Tropical Coasts Research Articles

The plastic homes of hermit crabs in the Anthropocene

Plastic is the most pervasive element of marine waste, with harmful impact on wildlife. By using iEcology (i.e., internet Ecology, use of online data sources as a new tool in ecological research), we report on the emergence of a novel behaviour in hermit crabs related to the use of plastic or other anthropogenic materials as protective shells. We analysed images posted on social media to identify 386 individuals with artificial shells — mainly plastic caps (85 %). We report that 10 of the world's 16 terrestrial hermit crabs use artificial shells, a behaviour observed on all of the Earth's tropical coasts. Four non-exclusive mechanisms may drive individual choice for artificial shells: sexual signaling, lightness of artificial shells, odour cues, and camouflage in a polluted environment. Further research is needed to determine the impact of this behaviour on hermit crab evolutionary trajectories.

Anthropogenic debris pollution in peri-urban mangroves of South China: Spatial, seasonal, and environmental drivers in Hong Kong

Excessive mismanaged debris along tropical coasts pose a threat to vulnerable mangrove ecosystems. Here, we examined the spatial, seasonal and environmental drivers of anthropogenic debris abundance and its potential ecological impact in peri-urban mangroves across Hong Kong. Seasonal surveys were conducted in both landward and seaward zones, with identification, along belt transects, of macrodebris (>5 mm) based on material type and use. Our results indicate spatial variability in debris abundance and distribution, with plastic being the predominant material type identified. Both plastic and non-plastic domestic items covered the most surface area. Debris aggregation was highest at the landward zones, consistent with the literature. In the dry season, more debris accumulated and covered greater surface area in both seaward and landward zones. These results confirm that land-derived debris from mismanaged waste, rather than debris coming from the Pearl River, is the primary source of anthropogenic debris pollution threatening Hong Kong's mangroves.

Rise and fall of Caribbean mangroves

Mangrove forests, which are essential for the maintenance of terrestrial and marine biodiversity on tropical coasts and constitute the main blue‑carbon ecosystems for the mitigation of global warming, are among the world's most threatened ecosystems. Mangrove conservation can greatly benefit from paleoecological and evolutionary studies, as past analogs documenting the responses of these ecosystems to environmental drivers such as climate change, sea level shifts and anthropogenic pressure. A database (CARMA) encompassing nearly all studies on mangroves from the Caribbean region, one of the main mangrove biodiversity hotspots, and their response to past environmental shifts has recently been assembled and analyzed. The dataset contains over 140 sites and ranges from the Late Cretaceous to the present. The Caribbean was the cradle of Neotropical mangroves, where they emerged in the Middle Eocene (∼50 million years ago; Ma). A major evolutionary turnover occurred in the Eocene/Oligocene transition (34 Ma) that set the bases for the shaping of modern-like mangroves. However, the diversification of these communities leading to their extant composition did not occur until the Pliocene (∼5 Ma). The Pleistocene (the last 2.6 Ma) glacial-interglacial cycles caused spatial and compositional reorganization with no further evolution. Human pressure on Caribbean mangroves increased in the Middle Holocene (∼6000 years ago), when pre-Columbian societies began to clear these forests for cultivation. In recent decades, deforestation has significantly reduced Caribbean mangrove cover and it has been estimated that, if urgent and effective conservation actions are not undertaken, these 50 million-year-old ecosystems might disappear in a few centuries. A number of specific conservation and restoration applications based on the results of paleoecological and evolutionary studies are suggested.

Are urban mangroves emerging hotspots of non-indigenous species? A study on the dynamics of macrobenthic fouling communities in fringing red mangrove prop roots

