Algerian Coast Research Articles

Age and growth of the echinoid Sphaerechinus granularis from the Algerian coast

The growth bands in the plates of the echinoid Spharechinus granularis settled on the Algerian coast were analysed. Two distinct groups of sea urchins were identified with different growth patterns related to the period of recruitment, i.e. spring or autumn. The growth rate of the autumn cohort was higher over the year following the first winter after settlement. From the second winter there was little growth difference between the two cohorts. Compared to populations from Atlantic sites, the Algerian population has a lower growth rate and reduced longevity.

Complex empirical orthogonal functions analysis of ERS‐1 and TOPEX/POSEIDON combined altimetric data in the region of the Algerian current

Maps of sea level anomalies (SLA) relative to the 1993 annual mean sea level combine the data from the two altimetric missions, ERS‐1 and TOPEX/POSEIDON, during the overlap period (October 1992 to December 1993). These regular maps in space and time of residual sea level every 10 days on a 0.2° regular grid are used in the region of the Algerian current where the mesoscale eddies are of primary importance to the circulation of all the Mediterranean water masses. They are first compared with ERS‐1 along‐track scanning radiometer sea surface temperature images to get information on two anticyclonic eddies produced by instabilities of the Algerian current and visible in both infrared and altimetric data sets. Then, an analysis of complex empirical orthogonal functions (CEOFs) is performed on the SLA data set to see the correlation of the different dynamic features of the observed variability. The CEOF analysis is applied to the complex time series formed from the original SLA time series and their Hubert transforms to separate the variability into spatially coherent modes. The spatially correlated signal in the study area (0–15°E and 35°–40°N) was found to be dominated by the first two CEOFs. These first two modes explain nearly 85% of the variability, with 80% of the total variance for the first one and 5% of the total variance for the second one. The temporal phase of the first mode indicates that a constant frequency of one cycle per year is clearly dominant, corresponding to the seasonal signal. The strongest amplitude is obtained in the southern part of the channel of Sardinia and south of the Strait of Sicily. The temporal amplitude and the temporal phase of the second mode show a periodicity of about 6 months which appears to be associated with the variability of the Algerian current as the phase isolines are parallel to the mean current path along the Algerian coast. The strongest amplitude of the second mode is located near the African coast at ∼4°E and 8°E. These two points of high variability could correspond to eddy detachments from the main current.

Chaunax pictus Lowe 1846—first record of the family Chaunacidae in the Mediterranean Sea

A medium‐sized coffinfish, 183 mm total length and 170 g body weight, Chaunax pictus Lowe 1846, a species previously unrecorded in the Mediterranean Sea, has been trawled recently on deep‐sea red shrimp grounds near the Sentinelle Bank (off the Algerian coast, central Mediterranean Sea).

The October‐1987 floods in Catalonia: Synoptic and mesoscale mechanisms

AbstractA heavy rainfall event which produced floods in Catalonia (Spain) during October 1987 is presented. Convection was located over the same area for several days, producing up to 431 mm of rain (67% of the mean annual rainfall). The synoptic‐scale pattern and forcing are studied using objective techniques, while mesoscale features are investigated with satellite imagery and subjective surface analysis. Strong quasi‐geostrophic forcing for vertical motion was diagnosed at low levels white only a weak forcing was evident at 500 hPa. Convective and latent instability characterized the region during the period of heavy rainfall. Also, there was strong low‐level moisture convergence combined with high ‐values of precipitable water over the north‐west Mediterranean Sea. Composite charts delineating the area covered by the indicated synoptic factors seem to be an effective tool for identifying the area where mesoscale focusing mechanisms became effective. Sub‐synoptic analyses show that the main focusing mechanism was a quasi‐stationary convergence line, located near the coast of Catalonia. This lay between the south‐eastern warm and humid flow, caused by a weak low centred north of the Algerian coast, and the cold outflow from a mesohigh located in Catalonia and mainly originated by the orographic blocking of the Pyrenees.

