Relationship Between Ecosystem Of Kelp Beds And Seasonal Variation Of Fish Assemblages At Waters Around Gouqi Island

Gouqi Island coast ecosystem is one of the representative island ecosystems along coast of China, lies in Shengsi, Zhejiang Provence (N30o40’~30o44’; E122o43’~122o48’). The geographical position of Gouqi Island affects the characteristic of climate, tide and current, resulted in the species and distribution of macroalgae and fishes. It makes the environment of Gouqi Island keep pace with the environment of Shengsi Archipelago. The topography characteristic of Gouqi Island shaped the distribution pattern of kinds of smaller habitats, which affects the resident and migration of fish assemblages. Three habitats—rocky reef, sandy beach and mussel cultivation rafts distribute along the coast of Gouqi Island. Rocky reefs, one of these habitats, covered by vast area of macralgae with different species and huge biomass, form the kelp beds ecosystem, one of the representative coast ecosystems. Ecosystem is composed of organisms and environment. The support organisms of kelp beds ecosystem are macroalgaes, the composition species decided the characteristic of the system. The characteristic of dominant macroalgaes’life history and morphology affect the environment variety of kelp beds ecosystem. Spatial heterogeneity formed, compared to outside of kelp beds, affected the activities of organisms and the conditions of kelp bed ecosystem. Macroalgaes as the primary producer of the system, connected with the higher trophic level organisms through food web, and affected the energy flow in the ecosystem. Based all above understanding on Gouqi Island, we surveyed the environment and fish assemblages along the coast of the Island. For the first time, we studied the relationship between the kelp beds ecosystem and fish assemblages’variety, in order to provide scientific theory to support the management of coast fishery resources, research on coast habitats and coast fishery resources protection.Two methods were used during the survey of May to June, 2010 along Gouqi Island coast. Biosonics DT-X scientific echo sounder were used to scan the distribution of macroalgae along the coast and traditional survey methods, diving and sampling, were used to assist the scan and to observe the variety of kelp beds during a year. The physical and chemical environment inside of kelp beds were measured by regular investigation machine for physical environment and chemical lab experiment during 2005 to 2010. Custom bottom gill nets were used to sample the fish assemblages from January 2009 to January 2010. The main contents of the investigation are as follows: (1) concluded and analyzed the characteristic of kelp bed habitat, including the distribution and variety of a year, to find out the influencing factors by using correlativity analysis and influence on physical and chemical environment in kelp beds inside; (2) biological statistical analysis methods, such as nMDS, UPGMA, ANOSIM, BIOENV were used to show the variety pattern of fish assemblages structure among sites and habitats except for the indexes of Jaccard similarity, Margalef richness and Shannon-wiener diversity etc.; stomach content analysis of fish samples were also carried out to estimate the diet list and ratios of different target. (3) established the ecosystem of Gouqi Island coast by Ecopath to show the energy flow in the system and indicated the relationship between macroalgae and fish assemblages in kelp beds ecosystem.Major results of the study were as follows:1. Habitat characteristic of kelp bed ecosystem(1) The diversity of macroalgae living in the intertidal zone was higher than the diversity in the subtidal zone along Gouqi Island coast. Two kinds of kelp bed were found, one was dominated by larger standing macroalgae as Sargassum horueri, the other was dominated by smaller macroalgae as Ulva pertusa. Larger standing macroalgaes live on the coast of 0~10 depth sea water with level landscape. They prefer to covering on the surface of rocks with gentle slope. The distributions of larger standing macroalgaes are affected by the flow velocity. If the flow velocity is over 120 cm/s, it would too fast larger standing macroalgae to live, but smaller macroalgae can survive. The diversity of macroalgae in the intertidal of smaller kelp beds is higher than that of larger kelp beds. There is positive correlation between the density of Sargassum horueri and salinity of sea water.(2) The variety of kelp beds in a year affected by constitute of macroalgae species, and relevant to the life history and morphology of dominant species. The smaller kelp bed existed all the year and differed less. Its affection is in constant and steadier than larger kelp bed as a habitat for fishes to prey and for benthic invertebrates to resident and prey. The variety of larger kelp beds are affected by the life history and morphology of Sargassum horueri, which are impacted by water temperature, landform, current and nutrition. Water temperature is the key influence factor for variety of kelp beds. According to the life history of Sargassum horueri, the variety period can be divided into four stages: young seedling development period (August to September), slow growth period of seeding (October to February in next year), fast growth and reproduction period (March to May) and decomposing and declining period (June to July). Reproduction usually starts in May.