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Impacts of intensive mariculture on coastal ecosystem and environment
in China and suggested sustainable management measures
Qisheng Tang, Jianguang Fang
Yellow Sea Fisheries Research Institute, Qingdao, 266071, P. R. China
1. INTRODUCTION
Mariculture in China has grown dramatically since the late 1970s. In 2000, the total mariculture production of
China was 10.6 million MT. Figuring most prominently was the production of both bivalves and macroalgae
(82% and 11% respectively) mostly cultivated in coastal zones by the suspension culture method. As is well
known, the growth and reproduction of bivalves rely mainly on the supply of microalgae and detritus; however,
the growth and reproduction of macroalgae, microalgae and seaweeds depend mostly on the supply of inor-
ganic nutrients coming from their living water body. Any variation in phytoplankton, the basic food chain ele-
ment in marine ecosystems, will not only directly influence the growth and reproduction of bivalves, but will
also cause changes in the whole marine ecosystem in the coastal zone by limiting secondary production and
then influencing the fisheries resources. Similarly, if the supply of inorganic nutrient is limited in the mariculture
region, competition for inorganic nutrients will take place between phytoplankton and macroalgae.
In addition to what is described above, great attention should be paid to the study of the impacts of mariculture
on the coastal zone environment. All aquaculture is based on an underlying requirement for a clean environ-
ment for two very practical reasons. First, since the final marketed product is for human consumption, the prod-
uct must meet high quality standards. Second, as in any husbandry operation, production is highest when envi-
ronmental stresses are minimized. To some extent, then, environmental degradation due to mariculture is
directly related both to human health and to the water quality of the coastal zone.
2. IMPACTS OF MARICULTURE ON ECOSYSTEMS AND THE ENVIRONMENT
Certain projects have therefore been launched by the Chinese government to investigate the impact of maricul-
ture on ecosystems and the environment. Summarizing the projects, some research results are showed as fol-
lows:
2.1. Effects of intensive macroalgae mariculture on ecosystem and environment
Macroalgae such as kelp Laminaria japonica, porphyra spp. etc., are important economic species cultivated in
the coastal zone of China. In 2000, the total macroalgae mariculture yield of China was more than 1 million MT.
The results of these studies showed that 1MT Kelp in dry weight would absorb about 10-15 kg N from seawa-
ter. Such quantities of N can produce 100-150 kg POC. If the mariculture sites are N deficient, the intensive
macroalgae culture will certainly reduce the primary production. Therefore, intensive macroalgae mariculture
on a large scale will influence the stabilization of coastal ecosystems by depleting the nutrients. In addition, the
decay of kelp will occur during the summer season if they cannot be harvested in time. The detritus dropped
from the decayed front part of kelp can make the seawater so mucous that it will be harmful to the hatcheries,
or may cause blooms of some species of harmful macroalgae in the mariculture sites.
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2.2. Effects of intensive bivalves mariculture on ecosystems
Study results showed that the mean feeding ration of scallop Chlamys farreri with shell height of 5-6 cm is
about 11 mg POC/d/ ind. Moreover, bivalves have a strong capability of filtering water at optimal temperatures.
For example, scallops Chlamys farreri with shell height of 3-4 cm, 4-5 cm, and 5-6 cm can filter about 60 L,
100 L and 120 L water respectively during a period of 24 hours. Experimental results showed that one scallop
Chlamys farreri (shell height: 5 cm) could decrease the phytoplankton concentration from 8800 cell/ml to
200 cell/ml within 1h in 3000 ml water volume at temperature 15200. If the culture biomass of bivalves
exceeds the carrying capacity of mariculture regions, intensive bivalve mariculture will decrease the quantity
of phytoplankton rapidly so as to decrease the primary production. Without sufficient phytoplankton in the
coastal seawater, the growth and reproduction of zooplankton and other herbivorous marine animals will be
affected and then the coastal eco-system will change.
2.3. Effects of intensive mariculture on benthos ecosystem
Experimental results show that scallop Chlamys farreri (shell height: 56 cm) and oyster (shell height: 810 cm)
can produce amounts of faeces up to 5060 gr and 120 gr in dry weight respectively each year. Some parts of
such faeces will be decomposed into dissolved matter and will be carried by the current away from the culture
site, but most will sediment to and accumulate on the sea bed under the suspension culture facilities. This par-
ticulate organic matter is so fine that it will change the texture composition of the seabed. When the texture of
the seabed is changed, the population of organisms living on or in the mariculture seabed will consequently
change, and then the benthos ecosystem will change in conjunction with the accumulation of the bio-sediment
on the seabed year by year. Comparing the present data of benthos biomass of organisms with the historical
data, we found that the biomass of seaweed and bivalves in the seabed of intensive mariculture areas has
declined dramatically since the 1970s. For example, although the resources of eelgrass Zostera marina were
so rich that it could be found almost everywhere along the coastal zone from north to south of China before
the 1970s, it is now very difficult to find. Although there are many factors causing the decline of eelgrass
resources, the accumulation of bio-sediment from the intensive suspending culture may be the one of the most
important factors involved.
2.4. Effects of resuspension of bio-sediment on cultivated organisms
Generally speaking, the longline culture density of bivalves (scallops, oysters) is about 50ind./m
2
, and most of
the intensive mariculture areas in China have been developed for about 20 years. This means that the bio-sed-
iment accumulated on these intensive mariculture areas reaches so far about 10 cm in the seabed. This bio-
sediment matter can change not only the texture of the seabed, but can also be disturbed into the water col-
umn, especially during the storm season. This resuspended particulate not only can cause heavy mortality by
blocking the gills of bivalves, but may sometimes induce the occurrence of harmful microalgae blooms because
it can increase nutrient concentrations such as N, P, etc., in the intensive mariculture areas very rapidly during
a very short period after storms. According to the statistical data, heavy mortality of bivalves cultivated in
coastal zone has increased year by year since early 1990s in China. Though it is not known whether such
heavy mortalities are caused by the turbidity of seawater, or by disease, it is recognised that the accumulation
of bio-sediment on the intensive mariculture seabed is harmful to the ecosystem, the environment, and to mari-
culture.
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3. RECOMMENDATIONS
In order to develop the marine aquaculture resources in a sustainable way, some suggestions or recommenda-
tions are made as follows:
1) To establish models to predict the potentiality of new sites for mariculture based on their mariculture carry-
ing capacity and ecological carrying capacity.
2) To pay great attention to study the impact of mariculture on ecosystem and environment, the interaction
between mariculture and environment, the relationship between intensive mariculture in the coastal zone
and the variability of marine fisheries resources, etc.
3) To re-evaluate intensive mariculture sites in coastal zones not only based on their carrying capacity, but also
according to standards of human health.
4) To establish a sustainable management system that can determine and control the mariculture species,
areas and scale, density, culture models in different sites based on the specific ecological and environmen-
tal conditions of different regions.
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