Life Cycle and Population Dynamics of the Polychaete Perinereis cultrifera from the Algerian Mediterranean Coast

Abstract. The polychaete Perinereis cultrifera ( Grube, 1840 ) (Nereididae) is common along Algerian coasts in algal‐covered hard bottoms. An intensive study was conducted from June 2000 to June 2001 to characterise the life cycle of an intertidal and upper subtidal population of P. cultrifera in Algeria near the Tunisian border (30 km). P. cultrifera has a 3‐year life span and reproduces exclusively by epitoky. The reproductive season is short, and spawning occurs in late April/early May when the sea‐water surface temperature starts rising. Female sexual differentiation starts in February in the second year of life; thus, the oocytes take 16 months to mature and their diameter at maturity is approximately 250 μm.     

Multicausal environmental severity: A flexible framework for microtidal sandy beaches and the role of polychaetes as an indicator taxon

The aim of this paper is to study the macrofaunal community dynamics and the biological–environmental interactions in the mid- and sublittoral ecosystems of the microtidal Mediterranean sandy shores. Four sandy beaches, three on the island of Crete and one on the northwest coast of Italy were selected to investigate the spatial and temporal changes in the community structure and the associated environmental variables. The littoral zone, which has not been adequately studied in the Eastern Mediterranean, presents special interest not only from the scientific point of view but also for practical reasons of ecological management. The multivariate techniques revealed that the community pattern of the sandy beach macrofauna is mainly spatial rather than temporal. There are pronounced differences in species composition and abundance of the macrofaunal assemblages of the mid- and sublittoral zone. The multicausal environmental severity hypothesis appears to be valid for the sandy beach macrofaunal communities of the Mediterranean. The abundance and composition of the macrofaunal assemblages are highly variable and are affected by the synergistic effects of many environmental variables. The polychaete taxonomic assemblage structure closely follows the macrofaunal community pattern. Differences between the two patterns may arise from the different responses that polychaetes may show to the environmental stress.     

厦门和东山外来物种沙筛贝的种群动态和结构

１９９０年首次在中国大陆沿岸厦门马銮湾和东山八尺门海堤西侧,发 现外来物种沙筛贝（Ｍｙｔｉｌｏｐｓｉｓ ｓａｌｌｅｉ）。通过挂放试板和定点取样,研究其种群动态和 结构,包括水平分布、垂直分布和季节分布,以及壳长的组成。     

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.     

Population dynamics of Acartia pacifica (Copepoda: Calanoida): the importance of benthic-pelagic coupling

1Introduction Benthic -pelagic coupling refers to the two -way exchange or flux of matter between benthic andpelagic environments in aquatic systems. Most stud-ies have focused on the deposition of non-living or-ganic matter to the seabed, resuspension an…     

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.     

Population dynamics and production of the seagrass Zostera noltii in colonizing versus established meadows

The dynamics of the seagrass Zostera noltii in established and colonizing meadows were assessed in Ria Formosa lagoon, Southern Portugal. Shoot weight, above:belowground biomass ratio, flowering shoot density, meadow production, and biomass–density relationships were investigated. Results indicate that the species population dynamics differ clearly in different development stages of the meadows. The overall mean of flowering shoot density was five times higher in the colonizing (83 flowering shoots m⁻²) than in the established meadow (16 flowering shoots m⁻²), revealing a greater contribution of sexual reproduction during the species colonization process. The temporal variation of the biomass–density relationship in the colonizing meadow showed a cyclic seasonal trajectory, a wider range of data, and a simultaneous peak of biomass and density, suggesting no space limitations constraining the internal packing of shoots during the growing season. In the established meadow, density peaked before biomass in agreement to the dominant role of the clonal architecture of seagrasses in the configuration of closed meadows, suggesting the occurrence of self-thinning and/or regulation of ramet formation. Slope of the biomass–density relationships was similar in the established and colonizing meadows, generally suggesting similar nutritional conditions, regardless of their muddy and sandy sediments. Plants of the colonizing meadow invest mainly on the belowground fraction (above:belowground biomass ratio <1), as meadow expansion is mainly controlled by the elongation of horizontal rhizomes. The annual total production (1163 g C m⁻² year⁻¹) and the biomass turnover (34.8 year⁻¹) were also higher in this meadow, corroborating the high investment of the species during the meadow expansion. The faster biomass turnover of the colonizing meadow implies a more limited capacity to accumulate biomass, indicating a greater exportation of organic carbon and nutrients to the coastal area. The different biomass turnover rates suggest different trophic and structural roles of Z. noltii communities in established and colonizing meadows.     