Urbanization represents a radical transformation of natural habitats that alters all the biotic and abiotic properties governing ecosystems. Urban expansion often results in oversimplified communities, where most specialists decline or disappear and a few generalist or exotic species become dominant. The consequences of urban expansion in mangrove forests are understudied, although these systems have been altered by humans for centuries and the growth of human population in tropical coasts is expected to be faster than in higher latitudes. To assess the importance of indigenous and non-indigenous species in driving temporal and spatial changes in community structure of red-mangrove prop-root macrobenthic communities, we studied heavily altered mangrove forests from two bays from the Caribbean coast of Colombia in 2005 and 2021. In all places/periods, the community richness was low, a few taxa were dominant (11 taxa, out of 40, comprised ~ 90% of the total abundance) and 35% of those taxa were non-indigenous species whose presence is related with known stressors in urbanized systems. Hence, call for efforts to assess whether urban mangrove forests are emerging as hotspots for non-indigenous biota. Community structure did not change within or between bays, there was a clear, significant turnover of core species between 2005 and 2021, with non-indigenous species playing a prominent role in this variability. This was puzzling—ecological theory asserts that the abundance of a species is related to their permanence: core species are relatively stable through time, while rare species appear or disappear—but this may not apply for stressed communities influenced by non-indigenous biota.

The effect of biochar on mycorrhizal fungi mediated nutrient uptake by coconut (Cocos nucifera L.) seedlings grown on a Sandy Regosol

Biochar amendment of soil may ameliorate inherently infertile soils, such as in the typical coconut (Cocos nucifera L.) growth areas along tropical coasts, where, moreover, temporary moisture stress commonly occurs. We conducted a pot experiment to evaluate the effects of biochar soil amendment (1% w/w) produced from Gliricidia sepium stems (BC-Gly) and rice husks (BC-RiH) on the growth of coconut seedlings and on N and P uptake mediated by mycorrhizae under wet or dry conditions in a Sandy Regosol. The pots were divided into root and hyphal zones by a nylon mesh, where 15N labelled N and P nutrients were only provided in the hyphal zone. Under wet conditions, biochar application did not affect plant growth, while under dry conditions, the BC-Gly increased root and plant growth similar to that under wet conditions. BC-Gly increased the acidic pH of the soil to a neutral level, and the microbial community shifted towards a higher fungal abundance. The P accumulated (Pacc) in roots was higher with BC-Gly and BC-RiH under dry and wet conditions, respectively. Pacc weakly correlated with the abundance of arbuscular mycorrhizal fungi (AMF) in the hyphal zone. With BC-Gly roots showed lower N derived from fertilizer. We conclude that biochar application has no impact on crop growth under wet conditions, while under dry conditions, BC-Gly stimulates crop growth and P uptake, probably through liming induced P availability but also possibly by some enhancement of AMF growth. The shift in the fungal-oriented microbial community and reduced plant fertilizer N uptake suggested that BC-Gly acted as an additional N source.Graphical

Exploring feedback mechanisms for nitrogen and organic carbon cycling in tropical coastal zones

The anthropogenic introduction of significant amounts of reactive nitrogen in the coastal zone particularly since the discovery and application of the Haber-Bosch process has profound consequences over organic carbon storage and transformations at both regional and global scales. Here, we review our current knowledge on cause-effect chains for nitrogen, especially dissolved inorganic nitrogen, on organic carbon cycling in coastal tropical systems. We focus on the feedback mechanisms for turnover of different organic carbon species to nitrogen excess and links to current environmental and climate changes. We pay special attention to organic carbon dynamics in tropical coasts due to their high primary productivity, rapid sedimentation, and significant needs of nitrogen for agriculture and industry usages. Together with land-use changes and economy development, we highlight the vulnerability of carbon storage in tropical coasts triggered by nitrogen overloading and outline possible industrial strategies with low carbon cycling disturbance to benefit the development of tropical countries.

Evolution of coastal forests based on a full set of mangrove genomes.

Genomic studies are now poised to explore whole communities of species. The ~70 species of woody plants that anchor the coastal ecosystems of the tropics, collectively referred to as mangroves, are particularly suited to this exploration. In this study, we de novo sequenced the whole genomes of 32 mangroves, which we combined with other sequences of 30 additional species, comprising almost all mangroves globally. These community-wide genomic data will be valuable for ecology, evolution and biodiversity research. While the data revealed 27 independent origins of mangroves, the total phylogeny shows only modest increases in species number, even in coastal areas of active speciation, suggesting that mangrove extinction is common. A possible explanation for common extinction is the frequent sea-level rises and falls (SLRs and SLFs) documented in the geological record. Indeed, near-extinctions of species with extremely small population size (N) often happened during periods of rapid SLR, as revealed by the genome-wide heterozygosity of almost all mangroves. Reduction in N has possibly been further compounded by population fragmentation and the subsequent accumulation of deleterious mutations, thus pushing mangroves even closer to extinction. Crucially, the impact of the next SLR will be exacerbated by human encroachment into these mangrove habitats, potentially altering the ecosystems of tropical coasts irreversibly.

