Eastern Cape Estuaries Research Articles

Fish and tadpole composition as an indication of differences between micro-estuaries and micro-outlets in the Eastern Cape Province, South Africa

The fish and tadpole assemblages inhabiting micro-estuaries and micro-outlets along a warm-temperate section of the Eastern Cape coast were investigated over four seasons between 2015 and 2016. The specific aim of this study was to elucidate whether nekton assemblages in coastal microsystems are similar to those found in larger estuarine systems on the same coastline, and whether the presence or absence of tadpoles can indicate a difference between the two microsystem types. Oligohaline and/or freshwater conditions prevailed in micro-outlets for much of the sampling period, while micro-estuaries were mostly mesohaline. Nekton communities in micro-outlets were dominated by tadpoles (Xenopus laevis), with juvenile Pseudomyxus capensis sometimes present, while Oreochromis mossambicus, Gilchristella aestuaria, P. capensis and Mugil cephalus were the most common fish species in micro-estuaries which had an almost complete absence of tadpoles. The micro-estuaries had a low estuarine function when compared to temporarily open/closed estuaries, while the micro-outlets had very limited estuarine characteristics and an almost complete absence of fishes. Due to their restricted periods of stability and small size, micro-estuaries served as only intermediate nursery areas for small numbers of 0+ marine fish which, after less than a year, need to migrate to nearby larger estuarine systems that can provide the full range of nursery habitats for subsequent growth and development. The limited numbers of estuarine resident fishes (e.g. G. aestuaria) and freshwater fish species (e.g. O. mossambicus) confirm the marginal habitat and food availability in these microsystems for fishes that are normally abundant in other types of Eastern Cape estuaries and rivers. The results of this study confirm that there are clear distinctions between the nekton of the two microsystem types, thus making fish and tadpole assemblages a viable tool for differentiating between micro-estuaries and micro-outlets in this province.

The effects of increased freshwater inflow on metal enrichment in selected Eastern Cape estuaries, South Africa

The concentrations of select metals (Cd, Co, Cu, Fe, Pb, Ni and Zn) within the water column and sediment of the permanently open Kariega Estuary and temporary open / closed Riet and East Kleinemonde Estuaries were investigated during a dry and a wet season. Enrichment factors (EFs), using Fe as a reference element, and baseline linear regression models for metals vs Fe were used to assess the extent of metal enrichment in the sediments. The results of the study indicate that Cd, Co Ni and Pb were enriched above baseline concentrations (1.0 < EF < 4.1) in the sediments of all three estuaries. Co, Pb and Ni enrichment in the Kariega Estuary sediments was significantly higher during the dry season, and the mean concentrations of Pb and Cd in the water column were 19-fold and 66-fold higher in the dry season. The elevated concentration of metals during the dry season could be related to accumulation of diffuse pollution from human activities within the catchment area. Conversely, inflow of freshwater into the estuary had the net effect of reducing the concentration and enrichment of these metals within the Kariega Estuary due to scouring and outflow of estuarine water and sediment into the marine environment. The temporal variations in metal concentrations and enrichment factors were less pronounced in the temporary open / closed estuaries than the Kariega Estuary. The observed trend can probably be related to the low anthropogenic impact within the catchment areas of these systems, and the relatively smaller size of the catchments. Significant spatial variations existed in metal enrichment in the sediment of both the East Kleinemonde and Riet Estuaries, with the highest degrees of enrichment occurring in the sediments from the marine environment and lower reaches.

Macrofaunal community structure in the littoral zone of a freshwater-deprived, permanently open Eastern Cape estuary

Spatial patterns in the macrofauna community structure within four distinct zones of the permanently open, freshwater-deprived Kariega Estuary on the southeastern coastline of southern Africa were investigated in March–May 2010. The zones within the littoral zone comprised a band of Zostera capensis (Setchell) exposed at spring low tide and comprising Zone I; a band of mud or sand, lacking vegetation, corresponded to Zone II; stands of Spartina maritima (Curtis) formed Zone III and a belt of Sarcocornia perennis (Miller) constituted Zone IV. Total macrofauna abundance and biomass during the study ranged from 16–816 ind/m2 and from 0.032–390.76 mg wwt/m2 and demonstrated no significant horizontal or vertical patterns (P > 0.05 in both cases). Multidimensional scaling (MDS) indicated that there were no significant spatial patterns in the macrofaunal community structure within the four zones which could be related to the predominance of euryhaline species, including Marphysa sanguinea (estuarine wonder worm), Arcuatula capensis (estuarine mussel), Macoma litoralis (littoral tellin) and Nassarius kraussianus (tick shell) throughout the estuary. The absence of any distinct spatial patterns in the community structure of the macrofauna appears to be related to the virtual absence of any horizontal patterns in selected physico-chemical variables and availability of submerged macrophytes along the length of the estuary. Comparisons with historical data indicate that while there have been no significant changes in the estimates of the total macrofauna abundance and biomass within the estuary over the past three decades, abundances of selected species have declined by as much as 80%. The decline in the abundances of these species appears to reflect the predominance of hypersaline conditions within the upper reaches of the estuary and intense fishing activities in the lower reaches of the system.

