| Fish community ecology is one of the most important components in marine ecosystem studies. Fish communities with multi-trophic levels and functional guilds are always needed in order to keep balance of marine ecosystems and to maintain a dynamic aquatic system. Marine lives, including fishes, utilize specific habitat during some or all of their life history stages. Predation and competition were two most important processes in those stages, due to the help of that, a fish community with dynamic changes in small time scale and long time balanced pattern is formed. The species diversity, as one of the biological variance in fish community ecology, has become great topic for decades. It is probably because of the seafood demands from those communities and our needs to explore, to entertain human beings within those habitats with high level species diversity. It is increasingly important to understand the key roles of fish habitats under such circumstances, since we all want to make those living resources sustainable for ourselves. However, marine habitats are facing great threats from human activities like fishing, pollution and dredging, which also cause big troubles such as habitat degradation, fragmentation and lose. Fishes living in those habitats are now in great danger. So more and more governments and scientists are devoted to rehabilitation of marine habitats, which are usually combined with deployments of artificial reefs (ARs) and developing of marine ranching. The purpose of those actions is simple, mainly to stop further damages to natural habitats. Meanwhile, some other fisheries management approaches such as total allowable catch (TAC), marine protected area or marine reserves (MPA) and essential fish habitat (EFH), were used to ensure a heather and long-time fishery development.Along with the implementation of multi-rule management and utilization strategies, aquatic regions, usually in small scales, are becoming much more complicated on seafloor physical structures and specific epifauna will arise due to habitat change. We name this combined habitats, which including many artificial structures, meta-habitat, also called complex habitats or integrated habitats. We can’t protect what we don’t understand. So it is urgent for us to evaluate the impacts of those temporally or permanently habitat changes to fish community, especially to those species dwell on classic habitats, such as mangroves, coral reefs, seagrass beds, giant kelp forest and rocky shores et al. Some regions like rocky shores are always considered as essential fish habitats for many local species and maintain great amount of fishery resources. A better understanding on the roles of different habitats in regulating the dynamics of fish community both in local and regional scales is needed. We choose an area which located in Shengsi, eastern Yangtze River estuary and northern part of Zhoushan archipelago, as our study area. It is embraced by special marine protected area (SMAP) of Ma’an Archipelago. More than 90% of this area are covered by waters which is composed of four kinds of natural habitats, namely, soft bottom (SB), hard bottom (HB), sandy beaches (SBs) and rocky reef habitat (RR), and three typical artificial habitats, which are ARs, mussel farms (MFs) and cage aquaculture (CA). Ma’an archipelago provides a perfect experimental area to address this study objective. The existed aquaculture facilities set on soft-bottom habitat near rocky shores are widely distributed to a scale no one can neglect. Two artificial reef systems were built in 2005-2006 and 2008 in western marine reserve around the rocky shores. Beginning with a brief introduction of concepts of EFH, we reviewed some of the recent progresses on studies of scales in fish community ecology, which is easily neglected by scientists in our country. Besides that, we make some supplements on ideas of natural and human impacts on fish communities.It is hoped that those reviews can be efficiently used by further researchers. Monthly surveys of fish assemblages were conducted in 2009 using multi-mesh trammel nets within 6 habitats, namely, ARs, MFs, CA, RR, SBs and SB. Meanwhile instruments such as CTD were used to collect environmental data synchronized. The time of each survey ranged from 10-15 days, so a total of 143 days were spent to collect all the data. Fish assemblages between or within each of the chosen habitats were compared on four time scales, which are diel variations, monthly changes, seasonal variations and changes on different stages based on macro-algae growth characteristics. As to spatial scales, we made comparisons of fish assemblages between habitats (site scale, mostly site to site) and local to local scale within a specific habitat (compared local scales on regional scale). Each of the sampling sites represented a specific habitat, and had a sampling area not exceed 0.05km2. The whole study area is about 29km in length and 15km in width. 