Morphometry and diet of Mormyrus rume in the Lekki lagoon,Nigeria

Aspects of the biology of Mormyrus rume (Cuvier and Valenciennes) in Lekki lagoon were investigated. This included the length-weight relationship, condition factor, food and feeding habits and the fecundity of the fish species. The major fishing methods employed for collecting the 225 specimens were castnetting and setnetting. The total lengths ranged from 15.0 to 24.9 cm while the standard lengths ranged from 13.0 to 23.0 cm. The body weights also ranged from 26.2 to 99.3 g. The fish exhibited isometric growth in the lagoon. The mean condition factor obtained was 1.20. The condition factor generally decreased with increase in individual sizes. The major food items were detritus and plant parts. The population of males was significantly higher than the females. The gonadosomatic index showed that M. rume in the Lekki Lagoon uses an average of 7.89% of its body weight in egg production. Fecundity ranged from 741 to 6000 eggs with an average of 2991 eggs per female.     

Helminth parasites of Clarias gariepinus (Clariidae) in Lekki Lagoon, Lagos, Nigeria

A total of 360 randomly selected specimens of Clarias gariepinus (Clariidae) recovered from Lekki Lagoon were examined for intestinal helminth parasites. Parasite prevalence and worm burden were low; 17 (4.72%) of the specimens examined were infected with gastrointestinal helminths. The helminth worms recovered include, three cestodes Polyonchobothrium clarias, Stocksia pujehuni and Wenyonia acuminata and a nematode, Paracamallanus cyathopharynx. There was no statistically significant difference in the infection of the male and female Clarias gariepinus; the infection rates in male and female samples were 5.75% and 3.76% respectively. Parasite prevalence was related to the length and weight of the specimens. The fish samples were observed to show negative allometric growth and smaller samples recorded higher helminth infection.     

Distribution, reproduction and growth of the catfish, Chrysichthys walkeri (Gunther) in the Lekki Lagoon, Nigeria

An investigation was made on the biology of the catfish, Chrysichthys walkeri (Gunther) occurring in the Lekki Lagoon. The catfish was evenly distributed over the six sampled stations of the lagoon with the sites of the shallow water stations probably serving both as breeding and nursery grounds.
Fecundity estimates for this species ranged from 896 to 4168 eggs. The average number of eggs per female was 2084. Laboratory incubated eggs hatched after 3 days with the yolk sac being completely absorbed on the seventh day. The fry averaged 8.6 mm on their first day of life.
The catfish attained a maximum total length of 25.7 cm within a period of 2 years. There were no significant differences in the growth pattern of this species during the dry and rainy seasons.     

The diversity of small eukaryotic phytoplankton (< or =3 microm) in marine ecosystems

Small cells dominate photosynthetic biomass and primary production in many marine ecosystems. Traditionally, picoplankton refers to cells ≤2 μm. Here we extend the size range of the organisms considered to 3 μm, a threshold often used operationally in field studies. While the prokaryotic component of picophytoplankton is dominated by two genera, Prochlorococcus and Synechococcus , the eukaryotic fraction is much more diverse. Since the discovery of the ubiquitous Micromonas pusilla in the early 1950s, just over 70 species that can be <3 μm have been described. In fact, most algal classes contain such species. Less than a decade ago, culture-independent approaches (in particular, cloning and sequencing, denaturing gradient gel electrophoresis, FISH) have demonstrated that the diversity of eukaryotic picoplankton is much more extensive than could be assumed from described taxa alone. These approaches revealed the importance of certain classes such as the Prasinophyceae but also unearthed novel divisions such as the recently described picobiliphytes. In the last couple of years, the first genomes of photosynthetic picoplankton have become available, providing key information on their physiological capabilities. In this paper, we discuss the range of methods that can be used to assess small phytoplankton diversity, present the species described to date, review the existing molecular data obtained on field populations, and end up by looking at the promises offered by genomics.     

Successional patterns of aquatic macrophytes in Jebba Lake, Nigeria

Macrophyte succession in Jebba Lake, Nigeria, was observed through the first four years after impoundment. Two distinct serai phases, a floating fern phase and a draw-down flora phase could be recognized. The floristic composition of the macrophyte vegetation was also investigated to check earlier predictions (Obot & Mbagwu, 1986) on the probable structure of the macrophyte flora. The failure of obligate floating macrophytes such as Pistia, Azolla and Salvinia to establish in the lake as predicted is discussed. However, rooted emergent macrophytes were observed to be more successful than would be expected from the predictions.     

