Departament de recursos
marins renovables

Keywords: nutrients, pigments, plankton, Rhone plume.

We studied physico-chemical (temperature, salinity, inorganic nutrients) and biological (phytoplankton pigment composition, bacterial numbers, protein, DNA, RNA, and POM) characteristics of a hydrographically diverse area of the northern Catalan sea during the stratification period (June 2000). The sampled stations were affected by a) continental shelf (coastal waters), and b) low salinity surface waters from the Gulf of Lions influenced by the Rhone runoff (called Plume), carried by the shelf-slope Catalan current. We compared these areas with oceanic waters. The relative fertilising effect of the Plume for the plankton communities is discussed

Keywords: Sardina pilchardus, larvae, growth, NW Mediterranean, temperature.

the long- and short-term growth of 3.5 to 16 mm standard length Sardina pilchardus larvae was compared between two cruises conducter in autumn and winter in the Catalan Sea (NW Mediterranean). Growth was significantly higher in November than February, as assenssed by muscle fibre recruitment and RNA/DNA ratios. Otolith age-length relationships suggested a similar trend. Sea temperature is regarded as a plausible explanatory factor for the differences in growth.

The spatial distributions of temperature, salinity, density, zooplankton and ichtyoplankton were analysed on the basis of CTD sampling and plankton hauls performed during two oceanographic cruises in July and September 2003 along the Catalan coast. This summer season was anomalously long, hot and dry. The comparison of preliminary results with the data obtained in the same area in 1983 show higher temperatures and salinities at surface in July but not in September, while similar spatial distribution of the oceanographic parameters were found in both cases.

Keywords: Pandalid shrimps · Diet · Feeding guilds · Primary production.

The feeding habits of 4 species of Plesionika inhabiting the Alboran Sea (SW Mediterranean) at depths between 29 and 790 m were analyzed. Included within the trophic guild of nonmigratory macroplankton feeders, Plesionika spp. preferably exploited mesopelagic resources (mainly euphausiids and Myctophidae). Deep-bathyal species (P. martia, P. gigliolii and P. edwardsi) fitted better within this guild, while the shallower living species P. heterocarpus, which inhabits the shelf-slope break, consumed benthic organisms (e.g. polychaetes, bivalves and tanaids). In a multispecies MDS analysis, diets of P. martia and P. heterocarpus were grouped as a function of depth. Latitude, phytoplankton pigment (PP) concentration recorded 4 wk before the sampling date (PP4) and depth were the explanatory variables of stomach fullness of Plesionika (all species: R2 = 0.674 in a multiple linear regression model, MLR). The abundance of P. martia also showed a positive significant correlation (Spearman r) with PP4. Possible causes of higher shrimp aggregations in P. martia could be related to reproductive processes because peaks of mature females were reported at similar periods in neighboring areas. In both dominant Plesionika species (P. martia and P. heterocarpus), MDS dimensions for diets were also correlated with PP4, although significant correlations with other PP data taken at different periods (from simultaneous PP data to PP6, 6 wk before sampling) were also found. These trends suggest that macroplankton-feeder Pandalidae may couple some aspects of their biology with blooms of plankton and ultimately with peaks of primary production. Prey size selection occurred among Plesionika spp., which suggested a hunting activity. Correlations between Plesionika spp. size (CL, mm) and prey size were positive, both for fish (R2 = 0.437) and for euphausiids (R2 = 0.440). Otolith length (mainly of Benthosema glaciale) and the size of euphausiid mandibles (Meganyctiphanes norvegica and Euphausia hemigibba) increased with predator size. Further evidence of active predation by deep pandalids, for example changes in the daily feeding activity of species, were evidenced for P. martia with higher foregut fullness at the beginning of the daytime period (from 06:00 to 08:00 h) related to predation on euphausiids.

Keywords: Box-Jenkins transfer function models, Ebre (Ebro), Engraulis encrasicolus, Mediterranean, river runoff, Sardina pilchardus, wind mixing.