92% of our samples were from an area less than 100km2. The species composition, mainly on taxa and dominant species, were described in details. Indices like abundance catch rate (ACR) and biomass catch rate (BCR), Margalef’s species richness (R), Whilm’s species diversity (H”), Pinkas’relative importance index (IRI) and Jaccard’s species similarity (I) were compared in different spatial and temporal scales among those habitats. Dominance curves for abundance and biomass (ABC curves) were also compared between fish communities from multiple scales. Multivariate statistical analysis, such as non-metric multidimensional scaling (nMDS) and cluster (UPGMA) (both of them are based on Bray-Curtis similarity matrix), canonical correspondence analysis (CCA) as well as detrended correspondence analysis (DCA) were used to discuss fish assemblage patterns and environmental impacts on associated communities. Based on those biological analysis results, we used bio-environmental analysis to decide relationships of each of the environmental factors with fish community composition. Factors such as temperature (T), salinity (S), turbidity (TU), transparency (TR), chlorophy-a (Chl-a), water depth (D), dissolved oxygen (DO) and fishing pressure (FP) etc. were included in our BIOENV analysis. Univariate ANOVA, Turkey’s tests, spearman’s correlation tests, single- factor- ANOVA etc. were applied to test the significant levels of each of the discussed index. A minimum of 0.05 were considered as our significance level.We test the following assumptions: (a) Natural habitats in Ma’an Archipelago waters are teeming with marine lives. Habitat such as rocky reef is EFH to most of the permanent fish species, and offer valuable feeding ground, nursing ground and mating ground for those species. Rocky reef habitat maintains the highest levels of fish diversity. (b) Being constrained in an area controlled periodically by runoff from the Qiantang and Yangtze Rivers and the offshore Kuroshio current, it is supposed that fish assemblages in this area should be revealed with significant temporal variations. (c) Fish individuals have different strategies and intensity by utilization of meta-habitat in different life stages. (d) Artificial structures, such as artificial reefs and aquaculture facilities, may vary its original physical structures, thus changing distribution patterns for the same species, forming different fish behavior by predation and competition process, and eventually building a new fish community within limited areas. (e) We believe ARs and other artificial structures can act as a population enhancement tools for specific fishes, such as Sebastiscus marmoratus, since them depend on hard bottom habitat during most of their life time. (f) Fish assemblage in RR habitat may change within our sampling region. (g) Different habitat offer suitable microhabitat in different scales. Due to high habitat complexity in RR and ARs habitat, and needs to feed or avoid predators for individual fishes, may impact fish assemblage pattern on diel scale. We did studies accordingly based on assumptions above, and our results and conclusions were listed below:(1) Spatial and temporal patterns of fish community in rocky reef habitat: A total of 87 species, which belonged to 3 classes, 14 orders, 50 families and 73 genera, were identified from our monthly collections. Most of the dominant species are reef fishes and pelagic Clupeiformes species, such as Sebastiscus marmoratus and Engraulis japonicus respectively, indicating permanent dominance and seasonal dominance patterns. ANOVA suggests that fish community in RR habitat vary significantly within month, through seasons and different stages. Fish community was different in different regions. Adult fishes were most attracted to some area in the north-west, while juvenile fish tend to have a higher concentration in the south-east area, which indicated that these two areas may act as different grounds for the same fish. Area near estuarine is a better place for mating and spawning, while those in the east part were most welcome to small and warm water fishes. Larger quantity of juvenile fishes was collected in area B suggests that RR habitat in this area is serving a better feeding ground for them in this area than area A. nMDS analysis revealed that fish community in area A and B is significantly different. BIOENV analysis shows that different fishes have different respond strategies to the same factor. However the impact from environmental factors such as T and S was were quite similar during the same season. We believe that abundance of prays regulated by runoff and currents dominants this pattern. Our study revealed that fish community pattern in Ma’an Archipelago was mostly controlled by interactions of runoffs from Yangtze River and currents in regional scale, while temporal change was mostly impacted by temperature, salinity and dissolved oxygen. High diversity of fish taxa and great abundance of reef fishes in RR habitat suggests that it is an important perhaps the most valuable habitat, in this area, and serve as EFH to most of the reef species. However, fish diversity has been impacted severely compared to its level in 1980s (210 fish species recorded). Much more management rules on rocky reef habitat are needed to protect this essential area for fishes.