浙江省健跳港蛎江滩牡蛎多样性和资源量的时空变化

Diversity and spatialtemporal changes of oyster communities at Lijiangtan oyster reef in Jiantao Bay,Sanmen County,Zhejiang Province

调查了浙江省三门县健跳港蛎江滩牡蛎礁中牡蛎的种类、资源量和幼体补充量,并分析了牡蛎的遗传多样性及资源量和幼体补充量的时空变化特征。结果显示,蛎江滩牡蛎礁中分布有6种牡蛎,即近江牡蛎(Crassostrea ariakensis)、熊本牡蛎(C.sikamea)、福建牡蛎(C.angulata)、香港牡蛎(C.hongkongensis)、猫爪牡蛎(Talonostrea talonata)和长牡蛎(C.gigas)。在牡蛎群落组成中,熊本牡蛎、香港牡蛎和近江牡蛎的占比分别为92.92%、5.00%和2.08%,其他3种牡蛎仅在定性调查中发现。夏初和秋季牡蛎平均密度分别为(97±40)个·m^(-2)和(1770±467)个·m^(-2);随着潮间带高程的降低,熊本牡蛎密度逐渐降低,而近江牡蛎和香港牡蛎的密度逐步升高。牡蛎幼体附着与补充开始于6月初、结束于10月初左右,补充量呈现显著的时空变化特征;熊本牡蛎在整个礁区均有较高的补充量,近江牡蛎和香港牡蛎则在中、低礁区补充量较高。结果表明,蛎江滩牡蛎礁中的牡蛎群落具有较高的物种多样性。未来需进一步研究泥沙淤积和香港牡蛎入侵对蛎江滩生境和牡蛎种质资源的影响。

Jiantiao Bay is a long,narrow and curved inlet in Sanmen County of central Zhejiang Province.The upstream of Jiantiao Bay provides suitable environment for settlement,recruitment and growth of Crassostrea ariakensis and C.sikamea.A natural oyster reef called Lijiangtan has formed in the intertidal zone.In the past decades,the natural oyster stocks and habitats have largely declined due to watershed exploitation,overfishing and bivalve aquaculture.To conserve and restore oyster stocks and their habitats,Sanmen County listed Lijiangtan oyster reef as the sanctuary in 2021.This study described the species composition,biodiversity and densities of oyster communities at the reef by field observation,and explored the spatial-temporal changes in oyster densities.Along the elevation gradient,Lijiangtan oyster reef was divided into low reef area,middle reef area and high reef area and field observations were done from early June to early October in 2021.At each reef area,six or nine 0.4 m×0.4 m quadrates were set to investigate oyster communities at the reef.All live oysters were analyzed for species identification,counting,and size measurement.Morphological and molecular methods were combined to identify the oyster species.Most of the oysters collected could be easily classified by morphological differences.The remaining oysters were identified by PCR primers.Oyster settlement units were created using porcelain tiles by drilling a hole near each of four corners.Five experimental rafts for recruitment monitoring were built up with stainless steel pipes at the lower tidal zone of the oyster reef.A total of six oyster species were identified at the natural oyster reef,including Crassostrea ariakensis,C.sikamea,C.angulata,C.hongkongensis,Talonostrea talonata,C.gigas.In terms of numeric abundance,C.sikamea,C.hongkongensis,C.arikensis accounted for 92.92%,5.00%and 2.08%of the oyster communities,respectively.The other three species were found only from qualitative sampling.The average total densities of oysters at the natural reef were(97±40)ind·m^(-2)in early summer and(1770±467)ind·m^(-2)in autumn.The spatial-temporal changes in densities were evident for each oyster species.The densities of C.hongkongensis and C.ariakensis gradually increased with the decreasing elevation gradient,while the converse spatial pattern was found in C.sikamea.The density of C.sikamea in early summer was significantly higher at high reef than that at low reef,while no difference was found among three reef areas in autumn.At each reef area,the densities of C.sikamea were significantly greater in autumn than that in early summer.In both middle and low reef areas,the density of C.ariakensis was significantly higher in autumn than that in early summer.In early summer,the density of C.hongkongensis was significantly higher at low reef area than that at high reef area.In autumn,the density of C.hongkongensis among 3 reef areas ranked as follows:high reef area<middle reef area<low reef area.In both middle and low reef areas,the total oyster density was significantly higher in autumn than that in early summer.The experiment for monitoring recruitment found that C.ariakensis,C.hongkongensis,C.angulata and Talonostrea talonata recruited more in 0.6 m tidal zone,while the recruitment of C.sikamea was slightly more in 1.6 m tidal zone than that in 0.6 m tidal zone.Except in the first monitoring period of 0.6 m tide zone when the proportion of C.ariakensis was higher than that of C.sikamea,C.sikamea dominated the recruitment communities.The recruitment in 0.6 m tidal zone had two peaks.The temporal pattern for oyster recruitment in 1.6 m tidal zone was generally consistent with that in 0.6 m tidal zone,but the exception was that the first recruitment peak in the 1.6 m tidal zone appeared half month earlier than that in 0.6 m tidal zone.Except for the first two and the last monitoring periods,the recruitment densities significantly differed between two tidal zones.The oyster recruitment at the natural reef showed significant temporal and spatial variations.C.sikamea had consistently high recruitment in three reef areas during the spawning season,while C.hongkongensis and C.ariakensis had more recruits in low and middle reef areas than in high reef area.The study conclude that the Lijiangtan oyster reef have abundant and sustainable oyster communities.Further studies shall be done to explore the effects of sedimentation and C.hongkongensis invasion on the habitat quality and living oyster resources at Lijiangtan oyster reef.