Gouqi Island Research Articles

Estimation of Seaweed Biomass Based on Multispectral UAV in the Intertidal Zone of Gouqi Island

UAV remote sensing inversion is an efficient and accurate method for obtaining information on vegetation coverage, biomass and other parameters. It is widely used on forest, grassland and other terrestrial vegetation. However, it is rarely used on aquatic vegetation, especially in intertidal zones and other complex environments. Additionally, it is mainly used for inversion of coverage, and there have been few studies thus far on biomass assessment. In this paper, we applied multispectral UAV aerial photography data to evaluate the biomass of seaweed in an intertidal zone. During the ebb tide, UAV aerial photography and in situ sampling data were collected in the study area. After optimizing the spectral index and performing a multiple linearity test, the spectral parameters were selected as the input of the evaluation model. Combined with two machine learning algorithms, namely random forest (RF) and gradient boosting decision tree (GBDT), the biomasses of three species of seaweed (Ulva pertusa, Sargassum thunbergii and Sargassum fusiforme) in the intertidal zone were assessed. In addition, the input parameters of the machine learning algorithms were optimized by one-way ANOVA and Pearson’s correlation analysis. We propose a method to assess the biomass of intertidal seaweed based on multispectral UAV data combined with statistics and machine learning. The results show that the two machine learning algorithms have different accuracies in terms of biomass evaluation using multispectral images; the gradient boosting decision tree can evaluate the biomass of seaweed in the intertidal zone more accurately.

Assessment of intertidal seaweed biomass based on RGB imagery.

The Above Ground Biomass (AGB) of seaweeds is the most fundamental ecological parameter as the material and energy basis of intertidal ecosystems. Therefore, there is a need to develop an efficient survey method that has less impact on the environment. With the advent of technology and the availability of popular filming devices such as smartphones and cameras, intertidal seaweed wet biomass can be surveyed by remote sensing using popular RGB imaging sensors. In this paper, 143 in situ sites of seaweed in the intertidal zone of GouQi Island, ShengSi County, Zhejiang Province, were sampled and biomass inversions were performed. The hyperspectral data of seaweed at different growth stages were analyzed, and it was found that the variation range was small (visible light range < 0.1). Through Principal Component Analysis (PCA), Most of the variance is explained in the first principal component, and the load allocated to the three kinds of seaweed is more than 90%. Through Pearson correlation analysis, 24 parameters of spectral features, 9 parameters of texture features (27 in total for the three RGB bands) and parameters of combined spectral and texture features of the images were selected for screening, and regression prediction was performed using two methods: Random Forest (RF), and Gradient Boosted Decision Tree (GBDT), combined with Pearson correlation coefficients. Compared with the other two models, GBDT has better fitting accuracy in the inversion of seaweed biomass, and the highest R2 was obtained when the top 17, 17 and 11 parameters with strong correlation were selected for the regression prediction by Pearson’s correlation coefficient for Ulva australis, Sargassum thunbergii, and Sargassum fusiforme, and the R2 for Ulva australis was 0.784, RMSE 156.129, MAE 50.691 and MAPE 28.201, the R2 for Sargassum thunbergii was 0.854, RMSE 790.487, MAE 327.108 and MAPE 19.039, and the R2 for Sargassum fusiforme was 0.808, RMSE 445.067 and MAPE 28.822. MAE was 180.172 and MAPE was 28.822. The study combines in situ survey with machine learning methods, which has the advantages of being popular, efficient and environmentally friendly, and can provide technical support for intertidal seaweed surveys.

Allometric Growth of Sargassum fusiforme (Ochrophyta, Fucales) Organs in the Maturation Period Based on Biomass Analysis of Samples from Gouqi Island

Sargassum fusiforme is a seaweed species that plays an important role in the diverse communities of the flora and fauna of coastal food webs. Assessments of its biomass and energy allocation in addition to allometric organ growth have important ecological value for understanding the community structure, carbon storage, and resource assessment of seaweed beds during periods in which they thrive. In this study, the morphology of Sargassum fusiforme and the biomass of organs and total organisms in the maturation period were studied, and the allometric relationships for different organs of Sargassum fusiforme were analyzed using the standardized major axis (SMA). In the maturation period of Sargassum fusiforme, branch number, height × stem diameter were the prior independent variables, and the optimum biomass was y = 0.002x1.107 (R2 = 0.923). The biomass allocation ratio of blades was the highest (38.33%), followed by stems (32.90%) and receptacles (28.77%). The growth rates of the various organs were found to differ, and the rate of biomass increase for the blades and stems tended to converge. The rate of receptacle biomass growth of Sargassum fusiforme was the highest in the maturation period, and the rate of organ biomass increase was Wb &lt; Ws &lt; Wt &lt; Wr, which reflects the trade-off with energy allocation as a strategy used by Sargassum fusiforme.

