species studied had significant seasonal variability (p < 0.05) in the decay rate. Species-specific decay was highest throughout the monsoon and least during the post-monsoon season. The mean dry weight composition (i.e. percentage of dry weight of the leaf litters remaining at the end of weekly intervals) of the true mangroves was 10–12 % higher than the mangrove associates throughout the sampling period. The mean decay constants (K in week^?1) of the true mangroves were 0.15 ± 0.05, 0.20 ± 0.06 and 0.16 ± 0.05 in the pre-monsoon, monsoon and post-monsoon season respectively. The mangrove associates had significantly higher decay constants in the respective seasons that followed the order 0.23 ± 0.09, 0.25 ± 0.06 and 0.24 ± 0.09. As a consequence, the computed mean half-life period of the true mangrove litters (32 ± 11 days) was much higher than the mangrove associates (23 ± 11 days). This showed that collectively the leaf litters of mangrove associates degraded at a much faster rate than the true mangroves throughout the annual cycle and thus our hypothesis was justified.     

G Model Revisited: Seasonal Changes in the Kinetics of Sulphate-reducing Activity in the Salterns of Ribander,Goa, India

To evaluate the contribution of Sulfate-Reducing Bacteria (SRB) to the carbon flux from marine salterns, sulfate reducing activity (SRA) was measured for a year (Sept 2000–Aug 2001) This covered the pre-monsoon period (Feb–May), the monsoon (June–Sept) and the post-monsoon (Oct–Jan) in the salterns of Ribandar, Goa, India. Sulphate reduction was examined to gain insights into the decomposition characteristics (kinetics) of organic carbon; this connection is based on the theory of stoichiometric coupling between anaerobic carbon degradation and sulphate reduction to sulphide. SRA was measured using radiotracer techniques. Spatially, recalcitrance of the substrates, as depicted by the reaction rate coefficient (k), increased with depth, except during the monsoons. The values ranged from 0.0061 during the pre monsoon to 0.06 month^?1 during the post-monsoon at 5–10 cm depth. The recalcitrance was highest at the surface during the monsoons at a k value of 0.014 month^?1. The anaerobic degradation of labile organic matter followed first order kinetics or G model during non-monsoon seasons when the substrate was limiting due to closure of the system to the addition of extraneous source of organic matter. However, the integrated recalcitrance or the reaction rate coefficient was much higher during the post monsoon at 0.642 month^?1 compared to 0.053 month^?1 during the pre-monsoon season. Interestingly, the reaction rate followed zero-order kinetics when the substrate was non-limiting during monsoon due to exposure to external inputs.     

Impact of season on haematological and biochemical parameters of crossbred female calves in hot and humid tropics

The objective of the present study was to assess the impact of season on haematological and biochemical parameters of crossbred female calves. Seven crossbred female calves of 6–12 months of age were selected. The study was conducted in three different spells of 30 days each in pre-monsoon, monsoon and post-monsoon seasons. Ambient temperature (AT), relative humidity (RH) and temperature humidity index (THI) was recorded in all the three seasons. Whole blood was collected for estimation of haematological and plasma was used estimation of biochemical parameters. Highest AT and THI was recorded in pre-monsoon while highest RH was recorded in monsoon. The study revealed that season had no effect on haematological parameters such as total leucocyte, haemoglobin, packed cell volume, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration, while total erythrocyte count was significantly lower in monsoon compared to pre and post-monsoon seasons. Glucose and cholesterol were significantly lower in pre-monsoon and monsoon compared to post-monsoon. Glutathione peroxidase activity was significantly higher in pre-monsoon compared to monsoon and post-monsoon. No significant difference between seasons in the concentration of total protein, albumin, globulin and albumin globulin ratio was noticed. The results indicate that hot conditions have profound effect on haematological and biochemical parameters of crossbred calves.     

