Functional Traits of Terrestrial Plants in the Intertidal: A Review on Mangrove Trees.

AbstractTrue mangroves are vascular plants (Tracheophyta) that evolved into inhabiting the mid and upper intertidal zone of tropical and subtropical soft-sediment coasts around the world. While several dozens of species are known from the Indo-West Pacific region, the Atlantic-East Pacific region is home to only a mere dozen of true mangrove species, most of which are rare. Mangrove trees can form dense monospecific or multispecies stands that provide numerous ecosystem services. Despite their eminent socioecological and socioeconomic relevance and the plethora of studies on mangroves, many details of the ecology of mangrove ecosystems remain unknown; and our knowledge about general ecological principles in mangrove ecosystems is scarce. For instance, the functional trait concept has hardly been applied to mangroves. Here we provide an inventory of 28 quantitative and 8 qualitative functional traits of true mangrove species and stipulate some insight into how these traits may drive ecosystem structure and processes. The differentiation between true mangroves and mangrove associates, which can dwell inside as well as outside mangrove forests, is reflected by a number of leaf traits. Thus, true mangroves exhibit lower specific leaf area, lower leaf N content, and lower K∶Na ratio, and higher leaf succulence, higher Na and Cl content, and higher osmolality than mangrove associates. True mangrove species that form pure stands produce larger leaves and exhibit higher N content per leaf area, higher leaf K and Ca content, greater maximum plant height, longer propagules, and lower root porosity than more sporadic species. The species-specific expression of most traits does not reflect the species' position along intertidal gradients, suggesting that adaptation to tidal inundation does not explain these traits. Rather, many of the traits studied herein exhibit strong phylogenetic signals in true mangroves. Thus, wood density is high in most species of the Rhizophoraceae, irrespective of their habitat or maximum height. On the other hand, species of the genus Sonneratia exhibit low wood density and do not grow taller than 20 m. Some leaf traits of true mangroves are more like those of plants from drier environments, reflecting the perception that a saline environment creates physiological drought stress. Along the same line, most true mangrove species exhibit sclerophyllous leaf traits. The few major mangrove tree species of the Atlantic-East Pacific are as distinct from each other, with regard to some traits, as are the many mangrove species of the Indo-West Pacific. We hypothesize that this phenomenon explains the similarly high biomass of mangrove forests in both the species-rich Indo-West Pacific and the species-poor Atlantic-East Pacific.

A DNA barcode library for mangrove gastropods and crabs of Hong Kong and the Greater Bay Area reveals an unexpected faunal diversity associated with the intertidal forests of Southern China.

BACKGROUND: Mangroves are tropical and subtropical intertidal forests colonising sheltered coasts across the world. They host a unique faunal community, dominated by brachyuran crabs and gastropods. These invertebrates strongly contribute to the functionality of the entire forest. The reliable assessment of mangrove faunal diversity is, thus, a crucial step for efficient management and conservation plans, but it is hindered by difficulties in species identification. Here we provide a verified DNA barcode library for brachyuran crabs and gastropods inhabiting the mangroves of the Greater Bay Area, Southern China. In particular, we collected and morphologically identified 1100 specimens of mangrove associated brachyuran crabs and gastropods. The partial sequences of the mtDNA cytochrome oxidase subunit I gene were obtained from 275 specimens. Barcode sequences were then used to delineate Molecular Operational Taxonomic Units (MOTUs), employing three different delimitation methods: the automatic barcode gap discovery (ABGD) method, the general mixed Yule coalescent (GMYC) model and a Bayesian implementation of the Poisson tree processes (bPTP) model. RESULTS: By integrating DNA barcodes with morphology, we identified 44 gastropod species and 58 brachyuran species associated with Hong Kong mangroves, with five and seven new records, for gastropods and crabs, respectively, for the Greater Bay Area. The delineation of MOTUs based on barcode sequences revealed a strong congruence between morphological and molecular identification for both taxa, showing the high reliability of the barcode library. CONCLUSIONS: This study provides the first reference barcode library for mangrove-associated macrobenthic fauna in the Greater Bay Area and represents a reliable tool to management and conservation plans. Our molecular analyses resolved long lasting taxonomic misidentifications and inconsistencies and updated the knowledge on the geographical distribution of Asian mangrove associated fauna, ultimately highlighting a level of biodiversity higher than previously thought for Southern China.

