Project

Fishery habitat restoration and resource conservation technology in important estuaries

Goal: Identified the habitat needs of important fishery species such as Chinese mitten crab, Coilia Coilia, for key estuarine habitats;
Research and develop habitat restoration and reconstruction technologies and supporting facilities such as "floating wetland", "tidal vegetation zone" ;
Establish technical measures for proliferation, conservation and comprehensive management and control of important fishery species; Establish the restoration and reconstruction technologies for the spawning grounds of Eriocheir sinensis and Coilia Coilia in the Yangtze River Estuary, and build the models and technical systems for the restoration of fishery habitats and resource conservation in estuaries.

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Project log

Sikai Wang
added 5 research items
The reed density has basically maintained a stable state, and the plant height has reached about 600 mm, the density is reached 125 ind./m2 after the floating wetland fixed 50 days later in the Yangtze River estuary. The reed in the artificial wetland can complete the growth season of the current year. In addition, the floating wetland also withstood the typhoon in July, indicating that the design of the three-dimensional reed floating wetland can adapt to the complex estuarine hydrological environment and even extreme weather.
Sikai Wang
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1. Background
The Yangtze River is the longest river in China, ranking third in the world. The river originates from the Plateau of Tibet and empties into the East China Sea. The Yangtze River estuary covers a large portion of Shanghai and a portion of Jiangsu Province. The estuary includes a river part whose upper boundary is Datong in the main stream of the Yangtze River (624 km upstream of the estuary) and a near-shore zone (the near-shore zone of the East China Sea) (Mikhailov et al., 2001).
Like other estuaries, the Yangtze River estuary provides great ecosystem services for humans and wildlife in the region; thus it is an important ecoregion. The estuary has a diversity of wetland ecosystems, such as shallow open waters, mudflats, salt marshes and brackish ecosystems, which make an important habitat for aquatic species. Therefore, maintaining the integrity of the native ecosystems and conserving biodiversity in the estuary are of both regional and international importance. However, the mudflats and salt marshes in the estuary are now heavily degraded by human activity.
The total area of the original wetland in the Yangtze River estuary is 350,000 hm2. Human beings have carried out large-scale land reclamation (such as beach reclamation) and water engineering construction, resulting in the loss of 57% of the wetland area in the intertidal zone of the Yangtze River Estuary. The natural coastline of the Yangtze River Estuary has been seriously degraded, which has not only caused great damage to the important fishery habitat, but also affected the function of the ecological barrier in the Yangtze River Estuary.
Fish populations have declined in many estuarine and freshwater ecosystems in part due to the loss of habitat in recent decades. Reconstructing lost habitat for fish is a potential method for recovering fish populations. Many scientific methods have been used to reestablish the deteriorated habitats of fish species. Vegetation is a method that has been used to create habitat for fish and crustaceans. The main reason for this is that these plants represent ideal food resources and suitable habitat for these species (Thom et al., 2004; Weinstein et al., 2009; Putnam et al., 2010). In view of the aggravation of erosion of salt marshes in the Yangtze River Estuary caused by global climate change and human activities, we carried an ecological restoration measures to maintain the habitat diversity of estuarine wetlands, so as to provide support for sustainable fishery output.
2. Objectives
This project plans conduct ecological restoration research in the Yangtze River Estuary, focused on the habitat needs of key fishery species in the Yangtze River Estuary, and carried out targeted research and development of common technologies for habitat restoration based on the current situation of fishery habitats. The project plans development of the ecological restoration technology mode with "artificial floating wetlands + plant transplanting" as the main means. The main objective is speed up the greening of beaches, repair and rebuild important fishery biological habitats, and protect the fishery resources in the Yangtze Estuary. Through the implementation of the project, a reproducible ecological restoration technology model of key fishery habitats in the Yangtze River Estuary can be formed, which provides scientific support for maintaining the normal function of the ecosystem in the Yangtze River Estuary. The study constructed reed ecological floating bed through artificial measures, carry out experimental research on beach plant planting, and evaluate the effect of ecological restoration measures.
