Distribution,Population Structure, ­Population Biomass and Morphological Characteristics of the Tunicate Pyura stoloniferain the Bay of Antofagasta,Chile

Abstract. The present study analyzes the distribution, population structure, population biomass and morphological characteristics of the intertidal tunicate Pyura stolonifera (Heller, 1878) in the Bay of Antofagasta, Chile, where the species shows a reduced geographical range extending around 60 – 70 km. Three sites along its distribution were studied. At the central site the tunicate presents the widest intertidal belts, reaching nearly 11 m (the mid‐intertidal‐Pyura‐zone shows the higher percent cover). Population dry biomass here averaged up to 20.45 kg·m^–2, representing one of the highest intertidal specific biomasses reported in the literature. Lower values occur towards the borders of its distribution. Population densities were over 1800 indiv.·m^–2 at mid‐intertidal‐Pyura‐belts. Crowding and competition potentially affect morphological characteristics and the energy/tissue allocation along the intertidal and geographical gradient of P. stolonifera.     

台湾海峡中北部海域刺鲳种群生态学参数及其变动趋势

以2001～2002年周年逐月采集台湾海峡中北部单拖渔船渔获的刺鲳样品578尾,进行群体结构和生长与死亡关系的研究,与1982～1984年渔获群体结构进行了比较,并结合1995～2008年渔业投入量和产出量的变化,探讨其种群变化趋势及管理策略.结果表明：2001～2002年刺鲳群体的L∞值为238.17 mm,W∞值为506.31 g,k值为0.338 3,t0值为-0.953 4a,tr值为2.146 2a.总死亡系数为2.364 1,自然死亡系数为0.841 5,捕捞死亡系数为1.523 0.与1982～1984年相比,渔获群体发生了个体小型化、结构低龄化、性成熟提早等生态学变化.这些变化与该渔场自1993年以来不断加大捕捞的投入和渔获量的产出且大量捕杀幼鱼,开发比率高达0.644 1,处于过度开发有关.因此必须强化对渔业资源的管理,同时实施最小可捕叉长为126.19 mm和最小可捕体重为58.81 g的管理制度,使该海域渔业资源得以恢复,实现渔业的可持续发展.     

Fecundity and spawning of the Atlantic horseshoe crab, Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, USA

This study provided the first comprehensive analysis of Atlantic horseshoe crab (Limulus polyphemus) fecundity. Limulus appear to be a determinate spawner, maturing all eggs for the breeding season before spawning begins. On average, larger females held a larger number of eggs (63,500) than smaller females (14,500). By the end of the breeding season there was an average of 11,600 mature eggs per female left undeposited, regardless of female size. Larger females laid a higher percentage of the eggs they contained. Thus they not only contain more eggs, but are more effective at laying them as well. Size of spawning females ranged from about 185–300 mm prosomal width, with by far the highest concentration in the mid‐size ranges. Although on an individual basis large females carry and lay the greatest number of eggs, mid‐size crabs as a group contributed more to the horseshoe crab population in Pleasant Bay because they were more plentiful (net fecundity was highest for mid‐size crabs). These results have implications for the management of this important species, which is harvested for bait, scientific, and biomedical uses. Incorporation of these results into models and other management tools can help predict growth rates, effects of size‐selective harvest, reproductive value, and stable stage distribution of populations.     

Dynamics of water exchange and salt flux in the Macuse Estuary,central Mozambique,southern Africa

The Siberian subspecies of the red knot Calidris canutus canutus spends the non-breeding season largely in West Africa (Mauritania and Guinea Bissau), where approximately half a million occurred in the 1980s. It was a rarely seen in southern Africa in the early part of the 20th century, but there were about 12 500 in the 1970s and 1980s. The main sites were Langebaan Lagoon, Berg River Estuary, Olifants River Estuary (South Africa) and Walvis Bay Lagoon (Namibia). There was a decline in the number of red knots at Langebaan Lagoon in the 1990s, to around 20% of the number that occurred there in the 1980s. Numbers remained low in the 2000s. In addition, the percentage that remained during the austral winter (the breeding season in the Arctic) declined, and there was none during the period 2001–2009. This suggested that first-year birds, which largely comprise the austral winter population, were no longer travelling to southern Africa. The decline in numbers coincided with the decline in West Africa, but it was disproportionately larger in southern Africa. The observed pattern of change is consistent with a buffer effect, whereby southern Africa represents an extension to the range to less suitable habitat (requiring a 6 000 km extension to the migration) when the population size and competition is high in the main localities in West Africa. We are probably now witnessing the gradual decline in the number of adult birds who are fixed in their use of southern Africa as their non-breeding quarters.     

