Factors controlling dissolved silica in coral reef surface water of Urasoko Bay, Ishigaki Island, Japan

From August 2006 to August 2007, the concentrations of dissolved silica (Si(OH)₄) were monitored in the surface water of Urasoko Bay and the mouth of the stream that runs into the bay. Urasoko Bay is located on the northern coast of Ishigaki Island, Okinawa, Japan, which is in a subtropical area of the North Pacific Ocean and is surrounded by a relatively poorly developed fringing reef. Added to these samples were freshwater from the upstream area and brackish water that exudes at the beach site, which were collected from April to June 2007. Rainwater samples were also collected during the study period. The concentration of Si(OH)₄ generally decreased from upstream to the bay site, and, on clear days, Si(OH)₄ data from all study sites (the bay, beach, stream mouth, and upstream) plotted against salinity fell on a single straight line. When the influence of rainwater was, the results were scattered below the straight line, which suggests dilution by rainwater with a much lower Si(OH)₄ concentration. These findings show that offshore seawater, rainwater, and upstream freshwater regulate the concentration of Si(OH)₄ in the surface water of Urasoko Bay.     

The impact of overfishing and El Niño on the condition factor and reproductive success of Peruvian hake, Merluccius gayi peruanus

In this study we examine physiological responses of Peruvian hake (Merluccius gayi peruanus) to changes in their population structure and physical environment during the period 1971–2004. In particular, we assess the relative investment of energy in growth and/or reproduction of small (20–35 cm) and large (35–50 cm) hake. We calculated the (i) condition (Fulton’s K), (ii) gonad and (iii) gut fullness indices for 42,761 female hakes sampled from commercial landings; these indices indicate fish somatic, reproductive and feeding condition, respectively. Using Generalized Additive Models we then examined potential relationships between these indices and sea surface temperature anomalies and date. Drastic energy exhaustion and a decrease in female hake fecundity were observed during El Niño events. The long-term trend showed a general increase in condition factor and a decrease in gonad index for large hake between 1971 and 2004. Small hake exhibited a different trend with an increase in reproductive activity, which was accompanied by an earlier maturation. We hypothesise that the observed low investment of energy in reproduction by large female hake might be related to the lack of large males, due to a sex-selective fishery and the impact of El Niño. We suggest that fishing diminished hake reproductive capacity, modified the sex ratio in favour of females and increased population vulnerability to environmental stress, in particular to the El Niño. The impact of multidecadal variability and predators like the squid, Dosidicus gigas, remain unresolved until longer time series become available.     

Observations and analyses of floc size and floc settling velocity in coastal salt marsh of Luoyuan Bay, Fujian Province, China

In coastal environments, fine-grain sediments often aggregate into large and porous flocs. ElectroMagnetic Current Meters (EMCM) and Laser In Situ Scattering and Transmissometry (LISST-ST) have been deployed within a Spartina alterniflora marsh of the Luoyuan Bay in Fujian Province, China, to measure the current velocity, the floc size and the settling velocity between 15 and 22 January 2008. During the observations, the near-bed water was collected in order to obtain the suspended sediment concentration (SSC) and constituent grain size. Data show that: (1) the nearbed current velocities vary from 0.1 to 5.6 cm/s in the central Spartina alterniflora marsh and 0.1–12.5 cm/s at the edge; (2) the SSCs vary from 47 to 188 mg/dm 3 . The mean grain size of constituent grains varies from 7.0 to 9.6 μm, and the mean floc sizes (MFS) vary from 30.4 to 69.4 μm. The relationship between the mean floc size and settling velocity can be described as: w s =ad b , in which w s is the floc settling velocity (mm/s), a and b are coefficients. The floc settling velocity varies from 0.17 to 0.32 mm/s, with a mean value of 0.26 mm/s, and the floc settling velocity during the flood tide is higher than that during the ebb tide. The current velocity and the SSC are the main factors controlling the flocculation processes and the floc settling velocity.     