Variability and interactions of phytoplankton and bacterioplankton in Varano lagoon (Adriatic Sea)

Bacterial abundance was investigated in Varano lagoon for a12 month period. The concentrations were found to be quite high(1.8 ± 2.2x10⁹cells l^-1) as well as being coupled tophytoplankton biomass and phosphorus content. However, an inverserelationship with nitrogen was detected.     

A quantitative analysis of the annual phytoplankton cycle of the Magdalena lagoon complex (Mexico)

An annual cycle of the micro- and nanophytoplankton cell densitiesof whole water samples in combination with the species composition,distribution and diversity of the microphytoplankton fractionin the Magdalena lagoon system, Mexico, has been studied ona bi-monthly basis. Two major patterns were detected: from Novemberto May, high microphytoplankton densities (0.5–1.5 10⁶cells l^–1 prevail throughout a large part of the investigatedarea; from late spring to late autumn cell densities are muchlower (5–250 10³ cells l^–1). During each perioda number of microplankton assemblages occur, each with its characteristicdiversity and stability. The distribution and density of themicrophytoplankton is clearly related to the presence of nutrient-richwater pockets and the prevailing winds for part of the year,as documented in earlier hydrological studies. The nanophytoplanktonplayed a minor role during most of the year; this fraction dominatedquantitatively in only a few cases. Based on these data, theMagdalena lagoon complex can be considered a very productivearea. This is further substantiated by the presence of largequantities of several sardine and mackerel species, feedingalmost exclusively on microphytoplankton. This reveals the existenceof an important short chain pathway in the food web of thiscoastal lagoon system     

On the phytoplankton of Awba reservoir, Ibadan, Nigeria

The physico-chemical characteristics and phytoplankton of Awba reservoir in the University of Ibadan, Nigeria, were monitored to determine the impact of eutrophication on phytoplankton composition. The principal component analysis identified three major components influencing the physicochemistry of the water, namely trace metals, dissolved oxygen and ionic composition. Comparative analysis with a previous study showed a phenomenal increase in zinc, copper and iron levels over a 10-year period. Furthermore, the ferruginous nature of the soil contributed to the high levels of iron which exceeded the World Health Organization Standards for drinking water quality. The most abundant phytoplankton species was Microcystis aeruginosa which has been implicated in toxic blooms in freshwaters. The conditions favouring cyanophyte blooms and their implications are discussed.     

Seasonal distribution of phytoplankton in the Aby lagoon system,Ivory Coast,West Africa

Seasonal variability of phytoplankton species composition, abundance and physical and chemical factors influencing phytoplankton dynamics were investigated in the Aby lagoon system, south-eastern Ivory Coast, covering the main climatic seasons in 2006–2007. Seasonal and spatial variability of nutrient concentrations in the system were influenced by freshwater inflow from the Bia and Tanoé rivers. The decrease in the salinity gradient in Aby Lagoon, which is permanently stratified during the long dry season, increased the bottom inputs of soluble reactive phosphate and soluble reactive silicate which, in combination with good light penetration during the long dry season, enhanced phytoplankton production in the system. During the rainy seasons, water discharges into the system washed phytoplankton biomass out, preventing the development of blooms. Overall, 192 taxa from eight phyla were recorded: Bacillariophyta (32%), Chlorophyta (31%), Cyanobacteria (23%), Euglenophyta (12%), Dinophyta (0.5%), Xanthophyta (0.5%), Chrysophyta (0.5%) and Rhodophyta (0.5%). During the long dry season, Cyanobacteria cells comprised >50% of the phytoplankton abundance. The main phytoplankton taxa responsible for this high abundance were Microcystis aeruginosa, Oscillatoria princeps, Pseudanabaena limnetica, Aphanizomenon sp. 2 and Anabaena planctonica.     

Successional dynamics of the phytoplankton in the lower part of the river Ebro

The temporal and spatial dynamics of phytoplankton have beenstudied in four sites located along the last 60 km of the riverEbro, over a period of 1 year. Diatoms and green algae werethe most abundant groups; blue-green algae were frequent onlyin autumn. Asterionella formosa dominated the winter phytoplanktonassemblages. In autumn, spring and early summer centric diatomswere dominant: Aulacoseira granulata (Ehr.) Simonsen in autunm;Cyclotella sp. p1., Skeletonema potamos (Weber) Hasle and StephanodisciLssp. p1. in spring. A great abundance of green algae was observedduring the summer, mainly in the lower sites. In the sites closerto the mouth, the spring maximum of centric diatoms extendedto the summer. Mainly in the downstream sites, a remarkablegrowth of Acrinocyclus normanii f. subsalsa (Juhl.-Daunf.) Hustedtand Stephanodiscus hantzschii f tenuis (Hust.) Hak. & Stoerm.was added to green algae in the late summer. As has been investigatedthrough a principal component analysis, the phytoplankton temporalsuccession and longitudinal differences between the sites maybe affected by the variations in flow and the increase of waterconductivity downstream; both factors seem to act together.The river is rather homogeneous with respect to the phytoplanktonassemblages during the winter and spring months, and from latespring to the following autumn, differences greatly increaseboth in time and downstream.     

