This study is aimed at analyzing key indicators for the evaluation of changes and tendencies of sustainable utilization and management in some marine ecosystems in the coastal waters of Hai Phong - Quang Ninh area. To complete this study, the methods employed consisted of the application of remote sensing data and geographic information systems to extract information on spatial distribution of mangrove and tidal flat ecosystems, as well as on the reclamation area for human development and indicator investigation and analysis, using remote sensing extracted and field survey monitored data with Microsoft Excel (MS Excel). Applying indicators for sustainable utilization and management of marine ecosystems, developed in recent studies for the Hai Phong - Quang Ninh area, demonstrated changes and trends in significant ecosystems, such as coral reefs and mangroves. The outcomes showed that from 1998 to 2003, living coral cover was reduced by 20% on average in the Ha Long Bay area and by 13% in Cat Ba (Hang Trai - Dau Be), and projected that living coral cover would be reduced by a further 10% to 50% by 2010. The number of coral species was much reduced by 15% to 72% in the Ha Long—Cat Ba area. Mangrove area also decreased between 1995 and 2004, particularly after 2000, and is projected to be only 10,000 ha in 2010 in Quang Ninh. Marine ecosystems in the coastal waters of Hai Phong - Quang Ninh area have degraded significantly, particularly coral reefs, mangroves and tidal flats.
The development of state (S) and pressure (P) indicators following indicator classification by the Organization for Economic Cooperation and Development (OECD, 1991) as a quantitative method for sustainable utilization and management of natural ecosystems, is very important to the coastal area of Hai Phong – Quang Ninh, Vietnam, where the potentials of economic development and natural conservation are considered to be very high. In the study area (Figure 1) of Hai Phong – Quang Ninh, there are three typical natural ecosystems of mangroves, tidal muddy flats and coral reefs belonging to a larger coastal zone system (Lan, 2004a). However, the assessment of these natural systems, in terms of their response to the pressure of human activities for economic development, is still poorly known. Therefore, these ecosystems were selected for this study.
Each ecosystem in this coastal area is affected by human activities in specific ways. To analyze the relation between the ecosystems and human development, some core indicators for assessment of these coastal ecosystems were developed: such as living coral cover, total species number, ecosystem area, and aquaculture development (Lan, 2006; 2007). Of these, the spatial distribution of ecosystem indicators has the potential to be used to assess the impacts of human activities and natural processes on these ecosystems. This study was completed with the focus on the application of remotely sensed data in combination with field survey monitoring data for the investigation of ecosystem indicators. To analyze the spatial distribution indicator, sequences of satellite images with high spatial resolution and digital processing and analysis (using remote sensing data and geographic information system – GIS) of these data were employed. The results of the processing and analysis were used for the evaluation of the dynamics and trends of these indicators. Also, ecosystem sustainable utilization and management were assessed to support further planning of the area.
Materials and methods
Materials for this study were mainly from 1/50,000 maps published in 1998 (references), remote sensing image sequences of SPOT and Landsat from 1995 to 2004 (1995, 1997, 2000, 2002 and 2004) during the same season (wet and dry), GIS databases of several projects implemented in the area (Dien, 2004; Hoi, 2003; Lan and Binh, 2004) and surveying and monitoring data conducted by the Institute of Marine Environment and Resources since 2004.
The main methods employed are the processing and analysis of remotely sensed data using PCI software package in combination with visual interpretation. To assess ecosystem changes in area, sequences of seasonally-collected remote sensing images are corrected to have the same resolution and to cover the same spatial area. The parameters were collected from remotely sensed imageries of SPOT and Landsat with support from GIS technology (Arcview GIS) to organize databases, including the area of mangrove forests, the area of aquaculture ponds, the area of tidal muddy flats, and the area of reclamation (for agriculture, land filling for urbanization, industrial zones). Field survey monitoring data of coral reef ecosystem including living coral cover and total species of living coral were collected by using the technique described in Survey Manual for Tropical Marine Resources (English et al., 1997) and ReefCheck coral reef monitoring (Hodgson et al., 2004), then input into databases. Processing, statistical analysis and interpretation of outputs were done using MS Excel.
