Detrital pathways in Davies Reef lagoon, Great Barrier Reef

Four sampling stations were established in the lagoon at Davies Reef in February 1986. Two stations were located in the shallow zone, immediately behind the reef flat, and two stations were located the deeper zone in the centre of the lagoon. The stations were sampled on four occasions during 1986: Summer (February); Autumn (May); Winter (August); and Spring (November). At each station, samples were collected using cylindrical PVC corers pushed manually to a depth of 200 to 250 mm into the sediment. Smaller infauna were sampled from 4 sets of five 55 mm diameter cores. Each set of cores was collected over an area of 1 m² and sets of cores were spaced about 4 m apart. Larger infauna were sampled in a similar manner using 4 sets of six 143 mm diameter corers. At one of the deeper sites, 8 contiguous series of samples, consisting of seven to sixteen 55 mm cores were also taken through Callianassid shrimp mounds. After separation from the sediment, animals were identified to family level, counted and grouped into 6 categories (macrophagous polychaetes, microphagous polychaetes, crustaceans, bivalves, gastropods and other taxa) and assigned to 2 size classes (small, 0.5-2.0 mm; large, >2 mm). Ash-free dry weight (AFDW) was calculated for each group after decalcification of those specimens with calcareous skeletons or shells. Published allometric relationships were used to estimate respiration rates, secondary production and consumption of organic material.Two sets of paired sediment traps were deployed for 2 to 4 consecutive days at mid-depth in the water column at each sampling station. Collecting jars were replaced every 24 hours by divers and the samples filtered onto pre-ashed GF/F filters and frozen. In the laboratory samples were dried at 60°C, weighed, decalcified, reweighed and analysed using a Perkin Elmer CHN analyser.Oxygen flux, a measure of rates of benthic community metabolism was measured in cylindrical chambers, enclosing a portion of the sediment. Each perspex chamber had a volume of 3.4 litres, a base area of 283 cm² and two sampling ports sealed with rubber stoppers through which water samples could be extracted with a syringe. Six chambers were deployed at each site. Duplicate samples were extracted over a four hour period from 10:00 to 14:00 hrs and at night and the oxygen concentration measured using a polarographic oxygen probe. Gross primary production and respiration rates were then calculated.Bacterial abundance was determined by direct counts of acridine-orange-stained cells and epifluorescence microscopy. Three sediment cores (0.5 cm inner diameter, 1 cm deep) were collected at each site and preserved in 4% formalin-seawater. The sediments were treated with 10% acetic acid (v/v in distilled water) overnight to dissolve the carbonate sediment, then homogenised for 3.5 min with a laboratory disperser (Ystral, Germany). Cell biovolumes were determined by microscopy. Carbon content was assumed to be 220 fg C/µm³.Bacterial production rates were measured as the incorporation of tritiated thymidine into DNA. Five 0.6 cm³ sediment samples were collected at each sampling site. Each core was incubated in a tube with 48 µl of 16 Ci/mmol [methyl-³H] thymidine for 10 min at in situ temperature. Incubations were terminated with 10 ml 90% ethanol. A conversion factor of 1x10^18 cell divisions/mol thymidine incorporated was used in calculating bacterial production.Protozoa were extracted from five replicate cores (1.1 cm inner diameter, 1 cm deep) using the silica gel Percoll. Each core was centrifuged at low speed (490 x g) for 20 min in a 30 ml centrifuge tube containing 10 ml of a Percoll-sorbitol mixture. The procedure was repeated three times. Ciliates and flagellates (>=20 µm) were counted in a petri dish with the glass bottom marked into 1 cm² grids.Chlorophyll and phaeopigments were estimated from three to five replicate cores of sediment (1.1 cm inner diameter, 1 cm deep) per site by extraction with acetone (90% v/v with water). After extraction in the dark overnight at 0°C, samples were centrifuged to remove particulates. Absorbance of the extracts before and after acidification was measured at 665 and 750 nm on a Varian spectrophotometer.Total organic carbon and nitrogen were measured from three replicate sediment cores per site. Sediments were dried at 60°C to constant weight, then ground to a powder. Total nitrogen was determined by combustion of sediments in a Perkin Elmer CHN analyser. Total organic carbon was measured on a Beckman TOC analyser.Grain size analyses were carried out on two replicate cores of surface sediments collected at each site. Percent silt and clay were estimated by sieve and pipette analysis. The sand fraction was dry-sifted and weighed to determine particle size distribution.
This research was undertaken to determine whether biomass and production of the major groups of sediment-living animals varied seasonally and/or with distance from the reef flat. Callianassid shrimp mounds were also sampled to determine whether disturbance caused by sediment reworking by these shrimps affects infaunal abundance.A second study was conducted to examine seasonality in bacterial numbers and production, protozoan numbers, community primary production and respiration in the sediments of Davies lagoon.
This research was part of a multi-disciplinary study of sediment communities at Davies Reef lagoon in 1986. The study involved seasonal measurements of total community respiration and production, estimation of production by microbial, meiofaunal and macrofaunal communities, and measurements of rates of detrital inputs to the lagoon.