Substrate selection and seasonal variation in densities of invertebrates in stream pools of a tropical river

Spatial distribution and seasonal variation in densities of the invertebrates were investigated for a year in three stream pools of a South Indian river. The effects of season, substrate type and water depth on the distribution were analyzed. Substrate type and season influenced the invertebrate distribution the most. Leaf packs harboured most of the organisms followed by macro-algal substrate and sand. The lowest densities were observed on rocky substrates and in the water column. Rocky substrates in shallow water supported higher densities of total invertebrates than deeper areas. Chironomid larvae dominated all benthic substrates throughout the year. Of the 19 invertebrate taxa studied, 6 showed no seasonality in densities, and most of the rest showed their highest densities in the pre-monsoon period and lowest in the SW monsoon or post-monsoon periods. However, in two of the three pools, the densities of total invertebrates were highest during the post-monsoon period with secondary peaks in the pre-monsoon period.     

Salinity drives growth dynamics of the mangrove tree Sonneratia apetala Buch. -Ham. in the Sundarbans,Bangladesh

Mangroves throughout the world are threatened by environmental changes apart from anthropogenic disturbances. Many of these changes may inhibit the growth and survival of mangrove species. To understand and predict the effects of global change on mangrove forests, it is necessary to obtain insights on the growth dynamics of mangroves in relation to environmental factors. This study was conducted on Sonneratia apetala, a mangrove species which grows under a range of salinity conditions across the Sundarbans in Bangladesh. We studied trees growing under respectively high, medium, and low salinity conditions based on the influence of freshwater discharge. First, the periodicity of radial growth across the year was detected by applying cambial analyses. Based on tree-ring analyses, we calculated the growth response of S. apetala to monthly variation in precipitation and temperature as well as river discharge, as a proxy for salinity. We found the cambium of S. apetala being active during the monsoon and post-monsoon period whereas it was dormant in the pre-monsoon. This periodicity in radial growth leads to the formation of distinct annual rings with ring boundaries being marked by radially flattened fibres. S. apetala trees growing under low salinity conditions generally show higher growth rates indicating the positive impact of river discharge, i.e. freshwater input on mangrove growth. Wet and warm conditions during the monsoon period positively affected S. apetala growth, especially in the low salinity zone. Our results show that salinity is the primary driver of growth dynamics of S. apetala in the Sundarbans. A gradual or seasonal increase in salinity, e.g. as a consequence of sea-level rise may therefore importantly alter the growth of this species, possibly leading to changes in mangrove forest dynamics and zonation.     

Influence of suspended particulate matter on nutrient biogeochemistry of a tropical shallow lagoon,Chilika, India

The behaviour of suspended particulate matter (SPM), salinity profile, dissolved nutrients, total (T.Chl-a) and size fractionated chlorophyll-a (F.Chl-a) were studied seasonally at Chilika Lagoon, east coast of India, during 2008–2009. The study showed large spatio-temporal variations among these parameters. The concentration of dissolved inorganic nitrogen and inorganic phosphate were found to be maximum during the monsoon, followed by post- and pre-monsoon, although the mean N:P ratios, which indicate the relative availability of N with respect to P, were 9.13 ± 3.09, 16.57 ± 11.53 and 5.47 ± 3.13, respectively. It was evident from the results that during pre-monsoon and postmonsoon, the lagoon exhibits nitrogen limitation. Mean T.Chl-a biomass in the lagoon showed distinct seasonality with maximum values during the pre-monsoon (23.12 ± 9.75 mg m^?3) followed by monsoon and post-monsoon. Irrespective of seasons, maximum T.Chl-a was found in the northern part of the lagoon. SPM concentrations during the monsoon were relatively higher in the freshwater dominated zones compared to seawater dominated areas, indicating its riverine sources. The correlation between SPM and various dissolved nutrients (p < 0.05) suggests its influence on the physico-chemical conditions at varying levels. It is summarized that seasonal variation of SPM and nutrients contributed by rivers, wind induced re-suspension events and in situ  regeneration processes play a crucial role in the lagoon biogeochemical cycle.     

