Diapause in copepods (Crustacea) from ephemeral habitats with different hydroperiods in Everglades National Park (Florida,U.S.A.)

Water management practices in the Everglades have severely stressed the natural system, particularly by reducing the hydroperiods of much of the region. During the dry season of 1999, we investigated the influence of hydroperiod on the species composition and dormancy patterns of freshwater copepod communities in seasonal wetlands of Everglades National Park, Florida, U.S.A. The habitats were characterized by an annual dry season, from December through June. We sampled at two locations: the Long Pine Key area of the Rocky Glades region (short hydroperiod, ca. 4–5 months), and western Taylor Slough (intermediate hydroperiod, ca. 8–10 months). Both areas have experienced a reduction in natural hydroperiods and an increase in the frequency of dry-down. We collected weekly plankton samples from Rocky Glades solution holes to assess the potential species pool of copepods. To document the taxa capable of surviving dry-down by resting, we performed three immersion trials in which we rehydrated, in laboratory aquaria, sediment patches from solution holes and surface soils from all stations. Only a subset of the planktonic species collected emerged from the dried sediments. The cyclopoids Microcyclops rubellus and Paracyclops poppei were dominant. This is the first record of diapause for P. poppei. Species distributions from the different hydroperiod soil patches indicated that more diapausing species occurred at the sites that dried for shorter periods. Emerging individuals of M. rubellus and P. poppei were mainly ovigerous females, demonstrating a resting strategy seldom before recorded. The cyclopoid Diacyclops nearcticushad not been previously reported to diapause, but they emerged from the dried sediments in our trials. Our collections included six new records for Florida: Diacyclops nearcticus, Megacyclops latipes, Orthocyclops modestus, Elaphoidella marjoryae, Bryocamptus sp. and Bryocamptuscf. newyorkensis. Paracyclops poppei, Macrocyclops fuscus and Arctodiaptomus floridanus are new records for Everglades National Park. Clearly, diapause is an important strategy for the persistence of copepods in short-hydroperiod wetlands. The duration of the dry period appears to be inversely related to the number of species that emerge from diapause.     

Differential dispersal rates in an intertidal meiofauna assemblage

Meiofaunal nematodes and copepods disperse passively with sediment bedload, and copepods also display active emergence and reentry behavior. Epigrowth-feeders may be the nematode feeding group most susceptible to passive transport because they live closest to the sediment surface. We used bottom traps at a nematode-dominated intertidal mudflat in Maine, USA, to test the hypotheses that (1) meiofauna taxa disperse in relative proportions different from those of the ambient community; (2) copepods have the highest relative dispersal rate (number of individuals trap⁻¹ day⁻¹ ambient individual⁻¹) and are not as tightly linked as other taxa to sediment flux; and (3) epigrowth-feeders have the highest nematode relative dispersal rate. Results supported all three hypotheses. Nematodes accounted for 95.8% of the individuals in cores, but only 38.9% of the individuals in traps. Copepods accounted for 1.5% of the individuals in cores, but 56.7% of the individuals in traps. Less common taxa also had different relative proportions in cores and traps, as did nematode feeding groups and individual species. The relative dispersal rate was far higher for copepods than for any other taxonomic group, and the absolute (number of individuals trap⁻¹ day⁻¹) and bulk (number of individuals g sediment⁻¹ trap⁻¹ day⁻¹) dispersal rates for copepods were equal to those of the 65-fold more abundant nematodes and higher than those for all other taxa. The non-selective deposit-feeders were the most abundant nematode feeding group in the ambient community, but the epigrowth-feeders as a group and as individual species had the highest absolute, relative, and bulk dispersal rates. Non-metric multidimensional scaling (MDS) using analysis of similarity (ANOSIM) and species similarity percentages (SIMPER) reflected these differences between ambient and dispersing nematode assemblages. Significant positive regression relationships between sediment weight and the number of individuals captured in traps for nematodes and some other taxa indicated that they moved passively in the bedload. Lack of a significant regression relationship for copepods suggested an active behavioral component to dispersal. Meiofauna populations in this soft-bottom community were highly dynamic, demonstrating that the role of dispersal must be included in any consideration of the ecology of soft-bottom systems at local and regional spatial scales.     