(3) The difference between inside and outside of kelp beds in the physical and chemical environment appeared to be obvious during the vigorously growing period, due to the affection from the morphological and biological characteristics of larger standing macroalgaes. Through the observations and analysis on physical and chemical environment difference between inside and outside of kelp beds, we found the larger kelp beds around Gouqi Island are not able to slow down the water flow and keep the water temperature steady. We supposed the reason was that Sargassum horueri is too weak to hinder the water flow. But there are obvious differences in chemical environment between inside and outside of larger kelp beds during the palmy period. The concentration of nitrogen inside of larger kelp beds was much lower than outside, especially for nitrate nitrogen, the concentration was close to zero. It is quite likely restrain the reproduction and growth of phytoplankton in the kelp beds, impacting the predators prey on phytoplankton, such as fishes.2. Characteristic of fish assemblages in kelp beds around Gouqi Island(1) The fishes inhabit in Gouqi Island are major two assemblages as follows: one is local reef fishes; the other is fishes with seasonal migration. The former is mainly based on the demersal fishes and mid-lower fishes; the latter is mainly based on the pelagic fishes and mid-higher fishes. There is significant difference in fish assemblages’structure among the three habitats, i.e. rocky reef, sandy beach and mussel cultivation rafts around Gouqi Island. Meanwhile, rocky reef associated with macroalgaes come into a habitat with much more complex structures for benthos to resident and prey. It made the structures of fish assemblages more complex with a higher diversity and a steadier homogeneity.(2) There are differences in fish assemblages’structure between two kinds of kelp beds due to the species of macroalgaes, as well as the life history and morphology. The constitution of fish assemblages in larger kelp beds is much steadier than that in smaller kelp beds. The changing trends of fish abundance and biomass were the same in larger kelp beds. Quite the contrary, fish abundance and biomass were different in smaller kelp beds, due to the fish migration from open sea area. These fishes with larger bodies came into Gouqi Island sea area in February to May. Therefore, the existence of larger kelp beds is benefit to dominant fish stock, to be attractive to small fishes and juveniles. It provides more food apportions for fishes, which is good for the stable of fish assemblages.(3) The fish assemblages inhabit in kelp beds around Gouqi Island are mainly based on demersal polyphagia fishes, most of which are less than two year old. Juveniles play a very important part of fish assemblages. Age structures of three dominant species were different, but sexual structure were similar. Female in the fish stock are more than male. It helps fish stock to remain the high recruitment ability and keep the stock to an amount at a certain level under the high fishing intensity. For the whole year, there is no obvious difference between the structures of fish assemblages in two kinds of kelp beds. But analyzing the difference in structures of fish assemblages in the two habitats based on four stages of larger kelp beds, it showed a same variety trend with both fish assemblages and lager kelp beds. It was contrary in smaller kelp beds.(4) The dominate fish species in kelp beds were Sebastiscus marmoratus, Agrammus agrammus and Nibea albiflora. Affected by the differences in life habits, prey targets and resident habit, they prefer to acting in different habitat at life history stages. Sebastiscus marmoratus and Nibea albiflora will transfer their living space following the variety of their prey targets and prey pressure from predators. They both act in all kinds of habitats around Gouqi Island. The former is local reef fish without long distance migration. The latter migrate to Gouqi Island sea area only during their reproduction period. Agrammus agrammus prefer to resident in kelp beds, due to the prey target, living on macoalgaes.3. Characteristic of energy flow in kelp beds ecosystem around Gouqi Island(1) The coast ecosystem of Gouq Island is a system with high recirculation rate and high primary production. The function groups are loosely connected, and the MPL of energy flow is shorter. There are much more surplus of production, which are mainly from macroalgaes. (2) Echinoderms—sea urchin is the main energy flow direction. The predator crabs play a key role of the ecosystem. If the crabs were overfished, it would lead to negative results. One is the threat of fast disappearance of kelp beds; the other is negative affection to the reproduction of Sebastiscus marmoratus and survives of dermersal and mid-lower fishes in kelp beds.