Habitat-specific predation susceptibilities of a littoral rotifer to two invertebrate predators

The rotifer Euchlanis dilatata lives associated with submerged vegetation in the littoral zone of freshwater lakes and ponds. I assessed habitat-specific predation susceptibilities for this rotifer in the presence of three aquatic macrophytes (Myriophyllum exalbescens, Elodea canadensis, and Ceratophyllum demersum) and two predators (damselfly nymphs — Enallagma carunculata; and cnidarians — Hydra). Rotifer survival was greatest on Myriophyllum in the presence of both predators. Conversely, the presence of the other macrophyte species actually increase rotifer suspectibility to predation by damselfly nymphs. I also manipulated plant structural complexity. As predicted, decreasing the relative complexity of each plant resulted in lower rotifer survival.     

The influence of macrophytes on the spatial distribution of littoral rotifers

1. The effect of macrophytes on the spatial distribution of littoral rotifers was examined in Lake Rotomanuka, New Zealand (37°55'S, 175°19'E). Total rotifer abundances and those of abundant species, were compared between three macrophyte species, Myriophyllum propinquum , Eleocharis sphacelata and Egeria densa , and spatially across a littoral transect in relation to these species.
2. The abundances of many species, for example Euchlanis dilatata, Lecane closterocerca and L. lunaris, differed significantly between macrophyte species. More planktonic forms, Ascomorpha saltans , Keratella cochlearis and Synchaeta oblonga, however, showed no significant preference for macrophyte species.
3. Differences in rotifer abundances were evident even when different species of macrophyte grew in close proximity to one another, indicating that variations in physical and chemical conditions, which occur in the littoral of Lake Rotomanuka, could be largely discounted for much of the variation between macrophyte species.
4. Variation in rotifers between macrophytes was probably the result of a number of factors, including differences in macrophyte morphology, macrophyte age, epiphytic algal growths and the differential effects of predation by invertebrates and fish between macrophytes.
5. Variability of rotifer abundances spatially across the ecotone was less marked than between macrophyte species. The species of macrophyte occurring, and therefore the community composition and distribution of macrophyte species in the littoral, appears to be a major influence in the spatial structuring of rotifer communities in the littoral region of lakes.     

Diurnal vertical distribution of rotifers (Rotifera) in the Chara zone of Budzyńskie Lake,Poland

Diurnal vertical distribution of rotifers was investigated in the Chara bed and the water immediately above it in the shallow region (ca. 1 m depth) of Budzyskie Lake (Wielkopolski National Park, Poland) in early September 1998. Eighty one rotifer species were identified – 71 among Chara and 59 in the open water. Significant differences in rotifer densities were observed in the Chara, with highest numbers during the day (2316 ind. l^–1) and lowest numbers early morning (521 ind. l^–1) and at dusk (610 ind. l^–1). Above the Chara, the numbers of rotifers did not change significantly (615–956 ind. l^–1). Littoral- or limnetic-forms differed in their diel vertical distribution between both zones. One group of littoral species was characterized by increased densities in the Chara in the daytime, while a second group increased in density during the night. The densities of limnetic species, which were much higher in open water, decreased in the morning or daytime in this zone. These differences in the diel behaviour of particular groups of rotifers may be dependent on microhabitat and may also be related to different kinds of predation, the exploitative competition for shared food resources between rotifers and crustaceans, as well as typical adaptation to littoral or limnetic life.     

Environmental Predictors of Rotifer Community Structure in Two Types of Small Water Bodies

The species diversity and distribution of rotifers between different habitats (elodeids, helophytes and open water) of 34 field and 31 forest ponds, differing in regard to origin, size, depth, macrophyte cover, overshading and the presence of fish were examined (N = 381). 197 taxa were found in both types of ponds with 32 species being rare, endangered or new to Polish fauna. The species composition and Shannon‐Wiener index distribution reflected heterogeinity of the habitats, while rotifer mean densities revealed a reverse pattern in both types of water bodies. The great variability of limnological features contributed to a lack of significant differences in rotifer abundance between both types of water bodies. Although some rotifers preferred one specific type of water body (forest vs. field), the type of habitat was a much stronger predictor of their distribution, which reflects a necessity to examine ponds in relation to their microhabitats created by various macrophytes. Rotifers revealed a strict division into two groups – of pelagic origin (e.g., Polyarthra vulgaris), which were attributed to the open water and helophytes, and of littoral origin (e.g., Lepadella patella), which were associated with elodeids, biomass of a plant habitat and a lack of fish. The selective choice of the most complex habitat (elodeids) by only littoral species suggests the weak impact of fish in the studied ponds and the most advantageous conditions for littoral rotifers among such a habitat. The first group comprised species characteristic of field ponds, while the second was characteristic of forest ponds. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diel microdistribution of physical and chemical parameters within the dense <Emphasis Type="Italic">Chara</Emphasis> bed and their impact on zooplankton

