Environmental drivers of diurnal visits by transient predatory fishes to Caribbean patch reefs
Harborne, A.R. ; Selwyn, J.D. ; Lawson, J.M. ; Gallo, M. - \ 2017
Journal of Fish Biology 90 (2017)1. - ISSN 0022-1112 - p. 265 - 282.
barracuda - mangroves - marine reserves - snapper - The Bahamas - video analysis
Video cameras recorded the diurnal visitation rates of transient (large home range) piscivorous fishes to coral patch reefs in The Bahamas and identified 11 species. Visits by bar jack Caranx ruber, mutton snapper Lutjanus analis, yellowtail snapper Ocyurus chrysurus, barracuda Sphyraena barracuda and cero Scomberomorus regalis were sufficiently frequent to correlate with a range of biophysical factors. Patch-reef visitation rates and fish abundances varied with distance from shore and all species except S. regalis were seen more frequently inshore. This pattern is likely to be caused by factors including close proximity to additional foraging areas in mangroves and on fore-reefs and higher abundances close to inshore nursery habitats. Visitation rates and abundances of C. ruber, L. analis, O. chrysurus and S. regalis also varied seasonally (spring v. winter), possibly as fishes responded to temperature changes or undertook spawning migrations. The abundance of each transient predator species on the patch reefs generally exhibited limited diurnal variability, but L. analis was seen more frequently towards dusk. This study demonstrates that the distribution of transient predators is correlated spatially and temporally with a range of factors, even within a single lagoon, and these drivers are species specific. Transient predators are considered an important source of mortality shaping reef-fish assemblages and their abundance, in combination with the biomass of resident predators, was negatively correlated with the density of prey fishes. Furthermore, transient predators are often targeted by fishers and understanding how they utilize seascapes is critical for protecting them within reserves.
Food from the Sulawesi Sea, the need for integrated sea use planning
Siahainenia, Audrie J. - \ 2016
Wageningen University. Promotor(en): Herbert Prins; Johan Verreth, co-promotor(en): Fred de Boer. - Wageningen : Wageningen University - ISBN 9789462578869 - 180
mangroves - mangrove forests - fishes - habitats - marine areas - marine environment - fish stocks - environmental management - ecological disturbance - disturbance - sulawesi - mangroves - mangrovebossen - vissen - habitats - mariene gebieden - marien milieu - visstand - milieubeheer - ecologische verstoring - verstoring - celebes
Mangroves occur in the tropics and subtropics region and an important coastal habitat for the artisanal fisheries along the coast of Indonesia. Around 19% of the total mangrove area in the world is located in Indonesia. Besides providing a barrier against coastal/Delta erosion, mangrove forest plays a significant role as a nursery area for most of the marine communities. Unluckily, 57% of the ±3.2 million ha of the mangroves in Indonesia is currently in degraded, mostly because of human activities (anthropogenic disturbance). The primary sources of anthropogenic disturbances to mangroves are increasing population growth rate and demand for seafood products as an essential protein, especially the wild shrimp, in the world market. These resulted in land-use conversion along estuarine areas not only for settlements and plantations but also for aquaculture ponds. The lack of awareness and understanding of the value and function of mangrove ecosystems contributed to the loss and damage the mangroves area.
Therefore, my research and field experiment aimed to quantify the effects of human disturbance on mangroves associated trophic cascades in Indonesia estuarine areas. The study was performed in the Berau District, East Kalimantan, Indonesia between 2005 and 2010. Data of mangrove extent from 1990 in the Berau Delta was used as base data with low human disturbance. We also interviewed the artisanal fishermen about their catches, origins, and fishing locations, in relation to the total catch per unit effort (CpUE).
The results had shown that the total mangroves area in the Berau Delta decreased by 54% between the 1990 and 2009, which led to fragmentation and alteration in the structural complexity of mangroves. The field experiment conducted at three locations with different levels of human disturbances revealed that the species richness was decreased with increased the level of human interference and the marine community tended to be dominated by only a few species. In the highly disturbed areas, the catch of small-scale fishermen tended to be lower. Furthermore, the result from a spatial statistical model indicated that the disturbance of mangrove habitats was influenced the distribution pattern of shrimp. The total CpUE of small-scale fishery in the study area was relatively small, and the area was probably not overexploited.
As a conclusion, mangroves habitat in the Berau Delta played a significant role in sustaining coastal fisheries. This important ecosystem supports a primary source of marine protein. Mangrove forests can only guarantee these marine resources if the people consciously maintain its viability through a strong management policy.
Balancing options for shrimp farming : a landscape approach to investigate the future of shrimp farming in the Mekong Delta
Joffre, O.M. - \ 2015
Wageningen University. Promotor(en): Johan Verreth; Arnold Bregt, co-promotor(en): Roel Bosma. - Wageningen : Wageningen University - ISBN 9789462574984 - 196
garnalenteelt - schaal- en schelpdierenteelt - kustgebieden - milieueffect - landschap - aquacultuur - mangroves - middelen van bestaan - hulpbronnengebruik - geïntegreerde systemen - duurzaamheid (sustainability) - mekong - delta's - shrimp culture - shellfish culture - coastal areas - environmental impact - landscape - aquaculture - mangroves - livelihoods - resource utilization - integrated systems - sustainability - mekong river - deltas
Balancing options for shrimp farming
A landscape approach to investigate the future of shrimp farming in the Mekong Delta
While providing an option for development in coastal areas, shrimp farming is usually associated with high environmental cost due to the loss of mangrove forest and high social cost as farmers suffer heavy financial losses due to disease outbreaks. Planning shrimp farming requires to integrate risk as well as social and environmental cost. This thesis, using the Mekong Delta as a case, presents an approach to investigate, with local stakeholders, options to plan a resilient and sustainable shrimp farming sector. First, Olivier Joffre analyzed the different shrimp production systems from economic point of view before analyzing farmer’s strategies and providing insights on drivers that will push or, at the opposite, constraint farmers to choose integrated mangrove shrimp systems. This knowledge was integrated in an Agent Based Model (ABM) that was calibrated using Role Playing Games (RPG).