Microbial populations regulate greenhouse gas emissions in Sundarban mangrove ecosystem,India

Mangrove ecosystems are significant sources of greenhouse gases (GHG) that is attributed to microbial activity. However, it is still unknown how the sediment microbial populations affect GHG emissions in mangrove ecosystem. Since little is known about microbial populations of mangroves, the present study was aimed to understand the structure and function of microbial communities in the Indian part of the Sundarban mangrove ecosystem in relation to environmental variables and variation of GHG emissions during three seasons: pre-monsoon (March–June), monsoon (July–October) and post-monsoon (November–February).Seasonal variations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) gas samples were taken from the mangrove bed. Culture methods were used to detect twelve different types of microbes such as heterotrophic (Htp), N₂ fixing (Nfix), nitrifying (Ntfn), sulfur oxidizing (Soxd), Gram-negative (GMn), Gram-positive (GMp), spore forming (Sfor), denitrifying (DNtfn), anaerobic (Anrb), phosphate solubilizing (Psol), cellulose degrading (Cdeg) bacteria and actinomycetes (Actm). In the monsoon, populations of the Htp, Anrb, Psol, and Cdeg bacteria were more prevalent, whereas populations of the GMn, GMp, Ntfn, DNtfn bacteria, and Actm bacteria were more prevalent in the post-monsoon. Monsoonal CO₂ and CH₄ fluxes were larger than pre-monsoon and post-monsoon, resulting in increased microbial soil respiration and breakdown of soil organic carbon. Because of higher denitrification and soil temperature, N₂O flux was higher in the pre-monsoon period, followed by monsoon and post-monsoon periods. A univariate statistical correlation was employed to assess the relationships between environmental variables and different microbial populations. An ANN (artificial neural network) model was proposed to evaluate the relevance of microbial population contribution to GHG emissions, and it indicated that the Htp, Anrb, and Dntfn microbial populations were most relevant for CO₂, CH₄, and N₂O emissions. The suggested model would be used to assess the drivers behind GHG emission in the mangroves located at different parts of the world.     

Species interactions within a fouling diatom community: roles of nutrients, initial inoculum and competitive strategies

Diatoms constitute an important component of the fouling community. Although a lot of work has dealt with the fouling diatom community structure, work on the species interactions within the community is still meagre. In this regard, a study was carried out by transferring natural diatom biofilms into controlled conditions in order to understand the roles of nutrients, initial cell inoculum and seasonal variation in species composition in structuring the fouling diatom community. This community exhibited seasonal variation during the monsoon, post-monsoon and pre-monsoon periods. During each of these seasons, diatom species interactions varied depending upon the species composition. It was observed that excess nutrients favoured those species with comparatively higher growth rates, thereby suppressing the growth of other co-existing species. This competitive trait was found to be effective at an appropriate cell density ratio of the competitive and target species. Understanding such pathways will be useful for modelling the interactions between diatom species in various habitats under different resource conditions.     

High bioassay values in Terminalia alata leaves: indication of Cu mineralisation in Malanjkhand Granitoid,Central India

Abstract

Eighteen plant species belonging to 11 families commonly growing in the Pathratola, Dhorli and Pipardhar areas of the Malanjkhand Copper Province were studied. High Cu values were observed in the leaves of the abundant species of Terminalia alata in Pipardhar area. The leaves of T. alata also show wide pre- and post-monsoon seasonal variations in their Cu contents (average: 593-1,713 μg g^-1). Amongst several samples from various species, most of the leaf samples of T. alata, collected from the Pipardhar area showed high Cu values that lie within and occupy the high ends of cumulative probability curves. Anomalous Cu values of > 200 and > 497 μg g^-1were obtained for most of the T. alata leaves of the Pipradhar area for pre- and post-monsoon periods, respectively. The correlation coefficient values between Cu contents of T. alata leaves and substrate soil do not show a significant relationship for any area in either season. However, t- test results between Cu contents of T. alata leaves and substrate soil samples indicated a significant relationship for the samples collected from the Pipardhar and Pathratola areas during the pre-monsoon period. For post-monsoon period, the t-test results show non-significant relationship in the Pipardhar area. Another sampling area selected adjacent to the Pipardhar area had significance in the t-test results between the two sample periods. Polynomial curves revealed that 465 and 480 μg g^-1 of Cu in the soil are the “toxicity threshold limits” for the pre- and post-monsoon periods, respectively. Possible reasons attributed to the high bioassay values found in the T. alata leaves have been discussed in the paper.     

