劉松林，江志堅(jiān)，吳云超，張景平，黃小平,*

1中國(guó)科學(xué)院南海海洋研究所，中國(guó)科學(xué)院熱帶海洋生物資源與生態(tài)重點(diǎn)實(shí)驗(yàn)室，廣州 510301 2中國(guó)科學(xué)院南海海洋研究所，廣東省應(yīng)用海洋生物學(xué)重點(diǎn)實(shí)驗(yàn)室，廣州 510301 3中國(guó)科學(xué)院大學(xué)，北京 100049

海草床育幼功能及其機(jī)理

劉松林1,2,3，江志堅(jiān)1,2，吳云超1,2,3，張景平1,2，黃小平1,2,*

1中國(guó)科學(xué)院南海海洋研究所，中國(guó)科學(xué)院熱帶海洋生物資源與生態(tài)重點(diǎn)實(shí)驗(yàn)室，廣州 510301 2中國(guó)科學(xué)院南海海洋研究所，廣東省應(yīng)用海洋生物學(xué)重點(diǎn)實(shí)驗(yàn)室，廣州 510301 3中國(guó)科學(xué)院大學(xué)，北京 100049

海草床是近岸海域中生產(chǎn)力極高的生態(tài)系統(tǒng)，是許多海洋水生動(dòng)物的重要育幼場(chǎng)所。從生物幼體的密度、生長(zhǎng)率、存活率和生境遷移4個(gè)方面闡述海草床育幼功能，并從食源和捕食壓力兩個(gè)方面探討海草床育幼功能機(jī)理。許多生物幼體在海草床都呈現(xiàn)出較高的密度、生長(zhǎng)率和存活率，并且在個(gè)體發(fā)育到一定階段從海草床向成體棲息環(huán)境遷移。豐富的食物來(lái)源或較低的捕食壓力可能是海草床具有育幼功能的主要原因，但不同的生物幼體對(duì)海草床的利用有差異，海草床育幼功能的機(jī)理在不同環(huán)境條件下也存在差異。提出未來(lái)海草床育幼功能的重點(diǎn)研究方向：(1)量化海草床對(duì)成體棲息環(huán)境貢獻(xiàn)量；(2)全球氣候變化和人類(lèi)活動(dòng)對(duì)海草床育幼功能的影響；(3)海草床育幼功能對(duì)海草床斑塊效應(yīng)和邊緣效應(yīng)的響應(yīng)，以期為促進(jìn)我國(guó)海草床育幼研究和海草床生態(tài)系統(tǒng)保護(hù)提供依據(jù)。

海草床；生物幼體；育幼功能；機(jī)理

海草床生態(tài)系統(tǒng)是近岸海域中生產(chǎn)力極高的生態(tài)系統(tǒng)[1]，雖然僅占全球海洋面積的0.15%，但卻貢獻(xiàn)了全球海洋1%的凈初級(jí)生產(chǎn)力[2]。近年來(lái)，海草床的生態(tài)功能與經(jīng)濟(jì)價(jià)值逐漸被人們所認(rèn)識(shí)[3]。研究表明，海草床是許多經(jīng)濟(jì)魚(yú)類(lèi)和無(wú)脊椎動(dòng)物的重要育幼場(chǎng)所，如大西洋鯖魚(yú)(Scomberscombrus)、紅鼓魚(yú)(Sciaenopsocellatus)、蠔隆頭魚(yú)(Tautogaonitis)、大西洋鱈(Gadusmorhua)、女王鳳凰螺(Strombusgigas)、青蟹(Carcinusmaenas)、藍(lán)蟹(Callinectessapidus)等[4-5]，而且海草床比沿岸其它生境具有更高水生動(dòng)物幼體的生物量和密度。因此，海草床的育幼功能得到了廣泛的認(rèn)可[4, 6-7]。

關(guān)于育幼功能，Deegan[8]認(rèn)為是指某些魚(yú)類(lèi)來(lái)到河口產(chǎn)卵孵化生長(zhǎng)后離開(kāi)該區(qū)域；而B(niǎo)eck等[6]認(rèn)為，若單位面積的某一生境區(qū)域能夠比其它生境吸引更多的某些生物幼體，并能正常生長(zhǎng)，就稱(chēng)該區(qū)域具有育幼功能；而且相比于其它棲息環(huán)境，育幼棲息環(huán)境對(duì)成體棲息環(huán)境要有更大的貢獻(xiàn)。生物幼體在育幼棲息環(huán)境下的生長(zhǎng)，以及育幼環(huán)境向成體棲息環(huán)境的貢獻(xiàn)量是育幼功能的重要特征[9]，主要從4個(gè)方面進(jìn)行比較：(1)生物幼體的密度；(2)生物幼體的生長(zhǎng)率；(3)生物幼體的存活率；(4)生物向成體生境的遷移運(yùn)動(dòng)[6]。