Prokaryotic and microeukaryotic communities in an experimental rice plantation under long-term use of pesticides.

Conventional agricultural practices, such as rice plantations, often contaminate the soil and water with xenobiotics. Here we evaluated the microbiota composition in experimental rice planting with a record of prolonged pesticide use, using 16S and 18S rRNA amplicon sequencing. We investigated four components of a complete agricultural system: affluent water (A), rice rhizosphere soil (R), sediment from a storage pond (S), and effluent (E) water (drained from the storage pond). Despite the short spatial distance between our sites, the beta diversity analysis of bacterial communities showed two well-defined clusters, separating the water and sediment/rhizosphere samples; rhizosphere and sediment were richer while the effluent was less diverse. Overall, the site with the highest evenness was the rhizosphere. Unlike the bacterial communities, Shannon diversity of microeukaryotes was significantly different between A and E. The effluent presented the lowest values for all ecological indexes tested and differed significantly from all sampled sites, except on evenness. When mapped the metabolic pathways, genes corresponding to the degradation of aromatic compounds, including genes related to pesticide degradation, were identified. The most abundant genes were related to the degradation of benzoate. Our results indicate that the effluent is a selective environment for fungi. Interestingly, the overall fungal diversity was higher in the affluent, the water that reached the system before pesticide application, and where the prokaryotic diversity was the lowest. The affluent and effluent seem to have the lowest environmental quality, given the presence of bacteria genera previously recorded in environments with high concentrations of pesticide residues. The microbiota, environmental characteristics, and pesticide residues should be further studied and try to elucidate the potential for pesticide degradation by natural consortia. Thus, extensive comparative studies are needed to clarify the microbial composition, diversity, and functioning of rice cultivation environments, and how pesticide use changes may reflect differences in microbial structure.

Dataset of "true mangroves" plant species traits.

BACKGROUND: Plant traits have been used extensively in ecology. They can be used as proxies for resource-acquisition strategies and facilitate the understanding of community structure and ecosystem functioning. However, many reviews and comparative analysis of plant traits do not include mangroves plants, possibly due to the lack of quantitative information available in a centralised form. NEW INFORMATION: Here a dataset is presented with 2364 records of traits of "true mangroves" species, gathered from 88 references (published articles, books, theses and dissertations). The dataset contains information on 107 quantitative traits and 18 qualitative traits for 55 species of "true mangroves" (sensu Tomlinson 2016). Most traits refer to components of living trees (mainly leaves), but litter traits were also included.

Tonic immobility in terrestrial isopods: intraspecific and interspecific variability.

Many arthropods, including terrestrial isopods, are capable of entering a state of tonic immobility upon a mechanical disturbance. Here we compare the responses to mechanical stimulation in three terrestrial isopods Balloniscus glaber, Balloniscus sellowii and Porcellio dilatatus. We applied three stimuli in a random order and recorded whether each individual was responsive (i.e. showed tonic immobility) or not and the duration of the response. In another trial we related the time needed to elicit tonic immobility and the duration of response of each individual. Balloniscus sellowii was the least responsive species and Porcellio dilatatus was the most, with 23% and 89% of the tested individuals, respectively, being responsive. Smaller Balloniscus sellowii were more responsive than larger individuals. Porcellio dilatatus responded more promptly than the Balloniscus spp. but it showed the shortest response. Neither sex, size nor the type of stimulus explained the variability found in the duration of tonic immobility. These results reveal a large variability in tonic immobility behavior, even between closely related species, which seems to reflect a species-specific response to predators with different foraging modes.