Measurement and analysis of underwater noise of offshore mussel suspended farming waters

Anthropogenic noise pollutions are gradually increasing in the world, especially in coastal waters due to shipping and seismic exploration. However, the need for high-quality aquatic products has led to more and more marine suspended farming, which may add to the new sources of low-frequency anthropogenic noises in the ocean. Waters around the Gouqi Island, one of the major reef islands in the northern Zhoushan Archipelago, are considered as important suspended farming waters of mussel. The units of suspended farming facilities composed of aquaculture lines with attached mussels, or the sleeves, are suspended in the surface layer by buoys. The length of the sleeves is 2.3-2.8 m and the water layer occupied by the aquaculture system is about 3.5 m. These suspended farming facilities can reduce the current speed significantly. In this paper, the underwater noises of mussel suspended farming waters of Gouqi Island were measured by a passive monitor system at two sites (inside and outside mussel farming waters) with depths of 5 m and 10 m, and boat noises were also recorded to determine the noise source. All sounds were monitored prior to record to ensure the minimum self-noise, and at least 10 recordings were made and separated by at least 5 min. Power spectra of sound recordings were presented as 1/3-octave sound pressure level (SPL) in dB. Results showed that the main frequency of boat motor noise was 250 Hz, and its SPL at 5 m (114.7± 1.7) dB was greater than that at 10 m (97.4±0.9) dB when the boat was anchored. There were three peak frequencies (63 Hz, 250 Hz, 500 Hz) of underwater noises generated outside the mussel farming waters, where the SPL of 250 Hz at 5m was greater than that at 10m, indicating that the environmental noise outside mussel farming waters was greatly affected by fishing boat. The average environmental noise SPL was (87.7±13.7) dB inside the mussel farming waters, there were also three peak frequencies (63 Hz, 250 Hz, 500 Hz), where SPL of 500 Hz at 10 m (85.13±0.5) dB was greater than taht at 5 m (179.4±0.9) dB, indicating that the suspended mussel farming facilities were the main source of 500 Hz inside the mussel farming waters. This vertical distribution of marine environmental noise may be due to the blocking effect of mussel suspended farming facilities on tidal currents. Owing to that tidal current velocity was reduced in the surface layer, underwater noise level at bottom was greater than that in the surface layer. The underwater noise from suspended farming facilities can contribute significantly to the local ocean noise, and it is clear that the frequency of the suspended farming noise overlaps with the frequency used for acoustic communication in fish. It is necessary to increase our understanding of marine soundscapes, especially when ocean soundscapes continue to be suffered from human activity. In the future, more studies on the effects of noise from aquaculture facilities on the biology and ecology of fish are needed to fill the missing link in acoustic ecology.

Taxonomy and Genetic Diversity of Amphipods Living on Ulva lactuca L. from Gouqi Coast, China1

Large-scale green tide disasters have been occurring for more than 10 years in China, with serious ecological consequences. However, limited research has focused on epiphytes that feed on macroalgae. In this study, amphipods were found living on the surface of Ulva lactuca, a green-tide-forming alga, around Gouqi Island, China. Through morphological and molecular methods, the amphipods were identified as Ampithoe lacertosa Bate, 1858, which has not previously been recorded in China. Sequence information about cytochrome c oxidase subunit I (mitochondrial COI) gene from China was compared to sequences reported from 5 coastal countries around the Pacific region. Network diagrams, phylogenetic trees and other methods of analysis revealed evidence of genetically distinct subspecies in the northeastern and northwestern Pacific. We believe that research on herbivorous amphipods will provide preventative strategies and control measures against green tide algae. International cooperation among Asian and North American biologists within the Pacific region will lead to a better understanding of the family Ampithoidae in the future.

Flavobacterium ajazii sp. nov., Isolated from Seaweed of Gouqi Island, China.

