Ichthyofaunal assemblages in estuaries: A South African case study

This review places the life-history styles of fishes associated with South African estuaries in a global context and presents a classification system incorporating all the major life-history categories for estuary-associated fish species around the world. In addition, it documents the early life histories of the major fish groups in South African estuaries, with particular emphasis on the differing modes of estuarine utilization by marine, estuarine and freshwater taxa.This review details factors influencing the ichthyofaunal community structure in South African estuaries. The availability of fish for recruitment into an estuary depends primarily upon the distributional range of euryhaline marine and estuarine species, with tropical and temperate taxa showing marked abundance trends. Within a particular biogeographic region, however, estuarine type and prevailing salinity regime have a major influence on the detailed ichthyofaunal structure that develops. There is an increasing preponderance of marine fish taxa when moving from a freshwater-dominated towards a seawater-dominated type of system, and a decline in species diversity between subtropical estuaries in the north-east and cool temperate systems in the south-west. Similar declines in fish species diversity between tropical and temperate estuaries in other parts of the world are highlighted.Fish assemblages in estuaries adjust constantly in response to changing seasons, salinities, turbidities, etc. Despite persistent fluctuations in both the biotic and abiotic environment, the basic ichthyofaunal structure appears to have an underlying stability and to be predictable in terms of the response of individual species to specific conditions. This stability seems to be governed by factors such as the dominance of eurytopic taxa within estuarine assemblages and the robust nature of food webs within these systems. The predictability arises from factors such as the seasonality associated with estuarine spawning cycles and juvenile fish recruitment patterns. These patterns, together with a well-documented resilience to a wide range of physico-chemical and biotic perturbations, appear to be an underlying feature of fish assemblages in estuaries around the world.In contrast to marine fish species, estuary-associated taxa have received little conservation attention. Apart from the designation of protected areas, the main direct means of conserving estuary-associated fish stocks include habitat conservation and controls over fishing methods, effort, efficiency and seasonality. Of these, the conservation of fish habitats, the most important, because healthy aquatic environments invariably support healthy fish populations. The use of estuarine sanctuaries for fish conservation is briefly reviewed, as well as the legislation governing the USA National Estuarine Research Reserve System (NERRS) and the Australian Marine and Estuarine Protected Area (MEPA) system. It is concluded that South Africa requires an expansion of the existing Estuarine Protected Area (EPA) network, as well as the upgrading of selected 'estuarine reserves' where fishing is permitted, into 'estuarine sanctuaries' where no exploitation of biological resources is allowed.     

Geographical and typological changes in fish guilds of South African estuaries

A comparative analysis of fish estuary association guilds was undertaken on some 190 South African estuaries. This pioneering study spanned three zoogeographic regions and included three broad estuarine types. The guild compositions of the estuaries were compared based on an importance value, incorporating taxonomic composition, numerical abundance and relative biomass. Multivariate analyses included both inter‐regional (zoogeographic) and intra‐regional (estuarine typology) comparisons. The major estuary‐associated guilds (estuarine species and marine migrant species) were important in all estuary types within all biogeographic regions. Significant differences both between regions and between estuary types within regions, however, were recorded. Cool–temperate estuaries were generally dominated by migratory species (estuarine migrants and marine migrant opportunists) while the importance of species dependent on estuaries (estuarine residents and estuarine‐dependent marine migrants) was higher in warm–temperate and subtropical regions. The significance of estuarine nursery areas, particularly in regions where estuaries are few in number, is highlighted. In terms of typology, migratory species assumed a greater importance in predominantly open systems, while freshwater and estuarine‐resident species were more important in predominantly closed systems. Predominantly closed estuaries, however, were also important for marine migrant species, which further highlights the significance of these systems as nursery areas for fishes.     