Vicariance, dispersal and scale in the aquatic subterranean fauna of karst regions

1. The causes of distribution patterns of stygobionts (obligate subterranean-dwelling aquatic species) were examined with special emphasis on vicariance and dispersal.
2. Dispersal was investigated on the premise that if migration is important, then migration at small scales should predict patterns at larger scales. Data on the copepod fauna of epikarst in Slovenia were especially useful for the study of migration, because data on habitat occupancy could be collected at scales of individual drips located metres apart to the scale of individual caves to entire karst regions. Occupancy of drips in one cave was a remarkably good predictor of occupancy of caves in a region, although not of the overall range of a given species. These results were also supported by occupancy patterns of the general stygobiotic fauna of West Virginia caves, compared at different scales.
3. Vicariance was investigated by noting that proximity to marine embayments increases the likelihood of vicariant speciation. In the U.S.A., only the fauna of the Edwards Aquifer of Texas has a significant component of marine-derived species. Differences in shape of the relationship between species number and number of caves in a county indicated that the marine-derived component represented an addition to rather than a replacement of the other stygobiotic species.
4. Thus, we found evidence for the importance of both vicariance and dispersal. The techniques employed could be used to study these patterns more generally, as more data become available.     

Harpacticoid copepod communities of floating seaweed: controlling factors and implications for dispersal

The structure of harpacticoid copepod communities of floating detached intertidal algae was studied by surveys and experiments. Seaweed clumps were sampled from Faxaflói, western Iceland, at various distances from the shore (0.2–14 km). Altogether 20 species of harpacticoids were found in these clumps, most of them typical phytal species. Multidimensional scaling ordination (MDS) separated the samples into three distinct clusters in which the communities were significantly different from each other. The distance from shore did not seem to affect the community structure. However, diversity and abundance of harpacticoids increased with size and complexity of the clumps. Experimental Ascophyllum nodosum fronds placed 300–600 m offshore were rapidly colonised by harpacticoids. Density and species diversity were, after 20 days afloat, higher than in the free-floating clumps. Species of the genus Harpacticus were successful colonisers, in particular Harpacticus chelifer and Harpacticus uniremis. In a survey of macrofauna (0.5-mm sieve) on floating algae clumps from various locations around Iceland, H. chelifer was present in all clumps studied, up to 117 km offshore. Its sex ratio was skewed towards females, often with a high ratio of ovigerous females. There was, however, no evidence that this species is using the algal clumps as a platform for reproduction.     

The influence of feeding strategies on trace element bioaccumulation in copepods (Calanoida)

Copepods are the most numerous taxonomic group in marine mesozooplankton communities. These planktonic organisms have an essential role in the function of marine trophic webs, as they are the link between phytoplankton and secondary consumers.The concentrations of 20 essential and non-essential trace elements were investigated by Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) in calanoid copepods with different feeding behaviors. The sampling was performed in the Northwestern Mediterranean Sea, at the border between the Northern Tyrrhenian Sea and the Ligurian Sea (Italy). Aluminum, iron, zinc and copper were present in the highest concentrations in herbivorous calanoids (Temora stylifera, Nannocalanus minor, Neocalanus gracilis). Conversely, the nonessential element – arsenic – and the essential elements selenium and molybdenum – were present in the highest levels in carnivores (Pontella mediterranea, Candacia ethiopica). In the omnivorous copepod Centropages typicus, metal concentrations were found at an intermediate level between herbivores and carnivores, reflecting the importance of dietary pathways in metal intake and bioaccumulation.Finally, the bioaccumulation factors (BAFs), expressed as a ratio of the total metal levels in copepods compared to the seawater metal levels, were as follows: herbivores (83699) > omnivores (47855) > carnivores (41648).     

Zooplankton on the move: first results on the quantification of dispersal of zooplankton in a set of interconnected ponds

In systems of interconnected ponds or lakes, the dispersal of zooplankton may be mediated by the active population component, with rivulets and overflows functioning as dispersal pathways and the dispersal being unidirectional. Such systems offer the possibility to study the impact of dispersal rates on local population dynamics and community structure, and provide opportunities to quantify dispersal in the field in a straightforward manner. In this study, dispersal of active zooplankton populations among interconnected ponds was quantified directly in the field by sampling the small waterways connecting the ponds. The number of dispersing zooplankton sampled in connecting elements was on average high (almost 7000 ind h^–1). However, the contribution of dispersing individuals to total population size in the target ponds was very limited (< 1% 24 h^–1.). Only a weak diel pattern in dispersal rates was observed.     