The effect of future scenarios and different policies on the farmers’ decisions was tested using a combination of RPG and ABM. For one coastal district of the Mekong Delta, the results showed that promotion of intensification of shrimp production has a high social cost and decreases the total production in the study area after 10 years. Policies for supporting the spread of integrated mangrove-shrimp systems, such as Payment for Ecosystem Services, or access to an organic value chain, are not strong enough to influence farmers’ decision toward adopting these systems. Without any adaptation to climate change a sharp decrease of the production is expected. The approach brought local farmers’ knowledge to the attention of decision makers.
Mainstreaming biodiversity where it matters most
Karlsson-Vinkhuyzen, S.I.S.E. ; Boelee, E. ; Cools, J. ; Visseren-Hamakers, I.J. ; Hoof, L.J.W. van; Hospes, O. ; Kok, M. ; Peerlings, J.H.M. ; Podvin, K.J. ; Tatenhove, J.P.M. van; Termeer, C.J.A.M. - \ 2014
Wageningen & Bilthoven : Wageningen University & PBL Netherlands Environmental Assessment Agency - ISBN 9789462573840 - 180
biodiversiteit - bosbouw - visserij - palmoliën - mangroves - wereld - biodiversity - forestry - fisheries - palm oils - mangroves - world
This report presents the result of applying the framework in five cases in or on the cross roads between agriculture, forestry and fisheries where considerable pressure on biodiversity is exerted. The cases were selected based on several criteria with the aim that they together cover as broad span as possible of: Relevance for biodiversity (from having very clear impacts to much more uncertain impacts) Governance levels (including both local, national, global levels) Governance context (type of actors, type of norms etc.) Regions (continents and eco‐climatic zones)
Ecosystem-based coastal defence in the face of global change
Temmerman, S. ; Meire, P. ; Bouma, T.J. ; Herman, P.M.J. ; Ysebaert, T. ; Vriend, H.J. de - \ 2013
Nature 504 (2013). - ISSN 0028-0836 - p. 79 - 83.
tidal marsh - scheldt estuary - climate-change - storm surges - sea-level - restoration - sedimentation - strategies - mangroves - carbon
The risk of flood disasters is increasing for many coastal societies owing to global and regional changes in climate conditions, sea-level rise, land subsidence and sediment supply. At the same time, in many locations, conventional coastal engineering solutions such as sea walls are increasingly challenged by these changes and their maintenance may become unsustainable. We argue that flood protection by ecosystem creation and restoration can provide a more sustainable, cost-effective and ecologically sound alternative to conventional coastal engineering and that, in suitable locations, it should be implemented globally and on a large scale.
Geographic coupling of juvenile and adult habitat shapes spatial population dynamics of a coral reef fish
Huijbers, C.M. ; Nagelekerken, I. ; Debrot, A.O. ; Jongejans, E. - \ 2013
Ecology 94 (2013)8. - ISSN 0012-9658 - p. 1859 - 1870.
larval dispersal - marine reserves - menidia-menidia - seagrass beds - life-history - connectivity - nurseries - mangroves - estuarine - chemistry
Marine spatial population dynamics are often addressed with a focus on larval dispersal, without taking into account movement behavior of individuals in later life stages. Processes occurring during demersal life stages may also drive spatial population dynamics if habitat quality is perceived differently by animals belonging to different life stages. In this study, we used a dual approach to understand how stage-structured habitat use and dispersal ability of adults shape the population of a marine fish species. Our study area and focal species provided us with the unique opportunity to study a closed island population. A spatial simulation model was used to estimate dispersal distances along a coral reef that surrounds the island, while contributions of different nursery bays were determined based on otolith stable isotope signatures of adult reef fish. The model showed that adult dispersal away from reef areas near nursery bays is limited. The results further show that different bays contributed unequally to the adult population on the coral reef, with productivity of juveniles in bay nursery habitat determining the degree of mixing among local populations on the reef and with one highly productive area contributing most to the island's reef fish population. The contribution of the coral reef as a nursery habitat was minimal, even though it had a much larger surface area. These findings indicate that the geographic distribution of nursery areas and their productivity are important drivers for the spatial distribution patterns of adults on coral reefs. We suggest that limited dispersal of adults on reefs can lead to a source–sink structure in the adult stage, where reefs close to nurseries replenish more isolated reef areas. Understanding these spatial population dynamics of the demersal phase of marine animals is of major importance for the design and placement of marine reserves, as nursery areas contribute differently to maintain adult populations.