Experimental study of the interspecific competition between two sibling marine herbivorous rotifers in relation to food availability and initial population density

Our laboratory study concerns the competitive interaction between two marine rotifer species Brachionus plicatilis and Brachionus rotundiformis at five algal (Nannochloropsis salina) concentrations (0.4×10⁶ to 32.4×10⁶ cells/ml) and at four initial inoculation densities (numerically, 100% B. plicatilis; 75% B. plicatilis and 25% B. rotundiformis, 50% each of the two species; 25% B. plicatilis and 75% B. rotundiformis and 100% B. rotundiformis. The initial biomass varied as 0.33 and 0.22 μg/ml for B. plicatilis and B. rotundiformis respectively. Experiments were performed at (25±1)℃. Population densities were enumerated and the medium was changed daily up to 8 d in the experiment. At the lowest food level tested, B. rotundiformis formed superior competitor than B. plicatilis, regardless of starting inoculation density. Generally when the food concentrations increased, B. plicatilis showed a greater increase in biomass than B. rotundiformis. B. rotundiformis formed the largest in population growth, regardless of increasing food concentrations. When grown alone, B. plicatilis reached peak abundances of (1.311 5±0.028) and (137.5±0.014) μg/ml at low and high food densities respectively. The corresponding values of B. rotundiformis were 0.724 5±0.016 and 18.15±0.021. The adverse effects of B. rotundiformis on the peak abundances of B. plicatilis were observed at the lowest food level and higher initial density. The rate of population growth in controls varied from (0.792±0.162) to (1.482±0.132) μm/d for B. plicatilis and (0.445±0.041) to (0.856±0.012) μm/d for B. rotundiformis, depending on food level. When both species were introduced together, low food levels favoured higher abundance of B. rotundiformis than B. plicatilis, suggesting that increased population density of the smaller B. rotundiformis was more successfull than larger B. plicatilis in brackish waters. Our work reveals that available food (type and quantity) along with starting inoculation density had significant effect on the interspecific competition between marine sibling rotifer species in zooplankton community structure.     

Food web and fish stock changes in central Chile: comparing the roles of jumbo squid (Dosidicus gigas) predation,the environment,and fisheries

We analyzed recent food web and fish stock changes in the central Chile marine ecosystem, comparing the roles of jumbo squid (Dosidicus gigas) as predator, the environment, and fishing. To accomplish this we used food web modeling and the Ecopath with Ecosim software (EwE). The principal fish stocks have experienced wide decadal fluctuations in the past 30 years, including stock collapses of horse mackerel (Trachurus murphyi) and hake (Merluccius gayi), and there was a large influx of jumbo squid during the mid-2000s. We used two EwE models representing the food web off central Chile to test the hypothesis that predation by jumbo squid has been significant in explaining the dynamics of the main fishing resources and other species in the study area. Results indicate that predation by jumbo squid on fish stocks is lower than that of other predators (e.g. hake) and the fishery. Long-term fluctuations (1978–2004) in the biomass of the main fish stocks (as well as other components of the food web) seem to be related to fishing and to variation in primary production, rather than to predation by jumbo squid alone. Jumbo squid seems to play a role as predator rather than prey in the system, but its impacts are low when compared with the impacts of other predators and fishing. Therefore, we conclude that jumbo squid predation on its prey was not the primary force behind the collapse of important fish stocks off central Chile. Future efforts should be directed to better understanding factors that trigger sudden increases in jumbo squid abundance off central Chile, as well as modeling its trophic impacts.     

Population dynamics and chemical ecology of New Zealand Demospongiae Latrunculia sp. nov. and Polymastia croceus (Poecilosclerida: Latrunculiidae: Polymastiidae)

For 3 years aspects of the population dynamics, growth, and bioactivity (measure of biologically active metabolite biosynthesis) of the Demospongiae Latrunculia sp. nov. and Polymastia croceus (Kelly‐Borges & Bergquist) were examined on a subtidal reef on the Wellington south coast, New Zealand. For both species, survival of adult sponges was high in all seasons, whereas juvenile sponges had poor survival. Recruitment of Latrunculia sp. nov. occurred in all seasons indicating that this species is reproductively active throughout the year. P. croceus recruited mostly in autumn, supporting previous work that found the sponge to be reproductively active in summer and early autumn only. For both sponge species, growth rates varied greatly between individuals and were unaffected by initial sponge size within the range examined. Sponges generally grew during winter and spring as the water temperature rose, and shrank during summer and autumn as the water temperature fell. This growth pattern may relate to seasonal variation in food abundance, and for P. croceus it may result also from seasonal differences in reproductive investment. After 2 years, Latrunculia sp. nov. and P. croceus had on average, halved and doubled in size, respectively. Latrunculia sp. nov. showed a seasonal pattern of bioactivity, being most active in spring possibly to prevent the surface overgrowth of fouling organisms. P. croceus had no seasonal pattern of bioactivity, but individuals were either very active or inactive. The bioactive metabolites in both species possibly aid in competitive interactions and prevent predation and biofouling.     