Seasonal variations in the fouling diatom community structure from a monsoon influenced tropical estuary

Seasonal variations in the fouling diatom community from a monsoon influenced tropical estuary were investigated. The community composition did not differ significantly between stainless steel and polystyrene substrata due to dominance by Navicula spp. The experimental evidence suggests that Amphora, which is a dominant fouling diatom in temperate waters, ultimately dominates the community in tropical regions when conditions are favourable. These observations reveal that a faster onset of macrofouling interferes with the microfouling community wherein the faster recruiters that have a higher abundance in ambient waters, dominate the community. Seasonal variations were observed in the fouling diatom community. Navicula delicatula dominated during the post-monsoon and tychopelagic diatoms (Melosira and Odontella) were observed during the monsoon. Low diatom abundance was recorded during the pre-monsoon season. The results indicate that although the fouling diatom community composition does not vary between substrata, there is a seasonal change in the community depending on the physical, chemical and biological interactions.     

Spatiotemporal variability in archaeal communities of tropical coastal waters

Spatiotemporal variations in the archaeal community structure from four locations along the central west coast of India were analyzed by denaturing gradient gel electrophoresis (DGGE) profiling and sequencing of prominent bands on the DGGE gels. A total of 36 water samples were collected during pre-monsoon, post-monsoon and monsoon seasons from three depths (surface, mid-depth , and close to bottom ～20 m). The community DNA extracts from these samples were subjected to DGGE analysis. The results of this study clearly indicate a significant difference in the community structure between sampling locations and seasons. Location-wise variation was more pronounced during pre-monsoon and post-monsoon seasons. During monsoon, however, the depth-wise variation was pronounced, suggesting monsoon influence on archaeal community structure. Sequencing of DGGE bands suggested the presence of marine group I and II archaea. Canonical correspondence analysis indicated that nitrate, nitrite and chlorophyll a were the significant explanatory variables responsible for > 60 % variation in archaeal community in these coastal waters.     

Microbial Ecosystem in Sunderban Mangrove Forest Sediment,North-East Coast of Bay of Bengal,India

This is the first documentation of seasonal and spatial fluctuation of the culturable microbial population collected from different zones in the sediment of the Sunderban mangrove forest. The population of cellulose degrading bacteria, [mean value of CFU 6.189 ± 1.025 × 10⁶ (g dry weight of sediment)^?1] was found to be maximum during post monsoon in the deep forest region, whereas, the fungal population [mean value of CFU 3.424 ± 0.886 × 10⁶ (g dry weight of sediment)^?1] was found to be maximum during pre-monsoon in the rooted region. The abundances of microbes, in decreasing order, studied from different zones are nitrifying bacteria [mean value of CFU 1.125 ± 0.359 × 10⁶ (g dry weight of sediment)^?1], phosphorous solubilizing bacteria (PSB) [mean value of CFU 0.805 ± 0.322 × 10⁶ (g dry weight of sediment)^?1], free living nitrogen fixing bacteria [mean value of CFU 0.417 ± 0.120 × 10⁶ (g dry weight of sediment)^?1] and sulfur reducing bacteria (SRB) [mean value of CFU 0.356 ± 0.125 × 10⁶ (g dry weight of sediment)^?1]. The content of organic carbon in the soil decreased from the deep forest region to the rooted and unrooted region but a reverse profile was found for soil salinity and soil silicate concentration. The results from the present study indicate that the monsoon cycle has a pronounced effect on the microbially dominated biogeochemistry in the sediment and consequently on the ecology of the Sundarban mangrove forest.     

Seasonal variations of calcium and phosphorus in the juveniles of freshwater murrel,Ophicephalus punctatus Bloch

Summary In young O. punctatus seasonal variations in calcium and phosphorus showed a direct correlation. Both of these minerals showed a bimodal cycle. High values occurred during pre- and post-monsoon months and low values during winter and monsoon months. These changes seem to be related to the feeding intensity and growth of the fish.     