Expression of a dispersal trait in a guild of mites colonizing transient habitats

Summary Dispersal as a means of escape from deteriorating habitats is of particular ecological relevance for organisms such as certain astigmatic mites that colonize habitats which vary unpredictably in space and time. The mites meet these ecological challenges by a facultative dispersal morph, the heteromorphic deutonymph, also called hypopus. The appearance or absence of hypopodes in natural populations is attributable to two fundamentally different, albeit interacting, causes. Genetic polymorphism for the propensity to induce a hypopus provides for heritable variation within the population and allows selection to favor or eliminate certain genotypes. The genotypic composition of a population reflects selection forces previously acting on the population. But it holds no predictive power. Rather, it adapts the population to cope with unpredictably varying living conditions because it ensures instantaneous fit of certain genotypes of the population (those displaying hypopus-free development) to favorable (moist) environmental conditions, and others (those expressing a hypopus) to detrimental (dry) conditions. In contrast, environmentally cued inducibility allows mites to anticipate food quality inasmuch as it allows each genotype of the population to adjust its development rapidly to impending adversity or benefit. Inducibility occurs by means of a developmental switching mechanism and leads either to a developmental pathway with a hypopus or else one without. The expression of a hypopus depends on interacting genetic and environmental (trophic) factors. High levels of additive genetic variation combine with considerable genetic-trophical interaction (comprising a threshold for phenotypic expression of the trait) to control hypopus induction. The results are consistent with a variable threshold whose level depends on diet quality. Different trophic conditions set the threshold at different points along the genetic scale resulting in different proportions of hypopus-forming and directly developing individuals within the population. The threshold, therefore, converts the concealed continuous genetic variation underlying the trait into a discontinuous response of the mite.     

Variation in dispersal mortality and dispersal propensity among individuals: the effects of age, sex and resource availability

1.  Dispersal of individuals between habitat patches depends on both the propensity to emigrate from a patch and the ability to survive inter-patch movement. Environmental factors and individual characteristics have been shown to influence dispersal rates but separating the effects of emigration and dispersal mortality on dispersal can often be difficult. In this study, we use a soil mite laboratory system to investigate factors affecting emigration and dispersal mortality.
2.  We tested the movement of different age groups in two-patch systems with different inter-patch distances. Differences in immigration among age groups were primarily driven by differences in emigration but dispersal mortality was greater for some groups. Immigration declined with increasing inter-patch distance, which was due to increasing dispersal mortality and decreasing emigration.
3.  In a second experiment, we compared the dispersal of recently matured males and females and tested the impact of food availability during the developmental period on their dispersal. Dispersal was found to be male biased but there was no significant sex bias in dispersal mortality. There was some evidence that food availability could affect emigration and dispersal mortality.
4.  These results demonstrate that both emigration and dispersal mortality can be affected by factors such as individual age and resource availability. Understanding these effects is likely to be important for predicting the fitness costs and population consequences of dispersal.     

Habitat use and dispersal of the invasive crayfish Procambarus clarkii in ephemeral water bodies of Portugal

We used radio-telemetry to analyze habitat use and dispersal of the invasive crayfish Procambarus clarkii in the extreme environmental conditions of a temporary river in southern Portugal. The rationale of this study was that an understanding of the properties that make this species a successful invader can be of help for the conservation of freshwater biodiversity. The results showed that: (1) crayfish displaced at a similar rate (ranging 2.5-38 m d^-1) as other European populations; (2) movement was faster at night; (3) crayfish movement had no clear environmental correlates, except for water temperature; (4) peaks of more intense locomotion were intercalated with longer periods of slow or null speed; and (5) P. clarkii did not excavate burrows in the study habitat, but took refuge under boulders and most often occupied complex microhabitats (e.g., vegetated sections of the river). The conclusion was that, notwithstanding their extreme conditions, ephemeral water bodies in southern Europe are highly susceptible to invasion by P. clarkii.     

