Biological Evaluation of Marine ­Protected Area: Evidence of Crowding Effect on a Protected Population of Queen Conch in the Caribbean

Abstract This study provides a first evaluation of the biological impact of a marine fishery reserve on the stock of queen conch (Strombus gigas) in the Turks and Caicos Islands. The density and the shell length of the population living in the reserve are compared with those of the individuals living in the surrounding fished areas. The results show that the adult density is six times higher in the reserve than in the fished areas. The shell length analysis shows that both adults and juveniles are significantly smaller in the reserve than in the fished area. This unexpected result suggests the existence of a crowding effect (i. e. a high density‐induced reduction in growth rate) within the ­reserve. It is hypothesised that this crowding effect is due to the superimposition of two factors leading to very high density values in the reserve: (a) the reduced fishing mortality following the creation of the reserve, (b) the existence of natural barriers that impede the emigration of adults outside the reserve. These results are then discussed in relation to current considerations on marine fisheries reserves.     

珠江三角洲全新世软体动物群记录与古环境演化

对珠江三角洲中部中山市东升镇附近PRD11孔的岩性和软体动物的分布特征进行分析,并与邻近的PRD10孔以及珠三角其他位置的钻孔记录比较。结果表明：受海平面变化、河流作用和构造升降影响,研究区晚第四纪经历了5个环境阶段：1）约9 010 cal. a B.P.以前,钻孔所在地暴露地表,沉积物遭受风化剥蚀,形成杂色黏土;2）9 010―7 000 cal. a B.P.为全新世大海侵时期,研究区开始发育河口湾环境;3）7 000―5 460 cal. a B.P.,研究区水深短暂下降;4）5 460―3 340 cal. a B.P.水深有所加大,并在约4 546 cal. a B.P.时达到全孔最大水深;5）约3 340 cal. a B.P.以来海水逐渐退出研究区,河流作用增强,研究区逐渐演变为上三角洲平原环境。     

Fossil gastropods from the MGS3 stratigraphic segment in the Salawusu River Valley and their climatic and environmental implications

Contemporaneous with MIS3, the MGS3 segment of the Milanggouwan stratigraphic section in the Salawusu River Valley, Mu Us Desert, China contains fossil gastropods (terrestrial and freshwater snails) in strata 33LS, 35LS, 37FL and 39LS. Examination of these fossils revealed 11 species belonging to 8 families and 10 genera. They can be classified as: (1) assemblage of Gyraulus and Galba mainly consisting of Gyraulus convexiusculus, Gyraulus sibiricus, Galba pervia and Galba superegra Gredler, etc. (2) assemblage of Vallonia mainly consisting of terrestrial snails, such as Vallonia patens, Pupilla muscorum and Discus paupe, etc. Based on the dating results, and the living habits, living conditions, and geographic distribution of their extant species, we suggest that: the ages of 33LS, 35LS, 37FL, and 39LS are 26000, 29000, 33000 and 38000 a, respectively, corresponding well to the interstadial period in GRIP 4, 5, 6 and 10 in terms of chronology and climatic characters; 33LS, 35LS and 39LS represent very warm-humid periods, while 37FL represents a less warm-humid period; the four periods of climatic fluctuations recorded in MGS3 were related to the strong impact of the summer monsoon in East Asia in Mu Us Desert of China during the interstadial of MIS3 on a global climatic background.     

Experimental assessment of Posidonia oceanica‐associated gastropods grazing on an early‐successional biofilm community: nutrient availability and species‐specific effects

Although grazing is considered an essential process controlling epiphyte biomass on seagrass leaves, there is still a lack of fundamental knowledge about the species‐specific consumption rates of the most common grazers in Mediterranean meadows. This study experimentally assessed the effect of Posidonia oceanica‐associated gastropod grazing on early successional biofilm and the species‐specific relationship between biofilm consumption rates and biofilm biomass. Two biofilms on artificial substrata, both developed in situ (in a P. oceanica meadow), one under ambient conditions and the other under nutrient‐enriched conditions, were offered in aquaria assays to nine species of grazers found in P. oceanica meadows. Biofilm consumption rates and their association with biofilm biomass were assessed. It was found that: (i) there was a positive association between biofilm consumption and biofilm biomass up to 20 mg Chl a·m^?2 for Bittium reticulatum, Gibbula ardens, Jujubinus exasperatus and Tricolia pullus; (ii) Alvania montagui, B. reticulatum and Jujubinus striatus showed the highest consumption rates and are thus expected to be amongst the leading consumers in early‐successional epiphytic communities; (iii) there was not an increase of consumption rate when a substratum colonized under nutrient‐enriched conditions was offered to any of the nine studied species. This study provides species‐specific consumption rates knowledge that is useful for the assessment of the strength of grazer–epiphyte interactions and trophic fluxes in P. oceanica meadows.     

欧洲白垩纪非海相软体动物及其地层分布

本文综述了欧洲白垩纪非海相软体动物群,列出了主要产自英格兰南部、法国和西班牙早白垩世的16个不同沉积层的59个分类单元。淡水动物群以珠蚌类双壳类和田螺类腹足类为主,但在有些地点也存有肺螺类腹足类。这些化石类群与现代类型很相似,说明白垩纪淡水中的水草、氧气与营养环境良好。在欧特里沃期和巴列姆期,淡水与边缘海环境中的动物群组成都发生了显著的变化。欧洲的淡水生物群落早在巴列姆期就已存在,此时的有些类群,如著名的Mar garitifera(s.l.)valdensis在欧洲西部有着广泛的分布。英格兰南部的早白垩世韦尔登群被认为是欧洲最连续的非海相白垩纪地层,其上部的生物群可与西班牙的LasHoyas动物群和法国的Wassy动物群相对比。这3个动物群,以及法国侏罗(汝拉)和英格兰南部波倍克的侏罗纪-白垩纪的过渡生物群——Purbeck动物群,是了解欧洲白垩纪淡水动物群的关键动物群。