Cd~(2+)对青蛤(Cyclina sinensis)的毒性及蓄积过程研究

利用水生动物急性毒性实验方法,在6个浓度下Cd2+对青蛤的急性毒性进行测定,经回归分析后,得到Cd2+对青蛤96h半致死浓度为20.09mg/L,安全浓度为0.201mg/L。分别对半致死浓度和安全浓度下Cd2+在青蛤体内不同组织的蓄积情况进行了分析。结果表明,在半致死浓度条件下,168h青蛤各组织Cd2+的含量依次为肌肉内脏团鳃;而在安全浓度下,其结果为内脏团鳃肌肉,内脏团对于Cd2+富集能力远高于肌肉。讨论了青蛤的养殖环境及产品检验等问题。     

Seasonal variations in faunal distribution and activity across the continental slope of the goban spur area (NE Atlantic)

Density, biomass and community structure of macrofauna were estimated together with several sediment characteristics at seven stations ranging from 208 m to 4460 m water depth along the OMEX transect in the Goban Spur area (NE Atlantic) during three seasons (October 1993, May 1994, and August 1995). Median grain size decreased with increasing water depth and showed no differences between the seasons. The percentages of organic carbon and total nitrogen were highest at mid-slope depths (1000 to 1500 m), and were significantly higher in August at the upper part of the slope to a depth of 1500 m. The C:N ratio in the surface layer amounted to 7 to 8 in May, 10 to 12 in August and 14 to 17 in October at all stations (except the deepest at 4460 m, where it was 11 in May and August), indicating arrival of fresh phytodetritus in May, and therefore seasonality in food input to the benthos. Densities of macrofauna decreased exponentially with increasing water depth. Significantly higher densities of macrofauna were found in May at the upper part of the slope to a depth of 1500 m. These differences were mainly due to high numbers of postlarvae of echinoids at the shallowest station and ophiuroids at the deeper stations. Biomass values also decreased with increasing water depth, but biomass was relatively high at the 1000 m station and low at 1500 m, due to relatively high and low mean weights of the individual macrofaunal specimens. No significant differences in biomass were found between the seasons. Respiration was high (15 to 20 mgC·m⁻²·d⁻¹) in May at the upper part of the slope to a depth of 1000 m and low (1–3 mg C·m⁻²·d⁻¹) at the deeper part. At the shallowest stations to a depth of 1000 m respiration was highest in May, at the mid-slope stations (1400–2200 m) it was highest in August, whereas the deepest stations (3600 to 4500 m) did not show any differences in respiration rates. In conclusion; seasonal variation in organic input is reflected in denstiy, community structure and activity of the macrofauna along the continental slope in the NE Atlantic.     

乐清湾近期海岸演变研究

乐清湾是一个与东海相通的半封闭型强潮海湾。通过对1934,1968和1992年的海图对比研究表明:近期乐清湾各等深线所围水域面积持续减小。后一阶段,围垦使岸线推进速度加快,滩涂面积由前一阶段的不断增加转变为不断减小。1934到1968年,西南部最大潮滩华岐潮滩岸线和零米线平均外推速率分别为4.88m/a和13.24m/a;1968到1992年平均淤进速率分别为6.17m/a和8.08m/a。实地采样分析表明:表层水样平均悬沙浓度为0.1043kg/m3,从湾顶向湾口呈不断增加的趋势。悬沙浓度虽较低,但湾内处于低能动力沉积环境,有利于细颗粒沉积物落淤,这是湾内地貌演变的要因。长江入海南移和陆架区再悬浮的细颗粒物质是乐清湾主要的泥沙来源。泥沙自然淤积和人类活动影响是近期乐清湾大部分岸线处于淤进状态的原因。漩门二期工程前后乐清湾的纳潮量减小了5.73%,落潮流相对携沙能力降低为工程前的79%。而根据实测落潮平均流速计算得围垦后落潮流的相对携沙能力减弱为原来的54%。而从1934年到漩门二期围垦工程后,纳潮量减小了22.57%。开辟盐田和围垦造陆工程等人类活动,对海岸演变的影响显著。     

CMODIS资料提取叶绿素a浓度的反演算法研究

中分辨率成像光谱仪(CMODIS)是我国“神舟3号”飞船上对地观测主载荷,是我国第一台上天的具有测量海面叶绿素a浓度能力的成像光谱仪.利用宽视场海洋水色扫描仪(SeaWiFS)反演叶绿素a浓度作为参考值建立CMODIS资料处理模型,得到三个基于蓝绿波段比值法的叶绿素a浓度反演算法,平均相对误差分别为26.6%,24%和33.5%,均方根误差分别为1.16,1.15和1.23 mg/m3.在叶绿素a浓度反演误差允许范围小于35%的条件下,比值算法的适用范围为悬浮泥沙浓度小于5 g/m3的海区.悬浮泥沙的强散射作用导致比值算法在高悬浮泥沙浓度条件下产生高估叶绿素a浓度反演值的现象;在中低悬浮泥沙浓度的海区,悬浮泥沙和浮游植物对离水辐亮度的综合作用使比值算法存在低估叶绿素a浓度的趋势.     

