Marine biology of the Sierra Leone River Estuary. 1. The physical environment

The Sierra Leone River Estuary is a relatively young drowned river valley, it is shallow except for a deep channel which passes close to the Freetown shoreline. The upper reaches merge into a network of creeks and channels fringed by large areas of mangrove swamps. It is a tidal estuary of the semi-mixed type with the saline oceanic water entering it on a diurnal cycle. The climate of Sierra Leone is marked by a very distinct change between a very wet rainy season and a dry season. The tidal range of the Estuary (spring 3.03m; neap 2.28m) does not impede normal use of the harbour. The tidal variations can be felt as far as 42 miles inland along the water courses of the Sierra Leone River and its tributaries. The volume of fresh water entering the Estuary is large during the rainy season and greatly reduced during the dry season. Consequently there is a marked fall in salinity during the rainy season and higher salinities due to the marine influence prevailing during the dry season. The nature of the shores and bottom, the hydrography and chemistry of the estuarine system have been outlined in relation to the prevailing climatic conditions.

A seven year study of the life cycle of the Mayfly Ephemera danica

Ephemera danica Müller, 1764 (Ephemeroptera) is one of the largest mayflies found in the British Isles with some females reaching over 30 mm. It is a common and widespread species found in rivers, lakes and streams throughout Europe and is particularly abundant in many of the lowland rivers of the British Isles. The larvae are burrowers – mainly found where silt accumulates below macrophytes. This article gives a general overview of research work on the factors affecting the life cycle of Ephemera danica over a seven year period (1995–2002) on two rivers, the River Test at Leckford in Hampshire and the North Wey at Tilford in Surrey.

Life cycle of Pisidium obtusale Jenyns. [Translation from: Informatsionnyi Byulleten Biologiya Vnutrennikh Vod No.3 17-21, 1969.]

Pisidium obtusale in the neighbourhood of Borka occurs in deep pools on upland bogs. The majority of water-bodies where this mollusc lives are temporary. Their bottoms are covered with sedges, and sometimes mosses occur. Evidently there is a marked attraction of P. obtusale to places overgrown by willow. In pools remote from scrub or woody vegetation it does not appear. Temporary water-bodies fill up with melt water in the middle or the end of April and finally dry up at the end of July or the beginning of August. Observations on the life cycle of P. obtusale started on 21 April 1966, following on the filling-up of the water-body by melt water. The findings of the study are presented in this paper.

Cytological aspects of gonadotropic cells and pre-opticoneurohypophysial neurosecretion during the ovarian cycle of Eudontomyzon danfordi. [Translation from: Studia Univ.Babes-Bolyai, Biologia 18 105-113, 1973.]

The connection between the activity of the gonadotropic cells of the hypophysis and the neurosecretion in the pre-optico neuro-hypophysial system in different groups of vertebrates has been examined by many authors. It has been established that in many species there exists some kind of synchronism between the sexual cycle and the cellular activity of neurosecretion, a fact that has led to the prevailing idea that gonadotropic activity in the hypophysis is regulated by the hypothalamus. This paper summarises the results of experiments made in this direction on Cyclostomata. The materials for research came from adult individuals of Eudontomyson danfordi Regan taken from the rivers Somes-Rece and Ivo (Harghita district) at different times of the year.

Diurnal periodicity of activity in the spawning perch P. fluviatilis L. [Translation from: Kalamies 1972(7) 3, 1972]

Diurnal periodicity of spawning in the perch so far are rather meagre and found to be partly contrary to experiences of perch anglers. Therefore a study was made on the spawning during a 5-day period in the spring of 1971 in the Kuusamo area. Observations were made during the main spawning season, between 4- 9 June 1971. The perch were often measured, weighed and then released back into the water. The differences between spawning and non-spawning perch were studied as well as the time of roe discharge in a 24 hour period. Activity and environmental factors such as light intensity were also taken into consideration.

