Leaf anatomical adaptation of eighteen mangrove plant species from the Sundarbans in Bangladesh

Investigation on leaf anatomical adaptation of 18 mangrove plant species was carried out. Among the 18 species 13 were dorsiventral and five were isobilateral type. All the species had special stomatal structure and variable cuticle layer to minimize transpiration. Most of the species had succulent leaves with leaf thickness ranging from around 232 to 1363 μm. As an indication of salt secretion, both glandular and non-glandular trichomes were observed in several species. Although presence of single to multilayered hypodermis might effectively function as water storage tissue, several studied mangrove plant species e.g. Cynometra ramiflora L., Phoenix paludosa Roxb., Pongamea pinnata (L.) Pierre, Sonneratia apetala Buch. - Ham., S. caseolaris (L.) Engl. and Xylocarpus moluccensis (Lamk.) M. Roem. showed complete absence of hypodermis. This might be due to moderate saline condition. In addition, marked terminal tracheids in mesophyll tissue of a number of species might help with capillary water storage within the leaf. To enhance mechanical support several species were found to develop considerable amount of diverse sclereids within the mesophyll tissue and surrounding vascular bundle. Although maximum anatomical adaptations are common for plants growing in saline habitat it may be suggested that these features were differentially developed in plants specifically grown in mesohaline zone.

Salt Shock Responses of Microcystis Revealed through Physiological, Transcript, and Metabolomic Analyses

The transfer of Microcystis aeruginosa from freshwater to estuaries has been described worldwide and salinity is reported as the main factor controlling the expansion of M. aeruginosa to coastal environments. Analyzing the expression levels of targeted genes and employing both targeted and non-targeted metabolomic approaches, this study investigated the effect of a sudden salt increase on the physiological and metabolic responses of two toxic M. aeruginosa strains separately isolated from fresh and brackish waters, respectively, PCC 7820 and 7806. Supported by differences in gene expressions and metabolic profiles, salt tolerance was found to be strain specific. An increase in salinity decreased the growth of M. aeruginosa with a lesser impact on the brackish strain. The production of intracellular microcystin variants in response to salt stress correlated well to the growth rate for both strains. Furthermore, the release of microcystins into the surrounding medium only occurred at the highest salinity treatment when cell lysis occurred. This study suggests that the physiological responses of M. aeruginosa involve the accumulation of common metabolites but that the intraspecific salt tolerance is based on the accumulation of specific metabolites. While one of these was determined to be sucrose, many others remain to be identified. Taken together, these results provide evidence that M. aeruginosa is relatively salt tolerant in the mesohaline zone and microcystin (MC) release only occurs when the capacity of the cells to deal with salt increase is exceeded.

Changes in the Fish Community of a Western Caribbean Estuary after the Expansion of an Artificial Channel to the Sea

Increased connectivity between coastal lagoons and the sea is expected to entail a greater proportion of marine species in the former. Chetumal Bay, estuary of the Hondo river into the Caribbean, had a limited access to the sea until the opening of the Zaragoza Canal. We sought changes in the fish community from 1999–2001 (just after an expansion of the canal) to 2015–2018. The same fishing gear was used, in the same localities, during all seasons. Total fish abundance and mean local richness decreased, although total abundance increased in the polyhaline zone. Diversity was greater in the oligohaline zone in 1999–2001, and in the mesohaline zone in 2015–2018. Three guilds were absent in 2015–2018: Medium-sized herbivores, large piscivores, and medium-sized planktivores. Abundance of small benthivores decreased by decade; medium-sized piscivores and small planktivores became more abundant in 2015–2018 in the polyhaline zone. These changes may be due to the opening of the channel, but illegal fishing outside the bay may explain the decrease in juveniles of large piscivores, and erosion in the innermost part may be destroying important habitats. Our findings can be a reference for similar situations, as coastal development and climate change interact and affect tropical estuaries.

Changes in the Fish Community of a Western Caribbean Estuary after the Expansion of an Artificial Channel to the Sea

Increased connectivity between coastal lagoons and the sea is expected to entail a greater proportion of marine species in the former. Chetumal Bay, estuary of the Hondo river into the Caribbean, had a limited access to the sea until the opening of the Zaragoza Canal. We sought changes in the fish community from 1999-2001 (just after an expansion of the canal) to 2015-2018. The same fishing gear was used, in the same localities, during all seasons. Total fish abundance and mean local richness decreased, although total abundance increased in the polyhaline zone. Diversity was greater in the oligohaline zone in 1999-2001, but in the mesohaline zone in 2015-2018. Three guilds were absent in 2015-2018: medium-sized herbivores, large piscivores, and medium-sized planktivores. Abundance of small benthivores decreased by decade; medium-sized piscivores and small planktivores became more abundant in 2015-2018 in the polyhaline zone. These changes may be due to the opening of the channel, but illegal fishing outside the bay may explain the decrease in juveniles of large piscivores, and erosion in the innermost part may be destroying important habitats. Our findings can be a reference for similar situations, as coastal development and climate change interact and affect tropical estuaries.