Deposition Rates of Terrestrial and Marine Organic Carbon in the Osaka Bay, Seto Inland Sea, Japan, Determined Using Carbon and Nitrogen Stable Isotope Ratios in the Sediment

Carbon and nitrogen stable isotope ratios (¹³C and ¹⁵N) of surface sediments were measured within Osaka Bay, in the Seto Inland Sea in Japan, in order to better understand the sedimentation processes operating on both terrestrial and marine organic matter in the Bay. The ¹³C and ¹⁵N of surface sediments in the estuary of the Yodo River were less than –23 and 5 respectively, but increased in the area up to about 10 km from the river mouth. At greater distances they became constant (giving ¹³C of about –20 and ¹⁵N about 6). It can be concluded that large amounts of terrestrial organic matter exist near the mouth of the Yodo River. Stable isotope ratios in the estuary of the Yodo River within 10 km of the river mouth were useful indicators allowing study of the movement of terrestrial organic matter. Deposition rates for total organic carbon (TOC) and total nitrogen (TN) over the whole of the Bay were estimated to be 63,100 ton C/year and 7,590 ton N/year, respectively. The deposition rate of terrestrial organic carbon was estimated to be 13,200 (range 2,000–21,500) ton C/year for the whole of Osaka Bay, and terrestrial organic carbon was estimated to be about 21% (range 3–34) of the TOC deposition rate. The ratio of the deposition rate of terrestrial organic carbon to the rate inflow of riverine TOC and particulate organic carbon (POC) were estimated to be 19% (range 3–31) and 76% (range 12–100), respectively.     

杭州湾枯季水沙若干特征分析

根据2014年1月及2017年2月杭州湾大、小潮水沙资料,计算了流速、含沙量、单宽潮量、单宽输沙量,进而分析了潮周期断面净潮量、净输沙量和区域冲淤分布。研究发现杭州湾涨、落潮平均流速比值整体较20世纪八九十年代增大,绝大部分区域大于1.0,涨潮流相对增强,澉浦南岸和金山北岸尤为显著。含沙量平面上分布澉浦、杭州湾南岸两个高值区(大潮大于3 kg/m³,小潮大于1.3 kg/m³)以及北岸湾口至乍浦之间的低值区(大潮小于2 kg/m³,小潮小于0.9 kg/m³),随潮汛变化显著,最大含沙量浓度通常滞后于急流时刻。各测站涨、落潮量和输沙量呈现“大涨大落”和“大进大出”的特征,造成杭州湾短时间尺度内的“大冲大淤”。大潮两涨两落金山与乍浦、乍浦与澉浦之间区域净输沙量可达几千万吨,净冲淤则在几百万吨。     

Reproductive biology of Parazoanthus axinellae (Schmidt, 1862) and Savalia savaglia (Bertoloni, 1819) (Cnidaria,Zoantharia) from the NW Mediterranean coast

Despite the wide distribution of zoanthids, little is known about their pattern of reproduction. Here we investigate the reproductive biology of two Mediterranean species, the common Parazoanthus axinellae (Schmidt) and the rare Savalia savaglia (Bertoloni). For both species, samples were collected during an annual cycle, from January to December 2005, in the Western Mediterranean (Ligurian Sea, Italy). Both species are gonochoric. In P. axinellae the sex‐ratio (n colonies = 30) showed a slight predominance of male colonies (M/F = 1.35), whereas in the population of S. savaglia (n colonies = 15) a predominance of females was found (M/F = 0.3). In P. axinellae the first gametocytes were visible in March, whereas in S. savaglia they became visible in May. Both species reproduce at the end of autumn when seawater temperature begins to decrease. Parazoanthus axinellae (10 m depth) spawns eggs and sperms in November, whereas S. savaglia (67 m depth) spawns in December. In P. axinellae sexes were segregated on a rocky wall, with males occurring deeper, whereas male and female colonies of S. savaglia were irregularly dispersed in the population. The maximum number of oocytes differed between the species, being higher in P. axinellae than in S. savaglia.