Comparación de cuatro métodos para contar peces en una bahía tropical: el caso del Área Marina de Manejo Bahía Santa Elena en el Pacífico de Costa Rica

Introduction: Tropical nature is experiencing an unprecedented threat that includes coastal fish communities that requires a close monitoring of species presence. The simultaneous use of several monitoring methods should reduce the bias caused by the selectivity of each method. Objective: This study used four different sampling methods over two years to assess and compare fish assemblages in the Santa Elena Bay Marine Management Area (AMM-BSE), North Pacific of Costa Rica. Methods: We examined changes in species richness and composition between upwelling and non-upwelling seasons from July 2019 and February 2020. We applied visual censuses, underwater remote cameras; bottom lines; and sport fishing. Results: We identified 140 species of fish (54 families); remote underwater cameras detected 83 %, followed by underwater visual censuses (65 %), sport-fishing (16 %) and bottom lines (14 %). Only the sport-fishing method detected differences in species richness and composition between seasons. Conclusion: Remote cameras appear to be the best method for species counts, and sport-fishing to detect seasonal differences in tropical coasts similar to the one studied here.

Characterization of four mitochondrial genomes of family Neritidae (Gastropoda: Neritimorpha) and insight into its phylogenetic relationships

Neritidae is one of the most diverse families of Neritimorpha and possesses euryhaline properties. Members of this family usually live on tropical and subtropical coasts and are mainly gregarious. The phylogenetic relationships between several subclasses of Gastropoda have been controversial for many years. With an increase in the number of described species of Neritidae, the knowledge of the evolutionary relationships in this family has improved. In the present study, we sequenced four complete mitochondrial genomes from two genera (Clithon and Nerita) and compared them with available complete mitochondrial genomes of Neritidae. Gene order exhibited a highly conserved pattern among three genera in the Neritidae family. Our results improved the phylogenetic resolution within Neritidae, and more comprehensive taxonomic sampling of subclass Neritimorpha was proposed. Furthermore, we reconstructed the divergence among the main lineages of 19 Neritimorpha taxa under an uncorrelated relaxed molecular clock.

Ecosystem Based Disaster Risk Reduction at Indian Sundarbans: A Lesson Learned from AMPHAN Supercyclone

Ecosystem based Disaster Risk reduction is the sustainable, green method to minimize cyclone damages at tropical coasts. As a part of a climate change resilience project initiated in 2012, 102 hectare of multispecies mangrove plantation was established at eastern corner of Indian Sundarbans. The AMPHAN supercyclone, have caused immeasurable destruction in the region, between 16-21st May, 2020. This research brings forward the field observations on effectiveness of community managed mangrove plantation in ameliorating disaster impacts. Study revealed that mangrove bio-shield minimized property damage during the cyclone by reducing flooding through earthen embankment stabilization and managing the wind speed, direction.

Effect of waste rubber particles on the shear behaviour of bio-cemented calcareous sand

Calcareous sand, a special type of sand commonly used for the construction of coastal engineering in tropical coasts, is usually required to be strengthened due to its poor engineering mechanical properties. Microbially induced carbonate precipitation has been proved to be a promising method for this purpose. A higher cementation level generally leads to a greater strength enhancement, but tends to cause brittle failure of bio-cemented calcareous sand, which in turn brings great potential risks for the coastal engineering. Therefore, the shear behaviour, especially the brittle behaviour, of bio-cemented calcareous sand needs to be understood properly, and taking some measures to improve its brittle behaviour is also necessary. In this regard, a series of triaxial compression tests were conducted to study the shear behaviour of bio-cemented calcareous sand with various cementation levels, and the waste rubber particles are used to improve the brittle behaviour of bio-cemented calcareous sand. The test results show that the shear strength of bio-cemented calcareous sand increases with the increase in cementation level, and the brittle behaviour is significant gradually. The waste rubber particles contribute to improve the brittle behaviour of bio-cemented calcareous sand, reducing the dilation of bio-cemented calcareous sand and slowing the changes in dilatancy with the increment of stress.