國(guó)外學(xué)者對(duì)海草床的育幼功能開(kāi)展了較多研究，主要涉及海草床與其它生境的育幼功能比較[10-12]，海草床育幼功能的機(jī)理分析[13-14]等方面。前人研究表明，海草床能夠?yàn)樯镉左w提供良好的棲息環(huán)境，在海草床分布具有較高的生物幼體密度，并且在促進(jìn)生物幼體生長(zhǎng)率、存活率、提供食物來(lái)源和庇護(hù)場(chǎng)所等具有重要作用[4, 7]。

目前，對(duì)海草床生態(tài)系統(tǒng)育幼功能的研究主要集中于北美洲和大洋洲地區(qū)[4]，而在我國(guó)未見(jiàn)相關(guān)的研究報(bào)道。因此，亟待開(kāi)展對(duì)我國(guó)海草床育幼功能的研究。本文將對(duì)國(guó)外關(guān)于海草床育幼功能的特征和機(jī)理的研究進(jìn)行回顧和總結(jié)，為我國(guó)的海草床育幼研究提供借鑒，并為我國(guó)的海草床生物資源保護(hù)和可持續(xù)開(kāi)發(fā)利用提供科學(xué)依據(jù)。

1 海草床育幼功能的特征

近岸海域的生境類(lèi)型多樣，包括海草床、紅樹(shù)林、珊瑚礁、鹽沼等[15]。目前，大多數(shù)研究主要通過(guò)比較海草床與其它生境生物幼體的密度、生長(zhǎng)速率、存活率以及幼體生長(zhǎng)后向成體生境的遷移運(yùn)動(dòng)，來(lái)研究海草床育幼功能的特征[4, 7]。

1.1 海草床生物幼體的密度

生物幼體的密度是反映某生境是否具有育幼功能的決定性指標(biāo)[6]。對(duì)于魚(yú)類(lèi)幼體密度的研究，主要是通過(guò)直接拖網(wǎng)調(diào)查[16-17]和可視化調(diào)查(浮潛或水肺潛水)[12, 18]。上述兩種方法都具有各自的優(yōu)缺點(diǎn)：拖網(wǎng)捕獲方法的優(yōu)點(diǎn)是能夠獲得魚(yú)類(lèi)的樣本，而缺點(diǎn)是會(huì)低估魚(yú)類(lèi)的密度和數(shù)量[19]，并且由于網(wǎng)口大小的原因，可能導(dǎo)致有些個(gè)體較小的魚(yú)不能被捕獲[16]；可視化調(diào)查方法的優(yōu)點(diǎn)是迅速、棲息地不被破壞以及可重復(fù)性調(diào)查等[19]，但其缺點(diǎn)是有些魚(yú)類(lèi)可能會(huì)被調(diào)查者所吸引或是驚散，且不同的調(diào)查者在估算魚(yú)類(lèi)數(shù)量和密度時(shí)會(huì)有差異[20-21]。因此，這兩種調(diào)查方式會(huì)獲得差異較大的結(jié)果，如Harmelin和Francour[22]在波喜蕩草(Posidoniaoceanica)海草床利用拖網(wǎng)捕撈和可視化調(diào)查方法進(jìn)行對(duì)比研究時(shí)，發(fā)現(xiàn)拖網(wǎng)能夠捕獲更多的底棲魚(yú)類(lèi)，而可視化調(diào)查則能夠觀(guān)察到鯛科(Sparids)和隆頭魚(yú)科(Labrids)等更多的中層食浮游生物魚(yú)類(lèi)。

海草床中的不同生物幼體密度與其它鄰近的棲息環(huán)境相比有著顯著的差異。Nagelkerken等[18]在加勒比海博奈爾島(Bonaire Island)對(duì)16種幼魚(yú)進(jìn)行可視化調(diào)查研究，發(fā)現(xiàn)黃仿石鱸(Haemulonflavolineatum)、藍(lán)仿石鱸(Haemulonsciurus)、黃尾笛鯛(Ocyuruschrysurus)、小帶刺尾魚(yú)(Acanthuruschirurgus)和綠鸚鯛(Sparisomaviride)這5種幼魚(yú)在海草床的密度顯著高于鄰近紅樹(shù)林及珊瑚礁的密度，其中黃仿石鱸在海草床的密度最大，為115.3條/1000m2，表明海草床是這5種幼魚(yú)的重要育幼場(chǎng)所。同樣，Aguilar-Perera和Appeldoorn[12]在波多黎各西南部紅樹(shù)林-海草-珊瑚礁相連的棲息環(huán)境對(duì)20種幼魚(yú)進(jìn)行可視化調(diào)查，發(fā)現(xiàn)黃仿石鱸、藍(lán)仿石鱸和普氏仿石鱸(Haemulonplumieri)在海草床的密度也顯著較高，表明海草床是這3種幼魚(yú)重要的育幼場(chǎng)所。另外，幼魚(yú)在同一海草床不同區(qū)域的密度也具有差異。Dorenbosch等[23]在加勒比海阿魯巴島(Aruba Island)利用可視化調(diào)查方法，研究龜裂泰來(lái)藻(Thalassiatestudinum)海草床下的幼魚(yú)密度，發(fā)現(xiàn)距離珊瑚礁最遠(yuǎn)的海草床區(qū)域有著最高的育幼種幼魚(yú)密度，接近210條/100m2，而距離珊瑚礁最近的海草床區(qū)域，其育幼種幼魚(yú)密度最小，接近50條/100m2。