A novel bacterium designated SSM4.2T was isolated from seaweed of Gouqi Island, which is the center of the Zhoushan fishing ground in the East China Sea. Strain SSM4.2T was Gram-stain-negative, bright yellow-pigmented, short rod-shaped, non-flagellated, non-spore forming, aerobic and motile by gliding. Growth was observed at 4-37°C (optimum 25-30°C), pH 6.0-8.0 (optimum pH 7.0) and 0-2.0% (w/v) NaCl (optimum 0%) concentration. The strain was catalase- and oxidase-positive. Menaquinone-6 (MK-6) was found as the sole respiratory quinone and zeaxanthin as the main carotenoid pigment. The predominant fatty acids (≥ 10%) were iso-C15:0, iso-C15:1 G, iso-C17:0 3-OH and summed feature 3 (C16:1 ω7c /C16:1 ω6c). The major polar lipid was phosphatidylethanolamine (PE). The genome size was 5.7 Mbp. The DNA G + C content was 34.1mol%. 16S rRNA gene sequence revealed that strain SSM4.2T belongs to the genus Flavobacterium and shares high-sequence similarity with F. limi KACC 18851T (98.1%), F. hydrophilum KACC 19591T (97.6%), F. defluvii KCTC 12612T (97.1%), F. cheongpyeongense KACC 19592T (97.0%) and F. fluviatile KCTC 52446T (96.9%). Strain SSM4.2T had 73.2-84.6% average nucleotide identity and 19.1-29.4% digital DNA-DNA hybridization values with its closest type strains. Based on its phenotypic, chemotaxonomic, phylogenetic and genomic features, strain SSM4.2T represents a novel species of the genus Flavobacterium, for which the name Flavobacterium ajazii sp. nov. is proposed. The type strain is SSM4.2T (= KCTC 72807T = MCCC 1K04370T).

Diverse and unique viruses discovered in the surface water of the East China Sea

BackgroundViruses are the most abundant biological entities on earth and play import roles in marine biogeochemical cycles. Here, viral communities in the surface water of the East China Sea (ECS) were collected from three representative regions of Yangshan Harbor (YSH), Gouqi Island (GQI), and the Yangtze River Estuary (YRE) and explored primarily through epifluorescence microscopy (EM), transmission electron microscopy (TEM), and metagenomics analysis.ResultsThe virus-like particles (VLPs) in the surface water of the ECS were measured to be 106 to 107 VLPs/ml. Most of the isolated viral particles possessed a head-and-tail structure, but VLPs with unique morphotypes that had never before been observed in the realm of viruses were also found. The sequences related to known viruses in GenBank accounted for 21.1–22.8% of the viromic datasets from YSH, GQI, and YRE. In total, 1029 viral species were identified in the surface waters of the ECS. Among them, tailed phages turn out to make up the majority of viral communities, however a small number of Phycodnaviridae or Mimiviridae related sequences were also detected. The diversity of viruses did not appear to be a big difference among these three aquatic environments but their relative abundance was geographically variable. For example, the Pelagibacter phage HTVC010P accounted for 50.4% of the identified viral species in GQI, but only 9.1% in YSH and 11.7% in YRE. Sequences, almost identical to those of uncultured marine thaumarchaeal dsDNA viruses and magroviruses that infect Marine Group II Euryarchaeota, were confidently detected in the ECS viromes. The predominant classes of virome ORFs with functional annotations that were found were those involved in viral biogenesis. Virus-host connections, inferred from CRISPR spacer-protospacer mapping, implied newly discovered infection relationships in response to arms race between them.ConclusionsTogether, both identified viruses and unknown viral assemblages observed in this study were indicative of the complex viral community composition found in the ECS. This finding fills a major gap in the dark world of oceanic viruses of China and additionally contributes to the better understanding of global marine viral diversity, composition, and distribution.

Photosynthetic fluorescence characteristics of six macroalgae species in seaweed beds of Gouqi Island, Zhejiang, China.

