Spatial prediction of seaweed habitat for mariculture in the coastal area of Bangladesh using a Generalized Additive Model

Hypoxia cycle in shallow lakes during winter (ice-covered to melting period): Stable and decay, hypoxia, and recovery phases

This study investigates hypoxic processes beneath lake ice and explores the interactions between water environmental factors and dissolved oxygen (DO) during winter, aiming to systematically assess the influence of winter climate changes on lake ecosystems through environmental variables (physical, chemical, and biological characteristics of water). A complete hypoxic cycle in a high-altitude shallow lake was recorded using high-frequency monitoring technology, and based on a predetermined hypoxic threshold (DO<2 mg/L), it was divided into three phases: stable and decay phase, hypoxic phase, and recovery phase. Significant trend changes of environmental variables under different levels of DO were analyzed for each phase using the Mann-Kendall non-parametric test. On the basis of evaluating the overall trend of the time series, a GAM multi-factor optimization model integrating interactive effects was constructed to explore the response mechanism of environmental variables to hypoxic processes. The optimized model showed excellent explanatory performance with R2 values of 0.833 for the stable and decay phase and 0.932 for the recovery phase, with AIC values of 1554.72 and 721.03, respectively. The trend test combined with model analysis indicates that: (1) the decay of DO under the ice is primarily affected by the increase in EC, BGA, and EC*Temp, (2) the phytoplankton biomass in shallow lakes during winter has a definite contribution to the occurrence of oxygen deficiency, and (3) the water body experiences rapid reoxygenation after the ice layer breaks, but the DO level is restricted by the increase in temperature. This study highlights the ecosystem characteristics of shallow ice-covered lakes in cold arid regions, advancing our understanding of the response relationship between hypoxic aquatic environments under ice and environmental factors.

Acute copper stress showed toxic effects on the physiological metabolism of Ulva lactuca, a common green macroalgae

The pollution by heavy metals in coastal waters has gradually intensified due to industrial development. In this study, physiological responses of Ulva lactuca, one of the most common green seaweeds with important ecological and economic value in the global intertidal zone, to acute copper stress were investigated. Results showed that an increase in copper ions concentration significantly inhibited photosynthetic activity and inorganic nitrogen utilization by U. lactuca but, increased its respiration. Copper stress limited the activity and gene expression of enzymes related to carbon and nitrogen assimilation of U. lactuca. Under moderate copper stress, U. lactuca had higher soluble carbohydrate and soluble protein contents, whereas under high copper stress, these components decreased sharply. Copper stress increased malonaldehyde content, and relative electrical conductivity in U. lactuca, but changes in antioxidant enzyme activities were not significant and even slightly decreased. Moreover, the contents of 8-hydroxy-deoxyguanosine and polyADP ribose polymerase in U. lactuca increased by high Cu2+ concentration culture, indicating that oxidative damage caused by high Cu2+ level involved its DNA damage and interfered with DNA repair in the alga. Copper stress seemed to be more damaging to the carbon assimilation process of U. lactuca, resulting in weakened resistance to copper stress and lower growth rate. This reflected the threat of coastal high copper stress to intertidal biodiversity. This provided ecological reference for the assessment of offshore heavy metal pollution represented by copper.

Landscape transition-induced ecological risk modeling using GIS and remote sensing techniques: a case of Saint Martin Island, Bangladesh

Uncontrolled human activity and nature are causing the deterioration of Saint Martin Island, Bangladesh's only tropical island, necessitating sustainable land use strategies and ecological practices. Therefore, the present study measures the land use/cover transition from 1974 to 2021, predicts 2032 and 2042, and constructs the spatiotemporal features of the Landscape Ecological Risk Index based on land use changes. The study utilized Maximum Likelihood Classification (MLC) on Landsat images from 1974, 1988, 2001, 2013, and Sentinel 2B in 2021, achieving ≥ 80% accuracy. The MLP-MC approach was also used to predict 2032 and 2042 LULC change patterns. The eco-risk index was developed using landscape disturbance and vulnerability indices, Bayesian Kriging interpolation, and spatial autocorrelations to indicate spatial clustering. The research found that settlements increased from 2.06 to 28.62 ha between 1974 and 2021 and would cover 41.22 ha in 2042, causing considerable losses in agricultural areas, waterbodies, sand, coral reefs, and vegetation. The area under study showed a more uniform and homogenous environment as Shannon's diversity and evenness scores decreased. The ecological risk of Saint Martin Island increased from 4.31 to 31.05 ha between 1974 and 2042 due to natural and human factors like erosion, tidal bores, population growth, coral mining, habitat destruction, and intensive agricultural practices and tourism, primarily in Nazrul Para, Galachipa, and Western Dakhin Para. The findings will benefit St. Martin Island stakeholders and policymakers by providing insights into current and potential landscape changes and land eco-management.