Origin of high phytoplankton concentration in deep chlorophyll maximum (DCM) in a frontal region of the Southwestern Mediterranean Sea (algerian current)

In June 1990, we investigated the Atlantic flow along the Algerian coast in the Western Mediterranean. Intensive and fine resolution sampling along 13 longitudinal transects, consisting of 4–12 stations (3–5 nautical miles apart), was carried out with physical, chemical and biological measurements. This sampling enabled us to describe quasi-synoptically the spatial distribution over a large region between 1° and 4°E. Two oligotrophic systems, where the integrated chlorophyll was lower than 30 mg m −2, were separated by an almost continuous rich band characterized by integrated chlorophyll higher than 60 mg m −2. This chlorophyll-rich band, with concentrations greater than 2 mg m −3 (up to 15.8 mg m −3), was found along the boundary of the Atlantic flow, indicating that the phytoplanktonic biomass distribution is determined by hydrodynamics. The patchiness of phytoplankton, both in chlorophyll concentration and in species abundance, along a density surface resulted from interactions between Atlantic and Mediterranean waters. Also, a first assessment of the biological response to the mesoscale hydrodynamical features can be deduced from the comparative analysis of the physical, chemical and biological parameters. Large anomalies in nutrient and chlorophyll distributions indicated strong vertical advections along the front, either following density surface (isopycnal mixing) or crossing it (diapycnal mixing). Important isopycnal mixing of nutrients were evidenced on the inshore side of the current, while diapycnal mixing was observed only on the seaward side. These two processes seem to bring nutrients into the photic zone, leading to an enhanced in situ growth. A cross-front circulation is proposed to explain (i) the vertical distribution of chemical parameters near the front and (ii) the associated phytoplankton patchiness.

Descriptions of some planktonic larvae of the Calappidae (Crustacea: Decapoda; Brachyura)

Some unidentified planktonic larval stages have been assigned to the Calappidae using Rice's key of Brachyura families. Zoea stage I from the eastern region of the Algerian coast (western Mediterranean Sea) has been attributed, according to Manning and Holthuis (1980), to Calappa granulata (L.), the only recorded representative of the family from the Mediterranean Sea. Zoeal stages 1-lV from the Jordanian coast of the Gulf of Aqaba, Northern Red Sea, have been reported to the subfamily Matutinae. Comparisons of larvae of Calappa and of Hepatus and then, of larvae of Hepatus and of Matuta , show that Hepatus larvae are more closely related to those of Calappa , while those of Matuta are clearly distinct. It s suggested to place the genus Hepatus with the Calappinae. Guinot (1966. 1978) placed some genera, including Hepatus . in a 'unité parthenoxystomienne, lea Aethrinae'. Larval development is unknown for Aethra, Actaeomorpha. Hepatella and Osachila . However, comparison of Hepatus larvae with those of Parthenopidae shows that larval characters, particularly the setation of the endopod of the first maxilliped, are not conclusive for supporting such a regrouping. Moreover, the Calappidae have a combination of primitive and advanced features which suggest that their grouping in the Oxystomata seems more likely to be an adaptation to a similar way of life. The morphotypal taxon Oxystornata has been definitively rejected by Guinot (1978).

The Algerian eddies

This paper synthetizes various previous analyses of the Algerian eddies. These mesoscale anticyclonic eddies are of primary importance to the circulation of all the water masses in the Western Mediterranean. They are generated by instability processes disturbing the flow of Modified Atlantic Water (MAW) shortly after it reaches the African coast near 0°E, namely the Algerian Current. Young eddies, which have diameters of 50–100 km, and the upwelling generally attached to their southwestern edges, drift eastward along the coast at a few km per day, sometimes during several months; as they grow older and larger, the most vigorous ones leave the coastal zone and drift seaward. Some of them may reach the Sardinian continental slope where a well-defined vein of Levantine Intermediate Water (LIW) flows; we suspect them to be capable to pull fragments of LIW seaward, and in fact, the least modified LIW we encountered in the middle of the Algerian Basin had the form of rings or filaments trapped by one eddy. Eddies several months old may have diameters as large as ≈ 200km; they also entrain the Mediterranean Deep Water (MDW), and they probably extend down to the bottom. In 1984, two such eddies occupied most of the Algerian Basin; the MAW was deflected seaward by the westernmost one, from the Algerian coast at≈ 3°E as far as the Balearic Islands, and was then dispatched by other eddies through the whole basin as though by a set of paddle-wheels. Such interactions are perhaps not as exceptional as was previously expected. These mesoscale phenomena have strong biological implications. The Western Mediterranean Sea thus appears to be a very suitable place for the observation and modelling of such mesoscale coherent structures.