Macrofaunal Community Structure in the Littoral Zone of a Freshwater-Deprived, Permanently Open Eastern Cape Estuary

Spatial patterns in the macrofauna community structure within four distinct zones of the permanently open, freshwater-deprived Kariega Estuary on the southeastern coastline of southern Africa were investigated in March–May 2010. The zones within the littoral zone comprised a band of Zostera capensis (Setchell) exposed at spring low tide and comprising Zone I; a band of mud or sand, lacking vegetation, corresponded to Zone II; stands of Spartina maritima (Curtis) formed Zone HI and a belt of Sarcocornia perennis (Miller) constituted Zone IV Total macrofauna abundance and biomass during the study ranged from 16–816 ind/m2 and from 0.032–390.76 mg wwt/m2 and demonstrated no significant horizontal or vertical patterns (P > 0.05 in both cases). Multidimensional scaling (MDS) indicated that there were no significant spatial patterns in the macrofaunal community structure within the four zones which could be related to the predominance of euryhaline species, including Marphysa sanguinea (estuarine wonder worm), ...

Insights into the bacterial diversity in a freshwater-deprived permanently open Eastern Cape estuary, using 16S rRNA pyrosequencing analysis

The aim of this study was to conduct an investigation into the bacterial diversity in the freshwater-deprived Kariega Estuary, situated along the Eastern Cape coastline, using ribosomal RNA gene sequences obtained by pyrosequencing. Shifts in the microbial diversity were correlated to selected physico-chemical variables along the length of the estuary. More than 27 000 sequences were obtained and rarefaction analyses confirmed a comprehensive appraisal of the microbial diversity present in the Kariega Estuary. Distinct patterns in phylotype distribution from the hypersaline upper reaches to the mouth of the estuary were observed; notably, the importance of the detrital food web within the Kariega Estuary was highlighted by the high occurrence of Bacteroidetes and Actinomycetes. Moreover, while the observed chlorophyll-a concentrations were low (< 0.1 ìg..-1), the presence of Pelagibacter and Flavobacteria amongst the microbial community suggests a potentially important contribution of these microbes towards the total primary productivity of the ecosystem. No human pathogenic microbes were detected within waters of the system. We conclude that pyrosequencing provides a versatile and efficient tool for assessing the microbial diversity in the Kariega Estuary and propose that this technology may provide valuable information on the ecosystem functioning and health of aquatic ecosystems.

The population dynamics of the estuarine isopod Exosphaeroma hylocoetes (Barnard, 1940) within three temporarily open/closed southern African estuaries

ABSTRACT The population dynamics of the estuarine isopod, Exosphaeroma hylocoetes, was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances and biomasses ranged between 0 and 4791 ind/m2 and 0 and 9.65 mg/dwt/m2 in the West Kleinemonde Estuary and between 0 and 108 ind/m2 and 0 and 0.318 mg/dwt/m2 in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3650 ind/m2 and 0 and 5.105 mg/dwt/m2. Temporal changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum abundance and biomass was recorded in the middle reaches, which could be ascribed to the presence of submerged macrophytes. E. hylocoetes demonstrates strong sexual dimorphism, with males being significantly ...