Will climate change cause Sargassum beds in temperate waters to expand or contract? Evidence from the range shift pattern of Sargassum

Understanding the range shift patterns of foundation species (e.g., macroalgae) under future climatic conditions is critical for biodiversity conservation in coastal ecosystems. These predictions are typically made using species distribution models (SDMs), and severe habitat loss has been predicted for most brown algal forests. Nevertheless, some models showed that local adaptation within species can reduce range loss projections. In this study, we used the brown algae Sargassum fusiforme and Sargassum thunbergii, which are distributed in the Northwest Pacific, to determine whether climate change will cause the Sargassum beds in Northwest Pacific temperate waters to expand or contract. We divided S. fusiforme and S. thunbergii into northern and southern lineages, considering the temperature gradients and phylogeographic structures. We quantified the realized niches of the two lineages using an n-dimensional hypervolume. Significant niche differentiation was detected between lineages for both species, suggesting the existence of local adaptation. Based on these results, lineage-level SDMs were constructed for both species. The prediction results showed the different responses of different lineages to climate change. The suitable distribution area for both species was predicted to move northward, retaining part of the suitable habitat at low latitudes (along the East China Sea). Unfortunately, this expansion could not compensate for losing middle-low latitude areas. Our results have important implications for the future management and protection of macroalgae and emphasize the importance of incorporating intraspecific variation into species distribution predictions.

Development and analysis of a geospatial database for maritime spatial planning in Bangladesh

In this research we collect, prepare and analyze a geospatial database of maritime activities located in the northern Bay of Bengal with the final aim to simulate maritime spatial planning (MSP) - ready information source for future sectoral and multi-sector MSP in Bangladesh. The database is composed of 28 anthropogenic and environmental layers categorized into seven Blue Economy sectors. The database is analyzed with a set of geospatial models aimed at understanding the intensity distribution of human activities at sea and the potential marine use conflicts emerging from the aggregation of human activities. Ecological resources were characterized in terms of marine mammals, lobsters, commercially important and threatened fish species, and pelagic birds and mapped as biodiversity hotspots using geographic cluster analysis. Results show that the most intensely used sea areas are located along the northeastern coast of Bangladesh, as well as in the Swatch of No Ground (SoNG) area, with maximum Marine Use Intensity (MUI) scores ranging from 5 to 8. Offshore waters of Saint Martin's Island have higher MUI scores (≥ 5) as well. The pairwise spatial conflict analysis shows that nature protection sites particularly SoNG Marine Protected Area (MPA), Nijhum Dwip Marine Reserve (MR), and Saint Martin's Island MPA are exposed to the high Marine Use Conflicts (MUC) induced by fishing and shipping activities. Fishing operations generate the highest MUC value (MUC = 30) in SoNG MPA, whereas shipping activities produce the highest MUC value (MUC = 24) in Nijhum Dwip MR. Both of the MPAs exhibit 6 to 12 MUC scores induced by shipping. The proposed database together with the illustrated analytical techniques used in this study and key findings can provide the first understanding of the priorities for Ecosystem Based Management of Bangladesh's marine space and provide valuable insights on the urgency for MSP process in the country. The study concludes with an outlook on the utility of the database for future analysis.

Seaweeds for the sustainable blue economy development: A study from the south east coast of Bangladesh

Bangladesh is a maritime country with an area of 118000 km² which supports a large number of commercially important species. Currently seaweeds are considered as important component of blue economy development in Bangladesh and farming is practiced at small scale level (Hypnea spp, Caulerpha reacemosa, Gelidium sp. are cultured). For the expansion of the seaweed farming in Bangladesh, a complete understanding of social and economic status of current farmers is important. However, information on socio-economic status of seaweed industry in Bangladesh is very limited. Therefore, this study aimed to understand existing culture methods and their cost, marketing channel and problems with seaweed farming in south east coast of Bangladesh. We used questionnaire survey and focus group discussions to collect data from seaweed farmers, researchers, local community and entrepreneurs. The study found that farmers are currently practicing long-line and horizontal net methods for the seaweed farming in the south east coastal region. The study also found that these culture methods are economically profitable. Seaweeds are currently sold locally and a proper value chain for seaweed marketing is still missing. Existing seaweed farmers are facing the problems related to insufficient credits for starting seaweed farming, lack of proper guidelines for farming and processing of harvested seaweed. This study suggests that for industrial level expansion of seaweed production in Bangladesh a proper value chain, development of seaweed derived products, farm monitoring systems, smooth seed supply and information hubs are required.