Ecological rehabilitation of Lac Bonaire by wise management of water and sediments
Wosten, J.H.M. - \ 2013
Wageningen : Alterra (Alterra-rapport 2448) - 40
mangroves - zoutgehalte - sediment - vee - waterkwaliteit - waterbeheer - herstel - ecologisch herstel - bonaire - mangroves - salinity - sediment - livestock - water quality - water management - rehabilitation - ecological restoration - bonaire
Lac Bonaire is confronted with a gradually decreasing open water area because mangrove is occupying this area. At the same time mangrove growth deteriorates at the back of the mangrove belt, the area of hyper saline flats gradually increases and sediment is deposited in the bay area. During a field visit, the most prominent problems are identified and concrete management actions are proposed for the ecological rehabilitation of Lac Bonaire.
Bird communities of contrasting semi-natural habitats of Lac bay, Bonaire, during the fall migration season, 2011
Debrot, A.O. ; Bemmelen, R.S.A. van; Ligon, J. - \ 2013
Den Helder : IMARES (Report / IMARES Wageningen UR C165/12) - 25
habitats - vogels - mangroves - monitoring - nationale parken - caribisch gebied - bonaire - habitats - birds - mangroves - monitoring - national parks - caribbean - bonaire
The mangrove and seagrass lagoon of Lac Bay on Bonaire covers an area of roughly 700 ha. It is home to endangered green sea turtles, Chelonia mydas, and the Caribbean queen conch, Strombus gigas, and is a roosting and breeding area for several birds. Based on its nature values this 7 km2 bay has been designated as a legally protected Ramsar site. The area falls under the management responsibility of the National Parks Foundation of Bonaire.
Global and local governance of shrimp farming in the Mekong Delta, Vietnam
Tran Thi Thu, H. - \ 2012
Wageningen University. Promotor(en): Arthur Mol; Han van Dijk, co-promotor(en): Simon Bush. - S.l. : s.n. - ISBN 9789461733764 - 181
garnalen - garnalenteelt - governance - beleid - aquacultuur en milieu - markten - biologische landbouw - mangroves - vietnam - shrimps - shrimp culture - governance - policy - aquaculture and environment - markets - organic farming - mangroves - vietnam
The Mekong Delta is one of seven ecological regions in Vietnam where aquaculture and shrimp products are internationally traded and the shrimp farmers are firmly embedded in a global system of production and trade. The growth of shrimp aquaculture, in addition to population growth and higher levels of investment, has left coastal resources in the Mekong Delta increasingly vulnerable to rapid changes in land and resource use. The shrimp industry, made up of multiple stakeholders and fragmented market chains, is also now subject to a range of attempts to govern sustainable and/or responsible shrimp aquaculture. While striving for improved environmental performance to reduce bio-physical variability in production these governance systems have also brought stringent requirements for producers that determine their ability to access international markets. The general objective of the research is to investigate the interactions between existing state and non-state actors and institutions to develop a more informed understanding of how state, market and community-based governance arrangements at different levels influence decision-making in shrimp aquaculture in coastal areas of the Mekong Delta of Vietnam. The general research question explores how different material conditions and social relations affect the effectiveness and responsiveness of governance arrangements aimed at achieving multiple goals of maintaining rural livelihoods, environmental sustainability and improved food quality.
The first empirical chapter highlights two key transformations of Vietnamese shrimp aquaculture policy in Ca Mau province. The first transformation is an internal policy shift from quantitative to qualitative state-led production goals. The secondtransformation is in response to market demands, but is directed to the emergent ‘quality’ concerns about the environmental and social impacts of tropical shrimp farming. Together these two transformations present a complex balancing act between externally-led global market demands and consumer concerns for the improved environmental and social performance of tropical shrimp production, and the government’s interests in maintaining sovereign control over the shrimp industry. The results also show that the Vietnamese government should continue to position itself as a facilitator of global private governance arrangements, especially as farmers and global market actors are engaged in transnational regulatory networks operationalised at local scales. Moreover, the state needs to give far more attention to market incentives for fostering the participation and compliance of farmers in these transnational regulatory networks.
The second chapter analyses the case of Naturland organic certification and its implementation in meeting the government’s plan to create an organic coast scaling up the organic farming along southern part of Ca Mau by 2015. Our results support the claim that organic certification can provide a means of linking farm-level management to the sustainability of landscapes dominated by the shrimp-forest integrated farming system in Ca Mau. But this is only achievable if certain challenges are overcome. The first challenge is the tension between farmer practices and externally defined and regulated quality standards.The secondchallenge is to ensure that economic benefit are shared between actors in the organic certified value chain. Finally, the level of legitimacy given to private sector led auditing systems needs to be addressed.
The thesis then explores the development of shrimp farmer cooperatives and clusters by the government based on a policy to explicitly to increase the competitiveness of the sector in the international market and to improve economic condition for small producers. The results shows that vertical contractualisation under the form of contract farming between farmer cluster with up and downstream chain actors demonstrate economic benefits to small-holder producers engaged in intensive production.The improved extensive system, however, gives further impetus to determining how cooperative forms of production might assist small holders to complying with production-oriented quality standards, which in turn may also improving market performance. The cases therefore supports the claim that the development of shrimp farmer clusters should not solely focus on increasing production efficiency but also successful integration into the value chain; producing high-quality and safe products, and engaging in sustainable on-farm management practices.