Time series analyses (Box-Jenkins models) were used to study the influence of river runoff and wind mixing index on the productivity of the two most abundant species of small pelagic fish exploited in waters surrounding the Ebre (Ebro) River continental shelf (north-western Mediterranean): anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus). River flow and wind were selected because they are known to enhance fertilization and local planktonic production, thus being crucial for the survival of fish larvae. Time series of the two environmental variables and landings of the two species were analysed to extract the trend and seasonality. All series displayed important seasonal and interannual fluctuations. In the long term, landings of anchovy declined while those of sardine increased. At the seasonal scale, landings of anchovy peaked during spring/summer while those of sardine peaked during spring and autumn. Seasonality in landings of anchovy was stronger than in sardine. Concerning the environmental series, monthly average Ebre runoff showed a progressive decline from 1960 until the late 1980s, and the wind mixing index was highest during 1994-96. Within the annual cycle, the minimum river flow occurs from July to October and the wind mixing peaks in winter (December-April, excluding January). The results of the analyses showed a significant correlation between monthly landings of anchovy and freshwater input of the Ebre River during the spawning season of this species (April-August), with a time lag of 12 months. In contrast, monthly landings of sardine were significantly positively correlated with the wind mixing index during the spawning season of this species (November-March), with a lag of 18 months. The results provide evidence of the influence of riverine inputs and wind mixing on the productivity of small pelagic fish in the north-western Mediterranean. The time lags obtained in the relationships stress the importance of river runoff and wind mixing for the early stages of anchovy and sardine, respectively, and their impact on recruitment.

Keywords: fish larvae, Northwestern Mediterranean, vertical distribution.

The vertical distributions of the larvae of shelf and oceanic fish species that spawn during the winter-mixing period in the Mediterranean are described from 22 vertically stratified plankton tows. Diel differences in the vertical distribution patterns in relation to physical data and potential prey abundance throughout the water column were examined. Even in absence of stratification, the larvae of the various fish species showed different patterns of vertical distribution and diel changes. The larvae of shelf-dwelling species were found in the surface layers, mainly above 50-m depth, and with some exceptions, with very little diel variation in depth distribution. Therefore, the vertical distribution of the larvae of these species coincided with the maximum concentrations of their potential food, nauplii and copepodite stages of copepods. The larvae of mesopelagic fishes showed deeper distributions in the water column and most of these species were located closer to the surface during the day than at night. Given the homogeneity of the physical characteristics throughout the water column, except for light, this behaviour may be determined not only by the higher concentration of prey in the surface layers but also by adequate light levels for feeding.

Keywords: Shelf-slope front; Frontal oscillations; Meandering current; Fish larvae; NW Mediterranean.

Physical and biological coupling in frontal zones presents a high spatio-temporal variability as a result of both the hydrographic complexity of such systems and the biological activity of the organisms. A permanent frontal system (density front and associated current), parallel to the bathymetry, is present in the shelf-slope region in the Catalan Sea (NW Mediterranean). This study presents the results obtained froma detailed examination of the frontal systemand larval fish distribution in a small area in the Catalan Sea, over the span of just a few days. A repeated transect of 11 stations, spaced 2.5 miles apart, was sampled across the front. The shelf-slope front presented a meandering structure with a wavelength of about 50–60km and an amplitude of about 10-12 km. The position of the frontal system on successive transects was shifting gradually, fromquite close to the edge of the shelf to about 10 kmtowards the opensea. This shift may reflect a frontal oscillation due to the passage of a half wave of a meander. During the phase in which the front draws nearer to the shelf, slope to shelf exchanges take place, with fish larvae accumulating on the coastal side of the front along with very low concentrations fromthere oceanwards. During the phase in which the front moves away from the shelf, shelf to slope exchanges take place, and fish larvae were beginning to be dispersed so that high larval concentrations were shifted in an oceanwards direction. While there were still relative accumulations on the coastal side of the front, these accumulations were not nearly as pronounced. On that occasion there was heightened upwelling on the oceanic side of the front with local peaks in chlorophyll biomass in this region. The results presented here have revealed not only that the fertilization mechanisms are associated with the front but have also shown that oscillations in the front have a decisive role in supplying nutrients to the photic zone on an intermittent basis. The temporal scale at which the frontal system oscillates also exerts a decisive influence on processes affecting concentration/dispersal of larval fish populations.

