Decadal Changes in Mangrove Extent, Structure, and Anthropogenic Pressures at a Southern Range Limit

Avicennia marina (Forrsk.) Vierh. was planted in 1969 at Nahoon Estuary, East London, followed a few years later by the planting of Bruguiera gymnorrhiza (L.) Lam. and Rhizophora mucronata (L.) among the larger A. marina trees. This study tested the hypothesis that mangroves have expanded and replaced salt marsh over a 33-year period (1978–2011). It provides important information on mangroves growing at higher latitudes, where they were thought to not occur naturally due to lower annual average temperatures. It further provides insights on future scenarios of possible shifts in vegetation types due to climate change at one of the most southerly distribution sites worldwide. The expansion of mangroves was measured using past aerial photographs and Esri ArcGIS Desktop 10 software. In addition, field surveys were completed in 2011 to determine the population structure of the present mangrove forest and relate this to environmental conditions. The study showed that mangrove area cover increased linearly at a rate of 0.06 ha y−1, while the salt marsh area cover also increased (0.09 ha y−1) but was found to be variable over time. The mangrove area is still relatively small (<2 ha) and expanded mostly over a bare sandflat area. Avicennia marina was the dominant species and had high recruitment (seedling density was 33 822 ± 16 364 ha−1). Only a few Bruguiera gymnorrhiza and Rhizophora mucronata individuals were found (<10 adult trees), although observations indicate that some young plants are becoming established away from the parent plants. The site provides opportunities for studies on mangrove/salt marsh interactions in response to a changing climate. Mangroves should not be planted in non-native areas as they may become invasive outside their natural range. However, future increases in temperature will certainly lead to a southerly expansion of mangoves in South African estuaries.

1. Rock climbing enjoys enormous popularity world-wide. As a consequence, the anthropogenic pressure on the vegetation of formerly undisturbed cliff ecosystems is continuously increasing. 2. The impact of rock climbing on population structure and genetic variation of the rare plant species Draba aizoides was investigated representatively for many other typical central European cliff plants. Populations from eight climbed and from eight pristine cliffs were compared through the use of vertical transect analyses and molecular markers. 3. Population structure differed between climbed and pristine cliffs. Individuals of D. aizoides were significantly smaller and less frequent on climbed compared with pristine cliffs. On plateau sites, the species’ occurrence was unaffected by climbing activities; it was significantly less frequent on the faces, but more frequent on the tali of climbed in comparison with pristine cliffs. 4. Genetic variation was greater in populations from climbed compared with pristine cliffs, and genetic differentiation was stronger between subpopulations from pristine cliffs than between subpopulations from climbed cliffs. 5. Synthesis and applications. Rock climbing clearly affects population structure and genetic variation of D. aizoides. Seed dispersal is presumably enhanced by rock climbers but climbers remove and drop plant individuals from cliff faces, which causes a downward shift in population structure. This shift in turn reduces genetic differentiation between upper and lower subpopulations. In mountain regions that attract sport climbing, conservation management plans should therefore always ensure the provision of completely unclimbed cliffs to protect the native vegetation.

Dynamics of mangrove forests in Shenzhen Bay in response to natural and anthropogenic factors from 1988 to 2017

Abstract. Candraningtyas CF, Hafiffah AS, Widowati D, Mardiyanto MB, Saputri AB, Setyawan AD. 2024. Spatial and temporal dynamics of mangrove cover change in five estuaries along the North Coast of Central Java, Indonesia (2014-2024). Intl J Bonorowo Wetlands 15: 40-48. Mangrove ecosystems are critical coastal habitats that provide essential ecological services, including shoreline protection, carbon sequestration, and biodiversity support, yet they are increasingly threatened by anthropogenic pressures. This study investigates spatial and temporal changes in mangrove cover from 2014 to 2024 across five estuaries along the north coast of Central Java, Indonesia—Sriwulan, Pemali, Comal, Bodri, and Cisanggarung—using Landsat 8 satellite imagery processed via Google Earth Engine and ArcGIS. Mangrove extents were manually digitized and classified into zones of loss, gain, and stability, with field surveys and photographic documentation employed for validation. Results revealed significant mangrove loss in Sriwulan (-47.03%), Cisanggarung (-50.00%), Comal (-11.31%), and Bodri (-1.59%), driven by land conversion for aquaculture and settlements, destructive fishing practices, and hydrological disruptions. In contrast, the Pemali Estuary exhibited a notable 79.83% increase in mangrove cover, primarily due to sediment accretion and community-led restoration efforts, especially silvofishery-based rehabilitation. The study demonstrates that integrating remote sensing with ground truthing is a robust approach for monitoring mangrove dynamics and identifying localized drivers of change. The contrasting trends across estuaries highlight the heterogeneity of coastal ecosystem responses and underscore the importance of site-specific management strategies. While some estuaries face continued degradation, others show promising signs of recovery, illustrating both the challenges and potential in mangrove conservation. These findings emphasize the urgent need for adaptive coastal management that incorporates ecological monitoring, sustainable land-use planning, and active community participation. As mangrove loss continues globally, this research provides important insights into effective restoration and protection strategies for tropical estuarine environments, offering a model for balancing development and conservation in similar socio-ecological settings across Southeast Asia.

