The Ionian Abyssal Plain (central Mediterranean Sea): Morphology, subbottom structures and geodynamic history – an inventory

In order to understand the structure and evolution of the Mediterranean Ridge accretionary complex, it is necessary to understand the structure and history of its foreland. The Ionian Abyssal Plain is one of the varying types of foreland. The state of knowledge for that is presented. Its contour and detailed relief are described for the first time. Based on published and hitherto unpublished seismic data, information on the thickness of the Plio-Quaternary and on the Messinian evaporites are presented. Of particular interest are data concerning the pre-Messinian reflectors. They indicate a pattern of tilted blocks and horst-like features created in pre-Messinian time by tensional tectonics. Varying subsidence continued, however, during Messinian time and controlled the thickness of evaporites. At some places (e.g. Victor Hensen Seahill) vertical tectonics seem to be still active. The main tectonic structures of the Ionian Abyssal Plain are not related to the process of the present accretion and subduction at the Africa/Eurasia plate boundary but are pre-existing and should influence the internal structure of the Mediterranean Ridge which is still growing at the expense of the foreland. As a consequence of our structural evidence, we favour the following interpretation: the Ionian Abyssal Plain is not a remainder of the Jurassic Tethyan ocean but originated by extensive attenuation of continental crust.     

Mud volcanoes and gas hydrates in the Anaximander mountains (Eastern Mediterranean Sea)

Detailed multibeam, sedimentological, and geophysical surveys provide ample new data to confirm that the Anaximander Mountains (Eastern Mediterranean) are an important area for active mud volcanism and gas hydrate formation. More than 3000 km of multibeam track length was acquired during two recent missions and 80 gravity and box cores were recovered. Morphology and backscatter data of the study area have better resolution than previous surveys, and very detailed morphology maps have been made of the known targeted mud volcanoes (Amsterdam, Kazan and Kula), especially the Amsterdam “crater” and the related mud breccia flows. Gas hydrates collected repeatedly from a large area of Amsterdam mud volcano at a sub-bottom depth of around 0.3–1.5 m resemble compacted snow and have a rather flaky form. New gas hydrate sites were found at Amsterdam mud volcano, including the mud flow sloping off to the south. Gas hydrates sampled for the first time at Kazan mud volcano are dispersed throughout the core samples deeper than 0.3 m and display a ‘rice’-like appearance. Relative chronology and AMS dating of interbedded pelagic sediments (Late Holocene hemipelagic, sapropel layer S1 and ash layers) within the mud flows indicate that successive eruptions of Kula mud volcano have a periodicity of about 5–10 kyrs. New mud volcanoes identified on the basis of multibeam backscatter intensity were sampled, documented as active and named “Athina” and “Thessaloniki”. Gas hydrates were sampled also in Thessaloniki mud volcano, the shallowest (1264 m) among all the active Mediterranean sites, at the boundary of the gas hydrate stability zone. Biostratigraphical analyses of mud breccia clasts indicated that the source of the subsurface sedimentary sequences consists of Late Cretaceous limestones, Paleocene siliciclastic rocks, Eocene biogenic limestones and Miocene mudstones. Rough estimations of the total capacity of the Anaximander mud volcanoes in methane gas are 2.56–6.40 km³.     

The annual cycle of Synechococcus (cyanobacteria) in the northern Levantine Basin shelf waters (Eastern Mediterranean)

Abundance of picoplanktonic chroococcoid marine cyanobacteria Synechococcus was monitored weekly over the year 1998 in shallow coastal waters of the northern Levantine Basin. The ambient physical, chemical and biological variables (temperature, salinity, Secchi disk depth, total suspended sediment, nitrate, phosphate, Chl a and phytoplankton) were also measured. Synechococcus was found to be more abundant during summer and early autumn and less during winter and early spring. At the surface and 15 m depth, cell concentrations were in the range 6.4 × 10³–1.5 × 10⁵ and 3.2 × 10³–1.6 × 10⁵ cells·ml⁻¹, respectively. Based on the Pearson product–moment correlation analysis, a highly significant correlation between Synechococcus abundance and ambient temperature was observed (n = 40, r = 0.558, P < 0.01). As Synechococcus forms blooms that usually do not last more than a week, the short time‐scale survey achieved in this study was appropriate to reveal its abundance dynamics. Several factors such as rapid changes in nutrient concentration (especially nitrate), phytoplankton, light availability, temperature, salinity, freshwater input and vertical mixing played a relevant role on the abundance of Synechococcus over the year in the highly dynamic shallow coastal waters of the Levantine Basin.     

