Inglis G J
School of Biological Sciences, University of Sydney, AO8, 2006, New South Wales, Australia.
Oecologia. 1994 Sep;99(3-4):352-365. doi: 10.1007/BF00627749.
Field surveys over 2 years in contiguous beds of the seagrassesZostera capricorni andPosidonia australis showed that the green algaCodium duthieae was consistently more abundant inZ. capricorni than inP. australis. In 1 year, mature plants were also more abundant at the boundary between the seagrass beds than in either bed. Field experiments and programmes of sampling were used to investigate three potential explanations for the unusual distribution of this alga: (1) that the availability of substrata suitable for attachment of the alga differed between the two seagrass beds; (2) that mortality of matureC. duthieae differed between the seagrass beds; and/or (3) that the intensity of recruitment was different in the two seagrass beds.C. duthieae plants were exclusively epibionts of the bivalveAnadara trapezia. Detailed sampling showed that the abundance ofA. trapezia was similar in both seagrass beds and that the distribution of bivalves suitable as substrata forC. duthieae plants was not obviously related to proximity to the boundary between the beds. Two experiments investigated the survival ofC. duthieae plants in each bed. In the first, matureC. duthieae plants transplanted into theP. australis bed suffered similar rates of mortality to plants which were disturbed and moved within theZ. capricorni bed or which were left undisturbed in theZ. capricorni bed. Fewer of the host bivalves were recovered from theZ. capricorni bed, however, indicating that the mechanism of mortality differed between the beds, hosts being more frequently dislodged in theZ. capricorni bed. Removal of the leaves of the seagrasses had consistently greater effects on near-bottom current velocities in theZ. capricorni bed than in theP. australis bed and significantly increased mortality ofC. duthieae in theZ. capricorni bed. Survival of plants was greater in plots of artificial leaves ofP. australis placed in theZ. capricorni bed than in plots of the naturalZ. capricorni leaves or plots where the natural leaves were removed. Most mortality in theZ. capricorni bed was due to dislodgement of the alga and its bivalve substratum. Corresponding manipulations of leaves in theP. australis bed had consistently smaller effects on survivorship of both the alga and its host. Patterns in the recruitment of the alga most clearly reflected the distribution of adults.C. duthieae recruits were 5 times more abundant in theZ. capricorni bed and at the boundary between the two beds than in theP. australis bed. The results demonstrate how habitat structure, provided by the canopy of leaves of the two species of seagrass, can have contrasting effects on the recruitment and mortality of a macroalga. In the case ofC. duthieae, it appears that the differential pattern of recruitment is the primary determinant of the distribution of adult plants.
在连续两年对海草卡氏波喜荡草（Zostera capricorni）和南方波喜荡草（Posidonia australis）床层的实地调查中发现，绿藻杜氏蕨藻（Codium duthieae）在卡氏波喜荡草床层中的数量始终比在南方波喜荡草床层中更为丰富。在某一年，成熟植株在海草床层边界处也比在任一床层中更为丰富。通过实地实验和采样计划，研究了这种藻类异常分布的三种潜在原因：（1）适合该藻类附着的基质在两个海草床层中的可利用性不同；（2）成熟杜氏蕨藻在海草床层中的死亡率不同；和/或（3）两个海草床层中藻类的补充强度不同。杜氏蕨藻植物完全是双壳贝类梯形蛏（Anadara trapezia）的附生生物。详细采样表明，梯形蛏在两个海草床层中的数量相似，并且适合作为杜氏蕨藻植物基质的双壳贝类分布与靠近床层边界的距离没有明显关系。两项实验研究了每个床层中杜氏蕨藻植物的存活情况。在第一个实验中，移植到南方波喜荡草床层的成熟杜氏蕨藻植物的死亡率与在卡氏波喜荡草床层内受到扰动并移动的植物或在卡氏波喜荡草床层中未受扰动的植物相似。然而，从卡氏波喜荡草床层中回收的宿主双壳贝类较少，这表明两个床层中的死亡机制不同，宿主在卡氏波喜荡草床层中更频繁地被冲走。去除海草叶片对卡氏波喜荡草床层近底部水流速度的影响始终比对南方波喜荡草床层的影响更大，并且显著增加了卡氏波喜荡草床层中杜氏蕨藻的死亡率。放置在卡氏波喜荡草床层中的南方波喜荡草人工叶片地块中的植物存活率高于天然卡氏波喜荡草叶片地块或去除天然叶片的地块。卡氏波喜荡草床层中的大多数死亡是由于藻类及其双壳贝类基质被冲走。在南方波喜荡草床层中对叶片进行相应的操作对藻类及其宿主的存活率影响始终较小。藻类补充的模式最清楚地反映了成体的分布。杜氏蕨藻幼苗在卡氏波喜荡草床层以及两个床层的边界处比在南方波喜荡草床层中多5倍。结果表明，两种海草叶片冠层提供的栖息地结构如何对大型藻类的补充和死亡率产生截然不同的影响。就杜氏蕨藻而言，似乎补充的差异模式是成年植物分布的主要决定因素。