Diurnal periodicity of winter activity in the perch, Perca fluviatilis L. [Translation from: Kalamies 1973(1) 3.]

Since 1967 data have been collected on the distribution of fish caught in a 24 hour period during the winter angling season. The present study on activity periods is based on data from nearly 2000 perch collected between 1967 and 1971. The distribution of number of fish caught during 24 hrs during December - May was studied. Of the total, the most productive period was found to be between 0600 - l600 hrs., with the peak period occurring between 0800 - 1000 hrs. The present data together show that during the darkest months of the year, the perch is only active in the mid-day period. Throughout the whole winter fishing season, activity only occurs during the time between surise and sunset.

Seasonal variation in the diurnal periodicity of activity of the perch, Perca fluviatilis L. [Translation from: Kalamies 1973(3) 3.]

The most common catch of the amateur angler is the perch and it is the diurnal periodicity of activity (& catchability) which is examined in this study based on earlier articles and manuscripts by the authors. Of all environmental factors, variation in light and temperature are the chief reasons in establishing the times of activity periods. Winter, summer and autumn activity was studied. The spawning perch was found to be more active than the non-spawning perch. The time of day in which the fish may be active is dependant on its ability to sense changes in the external environment. Its adaptation to light is the reason for day-activity in the winter, and also accounts for the fact that hardly any activity occurs between sunset and sunrise when this period exceeds 6 hours.

Individual growth and seasonal cycle of Daphnia middendorffiana in an Alpine lake [Translation from: Memorie dell'Istituto Italiano di Idrobiologia Dott.Marco de Marchi 26 41-83, 1970]

The problem of the peculiar reproductive biology of the cladoceran Daphnia middendorffiana is investigated from a cytological viewpoint, and by direct observation the meiotic phenomena of the eggs both subitaneous and resting is studied. and during maturation, the true mechanism of the succession of reproductive phases of different ecological significance. Samples were collected in the Italian Alpine Lake of Campo 4°.

The role of ciliates in the pelagic life cycle of the Mediterranean [Translation from: Rapports et Proces Verbaux des Reunions-Conseil International pour l'Exploration de la Mer 17, 511-512, 1963]

During hydrographic and plankton studies carried out since 1960 in the coastal zone between the Ebro and Castellon (western Mediterranean), data has been collected which confirms the importance of ciliates in the composition and activity of the plankton. The ciliates in 413 samples of 100 ml of water were counted, having been examined with the Utermohl microscope after sedimentation. The samples studied were distributed according to the density of their population. subject for study. The author concludes that recognition of the role of ciliates as an important link in the food chain of the sea would simplify the interpretation of certain problems posed by the nutrition of certain groups of planktonic animals.

Physiological aspects of the life cycle of the river lamprey, Lampetra fluviatilis L

The life cycle of the river lamprey, L. fluviatilis, is reviewed. The larval lamprey, or ammocoete, is a blind, filter-feeding animal, which normally lies concealed in the silt deposits of streams and rivers. After a period of 3-5 years in fresh water the ammocoete undergoes a metamorphosis in the summer months into a sexually immature, non-feeding stage known as the macrophthalia, which is active. This stage migrates downstream in late winter. It adopts a parasitic existence, in intertidal areas. After 18 months it returns to spawn in fresh water, after a final freshwater stage lasting up to 9 months. The river lamprey dies within a few days after the spawning period of 3-4 weeks, and none survive to spawn the following year.

Alterations of the global water cycle and their effects on river structure, function and services

River structure and functioning are governed naturally by geography and climate but are vulnerable to natural and human-related disturbances, ranging from channel engineering to pollution and biological invasions. Biological communities in river ecosystems are able to respond to disturbances faster than those in most other aquatic systems. However, some extremely strong or lasting disturbances constrain the responses of river organisms and jeopardise their extraordinary resilience. Among these, the artificial alteration of river drainage structure and the intense use of water resources by humans may irreversibly influence these systems. The increased canalisation and damming of river courses interferes with sediment transport, alters biogeochemical cycles and leads to a decrease in biodiversity, both at local and global scales. Furthermore, water abstraction can especially affect the functioning of arid and semi-arid rivers. In particular, interception and assimilation of inorganic nutrients can be detrimental under hydrologically abnormal conditions. Among other effects, abstraction and increased nutrient loading might cause a shift from heterotrophy to autotrophy, through direct effects on primary producers and indirect effects through food webs, even in low-light river systems. The simultaneous desires to conserve and to provide ecosystem services present several challenges, both in research and management.