The relative importance of dispersal and local processes in structuring phytoplankton communities in a set of highly interconnected ponds

1. The recognition that both local and regional processes act together in shaping local communities makes determining their relative roles in natural communities central to understanding patterns in community structure. 2. We investigated the relative influence of these processes on the phytoplankton communities of a highly interconnected pond system. We sampled the phytoplankton communities of 28 ponds concurrently with 20 local environmental variables. 3. We found that phytoplankton community variation, in terms of both phytoplankton community composition (PCC) and diversity, was only significantly explained by local environmental variables. These were mainly associated with the contrasting clear‐water and turbid ecological states of the shallow ponds studied. Clear‐water conditions favoured only a few taxa, resulting in a significantly lower taxon diversity and richness under these conditions. 4. The failure to explain variation in PCC by a dispersal model based on the water flow between ponds points at very effective species sorting. This is attributed to the high population turn‐over rates and sensitivity to environmental conditions of phytoplankton communities. Some evidence was found, however, that dispersal influences local communities through mass effects between neighbouring ponds. 5. Overall, our results emphasize both the strong selection pressure that components of the food web exert on phytoplankton communities and the high potential of these communities to respond to such environmental change, thereby effectively opposing the homogenizing effects of continuous dispersal.     

Avian seed dispersal and seedling distribution of the endangered tree species,Taxus chinensis,in patchy habitats

Background: There is limited understanding about bird dispersal behaviour and seedling distribution of endangered tree species in patchy environments, although these processes are important for plant species persistence.

Aims: We tested how patch features affected bird behaviour and seed dispersal, and thus seedling distribution of the endangered Chinese yew tree (Taxus chinensis).

Methods: In the present study, we combined field data of bird dispersal behaviour and GIS-based information to elucidate the influence of spatial features of habitat patches on bird dispersal behaviour, and the resulting effects on the seedling distribution of the endangered Chinese yew in two patchy habitats.

Results: Our results showed that the only seed source patch could attract eight bird species for dispersal at the two sites. Post-foraging movements of bird dispersers was strongly related to both topography and the relative locations of habitat patches. Yew seedlings aggregated only at the seed source and bamboo recruitment patches, which was affect by both the spatial distribution of recruitment patches and patch use by dispersers.

Conclusions: Our results emphasise that bamboo patches in both patchy environments provide the necessary conditions for germination of yew seeds, and the post-foraging behaviour of dispersers determines seed deposited in these patches. Our study highlights the importance of the dispersal behaviour of frugivorous birds in the successful regeneration and colonisation of yew populations in patchy habitats.     

Locomotion in copepods: pattern of movements and energetics of Cyclops

The cost of swimming in copepods has generally been estimated through the application of fluid dynamics theory to data on velocity and acceleration obtained by means of movies. It has also been estimated through the changes in fat content of copepods after sustained swimming (i.e. vertical migration). However, the range of estimated costs of locomotion is exceedingly large (from 0.1% to 95% of total metabolism). This communication studies the pattern of swimming movements and the work done by Cyclops, using high speed cinematographic techniques. The contribution of swimming to the energy expenditure of the individual is estimated, and consideration of the possible role of rubber-like proteins in the cuticle of copepods is made.     

Dispersal and colonisation of plants in lowland streams: success rates and bottlenecks

Plant dispersal and colonisation, including rates of dispersal, retention, colonisation and survival of dispersed propagules (shoots and seeds), were studied in a 300-m stream reach in a macrophyte-rich lowland stream during one growing season. Relationships between colonisation processes and simple flow parameters were tested. Each fortnight during a growing season, the number of dispersed plant propagules and the number of new and lost plant colonisations since the last sampling day were recorded. The retention of dispersing shoots was tested on two occasions during the growing season by releasing plant shoots and subsequently re-collecting the retained shoots in the study reach. The main bottleneck for plant colonisation in macrophyte-rich lowland streams is the primary colonisation (development of attached roots in the sediment from vegetative propagules or seedlings) of retained shoots and seeds, due in part to low retention success (1% of the dispersed shoots per 100-m reach) and to unsuccessful colonisation of retained shoots (3.4% of retained shoots colonised). The number of drifting shoots and seeds per day during the growing season were 650–6,950 and 2,970–62,780, respectively, and caused no constraint to colonisation. The survival rate of primary colonists was high with 80% surviving during the first growing season and about 50% surviving the first winter. There was no relationship between number of drifting shoots and flow, but the number of drifting seeds increased with flow. The number of colonisations between two consecutive sampling days correlated to the extent of low flow in the period. The loss rate of colonisations correlated to high flow events, but was low overall. My study strongly indicates that the number of propagules is not a constraint to colonisation in macrophyte-rich lowland streams. Rather, I conclude that primary colonisation is the main constraint to regaining vegetation in lowland streams in general and in vegetation-free rehabilitated streams in particular. Therefore, if plant colonisation is a target for stream rehabilitation, it is important to enhance retention and colonisation of propagules by creating areas of low flow and by providing physical obstacles to work as retention agents in the stream. Handling editor: L. M. Bini     