The final case study looks at shrimp farming in the broader context of promoting ecological function in forested shrimp-mangrove farming systems. Attention is given to how incentives are generated for shrimp farmers to plant and protect mangroves by analysing farmer’s decision-making and their perspective on mangroves in relation with state-based governance arrangements, the forest allocation and benefit sharing policies. The results show that farmer’s perception on the role and value of mangroves are positive and they are willing to plant and to protect mangroves both for economic and environmental reasons. Moreover, they want to have control over mangroves although forests are still under the state regulation. However, farmer’s decision-making is very much influenced by the way in which the forest benefit sharing policy is implemented by the state-led forest management boards and forestry companies. The results show that the perception of shrimp farming as the main cause of deforestation and degradation should be reevaluated in the context of integrated shrimp mangrove model because farmers income is improved if mangroves are a part of the production system. Instead the evidence shows that shrimp farmers are potentially the best stakeholders to plant, protect and manage mangroves if they have full rights and responsibilities over forests. Seen as such, shrimp farming is a mangrove-friendly source of revenue which also promotes the planting and protection of mangroves.
The relation between farming practices, ecosystem, and white spot in syndrome virus (WSSV) disease outbreaks in penaeus monodon farms in the Philippines
Tendencia Alapide, E. - \ 2012
Wageningen University. Promotor(en): Johan Verreth, co-promotor(en): Roel Bosma; J.H. Primavera. - S.l. : s.n. - ISBN 9789461733702 - 135
garnalen - witte-vlekken-syndroom-virus - garnalenteelt - uitbraken (ziekten) - epidemiologie - infectieziekten - dierziektepreventie - aquatische ecosystemen - fysicochemische eigenschappen - mangroves - filippijnen - shrimps - white spot syndrome virus - shrimp culture - outbreaks - epidemiology - infectious diseases - animal disease prevention - aquatic ecosystems - physicochemical properties - mangroves - philippines
The white spot syndrome virus (WSSV) affecting shrimp aquaculture in most producing countries has caused huge economic losses resulting in bankruptcy to both large and small farmers. Studies done on WSSV epidemiology were mostly tank-based and on species other than Penaeus monodon. There is a need to investigate WSSV epidemiology in P. monodon in on-farm situations, thus including both risk and protective factors. This thesis aimed to generate knowledge that can improve prevention against WSSV in shrimp culture through better farm husbandry by studying the epidemiology of WSSV in on-farm situations. To achieve this goal data from cross-sectional and case studies were analysed to identify on-farm WSSV risk and protective factors, and longitudinal studies were done to assess factors affecting water quality and causing WSSV infection to result in an outbreak.
The thesis identified the following WSSV risk factors related to the physico-chemical parameters of the water: low and fluctuating temperature, low and fluctuating salinity, and pH fluctuation. The risk of high temperature and high salinity for an outbreak of WSV disease may be related to fluctuations in these two parameters. Risk factors related to farm husbandry techniques were feeding with molluscs, sludge removal and its deposition on the dike, sharing water source with other farms and having the same receiving and intake water. Identified WSSV protective factors were high mangrove to pond area ratio, feeding with natural food or phytoplankton, and higher percentage of beneficial bacteria like the yellow colonies that grow on thiosulphate citrate bilesalt sucrose agar, a Vibrio selective medium.
Results of the longitudinal studies demonstrated that WSSV infection may not result in outbreaks in greenwater pond and in ponds with mangroves in the receiving environment. Our results did not provide explanations why the WSSV infection did not result in an outbreak in farms with mangroves in the receiving environment. In greenwater ponds, this was attributed to the better water and soil quality, higher plankton count, and higher heterotrophic bacterial count.
Extent and health of mangroves in Lac Bay Bonaire using satellite data
Davaasuren, N. ; Meesters, H.W.G. - \ 2012
Den Helder : IMARES (Report / IMARES Wageningen UR C190/11) - 64
mangroves - gezondheidstoestand van het bos - gebied - satellietkarteringen - genormaliseerd verschil in de vegetatie-index - bosecologie - bonaire - mangroves - forest health - area - satellite surveys - normalized difference vegetation index - forest ecology - bonaire
Preference of early juveniles of a coral reef fish for distinct lagoonal microhabitats is not related to common measures of structural complexity
Grol, M.G.G. ; Nagelkerken, I. ; Bosch, N. ; Meesters, H.W.G. - \ 2011
Marine Ecology Progress Series 432 (2011). - ISSN 0171-8630 - p. 221 - 233.
seagrass beds - habitat complexity - field experiment - recruitment patterns - nutrient enrichment - mangroves - assemblages - predation - grunts - water
Coral reef populations of a variety of fish and invertebrate species are replenished by individuals that use inshore coastal habitats as temporary juvenile habitats. These habitats vary greatly in their architecture, and different characteristics of structure could play a role in their selection and utilization by resident fauna. To solely investigate the role of structural complexity in microhabitat selection, in situ habitat preference of 48 individuals of the early juvenile stage of a common reef fish (Haemulon flavolineatum) was studied for 4 structurally very different lagoonal microhabitats (i.e. mangrove, seagrass, rubble, coral), using a multiple-choice experiment in field enclosures. This fish species was selected as it utilizes these habitats during different parts of its life cycle. The structural complexity of each microhabitat was changed in each replicate experiment and assessed on the basis of 7 commonly used measures of structure using digitized photographs. We tested the hypothesis that in isolation of other factors, fish prefer the structurally most complex microhabitat that is available, independent of habitat type. However, fish always preferred seagrass and coral microhabitats even when offered at low complexity, and this choice was rather consistent over a 24 h time period. Structural characteristics appeared to be marginally important for the seagrass microhabitat only. Therefore, the differential preference for distinct lagoonal microhabitats does not appear to be driven by measures of structural complexity that are known to be important at the level of individual habitat types. In this light, continuing loss of coral and seagrass habitats in lagoonal environments due to anthropogenic effects is alarming as it affects preferential habitat of certain stages of the life cycle of fishes.
