• Energy Research

The outwelling paradigm argues that mangrove and saltmarsh wetlands export much excess production to downstream marine systems. However, outwelling is difficult to quantify and currently 40-50% of fixed carbon is unaccounted for. Some carbon is thought outwelled through mobile fauna, including fish, which visit and feed on mangrove produce during tidal inundation or early life stages before moving offshore, yet this pathway for carbon outwelling has never been quantified. We studied faunal carbon outwelling in three arid mangroves, where sharp isotopic gradients across the boundary between mangroves and down-stream systems permitted spatial differentiation of source of carbon in animal tissue. Stable isotope analysis (C, N, S) revealed 22-56% of the tissue of tidally migrating fauna was mangrove derived. Estimated consumption rates showed that 1.4% (38 kg C ha-1 yr-1) of annual mangrove litter production was directly consumed by migratory fauna, with <1% potentially exported. We predict that the amount of faunally-outwelled carbon is likely to be highly correlated with biomass of migratory fauna. While this may vary globally, the measured migratory fauna biomass in these arid mangroves was within the range of observations for mangroves across diverse biogeographic ranges and environmental settings. Hence, this study provides a generalized prediction of the relatively weak contribution of faunal migration to carbon outwelling from mangroves and the current proposition, that the unaccounted-for 40-50% of mangrove C is exported as dissolved inorganic carbon, remains plausible.

Las complejas redes de raíces y troncos sobre el suelo hacen que los bosques de manglares atrapen la basura plástica. Probamos cómo los macroplásticos se relacionan con la biomasa de los árboles, la abundancia de raíces, la geomorfología de los manglares y la proximidad a la desembocadura de los ríos, estudiando los márgenes terrestres y marítimos de siete bosques en Filipinas, un punto de acceso global para la contaminación plástica marina. Los macroplásticos fueron abundantes (media ± s.e.: 1.1 ± 0.22 ítems m-2; rango: 0.05 ± 0.05 a 3.79 ± 1.91), más grandes en la zona terrestre (media ± s.e.: 1.60 ± 0.41 m-2) y dominados por ítems derivados de la tierra (sobres, bolsas). La abundancia y el peso del plástico aumentaron con la proximidad a las desembocaduras de los ríos, y la abundancia de las raíces predijo el área de superficie de la basura plástica (es decir, la suma acumulada de todas las áreas de superficie de cada elemento plástico por parcela). El estudio confirma que los ríos son una vía importante para la contaminación plástica marina, y que las raíces de los manglares son el atributo biológico que regula la retención de basura. Los resultados sugieren que la gestión de residuos terrestres que evita que los plásticos entren en los ríos reducirá la contaminación plástica marina en el sudeste asiático. Des réseaux complexes de racines et de troncs hors sol font que les forêts de mangroves piègent les déchets plastiques. Nous avons testé la relation entre les macroplastiques et la biomasse des arbres, l'abondance des racines, la géomorphologie des mangroves et la proximité de l'embouchure des rivières, en étudiant les marges terrestres et maritimes de sept forêts des Philippines, un point chaud mondial pour la pollution plastique marine. Les macroplastiques étaient abondants (moyenne ± s.e. : 1,1 ± 0,22 éléments m-2 ; plage : 0,05 ± 0,05 à 3,79 ± 1,91), les plus importants dans la zone terrestre (moyenne ± s.e. : 1,60 ± 0,41 m-2) et dominés par les éléments d'origine terrestre (sachets, sacs). L'abondance et le poids du plastique augmentent avec la proximité des embouchures des rivières, l'abondance des racines prédisant la surface de la litière en plastique (c'est-à-dire la somme cumulative de toutes les surfaces de chaque élément en plastique par parcelle). L'étude confirme que les rivières sont une voie majeure de pollution plastique marine, les racines de mangrove étant l'attribut biologique qui régule la rétention des litières. Les résultats suggèrent que la gestion des déchets terrestres qui empêche les plastiques de pénétrer dans les rivières réduira la pollution plastique marine en Asie du Sud-Est. Complex networks of above-ground roots and trunks make mangrove forests trap plastic litter. We tested how macroplastics relate to tree biomass, root abundance, mangrove geomorphology and river mouth proximity, surveying landward and seaward margins of seven forests in the Philippines, a global hotspot for marine plastic pollution. Macroplastics were abundant (mean ± s.e.: 1.1 ± 0.22 items m-2; range: 0.05 ± 0.05 to 3.79 ± 1.91), greatest at the landward zone (mean ± s.e.: 1.60 ± 0.41 m-2) and dominated by land-derived items (sachets, bags). Plastic abundance and weight increased with proximity to river mouths, with root abundance predicting plastic litter surface area (i.e., the cumulative sum of all the surface areas of each plastic element per plot). The study confirms rivers are a major pathway for marine plastic pollution, with mangrove roots are the biological attribute that regulate litter retention. The results suggest land-based waste management that prevent plastics entering rivers will reduce marine plastic pollution in Southeast Asia. تجعل الشبكات المعقدة من الجذور والجذوع فوق الأرض غابات المانغروف تحبس القمامة البلاستيكية. اختبرنا كيفية ارتباط اللدائن الكلية بالكتلة الحيوية للأشجار، ووفرة الجذور، والجيومورفولوجيا في غابات المانغروف، وقرب مصب النهر، وقمنا بمسح الهوامش البرية والبحرية لسبع غابات في الفلبين، وهي نقطة ساخنة عالمية للتلوث البلاستيكي البحري. كانت المواد البلاستيكية الكبيرة وفيرة (متوسط ± s.e: 1.1 ± 0.22 عنصر m -2 ؛ النطاق: 0.05 ± 0.05 إلى 3.79 ± 1.91)، وأكبرها في المنطقة البرية (متوسط ± s.e: 1.60 ± 0.41 m -2) وتهيمن عليها العناصر المشتقة من الأرض (الأكياس، الأكياس). زادت الوفرة البلاستيكية والوزن مع القرب من مصبات الأنهار، مع توقع وفرة الجذور لمساحة سطح القمامة البلاستيكية (أي المجموع التراكمي لجميع المساحات السطحية لكل عنصر بلاستيكي لكل قطعة أرض). تؤكد الدراسة أن الأنهار هي مسار رئيسي للتلوث البلاستيكي البحري، مع جذور المنغروف هي السمة البيولوجية التي تنظم الاحتفاظ بالقمامة. تشير النتائج إلى أن إدارة النفايات البرية التي تمنع دخول البلاستيك إلى الأنهار ستقلل من التلوث البلاستيكي البحري في جنوب شرق آسيا.