The study of photosynthetic fluorescence characteristics of algae is important for the analy-sis of photosynthesis and carbon sequestration of algae. In July 2017, six common species of macroalgae found in Gouqi seaweed beds were collected, including Ulva pertusa, Cladophora stimpsonii, Grateloupia livida, Sargassum thunbergii, Polysiphonia urceolata, and Hizikia fusifarme. In the field, the maximal quantum yieids of photosystem2(Fv/Fm) and rapid curves (RLCs) were mea-sured by using pulse-amplitude modulated fluorometer (Diving-PAM). The results showed that the measured maximal quantum yields of U. pertusa, C. stimpsonii, G. livida, S. thunbergii, P. urceolata, and H. fusiforme were 0.702, 0.704, 0.457, 0.618, 0.421 and 0.567, respectively. The Fv'/Fm' of six species were in order of C. stimpsonii>U. pertusa>S. thunbergii＞H. fusiforme＞G. livida＞P. urceolata. The difference between each species and significant difference was found in U. pertusa, C. stimpsonii, and H. fusiforme. H. fusiforme, S. thunbergii and U. pertusa had higher Pm and α than other species, indicating their higher photosynthetic capacity and better adaptation in higher light condition. However, G. livida had higher α but lower Ik, indicating G. livida had higher photosynthetic capacity in low light condition. In a word, differences of photosynthetic capacity and light intense tolerance between the three phyla of macroalgae were found and we suggested H. fusiforme, S. thunbergii and U. pertusa had stronger photosynthetic capacity and light intense tolerance. Our results could provide theoretical basis for the seaweed bed conservation and carbon sequestration of macroalgae.

Assessment of the genetic connectivity between farmed and wild populations of Undaria pinnatifida (Phaeophyceae) in a representative traditional farming region of China by using newly developed microsatellite markers

Undaria pinnatifida is an important economic macroalga extensively farmed in East Asia. Wild individuals of U. pinnatifida, which can be easily discriminated due to their peculiar morphology, are usually observed to occur on the cultivation infrastructure adjacent to the farmed ones in the farming area. The genetic connectivity between the wild and farmed populations, however, remains unidentified. In this study, 30 informative microsatellite markers were developed and characterized through the next-generation sequencing technology. Ten of them were used to analyze the genetic structure of wild and farmed populations sampled from a representative Undaria farm in Lushun (latitude: 38° 47′ N) from 2015 to 2017, with two wild populations from Qingdao (36° 03′ N) and Gouqi Island (30° 42′ N) as controls. The dendrogram clearly separated farmed populations from wild ones by large genetic distance. The Bayesian model-based structure analysis grouped all the populations into five clusters. The wild individuals on the farm were found to contain relatively a large proportion of membership originated from farmed ones. In contrast, nearly no wild membership was detected in the farmed populations. These results imply asymmetric gene flow between farmed and wild populations and indicate that the pedigree of farmed cultivars has been well maintained through artificial control in the current seedling production system. Efforts should be made to popularize this system for the benefits of sustainable utilization of cultivars in Undaria farming.

A Carbon Cycle Model for the Social-Ecological Process in Coastal Wetland: A Case Study on Gouqi Island, East China.

Coastal wetlands offer many important ecosystem services both in natural and in social systems. How to simultaneously decrease the destructive effects flowing from human activities and maintaining the sustainability of regional wetland ecosystems are an important issue for coastal wetlands zones. We use carbon credits as the basis for regional sustainable developing policy-making. With the case of Gouqi Island, a typical coastal wetlands zone that locates in the East China Sea, a carbon cycle model was developed to illustrate the complex social-ecological processes. Carbon-related processes in natural ecosystem, primary industry, secondary industry, tertiary industry, and residents on the island were identified in the model. The model showed that 36780 tons of carbon is released to atmosphere with the form of CO2, and 51240 tons of carbon is captured by the ecosystem in 2014 and the three major resources of carbon emission are transportation and tourism development and seawater desalination. Based on the carbon-related processes and carbon balance, we proposed suggestions on the sustainable development strategy of Gouqi Island as coastal wetlands zone.

The effects of sediment on Sargassum horneri in the early life stages on rocky subtidal reefs

Sediment plays an important role in controlling the distribution of macroalgae. We examined the distribution of Sargassum horneri in the field considering the effect of sedimentation, and conducted sediment manipulation experiments to test the hypothesis that sedimentation affects the early settlement stages of S. horneri. Field samplings were conducted on rocky subtidal platforms off Gouqi Island, in Zhoushan Archipelago in the Eastern China Sea. Water depth and motion were also measured. Sediment traps and a suction pump were used to collect in situ sediment. In the laboratory, two experiments were conducted to test the effects of sediment cover on zygote attachment and germling survival, respectively. Attachment rate of S. horneri zygotes was reduced from 81.3% of the control group to 3.6% with a medium dusting of sediment (approx. 0.5mm thickness), and 0% with a heavy dusting (approx. 0.7mm thickness). For the germlings, 1.0% of survived when covered by medium (approx. 0.7mm thickness) sediment coverage, whereas high coverage (approx. 1.8mm thickness) caused 100% mortality. Our study showed: 1) in the field, distribution of S. horneri was negatively correlated with sediment amount, and S. horneri was always found abundant in sites with less sediment and intermediate water motion; 2) in laboratory-based experiments, small changes in the abundance of deposited sediment prevented zygote settlement; and 3) relatively small increases in settling sediment affected the survival of already settled zygotes/germlings. In conclusion, we found that sediment was an important driver of S. horneri distribution, especially during the early settlement stages.