Biomass and productivity of fishes in estuaries: a South African case study

Estuaries are well known for their role as nutrient and detrital sinks that stimulate high levels of both primary and secondary production which, in turn, support a large biomass of fishes per unit area. This study reviews available information on coastal fish biomasses (g m^?2 wet mass) and productivity (g m^?2 wet mass year^?1) in order to place South African data on these topics into a global perspective. Using biogeographic fish productivity estimates, together with estuarine water area, the approximate annual teleost production in South African estuaries was calculated at 585, 1706 and 13 904 t in the cool temperate, warm temperate and subtropical regions, respectively. Total annual fish production in estuaries on the subcontinent is conservatively estimated at 16 195 t, but this figure is likely to fluctuate widely, depending on recruitment success and annual environmental conditions pertaining to these systems. Approximately 2000 t of fish are estimated to be harvested by fishing activities in South African estuaries each year, which represents c. 12% of annual fish production. Although this figure may appear sustainable, the reality is that there are a few heavily targeted estuary‐associated marine species at the top of the food chain that are being overexploited by both anglers and subsistence fishermen. Natural mortalities due to piscivorous fish and bird predation has been estimated at c. 3% of total fish biomass per month in the East Kleinemonde Estuary, but this figure will vary considerably depending on bird abundance and foraging patterns along the coast. In contrast to catches made by the fishermen, piscivorous fishes and birds are targeting mainly juvenile marine fish and small estuarine resident species that are very abundant and generally low down in the food web.     

Jetski-based plankton towing as a new method of sampling larval fishes in shallow marine habitats

I tested jetski-based plankton towing as a new method of sampling larval fishes in a shallow marine environment in warm temperate South Africa. Larval fishes were collected by towing a stainless-steel ring net behind a three-man jetski. The sampling technique was designed and tested to overcome problematic sampling of shallow sandy beach surf zones and the adjacent, shallow nearshore immediately seaward of the surf zone (behind the breaker line) with the same type of equipment. The composition, density, stage of development, estuary association, and length frequency of larval fish catches obtained by the new sampling method in the surf zone and in the adjacent shallow nearshore were compared. The success of the technique was evaluated by determining the extent of replication of known trends observed in other surf studies in the same climatic region of South Africa using either a seine or pushnet. Preflexion and postflexion larval fishes were collected. Larvae of the family Sparidae dominated the catches. Trends in catch composition, estuary association, and length frequency of the larvae were similar to those found in other studies of warm temperate South African surf zones. Density of larvae varied depending on the type of equipment used, although these results are tentative given the subjectivity of calculation of the water volume sampled and the extent of nursery use by larvae in the habitats sampled in each study. Increased towing times are recommended. Jetski-based plankton towing is a useful alternative technique for sampling larval fishes in shallow habitats and can easily be applied in surf zones, shallow nearshore areas, and estuaries. The technique greatly increases sampling agility in previously problematic sampling areas.     

'Fish in hot water": the challenges facing fish and fisheries research in tropical estuaries

Tropical estuarine areas comprise small systems of a few km, larger estuaries, coastal lakes of hundreds of km 2 and vast shallow coastal waters that are contiguous with estuaries and have similar reduced salinities. Many of the world's great estuaries are in the tropics, e.g. the Amazon, Orinoco, Congo, Zambezi, Niger, Ganges and Mekong. The distribution of tropical and subtropical estuaries approximately follows that of mangroves. Like estuaries everywhere, they are a focus of human activity and are among the most exploited of ecosystems. In few other places do the activities of fishers, industrialists, shippers, farmers, conservationists, sports enthusiasts and biologists overlap to such an extent. Quite apart from the possible eects of all these activities, the fishes of subtropical and tropical estuaries already face one of the most rigorous of aquatic environments; but despite this, species diversity and productivity are high. Only in tropical estuaries are animals from such a wide range of taxa so closely associated, annelid worms, prawns, crocodiles, birds, ' hippos ', dolphins and of course fishes, all may form part of the overall community, often with functional ecological links. Unfortunately, the diculties of working in these often inhospitable environments, has meant that biologists have favoured projects in more appealing areas, such as coral reefs. While it is still true that most estuarine research is conducted in industrialized developed countries, nearly all of which are in cold or temperate regions, there has been a recent upsurge in tropical estuarine fish research. This is being driven by two imperatives, food security and the conservation and maintenance of biodiversity. Both these problems require knowledge of the ecology of tropical estuarine fishes, particularly their relationships with the environment and the extent to which they are dependent on estuaries or adjacent habitats for survival.     

Occurrence of Larval and Early Juvenile Fishes in the Surf Zone Adjacent to two Intermittently Open Estuaries, South Africa