The population dynamics of the estuarine isopod Exosphaeroma hylocoetes (Barnard, 1940) within three temporarily open/closed southern African estuaries

The population dynamics of the estuarine isopod, Exosphaeroma hylocoetes, was investigated monthly from February 2006 to August 2007 in three temporarily open/closed Eastern Cape estuaries, the East and West Kleinemonde and Kasouga Estuaries. Mean isopod abundances and biomasses ranged between 0 and 4791 ind/m2 and 0 and 9.65 mg/dwt/m2 in the West Kleinemonde Estuary and between 0 and 108 ind/m2 and 0 and 0.318 mg/dwt/m2 in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3650 ind/m2 and 0 and 5.105 mg/dwt/m2. Temporal changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations crashing when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum abundance and biomass was recorded in the middle reaches, which could be ascribed to the presence of submerged macrophytes. E. hylocoetes demonstrates strong sexual dimorphism, with males being significantly larger than females (P < 0.05). Sex ratios were skewed in favour of females in all three estuaries. Females were encountered carrying young from an overall length of 2.5 mm throughout the year

Population demographics of Palaemon peringueyi (Macpherson 1990) (Decapoda: Palaemonidae) in a small intermittently open Eastern Cape estuary

The population demographics of the caridean shrimp Palaemon peringueyi was investigated monthly at four sites over a period of one year in the small, intermittently-open Grants River Estuary situated on the south-east coastline of southern Africa. Mean total abundance and biomass of P. peringueyi ranged between 0 and 23.2 ind m−2 and 0 and 2.3mg wwt m−2, respectively. A peak in its abundance coincided with a breaching event that occurred in December 2004, and could be attributed to the mass recruitment of juveniles (carapace length <9mm) into the estuary. Minor peaks in abundance were also associated with marine waters overtopping the sandbar that separates the estuary from the marine environment. The highest biomass values were recorded when the estuary was separated from the sea. Maximum abundance and biomass values of P. peringueyi were generally recorded in the middle reaches of the estuary where extensive beds of submerged vegetation, mainly Potamogeton pectinatus, predominated. Pearson correlation analysis indicated that the total abundance of P. peringueyi was significantly correlated (r = 0.49; p < 0.05) to percentage cover of submerged vegetation. The spatial pattern in abundance and biomass values of the shrimp is thought to reflect the availability of refuge areas against predation. A distinct spatial pattern in the community structure of the shrimp was evident, with juveniles numerically dominating the samples in the lower reaches of the estuary, while mature females predominated in the upper reaches of the system. In the middle reaches, the community comprised both juveniles and adults.

The filtering capacity of selected Eastern Cape estuaries, South Africa

Four Eastern Cape estuaries, the Kromme, Gamtoos, Swartkops and Sundays Estuaries have a permanent connection to the adjacent ocean, but differ in the amount of freshwater inflows as well as in the land-use patterns in their respective catchment areas. The nutrient loading to the four estuaries in terms of phosphate, nitrate, nitrite and ammonia therefore varies. The aim of the study was to show how the nutrient loads received by the estuaries differ, and how they act as filters for nutrients. Discriminant analysis revealed such contrasts: The lower reaches of the four estuaries are similar in their inorganic nutrient concentrations, but concentrations diverge in their upper reaches and in the inflowing river water.

Affinities of some common estuarine macroinvertebrates to salinity and sediment type: empirical data from Eastern Cape estuaries, South Africa

Fourteen species of subtidal macrobenthos present in thirteen Eastern Cape estuaries, South Africa, were compared with regard to correlations with two important environmental variables (salinity and sediment mud content). Species were divided into five different faunal components based on their affinity with one of the two variables, namely marine species, oligohaline species, estuarine sand species, estuarine mud species, and species whose distribution seemed independent of either environmental variable. Although most species exhibited wide tolerance ranges to both environmental variables, preference ranges could be identified in many cases. Among the fourteen species studied, three were found mostly at high salinities, two were confined to sandy substratum, and four showed a clear preference for muddy sediment. The crab Paratylodiplax algoense was identified as a euryhaline marine species and the larvae of chironomid midges, previously believed to be oligohaline species, were found to be tolerant to near seawater salinities.

Distribution patterns of fishes in a freshwater deprived Eastern Cape estuary, with particular emphasis on the geographical headwater region

Small seine net fish assemblages in the headwater region of the Kariega Estuary are described and compared to the catch composition in other parts of the system. The geographical headwaters of the freshwater 'deprived' Kariega Estuary were utilised by a range of fish species but, in contrast to the nearby freshwater 'rich' Great Fish Estuary, few important angling species (e.g. spotted grunter Pomadasys commersonnii and dusky kob Argyrosomus japonicus) were recorded. The reduced riverine flow into the Kariega Estuary resulted in an extremely restricted river-estuary interface (REI) zone being made available to resident and migrant fish species. Despite the low freshwater input recorded, the catadromous freshwater mullet Myxus capensis was abundant within the REI zone and headwater reach, probably due to reduced access to riverine habitat above the estuary. Although salinity has been shown to be an important structuring force influencing ichthyofaunal assemblages in many South African estuaries, it is not the primary factor governing the distribution of fish in a freshwater-deprived, marine-dominated system such as the Kariega. Water SA Vol.29(1) 2003: 61-67

