| Ruditapes philippinarum is widely distributed in the north and south Seas of China.It is one of the four major cultured shellfish in China.Laizhou Bay Nature Reserve has become an important production area of natural clam seedlings due to its suitable environmental conditions,which provides an important guarantee for the restoration of clam resources in the coastal waters of northern China.In this paper,the hydrological and water quality conditions inside and outside Laizhou Bay reserve,the annual development of clam gonads in the reserve,the amount and distribution of planktonic larvae and benthic individuals,the velocity and direction of seawater in the reserve and the diameter of bottom plasmid were sampled and analyzed from 2019 to 2021.The results showed that:1.In the same period from 2019 to 2021(January,April,July and October),the seawater temperature,salinity,dissolved oxygen,active phosphate,nitrite,nitrate and ammonia nitrogen contents in the reserve were generally stable,with significant differences in only a few periods.There was no significant difference in hydrology and water quality between inside and outside the reserve.Taking the active phosphate and inorganic nitrogen as the judgment index and the seawater quality standard(GB 3097-1997)as the judgment standard,the water quality of Laizhou Bay Reserve was between class I and class II water quality,which provided suitable environmental conditions for the survival and growth of clams.2.From January to December 2020,adult clams in Laizhou Bay Reserve showed regular gonadal development.From April,the clam cubs enter the gonadal proliferative phase,the growth phase in late April,and the mature phase in early May,where germ cells begin to be produced,and then enter the resting phase.The gonadal index of clam cubs reached the highest value from May to June,and the plumpness of clam cubs showed a trend of slowing growth from May to June.3.In late May 2019,planktonic samples were collected at 69 of the 85 survey stations set in Laizhou Bay Reserve(the other 16 stations could not be reached by ships due to shallow water level or obstacles).D-shaped planktonic larvae were distributed in 69 effective stations in the reserve,and the abundance was 67.05?304580.21 ind./m~3,which showed that the larva abundance in the middle of the reserve was relatively large,while the larva abundance in nearshore and far shore was relatively small.4.In late July 2019,benthic samples were collected at 69 of the 85 survey stations set up in the Laizhou Bay Reserve.The abundance of benthic clam in the 69 effective stations in the reserve was 0-126520.68ind./m~2,of which 12 stations had no clam.In 2020,the abundance of benthic clam in the effective stations in the reserve is 0?121899.0ind./m~2,and there are 22stations where clam clam has not been investigated.In 2021,the abundance of benthic clam in the effective stations in the reserve is 0?37893.0ind./m~2,and there are 27 stations where clam clam has not been investigated.The abundance of clams in the central station was relatively high,while the abundance in the surrounding areas was relatively small.In the protected area,individuals with a shell length of 0.20-1.00 cm are the main ones,accounting for 77.82%.5.In June 2019,a station was set up in the middle of the reserve(119°47?35.88"E,37°24?7.92"N)to measure the direction and velocity of the ocean current.Laizhou Bay is characterized by irregular semidiurnal tides.The maximum velocity during spring tide is49.0cm/s,and the average velocity is 24.1cm/s.During high tide,the flow is mainly southwest(SW)with a frequency of 51%,and during low tide,it is mainly northeast flow(NE)with a frequency of 41%.During the neap tide period,the maximum velocity is 25.1cm/s,and the average velocity is 12.6cm/s.During the high tide period,the southwest(SW)flow is 53%,and the low tide period is mainly the northeast(NE)flow,with a frequency of 39%.The southwest-northeast flow of the ocean current in the reserve played a certain role in the dispersal and distribution of D-shaped planktonic larvae.6.In late July 2019,the sediment conditions in Laizhou Bay Reserve were investigated,and it was found that the sea area was mainly sandy sediment.The absolute value of Pearson correlation coefficient was 0.027?0.305 between the abundance of benthic clams and the percentage of each particle size group,which was positively correlated with the particle size composition of 426?850?m and 426?2000?m,and reached a significant level(P<0.05).The correlation coefficients were 0.244 and 0.305 respectively.To find out the hydrological and water quality conditions,the gonad development law of adult clams,the resource amount and distribution of planktonic larvae and benthic individuals,the influence law of seawater flow velocity and direction on the distribution of planktonic larvae,and the influence law of bottom conditions on the distribution of benthic individuals in Laizhou Bay Reserve,it can provide a basis for the rational conservation of clam resources in Laizhou Bay Reserve. |
PDF Full Text Request