Progressive deformation of an evaporite-bearing accretionary complex: SeaMARC I,SeaBeam and piston-core observations from the Mediterranean Ridge

The Mediterranean Ridge is an arcuate ridge of deformed sediment caught up in the convergent plate margin between the African plate and the Aegean. An intensive campaign of SeaMARC I and SeaBeam surveys followed by piston coring has been conducted along the contact between undeformed turbidites of the Sirte Abyssal Plain and folded and faulted sediments of the Mediterranean Ridge. Along the outer edge of the Ridge, surficial sediments have been deformed into sinusoidal ridges and troughs (wavelengths 0.5–2 km, amplitude 20–150 m), which we interpret as folds. In plan view, the ridge and the trough fabric parallels the NW-SE trending regional contours, suggesting that the folds formed in response to compression orthogonal to the Mediterranean Ridge. The outermost ridge is shedding a debris apron out onto the abyssal plain, implying that uplift and deformation are ongoing. We show that the geometry of the outermost folds can be produced by elastic bending of a packet of 5–10 relatively strong layers, each 10–20 m thick, interbedded between weaker layers; we equate the strong layers with gypsum beds in the Messinian upper evaporites. Folding the seafloor from a flat layer into the observed ridge and trough topography would shorten the layer by less than 2%. Two percent shortening (equals two percent thickening) is insufficient to create the observed relief of the Mediterranean Ridge even if the entire sediment column down to basement were involved; we infer that additional shortening/thickening is accommodated by thrust faulting above a decollement at the top of the Messinian salt layer. At distances > 15 km from the deformation front and more than 500 m from the abyssal plain, sharp-edged, fine-grained side-scan lineations with very little vertical relief cut across the kilometer-scale ridge and trough topography. These fine-grained lineations fall in two groups trending N/S to NNE/SSW and ~ENE. We interpret these lineaments as traces of conjugate strike-slip faults formed in the same compressional regime which formed the NW/SE trending folds. The onset of strike-slip faulting may coincide with the cessation of imbricate thrust fan development above the initial salt-controlled decollement surface. The following characteristics of the Mediterranean Ridge are attributed to the presence of evaporites in the incoming sedimentary section: (1) initial deformation by folding rather than thrust faulting; (2) narrow taper; (3) rapid rate of outward growth; (4) karstification.     

Characterization of bacterial symbioses in Myrtea sp. (Bivalvia: Lucinidae) and Thyasira sp. (Bivalvia: Thyasiridae) from a cold seep in the Eastern Mediterranean

Cold seeps have recently been discovered in the Nile deep‐sea fan (Eastern Mediterranean), and data regarding associated fauna are still scarce. In this study, two bivalve species associated with carbonate crusts and reduced sediment are identified based on sequence analysis of their 18S and 28S rRNA‐encoding genes, and associated bacterial symbioses are investigated using 16S rRNA gene sequencing and microscopy‐based approaches. The specimens are closely related to Myrtea spinifera and Thyasira flexuosa, two species previously documented at various depths from other regions but not yet reported from the Eastern Mediterranean. Both species harbour abundant gammaproteobacterial endosymbionts in specialized gill epithelial cells. The Myrtea‐associated bacterium is closely related to lucinid symbionts from both deep‐sea and coastal species, whereas the Thyasira‐associated bacterium is closely related to the symbiont of a T. flexuosa from coastal waters off the U.K. An epsilonproteobacterial sequence has also been identified in Thyasira which could correspond to a helicoid‐shaped morphotype observed by electron microscopy, but this was not confirmed using fluorescent in situ hybridization. Virus‐like particles were observed within some symbionts in Thyasira, mostly in bacteriocytes localized close to the ciliated zone of the gill filament. Overall, results indicate that very close relatives of shallow species M. spinifera and T. flexuosa occur at cold seeps in the Eastern Mediterranean and harbour chemoautotrophic symbioses similar to those found in their coastal relatives.     