A population experiment with Daphnia magna tested the hypothesis that short-term feeding inhibition provokes a shift in population structure that will vary with conspecific pressure (e.g., pressure occurring from individuals of the same species due to competition for food and space) and increases population sensitivity to a xenobiotic exposure due to size-dependent toxicity (e.g., decreasing sensitivity with increasing body length). Populations were exposed for one week to a feeding inhibitor (imidacloprid, 0.15 or 12.0 mg/L) followed by one week of recovery and one day of exposure to an acute toxin (carbaryl, 0.0098 mg/L). Identical exposure under low and high conspecific pressure was studied by delaying the start of exposure for half of the populations by two weeks; thus populations were in a different stage of population development when exposure occurred. Feeding inhibition of 97% (12.0 mg/L imidacloprid) caused a shift in population structure toward smaller individuals but also reduced population abundance by up to 56 ± 7% with a strong influence of conspecific pressure. Increased population sensitivity to carbaryl was observed after feeding inhibition of 97% as hypothesized. Carbaryl exposure for one day resulted in population decline of up to 23 ± 6% when populations were not previously exposed to imidacloprid. Identical carbaryl exposure provoked a four times stronger decline in population abundance when exposure occurred following feeding inhibition of 97%. In conflict with the hypothesis, this was at least in part due to changes in the reproductive strategy of daphnids following exposure to imidacloprid rather than driven by the shift in population structure. The differences in population sensitivity to additional stress (carbaryl) occurring one week after feeding inhibition caused by exposure to imidacloprid adds a further challenge to understanding potential impacts from multiple stressors as occurring in the field at the population level.

Abstract: Recent satellite imagery analysis in the Eastern Leyte province indicates significant growth in mangrove forests following the destruction of approximately 86% of these forests during Typhoon Yolanda (Haiyan) in 2013. However, there are no studies that explore the process of mangrove expansion in the region and the factors influencing its growth. This study aims to investigate and analyze the climatological and anthropogenic factors contributing to the expansion of mangrove forests in the area. Using the mangrove index derived from Sentinel-2A satellite imagery, a percentile-based threshold segmentation was applied to classify and identify mangrove extent. Annual mangrove area data from 2017 to 2023 were calculated and correlated with climatological variables and anthropogenic factors. The result of the analysis shows a strong positive correlation between mangrove coverage and sea level with a variance of r2=0.90 and α&lt;0.001 which is statistically significant. The relationship of the population to the mangrove coverage shows the model has a variance of r2=0.64 and α=0.030. In contrast, the rainfall shows a very weak and has no significant relationship with the mangrove coverage with a variance of r2= 0.022 and α=0.05. The findings reveal the significant role of sea level and population in the mangrove expansion. This study provides significant insights into accurate rehabilitation plans and strategies for mangrove preservation and conservation in the province.

Awareness of the significant benefits of mangroves to human lives and their role in regulating environmental processes has increased during the recent decades. Yet there remains significant uncertainty about the mangrove change trajectories and the drivers of change at national scales. In Colombia, the absence of historical satellite imagery and persistent cloud cover have impeded the accurate mapping of mangrove extent and change over time. We create a temporally consistent Landsat-derived dataset using the LandTrendr algorithm to track the historical land cover and mangrove conversion from 1984-2020 across Colombia. Over this period, mangrove extent decreased by ~48.000ha (14% of total mangrove area). We find a gradual reduction of mangrove extent along the Pacific coast since 2004, whereas, in the Caribbean, mangrove cover declined around during 1984-1988 and also after 2012. Our time-series analysis matches with drivers of mangrove change at three local sites. For instance, hydroclimatic events, dredging activities, and high sediment loads transported by the rivers have collectively improved mangrove recovery in some sites. In contrast, human activities pressure linked to agricultural expansion and road construction have degraded mangroves. The transition from dense mangrove to other vegetation types is the most significant conversion affecting mangrove cover in Colombia, impacting an area of 38,469 ± 2,829 ha. We anticipate increased mangrove loss, especially along the Pacific coast, resulting from intensified human activity. Prioritization of conservation areas is needed to support local institutions, maintain currently protected areas, and develop strategies (e.g. payment for ecosystem services) to preserve one of the most pristine mangrove regions in the Western Hemisphere.