Reef fishes of Saba Bank, Netherlands Antilles : Assemblage structure across a gradient of habitat types
Toller, W. ; Debrot, A.O. ; Vermeij, M. ; Hoetjes, P.C. - \ 2010
PLoS ONE 5 (2010)5. - ISSN 1932-6203 - 13 p.
coral-reef - seagrass beds - community structure - species richness - mangroves - nursery - biodiversity - hypothesis - complexity - islands
Saba Bank is a 2,200 km2 submerged carbonate platform in the northeastern Caribbean Sea off Saba Island, Netherlands Antilles. The presence of reef-like geomorphic features and significant shelf edge coral development on Saba Bank have led to the conclusion that it is an actively growing, though wholly submerged, coral reef atoll. However, little information exists on the composition of benthic communities or associated reef fish assemblages of Saba Bank. We selected a 40 km2 area of the bank for an exploratory study. Habitat and reef fish assemblages were investigated in five shallow-water benthic habitat types that form a gradient from Saba Bank shelf edge to lagoon. Significant coral cover was restricted to fore reef habitat (average cover 11.5%) and outer reef flat habitat (2.4%) and declined to near zero in habitats of the central lagoon zone. Macroalgae dominated benthic cover in all habitats (average cover: 32.5 – 48.1%) but dominant algal genera differed among habitats. A total of 97 fish species were recorded. The composition of Saba Bank fish assemblages differed among habitat types. Highest fish density and diversity occurred in the outer reef flat, fore reef and inner reef flat habitats. Biomass estimates for commercially valued species in the reef zone (fore reef and reef flat habitats) ranged between 52 and 83 g/m2. The composition of Saba Bank fish assemblages reflects the absence of important nursery habitats, as well as the effects of past fishing. The relatively high abundance of large predatory fish (i.e. groupers and sharks), which is generally considered an indicator of good ecosystem health for tropical reef systems, shows that an intact trophic network is still present on Saba Bank.
Lac Bonaire - Restoration Action Spear Points, September 2010
Debrot, A.O. ; Meesters, H.W.G. ; Leon, L. de; Slijkerman, D.M.E. - \ 2010
Den Helder : IMARES (Report / IMARES Wageningen UR nr. C131/10) - 25
zostera - mangroves - ecologische verstoring - natuurbescherming - oplossingen - natuurbeleid - zostera - mangroves - ecological disturbance - nature conservation - solutions - nature conservation policy
Lac Bay is the most important mangrove and sea grass area of Bonaire and has been undergoing steady ecological decline in the last decades. Based on an initial assessment of conservation management issue and potential solutions as conducted by IMARES in June 2010, the Dutch Ministry of Agriculture, Nature and Food Quality (LNV) asked IMARES to return to Bonaire to work with Stinapa Bonaire to choose narrower priorities and jointly make a short-list of topics as a working document for cooperation and action. In the beginning of September 2010, site visits and discussions were held in Bonaire with the manager of Lac Bay and various stakeholders to identify and agree on priority issues for action. This working report gives the results of the visit.
Assessment of Ramsar site Lac Bonaire - June 2010
Debrot, A.O. ; Meesters, H.W.G. ; Slijkerman, D.M.E. - \ 2010
Yerseke : IMARES (Report / IMARES Wageningen UR nr. C066/10) - 31
natuurbescherming - beschermingsgebieden - mangroves - ecologisch herstel - menselijke invloed - nadelige gevolgen - bonaire - nature conservation - conservation areas - mangroves - ecological restoration - human impact - adverse effects - bonaire
Following a helpdesk question from the Dutch Ministry of Agriculture, Nature and Food Quality (LNV) concerning potential threats to the Ramsar Site, Lac Bonaire, the authors visited Lac Bay from 27-29 May 2010. The mangroves, seagrass beds and the reef, both inside and outside of the bay were visited, and we were generously helped by many people on the island, including STINAPA Bonaire, DROB, STCB, and CIEE. In this study we review the main issues, recommend studies, and propose various pilot projects and solutions.