Geophysical evidence of mud diapirism on the Mediterranean Ridge accretionary complex

Mud volcanoes, mud cones, and mud ridges have been identified on the inner portion of the crestal area, and possibly on the inner escarpment, of the Mediterranean Ridge accretionary complex. Four areas containing one or more mud diapirs have been investigated through bathymetric profiling, single channel seismic reflection profiling, heat flow measurements, and coring. A sequence of events is identified in the evolution of the mud diapirs: initially the expulsion on the seafloor of gasrich mud produces a seafloor depression outlined in the seismic record by downward dip of the host sediment reflectors towards the mud conduit; subsequent eruptions of fluid mud may create a flat topped mud volcano with step-like profile; finally, the intrusion of viscous mud produces a mud cone.The origin of the diapirs is deep within the Mediterranean Ridge. Although a minimum depth of about 400 m below the seafloor has been computed from the hydrostatic balance between the diapiric sediments and the host sediments, a maximum depth, suggested by geometric considerations, ranges between 5.3 and 7 km. The presence of thermogenic gas in the diapiric sediments suggests a better constrained origin depth of at least 2.2 km.The heat flow measured within the Olimpi mud diapir field and along a transect orthogonal to the diapiric field is low, ranging between 16 ± 5 and 41 ± 6 mW m^–2. Due to the presence of gas, the thermal conductivity of the diapiric sediments is lower than that of the host hemipelagic oozes (0.6–0.9 and 1.0–1.15 W m^–1 K^–1 respectively).We consider the distribution of mud diapirs to be controlled by the presence of tectonic features such as reverse faults or thrusts (inner escarpment) that develop where the thickness of the Late Miocene evaporites appears to be minimum. An upward migration through time of the position of the décollement within the stratigraphic column from the Upper Oligocene (diapiric sediments) to the Upper Miocene (present position) is identified.     

Tectonic effects of a subducting aseismic ridge: The subduction of the Nazca Ridge at the Peru Trench

A 1987 survey of the offshore Peru forearc using the SeaMARC II seafloor mapping system reveals that subduction of the Nazca Ridge has resulted in uplift of the lowermost forearc by as much as 1500 m. This uplift is seen in the varied depths of two forearc terraces opposite the subducting ridge. Uplift of the forearc has caused fracturing, minor surficial slumping, and increased erosion through small canyons and gullies. Oblique trending linear features on the forearc may be faults with a strike-slip component of motion caused by the oblique subduction of the Nazca Ridge. The trench in the zone of ridge subduction is nearly linear, with no re-entrant in the forearc due to subduction of the Nazca Ridge. Compressional deformation of the forearc due to subduction of the ridge is relatively minor, suggesting that the gently sloping Nazca Ridge is able to slide beneath the forearc without significantly deforming it. The structure of the forearc is similar to that revealed by other SeaMARC II surveys to the north, consisting of: 1) a narrow zone (10 to 15 km across) of accreted material making up the lower forearc; 2) a chaotic middle forearc; 3) outcropping consolidated material and draping sediment on the upper forearc; and 4) the smooth, sedimented forearc shelf.The subducting Nazca plate and the Nazca Ridge are fractured by subduction-induced faults with offsets of up to 500 m. Normal faulting is dominant and begins about 50 km from the trench axis, increasing in frequency and offset toward the trench. These faults are predominantly trench-parallel. Reverse faults become more common in the deepest portion of the trench and often form at slight angles to the trench axis.Intrusive and extrusive volcanic areas on the Nazca plate appear to have formed well after the seafloor was created at the ridge crest. Many of the areas show evidence of current scour and are cut by faulting, however, indicating that they formed before the seafloor entered the zone of subduction-induced faulting.     

Ontogenetic shifts and temporal changes in the trophic patterns of the deep‐sea red shrimp,Aristaeomorpha foliacea (Decapods: Aristeidae), in the Eastern Ionian Sea (Eastern Mediterranean)