Population dynamics and condition index of natural stock of blood cockle,Tegillarca granosa(Mollusca,Bivalvia,Arcidae) in the Marudu Bay,Malaysia

The population parameters of blood cockles, Tegillarca granosa in the intertidal zone of Marudu Bay, Sabah,Malaysia were investigated based on monthly length-weight frequency data(July 2017 to June 2018). A total of 279 cockle individuals with shell length and weight ranging from 27.7 mm to 82.2 mm and 13.11 g to 192.7 g were subjected to analysis. T. granosa in Marudu Bay showed a consistent moderately high condition index 4.98±0.86 throughout the year. The exponent b of the length-weight relationship was 2.6 demonstrating negative allometric growth. The estimated asymptotic length(L_∞), growth coefficient(K) and growth performance(?) of the T.granosa population in Marudu Bay were estimated at 86.68 mm, 0.98 a~(-1) and 3.87, respectively. The observed maximum shell length was 82.55 mm and the predicted maximum shell length was 84.44 mm with estimated maximum life span(t_(max)) of 3.06 years. The estimated mean lengths at the end of 2, 4, 6, 8, 10 and 12 months of age were 21.31 mm, 31.16 mm, 39.53 mm, 46.63 mm, 52.67 mm and 57.79 mm. Total, natural, and fishing mortalities were estimated at 2.39 a~(-1), 1.32 a~(-1) and 1.07 a~(-1). The exploitation level(E) was 0.45. Results of the current study also demonstrated that T. granosa in the Marudu Bay has two major recruitment peaks; one in March and another in October. The exploitation level revealed that natural stock of T. granosa in the Marudu Bay was approaching the maximum exploitation level. If such trend continues or demand for T. granosa is increasing,coupled with no effective fisheries management in place, possibility of the T. granosa population in the Marudu Bay to collapse is likely to elevate.     

Microsatellites reveal fine‐scale genetic structure of the Chinese surf clam Mactra chinensis (Mollusca,Bivalvia, Mactridae) in Northern China

As a commercially important fisheries resource in East Asia, the Chinese surf clam Mactra chinensis has experienced severe population declines in the past decades, probably due to over‐exploitation. To provide scientific bases for fisheries management and artificial breeding, we investigated genetic variation and population structure of Mactra chinensis in Northern China using microsatellites. Samples collected from eight localities throughout natural habitats of the species in Northern China were genotyped. Nine microsatellites revealed high allelic diversity with 14–36 alleles per locus. Observed and expected heterozygosity varied from 0.593 to 0.945 and from 0.638 to 0.958, respectively. Pairwise F_ST values indicated that all population pairs had small but significant genetic differentiation. A Mantel test showed statistically significant correlations between genetic distance and geographical distance, indicating that genetic differentiation of the Chinese surf clam conformed to a pattern of isolation‐by‐distance. Cluster analysis using neighbor‐joining separated the eight populations into three groups. The three areas of low gene flow identified by barrier analysis corresponded with local oceanographic features, suggesting that marine currents and peninsulas play an important role in population structuring of this species.     

Population dynamics and fishery management of the paua,Haliotis iris

A population model is developed and used in conjunction with the results of a study of an unexploited population of paua (Haliotis iris Martyn) to examine the historical pattern of recruitment and yield per recruit. As H. iris cannot yet be aged, the population model uses size rather than age classes, but is structurally similar to the Leslie matrix model. Simulations suggest that the observed population size structure resulted from a short (about 5 year) period of high recruitment, preceded and followed by longer periods of low recruitment. Yield per recruit analysis shows that the present minimum legal size for the fishery (127 mm) provides close to the maximum yield per recruit for most stocks, although yield per recruit could be increased in some areas by a reduction in minimum legal size.     

广西珍珠湾红树种群结构与动态特征

本研究以种群生命表为基础,对位于广西珍珠湾内的桐花树(Aegiceras corniculatum)种群、白骨壤(Avicennia marina)种群、秋茄(Kandelia obovata)种群和木榄(Bruguiera gymnorrhiza)种群采用径级法及匀滑技术,编制种群特定时间生命表,绘制种群存活曲线、死...     

Variation in the post‐copulatory guarding behavior of Neohelice granulata (Brachyura,Grapsoidea, Varunidae) in two different habitats

Crab guarding behaviors are influenced by the biological and physical characteristics that each population experiences in a particular habitat. We studied post‐copulatory guarding behavior and the factors affecting it, such as the presence of burrows, female receptivity duration, operational sex ratio (OSR) and male size, in two different populations of Neohelice granulata: Mar Chiquita coastal lagoon (MCL) and San Antonio Oeste (SAO). Laboratory experiments showed that post‐copulatory guarding duration varied between the study areas. In MCL, it depended upon the presence of burrows and female receptivity duration, whereas it was independent of the OSR and male size. In SAO, it was dependent upon the OSR and female receptivity duration, whereas it was independent of the presence of burrows and male size. Thus, N. granulata males display different reproductive strategies related to their post‐copulatory guarding behavior pattern in different habitats. These strategies are related to the fact that this species constructs and defends a burrow that provides shelter and a place to mate, something that other varunids do not have.     