Distribution and relative density of cetaceans in the Hauraki Gulf,New Zealand

Understanding species distributions, and how they change in space and time, is vital when prioritising conservation or management initiatives. We assessed the distribution and density patterns of common dolphins (Delphinus sp.), bottlenose dolphins (Tursiops truncatus) and Bryde’s whales (Balaenoptera edeni) in the Hauraki Gulf, New Zealand. Dedicated boat-based surveys were conducted in the inner Hauraki Gulf (IHG) and off Great Barrier Island (GBI) during 2010–2012. Generalised linear models were used to investigate temporal changes in relative densities and kernel density estimation was implemented to examine spatial trends. Common dolphins were widely distributed during all seasons, with higher densities observed during winter and spring in the IHG but during autumn off GBI. There was inter-annual variation in Bryde’s whale distribution, with high densities recorded off GBI in 2011. Bottlenose dolphins were infrequently sighted in the IHG but regularly encountered off GBI, with the highest densities during spring and summer.     

不同盐度、饵料和光照条件培养下拟伍氏游仆虫的种群动力学响应

为探究不同盐度、饵料和光照条件培养下拟伍氏游仆虫(Euplotes parawoodruffi)的种群动力学响应,本实验采用酵母和杜氏盐藻2种不同类型的饵料喂食拟伍氏游仆虫,在一系列盐度梯度(5、10、15、20、25)及2种光照条件[光照(14 L∶10 D)、全黑暗]下,测定了拟伍氏游仆虫的种群动力学参数变化。使用种群动力学参数(环境容纳量K、种群内禀增长率r、及世代时间G)评价盐度胁迫和不同培养条件对拟伍氏游仆虫的影响。结果表明:在盐度15处理组拟伍氏游仆虫的环境容纳量达到峰值,高盐度下(20～25)拟伍氏游仆虫的环境容纳量显著下降(P<0.05)。随盐度变化,杜氏盐藻组拟伍氏游仆虫的种群内禀增长率呈先上升后下降的趋势,酵母组种群内禀增长率呈先下降后上升的趋势;酵母组喂养的拟伍氏游仆虫环境容纳量高于杜氏盐藻喂养组,内禀增长率低于杜氏盐藻喂养组。光照条件下拟伍氏游仆虫的环境容纳量高于全黑暗条件,内禀增长率低于全黑暗条件。拟伍氏游仆虫对盐度胁迫的响应敏感,可作为环境监测的指示生物,在盐度为15,光照条件(14 L∶10 D)下使用酵母投喂,可实现拟伍氏游仆虫高密度的培养。     

渤海湾海丰盐场卤虫种群动态及盐度对卤虫种群密度的影响

卤虫是鱼、虾、蟹幼苗极为理想的天然饵料.随着水产育苗发展,卤虫及卤虫卵的需求量在不断增加[1].为了更好地开发、利用和保护卤虫资源,其生态学研究近20a以来受到了明显的重视,但具体研究偏重于实验种群方面,如环境因子(如温度、盐度、饵料等)对卤虫生长、存活、生殖特征(如性成熟速度、生殖方式、生殖力)的影响[2~10],而关于卤虫的自然种群研究较少,原因是进行卤虫的野外生态学研究有诸多困难,如卤虫繁殖速度快且次数多,世代之间有重叠:盐湖或盐池的水文特征经常发生剧烈变化[11,12],故迄今只有Petra[13]和Petra等[14]对Mono湖的Artemiamonica,Gene等[17]对法国Giraud的孤雌生殖卤虫的自然种群进行了系统研究.     

Growth dynamics and bioactivity variation of the Mediterranean demosponges Agelas oroides (Agelasida, Agelasidae) and Petrosia ficiformis (Haplosclerida, Petrosiidae)

Growth dynamics and bioactivity variation of the Mediterranean demosponges Agelas oroides and Petrosia ficiformis were investigated over 15 months at Paraggi and Colombara within the Marine Reserve of Portofino Promontory (Mediterranean Sea, Ligurian Sea, Italy). For both species, growth rates varied between individuals and were unaffected by initial sponge size. The two species showed a different trend in growth pattern: A. oroides did not vary significantly between seasons, sites and depths; in contrast, some individuals of P. ficiformis showed a seasonal pattern, shrinking during winter as water temperature decreased and growing during summer when water temperature increased. Differences in growth between the two species may result from different reproductive cycles, food availability, species-specific thermophily and patterns of spatial competition. Moreover, spatial competition probably induced sponges to produce bioactive secondary molecules. Spatial and temporal variation of bioactivity of both species was examined for the first time by studying its effect on human neuroblastoma cells. The bioactivity of A. oroides extracts differed significantly between seasons, sites and depths, whereas the cytotoxicity of P. ficiformis differed significantly between seasons and depths (differences for sites were not determined). These results suggest the possible influence of environmental factors on bioactive metabolite biosynthesis.