Abyssal community analysis from replicate box cores in the central North Pacific

A 0.25 m**2 United States Naval Electronics Laboratory box corer was used to take replicate samples from an oligotrophic bottom under the North Pacific Central Water Mass (~28°N, 155°W). The bottom is a red clay with manganese nodules at a depth of 5500-5800 m.
Macrofaunal density ranges from 84 to 160 individuals per m**2 and is therefore much the same as in Northwest Atlantic Gyre waters. Of the macrofaunal taxa, polychaetes dominate (55 %), followed by tanaids (18 %), bivalves (7 %), and isopods (6 %). Meiofaunal taxa were only partially retained by the 297 µm screen used in washing. Even then, they are 1.5-3.9 times as abundant as the macrofaunal taxa, with nematodes being numerically dominant by far. Foraminifera seem to comprise an important portion of the community, but could not be assessed accurately because of the inability to discriminate living and dead tests. Remains of what are probably xenophyophoridans are also very important, but offer the same problem.
Faunal diversity is extremely high, with deposit feeders comprising the overwhelming majority. Most species are rare, being encountered only once. The distributions of only three species show any significant deviation from randomness. The polychaete fauna from box cores collected from 90 miles to the north was not significantly different from that of the principal study locality. Concordance appeared at several taxonomic levels, from species through macrofaunal/meiofaunal relationships. As a result, the variation in total animal abundance shows aggregation among cores.
We discuss Sokolova's concept of a deep-sea oligotrophic zone dominated by suspension feeders, and reconcile it with our present findings. The high diversity of the fauna combined with the low food level contradict theories that relate diversity directly with productivity.

本研究采用0.25平方米的箱式采泥器（box corer），于北太平洋中央水团（North Pacific Central Water Mass，约28°N，155°W）下方的贫营养海底采集重复样品。该海底位于水深5500~5800米处，为含锰结核的红黏土。

大型底栖生物（macrofauna）密度介于每平方米84至160个个体之间，与西北大西洋环流海域的大型底栖生物密度基本相当。在大型底栖生物类群中，多毛类（polychaetes）占比最高（55%），其次为涟虫类（tanaids，18%）、双壳类（bivalves，7%）与等足类（isopods，6%）。

小型底栖生物（meiofauna）类群在冲洗过程中仅能被297微米筛网部分截留。即便如此，其丰度仍为大型底栖生物类群的1.5~3.9倍，其中线虫类（nematodes）在数量上占据绝对主导优势。有孔虫类（Foraminifera）看似是该群落的重要组成部分，但因无法区分活体与死壳体，无法对其丰度进行准确评估。疑似异足虫类（xenophyophoridans）的残骸同样具有重要生态意义，但也存在相同的鉴定难题。

该群落的物种多样性极高，沉积物食性生物占绝对多数。绝大多数物种为稀有类群，仅被单次采集到。仅有3个物种的分布呈现显著的非随机偏离特征。从研究点以北90英里处采集的箱式采泥样品中的多毛类群落，与本研究主采样点的群落无显著差异。

在多个分类学层级上均存在类群一致性：从物种类别到大型/小型底栖生物的类群关系均呈现协调统一的特征。由此，总动物丰度的变异呈现出采样箱之间的聚集分布模式。

本研究讨论了Sokolova提出的"以滤食性生物为主的深海贫营养带"概念，并将其与本次研究的观测结果进行了整合协调。该群落的高物种多样性与极低的食物供给水平，与"物种多样性直接与生产力正相关"的经典理论相悖。