What limits the distribution of subtidal macrobenthos in permanently open and temporarily open/closed South African estuaries? Salinity vs. sediment particle size

Thirteen estuaries in the Eastern Cape Province, South Africa, were assigned to one of four types of estuaries (river-dominated permanently open, marine-dominated permanently open, medium-sized temporarily open/closed and small temporarily open/closed), and macrobenthic zonation patterns were compared using multivariate statistics. Three major habitat zones were identified: two relating to substrate (a sand zone and a mud zone), and a third zone characterised by water of low salinity (≤2.2). These zones are inhabited by four major groups of macrobenthos. The distribution of two of these (estuarine endemic sand fauna and estuarine endemic mud fauna) is limited by the nature of the substratum, whereas the distribution of the other two (fauna originating from the marine habitat and oligohaline fauna) is limited by salinity. Estuarine endemics were present in all four types of estuaries. Marine fauna was numerically important only in permanently open systems, while oligohaline fauna was abundant only in the upper reaches of river dominated open systems. Medium-sized temporarily open/closed estuaries lacked both marine and oligohaline forms, but these were present to a limited extent in small temporarily open/closed estuaries. Hence, salinity is not the primary environmental variable determining zonation patterns in Eastern Cape estuaries, and particularly in temporarily open/closed estuaries, it is of minor importance.

The influence of catchment management on salinity, nutrient stochiometry and phytoplankton biomass of Eastern Cape estuaries, South Africa

Three estuaries with differing catchment use and freshwater input were investigated in terms of their nutrient status, phytoplankton biomass, freshwater inflow and salinity between 1993 and 1995. The nutrients analysed include phosphate, nitrate, nitrite, ammonia and total particulate nitrogen. All the parameters were investigated for their relationship with land-use and freshwater abstraction. The Kromme River catchment area is relatively pristine, the river is impounded for ca. 133% of its mean annual runoff, and consequently, freshwater input into the estuary is only episodic. Nutrient and chlorophyll- a concentrations are low, but become elevated when freshwater does reach the estuary. The Geelhoutboom tributary contributes nutrients to the Kromme estuary during high freshwater inflow conditions, but is not a viable nutrient contributor during low flow conditions. Freshwater abstraction from the Swartkops River catchment is limited, and it is characterised by urbanisation and industrial development. The Swartkops River was the main source of phosphate in the estuary, whereas other small tributaries along the estuary were additional point sources for nitrate, ammonia and nitrite. The third system, the Sundays estuary, has no tributaries or other point sources except the Sundays River, where the catchment is extensively used for agriculture and freshwater input relatively high. The phytoplankton biomass (in terms of chlorophyll- a) was highest in the Sundays estuary, although phosphate concentrations were as low as in the Kromme estuary. Trends over time indicated a decrease in phosphate concentrations and showed variations for inorganic dissolved nitrogen concentrations since the previous 15 years in all the three estuaries. Nutrient stochiometry had changed in favour of inorganic dissolved nitrogen.

Assessment of the recreational linefishery in selected Eastern Cape estuaries: trends in catches and effort

Boat-based creel surveys were used to collect catch and effort data on the shore- and boat-based linefisheries of the Kromme, Gamtoos, Swartkops, Sundays, Bushmans, Kariega, Kowie and Great Fish estuaries in the Eastern Cape, South Africa, from January 1996 to April 1997. The surveys, which were performed primarily during routine fisheries law enforcement patrols by a regional conservation agency, recorded the catch and effort of 2 468 individual angler outings (12 840 angling hours) during 337 angler-count patrols. Although 26 species were recorded, a large proportion of the catch (85%) comprised only four species. Spotted grunter Pomadasys commersonnii (43%) was most commonly caught, followed by Cape stumpnose Rhabdosargus holubi (16%), dusky kob Argyrosomus japonicus (14%) and white seacatfish Galeichthys feliceps (12%). In terms of mass, the overall catch was dominated by A. japonicus (50%) and P. commersonnii (33%). Overall catch per unit effort (cpue) by number was highest during summer and lowest d...