Vegetation Structure and Damage Level Mangrove Forest in Manomadehe Island, Subdistrict South Jailolo, North Maluku Province

Mangrove forest is a natural resource typical of tropical coasts, which has multiple benefits with a very broad impact when viewed from social, economic and ecological aspects. Management of natural resources must be very prudent because it takes a long time to be able to recover when damage / extinction has occurred. The purpose of this study was to determine the composition of mangrove species, the structure of mangrove forest vegetation (species density, relative density of species, frequency of species, relative frequency of species, species cover, relative cover of species and important values) and to determine the level of damage. Extraction of mangrove vegetation using the "spot check" method. The transects are drawn perpendicular to the coastline along the mangrove vegetation. The composition of mangrove species were 7 species, namely Rhizophora apiculata, R. stylosa, Bruguirea gymnorrhiza, Ceriops tagal, Sonneratia alba, Xylocarpus granatum and Aegiceras floridum. In the vegetation structure, the highest density and relative density were found in Rhizophora stylosa and the lowest was Xylocarpus granatum. The highest species and relative frequencies were Rhizophora stylosa, R. apiculata and the lowest were Bruguiera gymnorrhiza. The highest type and closure were Sonneratia alba and the lowest was Ceriops tagal. Meanwhile, the highest importance was in Sonneratia alba and the lowest was Xylocarpus granatum. Overall, the density value of mangrove species on Manomadehe Island is 2796 trees / ha so that the condition of the mangrove forests on Manomadehe Island is still in the good category (very dense).

Functional Role of Mangrove Forests Along the Subtropical and Tropical Coasts of China

Mangroves forests inhabiting the south coast of China are crucial habitats for the functioning of the coastal zone. This role has not been carefully considered in China and compared to their functional role worldwide. China’s mangroves currently occupy 20,303 ha. Average forest biomass is equivalent to the global average, but the mean ratio of below-ground to above-ground biomass is high (46%), reflecting the young age of most forests. Rates of annual litterfall, net primary productivity, and root production are above the global average, indicating that China’s mangrove forests are highly productive within their latitudinal band. High productivity may reflect high rates of organic inputs, young forest ages, and high rates of precipitation. As China’s mangrove forests have short canopies, these data imply that the rates of forest turnover are more rapid than in most other mangroves. Mangrove organic carbon (C<sub>org</sub>) stock averaged 190.96 Mg C<sub>org</sub> ha<sup>-1</sup>, mostly (58%) in soils, less than the global average, reflecting young forest age and frequent soil disturbance. Total C<sub>org</sub> stored in China’s mangroves is 3.9 Tg, only 0.03% of the global total, but the total C<sub>org</sub> sequestration rate is 139.4 Gg C<sub>org</sub> a<sup>-1</sup> while the average C<sub>org</sub> sequestration rate is 6.87 Mg C<sub>org</sub> ha<sup>-1</sup> a<sup>-1</sup>, which is greater than the global average. C<sub>org</sub> losses via microbial mineralization are large as total C<sub>org</sub> export from mangroves accounts for 44% of the total C<sub>org</sub> exported to the South China Sea. Nutrients are efficiently retained suggesting their use and proper management as aquaculture filters. Mangroves have close links to other coastal food webs.

WAVES ON REEFS: HOW CORAL REEFS TRANSFORM OCEAN WAVES AND HELP PROTECT COASTS

Coral reefs help protect tropical islands and coasts against wave-induced flooding. Because ongoing population growth in coastal zones, sea level rise and coral reef degradation, flooding and subsequent damages will likely increase in the future. In this presentation we discuss our current knowledge of the physics of wave transformation on reefs derived from observations and modelling. We will also discuss research questions and data needs.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/JvTmDnoy8E0

Niche Differentiation of Active Methane-Oxidizing Bacteria in Estuarine Mangrove Forest Soils in Taiwan.