Hydrodynamic effect of a large offshore mussel suspended aquaculture farm

Hydrodynamic effect of a mussel suspended aquaculture farm on tidal currents off Gouqi Island, outside the Changjiang Estuary, China, was examined using observational data. The surface friction induced by suspended mussel aquaculture facilities in the top 3.5m was much stronger than bottom friction. As a result, tidal current velocity was reduced by 75–90% in the top layer and by about 45% at the bottom. The mean surface hydraulic roughness z0s̅ and surface drag coefficient C500̅, were estimated to be around 1.392–1.890m and 0.0875–0.1694, respectively. On the contrary, the mean bottom hydraulic roughness z0b̅ and bottom drag coefficient C100̅ within the farm, were estimated to be around 0.093–0.098m and 0.0226–0.0252, respectively. The observed surface friction velocity u⁎s have the same order of magnitude with the bottom friction velocity u⁎b. However, the surface hydraulic roughness z0s is about 20 times greater than that at the bottom. The local surface drag coefficient C500̅ is 3.5–7.5 times of that at the local bottom. The aquaculture facilities not only inhibited the horizontal tidal currents, but also appeared to have induced downwelling, which was shown by the vertical profiles of salinity, temperature, and chlorophyll-a (chl-a) fluorescence. Surface chl-a fluorescence was depleted to below 1.0μgL−1 inside the farm area, which was 80% less than the outside. The reduction of horizontal velocity and the presence of downwelling can significantly decrease food supply for filter-feeding mussels.

The source of the Ulva blooms in the East China Sea by the combination of morphological, molecular and numerical analysis

The Ulva blooms have been observed at the coast of Gouqi Island, East China Sea recently, which was never reported before 2011. This study was designed to identify the species composition, phylogenetic correlation and geographical exchange of the two free-floating Ulva populations in the Yellow Sea and East China Sea. The results showed that the two populations were all consisted of Ulva prolifera (type 5S-A) and U. prolifera (type 5S-B) using ITS and 5S rDNA spacer region sequences. Based on the further sequence analysis, the samples in the East China Sea were genetically same with the green tide samples in the Yellow Sea, revealing that the two populations originated from one source. Besides, a numerical circulation modeling experiment confirmed that the Ulva blooms in the East China Sea had drifted from the Southern Yellow Sea. This study increases our understanding of the importance of controlling the spread of Ulva macroalgae blooms and their impacts.

Lipophilic shellfish toxins in Dinophysis caudata picked cells and in shellfish from the East China Sea

We reported previously that okadaic acid (OA) and dinophysistoxin-1 (DTX1) were responsible for diarrhetic shellfish poisoning (DSP) incidents due to consuming cultivated mussels (Mytilus galloprovincialis) in coastal cities near the East China Sea in May 2011. Pectenotoxin-2 (PTX2) and its seco acids were also present in these mussels. Causative species of microalgae were not identified because detailed information on the location of the contaminated shellfish was not recorded. In order to explore potential causes for these poisoning events, the lipophilic toxin profiles in picked cells of Dinophysis and in shellfish samples collected from two mariculture zones in the East China Sea were analyzed in the present study. Single-cell isolates (100 cells total for each location) of Dinophysis were collected from the aquaculture zones of Gouqi Island (Ningbo City, Zhejiang Province) and Qingchuan Bay (Ningde City, Fujian Province) in July and September 2013, respectively, for lipophilic toxin profiling. Shellfish samples collected over the course of a year from the Gouqi Island aquaculture zone and mussels (M. galloprovincialis) collected four times from the Qingchuan Bay aquaculture zone were tested for lipophilic toxins by LC-MS/MS. The Dinophysis cells isolated from both sampling sites were identified under the light microscope as Dinophysis caudata. Average quota of PTX2, the predominant toxin in D. caudata isolated from the coastal waters of Gouqi Island and Qingchuan Bay, was 0.58 and 2.8 pg/cell, respectively. Only trace amounts of OA and DTX1 were detected in D. caudata. PTX2, PTX2sa, 7-epi-PTX2sa, OA, and/or DTX1 were found in samples of mussels (M. galloprovincialis and Mytilus coruscus) collected in the Gouqi Island aquaculture zone from the end of May to the beginning of July 2013. PTX2, PTX2sa, and 7-epi-PTX2sa were also detected in oyster (Crassostrea gigas) during that period, but almost no OA and DTX1 were present. Gymnodimine (GYM) was detected in almost all mussel (M. coruscus) samples, with the highest levels occurring in winter. Trace amounts of pectenotoxins (PTXs) and OAs were also found in mussels (M. galloprovincialis) collected from Qingchuan Bay. D. caudata is suggested as an important source of PTXs in shellfish cultivated in the East China Sea. This is the first report of toxin profiles for single-cell isolates of Dinophysis in the East China Sea.

