Naithirithi T. Chellappa

Dominant and co-existing species of cyanobacteria from a eutrophicated reservoir of Rio Grande do Norte State, Brazil

Abstract This paper reports on the cyanobacterial population, its ecology, dominance and coexistence characteristics in one annual cycle of a eutrophicated Gargalheiras reservoir (Marechal Dutra) of Acari, in the state of Rio Grande do Norte of Brazil. The study was conducted between November 1999 and May 2000, which included the dryand wet seasons. It is an old, man-made impounded water reservoir. The methodology included the collection of phytoplankton samples from the surface to the bottom in a fixed station to include four vertical profiles and to analyse them for physico-chemical and algological characteristics. Ecological indices, such as Shannon-Weaver for species diversity, Margalef’s species richness and Pielou’s evenness were calculated. The results reveal the characteristics of the eutrophic to the hyper trophic state for the Gargalheiras reservoir with the dominance of Cylindrospermopsis raciborskii, Raphidiopsis curvata, Microcystis aeroginosa and Oscillatoria sp during the dry period. Cages were suspended to culture Amazonian fish, Tambaqui, at the beginning of the wet period close to the sampling stations in the reservoir and treated for point source nutrient loading and disturbance factor. This localised disturbance stimulated the growth of Chlorophyceae species, which co-existed along with the species of cyanobacteria to finally dominate; coinciding with the stability of monsoon rain in May. The conclusion drawn from the study period revealed that the reservoir with high inorganic nutrients had reduced transparency, anoxic hypolimnion, elevated levels of electrical conductivity and the dominance of cyanobacteria during the dry period and the dominance of chlorophyceae in the wet period.

Harmful Phytoplankton Blooms and Fish Mortality in a eutrophicated reservoir of Northeast Brazil

The aim of this work was to study the eutrophication in the tropical freshwater ecosystems and the consequent cyanobacterial bloom formation and economical damage to fisheries and harmful effects to public health. Mass fish mortality due to toxin producing cyanobacterial blooms was registered during December 2003 in Marechal Dutra Reservoir, Acari/RN, Northeast Brazil. Phytoplankton and fish samplings were carried out on alternate days during the episode of fish mortality and monthly during January to June 2004. The cyanobacterial toxin was identified and quantified from the seston samples and liver of the dead fishes using the standard HPLC method. The results indicated that the toxic blooms of Cylindrospermopsis raciborskii and Microcystis aeruginosa were persistent for two weeks and represented 90% of the phytoplankton species assemblages. The lethally affected fishes were Oreochromis niloticus, Plagioscion squamosissimus, Cichla monoculus, Prochilodus brevis, Hoplias malabaricus and Leporinus friderici. The microcystin levels varied from 0.07 to 8.73µg L-1 the seston samples and from 0.01 to 2.59µg g-1in the liver samples of the fishes during the bloom period.

Phytoplankton community: indicator of water quality in the Armando Ribeiro Gonçalves Reservoir and Pataxó Channel, Rio Grande do Norte, Brazil

The current study analysed spatial-temporal modifications of the phytoplankton community and water quality, during dry and wet seasons. The phytoplankton community was studied in three areas: Armando Ribeiro Gonçalves Reservoir (ARG), which is an important public use reservoir in RN, Pataxó Channel (PC-before water treatment), Itajá, RN, and after the water treatment (WTP). Water samples from the reservoir were collected during both dry (January, February and November, 2006) and wet seasons (March to June, 2006). Quali-quantitative analyses of phytoplankton were carried out. Results indicated a qualitative similarity of the phytoplankton community in the three areas. However, significant differences were registered in these areas in relation to species relative abundance, with dominance of potentially toxic cyanobacteria, such as Planktothrix agardhii Gomont (dry season) and Microcystis aeruginosa Kutz (wet season). Ecological indexes obtained higher values before water treatment. Nevertheless, densities of cyanobacteria (organisms/mL) gradually reduced in the waters of the reservoir and of the Pataxó Channel before and after water treatment. After the treatment, density values of cyanobacteria were adequate for human consumption, according to the values established by the Health Ministry.

Ovarian development and spawning of Serra Spanish mackerel in coastal waters of Northeastern Brazil

The Serra Spanish mackerel, Scomberomorus brasiliensis is an important fishery resource of the Atlantic Ocean and is a major component of artisanal fisheries in northern and northeastern Brazil. Ovarian development and spawning period of S. brasiliensis were investigated using both macroscopic and histological techniques. Mean monthly values of GSI and ovarian maturation indicate that the main spawning period occurs during the rainy season.

Aspectos reprodutivos do cangati, Parauchenipterus galeatus Linnaeus (Osteichthyes, Auchenipteridae) da Lagoa de Extremoz, Rio Grande do Norte, Brasil

The Lake Extremoz is one of the three big lakes in the State of Rio Grande do Norte. The present work was carried out in this lake during the period of October 2000 to September 2001, which included the dry and the rainy seasons. Parauchenipterus galeatus Linnaeus, 1766 represent 10% of the commercially important species captured from this lake. Fish samples were collected on a monthly basis, besides registering the rainfall, temperature, and dissolved oxygen of the lake. The populational structure of cangati and the stage of maturation of the gonads were determined, besides the gonadosomatic relation. The results indicate that the study population presented higher mean values of total length and weight during the dry season. Mature fishes were caught during the months of May, June and July which represented the reproductive season.

