Parasitic monogenoideans of Sciades herzbergii as bioindicators of environmental quality in amazonian estuarines ecosystems

This study evaluated the use of gill parasitic monogenoideans from Sciades herzbergii (Siluriformes: Ariidae) as bioindicators of environmental quality in Amazonian estuarine ecosystems. Fish were caught in the tidal channels in an impacted area - IA, near the port of São Luís and a reference area - RA, in the Caeté estuary, Bragança. The influence of the capture site and seasonality on parasite abundance, environmental variables and biometric data of hosts were verified. A total of 416 S. herzbergii specimens were analyzed. The weight and total length of fish from the RA were greater than those of the IA. The relative condition factor was influenced by seasonality. A total of 4,265 monogenoidean specimens from the following species were identified: Chauhanellus boegeri, C. susamlimae, C. velum, Calceostomella herzbergii and Dactylogyridae gen. sp. The seasonal mean parasitic abundance of C. susamlimae was significantly different, with the highest values recorded during the dry season. The mean abundance of C. herzbergii was influenced by seasonality and by the capture site. During the rainy period, the parasite indices in the RA were higher than those of IA. C. herzbergii is a bioindicator sensitive to low water quality, especially in relation to water turbidity in Amazon estuaries.

The dynamics of a frictionally-dominated Amazonian estuary

The hydrodynamics, morphology and sedimentology of the Taperaçu estuary were investigated. This is one of several estuaries located within the largest mangrove fringe in the world, bordering the Amazon region, subject to a macrotidal regime and regionally atypical negligible fresh water supply. The results reveal widespread sand banks that occupy the central portion of the estuarine cross-section. Well-sorted very fine sandy sediments of marine origin prevail. Shorter flood phases, with substantially higher current velocities, were observed in the upper sector of Taperaçu, as expected for a shallow, friction-dominated estuary. However, ebb domination can be expected for estuaries with large associated mangrove areas and substantial estuarine infilling, both of which situations occur on the Taperaçu. The tidal asymmetry favoring flood currents could be the result of the absence of an effective fluvial discharge. Furthermore, it was observed that the Taperaçu is connected by tidal creeks to the neighboring Caeté estuary, allowing a stronger flux during the flood and intensifying the higher flood currents. As a whole, the results have shown a complex interaction of morphological aspects (friction, fluvial drainage, connections with neighbor estuaries, infilling and large storage area) in determining hydrodynamic patterns, thus improving the understanding of Amazon estuaries.

POPULATIONAL DYNAMICS OF Pseudodiaptomus marshi (CRUSTACEA: COPEPODA) IN THE CAETÉ ESTUARY (BRAZIL)

O presente estudo tem por objetivo principal avaliar a distribuição espacial e temporal da densidade e biomassa do copépodo planctônico Pseudodiaptomus marshi no Estuário do Caeté (Pará, Brasil), durante os meses de junho e dezembro de 1998 (estação seca), fevereiro e maio de 1999 (estação chuvosa). O Estuário do Caeté caracterizou-se por uma ampla variação espacial e temporal da salinidade (0,7±0,55 a 37,2±0,21). A análise de correlação de Spearman revelou uma correlação negativa significativa (rs = -0,75; p<0,05) entre a salinidade e a densidade de P. marshi, sugerindo a preferência desta espécie por áreas estuarinas onde foram dominantes os regimes oligohalino-mesohalino. A relação peso-comprimento foi do tipo linear, sendo expressa pela equação: PS = 125,46 + 0,1467CP (r = 0,32; p<0,05). No presente estudo, os valores de densidade e biomassa variaram respectivamente de 0,0 a 21,4±18,26 ind.m-3 e 0,0 a 0,583±0,51 mg PS. m-3. As diferenças mensais na densidade (H = 6,71; p<0,05) e biomassa (H = 6,76; p<0,05) entre as três áreas de amostragem foram significativas somente em junho, com os maiores valores registrados no estuário interno. Os resultados revelaram que a variabilidade espacial e sazonal na ocorrência e distribuição de P. marshi foi fortemente regulada pela salinidade, com as maiores densidades e biomassas registradas simultaneamente aos menores valores de salinidade. Palavras-chave: Biomassa, copépodo, salinidade, estuário amazônico.

Reproductive biology and spatio-temporal distribution of Stellifer rastrifer, Stellifer naso and Macrodon ancylodon (Sciaenidae) in the Caeté estuary, northern Brazil

This study analyses the spatial and temporal distribution of the dominant Sciaenids in the Caeté estuary on the northern coast of Brazil. Samples were taken by otter trawls in four areas of the Caeté estuary between October 1996 and August 1997 six bimonthly. Stellifer rastrifer, Stellifer naso and Macrododon ancylodon presented the highest biomass out of eleven species of Sciaenidae caught. Minimum and mean length at first maturity were calculated and the main spawning periods determined. Changes in the spatio-temporal distribution of the three species were related to seasonal changes in estuarine salinity and spawning pulses. Larvae and juveniles of S. rastrifer, S. naso and M. ancylodon were found in the inner estuary while larger specimens were more abundant in the outer estuary with higher salinities. M. ancylodon spawned from October to February and rested from April to August whereas S. rastrifer and S. naso spawned throughout the year, though with two peaks, in October-December and June.

Food categories reconstruction and feeding consumption estimates for the Sciaenid Macrodon ancylodon (Bloch & Schneider), and the congeneric fishes Stellifer rastrifer (Jordan) and Stellifer naso (Jordan) (Pisces, Perciformes) in the Caeté Estuary, Northern Coast of Brazil

A quantitative method to estimate fish feeding consumption and energy intake from different food categories through the reconstruction of ingested preys based on hard not digestible body structures is presented. In order to establish the equations of the functional relationships between preys weight and body structures, stomachs of 1.086 specimens of Macrodon ancylodon (Bloch & Schneider, 1801), Stellifer rastrifer (Jordan, 1889), and Stellifer naso (Jordan, 1889) fish species were dissected. Consequently, preys reconstruction enabled a quantitative evaluation of food categories consumption. Results indicate a marked difference in diet composition and energy requirements according to fish species ontogenetic development.