同時(shí)，無(wú)脊椎動(dòng)物幼體在海草床的分布也具有一定的變化特征。例如，Heck和Thoman[24]在美國(guó)低緯度的約克河(York River)河口和高緯度的派森島(Parson′s Island)對(duì)海草床的藍(lán)蟹進(jìn)行了為期2a的拖網(wǎng)調(diào)查，發(fā)現(xiàn)約克河河口海草床藍(lán)蟹幼體的數(shù)量比其鄰近的無(wú)植物裸露區(qū)域顯著高，并且也比派森島海草床區(qū)域顯著高，表明低緯度海草床區(qū)域是藍(lán)蟹的重要育幼場(chǎng)所；Murphey和Fonseca[25]在斑塊狀海草床和連續(xù)性海草床對(duì)桃紅對(duì)蝦(Penaeusduorarum)進(jìn)行了為期1a的調(diào)查，發(fā)現(xiàn)連續(xù)性海草床區(qū)域桃紅對(duì)蝦的密度顯著高于斑塊狀海草床區(qū)域，特別是在夏季7、8月份，連續(xù)性海草床區(qū)域的桃紅對(duì)蝦密度是斑塊狀海草床區(qū)域的3倍。

1.2 海草床生物幼體的生長(zhǎng)率

生物幼體生長(zhǎng)率是評(píng)判生境育幼功能質(zhì)量的重要指標(biāo)[26-27]，主要通過(guò)野外圍隔實(shí)驗(yàn)(Field Enclosure Experiments)[10-11, 27-28]或?qū)嶒?yàn)室模擬實(shí)驗(yàn)[29-30]來(lái)獲取。對(duì)于魚(yú)類(lèi)幼體生長(zhǎng)率的測(cè)定，主要包括體長(zhǎng)、體重[10, 27]或耳石日生長(zhǎng)量[11]等指標(biāo)；而對(duì)于無(wú)脊椎動(dòng)物幼體，則主要通過(guò)測(cè)定其生物學(xué)指標(biāo)(殼長(zhǎng)和殼寬等)來(lái)計(jì)算其生長(zhǎng)率[28-30]。

許多研究表明，海草床生境下生物幼體的生長(zhǎng)率比其它無(wú)植被生境下的顯著高[10-11, 14, 29-30]。例如，Stuns等[11]對(duì)紅鼓魚(yú)幼體進(jìn)行了7d的野外圍隔實(shí)驗(yàn)研究，發(fā)現(xiàn)在萊氏二藥藻(Halodulewrightii) 區(qū)域紅鼓魚(yú)幼體的生長(zhǎng)率最高，為0.42mm/d，在互花米草(Spartinaalterniflora)生長(zhǎng)的鹽沼區(qū)域次之，為0.4mm/d，而在蠔殼礁和無(wú)植物覆蓋的裸露區(qū)域，紅鼓魚(yú)幼體生長(zhǎng)率分別為0.12mm/d和0.21mm/d；Stoner等[30]通過(guò)實(shí)驗(yàn)室模擬不同棲息環(huán)境對(duì)女王鳳凰螺幼體生長(zhǎng)率影響的研究，發(fā)現(xiàn)在龜裂泰來(lái)藻環(huán)境下的生長(zhǎng)率最高，為62μm/d，在蠕形絨枝藻(Dasycladusvermicularis)環(huán)境下的生長(zhǎng)率次之，為55μm/d，而在大型藻類(lèi)、礁石以及海草碎屑環(huán)境中的生長(zhǎng)率為32—45μm/d，在擬剛毛藻屬(Cladophoropsisspp.)、沙質(zhì)裸露以及過(guò)濾海水環(huán)境下的生長(zhǎng)率最小，僅7—19μm/d。然而，Sogard[10]通過(guò)野外圍隔實(shí)驗(yàn)研究，發(fā)現(xiàn)美洲擬鰈(Pseudopleuronectesamericanus)幼體在大葉藻(Zosteramarina)海草床的生長(zhǎng)率，與鄰近的無(wú)植被區(qū)域無(wú)顯著差異。