Research on the diurnal distribution of physical and chemical parameters within a single macrophyte bed was carried out on the shallow Wielkowiejskie Lake (Poland). A non-parametric statistical analysis was used to compare the water quality features in different parts of a Chara hispida habitat including the middle, both edge (vertical and horizontal) parts of a macrophyte plant, and the open water next to-and above the stonewort stand. The obtained results showed a differentiation in the physical-chemical parameters of the environmental conditions within the Chara hispida stand. The greatest variability was found for dissolved oxygen. Its lowest concentrations were noted in the central part of the macrophyte stand, irrespective of the sampling time. The zooplankton communities within the examined Chara bed were strongly influenced by the concentration of dissolved oxygen. It was also found that two main components of zooplankton communities (rotifers and cladocerans) had a similar trend in their spatial and diurnal distribution within the stonewort stand.     

Periphyton in Lake Vechten,with emphasis on biomass and production of epiphytic algae

Summary Characteristics of the periphyton associated with the submerged macrophytesCeratophyllum, Elodea andMyriophyllum were similar. During the whole growing season the periphyton dry weight often exceeded that of the macrophyte. The periphyton contained much detritus and carbonates, and the epiphytic algae were accompanied by large numbers of bacteria, protozoans and rotifers. Attached algae were scarce, but motile diatoms were abundant throughout the year. Thus the periphyton showed the features of a benthic community. Consequently, the role of the macrophytes would be rather the extension of the bottom area instead of actively promoting the growth of microorganisms by providing minerals or excreting organic substances.During the peak of the littoral development the epiphytic algae expressed a high photosynthetic capacity, while at the same time the periphyton dark respiration was intense. After measurements of the depth distribution of biomass and light in aCeratophyllum stand, it was concluded that the contribution of the epiphytic algae to the production in the lake's littoral zone was substantial. Furthermore, on a daily basis, the total association of macrophytes and periphyton would be oxygen consuming due to heterotrophic activity, notably mineralization of the detritus.     

Aquatic macrophytes, macroinvertebrate associations and water levels in a lowland Tasmanian river

Aquatic macrophytes are a common habitat for macroinvertebrates and may occupy depth zones in the littoral region of lowland rivers. Studies have indicated that different species of macrophyte typically support different assemblages, abundances and numbers of species of macroinvertebrates. This has often been attributed to differences in the dissectedness of stems and leaves of the macrophytes, resulting in differences in the surface area and/or the number of microhabitats available to invertebrates. I set out to measure the abundance and taxonomic richness and to describe the macroinvertebrate assemblages associated with three species of aquatic macrophyte in a pool in the Macquarie River, Tasmania and to examine responses of these variables to changes in water levels over summer. The macrophyte species sampled wereMyriophyllum simulans/variifolium, Triglochin procera} and Eleocharis sphacelata, each one differing in the dissectedness of its stems and leaves and its location in the littoral zone. Whereas the greatest abundance of macroinvertebrates was found associated in all months (i.e. at all water levels) with the structurally complex and shallowest macrophyte species, Myriophyllum, the number of taxa associated with this species was in several cases lower than for the structurally simpler and deeper water Triglochin and Eleocharis. While water depth and total plant biomass of samples were often correlated with invertebrate abundance and richness, these relationships were different for each macrophyte species. Of the nine most common invertebrate taxa collected from all samples, the abundances of more than half showed consistent differences among macrophyte species across months, two showed differences among macrophytes, but with an interaction with month and two showed no differences among macrophytes. There were major differences in the invertebrate assemblages associated with each macrophyte species in any one month, however, there was also a large turnover of taxa associated with the species of macrophytes from one month to the next. Changes in water level and concomitant changes in environmental variables are suggested as factors influencing the invertebrate fauna in the littoral zone of the pool of the Macquarie River. It is thus important for river managers to be aware that species of macroinvertebrates are not evenly distributed across species of macrophyte and that water levels and their influence on macrophytes as invertebrate habitat may play an integral part in determining the abundance, richness and assemblage of invertebrates in rivers.     