The dynamics of shoreline wetlands and sediments of northern Lake Victoria
Azza, N. - \ 2006
Wageningen University. Promotor(en): P. Denny, co-promotor(en): J. van de Koppel; F. Kansiime. - [S.l.] : s.n. - ISBN 9789085044994 - 170
wetlands - meren - mangroves - sediment - oost-afrika - verandering - oevers - wetlands - lakes - mangroves - sediment - east africa - change - shores - cum laude
cum laude graduation (with distinction)
Remote sensing techniques for mangrove mapping
Vaiphasa, C. - \ 2006
Wageningen University. Promotor(en): Andrew Skidmore; Herbert Prins, co-promotor(en): Fred de Boer. - [S.l. ] : S.n. - ISBN 9789085043539 - 129
mangroves - mangrovebossen - vegetatie - remote sensing - karteren - classificatie - mangroves - mangrove forests - vegetation - remote sensing - surveying - classification
Mangroves, important components of the world's coastal ecosystems, are threatened by the expansion of human settlements, the boom in commercial aquaculture, the impact of tidal waves and storm surges, etc. Such threats are leading to the increasing demand for detailed mangrove maps for the purpose of measuring the extent of the decline of mangrove ecosystems. Detailed mangrove maps at the community or species level are, however, not easy to produce, mainly because mangrove forests are very difficult to access. Without doubt, remote sensing is a serious alternative to traditional field-based methods for mangrove mapping, as it allows information to be gathered from the forbidding environment of mangrove forests, which otherwise, logistically and practically speaking, would be extremely difficult to survey. Remote sensing applications for mangrove mapping at the fundamental level are already well established but, surprisingly, a number of advanced remote sensing applications have remained unexplored for the purpose of mangrove mapping at a finer level. Consequently, the aim of this thesis is to unveil the potential of some of the unexplored remote sensing techniques for mangrove studies. Specifically, this thesis focuses on improving class separability between mangrove species or community types. It is based on two important ingredients:
(i) the use of narrow-band hyperspectral data, and
(ii) the integration of ecological knowledge of mangrove-environment relationships into the mapping process.
Overall, the results of this study reveal the potential of both ingredients. They show that delicate spectral details of hyperspectral data and the spatial relationships between mangroves and their surrounding environment help to improve mangrove class separability at the species level. Despite the optimism generated by the overall results, it was found that appropriate data treatments and analysis techniques such as spectral band selection and noise reduction were still required to harness essential information from both hyperspectral and ecological data. Thus, some aspects of these data treatments and analysis techniques are also presented in this thesis. Finally, it is hoped that the methodology presented in this thesis will prove useful and will be followed for producing mangrove maps at a finer level.
Mangroves and sediment dynamics along the coasts of southern Thailand
Thampanya, U. - \ 2006
Wageningen University. Promotor(en): P. Denny; J.E. Vermaat. - [S.l. ] : S.n. - ISBN 9780415384865 - 116
mangroves - sediment - bomen - verspreiding - kusten - taxa - kolonisatie - zaden - milieubeheer - soorten - thailand - mangroves - sediment - trees - dispersal - coasts - taxa - colonization - seeds - environmental management - species - thailand
Mangroves are a specific type of evergreen forest that is found along the coastlines of tropical and subtropical regions, particularly along deltas and bays where rivers discharge freshwater and sediment to the sea. These mangroves provide important ecological and socio-economic functions to coastal dwellers and societies. For example, they are natural spawning and living ground for many species of fish and crustaceans. Their timber benefits local people as construction material, firewood and charcoals and their marvelous root systems contribute to sediment deposition, mud flat formation and substrate stabilization. Thus, these forests also function as a shelter belt during storms, cyclones and tsunamis. This function was evident when the mangroves in Southern Thailand helped to mitigate the recent 2004 tsunami's devastation on lives and properties of the villages situated behind them.>
The present status of these valuable resources is critical, particularly in Southeast Asia, where the mangrove forest area is estimated to have declined by more than 50 percent over the past 35 years. The major causes of this loss were encroachment due to population expansion, conversion to aquaculture ponds, coastal erosion, lack of awareness and obscure or poorly enforced regulations, In Thailand, for example, recent satellite images show ample evidence of established and widespread aquaculture ponds along the coast of the Gulf of Thailand due to lack of restriction. More recently, government and public awareness of the importance of mangroves has risen, which has translated into several restoration and afforestation projects. Restoration of degraded mangrove areas was found to require much effort and encountered land-right problems. Therefore, many projects had switched to afforest on newly formed mudflats. Such projects, however, have met with variable success or failed to achieve the stated goals. This was probably because planting was carried out straightaway without carefully determining site-species suitability, appropriate planting technique as well as self-recovery or self-colonization capabilities from nearby stands.
To obtain useful information for supporting sound mangrove and coastal zone management, this dissertation aims to gain a better understanding of mangrove (re)-colonization and factors effecting colonization success as well as factors underlying coastal changes. Firstly, the impact of sedimentation and water turbulence on seedling survival and growth of three common SE Asian mangrove taxa: Avicennia, Rhizophora and Sonneratia, were examined experimentally at the bay scale. Then, this research was broadened to assess the coastal dynamics of Southern Thailand by synthesizing data from coastal surveys over the period 1961-2000 along with field studies. Finally, simple demographic models were developed to simulate the mangrove colonization process.
The two experiments reveal that after successful establishment on the mudflat, seedlings were susceptible to mortality due to sudden high sediment burial and water turbulence. Mortality was found to increase with increasing sediment accretion and none of Avicennia seedlings was able to survive under the highest experimental burial of32 cm while those of Rhizophora and Sonneratia still showed substantial survival (30% and 60%, respectively). Among the three taxa, Sonneratia was the least affected due to burial and exhibited a rapid growth rate. Seedlings of Rhizophora survived less m highly exposed plots (low neighboring plant density) than in sheltered ones. In contrast, survival of Avicennia and Sonneratia seedlings were higher at more exposed plots. This finding confirms the behavior of Avicennia and Sonneratia as pioneer species that may colonize unoccupied mudflat and Rhizophora as a successor. It a!so suggests a higher success of the first two species in re-colonization. However, in areas where sudden high sediment loads are possible, Sonneratia might be better able to cope with burial than Avicennia.