The purpose of this paper is to provide the first detailed data concerning the diet and feeding activity of the giant red shrimp, Aristaeomorpha foliacea, in the Eastern Ionian Sea (Eastern Mediterranean), in relation to season, size class and sex. Feeding activity in A. foliacea was intense, based on its low vacuity index and high prey diversity, with a diet dominated by mesopelagic prey and less frequent occurrence of benthic taxa. Giant red shrimp displayed a highly diversified diet that exhibited slight seasonal fluctuations. The diets of both sexes consisted of 60 different prey categories belonging chiefly to three groups: crustaceans (e.g. decapods, such as Plesionika spp. and Pasiphaeidae, amphipods), cephalopods (mainly Enoploteuthidae) and fishes (Myctophidae, Macrouridae). These three prey categories accounted for 72–82% of the relative abundance and total occurrence for males and 70–88% for females, respectively. Variation in food availability, as well as increased energy demands related to gonad development and breeding activity, appear to be critical factors driving temporal changes in feeding strategy. Feeding activity increased during spring and summer, which coincides with reproductive activities (mating, gonad maturation, egg‐laying). Females seem to be more active predators than males, consuming prey with greater swimming ability. However, ontogenetic shifts in diet were also apparent, despite high dietary overlap among small, medium and large females. Large individuals, which are more efficient predators, selected highly mobile prey (e.g. fishes), whereas small individuals consumed low‐mobility prey (e.g. copepods, ostracods, tanaids and sipunculans).     

The Macrobenthic Associations of Haifa Bay, Mediterranean Coast of Israel

Abstract. Species composition, distribution, and relative abundance of macrobenthic fauna were examined at Haifa Bay on the Mediterranean coast of Israel. Benthic samples were taken over a two-year period at twenty sites ranging in depth from 10-80m. The relevant sedimentological features of the area are discussed. Classification of the faunal data produced a hierarchical grouping of sites and species, displayed as dendrograms. Ten sample groups and eleven species associations are identified. The obsérved qualitative differences arc related to the prevailing environmental conditions in the area. A unique species association, related to cobble-sized bioherms, is described. Massive penetration by four benthic species of Indo-Pacific origin, Lessepsian migrants, is reported.     

The morphotectonics and its evolutionary dynamics of the central Southwest Indian Ridge (49° to 51°E)

The morphotectonic features and their evolution of the central Southwest Indian Ridge （SWIR） are dis- cussed on the base of the high-resolution flfll-coverage bathyraetric data on the ridge between 49°-51°E. A comparative analysis of the topographic features of the axial and flank area indicates that the axial topogra- phy is alternated by the ridge and trough with en echelon pattern and evolved under a spatial-temporal mi- gration especially in 49°-50.17°E. It is probably due to the undulation at the top of the mantle asthenosphere, which is propagating with the mantle flow. From 50.17° to 50.7°E, is a topographical high terrain with a crust much thicker than the global average of the oceanic crust thickness. Its origin should be independent of the spreading mechanism of ultra-slow spreading ridges. The large numbers of volcanoes in this area indicate robust magmatic activity and may be related to the Crozet hot spot according to RMBA （residual mantle Bouguer anomaly）. The different geomorphological feature between the north and south flanks of the ridge indicates an asymmetric spreading, and leading to the development of the OCC （oceanic core complex）. The tectonic activity of the south frank is stronger than the north and is favorable to develop the OCC. The first found active hydrothermal vent in the SWIR at 37°47＇S, 49°39＇E is thought to be associated with the detach- ment fault related to the OCC.     

Bathymetry of the mid-atlantic ridge, 24°-31°N: A map series

This paper presents a series of eleven maps of the bathymetry of a 900 km long section of the crestal region of the Mid-Atlantic Ridge. Along with a twelfth key map, this series defines the morphology of fifteen discrete spreading segments and shows convincingly that no transform faults exist between the Kane and Atlantis fracture zones. The publication of these multi beam bathymetry data with a contour interval of 50 m and at a scale of 30 inches per degree of longitude is intended to allow easy access by a broad community of marine earth scientists to this unique and powerful data set.     

Oblique subduction of the Gagua Ridge beneath the Ryukyu accretionary wedge system: Insights from marine observations and sandbox experiments