(2) Seasonal variation of fish assemblages in sandy beaches off Gouqi Island: A total of 63 fish species, belonging to 11 orders, 38 families and 56 genera, were collected, of which 46 fish species were sampled in both sandy beaches and rocky reef habitat, respectively. Fishes in sandy beaches showed a much higher richness due to the appearance of more warm water species in sandy bottom. The abundance catch rates (ACR) from May to July in sandy habitat was significantly higher than those in rocky reef habitat, and a tendency of higher ACR for most of the rest months were found. However, the species richness and diversity during spring and summer in sandy beaches were significantly lower than those in rocky reef habitat, because of high species dominance and low evenness in the sandy habitat. Japanese tonguefish (Paraplagusia japonica) was the indicator species of sandy beaches. It dominated in early spring, later summer, autumn and winter, when there was no strong fishing pressure. A unique community structure in sandy bottom was formed and kept in dynamics, due to nursery use of sandy beaches by Japanese anchovy (Engraulis japonicus) from May to July, gathering of gray mullet (Mugil cephalus) in most of the months for feeding and appearance of plotosid catfish (Plotosus anguillaris) in large quantity in early Autumn. This was quite different from the community structure pattern dominated by reef fishes in rocky-algae habitat. The sublittoral sandy bottom of Gouqi Island was serving as both nursery and feeding grounds for many fish species, and being a suitable habitat for flatfishes. It was concluded that sandy beaches around Gouqi Island could be a very important habitat for economic fish species, especially being a nursery ground for juvenile fishes, thus contributing to the stock maintenance in specific area.(3) The role of artificial habitats in regulating the dynamics of local fish communities: In total 66 fish species were collected belonging to 2 classes, 12 orders, 39 families and 54 genera. This study suggests that artificial reef (AR) habitat attracted much more species and individuals than mussel farm (MF) and soft bottom (SB) habitats during most of the seasons, especially in spring and summer, with significantly higher species richness, abundance and diversity. Fish taxa in AR habitats were similar to rocky reef (RR) habitats. Two different fish assemblage patterns were revealed by non-metric multidimensional scaling ordination: an assemblage dominated by reef fishes in AR, RR and cage aquaculture (CA) habitats and an assemblage dominated by Sciaenidae species in MF and SB habitats. We believe that reef fishes were keys to differentiate fish community structures in studied area. Although few differences of fish abundance and diversity were found between CA and SB habitats, a much more diversified age structure was only observed in CA habitat. A much more complex fish assemblage and enhanced populations for local species were established due to presence of floating and bottom artificial structures. We suggest that one of the possible solutions to enhance reef fish population is to deploy ARs on soft bottom to improve survival rates of protected species.(4)Diel variation of fish assemblage in multiple habitats in Ma’an Archipelago: A total of 55 species, belonging to 2 classes, 8 orders, 37 families and 50 genera, among which, 28 families and 38 genera at daytime, 34 families and 44 genera at night, were collected from our 24 diel samplings in 12 sites. The diel shift patterns of habitat use by fishes varied with their eco-types, especially with their habitation on certain water levels. More ground fishes, such as Sebastiscus marmoratus and Plotosus anguillaris, were collected at night in hard-substrate habitats (i.e. rocky reef and artificial reef habitat) than daytime. The diel variations of near-ground fish assemblages varied at different habitats. Some of them had a much higher occurrence (e.g. Stephanolepis cirrhifer ) during daytime while others(e.g. Pagrus major) appeared frequently at night. Pelagic fishes such as Thryssa kammalensis were mostly collected during daytime in artificial habitats. In general, a much higher abundance catch rate (ACR) was found in artificial habitats (AHs) during daytime than it was at night. However, no significant diel variations were found in natural habitats (NHs) for both ACR and biomass catch rate. Only few species, including Larimichthys polyactis and Thryssa kammalensis, were observed with significant diel variations. No significant differences were found in species richness and diversity between daytime and night both in AHs and NHs. Significant changes of fish species were observed due to low species similarity between day and night. Three patterns of fish assemblages can be described, including the dominance of night-tendency fishes such as Sebastiscus marmoratus and Plotosus anguillaris at hard-bottom habitats, the dominance of day-tendency species such as Stephanolepis cirrhifer and Microcanthus strigatus at hard-bottom habitats, and high abundance of Sciaenidae at soft-bottom habitats. Based on the results of the present study, it is recommended that the time duration of any surveys on fish assemblages in coastal areas shall last more than 24h.We believed that Ma’an Archipelago is an area with comprehensive ecological functions and serve as a perfect essential fish habitats for marine lives based on our studies. Being a important spawning and feeding ground fish many economic fishes, this area has been an irreplaceable habitat in regulating fishery resources, and contributing a lot in maintaining high levels of fish diversity in local area. Recently, more and more ARs, MFs and CA were deployed in specific areas, leading to development of a meta-habitat with higher physical structure complexity, which in turn become alternative habitats for many more local fishes, and eventually enhance some of the severe disturbed reef fishes and other migrating species. It is concluded that meta-habitat is an integrated fish population enhancement function regulating by diversified habitats composition and dynamic fish communities. |
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