I monitored larval and early juvenile fishes in the surf zone adjacent to two warm temperate, intermittently open estuaries in South Africa. Mugilidae (59–67%) dominated fish assemblages in the surf zones adjacent to the Van Stadens and Kabeljous estuaries. Other dominant families included the Atherinidae, Sparidae and Soleidae. The most abundant species caught during the study were the catadromous mugilid Myxus capensis, in a postflexion or early juvenile stage of development, and the sparid Rhabdosargus holubi, in a postflexion stage of development. Species displaying a degree of dependence on estuaries during the early phase of their life cycle dominated (96–98%) surf zone catches. Most fish encountered were at the postflexion stage of larval development. Larval and early juvenile fishes were more abundant during the summer and autumn months with density peaking several-fold during natural estuary opening events, particularly in the surf zone adjacent to the Kabeljous Estuary. Decreases in salinity showed a significant relationship with increases in fish density during a March opening event in the surf adjacent to the Kabeljous Estuary where catches were concentrated along a current-driven estuarine plume. Catches adjacent to the Van Stadens Estuary also increased considerably during two smaller opening events in March and November although salinity played no statistically significant role in these increased catches. Results from the surf adjacent to the Van Stadens Estuary suggested that either very small amounts of estuarine water entering the surf zone can elicit an accumulation response by estuary-dependent larval and early juvenile fishes or that an additional characteristic of estuary/river water, other than salinity per se, is aiding the cueing process.     

Causes and consequences of human induced impacts on a ubiquitous estuary-dependent marine fish species

Decreasing populations of common estuary-associated marine fishes are being documented globally and red flags associated with such declines are often ignored due to the high relative abundance of these species when compared to more rare and threatened taxa. The Cape stumpnose Rhabdosargus holubi (Steindachner 1881) is an abundant and widespread southern African sparid that is dependent on estuaries as a primary nursery area. Historical and current information on the species is comprehensive and the accumulated evidence strongly suggests that this ubiquitous fish is under pressure, mainly due to degradation of estuaries and associated catchments, increasing fishing pressures from recreational and subsistence anglers, habitat loss relating to reduced submerged macrophyte areas in many systems, industrial and agricultural pollution, infrastructural developments in and around estuaries, and climate change. In particular, the temporary loss of Lake St Lucia, which accounts for approximately 50% of the estuarine surface area in South Africa, has drastically reduced the nursery area availability for R. holubi on the subcontinent. Overall we present strong evidence to support the hypothesis that present-day stocks of R. holubi are much smaller than those in the pristine state and that urgent management measures need to be considered and implemented to prevent current depleted populations of the species from declining further.     

A review of the influence of biogeography,riverine linkages,and marine connectivity on fish assemblages in evolving lagoons and lakes of coastal southern Africa

The Holocene evolution of eight South African coastal lakes and lagoons is examined and related to changes in fish composition over that period. Historical and current connectivity with riverine and marine environments are the primary determinants of present‐day fish assemblages in these systems. A small and remarkably consistent group of relict estuarine species have persisted in these coastal lakes and lagoons. The loss or reduction of connectivity with the sea has impacted on the diversity of marine fishes in all eight study systems, with no marine fishes occurring in those water bodies where connectivity has been completely broken (e.g. Sibaya, Groenvlei). In systems that have retained tenuous linkages with the sea (e.g., Verlorenvlei, Wilderness lakes), elements of the marine fish assemblage have persisted, especially the presence of facultative catadromous species. Freshwater fish diversity in coastal lakes and lagoons is a function of historical and present biogeography and salinity. From a freshwater biogeography perspective, the inflowing rivers of the four temperate systems reviewed here contain three or fewer native freshwater fishes, while the subtropical lakes that are fed by river systems contain up to 40 freshwater fish species. Thus, the significantly higher fish species diversity in subtropical versus temperate coastal lakes and lagoons comes as no surprise. Fish species diversity has been increased further in some systems (e.g., Groenvlei) by alien fish introductions. However, the impacts of fish introductions and translocations have not been studied in the coastal lakes and lagoons of South Africa. In these closed systems, it is probable that predation impacts on small estuarine fishes are significant. The recent alien fish introductions is an example of the growing threats to these systems during the Anthropocene, a period when human activities have had significant negative impacts and show potential to match the changes recorded during the entire Holocene.     

Habitat partitioning in juvenile fishes associated with three vegetation types in selected warm temperate estuaries,South Africa

Three common vegetation types were studied to assess habitat partitioning in juvenile fishes in select warm temperate estuaries of South Africa. Vegetated habitat types are known as productive and important areas for predator avoidance and feeding and are often preferred by juvenile fishes. Habitat partitioning is not well understood, with previous studies mostly focusing on seagrass (Zostera capensis). This study aimed to assess three common vegetated fish nursery areas in estuaries to aid conservation planning. Fishes were collected by means of double-winged, six-hooped fyke nets, 1 mm mesh size secured in placed on the nocturnal flood tide at each inundated vegetation type (Phragmites australis, Zostera capensis, Spartina maritima) and at an adjacent unvegetated site for three consecutive months in 2014 and 2015 during the summer recruitment period for juvenile fishes. Higher catches were frequently recorded in vegetated areas for solely estuarine and marine estuarine dependent species. In general, the previously unstudied reed, P. australis showed the highest species richness and abundance of juvenile fishes overall, followed by, Z. capensis and the intertidal salt marsh species, S. maritima. Results from this study supports international trends on the value of vegetated areas as refugia for young fishes in estuaries.     

