The dispersal of suspended matter in the Gulf of Cadiz (SW Spain) is related to its geographical position near the Strait of Gibraltar, and the continental margin, and to Atlantic and Mediterranean water flows and their interaction with the littoral tidal processes. The main direction for transport of suspended matter is towards the southeast, along the continental margin, from the mouths of the rivers Guadiana and Guadalquivir to the Mediterranean. This general transport pattern is perturbed by littoral processes such as those occurring in Cadiz Bay, where a portion of Atlantic suspended matter, driven by flood tide, comes into the inner bay and is deposited in the shallow waters of lagoons and salt marshes. Subsequently, because of the southeast wind and waves, these sediments are remobilized and transported to the west by the ebb tide, to deeper Atlantic waters. This dynamic interaction between Atlantic and littoral waters generates a different type of sediment layout, the origin of which is difficult to establish.

In order to understand the dispersal of the suspended matter and its effects on the inner continental shelf, the distribution of the main clay minerals has been determined by means of X-ray and Q-mode and R-mode factor analysis. The suspended matter dispersal paths were established through the distribution of main clay mineral associations and from the ratios amongst these minerals. The results allow us to determine the importance of the tidal flows in the suspended matter transport system of the Gulf of Cadiz. Therefore, a record was kept of which of the outgoing tidal flows from the inner parts of Cadiz Bay reached the continental shelf. The flows intercept the clear Atlantic waters giving rise to a complex sediment distribution and to the mix of clay minerals. The study has also allowed us to establish the sediment source areas and the extent of sediment transport and the paths they follow.

The Atlantic–Mediterranean transition zone between the Alborán Sea and the Gulf of Cádiz constitutes the most prominent marine geographic barrier in European waters and includes known phylogeographic breaks such as the Strait of Gibraltar and the Almería-Oran Front. A genetic shift in this area has been previously documented for the European littoral shrimp Palaemon elegans. Here we carried out a phylogeographic analysis with the congeneric and sympatric species Palaemon serratus to test for similar intraspecific genetic differentiation and geographic structure. This littoral prawn is distributed in the Northeastern Atlantic Ocean, the Mediterranean Sea and the Black Sea. We compared DNA sequences from the mitochondrial genes Cox1 and to a lesser extent from 16S rRNA of several Atlantic and Mediterranean populations. Furthermore, sequences from the nuclear gene Enolase were included for corroborating differences between Mediterranean and Atlantic individuals. A pronounced genetic differentiation was detected between the Mediterranean and Atlantic populations, amounting to 10.14% in Cox1 and 2.0% in 16S, indicating the occurrence of two independent evolutionary lineages. Interestingly, specimens from the Atlantic Gulf of Cadiz cluster together with the Mediterranean individuals, indicating that a biogeographic barrier appears to be located west of the Strait of Gibraltar.

A description of a specimen of Cynoscion nebulosus caught in the Spanish waters of the Gulf of Cadiz, in the north-east Atlantic is presented. This is the first record of this species at this longitude.

Living specimens of the amphi-Atlantic asteroid Hacelia superba have been collected in different areas of Gazul mud volcano in the Gulf of Cadiz, south-western Iberian Peninsula, at depths of 380–487 m. This starfish displayed low abundances (~1 ind. 2000 m−2) in beam trawl catches on the mud vulcano and adjacent soft bottoms. The absence of previous records in this area could be due to a low sampling effort on bathyal hard bottoms of the Gulf of Cadiz, especially those of dormant mud volcanoes, as well as a possible misidentification as Hacelia attenuata that also occurs in the area but is restricted to infralittoral and circalitoral bottoms.

Spatial distribution and species diversity of Cephalopoda caught in ARSA bottom trawlsurveys were studied out during two different seasons (autumn and spring) in the Gulf ofCadiz (Spain) from 2000 to 2007. Species composition of cephalopod assemblages wasanalysed, using both clustering analyses and non-metric multidimensional scaling analysis(nMDS). Spatial distribution of the assemblages identified and abundance of the mainspecies were mapped with Surfer 8.0 software, using kriging as the geostatistical griddingmethod. A total of 35 cephalopod species belonging to 6 families were found at depthsbetween 20 and 700 m. In each season, Sepiolidae was the most abundant family in terms ofnumber of species, followed by Octopodidae. The species richness increased up to 100–120 mdepth, where it reached the maximum value. From 120 m, the species richness decreasedprogressively with depth. In spring, the species with the highest occurrence wasEledone moschata (34%) and in autumn it was Alloteuthis media(70%). In both seasons, the most abundant species in terms of weight wasOctopus vulgaris, while Alloteuthis media showed thehighest yields in terms of numbers. Most species showed wide bathymetric ranges,especially in autumn. Three different assemblages were found in both seasons during thetime period analysed (although 2003 and 2006 were not included in the cluster analysis):shelf assemblage (20–160 m), deep shelf/upper slope assemblage (100–350 m) and middleslope assemblage (320–700 m). The specific composition of these three assemblages wassimilar between spring and autumn and an overlap could be observed between them, mainly inthe two continental shelf groups: shelf and deep shelf/upper slope assemblages.Alloteuthis media and Alloteuthis subulata were themost abundant species in the shelf assemblage as well as in the deep shelf/upper slopeassemblage. In the middle slope assemblage, Illex coindetii was the mostabundant species. The assemblages and their spatial distributions could be largely relatedto a combination of physical and biological factors and their interactions.

The biology, growth and reproduction of the axillary seabream, Pagellus acarne, was studied based on data obtained from the catches of the Andalusia commercial fleet operating off the coasts of southern Spain from October 2003 to September 2004. The axillary seabream had a very wide depth distribution, appearing from the surface down to 500 m depth. The length–weight relationship was given by TW = 0.0048 TL3.3207 (R2 = 0.98) (TW = total weight; TL = total length) for all fish from the Gulf of Cadiz and TW = 0.0093 TL3.1132 (R2 = 0.94) for all fish from the Alboran Sea. The proportion of females to males increases as length increases in both populations and the species is characterized by protandric hermaphroditism. Spawning males were present almost throughout the year although higher percentages were observed in spring and early summer. In females, the spawning period occurred mainly in spring. In both areas, the mean size at first maturity for males was smaller than for females. The mean lengths at first maturity were 18.04 cm for males and 21.7 cm for females from the Gulf of Cadiz, and 17.7 cm and 20.1 cm for males and females from the Alboran Sea, respectively. The average total fecundity was estimated at 290,070 and 173,509 oocytes for Atlantic and Mediterranean individuals, respectively. The parameters of the von Bertalanffy growth model were estimated by age readings of the 247 sagitta collected. Two rings, one opaque and one hyaline, were laid down each year on the otoliths. The opaque zone was formed during spring and summer and the hyaline one during the remaining months of the year. The relationship between otolith radius and total length of the fish was described by the equation: TL = 27.7 OR – 1.8 (r = 0.96) (where OR = otolith radius). The parameters of the fitted Von Bertalanffy growth equation were L∞ = 31.65 cm, k = 0.21 yr−1 in the Gulf of Cadiz and L∞ = 32.14 cm, k = 0.17 yr−1 in the Alboran Sea.

Description of the first specimen of Chloroscombrus chrysurus, caught in the Spanish waters of the Gulf of Cadiz, a rare species in north-east Atlantic waters. The nearest zone of frequent occurrence for this species is the Mauritanian coast, about 11 degrees south. Different hypotheses to account for the increase in reports are discussed.