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，研究人员在戴维斯礁（Davies Reef）的潟湖内设立了4个采样站位。其中2个站位设置于礁坪后方紧邻的浅水区，另外2个站位设置于潟湖中部的深水区。1986年共开展4次采样，分别为夏季（2月）、秋季（5月）、冬季（8月）及春季（11月）。

每个站位的沉积物与生物样品采集采用如下方法：使用圆柱形聚氯乙烯（PVC）采样管，手动推入沉积物200至250毫米深度采集样品。小型底内动物的采样采用4组每组5根直径55毫米的采样管完成，每组采样管的采样覆盖面积为1平方米，各组采样管间距约4米；大型底内动物的采样采用类似方法，使用4组每组6根直径143毫米的采样管完成。在其中一个深水区站位，研究人员还针对美人虾（Callianassid）丘采集了8组连续序列样品，每组包含7至16根直径55毫米的采样管。

将动物与沉积物分离后，研究人员将其鉴定至科水平，计数并划分为6个类群：多食性多毛类、微食性多毛类、甲壳类、双壳类、腹足类及其他类群；同时分为2个尺寸等级：小型（0.5-2.0毫米）、大型（>2毫米）。针对带有钙质骨骼或壳体的标本，先进行脱钙处理，随后计算各组的无灰干重（ash-free dry weight, AFDW）。研究人员采用已发表的异速生长关系，估算各生物类群的呼吸速率、次级生产力及有机物质消耗量。

在每个采样站位的水体中层，部署两组成对的沉积物捕集器，连续部署2至4天。潜水员每24小时更换一次收集罐，样品经预灰化的GF/F滤膜过滤后冷冻保存。实验室中，样品先于60℃烘干并称重，经脱钙处理后再次称重，随后使用珀金埃尔默（Perkin Elmer）CHN分析仪开展分析。

采用包裹部分沉积物的圆柱形舱室测量氧气通量，以此表征底栖群落代谢速率。每个有机玻璃（perspex）舱室体积为3.4升，底面积283平方厘米，带有两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10:00至14:00时段及夜间，每4小时采集重复水样，使用极谱氧探针测量氧气浓度，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细胞结合落射荧光显微镜直接计数法测定。每个站位采集3根内径0.5厘米、深度1厘米的沉积物采样管，以4%福尔马林-海水混合液保存。沉积物经10%乙酸（蒸馏水体积比配制）过夜处理以溶解碳酸盐组分，随后使用德国Ystral品牌实验室均质分散器均质化3.5分钟。通过显微镜测定细胞生物体积，研究假设细菌碳含量为220飞克碳/立方微米（fg C/µm³）。

细菌生产力通过氚标记胸腺嘧啶掺入DNA的量测定。每个采样站位采集5份0.6立方厘米的沉积物样品，每份样品置于试管中，加入48微升16 Ci/mmol的[甲基-³H]胸腺嘧啶，于原位温度下孵育10分钟，随后加入10毫升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/摩尔掺入的胸腺嘧啶。

原生动物通过硅胶珀可尔（Percoll）密度梯度介质从5份重复沉积物采样管（内径1.1厘米、深度1厘米）中提取：每份采样管置于含10毫升珀可尔-山梨醇混合液的30毫升离心管中，以490×g的低速离心20分钟，该步骤重复3次。在带有1平方厘米网格标记的玻璃底培养皿中，计数纤毛虫与鞭毛虫（≥20微米）。

叶绿素与脱镁色素的含量通过丙酮（90%体积比水溶液）萃取法测定：每个站位采集3至5份重复沉积物采样管（内径1.1厘米、深度1厘米），萃取过程于黑暗中0℃下过夜进行。萃取后离心去除颗粒物，使用瓦里安（Varian）分光光度计在665纳米与750纳米波长下，测量酸化前后萃取液的吸光度。

总有机碳与总氮的含量通过每个站位的3份重复沉积物采样管测定：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（Perkin Elmer）CHN分析仪燃烧法测定，总有机碳则使用贝克曼（Beckman）TOC分析仪测定。

粒度分析针对每个站点采集的2份表层沉积物重复采样管开展：采用筛析与移液管分析法估算粉砂与黏土的占比，砂级组分经干式筛分并称重以确定粒径分布。

本研究旨在明确沉积物栖息的主要动物类群的生物量与生产力是否随季节变化，以及是否与距礁坪的距离相关。同时对美人虾丘开展采样，以探究这些虾类通过沉积物再扰动所造成的干扰是否会影响底内动物的丰度。第二项研究旨在探究戴维斯礁潟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速率的季节变化规律。本研究为1986年戴维斯礁潟湖沉积物群落多学科研究的组成部分，涵盖了群落总呼吸与生产力的季节性测定、微生物、小型底栖生物及大型底栖生物群落的生产力估算，以及潟湖碎屑输入速率的测定。