The importance of the river-estuary interface (REI) zone in estuaries

A multidisciplinary and multi-institutional research programme studied the influence of river flow rate on salinity distribution and response of the biota in three Eastern Cape estuaries, South Africa. Elevated flow rates increased the size of the river estuary interface (REI) zone (< 10 g·l-1) both longitudinally and in volume. In the Gamtoos Estuary, a flow rate of between 0.8 and 1.2 m3·s-1 produced a maximum phytoplankton biomass, both as concentration and total within the estuary. There was no clear relationship between measurable mineral nutrient content in the water and phytoplankton biomass, presumably because minerals are taken up rapidly by microalgae and are therefore not reflected in the water analyses. The rate of water flow and the size of the REI were shown to affect the distribution of invertebrates. Pelagic and benthic invertebrates showed distinct species assemblages along the longitudinal salinity gradient, with filter-feeding forms dominating the benthic community in the REI region. The effect of the REI zone on fish was examined in the freshwater-rich Great Fish Estuary and in the freshwater-deprived Kariega Estuary. Estuarine associated fishes responded strongly to river flow in the Great Fish Estuary but a number of these taxa were limited or absent from the Kariega Estuary. These findings are discussed in relation to the determination of the quantity and quality of water required to sustain ecologically sound estuarine ecosystems in terms of the South African National Water Act (36) of 1998. WaterSA Vol.28(3) 2002: 271-280

Phytoplankton/protozoan dynamics in the Nyara Estuary, a small temporarily open system in the Eastern Cape (South Africa)

Most estuarine studies in South Africa have focused on larger estuaries, while numerous, smaller, temporarily open estuaries have received little research attention. This study examines the phytoplankton distribution in relation to physical and chemical variables through a quasi-seasonal cycle (from March to November 1997, including a flood event) in the Nyara, one of the smaller Eastern Cape estuaries. Vertical stratification of salinity was a persistent feature, indicating limited mixing of the water-column, except during flood events. Average chlorophyll-a concentrations for the estuary decreased from 1.3μg/l in March to 0.1μg/l in September, corresponding to the seasonal decline in rainfall and freshwater inflow. With the exception of the period during the November flood, the shallowness of the estuary as well as low chlorophyll-a concentrations always allowed an average of 30% of surface light to reach the sediment surface. Diatoms were most abundant in the water-column in March (mean = 105 cells/l), but numbers declined to below 104 cells/l in May and September. Picoplankton numbers increased over the study period, while nanociliates and dinoflagellates were fairly constant at 104 and 105 cells/l respectively. The most common group in terms of carbon, were the dinoflagellates. Freshwater, or possibly the input of nutrients associated with it, appears to be the most significant factor affecting phytoplankton biomass in the Nyara Estuary. When not receiving pulses of nutrients through freshwater inflow, the Nyara is best described as a predominantly low nutrient, low phytoplankton biomass, stratified system, dominated by the microbial food-web and possibly fed by detritus. This state can however, be altered rapidly by flood events that cause mouth opening.

The Influence of Freshwater Inflow on the Nature, Amount and Distribution of Seston in Estuaries of the Eastern Cape, South Africa

The influence of freshwater inflow in determining the particulate food resources for suspension-feeders in eastern Cape estuaries was investigated. The seasonal and spatial distribution of total particulate material (TPM), total particulate organic material (TPOM), chlorophylla, particulate protein and carbohydrate were compared in two hydrodynamically contrasting systems, the Kariega and the Great Fish estuaries, which differ markedly in respect of their freshwater inflow. As a result of high, sustained freshwater inflow, seston levels in the Great Fish estuary were of an order of magnitude higher than in the Kariega estuary which received minimal inflow. Chlorophyllameasurements showed that the Great Fish estuary is predominantly eutrophic/mesotrophic whereas the Kariega estuary is classified as oligotrophic. Correlation analyses indicated that the organic fraction of the seston was dominated by detritus in the Kariega estuary and by phytoplankton in the Great Fish estuary. Although the quality of organic seston was higher in the Great Fish estuary, the ‘masking’ effect of suspended inorganic particles associated with freshwater inflow was much greater. In both estuaries, the majority of seston occurred in the nanoplanktonic size range. The seasonal and spatial patterns of seston distribution differed markedly under conditions of contrasting freshwater inflow. Suspended particulates were more uniformly distributed along the length of the Kariega estuary and were seasonally elevated during the warmer months. By contrast, a pronounced spatial gradient was evident in the Great Fish estuary with highest values recorded towards the upper reaches. The nutrient status of the Great Fish estuary was considerably higher than that of the Kariega estuary and determined principally by freshwater inflow. High phytoplankton standing stocks generally developed episodically following high freshwater inflow. This was partly the result of an accumulation of phytoplankton of riverine origin by hydrodynamic trapping, however, species tolerant of brackish conditions responded to the enriched conditions by remaining viable and active for considerable periods within the estuary.