Tree dispersal strategies in the littoral forest of Sainte Luce (SE-Madagascar)

Zoochory is the most common mode of seed dispersal for the majority of plant species in the tropics. Based on the assumption of tight plant-animal interactions several hypotheses have been developed to investigate the origin of life history traits of plant diaspores and their dispersers, such as species-specific co-evolution, the low/high investment model (low investment in single fruits but massive fruiting to attract many different frugivores versus high investment in single fruits and fruit production for extended periods to provide food for few frugivores), and the evolution of syndromes which represent plant adaptations to disperser groups (e.g. birds, mammals, mixed). To test these hypotheses the dispersal strategies of 34 tree species were determined in the littoral forest of Sainte Luce (SE-Madagascar) with the help of fruit traps and tree watches. The impact of fruit consumers on the seeds was determined based on detailed behavioral observations. Phenological, morphological and biochemical fruit traits from tree species were measured to look for co-variation with different types of dispersal. No indication for species-specific co-evolution could be found nor any support for the low/high investment model. However dispersal syndromes could be distinguished as diaspores dispersed by birds, mammals or both groups (mixed) differ in the size of their fruits and seeds, fruit shape, and seed number, but not in biochemical traits. Five large-seeded tree species seem to depend critically on the largest lemur, Eulemur fulvus collaris, for seed dispersal. However, this does not represent a case of tight species-specific co-evolution. Rather it seems to be the consequence of the extinction of the larger frugivorous birds and lemurs which might also have fed on these large fruits. Nevertheless these interactions are of crucial importance to conserve the integrity of the forest.     

Endogenous swimming rhythms underlying secondary dispersal of early juvenile blue crabs, Callinectes sapidus

Blue crab, Callinectes sapidus Rathbun, megalopae settle in seagrass or other complex submerged aquatic habitats in estuaries, where they metamorphose to the first juvenile (J1) crab stage. Within tidal areas, early juveniles (J1-2) leave such nursery areas by undergoing secondary dispersal during nocturnal flood tides. The present study determined whether J1-2 blue crabs have a biological rhythm in vertical swimming activity that contributes to secondary dispersal. Endogenous rhythms in vertical swimming were determined for (1) J1-2 crabs collected from two estuaries with semi-diurnal tides, (2) J1 crabs that metamorphosed from the megalopal stage in the laboratory the day after collection, and (3) premolt megalopae that metamorphosed to J1 crabs under constant conditions during the experiment. In all cases, a circadian rhythm was present in which crabs swam vertically during the time of night in the field. The time of peak vertical swimming did not correspond to the time of flood tide at the collection sites, but did consistently occur at night, with a mean around midnight. While responses to environmental factors probably control the onset and end of vertical swimming by early juvenile blue crabs during flood tides in tidal areas, a circadian rhythm underlies secondary dispersal at night.     

Spatial scale and meiobenthic copepod recolonisation: testing the effect of disturbance size in a seagrass habitat