On relation to substrate in sessile rotifers

Information on the distribution of 45 sessile rotifers from diverse freshwaters in south and central Sweden was analyzed to reveal possible relationships to their substrates. Almost all of them showed an exclusively periphytic occurrence. The highest number of species was found on Utricularia, but otherwise it was not possible to correlate rotifer presence to any special macrophyte or category of plants (e.g., fine-leaved or floating-leaved species).     

The ecology of periphytic rotifers

The ecology of rotifer assemblages in the periphyton has received little attention relative to that of pelagic rotifers. This paper reviews the ecology of periphytic rotifers, with particular emphasis on the role of macrophytes in the structuring of rotifer assemblages spatially and temporally, and compares these aspects with the dynamics of better known pelagic rotifer communities. Littoral rotifer periphyton communities are typically diverse in lakes, and have composition dissimilar to that of the open water. In rivers, diversity and composition in the pelagic and littoral appear to be similar. Rotifers show preference for macrophyte species they associate with, probably through differences in physical structure or complexity, food concentration or composition, chemical factors, macrophyte age, and differences in the degree of protection from predation provided by macrophytes. These mechanisms are in general not well investigated in rotifers. Factors affecting the seasonal dynamics of periphytic communities appear to be similar to pelagic communities, with seasonal dynamics of substrates and disturbance by flooding or drying also being important.     

Summer zooplankton dynamics in the limnetic and littoral zones of a humic acid lake

The limnetic and littoral zooplankton were studied during summer 1989 in Triangle Lake, a humic acid (pH 4.9) bog lake in Ohio, USA. The limnetic zooplankton showed low species richness and biomass, and dominance by the rotifers Kellicottia bostoniensis and Polyarthra vulgaris. In the littoral, species richness and biomass were markedly higher, and the crustaceans Alona guttata, Ceriodaphnia quadrangula, Chydorus sphaericus, Simocephalus serrulatus and Tropocyclops prasinus, and the rotifer Ascomorpha ecaudis were the dominants. The extreme rotifer dominance and lack of cladocerans in the limnetic zone were likely the result of Chaoborus predation. A pronounced mid-summer decline in cladoceran biomass in the littoral was likely due to predation by T. prasinus and Utricularia (bladderwort).     

Crustacean and rotifer composition of temporary ponds in the Doñana National Park (SW Spain) during floods

The zooplankton of 18 temporary ponds in the Doñana National Park (SW Spain) was studied during floods in February and May 1997. A total of 37 rotifer taxa and 34 crustaceans species were identified (17 cladocerans, 2 ostracans, 4 diaptomids, 7 cyclopodids, 1 harpacticoid, 1 anostracan, 1 notostracan and 1 conchostracan). Zooplankton samples were collected separately from the littoral and the open-water of 12 different ponds. Commonly distributed zooplankton species (frequency of appearance 50%) were not segregated to either the littoral or the open-water according to a chi-square test (P>0.005). The study ponds were divided into seasonal, intermediate and ephemeral ponds according to the length of their hydroperiod. The total numbers of both crustacean and rotifer taxa were highest in the intermediate-hydroperiod ponds (26 and 32 taxa, respectively). The total number of zooplankton taxa collected in both February and May was not significantly correlated to the hydroperiod of the temporary ponds of Doñana during the study period (r=0.165, P=0.526). 21 rotifer taxa and 20 crustacean species were found in the ephemeral ponds; the number of restricted species was also relatively high (3 rotifers and 4 crustaceans). Therefore, the ephemeral ponds held a relatively rich community during floods compared to other temporary ponds of Doñana despite their small size and short wet phase.     

