Densities of mollusc species at different sites along the Chinese coast

Aim: Molluscs are important grazers, filter and deposit feeders,
scavengers and predators, which in turn are food for shorebirds, fish and
people. Some species, targeted as human food, have been cultured along the
Chinese coast for hundreds of years. To examine whether aquacultural
practices have meanwhile affected biodiversity gradients, we measured
mollusc community structure along the coast of China in habitats which are
intensively used by humans. Location: Chinese coast Methods: We sampled 21
intertidal sites spanning 20 latitudinal degrees and 18,400 km of
coastline. We assessed alpha diversity to verify whether mollusc
communities exhibit the expected biodiversity gradient with latitude, and
beta diversity gradients with distance. To examine whether human
activities such as transportation and culturing could have affected these
patterns, we distinguished commercial from non-commercial mollusc species
and compared the differences in distribution, density, alpha diversity and
beta diversity. Results: We found non-commercial species showed the
expected biodiversity gradients. Commercial species (i) dominated the
intertidal mollusc communities at 19 of the 21 sites, and compared with
non-commercial species, (ii) exhibited wider geographical distributions,
(iii) showed no significant change in Bray-Curtis index (abundance-based
beta diversity) with either geographical or climatic distance, (iv)
exhibited lower average dissimilarities, and (v) did not show a decrease
in species richness and Shannon diversity with latitude. Combining all
species, trends were the same as for the commercial species. Main
conclusions: A few cultured species dominated the intertidal mollusc
communities in high densities along the Chinese coastline, taking over the
ecological roles of the native species but not driving them extinct. In
this way aquacultural practices have exerted a homogenizing influence
strong enough to erase basic biodiversity gradients. Since molluscs are
food for the growing human population and the shrinking populations of
migratory animals, coastal planning and management of both intertidal
habitats and the exploitative activities employed need to incorporate
these dimensions.

Aim：软体动物是重要的食草动物、滤食性与沉积食性动物、食腐动物及捕食者，同时也是滨鸟、鱼类和人类的食物来源。部分作为人类食物的物种已在中国沿海养殖数百年。为探究水产养殖实践是否在此期间影响了生物多样性梯度，我们在人类密集利用的栖息地中测定了中国沿海软体动物群落结构。
Location：中国沿海
Methods：我们对跨越20个纬度、18400公里海岸线的21个潮间带站点进行了采样。通过评估α多样性（alpha diversity）以验证软体动物群落是否符合预期的纬度生物多样性梯度，并分析β多样性（beta diversity）与距离的梯度关系。为探究运输和养殖等人类活动是否影响上述模式，我们区分了商业与非商业软体动物物种，比较其分布、密度、α多样性及β多样性的差异。
Results：非商业物种表现出预期的生物多样性梯度。商业物种：（i）在21个站点中的19个占据潮间带软体动物群落主导地位；（ii）相较于非商业物种，地理分布范围更广；（iii）Bray-Curtis指数（基于丰度的β多样性）随地理或气候距离无显著变化；（iv）平均差异度更低；（v）物种丰富度及香农多样性（Shannon diversity）随纬度无下降趋势。所有物种的整体趋势与商业物种一致。
Main conclusions：少数养殖物种以高密度主导中国沿海潮间带软体动物群落，取代了本地物种的生态角色但未导致其灭绝。由此，水产养殖实践产生的同质化影响足以消除基本生物多样性梯度。鉴于软体动物是日益增长的人类人口及数量减少的迁徙动物的食物来源，潮间带栖息地及相关开发活动的沿海规划与管理需纳入这些维度。