另外，也有研究發(fā)現(xiàn)，生物幼體的生長(zhǎng)率還受到海草床生境中溫度、溶解氧和沉積物類(lèi)型等理化因子的影響[10, 27]。例如，美洲擬鰈的生長(zhǎng)率與沉積物中砂石的含量呈顯著正相關(guān)[10]； Phelan等[27]對(duì)美洲擬鰈和蠔隆頭魚(yú)幼體進(jìn)行野外圍隔實(shí)驗(yàn)，發(fā)現(xiàn)相對(duì)于生境類(lèi)型，溫度和溶解氧這兩個(gè)環(huán)境因子對(duì)這兩種幼魚(yú)的生長(zhǎng)率影響更大。

1.3 海草床生物幼體的存活率

生物幼體的存活率是反映生境是否具有育幼功能的重要指標(biāo)[18]。對(duì)生物幼體存活率的研究主要通過(guò)野外束縛實(shí)驗(yàn)(Field Tethering Experiments)[31-33]或?qū)嶒?yàn)室模擬[34-36]進(jìn)行，并通過(guò)計(jì)算實(shí)驗(yàn)種幼體在單位時(shí)間被捕食者的捕食幾率來(lái)說(shuō)明其存活率。

大多數(shù)研究表明，生物幼體在海草床的存活率顯著高于鄰近無(wú)植物裸露區(qū)域[4, 35]。例如，Rooker等[35]以瞬時(shí)死亡率[37]為比較參數(shù)，在菱體兔牙鯛(Lagodonrhomboides)的捕食作用下，紅鼓魚(yú)幼體在無(wú)植物的裸露區(qū)域的死亡率為0.166—0.189h-1predater-1(單位時(shí)間、單位捕食者的死亡率)，而在萊氏二藥藻和龜裂泰來(lái)藻海草床區(qū)域分別為0.047—0.069h-1predater-1和0.021—0.046h-1predater-1。同樣，生物幼體在海草床和鄰近棲息環(huán)境的存活率也存在差異[32, 36, 38-39]。例如，Chittaro等[32]通過(guò)90min的野外束縛實(shí)驗(yàn)，研究銀仿石鱸(Haemulonchrysargyreum)幼體在不同棲息環(huán)境下的存活率，發(fā)現(xiàn)在海草床的存活率接近40%，而在珊瑚礁區(qū)域僅為15%；Dance等[38]研究發(fā)現(xiàn)糙海參(Holothuriascabra)幼體在海草床邊緣區(qū)域3d后的存活率為70%，而在珊瑚礁區(qū)域，糙海參幼體48h后全部被捕食。Orth和van Montfrans[36]通過(guò)室內(nèi)模擬藍(lán)蟹在不同棲息環(huán)境受底鳉(Fundulusheteroclitus)捕食作用下的存活率，發(fā)現(xiàn)在大葉藻棲息環(huán)境下，藍(lán)蟹的后期幼體和一齡幼體的存活率分別為44%—57%和87%，而在互花米草棲息環(huán)境下的存活率僅分別為18%—19%和43%—48%。然而，Lipcius等[39]在約克河河口研究中發(fā)現(xiàn)，藍(lán)蟹幼體在海草床的存活率為20%，在鄰近的鹽沼區(qū)域的存活率卻高達(dá)80%。

另外，海草床的面積和莖枝密度等也會(huì)影響生物幼體的存活率[33, 40]。例如，哈克斯島(Harkers Island)的藍(lán)蟹存活率和海草床莖枝密度之間就有明顯的函數(shù)關(guān)系，在大斑塊海草床(>100m2)為雙曲線(xiàn)關(guān)系：Y=X0.14/2.5+ X0.14(r2=0.63,P<0.05)，而在小斑塊的海草床(1—3m2)卻為線(xiàn)性關(guān)系：Y=0.0002X+0.5(r2=0.83,P<0.01)[33]。

1.4 海草床生物的遷移運(yùn)動(dòng)

生物從幼體棲息環(huán)境到成體棲息環(huán)境的遷移運(yùn)動(dòng)，是評(píng)價(jià)幼體棲息環(huán)境育幼功能的重要指標(biāo)，也是評(píng)價(jià)這一生境為該生物幼體育幼場(chǎng)所最直接的檢驗(yàn)方式[6, 41]。有些在海草床生存的生物幼體生長(zhǎng)后會(huì)向成體棲息環(huán)境遷移，例如，熱帶和亞熱帶海草床中許多珊瑚礁魚(yú)類(lèi)幼體在海草床生長(zhǎng)，而后向珊瑚礁棲息環(huán)境遷移[42-44]。然而，溫帶海草床生物向成體棲息環(huán)境的遷移研究較少[45-46]。

