The Characteristics Of Mussel Farming Habitat And Its Effect On The Growth Of Juvenile Sebastiscus Marmoratus

With the increase of the scale of mussel farming,the impact of mussel farming on the ecological environment has become more and more obvious.In the process of mussel farming,the physical,chemical and biological environment of the farming waters and their surrounding waters have been affected.In this paper,the study area is the mussel farming area around Gouqi Island.The main research object is the Sebastiscus marmoratus which inhabits on the surface of mussel string.According to the environmental characteristics of mussel farming habitat and the growth difference of Sebastiscus marmoratus inside and outside the culture area,the conservation mechanism of mussel farming habitat to Sebastiscus marmoratus was studied,and the ecological effect of mussel farming was evaluated.In order to collect the Sebastiscus marmoratus in mussel farming area quantitatively,a self-made fishing net was used in May—July of 2018 for targeted sampling.At the same time,the seaweeds and macroinvertebrates attached to the mussel string were sampled quantitatively,the size of surface crevice of the mussel string and the hydrological environment of the site were measured.In order to study the growth characteristics of Sebastiscus marmoratus in mussel farming habitats,the biological characteristics of Sebastiscus marmoratus in mussel farming habitats were compared with those in natural reef habitats,and the growth differences of otolith rings of Sebastiscus marmoratus in the two habitats were analyzed,and the environmental differences between the two habitats were analyzed from the microscopic point of view.The results showed that all the Sebastiscus marmoratus inhabiting the mussel farming habitat were juveniles.The length of the samples collected ranged was16—62 mm,the dominant body length group was 20—30 mm,accounting for29.41%of the total,and the weight range was 0.16—7.61 g,the dominant body weight group was 0—1 g,accounting for 25.49%of the total.According to the scale of mussel farming and average habitat density of Sebastiscus marmoratus,the total resources of Sebastiscus marmoratus in the mussel farming habitat of Gouqi Island in May,June and July are estimate to be 1.4×10~7ind,12.95t,1.5×10~7ind,45.41t and5.6×10~6ind,22.67t respectively.Regression analysis based on the body length and body weight data of the samples collected showed that the growth rate of juvenile Sebastiscus marmoratus living in mussel farming habitat was higher than that of other habitats in previous years.Mussel farming habitats are multi-void structures,the water power is weaker,the dissolved oxygen content and transparency is high in mussel farming habitats,Seaweeds and macroinvertebrates are attached to the surface of mussel string.There are 61 species of seaweed were sampled in mussel farming habitats,including 13species of Prochlorophyta,38 species of Rhodophyta and 10 species of Phaeophyta.The dominant species is Pachydictyon coriaceum in May—July.Due to the influence of illumination,the seaweeds in the upper layer tended to be more than that in the lower layer,and the horizontal distribution of seaweeds in the outer layer tended to be more than that in the inner layer.A total of 46 species of macroinvertebrates were sampled,including 5 species of Cnidaria,2 species of Amphipoda,4 species of Polyplacophora,2 species of Porifera,7 species of Polychaeta,6 species of Gastropoda,3 species of Echinodermata,9 species of Crustacea and 8 species of Bivalvia.The dominant group is Caprellidae in May—July.The vertical distribution of large invertebrates is more in the lower layer than in the upper layer,and there is no obvious trend in the horizontal direction.Distribution and biomass of attached organisms on the surface of mussel farming strings are often affected by human activities due to the irregular cleaning of mussel farmers.From diving observation,it was found that the juvenile Sebastiscus marmoratus in the surface layer of mussel farming area usually crawled on the mussel shell,sometimes suspended in water,when they are in danger or frightene,they will swim quickly to the surface of the nearby mussel string,creep or drill into the mussel pore.Regression analysis showed that the entrance cross-sectional area of mussels was positively correlated with the catches,but not significantly.The juvenile Sebastiscus marmoratus have the widest body length distribution and the highest resource density in the pore range of 10—20 cm,which is 13(ind/string),most of the length of juvenile Sebastiscus marmoratus are 20—30mm.According to the analysis of stomach contents and C,N stable isotope detection,it was found that the juveniles Sebastiscus marmoratus in mussel farming habitats trophic levels is 2.16,mainly ate Amphipoda,The biomass of amphipods in mussel farming area is relatively high,and they are supersaturated for the food supply of juveniles Sebastiscus marmoratus.Therefore,the behavior of juveniles Sebastiscus marmoratus is not limited by the distribution of food organisms,and the survival rate of juveniles Sebastiscus marmoratus is improved.Comparing the otolith fingerprints of fish in mussel culture habitat and natural rocky habitat,it is found that the otolith pattern of fish in mussel farming habitat was more uniform and clear,while the otolith of fish in natural reef habitat was relatively disordered and have more tags ring.Most of the otolith patterns collected in rocky area showed clear and regular patterns in the initial stage,after a tags ring,begin to appears chaotic ring.This study indicated that mussel farming sturctureis providing a relatively stable habitat for juveniles Sebastiscus marmoratus and playing an essential role in the conservation of juveniles Rockfish in local waters,compared to natural rocky reef habitat.The construction of local marine ranching can refer to the conservation mode of mussel farming facilities to ensure the sustainable output of target species,Sebastiscus marmoratus with this otolith structure may have previously inhabited mussel farming habitats.