Abundance of larval and 0+ juvenile marine fishes in the lower reaches of three southern African estuaries with differing freshwater inputs

Although numerous studies have been conducted on the biology and ecology of larval and juvenile marine fishes in estuaries, information on the factors influencing abundance, which in turn reflects the magnitude of immigration into these systems, is generally lacking. In an effort to provide some insight into the posslble role of freshwater discharge on the abundance of marine larval and juvenile fishes, 3 permanently open eastern Cape Province estuaries with similar tidal prisms and mouth dimensions, but differing riverine inputs and turbidity characteristics, were selected as study sites. The Great Fish system can be characterized as a turbid estuary (>50 NTU) with a moderate axial salinity gradient (> 20 g kg-'), the Sundays as a semi-turbid estuary (> 10 NTU) with a strong axial salinity gradient (>30 g kg-'), and the Kariega as a relatively clear estuary (< 10 NTU) with a weak axial salinity gradient (< 10 g kg-'). Although the number of marine fish taxa entering the 3 estuaries was similar (18 to 20 species), Littoral densities of larvae and 0+ juveniles in the lower reaches of the Great Fish (280 ind. 100 m-2) and Sundays (290 ind. 100 m-2) estuaries were significantly (p < 0.01) greater than those in the Kariega system (50 ind. 100 m-'). lchthyoplankton densities in the lower reaches of the 3 estuaries were highest in the Great Fish estuary (13 ind. 100 m-3), followed by the Sundays Estuary (7 ind. 100 m-3) and Kariega Estuary (4 ind. 100 m-3). Regression analyses indicated that several factors were associated wlth the abundance of the early life stages at the ichthyonekton study sites, the most important of which were estuarine axial salinity gradient, water temperature and axial turbidity gradient. The possible significance of these and other associated variables in influencing migration processes into eastern Cape estuaries is discussed.

A comparison of the ichthyofaunas in two permanently open eastern Cape estuaries

The Kowie and Great Fish estuaries are situated less than 30 km apart, yet they differ considerably in terms of riverine inflow, turbidity, food resources and habitat availability. The ichthyofauna of the two estuaries were sampled using plankton, seine and gill nets. A greater ichthyofaunal richness (R) was recorded in the Kowie estuary and this is attributed to the wider range of habitats and greater degree of marine influence in this system. In contrast, all three sampling gears revealed an approximate 3:1 ratio between fish abundance in the Great Fish and Kowie estuaries. The higher abundance of fishes in the Great Fish estuary is partly attributed to the large organic and nutrient inputs into this system when compared with the Kowie system, and the influence of these inputs on estuarine primary and secondary production. Individual fish species are affected differently by turbid water conditions. Indications from this study were that piscivorous fishes (e.g. Lichia amia) which rely mainly on visual foraging methods were adversely affected by the high turbidity conditions within the Great Fish estuary, whereas piscivores (e.g. Argyrosomus hololepidotus) which rely mainly on non-visual methods were unaffected. Macrobenthic predators (e.g. Pomadasys commersonnii) and detritivo-rous fish species (e.g. Mugil cephalus) also appear to be unaffected by high suspensoid levels and were usually more abundant in the Great Fish than in the Kowie estuary. The length-frequency distributions of some of the dominanl fish species occurring in both estuaries are presented.

Changes in body composition associated with growth and reproduction inGaleichthys feliceps(Teleostei: Ariidae)

White seacatfish Galeichthys feliceps were collected from four Eastern Cape estuaries and the sea. Males utilized estuarine mouth regions for egg incubation, which peaked from September to December. The energy expended in mouth-brooding amounted to 8 per cent of male body energy (27% of body fat). The amount of energy invested in functional egg production equalled 26 per cent of female body energy (fecundity 70 ± 13). There was an increase in energy of fish bodies as body length increased whereas embryo energy decreased as development progressed.