The ecosystems of mangroves, tidal muddy flats and coral reefs are closely related to each other in terms of spatial growth as all three are in direct competition for limited spatial resources. The indicators for sustainable utilization and management of ecosystems include indicators of geographical characteristics that clearly show this relationship in the study area (Lan, 2006; 2007).
To assess the change of mangrove ecosystems in the study area, two key indicators were selected, including mangrove spatial distribution and aquaculture pond area. The mangrove spatial distribution indicator is equal to the total area (ha, sq. m) of mangrove forests, which are distributed at the intertidal space from mean sea level to high tidal level. This indicator monitored by series of SPOT and Landsat imageries is a state (S) one (Lan, 2007) and shows the decline in mangrove spatial distribution since 1995 for the whole area (Figure 2).
The indicator of aquaculture pond area is a pressure (P) one (Lan, 2007) and equates to the total area of aquaculture ponds (ha), consisting of both aquaculture pond area in mangrove forests and on muddy tidal flats without mangroves. Analysis of this indicator using series of SPOT and Landsat imageries shows a tendency to increased aquaculture pond area since 1995. After 2000, there has been an obvious increase in aquaculture in contrast with the decline of mangrove distribution. The decline of total mangrove area is clearly related to the increase of total area of aquaculture ponds (Figure 3).
For the tidal muddy flat ecosystem, two indicators of tidal flat area and the area of reclamation were investigated. The indicator of tidal flat area (ha) is a state indicator (S) (Lan, 2007), defined as the total area of tidal flats without mangroves and outside aquaculture ponds. Similar to the mangrove status, the area of tidal flats of the whole area investigated using series of SPOT and Landsat imageries has decreased, especially after 2000 (Figure 4). This is also related to the development of aquaculture ponds and reclamation for urbanization, industrial expansion, etc. The area of reclamation (ha) indicator is a pressure indicator (P) (Lan, 2007), defined as the total area (ha) of tidal wetlands that is reclaimed for the purposes of socio-economic development. The reclamation area has increased since 2000. In the period of 2002 to 2004, the reclamation area has increased by factor of 2.5 (Figure 5). The area of reclamation has directly affected the growth of mangroves, tidal flats and sea soft bottom ecosystems in the study area.
Coral reefs are a unique ecosystem in Hai Phong - Quang Ninh area and have been threatened by sedimentation increase, dynamite fishing, uncontrolled mooring of tourist boats, etc (Lan and Binh, 2004). To assess the growth of coral reefs ecosystem in the study area, two key indicators of living coral covers and total living coral species were investigated. The indicator of living coral cover is a state one (S) (Lan, 2007), defined as the total living coral cover (%) in the study area. This indicator is analyzed with the monitoring data set from 1995 to 2004 (Lan, 2007), and the results show a decrease of living coral cover in the area (Figure 6).
The indicator of living coral species is also a state one (S) (Lan, 2007), defined by the total number of living coral species in the area. This indicator is also analyzed using data collected from the monitoring studies (Lan, 2007) and here the results also reveal the decline of living coral species in the period from 1995 to 2004 (Figure 7).
Analysis of the spatial area indicators shows the close relationship between the decline of mangrove and tidal flat ecosystems, with the development of aquaculture ponds and the reclamation for economic sectors and urbanization in the whole study area. Analyzing the direct relationship of the spatial use of mangrove forests and tidal flats for aquaculture pond development in Quang Ninh province (Figure 8), it can be projected that by 2010, aquaculture development with the rate of the past ten years will reach approximately 20,000 ha. Meanwhile, mangrove forest and natural tidal flat ecosystems will only have a combined area of approximately 35,000 ha. The mangrove forest area alone in Quang Ninh is predicted to approximate 10,000 ha (Figure 8). As a whole, it is shown that the decline in area of mangroves and tidal muddy flats is mostly related to the development of coastal aquaculture in the area (Lan, 2007).