Physio-chemical properties and dynamic of the surface sediment in riparian mangroves along the Tien river, Tien Giang province

This study was conducted to investigate the physio-chemical properties and vertical dynamic of the surface sediment (0–5 cm) in riparian mangroves along the Tien river, Tien Giang province. The distribution of riparian mangroves located from the polyhaline zone (transect S1 and S2) to the mesohaline zone (transect S3 and S4) and the oligohaline zone (transect S5). Three plots (10x10 m) per transect were set based on the elevation of the mangrove floor (cm + mean sea level) and dominant plants. A total of 28 sediment samples were collected in December 2016 and April 2017. Seasonal variation of pH, redox potential (Eh), electrical conductivity of saturated extract (ECse), bulk density, sediment organic matter (SOM) and total sulfur (TS) were measured in accordance with the standard protocols. Seasonal trends of vertical erosion and accumulation were tested by the tracer stick method. The ECse values and TS concentrations were higher in the dry season and in transects closed to the estuary (S1, S2 and S3) but these trends weren’t found for pH, Eh, and SOM. In most of the riparian mangroves along the Tiền river, low elevation (0–50 cm) was one of important factors affecting the Eh and ECse. In the rainy season, major changes in vertical erosion and acumulation have occurred in the transects near the mouth of the river.

Salinity gradient meiobenthos distribution on the Razdolnaya River’s estuary

The paper studies salinity gradient meiobenthos distribution based on the results of the benthic surveys of the Razdolnaya estuary (the Sea of Japan, Amursky Bay). The density was increased with salinity growth on the Razdolnaya Rivers estuary. Meiobenthos was comprised by 8 taxonomic groups (Nematoda, Copepoda, Ostracoda, Oligochaeta, Mollusca, Amphipoda, Polychaeta и Chironomidae) with the dominance of nematodes. Most of meiobenthic species are presented by marine euryhaline species and registered throughout the Razdolnaya Rivers estuary. Fresh water species Dorylaimus chassanicus, Hofmaenneria gratiosa, Theristus brevisetosus and nematodes of the genera Paradontophora , widespread on estuaries of Far East of Russia, were dominated in meiobenthos in oligohaline zone of estuary; Monhystrella sp. Oncholaimium japonicum, Anoplostoma cuticularia, Daptonema inversum and Harpacticoid Copepods Remanea naksanensis, Onychocamptus mohammed, Huntemannia biarticulatus, Halectinosoma sp. were dominated in mesohaline zone. Nematode community are changed by zones throughout the estuary: Paradontophora genera are dominated in freshwater and olihaline zones, as well as freshwater species ( Dorylaimus chassanicus, Hofmaenneria gratiosa, Theristus brevisetosus ) were presented; Monhystrella sp. are dominated and freshwater spicies are decreased in the number at the mesohaline zone; Paracanthonchus macrodon, Onсholaimium paraolium, Sabatieria finitima, Dorylaimopsis peculiaris and S. palmaris are dominated at the euhaline zone. The nematocenes of inner part of estuarine zone arent characterized by specific species assemblage and consist of species typical for nematode community of shallow water and of marine zones.

Spatial patterns and seasonality in the epibenthic communities of the Westerschelde (Southern Bight of the North Sea)

Beamtrawl samples were taken monthly between January 1988 and December 1989 in 14 subtidal stations along the longitudinal axis of the Westerschelde Estuary. The estuary harboured high densities of epibenthic species (total average of 2250 ind 1000 m−2). Only 37 fish species were recorded and three mobile macroinvertebrate species were quantified. Seventeen epibenthic species were common, only eight of which were very abundant. An overall dominance of the brown shrimp Crangon crangon was noted. The near absence of anadromous and freshwater species was correlated with the low oxygen concentrations upstream the Dutch–Belgian border. The epibenthic species could be divided into a polyhaline and a mesohaline community along the main salinity–oxygen–turbidity gradients of the estuary. The mesohaline zone was characterized by higher densities and biomasses for shrimps, gobies and flatfish. The spatial structure in the epibenthic community of the polyhaline zone was more influenced by the watermasses from the sea and inflowing channels, and was correlated with the degree of exposure (current velocities and tides). A classification is proposed, based on the season in which the epibenthic species occur in the estuary, and on their life stages and abundances during that period. The monthly data demonstrate that while the eight abundant epibenthic species were generally present throughout the year (summer or winter resident), the majority tended to appear in the Westerschelde at varying times (summer, winter or bimodal) and often remained in large numbers (nine common species) for only a short time. The fact that mainly juveniles were recorded in the higher density-classes, suggests that the Westerschelde Estuary still acts as a nursery area for many epibenthic species.

Meiofauna of the industrialised estuary and Firth of Forth, Scotland

SynopsisKnowledge concerning the meiofauna of the Forth is reviewed and extended by presentation of the results of new surveys of the intertidal and subtidal provinces of the estuary. Most of the published information concerns the influence of sewage pollution on shores of the firth. Before 1979, the meiofaunal communities of sandy beaches along the Edinburgh coastline exhibited reduced species richness, although certain taxa displayed enhanced densities. Improvements in the sewage treatment process have initiated a phase of meiofaunal recovery.In the estuary the salinity regime plays a key role in the determination of species composition, although the influence of local changes in sediment type and stability is recognised. Meiofaunal communities of lower shore mudflats in different salinity zones of the estuary are described. Pollution plays a major modifying role. In the upper reaches of the estuary, which suffer oxygen depletion in summer, only nematodes and oligochaetes were recorded in the oligohaline zone and impoverished nematode and copepod faunas in the mesohaline zone. In the polyhaline zone discharges from the industrialised region around Grangemouth modify meiofaunal community structure over an extensive area of mudflat. The subtidal meiofauna of the lower estuary is briefly described, particularly with respect to the copepods. Impoverishment again occurs in the vicinity of Grangemouth.