3. Materials and methods
3.1 Study area
The project conduct ecological restoration research at the Chongming Island in the Yangtze River Estuary, China (Fig 1). The coastal waters of the South Branch of the Yangtze River Estuary as the demonstration study area (E121.64o, N31.52o). This area is located in the experimental area of the Yangtze River Coilia nasus National Aquatic germplasm resources protection zone. It is the traditional feeding ground, migration channel and key habitat of Coilia nasus, Eriocheir sinensis, Acipenser sinensis and other important organisms.
The study area is influenced by a sub-tropical monsoon climate. Mean annual precipitation is 1,145 mm, mainly falling during summer. Mean annual temperature is 15.7°C, with a mean temperature of the coldest and warmest months being 4.2°C in January and 27.3°C in July, respectively. The intertidal zones of the wetland are flooded by semi-diurnal meso-tides with a pronounced neap-spring inequality. Mean tidal range is 2.67 m, and the maximum tidal range is 4.62 m. Salinity is higher in winter than in summer due to variable precipitation and freshwater runoff of the Yangtze River from the dry season (November–January) to the wet season (July–September) (Wang et al., 2015). The key native plant species include Two native plants, Scirpus mariqueter and Phragmites australis and one exotic plant Spartina alterniflora. Therefore, this project avoid used exotic plant, which may threaten the estuarine ecosystems and their biodiversity.
Due to agricultural development and metropolis expansion along this estuary, the course of this estuary has been highly regulated in recent decades. The hardening of the coastline leads to few plants can grow along the estuary, so the fishery habitat function in this area is seriously degraded or even lost.
3.2 Construction of floating wetland
The floating wetlands have been applied to recover deteriorated habitat for various animals. Both the physical complexity of the simulated structures and their location in the water column could facilitate the formation of a suitable environment. Moreover, all kinds of cultivated plants could attain nutrients directly from the water column because they were not rooted in any substrate, which may improve the rate of nutrient uptake into biomass. These plants facilitated the attachment of microorganisms, which favored the decomposition of organic matter and the entrapment of suspended solids.
Each artificial floating wetlands framework can be divided into two parts: artificial plant bed on the water surface and palm sheets hung over the frameworks. Substrate-rooted plants and floating structures that consisted of aquatic or terrestrial plants growing in a hydroponic manner with buoyant frames floating on the surface of water bodies (Fig. 2, Fig. 3). Artificial floating wetlands were constructed by reed (Phragmites australis) in to recover the lost habitat in the Yangtze River estuary from March to July 2021. Because two high tides and two low tides every day in the Yangtze River estuary, the water environment is very complicated, all floating wetlands were anchored at the study area. Total 32 individual floating wetlands with 1m×1m were placed in the tidal flat for experimental research. The distance between the sampling site and each floating wetlands unit was 10 m.
3.3 Plant transplanting
In the Yangtze River estuary, the key native plant species include Scirpus mariqueter and Phragmites australis. The P. australis is suitable for tidal flat with relatively high elevation, while S. mariqueter is generally a pioneer plant, which can withstand tidal inundation for a long time. Therefore, the project has carried out the research on the transplanting and planting of S. mariqueter in the study area, hoping to provide a reference basis for the restoration of intertidal wetlands.
To explore the process and mechanism of colonization and expansion of salt marshes on tidal flats, and develop the scientific and effective methods for the restoration of S. mariqueter, we carried out the restoration experiment in the project area of dynamically changing tidal flat at Chongming island. We found that under the condition of dynamic tidal flat, adding manual support could create the windows of opportunity for seed emergence and could significantly improve the emergence rate of S. mariqueter. The seedling establishment needs to pass a tipping point of tidal flat elevation which is higher than 2.2 m, and the sedimentation dynamics should be benign. Restoration techniques based on seed sowing and plant transplanting developed by ecological theory might be feasible for the restoration of intertidal salt marsh.
Based on the above research results, S. mariqueter were planted in the mudflat, and forming an about 5000m2 new intertidal salt marsh community in the study area from March to July in 2021(Fig. 4).