The Gagua Ridge, carried by the Philippine Sea Plate, is subducting obliquely beneath the southernmost Ryukyu Margin. Bathymetric swath-mapping, performed during the ACT survey (Active Collision in Taiwan), indicates that, due to the high obliquity of plate convergence, slip partitioning occurs within the Ryukyu accretionary wedge. A transcurrent fault, trending N95° E, is observed at the rear of the accretionary wedge. Evidence of right lateral motion along this shear zone, called the Yaeyama Fault, suggests that it accommodates part of the lateral component of the oblique convergence. The subduction of the ridge disturbs this tectonic setting and significantly deforms the Ryukyu Margin. The ridge strongly indents the front of the accretionary wedge and uplifts part of the forearc basin. In the frontal part of the margin, directly in the axis of the ridge, localized transpressive and transtensional structures can be observed superimposed on the uplifted accretionary complex. As shown by sandbox experiments, these N330° E to N30° E trending fractures result from the increasing compressional stress induced by the subduction of the ridge. Analog experiments have also shown that the reentrant associated with oblique ridge subduction exhibits a specific shape that can be correlated with the relative plate motion azimuth.These data, together with the study of the margin deformation, the uplift of the forearc basin and geodetic data, show that the subduction of the Gagua Ridge beneath the accretionary wedge occurs along an azimuth which is about 20° less oblique than the convergence between the PSP and the Ryukyu Arc. Taking into account the opening of the Okinawa backarc basin and partitioning at the rear of the accretionary wedge, convergence between the ridge and the overriding accretionary wedge appears to be close to N345° E and thus, occurs at a rate close to 9 cm yr^–1. As a result, we estimate that a motion of 3.7 cm yr^–1±0.7 cm should be absorbed along the transcurrent fault. Based on these assumptions, the plate tectonic reconstruction reveals that the subducted segment of the Gagua Ridge, associated with the observable margin deformations, could have started subducting less than 1 m.y. ago.     

Vertical Distribution of Meiobenthos in Bathyal Sediments of the Eastern Mediterranean Sea: Relationship with Labile Organic Matter and Bacterial Biomasses

Abstract. Quantitative information on the vertical distribution of meiofaunal abundances and biomass were obtained from samples collected at 3 bathyal stations in the Eastern Mediterranean Sea located at the same depth but characterized by different food supply. Vertical distribution patterns of nieiofauna were investigated in relation to the biochemical composition of the sediment organic matter (proteins, carbohydrates, and lipids) and compared to benthic bacterial standing stocks. No significant relationship between bacteria and meiofauna was found, whereas a significant relationship between protein and lipid concentrations and total meiofauna density was observed. These data suggest that labile organic matter. considered as material readily aVdihbk to benthic consumers, may be an important factor regulating meiofaunal abundance and vertical distribution in deep-sea sediments.     

Feeding Habits of Trisopterus minutus capelanus (Gadidae) Off the Eastern Coast of Spain (Western Mediterranean)

Abstract. The stomach contents of poor cod, Trisopterus minutus capelanus (Lacepède), were taken at monthly intervals off the eastern coast of the Gulf of Valencia (Spain). A total of 1276 were analyzed to determine diet according to fish size and season. The basic food consists of crustaceans (Mysidacea and Decapoda) and teleosts. Feeding habits varied with size: decapods and fishes were more abundant in the stomachs of larger specimens. Little seasonal variation in food habits was recorded.     

The Agulhas Ridge, South Atlantic: The Peculiar Structure of a Fracture Zone

The Agulhas Ridge is a prominent topographic feature that parallels the Agulhas-Falkland Fracture Zone (AFFZ). Seismic reflection and wide angle/refraction data have led to the classification of this feature as a transverse ridge. Changes in spreading rate and direction associated with ridge jumps, combined with asymmetric spreading within the Agulhas Basin, modified the stress field across the fracture zone. Moreover, passing the Agulhas Ridge’s location between 80 and 69 Ma, the Bouvet and Shona Hotspots may have supplied excess material to this part of the AFFZ thus altering the ridge’s structure. The low crustal velocities and overthickened crust of the northern Agulhas Ridge segment indicate a possible continental affinity that suggests it may be formed by a small continental sliver, which was severed off the Maurice Ewing Bank during the opening of the South Atlantic. In early Oligocene times the Agulhas Ridge was tectono-magmatically reactivated, as documented by the presence of basement highs disturbing and disrupting the sedimentary column in the Cape Basin. We consider the Discovery Hotspot, which distributes plume material southwards across the AAFZ, as a source for the magmatic material.     