1986年2月，研究团队于戴维斯礁（Davies Reef）泻湖内设立4个采样站位：其中2个站位设于紧邻礁坪（reef flat）的浅水区，另外2个站位设于泻湖中部的深水区。1986年共开展4次采样，分别为夏季（2月）、秋季（5月）、冬季（8月）与春季（11月）。

每个站位均采用圆柱形聚氯乙烯（PVC）采样管手动插入沉积物200~250 mm深度采集样品。小型底内生物（infauna）通过4组直径55 mm的采样管采集，每组采样管覆盖1 m²区域，组间间距约4 m；大型底内生物则采用类似方式，使用4组直径143 mm的采样管采集。其中1个深水区站位还在卡利安虾（Callianassid shrimp）丘体处采集了8组连续样品，每组由7~16个直径55 mm的采样管组成。

将动物与沉积物分离后，研究人员将其鉴定至科水平并计数，随后划分为6个功能类群：食碎屑多毛类（macrophagous polychaetes）、食微多毛类（microphagous polychaetes）、甲壳类、双壳类、腹足类及其他类群，并分为2个尺寸等级：小型（0.5~2.0 mm）与大型（>2 mm）。对具有钙质骨骼或壳体的标本进行脱钙处理后，计算各组的灰分干重（AFDW）。利用已发表的异速生长关系，估算动物的呼吸速率、次级生产力与有机物质消耗量。

在每个采样站位的水层中部，布设2组成对的沉积捕集器，连续部署2~4天。潜水员每24小时更换收集罐，样品经预灰化的GF/F滤膜过滤后冷冻保存。实验室阶段，样品于60℃烘干、称重、脱钙后再次称重，随后使用珀金埃尔默（Perkin Elmer）CHN分析仪进行碳、氢、氮元素分析。

采用圆柱形舱室包裹部分沉积物，以测量氧通量——底栖群落代谢速率的核心指标。每个有机玻璃舱室体积为3.4 L，底面积283 cm²，带有2个以橡胶塞密封的采样口，可通过注射器抽取水样。每个站位部署6个舱室。分别于日间10:00至14:00及夜间时段，每4小时采集重复水样，使用极谱式氧探头（polarographic oxygen probe）测定氧浓度，随后计算总初级生产力与呼吸速率。

细菌丰度通过吖啶橙染色（acridine-orange-stained）细胞直接计数法结合荧光显微镜（epifluorescence microscopy）测定。每个站位采集3个沉积物芯样（内径0.5 cm，深度1 cm），以4%甲醛海水溶液保存。沉积物经10%乙酸（蒸馏水配制，体积比）过夜处理以溶解碳酸盐组分，随后使用德国Ystral公司实验室分散器均质3.5分钟。通过显微镜测定细胞生物体积，假定单位细胞碳含量为220 fg C/µm³。

细菌生产力通过氚标记胸苷（tritiated thymidine）掺入DNA的量进行测定。每个采样站位采集5份0.6 cm³的沉积物样品，每份样品置于试管中，加入48 μl浓度为16 Ci/mmol的[甲基-³H]胸苷，在原位温度下孵育10分钟。随后加入10 ml 90%乙醇终止孵育。计算细菌生产力时，采用的转换因子为1×10^18 细胞分裂数/摩尔掺入的胸苷。

原生动物通过硅胶凝胶Percoll从5个重复沉积物芯样（内径1.1 cm，深度1 cm）中提取。每份芯样置于含10 ml Percoll-山梨醇混合液的30 ml离心管中，以490×g低速离心20分钟，该步骤重复3次。在带有1 cm²网格标记的玻璃底培养皿中，计数纤毛虫与鞭毛虫（≥20 μm）。

叶绿素与脱镁色素通过丙酮（90%体积比水溶液）萃取法测定，每个站位采用3~5个重复沉积物芯样（内径1.1 cm，深度1 cm）。于0℃黑暗环境中萃取过夜后，离心去除颗粒物。使用瓦里安（Varian）分光光度计，在665 nm与750 nm波长处测定酸化前后萃取液的吸光度。

总有机碳与总氮的测定：每个站位采集3个重复沉积物芯样。沉积物先于60℃烘干至恒重，随后研磨成粉末。总氮通过珀金埃尔默CHN分析仪燃烧法测定，总有机碳则通过贝克曼（Beckman）总有机碳分析仪测定。

粒度分析：每个站位采集2个表层沉积物重复芯样。通过筛分与移液管分析法估算粉砂与黏土占比，砂粒组分经干式筛分并称重，以确定粒径分布。

本研究旨在探究栖息于沉积物中的主要动物类群的生物量与生产力是否存在季节变化，以及是否随距礁坪的距离变化而产生差异；同时对卡利安虾丘体进行采样，以明确这些虾类通过沉积物扰动所造成的干扰是否会影响底内生物的丰度。

第二项研究聚焦于戴维斯泻湖沉积物中细菌数量与生产力、原生动物数量、群落初级生产力及呼吸作用的季节变化规律。

本研究为1986年戴维斯礁泻湖沉积物群落多学科综合研究的一部分，该研究涵盖了底栖群落总呼吸与总生产力的季节测定、微生物、小型底栖生物与大型底栖生物群落生产力的估算，以及泻湖碎屑输入速率的测定。