Influence of climate on multiple tree-ring parameters of Pinus kesiya from Manipur,Northeast India

Tree-rings of Pinus kesiya from southern region of Manipur, Northeast India were used to develop chronologies of multiple tree-ring parameters that are: total-ring width (TRW), earlywood width (EW), latewood width (LW) and adjusted latewood (LWadj). The time span of these chronologies is 39 years (1980–2018 C.E.) and we compared their growth responses with monthly and daily climatic records. The comparison revealed a broadly consistent pattern of climate sensitivity with daily climate exhibiting higher correlation. The climate signals during pre-monsoon (March–May) were recorded in TRW and EW, whereas late-monsoon to post-monsoon climate signals were recorded in LW and LWadj. The spatial correlation analysis of tree-ring parameters and global sea surface temperature (SST) showed a positive relationship between tree growth with tropical Pacific Ocean and Indian Ocean during winter (December–February) and pre-monsoon (March–May) seasons. The LW and LWadj were also correlated with peak summer monsoon (July–August) SST over the tropical Pacific Ocean. IADFs observed in EW (E-IADF) were caused by dry and warm conditions during March–April. IADFs in LW (L-IADF) occurred due to a combination of enhanced rainfall and temperature during post-monsoon (October–November) season. Evidence of stand-specific micro-climatic conditions in the formation IADFs in this species was also found. This study showed that multiple parameters of P. kesiya provides a lucid understanding of climate response on its growth and can be considered as a proxy for studying sub-seasonal changes in past environmental conditions in longer records.     

印度加尔各答市区外围一地的露尾甲物种组成、多度和季节性发生(英文)

【目的】印度大部分露尾甲在腐烂的水果和蔬菜上大量发生,其种群在一年中表现出明显的季节性波动。据推测,露尾甲种群很大程度上依赖于温度、湿度和降雨之类的环境因子。【方法】本研究调查了2013-2015年印度加尔各答市区外围一地Garia的露尾甲物种组成、季节性发生和种群结构,记录了其活跃时期、季节性多度和影响其发生的因素。【结果】调查期间在调查地共发现数目不等的6个物种。其中最常见露尾甲为Urophorus humeralis,它是个体数量最多的物种且在一年中几乎所有月份均有发生;其他常见物种为Epuraea ocularis和E. luteola。不同物种在食物发酵的连续阶段进入诱捕器中。最初12 h被捕获的是Epuraea 属的种类,而在诱捕器中食物严重腐烂的后续阶段发现最多的是U. humeralis。在合适范围的气温(22~29℃)和相对湿度(82.5%~86%)下,物种丰富度最高,表明这些环境变量对露尾甲种群具有重要影响。【结论】加尔各答主要水果和蔬菜在季风后季节种植,在季风后季节取食这些作物的露尾甲发生量(物种丰富度和多度)最高。这一研究结果可能有助于制定针对这些甲虫的有效田间治理策略。     

Density,distribution and population structure of <Emphasis Type="Italic">Opusia indica</Emphasis> (Ocypodoidae: Camptandriidae) in a coastal mangrove creek in Pakistan

The density, distribution and population structure of Opusia indica were studied through transects method. Two transects were delimited in a mangrove area of Korangi creek (24°79′ N/67°20′ E). On each transect, three 0.25 m² quadrats were sampled at three tidal levels on a monthly basis during low tide. A total of 1919 crabs were obtained, of which 775 were males, 945 were non-ovigerous females and 199 were ovigerous females. Density of crabs varied between 198 m⁻² to 798 m⁻². The density and size distribution showed significant difference from low tide level to high tide level and were positively correlated with the percent moisture, percent organic matter and sediment structure. Based on carapace width (CW) males were significantly larger than the females indicating sexual dimorphism. The monthly size frequency distribution of crabs showed recruitment of juvenile crabs (< than 4 mm) nearly throughout the year except in few months. The monthly sex ratio deviated from 1:1 throughout the year, with female bias (χ ² = 31.633, P = 0.001 and df =11). Breeding was seasonal with peaks in SW monsoon. Size at sexual maturity based on smallest ovigerous female was CW = 4.0 mm. The average number of eggs per female were 2066 ± 479 (n = 25). Positive linear relationship was observed between the size of the female crabs and the egg numbers (r ² = 0.554).     