Habitat choice in rotifera communities of three shallow lakes: impact of macrophyte substratum and season

The distribution of rotifer communities between emergent (Typha angustifolia) and submerged (Chara tomentosa) vegetation and a comparatively open water zone were compared during the spring, summer and autumn seasons at three macrophyte-dominated lakes. This survey identified 107 rotifera species of which 58% of the taxonomical structure was common for the three examined lakes. Stoneworts with a more complicated spatial and morphological structure (having a much longer stem length than the narrow leaf cattail), supported higher rotifer densities. The stem length appeared to be the best predictor of all the macrophyte parameters and pH and chlorophyll a for the chemical variables, for explaining the variation of rotifer densities using the stepwise multiple forward regressions. The distribution of pelagic species did not differ between particular sites, which may have reflected the behavioural requirements of those rotifers. Some of them remained in the open water zone while others seeking an anti-predator refuge, gathered within macrophyte stands during the daytime. Moreover, there were nine Chara-associated species recorded and only one Typha-associated species was noted. The similarity of rotifer communities was most strongly influenced by particular habitat and season. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

Ecology of rotifers of Surinsar,a subtropical,fresh water lake in Jamme (J & K), India

17 species of rotifers have been recorded from Lake Surinsar, Jammu (J & K), India of which some are either exclusively limnetic (Brachionus angularis, Hexarthra sp., Filinia opliensis), or littoral (Brachionus patulus, M. ventralis, Trichotoria sp., Platyias quadricornis, Lecane (Monostyla) decipiens, L (M), bulla and Lecane sp.) and others (Keratella tropica, Anuraeopsis fissa, Brachionus quadridentatus, B. calyciflorus, Trichocera sp., T. similis, and Polyarthra sp.) seem to be wandering species. Seasonal maxima for both littoral and limnetic zones are reported. Most population maxima are contributed mainly by one or at best two species.Physico-chemical factors like temperature, pH, dissolved oxygen, free carbon dioxide, calcium, magnesium, and total alkalinity have been studied and their infuence on these rotifer species are discussed. On their thermal responses, the available rotifer species have been classified as warm stenothermal, cold stenothermal or eurythermal. The importance of Mytilina ventralis as a biological indicator for dissolved oxygen in this lake has been pointed out.     

Fish and nutrient enrichment effects on rotifers in a Mediterranean shallow lake: a mesocosm experiment

A mesocosm experiment was conducted “in situ” in a Chara dominated shallow lake near Valencia (Spain) to study top–down and bottom–up effects on rotifers by means of nutrient and fish additions. Both processes were important in determining rotifer abundance, biomass and diversity. A total of 36 mesocoms were established with triplicate treatment combinations of three fish levels (from no fish to 45 individuals of Gambusia holbrooki males) and four nutrient enrichment levels (from no additions to 10 mg l⁻¹ nitrate-N and 1 mg l⁻¹ phosphate-P). The main effect was a notable increase of planktonic and plant associated rotifers densities with fish. Rotifers benefited from mosquitofish predation on microcrustaceans and chironomids. The results showed a marked negative relationship between rotifer and cyclopoid abundances, indicating the importance of the predatory pressure of cyclopoids on rotifers. Effects on rotifer diversity were also evident, in general rotifer diversity decreased with nutrients and increased with fish. The effects of nutrients analysed at species level showed two contrasting density responses: an increase or a decrease with nutrients, which levelled off at high nutrient concentrations. High-level nutrient additions (from 5 mg l⁻¹ nitrate-N and 0.5 mg l⁻¹ phosphate-P) induced a switch to a turbid state with macrophyte disappearance. Most planktonic rotifer species, as well as plant associated ones, diminished when the turbid state was well established, especially in the mesocosms without fish. In the turbid mesocosms, relative abundance of plant-associated rotifers (as a whole) was higher than that of planktonic rotifers. The changes in rotifer species composition after the switch from a clear to a turbid water state are also described. Species of the genus Anuraeopsis, Trichocerca and Hexarthra, dominant in the clear water state, practically disappeared in the turbid water state, in which Proalides tentaculatus and Lecane nana were the main species. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research     

The composition and structure of rotiferan and crustacean communities of the lower rio nhamundá, amazonas,Brazil

The crustaceans and rotifers of 17 samples from the plankton and 3 from the littoral from lakes of the lower Rio Nhamundá, an affluent of the Amazon were studied.