Studies on breeding of Sargassum vachellianum on artificial reefs in Gouqi Island, China

The breeding of Sargassum vachellianum on artificial reefs was firstly performed in the Gouqi Island coast, Zhejiang Province, China. A new algal reef with pedestal and breeding boards was designed and produced for breeding S. vachellianum. The adult male and female plants with receptacles were collected and cultured in a breeding room for 7 days for eggs releasing out of conceptacles and for fertilizing. Approximately 3.41 million fertilized eggs were collected, and then sprayed evenly onto 105 breeding boards in 3 tanks for breeding. Fertilized eggs then sank and were attached on the bottom breeding boards for germination. After 35 days of culture, the seedlings' average length reached approximately 5 mm. And then, one hundred and five breeding boards with seedlings were transported to the Houtou coast of Gouqi Island by boats, and 21 artificial algal reefs (five breeding boards to one pedestal) were installed underwater at both Site A (slow current) and Site B (rush current). After being cultivated for 45 days in the open sea, the average length and density of seedlings on artificial reefs at Site A and Site B were 31.85 ± 0.62 and 41.31 ± 1.39 mm, 4.70 ± 1.40 and 5.19 ± 2.65 seedlings dm− 2, respectively. One year later, the length of the plants on artificial algal reefs in the Gouqi Island coast reached up to 15.51 ± 3.42 cm. All the results indicated that large scale artificial breeding of S. vachellianum with artificial algal reefs was feasible.

枸杞岛铜藻垂直分布格局及成因分析

枸杞岛铜藻垂直分布格局及成因分析

Spatial distribution pattern of Sargassum horneri around Gouqi Island,Shengsi,China

Spatial distribution pattern of Sargassum horneri around Gouqi Island,Shengsi,China

Constitution of fish assemblages in three nearshore habitats and the effect of benthic macroalgae on fish assemblages in Gouqi Island

Macroalgae covering on the rocky reef around coast of Gouqi Island were surveyed and sampled through diving during 2005 to 2006 and May to June 2010,in order to find out the distribution,constitution and life history of macroalgae.Two composing patterns of macroalgae were shown in the subtidal zone of rocky reef:one was dominated by standing macroalgae Sargassum horneri;another was dominated by smaller macroalgaes,such as Ulva pertusa,which is widely distributed both in intertidal and subtidal zone.The life history of S.horneri showed the four stages of the larger kelp bed: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),decomposing and declining period(June to July).The smaller kelp bed exists the whole year,without much difference to outside of the kelp bed.To estimate the composition of fish assemblages in three habitats around Gouqi Island nearshore,i.e.rocky reef,sandy beach and mussel cultivation rafts,we sampled the fish assemblages in three habitats by combined gill nets every month from February 2009 to January 2010.The indexes of Jaccard similarity,Margalef richness and Shannon-wiener diversity were used to compare the variety of fish community structures among habitats,combined with statistical analysis of variance,UPGMA and nMDS.It showed that the differences of fish community structures among above three habitats were significant.The dominant fish species in rocky reef habitat were Sebastiscus marmoratus,Agrammus agrammus and N.albiflora.Fish community was mainly based on the demersal omnivorous rocky fishes,which prey mainly on benthic invertebrates living on macroalgaes.The dominant fish species in sandy beach habitat were Paraplagusia japonica and Nibea albiflora.Fish community was mainly based on the mid-lower migration fishes.For fish assemblages in mussel cultivation raft habitat,which were mainly bigger-size fishes,Mugil cephalus and Decapterus maruadsi were dominant species.The diversity of fish assemblages in rocky reef habitat was higher than that in the other two habitats,due to the relative complex habitat structure.The dominant fish species in both kinds of kelp beds were the same,i.e.S.marmoratus,A.agrammus and N.albiflora.But the structures of fish community were different,due to the species composition of macroalgae covering on rocky reefs.Fish communities in rocky reef habitat dominated by standing larger macroalgae were more stable than those in areas with smaller macroalgae,varied following the life history of S.horneri.The biomass of fishes showed a similar trend to the abundance.But the biomass and abundance of fishes in rocky reef habitat dominated by smaller macroalgaes were quite different.Fish assemblages in areas controlled by smaller macroalgae were affected greatly by the external migration fish assemblages.The species diversity based on abundance of the former was smaller than the latter,but the species diversity based on biomass of the former was larger than the latter.The abundance and biomass have a significant monthly variation in rocky reef habitat with smaller macroalgae.This can be due to the fish assemblages,in which fish species were with larger size,which migrated to rocky reef habitat from open sea area during February to May.Rocky areas covered by standing macroalgae provided a more diversified food selection for local dominant fish species.They possessed an attraction for partial group larvae and small-size individuals.Meanwhile,they offered diversified food choices for upper class of fish,which contribute to the stability of fish community.