冲绳海槽中部伊平屋脊火山岩地球化学和Sr-Nd-Pb同位素组成：对岩石成因和地幔源区的指示

As an active back-arc basin, the Okinawa Trough is located in the southeastern region of the East China Sea shelf and is strongly influenced by the subduction of the Philippine Sea Plate. Major element, trace element and Sr-NdPb isotopic composition data are presented for volcanic rocks from the Iheya Ridge(IR), the middle Okinawa Trough. The IR rocks record large variations in major elements and range from basalts to rhyolites. Similar trace element distribution characteristics together with small variations in ~(87)Sr/~(86)Sr(0.703 862–0.704 884), ~(144)Nd/~(143)Nd(0.512 763–0.512 880) and Pb isotopic ratios, demonstrate that the IR rocks are derived from a similar magma source. The fractional crystallization of olivine, clinopyroxene, plagioclase, and amphibole, as well as accessory minerals, can reasonably explain the compositional variations of these IR rocks. The simulations suggest that approximately 60% and 75% fractionation of an evolved basaltic magma can produce trace element compositions similar to those of the intermediate rocks and acid rocks, respectively. The analysis of their Sr-Nd-Pb isotopic content ratios suggest that the source of the rocks from the IR is close to the depleted mantle(DM) but extends to the enriched mantle(EMII), indicating that the mantle source of these rocks is a mixture between the DM and EMII end members. The simulations show that the source of the IR volcanic rocks can be best interpreted as the result of the mixing of approximately 0.8%–2.0% subduction sediment components and 98.0%–99.2% mantlederived melts.     

Transient Eastern Mediterranean deep waters in response to the massive dense-water output of the Aegean Sea in the 1990s

We present a detailed account of the changing hydrography and the large-scale circulation of the deep waters of the Eastern Mediterranean (EMed) that resulted from the unique, high-volume influx of dense waters from the Aegean Sea during the 1990s, and of the changes within the Aegean that initiated the event, the so-called ‘Eastern Mediterranean Transient’ (EMT). The analysis uses repeated hydrographic and transient tracer surveys of the EMed in 1987, 1991, 1995, 1999, and 2001/2002, hydrographic time series in the southern Aegean and southern Adriatic Seas, and further scattered data. Aegean outflow averaged nearly 3 × 10⁶ m³ s⁻¹ between mid-1992 and late 1994, and was largest during 1993, when south and west of Crete Aegean-influenced deep waters extended upwards to 400 m depth. EMT-related Aegean outflow prior to 1992, confined to the region around Crete and to 1800 m depth-wise, amounted to about 3% of the total outflow. Outflow after 1994 up to 2001/2002, derived from the increasing inventory of the tracer CFC-12, contributed 20% to the total, of 2.8 × 10¹⁴ m³. Densities in the southern Aegean Sea deep waters rose by 0.2 kg/m³ between 1987 and 1993, and decreased more slowly thereafter. The Aegean waters delivered via the principal exit pathway in Kasos Strait, east of Crete, propagated westward along the Cretan slope, such that in 1995 the highest densities were observed in the Hellenic Trench west of Crete. Aegean-influenced waters also crossed the East Mediterranean Ridge south of Crete and from there expanded eastward into the southeastern Levantine Sea. Transfer into the Ionian mostly followed the Hellenic Trench, largely up to the trench’s northern end at about 37°N. From there the waters spread further west while mixing with the resident waters. Additional transfer occurred through the Herodotus Trough in the south. Levantine waters after 1994 consistently showed temperature–salinity (T–S) inversions in roughly 1000–1700 m depth, with amplitudes decreasing in time. The T–S distributions in the Ionian Sea were more diverse, one cause being added Aegean outflow of relatively lower density through the Antikithira Strait west of Crete. Spreading of the Aegean-influenced waters was quite swift, such that by early 1995 the entire EMed was affected. and strong mixing is indicated by near-linear T–S relationships observed in various places. Referenced to 2000 and 3000 dbar, the highest Aegean-generated densities observed during the event equaled those generated by Adriatic Sea outflow in the northern Ionian Sea prior to the EMT. A precarious balance between the two dense-water source areas is thus indicated. A feedback is proposed which helped triggering the change from a dominating Adriatic source to the Aegean source, but at the same time supported the previous long-year dominance of the Adriatic. The EMed deep waters will remain transient for decades to come.     

Plankton Distribution Patterns in a Mediterranean Dilution Basin: Amvrakikos Gulf (Ionian Sea, Greece)

Abstract. The present work describes Amvrakikos Gulf (Ionian Sea, Greece) as a dilution basin and provides information concerning the relationships between the hydrology and plankton composition and distribution.
Amvrakikos Gulf is characterized by a differentiated planktonic system which is apparently directly influenced by the input of the rivers located at the northern part of the gulf.