Keywords: NW Mediterranean, continental waers, advection, anchovy larvae, larval growth.

The results of a Lagrangian survey waters of continental origin from the Gulf of Lions are presented. Three drifters were launched at the edge of the continental shelf around the core of the shelf-slope current and followed up to near Barcelona . The current was carrying surface waters with relatively low salinity from the Gulf of Lions, influenced by Rhone runoff. Monitoring of environmental conditions, plaktonic communities and anchovy larvae living in the surface water parcel tracked by the drifters was conduced in order to evaluate the suitability of these waters for the survival of anchovy larvae.

Keywords: ageing, cephalopod, growth, growth modelling, octopus..

Octopuses are generally characterised by rapid non-asymptotic growth, with high individual variability. However, in situ octopus growth is not well understood. The lack of an ageing method has resulted in the majority of our understanding of octopus growth coming from laboratory studies. Despite not being applicable to cephalopods, Modal Progression Analysis (MPA) of length–frequency data is the most common method for examining in situ octopus growth. Recently, counting growth increments in beaks and vestigial shells, and quantifying lipofuscin in brain tissue, have all shown promise for the ageing octopus. Octopuses generally demonstrate two-phase growth in the laboratory, with physiological changes possibly associated with the switch between an initial rapid exponential phase and a slower power growth phase. Temperature and food ration and quality are key factors influencing the initial growth phase. Temperature, however, does not appear to affect the second phase in any consistent way, perhaps because maturity stage can influence the growth response. There may be basic differences in the mechanisms of octopus muscle growth compared with that of other cephalopods. Furthermore, higher relative maintenance energy expenditure, along with the low energy content of their prey, may account for the relatively slow growth of deep-sea octopuses compared to littoral species.

Keywords: Cephalopods; Amino acids; Larvae; Sepia; Loligo; Octopus.

During the present study, we aimed to provide a first look at the amino acid composition of the early stages of cephalopods and follow possible effects of certain dietary treatments. Amino acid profiles of cuttlefish Sepia officinalis, squid Loligo vulgaris and octopus, Octopus vulgaris hatchlings and wild juveniles of L. vulgaris and O. vulgaris were analysed. Cephalopod hatchlings showed high fractions of non-protein nitrogen (NPN), from 25% to 38% of the dry weight. Lysine, leucine and arginine represented half of the total content of essential amino acids (EAA), and glutamate and aspartate represented also nearly half of the non-essential amino acids (NEAA). In O. vulgaris, a general tendency for a decrease in the level of EAA from mature ovary and eggs to hatchlings was observed. Hatchlings after 4 days of fasting lost 28% of their dry weight and the level of EAA and NEAA decreased in both the total content and free forms. Free proline after 2 days of fasting and free tyrosine at 4 days of fasting were not detected. Comparison of the total EAA profiles of preys showed few differences between enriched Artemia nauplii and hatching crab zoeae (Pagurus prideaux and Maja squinado). The enriched Artemia nauplii EAA profiles showed no differences with the EAA profiles of O. vulgaris paralarvae during first 10 days of culture, except for histidine. Present results confirm the positive capacity for amino acid uptake from seawater by early stages of cephalopods. In the three species analysed, radiolabelled phenylalanine was incorporated in inverse relation to body size. After 10 days of culture, O. vulgaris paralarvae showed a tendency to increase the levels of total and free amino acids in the groups receiving a daily amino acids solution. At 20 days of age, the O. vulgaris cultures that received the amino acids solution had survivals that on average were three times that of the control group. However, the supposed beneficial effects of the amino acids solution remained unclear, as the dry weight of these paralarvae was equal or lower to that of paralarvae from the control group. In wild O. vulgaris juveniles, the percentage of protein and total amino acids increased with the dry weight of the individuals. These juvenile biochemical changes were associated with strong morphometric changes in body proportions after settlement with the development of the muscular, protein-rich arm crown.