Fish communities in temporarily open/closed estuaries from the warm- and cool-temperate regions of South Africa: A review

The majority of estuaries along the coastline of southern Africa are termed temporarily open/closed estuaries (TOCEs) and are closed off from the sea for varying periods by a sandbar which forms at the mouth. It is therefore important to understand the processes occurring within TOCEs and their importance to fishes in order to make sound management recommendations. Estuaries along the coast of South Africa and their associated fish assemblages are biogeographically distinct and occur in either a subtropical, warm-temperate or cool-temperate zone. There are 125 TOCEs found within the cool-temperate and warm-temperate zones. Most fish species found in TOCEs are the juveniles of marine taxa that breed at sea. Permanently open estuaries generally have a higher diversity of species than TOCEs, but TOCEs still provide important nursery areas for many marine species and numerically often have a higher proportion of estuarine resident species. Important taxa in terms of abundance and biomass in warm-temperate TOCEs include the sparids Rhabdosargus holubi and Lithognathus lithognathus, several mugilid species, estuarine residents (particularly Gilchristella aestuaria and Atherina breviceps) and the freshwater cichlid Oreochromis mossambicus. The diversity of fishes in cool-temperate TOCEs is low when compared with warm-temperate systems and Liza richardsonii tends to dominate catches by number and mass in most systems. Several species recorded in TOCEs show clear longitudinal distribution trends. For example Atherina breviceps is generally more abundant in the lower reaches of estuaries. Mouth state, particularly the frequency, timing and duration of mouth opening plays a key role in determining species richness, composition, diversity and abundance in TOCEs. Mouth state is directly linked to freshwater input. Reduced river inflow leads to prolonged mouth closure and shorter open phases, which inhibits immigration and emigration of marine fish species between estuaries and the sea. Understanding of the effects of various processes occurring within these systems, particularly variation in freshwater input, on the biota of these important systems facilitates the development of informed management recommendations.     

台湾海峡鱼类组成及其生态区系

本文依据台湾海峡鱼类物种的相关历史调查资料和文献, 分析了台湾海峡鱼类物种组成及其生态类型和区系特征, 探讨全球变化背景下台湾海峡鱼类物种组成变化。结果显示, 台湾海峡共有鱼类1,697种, 分隶40目206科740属, 其中, 目级分类阶元种类数最多的为鲈形目, 科级分类阶元种类数最多的为鰕虎科; 从适温性上看, 暖水性鱼类最多, 有1,560种, 其次为暖温性鱼类(128种)和冷温性鱼类(9种); 栖息地生态类型则以大陆架砂泥质底层鱼类和岩礁性鱼类种类数最多, 各有596种, 其后依次是大陆架近底层鱼类(249种)、大陆架中上层鱼类(158种)和大洋性鱼类(98种), 洄游性鱼类181种, 经济性鱼类735种; 海区间鱼类种类数对比显示, 台湾海峡鱼类与南海鱼类共有种最多, 共有种比例高达91.9%, 其次为东海(69.3%)和黄海(19.4%), 多为印度—西太平洋海区分布种, 仅288种广泛分布于中国各海区。由此, 台湾海峡鱼类区系特征兼有热带和亚热带海区鱼类区系特点, 属于印度—西太平洋暖水区系中—日亚区和印度—马来亚区的过渡海区, 其分界区域在台湾浅滩东部外缘至澎湖列岛偏北海域。     

