| The aim of this paper is to describe the relationship between mangroves and fishes, which is based on three hypotheses: (1) the structural heterogeneity hypothesis– juvenile fish are attracted to the structural heterogeneity of mangrove habitats per se, (2) the predation risk hypothesis– risk of predation lower in mangroves than in other habitats due to increased structural complexity, and (3) the food availability hypothesis– availability of food for juvenile fish is greater in mangrove habitats than in other habitats.But two points were not perfect resolved. Traditionally, trawls and seines are the primary gear used to collect fish. However, it is difficult to collect fish within treed areas of mangroves with well-developed aerial roots using such gear. Because of this issue, most previous studies have collected fish close to the mangrove fringe or in creeks. This study design, however, might not represent the real distribution of fish within treed areas of mangroves. The present study methods of nutrition relationship of mangrove and fish are analyses the cut content of the animals captured in mangroves. But it could not reflect the exact original carbon source of mangrove fish.From March 2004 to March 2006, the diversity of fishes, the distribution of species and number inside and outside of mangrove were detected. The seasonally changes of fishes and the dietary structure of dominant species in mangroves of Dongzhaigang, Hainan, have been investigated too. We sampled seasonally in three regions (treed area of mangroves, creeks and mudflat) with fixing nets within a tidal cycle (15 days). A total of 53,248 individuals comprising 115 species in 43 families were collected. Gobiidae family is the most diversity family who has 17 species.The cluster analysis using abundance of each species showed that the fish community at each site during each season could be divided into four major groups: Group I (Sep. 2004M, Sep. 2005M, Jun. 2004M, Jun. 2005C, Jun. 2005M) were samples from treed areas; group II (Mar. 2005B, Mar. 2005C, Mar. 2006C, Mar. 2006B, Dec. 2005B, Dec. 2005C, Mar. 2004B, Mar. 2004C) were samples from the treeless mudflat and creeks in dry seasons; group III (Dec. 2004C, Dec. 2004B, Sep. 2004C, Sep. 2005C, Sep. 2004B, Sep. 2005B); and group IV (Jun. 2004B, Jun. 2005B) were samples from the treeless mudflat and creeks in wet seasons.SPSS index that species diversity abundance and biomass have a significant spacial and seasonal variation. In all peaked in wet season especially in mudflat which was 20, 1147±613 and 9125±4120g respectively larger than it in dry season which was 16±3.7 224±150 and 2419±1260g respectively. Species diversity abundance and biomass in treed area of mangrove in wet season which was 10, 567±122 and 2558±764g respectively less than it in mudflat (20, 1147±613, 9125±4120g)and creeks (13, 707±567 3384±2257g respectively). The total species number in average sample, creeks has the largest 37 (wet season) and treed area of mangrove has the least 17(wet season).So the attraction of treed area of mangrove is not so attractive as creek and mudflat. In Dongzhaigang bay only four predators (Acentrogobius viridipunctatus, Bostrichthys sinensis, Ctenogobius brevirostris, and Pisoodonophis boro) showed. So the bay as a whole is a perfect refuge for small and juvenile fish.The stable isotopeδ13C in consumer is about -18.48‰±3.00 which is similar to algae's -16.95‰±0.28 and the stable isotope 13C in mangrove trees is about -28.44‰±1.73. So energy signature technology showed that the original carbon of fish is not primarily come from mangrove's primary production but algae and others primary producer. The consumer'sδ13C in deferent diet and sits have little change.And vertebrate and invertebrate almost have the sameδ13C value.The result of consumer's nutrition class usingδ15N method is similar to cut contain analyses method.Algae and other primary production sources (e.g. seagrass) have much higher productivity than mangrove in estuaries and nearshore waters, and are easy to obtain and digest. So these alternative carbon sources and the complicated food web structure mask the nutrition role of mangroves. If this hypothesis is true then it could offer an explanation for the observation that mangrove litter is heavily used by consumers when other primary production sources are scarce, a phenomenon that cannot be explained by the difficulty in assimilation or tidal dilution.Energy signature technology addresses the relative contribution of mangroves to the consumer's carbon sources, not the biomass in numbers. With that in mind energy signature technology is not inconsistent with the traditional view but is complementary. We hypothesize that all of mangrove litter production is used by aquatic consumers. The mode of the use is, however, not in terms of dominance in the consumer′s tissue but small contributions to many individuals.Energy signature technology is a useful method in study the nutrition relationship of mangrove and fish but is not perfect in some case, and needs further research. As the SPSS result showed the mangrove ecosystem is as a whole take action and attractive to fish using centipede net. The treed areas of mangrove have less effect than creek and mudflat. All that indexed us the mangrove is as system not exact treed area of mangrove, and should been protected as a whole not the treed area only.
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