Mangrove forests are one of the important ecosystems in tropical coasts because of their high primary production, which they sustain by sequestering a substantial amount of CO2 into plant biomass. These forests often experience various levels of inundation and play an important role in CH4 emissions, but the taxonomy of methanotrophs in these systems remains poorly understood. In this study, DNA-based stable isotope probing showed significant niche differentiation in active aerobic methanotrophs in response to niche differentiation in upstream and downstream mangrove soils of the Tamsui estuary in northwestern Taiwan, in which salinity levels differ between winter and summer. Methylobacter and Methylomicrobium-like Type I methanotrophs dominated methane-oxidizing communities in the field conditions and were significantly 13C-labeled in both upstream and downstream sites, while Methylobacter were well adapted to high salinity and low temperature. The Type II methanotroph Methylocystis comprised only 10–15% of all the methane oxidizers in the upstream site but less than 5% at the downstream site under field conditions. 13C-DNA levels in Methylocystis were significantly lower than those in Type I methanotrophs, while phylogenetic analysis further revealed the presence of novel methane oxidizers that are phylogenetically distantly related to Type Ia in fresh and incubated soils at a downstream site. These results suggest that Type I methanotrophs display niche differentiation associated with environmental differences between upstream and downstream mangrove soils.

<p class="Body"><strong>First report of marine intertidal mites of the family Fortuyniidae (Acari: Oribatida) from Iran, with description of a new species and an updated key to the world’s species of <em>Fortuynia</em></strong></p>

The marine intertidal zone constitutes one of the most interesting ecosystems on the earth. Oribatid mites of the family Fortuyniidae inhabit marine intertidal habitats in the tropical and subtropical coasts of the world. This family has not been known from Iran until now. The present work deals with a new oribatid species of this family found at the coast of the Gulf of Oman, southeastern Iran, from algae in the intertidal zone of a rocky shore. Fortuynia iranica sp. nov., is described from littoral environments of Chabahar Beach, Sistan and Baluchistan province based on adult and juvenile (deutonymph) stages. The new species is characterized by the presence of both prodorsal external and internal channels; fourteen smooth, thin and long notogastral setae, with a light-colored porose spot in the insertions, c3 completely absent; sensilli with a very slightly oriented head; glove-like lenticulus; epimeral setation 3-1-3-2 and presence of one pair of aggenital setae. An updated diagnostic key to the adults of known species of Fortuynia van der Hammen, 1960 is given.

Performance of the winged pearl oyster Pteria sterna (GOULD, 1851), implanted for half-pearl (mabé) production in two size groups

This study generated baseline information relative to overall performance of the winged pearl oyster Pteria sterna implanted at two groups (small and large) for half-pearl (mabé) production. This is a suitable technology to optimize the pearl production in the tropical coasts of Ecuador. The yield and quality of mabé pearl produced, as well as oyster condition index, increase in oyster survival, shell size and mass of tissues, and environmental variables were examined in this study. From 120 oysters used, 65 were of small size (25 nucleated, 25 non-nucleated and 15 for the initial sample; initial average shell length of 64.7 ± 5.3 mm; ~6 months old) and 55 were of large size (20 nucleated, 20 non-nucleated and 15 for the initial sample; 78.0 ± 5.8 shell length cm; ~10 months old). Hemispherical plastic nuclei (12.5 mm base diameter, 7 mm height) were used. All groups of oysters were anesthetized with 1% Eugenol and cultivated for five months (May through October 2017). At the end of the trials, only one dead oyster occurred in the small size group. A high percentage (29.2%) of adductor muscle over-growth on the nuclei occurred in small oysters, probably caused by the relatively fast growth rate (≥8 mm in 5 months). A lower percentage of muscle over-growth on the nuclei (5.6%), thicker nacre deposition, and higher occurrence of regular-shaped mabé pearls were observed in large oysters, compared to small oysters. This study suggests that large oysters (>80 mm) should be preferably used for half-pearl production in P. sterna to ensure the highest quality standards for commercialization.