3.4 Aquatic monitoring
3.4.1  Plant survival and growth
The vegetation area is estimated through field measurement to evaluate the survival and growth of plants. For floating wetland, the density of P. australis was recorded in the field, and the fresh weight and dry weight were measured in the lab. For S. mariqueter planting area, take 0.5m × 0.5m quadrat, use scissors to cut the aboveground part and record the density in the quadrat. Put the cut samples into plastic bags, weigh the fresh weight, and then dry them in the drying oven at 80 ℃ to constant weight to obtain the plant biomass (g/m2).
3.4.2  Benthic macroinvertebrate
The quantitative sampling of macrobenthos was carried out between the ecological restoration area and the control area in July 2021, respectively. Each sample was mixed with three sediment cores (20 cm long × 20 width × 15 cm depth), taken 3–5 m from each other, and sieved through a 0.5 mm mesh. All samples retained on the sieve were fixed in 10% formaldehyde. Animals were separated carefully from the debris and then identified to the lowest possible taxonomic level under a dissecting microscope (OLYMPUS SZX9 which located in the East China Sea Fisheries Research Institute).
3.4.3  Nektons (fish, shrimps and crabs)
Carry out the monitoring of swimming animals in the ecological restoration area and the control area, analysis the structure of swimming animal community (including species composition, dominant species, quantity, biomass change, etc.), the impact of restoration measures on swimming animal community, and explore the role of habitat change in the breeding and foraging of fish, shrimp and crab, as well as its contribution to the protection of fishery resources.
The monitoring of swimming animals is mainly to take samples during spring tide. Each monitoring survey is conducted for 3 days, and one sample is taken during daytime tide and night tide respectively. The survey nets are bottom cage nets and fixed fyke nets (Fig. 5). The specifications and methods are as follows: (1) Bottom cage net: Length, height and width, 18m´0.33m´0.45m, net mesh 2a=0.8cm, Sampling at ebb tide, twice a day. (2) Fixed fyke net: The net wing is 30m long and 1.5m high, and the net mesh 2a=0.8cm. Take samples at the ebb tide of day and night, twice a day.
All catches are brought to the laboratory for identification, counting and measurement. The length of the fish body is in mm. Use the fish measuring plate to measure the body length and total length, and use the balance to weigh. The length of the fish body is in mm and the mass is in g. all samples were taken simultaneously in the ecological restoration area and the control area in July 2021.
4. Mainly results
4.1 Plant growth
In the ecological restoration area, the plant of Scrips mariqueter has completed the colonization, and the patches combine to form a community, with a gradual expansion trend. By August 2021, the vegetation area is about 5000m2 (Fig. 6). “Reed three-dimensional floating wetland” completes 8 groups of splicing, and each group is composed of 4 modules composed of 1m×1m reed roots.
Through the continuous monitoring of the growth of S. mariqueter in the transplanting area and reed in the three-dimensional floating wetland (Fig. 7), we found that S. mariqueter can not only grow normally, but also expand outward; the average density of S. mariqueter showed the highest value of 1904 ind/m2 in May; the average plant height showed the highest value in June with 783 mm in June; the average fresh biomass of aboveground is 1731g/m2 and dry biomass is 432g/m2 in June.
The reed density has basically maintained a stable state, and the plant height has reached about 600 mm, the density is reached 125 ind./m2 after the floating wetland fixed 50 days later in the Yangtze River estuary (Fig. 7). The reed in the artificial wetland can complete the growth season of the current year. In addition, the floating wetland also withstood the typhoon in July, indicating that the design of the three-dimensional reed floating wetland can adapt to the complex estuarine hydrological environment and even extreme weather.
