Search

Understanding local patterns of species-specific litterfall can help predict spatial differences in the amount and quality of organic matter input to systems under different environmental conditions. However, little is known about the drivers of differences in litterfall production in mangroves. Here we combined data from leaf litterfall (LL) studies (n = 13) and floristic studies (n = 16) conducted in the mangroves of the Ajuruteua peninsula (North of Brazil), at sites composed mainly of Rhizophora mangle and/or Avicennia germinans. We investigated the relationship between LL and vegetation parameters (height, diameter, basal area, density, and relative density) using partial least-squares regressions (PLS-R), building four models with different combinations of these parameters. Vegetation parameters explained 69–85% of the annual LL of A. germinans and 50–66% of R. mangle. Relatively strong, univariate significant relationships were also found between basal area and A. germinans LL (R2 = 0.40), and between height and R. mangle LL (R2 = 0.41). Nonetheless, models with four to five predictors yielded better fits. To illustrate the applicability of our approach we used the PLS-R models to calculate the LL of simulated sites. This simulation indicated a clear increase in LL production along the transition from Avicennia- to Rhizophora-dominated mangroves. As the leaf litter of these species differ substantially in chemical composition and decomposability, such transition in species composition will likely affect nutrient dynamics in the region. Thus, we suggest reporting species-specific site characteristics along with LL in future studies to obtain more robust models to predict future LL production at sites of changing vegetation structure.

The structure and functioning of coastal ecosystems are shifting worldwide as a result of natural changes and, even more important, consequences of intense human intervention, of which habitat destruction, overexploitation of resources and environmental pollution are among the most serious. In this context, the 56th Conference of the Estuarine Coastal Sciences Association was held in Bremen, Germany, in September 2016 under the umbrella topic ‘Coastal Systems in Transition: From a natural to an anthropogenically-modified state’. The objective of this Special Issue is to demonstrate and synthesize the effects of both, natural variations and human intervention in estuaries and other coastal ecosystems. The 22 articles originate from various disciplines and cover a wide range of ecosystems, including temperate and tropical estuaries, hypersaline lagoons, mangrove forests, coral reefs and coastal dunes. The articles are categorized under four main topics, (1) drivers and dynamics of coastal systems, (2) impacts on estuarine biodiversity and community structure, (3) impacts on estuarine and bay functioning, and (4) management options for protecting estuarine diversity, functions and services. Several of the studies clearly show that estuarine systems are affected by multiple pressures, of which changes in salinity, hydrology, trophic state and habitat complexity as a consequence of human intervention are most frequently addressed. One of the main challenges remains distinguishing between natural and human-induced changes in biological, geochemical and physical processes and the interactions between them. A number of studies provide excellent examples of how biological indicators (e.g., benthic and fish diversity and community structure) are suitable for assessing the effects of stressors on ecosystems. It remains an important task to standardize these indicators for easier application in other locations and for evaluating the success of management measures. The high variability of coastal systems, the complex process interactions, and increasing pressure require interdisciplinary studies on a deeper understanding of processes as well as scenario experiments by model applications.