1980—2007年大亚湾鱼类物种多样性、区系特征和数量变化

根据2004—2005年大亚湾海域底拖网鱼类调查数据,并结合1980—2007年的历史资料,分析了该海域鱼类的种类组成、区系特征、多样性、优势种和数量变化趋势.结果表明： 2004—2005年,大亚湾海域共记录鱼类107种,分属13目50科,以中下层鱼类的种类最多,为48种,其次是中上层和底层种类,分别为37种和21种.大亚湾鱼类区系具热带和亚热带特性,以暖水性种类占绝对优势,为97种,暖温性种类为10种.多样性指数以夏季最高（3.82）,其次是冬季（3.37）和秋季（3.00）,春季最低（2.40）.Pielou均匀度指数的季节变化情况与多样性指数相似.1980—2007年大亚湾海域鱼类群落特征发生了明显的变化：鱼类种类数减少,优势种更替明显.鱼类种类数由1980年的157种减少至1990年的110种,2004—2005年继续减少至107种;鱼类优势种由1980年以带鱼和银鲳等优质鱼为主,更替为以小型和低值的小沙丁鱼、小公鱼和二长棘鲷幼鱼为主.用包含年际变化趋势和季节性周期变化的回归模型模拟1980—2007大亚湾鱼类资源密度的变化,鱼类资源密度在1980—1999年和1990—2007年两个时期均呈下降趋势,但1990—2007年间下降幅度比1980—1999年间大;1980—1999年鱼类资源密度的季节波动幅度较平缓（振幅为0.099）,而1990—2007年的季节波动较大（振幅为0.420）,说明1990—2007年阶段大亚湾鱼类数量的季节变化更为显著.     

Estuarine Typology and the Structuring of Fish Communities in South Africa

Synopsis Some 190 South African estuaries, covering all biogeographic provinces within the region, were classified into three types based on a combination of mouth condition and estuary size (surface area). The fish communities of the estuary types within each zoogeographic region were described and compared. Multivariate analyses revealed that each estuary type contained somewhat distinct fish communities. In addition, the study identified common patterns in species richness and ichthyofaunal composition. Open estuaries have relatively high species richness; this is a reflection of a permanent or near-permanent connection with the sea which allows access into these estuaries by all marine migrant species within the region. Intermittent connection with the sea limits the recruitment and utilisation of closed estuaries by marine migrant species; this results in reduced species richness in moderate to large closed estuaries. Small closed estuaries exhibit the lowest species richness and this is probably a result of their limited habitat and increased isolation from the sea. The key fishes that utilise estuaries could also be categorised into a number of groups based on their relative importance within each estuary type. Some species are largely restricted to predominantly open systems. Other taxa, while important in predominantly open estuaries, also occur in moderate to large closed systems. Some estuarine-associated species are well represented in all estuary types but exhibit a greater importance in closed estuaries. This study has shown that South African fish communities not only reflect estuarine typology but also respond to these differences in a consistent manner that spans all zoogeographic regions. The prevalence of similar patterns in other parts of the world suggests that estuarine typology is a major driver in the structuring of global estuarine fish communities.     

Growth and temperature relationships for juvenile fish species in seagrass beds: implications of climate change

The effect of water temperature on growth responses of three common seagrass fish species that co‐occur as juveniles in the estuaries in Sydney (34° S) but have differing latitudinal ranges was measured: Pelates sexlineatus (subtropical to warm temperate: 27–35° S), Centropogon australis (primarily subtropical to warm temperate: 24–37° S) and Acanthaluteres spilomelanurus (warm to cool temperate: below 32° S). Replicate individuals of each species were acclimated over a 7 day period in one of three temperature treatments (control: 22° C, low: 18° C and high: 26° C) and their somatic growth was assessed within treatments over 10 days. Growth of all three species was affected by water temperature, with the highest growth of both northern species (P. sexlineatus and C. australis) at 22 and 26° C, whereas growth of the southern ranging species (A. spilomelanurus) was reduced at temperatures higher than 18° C, suggesting that predicted increase in estuarine water temperatures through climate change may change relative performance of seagrass fish assemblages.     

Volatile fatty acids in the hindguts of herbivorous fishes from temperate and tropical marine waters

Relative volatile fatty acid composition in the hindgut of four seaweed-eating fishes ranged from acetate only in the cool temperate species to a full array of six types in the warm temperate species and the two tropical/subtropical species.     

Temperature and salinity tolerance of juvenile Rhabdosargus holubi [Steindachner (Teleostei: Sparidae)]

Temperature and salinity tolerances of juvenile Rhabdosargus holubi (Steindachner) were determined experimentally. Results indicated that they are tolerant over a wide range of salinities (0.7–70‰) and temperatures (10–30°C) and that little interaction between temperature and salinity occurs. R. holubi is restricted to the warm temperate waters of southeastern Africa. It is absent from the subtropical Indian Ocean and from temperate Atlantic Ocean waters. The juveniles occur mainly in the inshore waters and estuaries. Evidence from tolerance experiments and salinity and temperature data from southern African estuaries suggested that the distribution of R. holubi is controlled by temperature.     