A central problem in relating disturbance to community structure lies in determining how community structure is affected by the size of disturbance events. In soft-bottom habitats, recovery rate and patterns of macrobenthic community are usually affected by the spatial scale of disturbance. Thus far, no studies have explicitly addressed these issues for meiobenthic copepods. To test the effects of the size of hypoxia/anoxia disturbance on the recovery of meiobenthic copepod communities in a vegetated (Ruppia cirrhosa) sediment, a field experiment was set up in Valle Smarlacca, a brackish lagoon on the northern Adriatic coast of Italy. Plots of three different sizes—small (40×40 cm), medium (80×80 cm) and large (160×160 cm)—were exposed to experimentally induced hypoxia/anoxia for 5 days. Control plots of 40×40 cm were added, for comparison with ambient abundance. Recolonisation and community recovery were then observed for 12 days, with samplings on days 0, 1, 3, 5, 7, 9 and 12. Sampling was designed to focus on the distance from source pools of colonists. The induced anoxia had a severe impact on the copepods, but the impact of the disturbance was independent of plot size. Copepod abundance increased linearly over time, and no differences in recolonisation rate among the differently sized plots were observed. Recolonisation comprised two phases: until day 3, abundances were low and very similar in all plot sizes; from day 5 onwards, abundances of the dominant species (which were the same in control and disturbed plots) increased, and a more diversified pattern among disturbance sizes was observed. Multivariate analyses showed a gradual response of community structure to disturbance size: copepod assemblages in small plots attained the same structure of the control plots at day 5, while for larger-sized plots this occurred later and was observed on the following sampling date. However, clear differences among the three disturbance sizes were never detected. Variability in community structure seemed to respond more to the overall impact of disturbance than to the size of the disturbed area. In the seagrass meadows of the Valle Smarlacca, several factors seem to influence the structural organisation of meiobenthic copepod communities during recolonisation processes. Among others, the recovery of the vegetated habitat to suitable conditions seems to play a much more relevant role than the size of the disturbed patches.     

Post-settlement dispersal: the neglected link in maintenance of soft-sediment biodiversity

Seafloor integrity is threatened by disturbances owing to human activities. The capacity of the system to recover from disturbances, as well as maintain resilience and function, depends on dispersal. In soft-sediment systems, dispersal continues after larval settlement, but there are very few measurements of how far the post-settlers disperse in nature. Spatial scales of post-settlement dispersal are, however, likely to be similar to pelagic larval dispersal because of continued, frequent, small-scale dispersal over longer periods. The consequences of this dispersal may be more important for the maintenance of biodiversity and metacommunity dynamics than is pelagic larval dispersal, because of the greater size and competency of the dispersers. We argue that an increased empirical understanding of post-settlement dispersal processes is key for predicting how benthic communities will respond to local disturbances and shrinking regional species pools, with implications for monitoring, managing and conserving biodiversity.     

Chemically-mediated interactions in benthic organisms: the chemical ecology of Crambe crambe (Porifera,Poecilosclerida)

Five temporary forest pools at Noxubee National WildlifeRefuge,Noxubee Co., Mississippi were surveyed monthly for three yearstogain a better understanding of the dynamics of temporaryaquatichabitats. The objective of this study was to characterize thephysicochemical and biological changes in temporary pools inorderto assess the temporal habitat diversity. These ecosystems,allwithin no more than 4 km of one another, were heterotrophicwith adetrital-based food web derived from allochthonous leaflitter.These pools were chosen because of their close proximity tooneanother, they historically filled and dried seasonally, andtheywere known breeding sites for resident amphibian populations.Only47% of the amphibian cohorts inhabiting the pools appeared tothrive and metamorphose prior to pool desiccation. Successfuldevelopment and dispersal of larvae was variable among poolsandyears. We found that the filling cycles differed amonghabitats andthat physiochemical and biological parameters were highlyvariable.Our data suggest that ephemeral pools in this central piedmontregion of Mississippi are each unique and represent habitatsof lowpredictability for amphibian breeding and success. We concludethatit is erroneous to draw generalizations regarding a typicaltemporary pool ecosystem within this region.     

Diel and seasonal vertical distribution of meiobenthic copepods in muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay)

The vertical distribution of meiobenthic copepods was investigated within muddy sediments of a eutrophic lagoon (fish ponds of Arcachon Bay, France). The aim of the study was to determine if in muddy sediments, as previously established in sandy sediments, meiobenthic copepods migrate vertically according to the seasons or diel periods. Two experimental approaches were used, viz: a three-season comparison was made of the diel vertical distribution of the harpacticoid Canuella perplexa T. & A. Scott (1893) and secondly the depth distribution of a meiobenthic copepod assemblage was followed for a 24 h period, in shallow water subtidal locations. The harpacticoid C. perplexa vertically migrated through the top three centimeters of the sediment, showing diel and seasonal variations in depth distribution. The differential vertical distributions shown by the dominant meiobenthic populations suggest that emergence into the water column may mainly concern surface dwelling copepods. The physical and biological factors affecting seasonal and diel changes in the copepod assemblage of the fish ponds are discussed.