145 taxa of rotifers and 46 of crustaceans were found; two rotifers and three crustaceans are new to science: Keratella americana nhamundaiensis, Euchlanis triquetra var. nhamudaiensis, Echinisca superaculeata, E. sioli, and E. mira. In the taxonomical part 24 rotiferan and 22 crustacean taxa are described in more detail, drawings of them given, and partly remarks made about the geographical distribution.

In the biocenotical part the conditions of dominances were studied: Brachionus zahniseri and Keratella americana within the rotifers and Bosminopsis deitersi and Oithona amazonica within the crustaceans are the dominant species in the pelagial. In the littorial Synchaeta stylata and Stre‐blocerus pygmaeus were found to be dominant.

The species diversity and also the evenness is higher within the rotifers than in the crustaceans. By means of an index of similarity dendrograms were drawn where groups of lakes can be differentiated by using the similarity between the crustaceans. The proportion of neotropical species in relation to pantropical and cosmopolitical species is lowest in the rotifers, higher in the cladocerans and highest in the copepods at 100%.     

Swimming speed and Reynolds numbers of eleven freshwater rotifer species

We obtained data on the swimming speed of 11 freshwater rotifer species. These data were analyzed in terms of Reynolds numbers given the fact that rotifers are in the evolutionary boundary between the use of cilia and swimming appendages. Swimming speed ranged from 0.174 to 0.542 mm ^–1. Philodina acuticornis odiosa was the fastest rotifer in terms of absolute speed. However, Gastropus hyptopus, the smallest of the rotifers analyzed, was the fastest (2.849) in terms of body-lengths s^–1. Reynolds numbers (Re) among the 11 species analyzed varied from 0.023 to 0.301. Lecane furcata had the smallest Re, while Epiphanes senta had the highest Re. The two bdelloid rotifers analyzed in this work swam five times faster than they crept. The importance of Reynolds numbers and drag coefficients are discussed in view of the present results and data found in the literature.     

The Influence of the Spatial Structure of Hydromacrophytes and Differentiating Habitat on the Structure of Rotifer and Cladoceran Communities

Research on the similarity of zooplankton in various stands of water vegetation, including rushes (Typha angustifolia), nymphaeids (Nymphaea alba) and submerged macrophytes (Charahispida, C. tomentosa, Myriophyllumverticillatum and Utricularia vulgaris) was carried out on the shallow Wielkowiejskie lake (Poland). The analysis of the similarity of the Rotifera community revealed the strongest relationship between the Myriophyllum and Chara tomentosa beds, with C. hispida attaching them. A second pair of habitats was represented by Typha and Nymphaea stands. Cladocerans revealed the greatest similarity between both zones of Chara. Additionally, two more pairs of habitats were distinguished – Typha and Nymphaea and also Utricularia and Myriophyllum. In most cases, the Shannon-Weaver values were high among macrophyte stations. Forward stepwise regression revealed that the length of Nymphaea stems was a single negative predictor determining the Cladocera densities. The water lily stand possessed the richest pelagic community of zooplankton and had the highest cladoceran diversity index. In accordance with CCA-ordination, out of the environmental variables, the macrophyte stem length and the concentration of P_tot were the strongest predictors in determining the distribution of particular species of the zooplankton community. Mainly pelagic species displayed preferences towards physical parameters of habitat, which is manifested in their greater affinity to a denser spatial structure of macrophyte substratum. The similarity of zooplankton communities in Wielkowiejskie lake was based on the characteristic architecture of particular macrophyte species, where the plant length was the strongest predictor. Moreover, the character of the zooplankton communities was also influenced by the concentrations of chlorophyll ‘a’ and the chemical variables, with the strongest impact of P_tot, of periphyton received from a particular macrophyte habitat and from water filling the spaces between plant stems.     

Species composition,distribution and seasonal dynamics of Rotifera in a Rift Valley lake in Ethiopia (Lake Awasa)

The species composition of rotifers in Lake Awasa was studied and 40 species recorded. Seven species appeared in large numbers in the plankton seasonally. Brachionus and Keratella species made up more than 50% of the rotifer community by numbers during the observation period (1983–1987). The standing stock numbers of rotifer species are low with a maximum of 50 individuals L^–1, and some possible reasons for this observation are discussed. Most rotifer species are distributed randomly in the lake and show 3-fold fluctuations between consecutive days.The seasonal dynamics of most rotifer species are correlated with mixing periods in the lake, and the amplitude of seasonal fluctuation may be as high as 50-fold. Clear-cut seasonal succession of rotifer species was observed during the study period, but no consistent seasonal pattern for individual species was obvious. Also, observations indicate that rotifer biomass is partly sustained by availability of carbon through the bacterial pathway and that competitive exclusion for food by nauplii and ciliates probably keeps rotifer abundance low.     