研究魚(yú)類(lèi)遷移運(yùn)動(dòng)的方法主要為調(diào)查對(duì)比魚(yú)類(lèi)在各棲息環(huán)境下的密度和體長(zhǎng)的空間分布規(guī)律[18, 44, 47]、食源分析[48-49]、耳石微化學(xué)分析[45, 50]和人工標(biāo)記[51-52]等方法。Cocheret de la Morinière等[47]在加勒比海的庫(kù)拉索島(Cura?ao Island)對(duì)9種魚(yú)進(jìn)行體長(zhǎng)的空間分布調(diào)查，發(fā)現(xiàn)小帶刺尾魚(yú)、藍(lán)仿石鱸、灰笛鯛(Lutjanusgriseus)和八帶笛鯛(Lutjanusapodus) 這4種魚(yú)在海草床的平均體長(zhǎng)分別為11、11.5、12.6cm和11.3cm，而在珊瑚礁區(qū)域的平均體長(zhǎng)分別為17、21.5、16.6cm和18.5cm，兩個(gè)生境下4種魚(yú)體長(zhǎng)分布差異顯著，表明這4種魚(yú)的幼體階段是在海草床生活，隨后向珊瑚礁區(qū)域遷移運(yùn)動(dòng)。Cocheret de la Morinière等[48]和Verweij等[49]通過(guò)比較海草床灰笛鯛、八帶笛鯛和黃尾笛鯛幼體和珊瑚礁成體這3種魚(yú)肌肉組織的δ13C，發(fā)現(xiàn)在珊瑚礁的魚(yú)成體δ13C顯著小于海草床的幼體，表明上述魚(yú)類(lèi)在海草床和珊瑚礁的食物來(lái)源存在差異，這3種魚(yú)類(lèi)幼體階段在海草床生活，隨后向珊瑚礁區(qū)域遷移。Gillanders和Kingsford[45]比較溫帶海草床和巖礁區(qū)綠唇藍(lán)魚(yú)(Achoerodusviridis)幼體生長(zhǎng)期耳石中微量元素的含量，發(fā)現(xiàn)兩種棲息環(huán)境中綠唇藍(lán)魚(yú)耳石中錳、鋇和鍶的含量存在顯著差異，表明巖礁棲息環(huán)境中41%綠唇藍(lán)魚(yú)的幼體階段在海草床區(qū)域。Verweij等[51]通過(guò)對(duì)海草床中叉長(zhǎng)為13.2—21cm八帶笛鯛亞成體進(jìn)行外部標(biāo)記，研究其遷移，結(jié)果發(fā)現(xiàn)叉長(zhǎng)為17.8—20cm的魚(yú)體從海草床遷移到鄰近的珊瑚礁區(qū)域。

生物個(gè)體從海草床育幼環(huán)境向成體棲息環(huán)境遷移的原因，主要是攝食或躲避捕食的需要[42, 48, 53]。例如，Nakamura等[42]對(duì)海草床太平洋黃尾龍占(Lethrinusatkinsoni)幼體的胃含物分析，發(fā)現(xiàn)隨著體長(zhǎng)的增加，其對(duì)大型底棲動(dòng)物，如腹足類(lèi)、雙殼類(lèi)等的需求顯著提高，表明攝食需求是太平洋黃尾龍占從海草床向珊瑚礁區(qū)域遷移的主要原因。而Grol等[53]在西班牙灣口區(qū)海草床和鄰近珊瑚礁生境研究黃仿石鱸的存活率和生長(zhǎng)率，發(fā)現(xiàn)幼體的存活率分別為24%和0%，差異顯著；而隨著魚(yú)體的生長(zhǎng)存活率分別為56%和77%，珊瑚礁生境下魚(yú)的生長(zhǎng)率顯著高于海草床的，表明控制其向珊瑚礁生境遷移的主要原因是躲避捕食的需要。

然而，并不是所有生活于海草床的生物幼體都以海草床作為育幼場(chǎng)所，而且不同的生物幼體在海草床的育幼特征也不一樣。因此，根據(jù)育幼功能指標(biāo)來(lái)確定以海草床作為育幼場(chǎng)所的典型生物幼體見(jiàn)表1。