Anthropogenic disturbances, such as illegal harvesting and livestock browsing, often affect natural forests. However, the resulting tree species diversity, composition, and population structure have rarely been quantified. We assessed tree species diversity and importance value indices and, in particular, Balanites aegyptiaca (L.) Del. population structure, across 100 sample plots of 25 m × 40 m in disturbed and non-disturbed sites at the Dinder Biosphere Reserve, Sudan, from April 2019 to April 2020. We found that the tree species diversity in non-disturbed sites was more than double that of disturbed sites (p < 0.001, T = 32.6), and seedlings and saplings comprised more than 72% of the entire tree population (F2,48 = 116.4, p = 0.034; F2,48 = 163.2, p = 0.021, respectively). The tree density of B. aegyptiaca in the disturbed site was less than half that of the non-disturbed site (p = 0.018, T = 2.6). Balanites aegyptiaca was seven times more aggregated in disturbed sites compared to more regularly spaced trees in non-disturbed sites (T = 39.3 and p < 0.001). The poor B. aegyptiaca population status of the disturbed site shows that the conservation of this vulnerable species is essential for a sustainable management and utilization scheme.

Transitions in Ancient Inland Freshwater Resource Management in Sri Lanka Affect Biota and Human Populations in and around Coastal Lagoons

Mangrove habitats are crucial for maintaining the biodiversity of coastal ecosystem. Climatic change, sea level rise and anthropogenic pressures are the major threats to mangrove forests. The Nicobar Islands comprised one of the pristine mangrove stands in India. The mega earthquake of &gt;9 M and subsequent tsunami during 2004 caused destruction of over 70% of mangrove vegetation in Nicobar Islands. The present study was carried out in the Central Nicobar Group of Islands (Camorta, Nancowry, Katchall and Trinkat), where tsunami has entirely wiped out the mangrove vegetation. Re-colonization started on its own course. We enumerated nine species of mangrove plants and 30 species of mangrove associates from the surveyed locations. Lumnitzera racemosa has been recorded for the first time from the study area. Rhizophora mucronata and Bruguiera gymnorrhiza were the common pioneer mangrove species. Long-term monitoring of re-colonization process will help us in understanding succession of mangrove forests.

Mangrove trees are continuously under stress due to environmental and/or anthropogenic pressures, which expose them to attack by pathogens, compromising their survival. Ophiostomatoid fungi cause sap stain and diseases of a wide spectrum of tree species globally. These fungi infect trees through natural, insect, animal and/or human made wounds. During routine surveys of mangrove trees in South Africa, wounds on branches and stems of Avicennia marina were regularly monitored for the presence of ophiostomatoid fungi at ten study sites in the country. The stems of four mangrove species, A. marina, Bruguiera gymnorrhiza, Rhizophora mucronata and Barringtonia racemosa were also wounded and evaluated for the appearance of these fungi. Ophiostomatoid fungi were obtained from the mangrove associate B. racemosa, but not from any of the true mangroves. Analyses of DNA sequence data for the internal transcribed spacer, β-tubulin, calmodulin and translation elongation factor gene regions revealed that the fungi isolated from the wounds on B. racemosa belong to three species in the Ophiostomataceae, including a new taxon described here as Ophiostoma palustre sp. nov. These results suggest that the mangrove associate B. racemosa is more prone to colonization by ophiostomatoid fungi than the true mangroves.