Conservation status of an endangered annual fish Hypsolebias antenori (Rivulidae) from Northeastern Brazil

This work presents information regarding the biology and state of conservation of an endangered annual fish Hypsolebias antenori. Fish were captured from small seasonal pools located in Northeastern Brazil. The total body length, body mass, sex ratio, first sexual maturity were investigated. The sampled population showed sexual dimorphism. There was a predominance of females (60%) over males (40%) with a sex ratio of 1: 1.4 and males were bigger and heavier than the females. Amplitude of total length of males ranged from 2.6 to 7.1cm (4.1 ± 1.15) and that of females from 2.2 to 5.4 cm (3.6 ± 0.9). Amplitude of body mass of males varied from 0.25 to 7 g (1.3 g ± 1.4) and that of females from 0.12 to 2.1g (0.7 g ± 0.5). The total weight-length equation of males was Wt = 0.0108Lt3.172 with r = 0.9826 and of females was Wt = 0.0122Lt3.0114 with r = 0.9608. Females attained first sexual maturity at 3.2 cm (± 0.25) total length and males at 3.3 cm (± 0.08) total length. All temporary pools surveyed in Northeastern Brazil were in a high degree of degradation, suffering due to anthropogenic action. Reduced rainfall resulting from global climate change prevents the filling up of these pools, thus preventing the completion of the reproductive cycle of annual fishes. One factor hindering development of conservation strategies is limited literature on biology and conservation status of annual fishes. There is a need for conservation measures to protect annual fish populations, especially creation of protected areas in the Brazilian semiarid region.

ESTRATÉGIAS REPRODUTIVAS DE SETE ESPÉCIES DE PEIXES DAS ÁGUAS COSTEIRAS DO RIO GRANDE DO NORTE, BRASIL

O presente trabalho verificou as estrategias reprodutivas de sete especies de peixes marinhos da regiao costeira do Rio Grande do Norte, Brasil. Tracos da historia de vida dos peixes em ambientes relativamente estaveis sugerem um modelo de tres estrategias reprodutivas: (1) estrategistas oportunistas, sao peixes de pequeno tamanho corporal com primeira maturacao precoce, periodo de vida curto com baixa fecundidade; (2) estrategistas sazonais, sao peixes de tamanho corporal intermediario, primeira maturacao intermediaria e fecundidade intermediaria a alta; e (3) estrategistas de equilibrio, sao peixes de tamanho corporal grande, primeira maturacao tardia com longo periodo de vida, alem de alta fecundidade. Os aspectos reprodutivos de Hirundichythys affinis , Hemiramphus brasiliensis, Pomadasys corvinaeformis , Oligoplites palometa , Scomberomorus brasiliensis , Lutjanus synagris e Mugil curema foram verificados, considerando-se o tamanho do corpo, proporcao sexual, comprimento de primeira maturacao sexual, aspectos do desenvolvimento das gonadas, fecundidade, tipo de desova e periodo reprodutivo dos peixes. Os resultados indicam que H. affinis , H. brasiliensis , P. corvinaeformis e O. palometa podem ser considerados como estrategistas oportunistas. Entretanto, S . brasiliensis, L. synagris e M. curema podem ser considerados como estrategistas de equilibrio. Este estudo fornece informacoes sobre os aspectos reprodutivos dos peixes dos estoques pesqueiros das aguas costeiras do Rio Grande do Norte, Brasil.

Morphofunctional changes of phytoplankton community during pluvial anomaly in a tropical reservoir

The present study focuses on the structure and function of phytoplankton community during periods of marked changes in hydrological traits, influenced by an atypical climatic event (La Niña) and its impact on Armando Ribeiro Gonçalves Reservoir of Rio Grande do Norte, situated in the Caatinga biome of northeastern Brazil. The main questions addressed were: What are the effects of environmental factors on the temporal variation of Morphologically Based Functional Group (MBFG) of phytoplankton community? How does the composition of cyanobacterial species shift in relation to high and low trends of phytoplankton diversity? The samples were collected monthly during 2008-2009 and analyzed for pH, temperature, electrical conductivity, dissolved oxygen content and the nutrients, such as, nitrate-nitrogen, ammoniacal nitrogen, total nitrogen and orthophosphate. Phytoplankton samples were collected for both qualitative and quantitative analyses to evaluate species richness index and species diversity index. The data was divided into two distinct hydrodynamic periods of instability and stability. The results demonstrate considerable changes in dissolved oxygen content, water transparency and nitrogen nutrients, which directly influenced the MBFG of phytoplankton community in space and time. The instability of reservoir water was caused by heavy rainfall, which exerts atypical external disturbances. The seasonal variation of MBFG demonstrates a change in cyanobacterial composition and their diversity during instability and stability periods. MBFG VII, composed by colonial cyanobacteria with mucilage, was associated with reduced values of electrical conductance and alterations in pH. The predominance of filamentous species with heterocyst (MBFG III) occurs only during the hydrodynamic stability period and did not show significant association with analyzed parameters. The co-dominance of MBGFs III, V and VII along with high species diversity of phytoplankton community occurred during the second hydrodynamic instability period which was associated with the reduction in water temperature. It is concluded that the decrease in cyanobacterial species dominance and the general increase in the diversity of phytoplankton community are influenced by pluvial anomaly. The higher water level during the period of pluvial anomaly resulted in nutrient pulse and the mixing of water column in the reservoir, which determined the MBPG phytoplankton community distribution.