表1 海草床典型生物幼體Table 1 Typical juvenile species in seagrass beds

2 海草床育幼功能的機(jī)理

海草床育幼功能的機(jī)理主要有兩個(gè)方面：(1)食物來(lái)源，海草床可以為生物幼體提供豐富的食物；(2)被捕食風(fēng)險(xiǎn)，海草床低密度的捕食者、復(fù)雜的環(huán)境多相性以及高渾濁度的水環(huán)境形成了較小的捕食風(fēng)險(xiǎn)[7,18,55]。但這兩個(gè)方面并不對(duì)立，如海草床莖枝密度越大，棲息地結(jié)構(gòu)越復(fù)雜，能夠?yàn)樾⌒蜕锖透缴锾峁└嗟臈h(huán)境，降低被捕食幾率，也提供了豐富的食物來(lái)源[7]。同時(shí)，不同的生物幼體對(duì)海草床的需求不同，如植食性和營(yíng)白天覓食的底棲魚(yú)類(lèi)主要以海草床作為攝食場(chǎng)所，而營(yíng)夜間覓食的魚(yú)類(lèi)卻主要以海草床作為躲避捕食的棲息場(chǎng)所[55]。

2.1 食物來(lái)源

海草床不僅為海洋水生動(dòng)物提供良好的棲息地[59]，還為其提供豐富的有機(jī)碳食源[60]。例如，海草床中的海草、海草碎屑、海草上的附生藻類(lèi)或浮游藻類(lèi)等初級(jí)生產(chǎn)者，為許多魚(yú)類(lèi)和無(wú)脊椎動(dòng)物的幼體提供了豐富的食物[61-62]。并且在底質(zhì)環(huán)境下，海草床比鄰近的珊瑚礁和無(wú)植被裸露區(qū)域分布有更高密度的橈足類(lèi)(Copepoda)、端足目(Amphipoda)、多毛類(lèi)(Polychaetes)，它們是生物幼體重要的食物來(lái)源[42, 63]。

海草床下的豐富食物來(lái)源，可促進(jìn)生物幼體的生長(zhǎng)[10-11, 14]，如紅鼓魚(yú)[11]、藍(lán)蟹[29]、女王鳳凰螺[30]等生物幼體在海草床都有較高的生長(zhǎng)率。相關(guān)研究表明，海草床下豐富食物能夠吸引生物幼體[13, 55-56]。例如，Horinouchi 和Sano[56]通過(guò)人為改變大葉藻植株密度，發(fā)現(xiàn)普氏細(xì)棘鰕虎魚(yú)(Acentrogobiuspflaumii)幼體的密度甚至在海草被完全移除的區(qū)域都比無(wú)植物的沙質(zhì)裸露區(qū)域顯著高；Verwey等[55]通過(guò)人工材料模擬海草結(jié)構(gòu)研究魚(yú)類(lèi)的行為，發(fā)現(xiàn)小帶刺尾魚(yú)、月尾刺尾魚(yú)(Acanthurusbahianus)和虹彩鸚嘴魚(yú)(Scarusguacamaia)幼體，在有食源供應(yīng)的海草床數(shù)量是無(wú)食源供應(yīng)的海草床的2.4倍。另外，許多營(yíng)夜間捕食的魚(yú)類(lèi)晝間以其它棲息環(huán)境作為躲避捕食的棲息場(chǎng)所，而夜間則會(huì)運(yùn)動(dòng)到海草床進(jìn)行捕食[54, 64-65]，如石鱸科(Haemulidae)和笛鯛科(Lutjanidae)魚(yú)類(lèi)幼體在夜間從其它棲息環(huán)境到海草床攝食異足目(Tanaidacea)和十足目(Decapoda)等底棲生物[64]；Verweij等[54]通過(guò)研究黃仿石鱸的捕食行為，發(fā)現(xiàn)體長(zhǎng)為 10—15cm的亞成體魚(yú)主要棲息于紅樹(shù)林區(qū)域，而夜間它們主要在海草床攝食。

2.2 被捕食風(fēng)險(xiǎn)