13 - Measuring the vulnerability of coastal ecosystems in a densely populated west coast landscape, India: a remote sensing perspective

The research aimed at monitoring the condition of mangrove communities in Batanta Island and Salawati Island, Raja Ampat District, West Papua Province. It used method developed by the Indonesian Institute of Sciences Research Center for Oceanography (P2O LIPI). Method in determining the percentage for the coverage of mangrove communities used a hemispherical photography and the data analysis used ImageJ software in excel tabulation. The result showed that mangrove canopy coverage has decreased from 85.73% in 2017 to 84.14% in 2018. Since the observations in 2015, the percentage of mangroves had no significant change. In average the percentage increased as much as 3.45% from 75.09% in 2015 to 78.54% in 2016. Moreover, it increased again by 7.20% in 2017 (85.73%). It indicates that the average change percentage of mangroves is not significant, and it can be concluded that the mangrove ecosystem in this area does not degrade significantly and has a good growth rate. The average density value was 1254.3 trees per hectare in the period of 2016-2018 or it increased to about 16.5% since 2015. The number of species found at the observation site were 5 species (Rhizophora mucronata, Rhizophora apiculata, Bruguiera gymnorrhiza, Sonneratia alba, and Xylocarpus granatum) scattered in eight observation stations. From these results it can be concluded that mangrove condition at the research location is stable and gets support for the survival of biota associated therein.

The mangrove communities along the coastline of the former Transkei, now part of the Eastern Cape Province, have not been looked at in detail since Ward and Steinke’s survey in 1982. Mangroves previously occurred in 17 estuaries but were now found in only 14 of the 76 estuaries visited, with a complete loss of mangroves evident in the Mnyameni, Mzimvubu and Bulungula estuaries amounting to 7.5 ha. Total mangrove loss amounted to 17.6 ha which represents a 6.5% loss over 17 years or 1.04 ha per annum. Tree cover had increased by 16.15 ha in eight other estuaries. This increase could be attributed to the inaccessibility of mangrove stands or to protection afforded by provincial nature reserves and hotel resorts. No new mangrove stands were recorded, although Steinke (pers. comm.) has recently recorded mangroves along the north bank of the Kei River. There has been little change in mangrove species composition in the different estuaries over the past 17 years. Total mangrove loss amounted to 17.6 ha which represents a 6.5% loss over 17 years or 1.04 ha per annum and the species recorded included Avicennia marina, Bruguiera gymnorhiza and Rhizophora mucronata. The mangrove fern Acrostichum aureum L. was recorded for the first time in the Mkozi estuary. Tree density for all estuaries was between 10 and 2594 trees ha−1. The Mngazana and Mntafufu estuaries had the highest tree densities of 2594 and 1402 trees ha−1 respectively, typical of riverine mangrove forests. Fringe mangroves were evident in most other systems. Removal of trees for wood has the greatest impact on mangrove cover. Fringe mangrove stands are particularly accessible to harvesters. Only 6% of the current area of trees is afforded some protection in conservation areas. The Mdumbi, Mzamba and Kobonqaba estuaries receive no conservation protection and harvesting has resulted in more than 50% of the trees being removed. The density of dead tree stumps was greater than the number of living trees and no seedlings or juvenile trees were found. Further removal of mangroves within the estuaries south of the Mzimvubu River is expected in the fringe mangroves, as most are unprotected and easily accessible.

Minaluli Village has the availability of mangrove ecosystem resources in coastal areas. The availability of evenly distributed mangrove ecosystems can have a direct impact on the community. Determination of mangrove status conducted previously using conventional methods such as transect quandrat and spot check. Hemispherical photography method is one of the new methods used and developed in Indonesia. The study was conducted in July 2018 in Minaluli Village, North Mangoli District, Sula Islands Regency. North Maluku Province. The research objective is to obtain information on the condition of the mangrove ecosystem using the Hemispherical photography method. The results of the study obtained measurements of environmental parameters showed that environmental ecological conditions support the existence of mangroves. Morphological identification was obtained as many as 8 species from 3 families. Station I found 82% mangrove cover presentation value, for station II found 77% cover presentation, at station III found a presentation found 78% while at station IV found a presentation of mangrove cover 72%. The total presentation of mangrove cover obtained in the solid category, based on the standard criteria for mangrove damage. The density of the mangrove ecosystem obtained shows high density at each station. Based on the standard criteria for damage, the density of mangroves in this location is in the medium to very dense category with a value range between 1,067-2,022 trees / ha. Important value index (INP) analysis of each type of mangrove found a range of values ​​between 31.73-95.55 The highest value index of the highest species was found in the Rhizophora stylosa type with a value of 95.55% then Rhizophora apiculata with a value of 95.08%, Rhizophora mucronata namely 81.05%, Xylocarpus granatum is 45.68, Ceriops stagal with value of 40.83%, Sonneratia alba with a value of 36.27 and Bruguiera gymnorhiza 31.73%.