Circulation in the Algerian Basin during June 1986

Hydrographic measurements, made in the Algerian Basin during June 1986 as part of the Western Mediterranean Circulation Experiment, together with satellite infrared images, are used to describe the flow of major water types in the region. Modified Atlantic Water flows eastward along the Algerian coast as the Algerian Current to 4°E, where it breaks into a series of eddies and spreads far offshore. It then flows partly northward into the Ligurian‐Provencal Basin and partly eastward through the Strait of Sardinia. The subsurface Levantine Intermediate Water turns sharply northward after flowing westward through the Strait of Sardinia and forms a narrow vein along the Sardinian Coast. Winter Intermediate Water flows southward around the Balearic Islands. Its eastern branch recirculates back to the north, whereas part of the western branch contributes to the Algerian Current by flowing eastward beneath the Modified Atlantic Water. Two large, long‐lived eddies are confirmed in the area. The easternmost of these, and other features with unresolved horizontal structure between Sardinia and Menorca, extend from the surface through the pycnocline.

The origin and characteristics of the Algerian Current

Satellite and ship data collected between May 1 and 22, 1986, show that the Algerian Current originates in the Almeria‐Oran Front and remains within 30 km of the Algerian coast for over 300 km, between Oran and Algiers. The differences between the water masses of the current and the resident regional waters are clearly observed in the chlorophyll concentrations and optical characteristics, thus permitting the resulting patterns to be used as tracers of the circulation. During this field period, the Algerian Current begins as an extension of the Almeria‐Oran Front, which is found at the western periphery of the Eastern Alboran Gyre. This major oceanographic salinity front (ΔS > 1/km) delineates the boundary of the Algerian Current, which has average surface velocities of 40 cm/s and maximum speeds reaching 80 cm/s. The current, which has a volume transport between 0.4 and 0.5 Sv, is confined to the upper 150 m and is in geostrophic balance. A sequence of coastal zone color scanner (CZCS) and advanced very high resolution radiometer (AVHRR) satellite imagery showing the rapidly evolving surface circulation features is augmented with in situ ship data of current and water mass characteristics. Rapid undulations and frontal movements of the current were observed during the study period; however, the flow remained unbroken between 1° and 3°E. Current instability increased eastward as the undulations were sharper and the current appeared to depart from the coast near Algiers.

Some planktonic larval stages of Albunea carabus (L., 1758) (Crustacea, Decapoda, Anomura)

Descriptions are given of larvae of Albunea carabus (L.) in zoeal stages I, II and III from plankton collected off the Algerian coasts. The larvae are compared with those ascribed to other species of Albunea and with others belonging to the albuneid genera Blepharipoda and Lepidopa. Larvae of the three genera show great diversity, both in general appearance and in detailed structure, and it is difficult to define the Albuneidae on larval characters.

A Study of an Intense Density Front in the Eastern Alboran Sea: The Almeria–Oran Front

Abstract Studies of satellite imagery and space shuttle photographs of the western Mediterranean have indicated that the main path of inflowing Atlantic Water is around two large anticyclonic gyres in the Alboran Sea and along the Algerian Coast. These studies have also shown that a strong ocean front is present between Almeria, Spain, and Oran, Algeria, which is part of the easternmost segment of the Eastern Alboran Gyre. Based on these satellite studies, the first in situ investigation of the front, called here the Almeria–Oran Front, was conducted in March 1986 as part of the winter campaign of the Western Mediterranean Circulation Experiment (WMCE). Analyses of the resulting data show that the Almeria–Oran Front is a large-scale density front, formed by the convergence of two distinct water masses and controlled by the geographic position and strength of the Eastern Alboran Gyre. Physical and biochemical data indicate that the front is limited to the upper 300 m, with a strong southward baroclinic jet...