Hypoxic and low pH water in the nearshore marine environments of Monterey Bay, California: characterizing a decade of oxygen and pH, and drivers of variability.

A decade-long time series recorded in southern Monterey Bay, California demonstrates that the shallow, near-shore environment (17 m depth) is regularly inundated with pulses of cold, hypoxic and low pH water. During these episodes, oxygen can drop to biologically threatening levels, and pH levels were lower than expected. Weekly water chemistry monitoring revealed that the saturation state of aragonite (the more soluble form of calcium carbonate) was often below saturation and had a moderate positive relationship with pH, however, analytical and human error could be high. Pulses of hypoxia and low pH water with the greatest intensity arise at the onset of the spring upwelling season, and fluctuations are strongly semidurnal (tidal) and diurnal. Arrival of cold, hypoxic water on the inner shelf typically occurs 3 days after the arrival of a strong upwelling event and appears to be driven by upwelling modulated by internal tidal fluctuations. I found no relationship between the timing of low-oxygen events and the diel solar cycle nor with terrestrial nutrient input. These observations are consistent with advection of hypoxic water from the deep, offshore environment where water masses experience a general decline of temperature, oxygen and pH with depth, and inconsistent with biochemical forcing. Comparisons with concurrent temperature and oxygen time series taken ~20 km away at the head of the Monterey Canyon show similar patterns but even more intense hypoxic events due to stronger semidiurnal forcing there. Analysis of the durations of exposure to low oxygen levels establishes a framework for assessing the ecological relevance of these events. Increasing oceanic hypoxia and acidification of both surface and deep waters may increase the number, intensity, duration and spatial extent of future intrusions along the Pacific coast. Evaluation of the resiliency of nearshore ecosystems such as kelp forests, rocky reefs and sandy habitats, will require consideration of these events.

Eléments nutritifs et production primaire dans les lagunes du Côte d'Ivoire : cycle annuel

This paper collects most of the information gathered between October 1974 and July 1976 within the framework of a research program concerning the hydrobioclimate of ivorian lagoons and especially the Ebrié lagoon. Monthly surveys concerning the latter were carried out during 1975. The following parameters - and their vertical distribution wherever it had a meaning - were systematically gathered in a system of fifty-five stations: Transparency (Secchi), Temperature, Salinity, Chlorophylla, Dissolved oxygen, phosphate, nitrate, nitrite. These data provide an outline of the annual cycle of nutrients and primary production of the Ivoirian lagoons

Cycle sexuel et fécondité du machoiron Chrysichthys nigrodigitatus en Lagune Ebrié, Côte d'Ivoire

Changes in the seasonal development of the gonads of female Chrysichthys nigrodigitatus, in Ebrié lagoon (Côte d'Ivoire) are described over an annual reproductive cycle. Seven macroscopic stages of gonad maturity were identified. There is a major spawning period from July to November. The mature fish spawn only once during the breeding season. There was a slightly higher correlation between fecundity and fish length than between fecundity and fish weight or gonad weight. Fecundity estimates ranged from 5438 to 36257 eggs and from 4878 to 87724 eggs, respectively for the fish in captivity and those in the natural environment.

Étude histologique du cycle sexuel de l'albacore (Thunnus albacares) Bonnaterre 1788

The evolution of the general microscopic structure of the ovary of Thunnus albacares related to the gonad index, and the ovocyte maturation process were studied. Some stages of the males sexual maturation were characterized.