The assessment of changes along Southern Thai coastlines revealed that the coast of the Gulf of Thailand had undergone more change than the western side of the peninsula. Ongoing erosion occurred irregularly at the high energy coastal segments and was observed along 29% and 11% of the total coastal length of the east and the west coasts, respectively. Subsequent total area loss accounted for 116 ha annually (91 and 25 ha for the east and the west coasts, respectively). Factors responsible for coastal erosion were found to be mangrove area loss, increase of shrimp farming area, less sediment delivery to coastal area due to upstream river damming and exposure to fetch from the monsoonal wind. Erosion was less in mangrove-dominated coastlines, and progression occurred mainly in sheltered and mangrove-dominated coastal segments. Areal progress accounted for 37 ha per annum on the east and 5 ha on the west coasts. Thus, summed over the whole of Southern Thailand, a net erosion of 74 ha y-1 was observed over the past three decades. These results also reveal that the existence and progression of the mangroves as well as sufficient sediment supply to coastal area contributed significantly to coastal stability.
Thirty-year runs of the demographic simulation model revealed that herbivory and water turbulence were the main factors influencing the success of colonization in a mangrove-dominated bay while gradual sedimentation and salinity had little effect. Avicennia was the most successful taxon in colonizing open mudflats followed by Sonneratia while Rhizophora exhibited less success. However, colonization success may vary with changes in environmental conditions as revealed by our predictive scenarios. For example, accelerated sea level rise will reduce the success in colonization of all three taxa and lack of freshwater discharge due to river damming may enhance the colonization success of Avicennia but adversely affect Sonneratia.
Overall, this study suggests that success in re-colonization of mangroves depends on both ecological and hydrological factors. Seedling herbivory and water turbulence are important factors that may seriously hinder colonization success. Also, the three taxa studied were found to differ critically in colonization capacity. Gradual sedimentation has little effect on mangrove colonization but positive sedimentation provides habitats for mangrove to colonize, particularly, in sheltered coastal segments. Less sediment delivery due to upstream river damming associated with conversion of mangrove and beach forest to aquaculture ponds will probably intensify coastal erosion in vulnerable areas. Therefore, managers should pay more attention to the balance between ecological and socio-economic demands for sustainable development of the coastal zone.
Penaeus monodon post-larvae and their interaction with Rhizophora apiculata
Nga, B.T. - \ 2004
Wageningen University. Promotor(en): Marten Scheffer, co-promotor(en): Rudi Roijackers. - Wageningen : WUR - ISBN 9789085040934 - 111
penaeus monodon - garnalen - rhizophora apiculata - mangroves - interacties - aquacultuur - garnalenteelt - schaal- en schelpdierenvisserij - populatiedynamica - mortaliteit - ligstro - voedingsstoffen - toxiciteit - vietnam - penaeus monodon - shrimps - rhizophora apiculata - mangroves - interactions - aquaculture - shrimp culture - shellfish fisheries - population dynamics - mortality - litter - nutrients - toxicity - vietnam
In recent years, expansion of shrimp aquaculture in Vietnam has brought considerable financial benefits to farmers and local communities. In the coastal provinces in the Mekong Delta, brackish shrimp aquaculture is the major economy activity. Extensive shrimp-mangrove culture systems are popularly practiced here. Although the average shrimp production is low, due to over-exploitation and destruction of mangrove forests and salt marshes, these systems are of special interest in view of the problems of sustainability of intensive aquaculture (Naylor et al. 2000 Nature 405: 1017-1024). Several studies demonstrated that mangrove swamps are highly productive ecosystems providing food, shelter and nurseries for various aquatic organisms, many of which are commercially important. The tiger shrimp, Penaeus monodon , is a clear example in this case. Natural shrimp production in these areas is believed to depend to a large extend on the presence of mangroves. However, the complex of mechanisms through which mangroves affect shrimp production is still poorly understood. The work in this thesis is an attempt to unravel some of the key-processes involved. It confirms the picture that mangrove litter represents a formidable input of organic material and nutrients into the aquatic system, and reveals how this input may have positive as well as negative effects on growth and survival of post-larval shrimp.Mangrove stands of different age have been studied for one year with respect to their litter fall and nutrient input (chapter 2). Litter fall consisted for 70% of leaf litter and organic matter accounted for 90% of the dry weight. Litter fall declined with the age of the mangrove stands, and also nitrogen and phosphorus levels were considerably higher in the leaf litter of younger stands (7 and 11 years) as compared to the older stands (up to 24 years). Thus, both the amount and the quality of litter input to the aquatic systems are highest in younger mangrove stands.As a next step key factors affecting the decomposition of mangrove leaves were analyzed (chapter 3). Decomposition rates tended to be highest at lower salinities, and reached an optimum at 5 . The decomposition rates were also highest in the wet season, and this may well be due torelatively low salinities in this period. Wet season salinity in the Camau area was in the range of 4 - 9 , close to the optimum for decomposition derived from laboratory experiments. Our studies also indicated an effect of humidity per se. We found that the decomposition rate was higher for leaves submerged in the ditches, than for leaves incubated near the roots of mangrove stands in the