The seasonal dynamics and persistence of stream macroinvertebrates in Nepal: do monsoon floods represent disturbance?

1. The monsoon causes major flood events in some Himalayan streams, but their seasonal predictability might reduce the resulting disturbance. We assessed seasonal change in the benthos of 16 streams in central Nepal over a gradient of declining rainfall and increasing altitude from 600 to 3800 m. All sites were surveyed on four occasions, two in winter (November) and two pre-monsoon (June), with additional sampling during the monsoon (August) at four low altitude sites. Invertebrate abundance, taxon richness and persistence were assessed at all sites, and density and meso-habitat distribution at the four low altitude sites only.
2. Strong seasonal variation among invertebrates was confined primarily to streams at low altitude (600–800 m) where monsoon rainfall was greatest and catchments were dominated by terraced agriculture. At these sites, a significant reduction in benthic density (on average by 77%) and taxon richness (by 20%) occurred between the winter and pre-monsoon periods, so that invertebrate numbers were already low before the monsoon. A further significant decline occurred in all meso-habitats during the monsoon, but the change in density was small in absolute terms.
3. Persistence in rank abundance was equally low at all sites, but turnover in composition was significantly lower at sites in semi-natural forest than in catchments managed for terracing or alpine pasture.
4. These data provide no evidence that monsoonal floods represent major disturbance, instead supporting the view that the ecological response might reflect an adjustment to predictable flow pattern. However, catchment land use in the Himalaya appears to be a significant source of ecosystem instability, and confounds the simple interpretation of monsoon effects.     

Biodiversity of freshwater microfauna in the floodplain of the River Mun, Northeast Thailand: the Rotifera monogononta

We report on the γ- diversity of Rotifera in freshwater habitats of the River Mun floodplain, Northeast Thailand. Qualitative samples were collected during the pre-monsoon (April) and post-monsoon (October) periods of 2000, from 70 habitats spanning a diverse array of freshwater habitat types. Of the 184 species identified, most belong to Lecane (31.0%), followed by Trichocerca (12.0%), Lepadella (11.4%) and Brachionus (8.2%). Oriental, Australasian, and Eastern hemisphere taxa account for 4.3%, 3.3% and 7.1%, respectively, of the total rotifer fauna, and 8.8%, 1.7% and 10.5%, respectively, of Lecane. Although comparison between studies is difficult, these numbers conform to previous reports on the diversity and composition of the rotifer fauna of Thai freshwater habitats, and of tropical floodplain ecosystems. Diversity is lowest during the post-monsoon period, which may result from disturbance by monsoon conditions. Two morphospecies, Brachionus srisumonaen. sp., and Lecane niwati n. sp., are described as new to science. Additional noteworthy occurrences are, Lecane robertsonae Segers, previously considered a Neotropical endemic, and L. subtilis Harring & Myers, a tropicopolitan species new to Thailand and the Oriental region.     

Seasonal variations in the fouling diatom community structure from a monsoon influenced tropical estuary

Seasonal variations in the fouling diatom community from a monsoon influenced tropical estuary were investigated. The community composition did not differ significantly between stainless steel and polystyrene substrata due to dominance by Navicula spp. The experimental evidence suggests that Amphora, which is a dominant fouling diatom in temperate waters, ultimately dominates the community in tropical regions when conditions are favourable. These observations reveal that a faster onset of macrofouling interferes with the microfouling community wherein the faster recruiters that have a higher abundance in ambient waters, dominate the community. Seasonal variations were observed in the fouling diatom community. Navicula delicatula dominated during the post-monsoon and tychopelagic diatoms (Melosira and Odontella) were observed during the monsoon. Low diatom abundance was recorded during the pre-monsoon season. The results indicate that although the fouling diatom community composition does not vary between substrata, there is a seasonal change in the community depending on the physical, chemical and biological interactions.