海草床捕食者的豐度、棲息地環(huán)境多相性及水環(huán)境的渾濁度是影響被捕食風(fēng)險(xiǎn)大小的重要因素[7]。研究表明，捕食者在海草床的豐度比其它鄰近的生境少，生物幼體的存活率相對(duì)較高[58, 66]。例如，Dorenbosch等[58]在加勒比海庫(kù)拉索島比較海草床、珊瑚礁、紅樹(shù)林等棲息環(huán)境下捕食者的密度以及黃仿石鱸幼體的存活率，發(fā)現(xiàn)海草床下捕食者的密度和種類(lèi)豐富度最低，而海草床下黃仿石鱸幼體的存活率最高。迄今為止，大部分研究是關(guān)于海草床棲息環(huán)境多相性對(duì)被捕食風(fēng)險(xiǎn)的影響[67-68]。棲息環(huán)境的多相性能夠?yàn)樯镉左w提供良好的庇護(hù)場(chǎng)所[69]，許多生物幼體選擇海草床作為自己良好的庇護(hù)場(chǎng)所，如銀仿石鱸[32]、紅鼓魚(yú)[35]、糙海參[38]、藍(lán)蟹[36]等幼體在海草床都呈現(xiàn)較高的存活率；同時(shí)Gotceitas等[57]通過(guò)室內(nèi)模擬實(shí)驗(yàn)比較捕食者的存在與否對(duì)大西洋鱈魚(yú)幼體的影響，發(fā)現(xiàn)沒(méi)有捕食者時(shí)幼體主要棲息于裸露的砂質(zhì)環(huán)境，而在捕食者出現(xiàn)后幼體主要以海草床為庇護(hù)場(chǎng)所，表明海草床能夠?yàn)橛左w提供良好的保護(hù)。海草莖枝密度越高，海草床多相性結(jié)構(gòu)越高，生物幼體被捕食的幾率越低[70]。如藍(lán)蟹幼體存活率隨著海草莖枝密度的增加而上升[33, 40]。同樣，在美國(guó)德州南部，萊氏二藥藻莖枝密度是龜裂泰來(lái)藻的8—10倍[71]，在萊氏二藥藻海草床的紅鼓魚(yú)豐度比在龜裂泰來(lái)藻的顯著高，有接近75%的紅鼓魚(yú)分布在萊氏二藥藻海草床，這可能是因?yàn)榧t鼓魚(yú)在萊氏二藥藻棲息能夠降低被捕食的幾率[72]。

棲息環(huán)境渾濁度增加可能會(huì)降低幼體被捕食的風(fēng)險(xiǎn)存在一定爭(zhēng)議[73-74]。例如，渾濁度通過(guò)影響三刺魚(yú)(Gasterosteusaculeatus)幼體的分布和活動(dòng)水平，來(lái)降低其被捕食風(fēng)險(xiǎn)[73]；不過(guò)維氏雙邊魚(yú)(Ambassisvachelli)和短棘鲾(Leiognathusequulus)的豐度卻與河口的渾濁度并沒(méi)有相關(guān)關(guān)系[74]。然而，水體渾濁度上升會(huì)降低透光性，限制海草生長(zhǎng)，使海草床退化[75]，進(jìn)而會(huì)影響海草床育幼功能[76]。目前，關(guān)于海草床水體高渾濁度對(duì)生物幼體育幼的影響機(jī)理尚不清楚，仍需深入研究。

3 研究展望

盡管海草床的育幼功能已被廣泛認(rèn)可，但大多數(shù)研究?jī)H從育幼功能單個(gè)指標(biāo)來(lái)探討海草床育幼功能[4]。而B(niǎo)eck等[6]提出的育幼功能4個(gè)方面，迄今為止在海草床還沒(méi)有被同時(shí)證實(shí)[7]，且大多數(shù)研究沒(méi)能明確闡明生物從海草床向成體生物棲息環(huán)境的遷移運(yùn)動(dòng)[4, 7]。國(guó)外對(duì)海草床育幼的研究開(kāi)展較多，我國(guó)尚未有相關(guān)研究報(bào)道，明顯滯后。因此，針對(duì)我國(guó)在海草床育幼方面研究的不足，結(jié)合目前國(guó)外學(xué)者研究的熱點(diǎn)，提出幾個(gè)可能成為海草床育幼功能和機(jī)理的研究趨勢(shì)。

(1)量化海草床對(duì)成體棲息環(huán)境貢獻(xiàn)量。未來(lái)對(duì)于海草床育幼功能的研究將盡可能地從育幼功能的四個(gè)方面闡述[6]，尤其是生物的遷移運(yùn)動(dòng)，需結(jié)合穩(wěn)定性同位素[49]、耳石微化學(xué)[50]或人工標(biāo)記技術(shù)[77]等方法來(lái)探討海草床生物幼體向成體棲息環(huán)境的遷移運(yùn)動(dòng)，以量化海草床棲息環(huán)境對(duì)成體棲息環(huán)境的貢獻(xiàn)量[7]。

(2)全球氣候變化和人類(lèi)活動(dòng)對(duì)海草床的育幼功能的影響。海草床棲息環(huán)境理化性質(zhì)(鹽度、溫度、pH值、營(yíng)養(yǎng)鹽和溶解氧等)發(fā)生改變，影響海草床的育幼功能特征[78]。如溶解氧影響菱體兔牙鯛和絨須石首魚(yú)(Micropogoniasundulatus)幼體對(duì)海草床棲息環(huán)境的利用[79]；溫度上升影響海草床生物群落結(jié)構(gòu)[80]。但目前關(guān)于環(huán)境變化對(duì)海草床育幼功能影響的研究還較少。因此，建立長(zhǎng)期的海草床育幼功能的研究系統(tǒng)，對(duì)于評(píng)價(jià)和預(yù)測(cè)環(huán)境改變對(duì)海洋漁業(yè)的影響具有重要意義[78]。