Seasonal pattern of ammonium (methylamine) uptake by phytoplankton in an oligotrophic lake

Our primary objective was to determine if a relationship existed between seasonal change in phytoplankton and high affinity for (K _m) or uptake rates (V _maX) of ammonium which might explain seasonal phytoplankton succession in oligotrophic ecosystems. We measured ammonium uptake using [¹⁴C]-methylamine and estimatedK _m andV _max using Hanes Plots at 2-week intervals during 6 months of thermal stratification in Mountain lake, Virginia (37° 22 N, 80° 32 W). Community composition, nutrient levels, and other variables were determined in all uptake experiments. A second objective was to determine if ammonium was preferentially utilized over nitrate and to characterize further the ammonium transport system.V _max increased steadily from May until the end of July, each increase coinciding with major changes in the phytoplankton community. Cryptophyceans dominated in May, chlorophyceans in June and July, and cyanophyceans from the end of July to late October. With cyanophycean dominance,V _max declined until chlorophyceans reestablished dominance in late October. By contrast,K _m values increased from May to the end of July, but thereafter showed no correlation. Acetylene reduction experiments showed no nitrogen fixation during late summer and fall when blue-green algae were present. Preference for ammonium was implied also by negative nitrate reductase assays. Overall, the coincidence ofV _max andK _m values for [¹⁴C]-methylamine uptake and changing phytoplankton community structure suggests the possibility that successive algal communities may be changing as a result of specific species differences in ammonium affinity and uptake rates.     

The meiofaunal community structure of a Mediterranean lagoon (Gialova lagoon, Ionian Sea)

The higher taxonomic structure of a meiofaunal community was investigated in an Eastern Mediterranean lagoon (Gialova lagoon, Ionian Sea). Seven stations were sampled on a seasonal basis during 1995–1996. Stations within the lagoon were found to support a maximum of 14 meiofaunal taxa with densities ranging from 17 to over 2000 individuals per 10 cm². Nematodes were not always the most abundant taxa, although they dominated about half of the total 28 samples. Uni- and multivariate analyses were employed to study the community structure. The distribution pattern of the meiofaunal community varied both across the lagoon and over the seasons. On the basis of the spatial differences a meiofaunal coenocline, correlated with the degree of isolation, was observed, composed of mainly two zones: one defined by the area close to the marine channel and the other the more isolated area in the inner lagoon. Meiofaunal distribution pattern was not clearly correlated to one environmental variable, but rather to many, and spatial and seasonal effects could be seen. Received: 2 March 1999 / Received in revised form: 6 December 1999 / Accepted: 9 December 1999     

Temporal and spatial fluctuations of phytoplankton in a tropical coastal lagoon, southeast Brazil.

Spatial and temporal variability of the phytoplankton community in the tropical coastal Imboassica lagoon, an environment naturally isolated from the ocean by a narrow sandbar, was analysed every two weeks for 19 months by sampling three sites. During this study, the lagoon received direct input of marine water three times, resulting in remarkable salinity, nutrient concentrations and phytoplankton biomass variations in both temporal and spatial aspects. The phytoplankton biomass presented relatively low values ranging, on average, from 0.54 mg x L(-1) in the station closest to the sea (station 1) to 1.34 mg x L(-1) in the station close to a macrophyte bank (station 3). Diatoms and cryptomonads dominated in stations 1 and 2 (located relatively close to station 1, yet receiving the runoff of domestic sewage), and euglenoids, cryptomonads and dinoflagellates at station 3. Stations 1 and 2 usually presented the same dominant species but station 2 presented a higher phytoplankton biomass. On the other hand, station 3 showed more similar results concerning phytoplankton biomass with station 2, however the dominant species were usually different. The high fluctuations of salinity and the reduced nutrient availability are pointed out as the main factors structuring the dynamics of the phytoplankton community at the Imboassica lagoon.     