Feeding habit of &lt;I&gt;Sebastisous marmoratus&lt;/I&gt; in seaweed bed around Gouqi Island

By analyzing 297 stomach contents of Sebastisous marmoratus in seaweed bed around Gouqi Island in April,May,June 2008 and August 2007,this paper studied the feeding habits of this species and its diet composition that varied with seaweed growth. Results showed that feeding intensity was low throughout the study period and percentage of empty stomachs and mean stomach fullness index varied significantly(P0.05). Percentage of empty stomach varied insignificantly among the size classes(P0.05). The mean stomach fullness varied insignificantly among specimens less than 80.0mm TL(P0.05). S.marmoratus was benthivorous and the diet of it consisted of at least 29 different prey species belonging to 12 major groups(Amphipoda,Shrimps,Crabs,Echinodermata,Polychaeta,etc.). Amphipoda were the most important prey and accounted for 97.03% by %IRI of all the prey. The composition of the prey varied with different growth periods of seaweed bed and S.marmoratus size classes. Shrimps and crabs were more important during booming period and flourish period,whereas amphipods were more important during lasting peroid and decay period. Amphipoda were more important in the diet of specimens less than 80.0 mm TL,shrimps and crabs were more important in the diet of specimens 80.0-99.9 mm TL,whereas fish and amphipods occurred more in the diet of specimens less than 100.0 mm TL.

Algal communities at Gouqi Island in the Zhoushan archipelago, China

The kelp bed of Gouqi Island lies in the east of the East China Sea, in the Shengsi Archipelago. It is a key component of the island-reef ecosystem. This study evaluated kelp beds on intertidal and subtidal zones from 2004 to 2006. We evaluated seasonal variations in the community structure of macroalgae, and their relationship with water temperature, nitrogen and phytoplankton. The Gouqi Island kelp bed consists mainly of species of Sargassum. Sargassum horneri was the dominant species in subtidal zones, representing 90% of the total biomass. The dominant species in intertidal zones were S. fusiforme, S. horneri, S. thunbergii and Undaria pinnatifida. Fifty-four phytoplankton species were found in the Gouqi Island kelp bed, of which 51 species were found inside the kelp beds, 43 species outside the kelp beds, and 40 species were present both inside and outside the kelp beds. Diatoms were dominant both inside and outside the kelp beds. Except in winter, Skeletonema costatum was dominant, and its abundance in autumn was over 98% of the total abundance. Water temperature was found to be the primary factor influencing the growth of S. horneri in the Gouqi Island kelp bed. S. horneri grew slowly from November to March, and rapidly from March to June. The upper temperature limit for growth of S. horneri was about 18°C. Higher water temperatures can result in a decline in the kelp bed. Nitrogen seemed to be a limiting factor for macroalgal growth. This was particularly true for S. horneri and phytoplankton. Since nitrate is the primary nutrient for S. horneri, its absorption by S. horneri resulted in seasonal changes of nitrate in the ecosystem.