Herbivory in omnivorous fishes: effect of plant secondary metabolites and prey stoichiometry

1. Many animals that consume freshwater macrophytes are omnivorous (i.e., they include both plant and animal matter in their diet). For invertebrate omnivorous consumers, selection of macrophyte species depends partly on the presence of secondary metabolites in plants, plant carbon/nutrient balances and/or physical structure of plants. However, little is known about the mechanisms influencing consumption of macrophytes in aquatic vertebrates. 2. For two fish species, the omnivorous rudd (Scardinius erythrophthalmus) and herbivorous grass carp (Ctenopharyngodon idella), feeding preferences were determined in three choice experiments. We tested (i) whether the presence of secondary metabolites and macrophyte stoichiometry affects macrophyte species selection by fish, (ii) the importance of macrophyte stoichiometry by manipulating the macrophytes experimentally and (iii) the rate of herbivory when the most palatable macrophyte is offered simultaneously with a common animal prey. 3. In a choice experiment with five species of submerged macrophytes (Callitriche sp., Chara globularis, Elodea nuttallii, Myriophyllum spicatum and Potamogeton pectinatus), Myriophyllum was clearly consumed least by both fishes, which strongly correlated with the highest phenolic concentration of this macrophyte. Additionally, a significant negative relationship was found between consumption and C : N ratio of the five macrophytes. The two most consumed macrophytes also had the lowest dry matter concentration (DMC). 4. In a second choice experiment, the C : N ratio of the least (Myriophyllum) and most (Potamogeton) palatable plants was manipulated by growing the macrophytes under fertilised and unfertilised conditions and subsequently feeding them to rudd. The avoidance of consumption of the chemically defended Myriophyllum by rudd was partly alleviated by the lowered C : N ratio. 5. The third choice experiment showed that both fishes preferred animal prey (the amphipod Gammarus pulex) over the most palatable macrophyte (Potamogeton) when offered simultaneously. The C : N ratio of the amphipods was about half that of the lowest C : N ratio measured in the macrophytes. Consumption by the fishes could not clearly be related to C : P or N : P ratios of prey items in any of the experiments. 6. We conclude that omnivorous fish avoid macrophytes that are chemically defended. However, when these defences are only minor, stoichiometry (C : N ratio) in combination with DMC may be a determining factor for consumption by vertebrate facultative herbivores.     

Fish community structure response to major habitat changes within the littoral zone of an estuarine coastal lake

Synopsis The littoral environment and fish fauna of Swartvlei, an estuarine lake, was monitored for four years during which major habitat changes occurred. Initially (1979) the zone was dominated by the submerged macrophytes Potamogeton pectinatus, Chara globularis and Lamprothamnium papulosum. This plant community was replaced by filamentous algal mats during 1980 and with the disappearance of these mats in 1981 the littoral zone was transformed into a sandy habitat. There was a highly significant decline in the numbers of fishes in the littoral zone between the macrophyte and sand phases but no significant decrease in fish biomass between the two phases. Analysis of gill net catches revealed an increase in the CPUE of the family Mugilidae between the macrophyte and sand phases but a decline in the CPUE of vegetation associated species such as Monodactylus falciformis and Rhabdosargus holubi over the same period. The increase in mullet stocks during the sand phase was attributed to epipsammic micro-algal production and the input of allochthonous detritus during the 1981 floods. The three fish species diversity indices used in this study showed minor fluctuations between the habitat phases and these variations were related to changes in the equitability of distribution between the individual species within each habitat type. The numbers of fish species recorded during the macrophyte, algal mat and sand phases varied by less than 20%. The resilience of estuarine fishes to major alterations in their environment was illustrated by the fact that all fish species recorded at the beginning of 1979 were present at the end of 1982, despite major habitat and food resource changes.