Mangrove leaves form a large pool of carbon, nitrogen and energy that is a major driver of element cycles and detrital food webs inside mangrove forests as well as in adjacent coastal waters. However, there are large gaps in knowledge on the transformation pathways and ultimate fate of leaf nitrogen. Therefore, the main objective of this study was to determine the amount and composition of nitrogenous organic matter and possible species-specific differences during the decomposition of mangrove leaf litter. For that purpose a three month decomposition experiment with litterbags was conducted using leaves of Aegiceras corniculatum, Avicennia alba, Ceriops decandra, Rhizophora apiculata, and Sonneratia caseolaris in the mangrove forest of the Segara Anakan Lagoon, Java, Indonesia. Detrital leaves were analyzed for bulk carbon and total nitrogen (N), stable carbon and nitrogen isotope composition (δ13C, δ15N), total hydrolyzable amino acids (THAA) and total hydrolyzable hexosamines (THHA). Decomposition rates (k d−1) were highest and tM50 values (when 50% of the original mass had been degraded) lowest in S. caseolaris (k = 0.0382 d−1; tM50 = 18 days), followed by A. alba, C. decandra, A. corniculatum, and R. apiculata (k = 0.0098 d−1; tM50 = 71 days). The biochemical composition of detrital leaves differed significantly among species and over time. S. caseolaris and A. alba had higher concentrations of N, THAA and THHA and a lower C/N ratio than the other three species. For most of the species concentrations of N, THAA and THHA increased during decomposition. The hexosamine galactosamine, indicative of bacterial cell walls, was first found in leaves after 5–7 days of decomposition and increased afterwards. Our findings suggest an increasing, but species-specific varying, portion of labile nitrogenous OM and total N in decomposing leaves over time that is partly related to the activity of leaf-colonizing bacteria. Despite a higher relative nitrogen content in the remaining litter of the fast decomposing S. caseolaris and A. alba as compared to the other three species, the total loss of nitrogen was even higher because of the much higher mass loss after three months of decomposition. It is inferred that the amount of labile nitrogenous organic matter plays a major role in determining the rate of decomposition of leaf litter in mangroves.

Antibiotic residues and antibiotic resistance genes (ARGs) have been found worldwide. Chloramphenicol, one of antibiotics, had been banned for its use in breeding industry in many countries. The status about chloramphenicol resistance genes (CRGs) in mangrove ecosystems is still unknown. In the present study, quantitative PCR was employed to investigate the abundance of CRGs. The residual determination of chloramphenicols was performed via ultra-high pressure liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Although the concentrations of chloramphenicol residues were at undetectable or relatively low levels, the abundance of CRGs was still alarming. The CRG abundance was dynamically different with the season change, and was highest in the surface layer and gradually decreased with the sampling sites away from the mangrove. The 16S rRNA high-throughput gene sequencing results revealed that cyanobacteria, fusobacteria and planctomycetes were the most dominant phyla co-occurring with CRGs. The results indicated that antibiotic residues could make a long term impacts on the environment eventhough after their degradation.

Indonesia has the largest area and the highest tree species richness but also one of the highest loss rates of mangroves worldwide. The Segara Anakan lagoon is a mangrove-fringed estuarine system in Java which is highly affected by deforestation, sedimentation, and land-use changes. The spatial variability of diversity, community composition, density, height, aboveground biomass and habitat complexity of the mangrove forest in relation to abiotic conditions was studied in 2014/2015. Vegetation characteristics were compared with those available from 2005/2006, and the effects of deforestation on the forest condition were assessed. In total, 15 mangrove tree species were recorded in 2015, six less than ten years ago. The two main areas of the lagoon, the central and eastern one, had a significantly different tree community composition. The central area was dominated by the palm Nypa fruticans and Aegiceras corniculatum and 74% of the ground was covered by the understorey plants Acanthus spp. and Derris trifoliata. Tree density, stand basal area, species number, aboveground biomass, and habitat complexity were significantly lower in the central area as a result of deforestation. Stand basal area and aboveground biomass decreased significantly over the 10 years as well as the density of Avicennia spp., Sonneratia spp., Ceriops spp., Aegiceras corniculatum, and Bruguiera spp. The eastern area was dominated by A. corniculatum and Rhizophora apiculata, and coverage with understorey plants was only 11%. The density of R. apiculata increased significantly over the 10 years as a result of natural regeneration and reforestation. The overall low tree height (2.8 m) and aboveground biomass (18.4 t dry mass ha−1) point to a young and degraded forest. In the central lagoon, mangrove reforestation is probably extremely difficult due to the strong expansion of understorey plants. It is assumed that ongoing deforestation will cause a further spread of understorey plants, a decrease in species number, tree density and habitat complexity. A decline in microhabitats and aboveground biomass can lead to a decrease of faunal species and biomass which in turn would influence nutrient cycling and impair the nursery function of the area. Also, important ecosystem services, particularly coastal protection against storms and prevention of coastal erosion are most likely affected.

