Discrepancy between otolith and tag-recovery estimates of growth for two South African surf-zone teleost species

Growth rates determined from recovered tagged galjoen Dichistius capensis and white steenbras Lithognathus lithognathus were compared to predictions from growth models based on otolith ring counts. Galjoen could not be sexed externally, but it was assumed that all fish >450 mm total length were females, which grow faster than males. Those smaller than this were assumed to include mostly males and were treated as a "male" sample. Male and female white steenbras grow equivalently. Tagged "male" (n = 322), and female galjoen (n = 34) and white steenbras (n = 14) grew more slowly than the model predictions. The discrepancy is likely attributable to the physiological effect of external tags on growth.     

Long-term trends in catch and effort of commercial linefish off South Africa's Cape Province: snapshots of the 20th century

The Cape commercial linefishery, established during the first half of the 19_th century, currently consists of about 2 500 vessels (±20 000 crew), which land some 15 500 tons of fish each year. In spite of a long history, a lack of a long-term catch and effort data series has severely hindered the management of the fishery. This paper providcs commercial catch and effort data for three periods during the 20_th century: 1897–1906, 1927–1931 and 1986–1998. Trends in catch per unit effort (cpue) were verified with additional data from the inshore trawl-fishery, from fishery-independent surveys and, where possible, stock assessment. According to a Linefish Management Protocol developed for the Linefishery, any stock demonstrating a historical reduction in cpue or catch contribution of more than 75% is to be regarded as overexploited. Evaluations based on present datasets support this arbitrarily determined reference point for cpue, but reveal that catch composition is a poor indicator of stock status and should be used with caution. In spite of technological advances such as the advent of combustion engines, nylon lines. echo-sounders, electronic navigational aids, onboard freezer facilities and larger vessels, declines in catch rate indicative of severe overexploitation (i.e. 75–99%) were observed for many important linefish species during the 20_th century. Most of these were higher-trophic-Level species from the warm/temperate East Coast, several of which are also endemic. Life-history characteristics of the vulnerable species (i.e those demonstrating declines in cpue of >75%) include predictable location in time and space (either coastal migrant or resident), longevity (>15 years) and late maturity (relative to maximum age). Apart frorreduced productivity associated with stock depletion, other setbacks, such as ecosystem alteration, loss of genetic diversity and shor-term commercial extinction, are also anticipated. In order to rebuild depleted linefish stocks it is deemed essential to create additional marine reserves, dramatically improve enforcement, develop extensive public awareness programmes and substantially reduce commercial effort.     

Patterns in subtidal seaweed communities on coral-dominated reefs at Sodwana Bay on the KwaZulu-Natal coast,South Africa

Subtidal seaweed communities of the northern coast of KwaZulu-Natal (KZN) have not been studied before. At Sodwana Bay, we tested the hypotheses that the seaweed communities would (1) differ floristically with depth, (2) be more species-rich in shallower water, (3) show similar biomasses within the depth range sampled and (4) be affected (biomass and/or species composition) by sand. Samples were collected (using SCUBA) from reefs ('sites') at depths of about 1m, 7m, 10m, 15m and 26m. Each sample comprised all macroscopic (non-crustose) seaweeds within a 25cm × 25cm quadrat (five quadrats per depth). Environmental factors, including percentage sand cover and depth, were recorded. The seaweed communities were mainly compact turfs; a total of 82 Rhodophyta, 14 Chlorophyta and eight Phaeophyta were recorded. Ordination (canonical correspondence analysis) and classification (Twinspan) of the data showed clear differences in the floristic composition (either as species biomass or presence/absence) with depth, mainly between shallow subtidal communities (0.5–1.0m depth) and those at intermediate depths (5.5–15.0m), followed by the deepest communities (25.7–29.0m) and those at intermediate depths. The shallow samples showed the greatest species diversity. Total seaweed biomass decreased significantly with depth and percentage bare (seaweed-free) substratum increased significantly with depth, possibly because of lower wave action, light penetration, or different grazing patterns. Sand (as percentage sand cover) also affected seaweed community composition, but this showed no pattern with depth. The algal communities on these reefs at Sodwana Bay showed exceptional α-diversity, with 104 taxa (>20% of the recorded KZN flora) occurring in the total sample area of only 1.56m². The seaweed communities of northern KZN are structurally and floristically similar to those of other tropical coral reefs around the world.     