The circulation of the Levantine Intermediate Water in the Algerian Basin

Markedly different scenarios have been proposed for the circulation of the Levantine Intermediate Water (LIW) in the southern part of the western Mediterranean Sea. Discrepancies result from the fact that large temperature and salinity values, which characterize LIW, are encountered both in the vicinity of Sardinia and off Algeria. Thus it was assumed that the circulation of LIW was divided into two major branches, one northward along the Sardinian continental slope and the other across the Algerian basin. Being dissatisfied with such a branch image of the circulation, we have put forth hypotheses (Millot, 1985, 1987) which now appear to be supported by the results of the Médiprod 5 experiment conducted in June 1986. We propose a scheme for the circulation of LIW in the Algerian Basin wherein a gravity flow is constrained by the topography around Sardinia and is subjected to sporadic spreading toward the open basin due to erosion of this vein by mesoscale eddies. Therefore it seems admissible that no branch of LIW flows off the Algerian coast.

Seasonal changes in tissue weight and biochemical composition for the bivalve Donax trunculus L. on the Algerian coast

Seasonal changes in the body weight and composition of the bivalve Donax trunculus L. from Azur Plage near Algiers, Algeria, were studied during the period September 1971-June 1974. Percentage dry tissue weight was minimal in October–December and rose to reach a peak in spring or summer, the rise corresponding with rapid maturation of the gonads. Decrease in tissue weight in the autumn also coincided with a rapid decline maturity of the gonads between August and October. Lipid content increased with sexual maturity, while carbohydrate content was greatest in the autumn and declined to a seasonal minimum in April–May. The changes are compared with those for D. trunculus in other Mediterranean populations, and for D. vittatus (da Costa) elsewhere in Europe.

A Conductivity Anomaly in the Western Mediterranean

Summary A detailed study of differences in the values of the geomagnetic field intensity F observed at cross-points of flight lines and tie-lines from the Alboran Sea aeromagnetic survey was performed. This study reveals anomalies in the transient variations of F over an elongated zone located between the Spanish and algerian coasts. We think that these anomalies are due to a conducting channel of ENE-WSW orientation, probably located in the upper mantle half way between the iberian and african continental slopes. We feel that this channel may be linked to a similar channel found in Northern Morocco.

Diversidad liquénica en la península Edough, noreste de Argelia

Se ha realizado este estudio con el objetivo de enriquecer la lista de líquenes de Argelia donde se han prospectado 2 estaciones “Les Cascades de Vautours” y “Dar smayer” situadas a 442 y 856 m de altitud respectivamente de la Península de Edough en el NE de Argelia. La precipitación anual es abundante y cercana a los 1000 mm. Se han encontrado 73 taxones pertenecientes a 15 familias diferentes, con 8 taxones: Cladonia cervicornis subsp. Verticillata (Hoffm.) Ahti, C. ramulosa (With.) J.R. Laundon, C. humilis (With.) J.R. Laundon, Nephroma parile (Ach.) Ach., Parmelinopsis afrorevoluta (Krog & Swinscow) Elix & Hale, Ramalina siliquosa (Huds.) A.L. Sm., Usnea esperantiana P. Clerc y Xanthoparmelia conspersa (Ehrh. ex Ach.) Hale, que constituyen novedad para la flora liquénica argelina.

Recherches de geologie sous-marine profonde

Abstract Reviews investigations in the field of submarine geology which have been carried out during the last decade and discusses their geologic significance, with particular reference to French studies of the continental platform off the coast of France, the submerged area between Corsica and Liguria, and the Algerian coast.

Morphotectonique de la marge continentale nord-africaine

Abstract A morphotectonic study of the continental shelf off north Africa clearly demonstrates the effects of Quaternary deformation. The continental flexure is well-defined along part of the Algerian coast. Submarine valleys were produced by erosion or collapse prior to the folding.

Contribution a l'etude du Quaternaire ancien des environs de Tenes et Cherchel (Algerie)

Abstract Wave-cut platforms between Tenes and Tipasa in Algeria are considered evidence of two Tyrrhenian (Quaternary) transgressions. The lower level, at elevations of five to ten meters, corresponds to the Ouljian of the Atlantic coast of Morocco. This part of the Algerian coast appears to have been stable during the Quaternary except near Tipasa, where subsidence has been taking place continuously from Calabrian to recent time.