Analysis of the living coral cover indicator shows the poor growth of coral ecosystems in Hai Phong - Quang Ninh. In almost sites of coral living, after 2000, living coral cover percentage has changed dramatically. In only Long Chau Islands of Cat Ba District in Hai Phong, living coral cover has been maintained at 30% thanks to very few impacts of human activities at this site. Poor growth after 2000 indicates the degradation of the coral reef ecosystem with unclear causes.
Application of a linear regression obtained from investigating the living coral cover indicator in the period of 1995–2004 projects that by 2010, the living coral cover in the area of Ha Long Bay area will only be 10% of the total reef area if no protection and restoration measures are taken.
Analysis of the indicators of area of mangroves and tidal flats with supporting data from remote sensing imageries and field surveys showed that the decline in area of these ecosystems corresponds to the increase in area of coastal aquaculture and urbanization in the period of 2000 to 2004. For example, in Quang Ninh province (before 1995), the area of aquaculture ponds covered 4% of the total mangrove and tidal flat area. This rate reached 8%, 11% and about 30% in 2000, 2002 and 2004, respectively. The rate would be acceptable if aquaculture ponds were not concentrated in mangrove forest but in tidal muddy flats (without mangroves). However, coastal aquaculture ponds in the study area have been in fact developed most in mangrove forests. Therefore, the recalculating rates of coastal aquaculture development at the expense of mangroves were 13%, 24%, 33% and approximately 90% before 1995, in 2000, 2002 and 2004, respectively. As such, the mangrove ecosystem was no longer fully ecologically functioning, with respect to environmental filters, nursery grounds, etc. which require a mangrove area of 3 to 4 times higher than the area of aquaculture ponds (Hong, 2005). In the case of Quang Ninh province, in 2002, 33% of mangrove forests were converted into aquaculture pond area, meeting the rational utilization rate of mangrove forest area. After 2002, the increased conversion from mangrove area to aquaculture ponds, showed the overexploitation of the mangrove ecosystem in Quang Ninh. Mangrove ecosystem in Hai Phong City is also declining due to replacement by aquaculture ponds. As such, it is urgent to replant mangroves to have at least a minimum area equal to that of 2002 (approximately 20,000 ha) to maintain the ecological functions of the ecosystem. Other management measures, including environmental fees for restoration, protection of the environment and resources (Hoi, 2005; Lan, 2004b; Lan and Minh, 2005) and developing adaptive aquaculture in mangroves must be taken.
The ecosystem of tidal muddy flats without mangroves that is distributed in low tide areas can not be used for development of aquaculture ponds. There should be consideration for culture mollusks and sea weeds in combination with the establishment of species or habitat protected areas in this ecosystem. Coral reef ecosystems have been rapidly degrading, particularly after 2000. This situation might be the consequence of human activities in the coastal area of Hai Phong - Quang Ninh, such as coal mining and deforestation, which increase sea water turbidity and fishing that directly destroy coral reefs.
Outcomes from investigation of the key indicators for three typical ecosystems of mangroves, coral reefs and tidal muddy flats showed that for the last ten years, these ecosystems have been degraded. The spatial distribution of these ecosystems has been dramatically narrowed and the ecological unbalancing may become worse in the coastal waters of Hai Phong - Quang Ninh. Analysis of the results of a series of ecosystem indicators quantified a trend in the coastal and marine ecosystem development and provided warning to managers and communities to take necessary actions for environmental and ecological security.
This paper is made available with the support of the project coded 7 140 06 under the Fundamental Research Programme of Vietnam and the project “Developing sustainability indicators for tidal wetland resources in the west coast of the Gulf of Tonkin” funded by Vietnam Academy of Science and Technology.