中国产的几种寄生红藻

寄生红藻是一大类比较特殊的藻类，其中又可分为两群，一群是与寄主关系密切或属于同科的种类，称作近缘寄生红藻(ade1phoparasites)，另一群是与寄主不相关的种类，称作远缘寄生红藻(alloparasites)。 寄生红藻一名的提出始于H. Solms-Laubach(1877)，在他以前，Reinsch(1874-1875)虽曾注意到一些红藻个体上的瘤状物，也称为寄生红藻，但他没有发现任何一种的囊果，因此，很难确定寄主和瘤状物之间的区别；而H. Solms-Laubach则第一次充分地描述一种具有特殊生殖器官的寄生红藻。 寄生红藻的起源问题，藻类学家间有几种假说，目前还存在着争论。我国迄今还没有寄生红藻的报道。本文首次记述了我国产的四种寄生红藻，全部属于近缘寄生红藻，内计松节藻科、凹顶藻亚科的菜花藻属(Janczewskia)一种和江蓠科的蓠生藻属(Gracilariophila)三种，这对研究寄生红藻的一些理论问题是有意义的。     

海南岛及其邻近地区无节珊瑚藻的研究 Ⅰ

海南岛及其邻近海域的珊瑚藻类，特别是无节珊瑚藻，除曾呈奎教授在1937年报告过产于我国海南岛等地的巨胞宽珊藻Mastophora marcrocarpa Mont.［宽珊藻M. rosea(C. Ag.) Setch.的同物异名］外，基本上尚无报道，更谈不上对这一大类海藻细致地进行形态解剖学的观察研究。近年来，作者对中国科学院海洋研究所于1957-1965年，1973-1976年，1980-1982年以及曾呈奎教授于1933-1934年在本海区调查采集的标本进行整理，并着手这方面的系统研究工作，有关结果将陆续发表。 本文报道产于海南岛和硇洲岛的十种二型无节珊瑚藻．其中比较难得的是，在海南岛几个地区都发现了现代存活的古石枝藻属的化石种类——红古石枝藻Archaeolithothamnium erythraeum (Rothpl.) Fosl.[=红孢石藻 Sporolithon erythreaum (Rothpl.) Kylin］，这在我国尚属首次报道。其余九种中，有四种，即瑰红中叶藻 Mesophyllum erubescens (Fosl.) Lemoine ，拟中叶藻标准变型 Mesophyllum simulans (Fosl.) Lemoine f. typica (Fosl.)，拟中叶藻卷皱变型M. simulans (Fosl.) Lemoine f. crispescens (Fosl.)Lemoine ，微凹石叶藻Lithophyllum kotschyanum(Unger)Fosl 摩鹿加石叶藻 Lithophyllum moluccense Fosl.，作者除在 Common Seaweeds of China一书中已作初步报道外，本文对其产地和形态解剖学特征作了详细补充；另有四种，即水石藻 Hydrolithon reinboldii (Weber-van Bosse et Fosl.) Fosl. ，小石孔藻 Lithoporella melobesioides Fosl. ，太平洋小石孔藻 Lithoporella pacifica (Heydr.) Fosl. ，本文对其在海南岛和硇洲岛的分布和形态特征等与同种西沙群岛标本作了一些比较观察；本文还对宽珊藻 Mastophora rosea (C. Ag.) Setch. 的解剖特征作了补充描述。     

Further refutation of the primary-secondary settlement hypothesis for the brown mussel Perna perna

The primary-secondary settlement hypothesis, that mussels first settle in algae and then move to mussel beds, was rejected as the only mode of recruitment for the brown mussel Perna perna in a previous study at one location over one year on the south coast of South Africa. We investigated recruitment of P. perna into mussel beds and algal turfs over a five-year period (1995–2000) at 3–4 sites at each of four locations on the South and East coasts. Attachment to the two substrata was significantly temporally synchronous at two of the four locations. The disparity among locations could be due to differences in the algal species present or to differences in the importance of turf algae as a facilitator of recruitment. At Zululand, on the East Coast, attachment to mussel beds and algae was measured monthly and found not to be temporally synchronous. At this location, primary settlement into algae was significantly correlated with an increase in the density of juveniles in the mussel beds 2–3 months later, indicating that turf algae can act as irregular but important facultative facilitators of mussel recruitment, supplementing direct input into the mussel beds. However, as amounts of settlers and recruits in mussel beds exceeded those found in algal turfs most years and places, the primary-secondary settlement hypothesis is inapplicable to P. perna under most circumstances.