open air, where decomposition rates were higher in the wet than in the dry season. We also analyzed the dynamics of nutrient concentrations in decomposing litter. Nitrogen and phosphorus levels in decomposing leaves increased during the decomposition period. This enrichment indicates an increase of food quality over the first period of decomposition .The following chapters show that the effects of decomposing mangrove leaves on shrimps can be positive but also negative (Chapter 4 and 5). The amount of decomposing leaves appeared key. At high concentrations of leaves negative effects prevailed. These effects were probably due tothe release of nitrite and sulphide, and a decrease in dissolved oxygen concentration. On the positive side, mangrove moderate concentrations of leaves promoted growth of Penaeus monodon post-larvae, and apparently served as a shelter and as a food source.The fact that micro-organisms growing on the leaves, rather than the leaf material itself may be important as food was illustrated by the result that shrimps feeding on mangrove leaves grew better when a periphyton layer covered these leaves (chapter 5). A somehow surprising positive effect of leaves was the apparent prevention of excessive concentrations of ammonium and nitrite. The results suggest that adding conditioned mangrove leaves might ameliorate negative effects of high protein pellets on the water quality. The high C/N-ratio of leaves tends to balance the stochiometry of the system which may otherwise be dominated by the excessive N-input through CP pellets.In the final chapters the interaction among the shrimp larvae themselves, i.e. the effects of stocking density and the release of crowding chemicals and possible alarm pheromones on the shrimp populations are addressed (chapter 6, 7). A strong effect of crowding on shrimp growth and survival was shown. Physical interference stress and cannibalism could be excluded as causal factors. It was thus clear that the effects were caused by other water quality variables. Temperature, pH, salinity, dissolved oxygen, chlorine, nitrite and nitrate appeared of minor influence. However, ammonia toxicity could not be excluded as the causal factor for the observed mortality and reduced growth of P. monodon post-larvae in our experiments.On the other hand, alarm cues, as released by crushed conspecifics had negative effects on post-larval survival at high concentrations (100, 70, 50 and 30 crushed shrimps.l -1 ). Surprisingly, low concentrations of crushed conspecifics (1 crushed shrimp.l -1 ) were shown to have rather stimulatory effects on body size and dry weight.Put in an applied perspective, this study suggests simple ways to improve the management of mangrove-shrimp systems. Clearly, mangrove leaves can promote the survival and growth of shrimp post-larvae. However, at high leaf concentrations negative effects may prevail related to a drop in dissolved oxygen and the release of sulphide. A straightforward way to ameliorate such negative effects may be to increase the water flow. This will reduce the risk of local anoxia, and may help spreading the litter over the area, thus avoiding accumulation of these leaves at some sites. The reduction of potentially toxic nitrite and ammonium concentrations by decomposing leaves suggests that mangrove leaves may serve as a useful complement to CP pellets in semi-natural production systems.
Environmental impacts of abandoned dredged soils and sediments; available options for their handling, restoration and rehabilitation
Ohimain, E.I. ; Andriesse, W. ; Mensvoort, M.E.F. van - \ 2004
Journal of Soils and Sediments 4 (2004)1. - ISSN 1439-0108 - p. 59 - 65.
sediment - bagger - bodemverontreiniging - stort - mangroves - west-afrika - sediment - dredgings - spoil - soil pollution - mangroves - west africa
Aim and Background. In the process of creating safe navigable waterways for oil exploitation, the companies operating in the Niger Delta generate tons of sulfidic spoils. These are often deposited over bank, mostly upon fringing mangroves, and abandoned. This leads to a myriad of environmental problems. The extent of these impacts is not exactly known, but was inferred from the activities of oil companies operating in the area. This paper describes the impacts following the disturbance of sulfidic sediment through dredging and by subsequent poor spoil management practices. Environmental impacts of exposed and abandoned sulfidic sediments. The practice of dumping and abandoning sulfidic dredged spoils along canal banks triggers a series of environmental problems leading to extreme acidification, heavy metal pollution, and general habitat degradation which prevent the re-colonization of the sites by native species. The resultant spoil dumps remain bare for several years and they become colonized by invasive species later. Later still they may become attractive to the local population as sites for houses, fishing camps and home gardens, which is nevertheless regarded as a positive impact. Management of abandoned sulfidic spoil dumps. As a panacea to environmental problems caused by the sulfidic spoils, they need to be properly handled to prevent their acidification. This should be followed by mangrove restoration to pristine conditions or rehabilitation to other beneficial uses. Conclusion and Recommendation. The abandoned sulfidic spoils in the Niger Delta have resulted in the death of several thousands of hectares of mangrove habitat and their associated biota. Despite the increasing scale of dredging and spoil abandonment, the accompanying problems have been recognized by neither the oil companies nor by national government. This paper attempts to highlight these problems and concludes by recommending sound spoil management strategies involving the handling, restoration and rehabilitation of impacted areas. Furthermore, possible beneficial use of dredged spoils for civil construction, beach nourishment / shoreline protection is identified. The Nigerian Government needs to promulgate and enforce laws that will permit the sustainable use of mangrove resources.