Studies on the population ecology of Upogebia deltaura (Leach) (Crustacea, Thalassinidea)

Upogebia deltaura was collected quantitatively and qualitatively between June 1980 and August 1982 from a level, sandy bottom at a 12 m depth in the archipelago of Lysekil (on Gullmarsfjorden) about 70 km north of Göteborg, in western Sweden. A total of 347 individuals were obtained. The deepest burrows reached a depth of more than 65 cm into the substrate. During the cold season, U. deltaura was situated much deeper in the substrate than it was during the summer, probably as a result of ‘hibernation’. The average density was 5·0 individuals 0·1 m⁻², and the maximum of 10 specimens was found in one 0·1 m² sample. Out of the 341 individuals identifiable as to sex, 186 (54·6%) were females and 155 (45·4%) were males. Berried females were found between May and August, and the average number of eggs carried was 4757. Ecdysis took place between May and August; most females moulted in the middle of June and most males about one month later, in mid July. The chelipeds of large males were proportionally bigger than were those of large females. Maximum total body length of the females was 65·7 mm, and that of the males was 65·3 mm.     

Effects of hypoxia on macrobenthos of the inner shelf off Cameron,Louisiana

The effects of hypoxic bottom water, an annual event, were documented on the inner shelf off Cameron, Louisiana during the summer of 1981. Populations of most species of macrobenthos were dramatically reduced. In an area of fine sediment that was numerically dominated by polychaetous annelids, the most severely affected populations were those of tube-dwelling and surface-feeding species. Burrowing species were less influenced by the hypoxia.     

鱼类种群行为及其与环境变化的关系

任何渔业的重要生物特征是鱼类种群的变动.经典的鱼类种群动态模型是以稳定的种群行为为基础的.作者阐述了鱼类种群的行为,并划分为三种类型: (1)稳定型:种群在较稳定产量上维持较长时间(反应系数0.02).(2) 周期型:种群表现出周期性的高产量和低产量(反应系数0.22).(3) 不稳定型:种群产生高产量后无可挽回地崩溃了(反应系数0.3).在环境变化较大时,白色噪音水平(变动系数)增加至35%,稳定型种群变为不稳定型.在白色噪音水平(变动系数)增加至20%时,周期型种群变为不稳定型.     

Ingestion rates and grazing impact of the brackwater mussel Brachidontes virgiliae in Lake St Lucia,iSimangaliso Wetland Park,South Africa

Bivalves feed on a combination of phytoplankton and zooplankton and have the potential to impact considerably the planktonic biomass, especially when they occur in high densities, such as in oyster and mussel beds. The brackwater mussel Brachidontes virgiliae is numerically dominant during wet phases within Africa’s largest estuarine lake, St Lucia, in the iSimangaliso Wetland Park on the east coast of South Africa. The ingestion rates and potential grazing impact of this small mussel (maximum shell length = 2.5 cm) were estimated for both the wet and dry seasons using an in situ gut fluorescence technique. Ingestion rates were higher during the wet season (5.78 µg pigment ind.^?1 d^?1) than during the dry season (4.44 µg pigment ind.^?1 d^?1). This might be explained by the increased water temperature and food availability during the wet season. Because of the patchy distribution of mussel populations, there could be higher localised grazing impact near mussel aggregations. Results showed a potential grazing impact of up to 20 times the available phytoplankton biomass at specific sites. These high grazing impacts have the potential to deplete phytoplankton stocks in the lake, especially during wet phases in the northern reaches, where mussel densities are highest. This needs to be factored into ecological models of Lake St Lucia, because the system might function differently during increased flood events.     

巴拿马珠母贝两个群体的生化遗传变异比较

用淀粉凝胶电泳检测和比较了加利福尼亚湾拉巴斯和马萨特兰两海区巴拿马珠母贝Pinctada mazatlanica的28个基因座位的生化遗传变异。结果发现,两群体的平均杂合度分别为0.153和0.124,与已报道的珠母贝属的其他种很接近。说明这种珠母贝的遗传变异相当丰富,未受40多年前过度采捕所引起的群体数量大幅度起伏的影响。两群体的遗传距D=0.012,预示两地间有相当强的基因流。