Status of Marine Biodiversity of the China Seas

China''s seas cover nearly 5 million square kilometers extending from the tropical to the temperate climate zones and bordering on 32,000 km of coastline, including islands. Comprehensive systematic study of the marine biodiversity within this region began in the early 1950s with the establishment of the Qingdao Marine Biological Laboratory of the Chinese Academy of Sciences. Since that time scientists have carried out intensive multidisciplinary research on marine life in the China seas and have recorded 22,629 species belonging to 46 phyla. The marine flora and fauna of the China seas are characterized by high biodiversity, including tropical and subtropical elements of the Indo-West Pacific warm-water fauna in the South and East China seas, and temperate elements of North Pacific temperate fauna mainly in the Yellow Sea. The southern South China Sea fauna is characterized by typical tropical elements paralleled with the Philippine-New Guinea-Indonesia Coral triangle typical tropical faunal center.This paper summarizes advances in studies of marine biodiversity in China''s seas and discusses current research mainly on characteristics and changes in marine biodiversity, including the monitoring, assessment, and conservation of endangered species and particularly the strengthening of effective management. Studies of (1) a tidal flat in a semi-enclosed embayment, (2) the impact of global climate change on a cold-water ecosystem, (3) coral reefs of Hainan Island and Xisha-Nansha atolls, (4) mangrove forests of the South China Sea, (5) a threatened seagrass field, and (6) an example of stock enhancement practices of the Chinese shrimp fishery are briefly introduced. Besides the overexploitation of living resources (more than 12.4 million tons yielded in 2007), the major threat to the biodiversity of the China seas is environmental deterioration (pollution, coastal construction), particularly in the brackish waters of estuarine environments, which are characterized by high productivity and represent spawning and nursery areas for several economically important species. In the long term, climate change is also a major threat. Finally, challenges in marine biodiversity studies are briefly discussed along with suggestions to strengthen the field. Since 2004, China has participated in the Census of Marine Life, through which advances in the study of zooplankton and zoobenthos biodiversity were finally summarized.     

Temperate macroalgae impacts tropical fish recruitment at forefronts of range expansion

Warming waters and changing ocean currents are increasing the supply of tropical fish larvae to temperature regions where they are exposed to novel habitats, namely temperate macroalgae and barren reefs. Here, we use underwater surveys on the temperate reefs of south-eastern (SE) Australia and western Japan (~33.5°N and S, respectively) to investigate how temperate macroalgal and non-macroalgal habitats influence recruitment success of a range of tropical fishes. We show that temperate macroalgae strongly affected recruitment of many tropical fish species in both regions and across three recruitment seasons in SE Australia. Densities and richness of recruiting tropical fishes, primarily planktivores and herbivores, were over seven times greater in non-macroalgal than macroalgal reef habitat. Species and trophic diversity (K-dominance) were also greater in non-macroalgal habitat. Temperate macroalgal cover was a stronger predictor of tropical fish assemblages than temperate fish assemblages, reef rugosities or wave exposure. Tropical fish richness, diversity and density were greater on barren reef than on reef dominated by turfing algae. One common species, the neon damselfish (Pomacentrus coelestis), chose non-macroalgal habitat over temperate macroalgae for settlement in an aquarium experiment. This study highlights that temperate macroalgae may partly account for spatial variation in recruitment success of many tropical fishes into higher latitudes. Hence, habitat composition of temperate reefs may need to be considered to accurately predict the geographic responses of many tropical fishes to climate change.

     

Fish trophic structure in estuaries,with particular emphasis on estuarine typology and zoogeography

A comparative analysis of the fish trophic structure was undertaken on some 190 South African estuaries spanning three zoogeographic regions and incorporating three broad estuarine types. Fish biomass trophic guild compositions and biomass trophic spectrum profiles were analysed using multivariate statistical techniques and included both inter‐regional (zoogeographic) and intra‐regional (estuarine typology) comparisons. Differences in the fish trophic structure of the various estuary types within each zoogeographic region were observed; these were linked to the relative biomass contribution of the various trophic guilds and also to differences in biomass trophic spectrum profiles of the fishes in each estuary type within each region. In spite of these differences in trophic structure, all estuaries were dominated by detritivores, which suggests that the main food source (detritus) is similar in all biogeographic regions. Preliminary indications are that a similar dependence by estuary‐associated fishes on detritus food sources exists on a global basis but that detailed studies are required in order to confirm this assertion.