Convergent adaptation of the genomes of woody plants at the land-sea interface.

Sequencing multiple species that share the same ecological niche may be a new frontier for genomic studies. While such studies should shed light on molecular convergence, genomic-level analyses have been unsuccessful, due mainly to the absence of empirical controls. Woody plant species that colonized the global tropical coasts, collectively referred to as mangroves, are ideal for convergence studies. Here, we sequenced the genomes/transcriptomes of 16 species belonging in three major mangrove clades. To detect convergence in a large phylogeny, a CCS+ model is implemented, extending the more limited CCS method (convergence at conservative sites). Using the empirical control for reference, the CCS+ model reduces the noises drastically, thus permitting the identification of 73 convergent genes with Ptrue (probability of true convergence) > 0.9. Products of the convergent genes tend to be on the plasma membrane associated with salinity tolerance. Importantly, convergence is more often manifested at a higher level than at amino-acid (AA) sites. Relative to >50 plant species, mangroves strongly prefer 4 AAs and avoid 5 others across the genome. AA substitutions between mangrove species strongly reflect these tendencies. In conclusion, the selection of taxa, the number of species and, in particular, the empirical control are all crucial for detecting genome-wide convergence. We believe this large study of mangroves is the first successful attempt at detecting genome-wide site convergence.

How to restore mangroves for greenbelt creation along eroding coasts with abandoned aquaculture ponds

Globally, erosion of muddy tropical coasts that are dominated by aquaculture ponds, is an increasing problem. Restoration of mangrove greenbelts may counteract such erosion, by restoring the sediment balance. Hence, we aim to unravel the processes controlling natural mangrove regeneration in both “landward” (i.e., into aquaculture ponds) and seaward direction, using the fast eroding coastline of Demak (Indonesia) as case study. Firstly, we investigated which physical and chemical factors drive landward mangrove expansion by relating them to the presence/absence of mangrove seedlings in abandoned aquaculture ponds. Secondly, we investigated which physical parameters control seaward mangrove expansion by relating them to expansion and retreat at the sea-side of mature mangrove stands.Landward mangrove expansion into abandoned aquaculture ponds was positively related to both emergence time (%) and sediment stability (i.e., shear strength), which are in turn both associated to bed level elevation and pond drainage. Surprisingly, there was no effect of soil chemistry. Seaward expansion of existing mangrove stands was strongly associated to foreshore morphology. Mangroves only expanded in the presence of an elevated mudflat, whereas the absence of a mudflat in combination with a concave (hollow) profile was associated with mangrove retreat. Our findings suggest that restoration of a mangrove greenbelt can be stimulated landward by improving drainage of abandoned aquaculture ponds. This enhances sediment stability and allows ponds to accrete. Seaward expansion can be induced by restoring foreshore morphology. Present results are discussed in the context of large-scale applications.

Mudskippers in the Mekong Delta might tell us something about vertebrate transition to land?

Rise of vertebrates from water to land, which seems to be occurred in the mid to late Devonian Period (about 390 to 360 million years ago), shows one of the most crucial events throughout the existence of life [1]. There are many longstanding debates about emergence of vertebrates in the Paleozoic from marine environment or freshwater environments [2-6]. Through our four-year survey in the field in the place called Mekong Delta which is situated in Vietnam, we explored mudskippers a special species, Periophthalmodon septemradiatus, which inhabits the littoral zones in brackish waters near the coast of fully freshwater areas 150 km from the river mouth along the Mekong River [7]. Mudskippers which are amphibious gobies which usually inhabits intertidal mudflats from estuaries, subtropical coasts and tropical coasts and shows behavioral, physiological and morphological adaptations of life on land [8]. The most terrestrial fishes named Periophthalmodon septemradiatus are living today. During the period of our field survey, we have not seen any P. septemradiatus ventures into water. The substantial portal of gut content of this fish is constituted by ants, further supporting the high terrestriality of the fish