Diversity and composition of the intertidal brachyuran crab community in the Segara Anakan Lagoon (SAL), Java, Indonesia, during the dry season of 2005 and the rainy season of 2006, shows that crab community composition and structure alone appeared to be poor indicators for the state of a forest in terms of tree diversity and wood-cutting intensity. The lagoon is surrounded by the largest mangrove stand in Java and is under constant anthropogenic pressure, mainly due to logging, land conversion for agriculture, overfishing and industrial pollution. This study aims to determine the crab community composition at different sites of the lagoon in relation to vegetation composition and sediment parameters. In addition it investigates if mangrove crabs can be used as bioindicators to describe the environmental state of mangrove forests (tree diversity, degree of logging). It was assumed to find a low crab diversity and species richness and a strong dominance of a single species at highly disturbed forest sites compared to moderately disturbed sites. A stratified, hierarchical design was used to sample the crab fauna at 13 stations distributed over the entire lagoon. Additionally, abiotic parameters and vegetation composition were recorded. In total 6463 crabs were caught belonging to 49 species, 5 superfamilies and 10 families, with Ocypodidae and Sesarmidae being the families of most note. Mean density of adult crabs was 27.7 individuals*m −2 and mean biomass was 12.8 g wet mass*m −2 or 1.3 g ash free dry mass*m −2 . Density and biomass varied strongly within and between stations but they where within the range reported for other mangrove forests of the Indo-West-Pacific. Species composition was significantly different between stations. The distribution of facultatively leaf-feeding grapsid crabs was related to vegetation parameters (tree, seedling and undergrowth density), but the occurrence of single crab and tree species was not correlated. The distribution of ocypodid crabs, feeding on detritus and microphytobenthos, correlated with sediment characteristics like median grain size and organic content. The crab community was strongly dominated by one species at six stations, however, this was not correlated to the degree of logging. Leaf-feeding crab and mangrove tree diversity was correlated at areas of one hectare (stations), but not at a lower spatial scale (areas of 100 m 2 , “zone”). Species richness of leaf-feeding crabs was not linked to forest diversity. Hence a functional relation between leaf-feeding crab and tree species diversity could not be proven.

This study provides the first quantification of the population food intake of the litter-consuming mangrove crab Ucides cordatus (Ocypodidae, L. 1763) in a New World mangrove forest. Diet, feeding periodicity, gastric evacuation rates and size-dependent consumption were determined for this intensively exploited semi-terrestrial crab in different types of mangrove forest. Unlike many other crabs Ucides cordatus is a continuous feeder, as shown by gastrointestinal contents over a day's cycle. Starvation experiments revealed that most gastric evacuation occurs during the first 12 h after feeding, following an exponential decay function. Evacuation rates (0.35 h −1 and 0.31 h −1 ) for small (carapace width CW 2.5–3.5 cm) and large (CW 6.5–7.5 cm) crabs, respectively, and the mean daily gastrointestinal contents were used to calculate the daily food intake (DFI) of U. cordatus for both sexes and different size classes. DFI was strongly correlated to body size and ranged from 19.8 to 6.0% of body dry weight in small and large crabs, respectively. The daily energy intake of U. cordatus (37.6 kJ for a 65 g wet weight specimen) was high when compared to other leaf-eating crabs. Litter fall and propagule production were calculated as 16.38 t ha −1 y −1 , corresponding to a daily mean of 4.49 g m −2 in a high intertidal Rhizophora mangle forest stand. The estimated population food intake of Ucides cordatus (4.1 g dw m −2 d −1 ) corresponds to 81.3% of this production. This high litter removal rate, a low litter quantity in burrows and high consumption rates during field experiments suggest that the local crab population is food-limited in many parts of the study area. The very efficient coupling of forest litter production and crab litter consumption is possible due to the high crab density and the low inundation frequency of the mangrove forests, allowing for prolonged foraging periods. By processing the major part of the litter, U. cordatus helps to retain nutrients and energy within the mangrove ecosystem. The impact of this species on litter turnover in a New World mangrove is similar to or even higher than that of litter-feeding sesarmid crabs in the Indo-West Pacific region.