Macroinvertebrates associated with Chara in a tropical coastal lagoon (Imboassica lagoon,Rio de Janeiro,Brazil)

Imboassica lagoon is an urban coastal lagoon located in the municipality of Macaé (RJ), which has been exposed to a process of artificial eutrophication through the inflow of untreated sewage, as well as artificial openings of the sandbar that separates it from the ocean, provoking drastic modifications in this ecosystem. The sampling for the analysis of the community of macroinvertebrates associated with Charopyceae (Chara angolensis e C. fibrosa) were performed between October 1995 and October 1997, with a total of 9 samplings at two sampling stations: one located in the innermost area of the lagoon and another at the mouth of the main sewage channel, close to the sandbar. Throughout this period, four artificial sandbar-opening events were recorded, resulting in changes in the biomass of the macroalgae and in the densities of the macroinvertebrate populations. Through the analysis of the density of organisms per square meter, and density of organisms per 100 g dry weight of Chara, it was established that the biomass of the macroalgae has a direct influence on the density of the associated macrofauna. The greater development of the periphytic community in the area close to the inflow of sewage allows for the development of a community of macroinvertebrates with high densities, composed mainly of scraping organisms, such as the mollusc Heleobia australis (Hidrobiidae).     

Diversity, biomass and distribution pattern of Sargassum beds in the South West lagoon of New Caledonia (South Pacific)

Sargassum (Phaeophyceae, Fucales) is a genus of worldwide distribution recently recognised to proliferate in several regions of the South Pacific. In New Caledonia, species of this genus naturally structure one of the major lagoon habitats but their extent, composition and biomass remain largely unknown. To fill these gaps in our knowledge over large areas, we applied a combination of remote sensing and in situ methods applied to the Neo Caledonian South West Lagoon. Space borne high resolution Landsat (30-m resolution) and Quickbird (2.4-m resolution) images of the Neo Caledonian South West lagoon were used to estimate the spatial extent of the different beds of interest. Species composition was determined for 11 Sargassum beds and seasonal variations were investigated for four representative beds over an 18 month period using quadrats and transects. Relationships between surface cover and biomass were estimated from seasonal field data sets. Finally, four methods requiring variable levels of sampling effort were designed to estimate the total biomass at the scale of each bed, considering (or not) the specific composition, and spatial and temporal variations. Seven Sargassaceae species were identified. Mean surface cover (24.4–51.6%) and total biomass [3.4–1,461.9 t dry matter (DM)] varied widely between beds. Overall, biomass temporal variations were not significantly different, but species-level variations seemed to be bed-specific. The extent of the 11 beds was 9 km²; their total biomass was estimated and compared using each of the four methods, and the most precise method provided an estimate of 2,900 t DM. This study demonstrates a way of characterising Sargassum beds, efficiently and on a large scale, using a combination of remotely sensed and in situ data. These methods should be useful for possible future biomonitoring of Sargassum beds in New Caledonia, and in other areas worldwide.     

Pigment-specific rates of phytoplankton growth and microzooplankton grazing in a subtropical lagoon

Phytoplankton growth and microzooplankton grazing rates wereevaluated in one station in Bahía Concepción,located in the middle region of the Gulf of California, México.We used high-performance liquid chromatography (HPLC) estimationsof phytoplankton pigment signatures to evaluate the annual variationof taxon-specific grazing and growth rates obtained with thedilution technique. Chlorophyll-a (Chl-a) concentrations variedwidely (0.34–3.32 µg L^–1) and showed two maxima,during late spring and autumn, associated with the transitionbetween mixed and stratified conditions. Phytoplankton growthrates varied seasonally with the lowest rates during summer(range: 0.01–2.55 day^–1 for Chl-a; 0.00–3.84day^–1 for Chl-b; 0.26–3.29 day^–1 for fucoxanthin;0.00–6.27 day^–1 for peridinin; 0.00–4.35 day^–1for zeaxanthin). Microzooplankton grazing was an important lossprocess (range: 0.0–1.89 day^–1 for Chl-a; 0.00–3.12day^–1 for Chl-b; 0.26–3.29 day^–1 for fucoxanthin;0.00–2.03 day^–1 for peridinin; 0.00–3.51 day^–1for zeaxanthin). Average grazing rates accounted 68–89%of estimated average phytoplankton pigment-specific growth rates.The analysis of pigment signatures indicates that diatoms anddinoflagellates were the dominant groups, and contrary to expectationfor typical subtropical lagoons, the specific growth rates inBahía Concepción showed a pronounced seasonalvariability, linked to transitional hydrographic conditions.Our results indicate a close coupling between the communitymicrozooplankton grazing and phytoplankton growth rates, withoutselective feeding behavior. These results suggest that microzooplanktonplay a critical role and may significantly modify the availabilityand efficiency of transfer of energy to higher trophic levels.     