4.2 Benthic macroinvertebrate
The investigation and assessment of macrobenthos were carried out three months after the completion of habitat restoration. Survey and sampling were conducted in the restoration area and the control area respectively. The results showed that the number of macrobenthos species significantly increased from 5 to 10, the growth rate reached 100%; the biomass increased from 38±16 g/m2 to 59±17 g/m2; density increased from 76±10 ind/m2 to 177±27 ind/m2 (Fig. 8)。
4.3 Larval fish
A total of 20 species of larvae and juveniles were detected in the study area in the Yangtze River estuary (Table 1), 16 fish species in the restoration area, while 14 in the control area. There are obvious more species in nigh than in daytime. For control area,  only 5 species in day, while 13 species in night; for restoration area, 9 and 14 species in day and night time respectively (Fig. 9).
4.4 Nekton
The investigation of nekton include fish and shrimp in this study. In the restoration area and the control area, the nekton investigation was conducted by bottom cage net and fyke net in July 2021. The result showed that, 18 fish species both in the restoration area and control area. The biomass of fish in the restoration area (2023 ± 1173 g/net/day) is significantly higher than that of in the control area (786 ± 129 g/net/day) (Fig. 10). In addition, the study also found that, all the fish individuals in the tidal flat of the Yangtze River Estuary were small size in July. The body length result showed about 83% of all individuals were less than 10cm; body weight result showed 95% of all individuals were less than 20g. Contrary to fish results, the number of shrimp species in the restoration area is less than that in the control area (Fig. 11). Four shrimp species include Palaemon annandalei, Palaemon modestus, Palaemon gravieri and Macrobrachium nipponense, were found in control area. While in the restoration area, only three shrimp species include Palaemon annandalei, Palaemon modestus, Palaemon gravieri were found.
5. Overall evaluation of the project
The technical model of accelerated development and restoration of wetland habitat in the Yangtze River Estuary has been established by this project, with a demonstration area of 5000 m2, and total 32 individual floating wetlands with 1m×1m were placed in the tidal flat for experimental research. The planting technology of Scirpus mariqueter has been developed and the three-dimensional reed floating wetland has been invented by the study. The technical model developed has obvious restoration effect on the damaged fishery habitat in the Yangtze River Estuary. For macrobenthos, the study found that the number of species in the restoration demonstration area increased by 100%, the density increased by 133%, the biomass increased by 55.3%; for fishes, the number of species increased by 22% and the average biomass increased by 157% compared with the control area.
Reference
Mikhailov, V.N., Korotaev, V.N., Mikhailova, M.V., Li, C.X., Liu, S.G., 2001. Hydrological regime and morphodynamics of the Yangtze River mouth area. Water Resour. 28, 351–363.
Putnam L A, Gambrell R P, Rusch K A. 2010. Cbod5 treatment using the marshland upwelling system. Ecological Engineering , 36 (4): 548-559
Thom C S B, La Peyre M K G, Nyman J A. 2004. Evaluation of nekton use and habitat characteristics of restored Louisiana marsh. Ecological Engineering , 23 (2): 63-75.
Wang S, Jin B, Qin H, Sheng Q, Wu J (2015) Trophic Dynamics of Filter Feeding Bivalves in the Yangtze Estuarine Intertidal Marsh: Stable Isotope and Fatty Acid Analyses. PLoS ONE 10(8): e0135604. doi:10.1371/journal.pone.0135604
Weinstein M P, Litvin S Y, Guida V G. 2009. Essential fish habitat and wetland restoration success: a tier III approach to the biochemical condition of common mummichog Fundulus heteroclitus in common reed Phragmites australis - and smooth cordgrass Spartina alterniflora dominated salt marshes. Estuaries and Coasts , 32(5): 1 011-1 022.
 
Sikai Wang
added a project goal
Identified the habitat needs of important fishery species such as Chinese mitten crab, Coilia Coilia, for key estuarine habitats;
Research and develop habitat restoration and reconstruction technologies and supporting facilities such as "floating wetland", "tidal vegetation zone" ;
Establish technical measures for proliferation, conservation and comprehensive management and control of important fishery species; Establish the restoration and reconstruction technologies for the spawning grounds of Eriocheir sinensis and Coilia Coilia in the Yangtze River Estuary, and build the models and technical systems for the restoration of fishery habitats and resource conservation in estuaries.