(3)海草床育幼功能對(duì)其斑塊效應(yīng)和邊緣效應(yīng)的響應(yīng)。全球全球海草床呈退化趨勢(shì)[81]，退化海草床會(huì)增加海草床斑塊效應(yīng)和邊緣效應(yīng)，從而影響海草床的育幼功能[76]。例如，海草床邊緣及斑塊的大小、形狀影響生物幼體的存活率、生長(zhǎng)率以及其分布的豐度[76, 82]。因此，加強(qiáng)生物幼體對(duì)海草床斑塊效應(yīng)和邊緣效應(yīng)響應(yīng)的研究，可以更好地揭示海草床育幼功能的機(jī)理和變化機(jī)制。

致謝：感謝中國(guó)科學(xué)院南海海洋研究所張霞副研究員和沈萍萍副研究員對(duì)寫(xiě)作的幫助。

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Nursery function of seagrass beds and its mechanisms

LIU Songlin1,2,3, JIANG Zhijian1,2, WU Yunchao1,2,3, ZHANG Jingping1,2, HUANG Xiaoping1,2,*

1KeyLaboratoryofTropicalMarineBio-resourcesandEcology,SouthChinaSeaInstituteofOceanology,ChineseAcademyofSciences,Guangzhou510301,China2GuangdongProvincialKeyLaboratoryofAppliedMarineBiology,SouthChinaSeaInstituteofOceanology,ChineseAcademyofSciences,Guangzhou510301,China3UniversityofChineseAcademyofSciences,Beijing100049,China

Seagrass beds cover about 0.15% of the global ocean and contribute 1% of the net primary production of the ocean.They are important nursery habitats for economic fishes and invertebrates such as red drum (Sciaenopsocellatus), Atlantic cod (Gadusmorhua), queen conch (Strombusgigas), and blue crab (Callinectessapidus).The nursery function of seagrass beds has been widely recognized because the biomass and density of juvenile fishes and invertebrates in seagrass beds are higher than in other habitats along the coast.We systematically reviewed the literature on the nursery function of seagrass beds.We evaluated the seagrass nursery function based on the juveniles′ density, growth rate, survival rate, and migration to adult habitats.The factors of food availability and predation risk were also summarized to explain the mechanism of nursery function.High density of juvenile organisms was the identifying factor of the nursery function of seagrass beds, and many juveniles in the seagrass beds showed high growth and survival rates, and migrated to adult habitats during juvenile ontogeny.Primarily, abundant food or lower predation pressure seemed to enable the seagrass nursery function.Seagrass leaves, epiphytes, and phytoplankton assemblages, which served as important food sources for many herbivorous juveniles, were abundant in seagrass ecosystems.In addition, some smaller macrofauna such as copepods, amphipods, and polychaetes showed high densities in the seagrass beds.Predator abundance, structural heterogeneity, and turbidity in seagrass beds contributed either directly or indirectly to predation risk.These mechanisms were not mutually exclusive in that high structural complexity in seagrass beds could provide more living space, higher food sources, and a reduction in predation risk for juveniles.However, different juvenile species inhabited the seagrass ecosystems for different purposes, and the mechanisms of seagrass nursery function also varied with different environmental conditions.Finally, future research directions of seagrass nursery function are indicated: (1) to quantify the contribution of migration of individuals from seagrass bed to adult habitats;(2) to clarify the impact of global climate change and human activities on the nursery function of seagrass beds;and (3) to investigate the response of nursery function to the “patch effect” and “edge effect” of seagrass beds.We believe that this study provides scientific perspectives for protecting the seagrass ecosystem in China.

seagrass bed;juveniles;nursery function;mechanism

國(guó)家重點(diǎn)基礎(chǔ)研究發(fā)展計(jì)劃項(xiàng)目(2015CB452905);國(guó)家自然科學(xué)基金項(xiàng)目(41306108, 41406128);廣東省自然科學(xué)基金項(xiàng)目(S2013040013155);國(guó)家海洋局公益性行業(yè)科研專(zhuān)門(mén)項(xiàng)目(201305030);中國(guó)科學(xué)院知識(shí)創(chuàng)新工程青年人才領(lǐng)域前沿項(xiàng)目(SQ201307, SQ201219)

2014-06-18; < class="emphasis_bold">網(wǎng)絡(luò)出版日期:

日期:2015-05-21

10.5846/stxb201406181269

*通訊作者Corresponding author.E-mail: xphuang@scsio.ac.cn

劉松林，江志堅(jiān)，吳云超，張景平，黃小平.海草床育幼功能及其機(jī)理.生態(tài)學(xué)報(bào),2015,35(24):7931-7940.

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