The seasonal variation and distribution of phytoplankton in the River Oshun, Nigeria

The seasonal variation in abundance of the phytopiankton groups in the river Oshun before and immediately after the closure of the Asejire dam is described. The river was dominated by the Bacillariophyceae throughout the period before impoundment but soon after, the Volcocaceae and the Dinophyceae became preponderant at the lake although the diatoms remained dominant at the source. Also, the period of maximum abundance of the diatoms occurred 8 weeks before the other phytoplankton groups attained their maxima in the river. Correlation coefficient values enumerated by computer revealed the controlling effect of the discharge, transparency and nitrate nitrogen on phytoplankton development in the Oshun.     

A preliminary check-list of the phytoplankton of the Oshun River, Nigeria

During hydrobiological investigations on the River Oshun, plankton samples were taken with a hand net of fine mesh for 14 months (May 1968-June 1969). Thirty-seven of the sixty species of algae identified have not been previously recorded in Nigeria. The qualitative character of the Oshun algae indicates the dominating nature of the floods in mixing bottom-living and rock-dwelling algae with the few euplanktonic species.     

Bucephaline digeneans (Bucephalidae) in <Emphasis Type="Italic">Sphyraena putnamae</Emphasis> Jordan &; Seale (Sphyraenidae) from the lagoon off New Caledonia

Lethrinitrema gibbus n. g., n. sp. and L. dossenus n. sp. are described from the fish Lethrinus rubrioperculatus Sato collected off New Caledonia, South Pacific. Members of Lethrinitrema n. g. (Ancyrocephalidae) are characterised by having two pyriform haptoral reservoirs and ventral anchors with lateral grooves. The elongate tubular distal end of each reservoir bifurcates, draining into a superficial lateral groove on each side of the ventral anchors. The haptoral reservoirs are postulated to store secretory products which assist in attachment to the host. Lethrinitrema spp. also possess tandem gonads, a male copulatory organ without an accessory piece or with thinly sclerotised accessory piece, and a dextrolateral, non-sclerotised vaginal bulb. The two new species have small, poorly demarcated haptors with small haptoral armament and a crown-like piece on the tip of the inner root of the ventral anchors. They differ from each other in the shape and size of the ventral bar and male copulatory organ (40–45 μm in length in L. gibbus vs 24–30 μm in L. dossenus). Three other species, previously included in Haliotrema Johnston & Tiegs, 1922, are transferred to Lethrinitrema, i.e. L. chrysostomi (Young, 1968) n. comb., L. fleti (Young, 1968) n. comb. (both briefly redescribed from paratypes) and L. lethrini (Yamaguti, 1937) n. comb. All species of Lethrinitrema parasitise Lethrinus spp. (Lethrinidae), and there is evidence for the existence of further Lethrinitrema spp. on Lethrinus spp. in the Indo-Pacific region.     

Effects of nutrient supply and nutrient ratio on diversity–productivity relationships of phytoplankton in the Cau Hai lagoon,Vietnam

Diversity and productivity of primary producers are known to be influenced simultaneously by resource availability and resource ratio, but the relative importance of these two factors differed among studies and so far only entire phytoplankton communities were investigated which might ignore specific nutrient requirements and stoichiometric plasticity of different functional groups. We measured nutrient availability (DIN, total N [TN], total P [TP]), nutrient imbalance (TN:TP, DIN:TP, N:P_seston), species richness, and abundance of the whole phytoplankton community, as well as those specific for cyanobacteria, diatoms, and dinoflagellates in Cau Hai lagoon in Vietnam. We determined the correlation among these variables, using structural equation modeling. The models applied to the whole phytoplankton community indicated that the nutrient availability (particularly TP and DIN) drove variation in phytoplankton abundance and richness, and that abundance also depended on species richness. The models applied to different functional groups differed considerably from the entire community and among each other, and only a part of the models was significant. The relationship between nutrient availability (mainly TP) and abundance was driven by cyanobacteria, and the relationship between nutrient imbalance (only with N:P_seston) and species richness was driven by diatoms. Remarkably, the positive relationship between species richness and abundance, as consistently observed for the whole phytoplankton community, was only observed for one of the three functional groups (diatoms), indicating that resource complementarity occurs particularly among species of different functional groups. Our results emphasized that nutrient availability (TP and to a lesser extent DIN) as well as nutrient imbalance (albeit only with N:P_seston as proxy) were driving factors for the phytoplankton community in the Cau Hai lagoon and hence alterations in both of these factors leading to a shift in phytoplankton species composition and productivity.