The abundance and distribution of mud crabs were studied in a replanted mangrove forest in Buswang, Aklan, Philippines. Two fishing gears, lift nets and bamboo traps, were used to monitor relative abundance of Scylla spp. populations from March 2002 to December 2003 inside the mangrove forest. A third gear, a stakenet set across a creek, was used to monitor crabs migrating out of the mangroves during the ebb tide. Scylla olivacea formed 99.3% and 70.3% of the catch in the mangrove and the stakenet, respectively. The percentage of Scylla tranquebarica increased from <1% in the mangrove catches to 29% in the stakenet. Scylla serrata was present at very low levels in both catches. The lack of modal progression in the sizeefrequency plots and the year-round catch rate of gravid females suggested that recruitment was constant throughout the year. Even though relative abundance decreased over the study period indicating that the stock is being over-exploited, mud crab production is more than equivalent to that of most natural mangroves. 2005 Elsevier Ltd. All rights reserved.

Seagrass beds form an important part of the coastal ecosystem in many parts of the world but are very sensitive to anthropogenic nutrient increases. In the last decades, stable isotopes have been used as tracers of anthropogenic nutrient sources and to distinguish these impacts from natural environmental change, as well as in the identification of food sources in isotopic food web reconstruction. Thus, it is important to establish the extent of natural variations on the stable isotope composition of seagrass, validating their ability to act as both tracers of nutrients and food sources. Around the world, depending on the seagrass species and ecosystem, values of seagrass N normally vary from 0 to 8 ‰ δ15N. In this study, highly unusual seagrass N isotope values were observed on the east coast of Qatar, with significant spatial variation over a scale of a few metres, and with δ15N values ranging from +2.95 to −12.39 ‰ within a single bay during March 2012. This pattern of variation was consistent over a period of a year although there was a seasonal effect on the seagrass δ15N values. Seagrass, water column and sediment nutrient profiles were not correlated with seagrass δ15N values and neither were longer-term indicators of nutrient limitation such as seagrass biomass and height. Sediment δ15N values were correlated with Halodule uninervis δ15N values and this, together with the small spatial scale of variation, suggest that localised sediment processes may be responsible for the extreme isotopic values. Consistent differences in sediment to plant 15N discrimination between seagrass species also suggest that species-specific nutrient uptake mechanisms contribute to the observed δ15N values. This study reports some of the most extreme, negative δ15N values ever noted for seagrass (as low as −12.4 ‰) and some of the most highly spatially variable (values varied over 15.4 ‰ in a relatively small area of only 655 ha). These results are widely relevant, as they demonstrate the need for adequate spatial and temporal sampling when working with N stable isotopes to identify food sources in food web studies or as tracers of anthropogenic nutrients.