Ana Sabatés

Relationship between zooplankton distribution, geographic characteristics and hydrographic patterns off the Catalan coast (Western Mediterranean)

We studied the distribution patterns of ten zooplankton taxa of the Catalan coast (Western Mediterranean) using data collected in six research cruises along the continental shelf from April to July and September to October 1983. Zooplankton biomass ranged from 0.2–0.4 mg m-3 to 48–60 mg m-3, the greatest values being recorded between April and May, when gelatinous zooplankton concentrations were consistently present along the edge of the continental shelf. We identified the main factors contributing to the observed pattern of zooplankton distribution as the high degree of environmental fluctuation close to the coast (thermal gradient from north to south), the structural heterogeneity inherent to the continental shelf, and the persistence of a hydrographical front along the margin of the shelf.

Effect of a shelf-slope front on the spatial distribution of mesopelagic fish larvae in the western Mediterranean

Abstract The results of a study on the spatio-temporal distribution of mesopelagic fish larvae off Catalan coast (northwestern Mediterranean) in relation to the hydrographic features in the region are presented. Large concentrations of larvae were detected over the edge of the continental shelf and occasionally close inshore. Shelf structure, locally narrow and punctuated with submarine canyons, and a density front situated over the slope are responsible for the special characteristics of the region and for the presence of mesopelagic fish larvae in waters shallower than normally expected in view of the typically oceanic habitat of the adults. The density front contributes to the formation of larval concentrations, attributable both to passive transport of larvae and to the active mechanism of spawning by adults in the most productive areas. Certain species, like Cyclothone braueri and Maurolicus muelleri, exhibit marked seasonality in their spawning season, whereas others, like Myctophum punctatum and Benthosema glaciale, do not present well-defined spawning periods.

PREDATOR AND PREY BODY SIZES IN MARINE FOOD WEBS

Knowledge of relationships between predator size and prey size are needed to describe interactions of species and size classes in food webs. Most estimates of predator and prey sizes have been based on dietary studies and apply to small numbers of species in a relatively narrow size range. These estimates may or may not be representative of values for other groups of species and body sizes or for other locations. Marine predator and prey size data associated with published literature were identified and collated to produce a single data set. If predator or prey length of mass were not measured in the original study, the length or mass was calculated using length–mass relationships. The data set consists of 34 931 records from 27 locations covering a wide range of environmental conditions from the tropics to the poles and for 93 types of predator with sizes ranging from 0.1 mg to over 415 kg and 174 prey types with sizes from 75 pg to over 4.5 kg. Each record includes: predator and prey scientific names, c...

Changes in the heterogeneity of mesoscale distribution patterns of larval fish associated with a shallow coastal haline front

Abstract In June 1983 there was a large outflow of inland fresh-waters from the Rhone River that covered a broad area off the northern coast of Catalonia (Northwestern Mediterranean), giving rise to a surface plume of fresh water with a distinct haline front at its southern edge. This hydrodynamic event brought about substantial changes in the structure of the larval fish community in the area, which was in turn reflected in an increase in spatial heterogeneity. Large numbers of species and individuals were found along the southern edge of the plume in association with the haline front, whereas, with the exception of certain species, larval fish concentrations in the area covered by the plume tended to be considerably lower than in the rest of the area. Species predominantly located in the surface water layers were probably transported by the plume out to the plumes edge. Other species, which apparently enjoy a broader vertical distribution range, were less affected by the surface advection processes.

Climate modulation of fish populations: the role of the Western Mediterranean Oscillation (WeMO) in sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) production in the north-western Mediterranean

This study investigates the connections between climate fluctuations and sardine and anchovy production in the NW Mediterranean, taking the Western Mediterranean Oscillation index (WeMOi) as an indicator of climate variability. The basic working hypothesis is that sardine and anchovy productivity is influenced by the WeMOi, a proxy for the local environmental conditions such as sea surface temperature (SST) and river runoff. Sardine and anchovy landings (1974–2009) in the Catalan Coast and landings per unit of effort (LPUE) were used as proxy for recruitment. The results demonstrated a clear link between climate fluctuations and sardine and anchovy production. Positive WeMOi values were significantly correlated with low SST, high river runoff and high LPUE, that is, with better-than-average recruitment of sardine and anchovy. Conversely, negative WeMOi values were associated with high SST, low river runoff and low LPUE. During the negative WeMOi phases (such as that at the end of the analyzed period), environmental conditions are unfavourable for the overall biological productivity in the NW Mediterranean and would decrease the survival, growth, condition and reproduction of sardine and anchovy during their life cycle. Despite the evidences on the appropriateness of the NAOi as an indicator of the climate in Europe and its impact on some biological variables, we suggest that using a regional index, such as the WeMOi, can provide a more accurate representation of the environmental conditions affecting small pelagic fish production in the NW Mediterranean.

Transitory hydrographic structures and distribution of fish larvae and neustonic crustaceans in the north-western Mediterranean

Abstract A hydrographic and zooplankton survey (neuston and water column) was performed over the Blanes submarine canyon (western Mediterranean) in June 1993. Abundance of fish and crab larvae was very low when compared with previous studies conducted in the same area. The horizontal distribution of fish and crab larvae whose adults inhabit the continental shelf was restricted to the coast. The offshore occurrence of low-salinity waters of continental origin, together with the absence of a component perpendicular to the coast in the system of currents observed throughout the study area, support the observed pattern of distribution. The occurrence of mesopelagic fish larvae and of the oceanic neustonic isopod Idotea metallica in some coastal stations may be associated with episodic inshore-offshore exchanges of water masses identified by drifting buoy trajectories.

Pelagia noctiluca in the Mediterranean Sea

Over recent decades, man’s expanding influence on the oceans has begun to cause change in some regions, including in the Mediterranean Sea. New proliferations of jellyfish may be occurring in the Mediterranean Sea, possibly in response to the cumulative effects of some of these anthropogenic impacts. In the Mediterranean Sea, many of these “proliferation events” are due to Pelagia noctiluca, an oceanic scyphozoan that has become very abundant along the coasts. Pelagia noctiluca is usually considered to be the most important jellyfish species in the Mediterranean Sea due to its widespread distribution, abundance, and ecological role and also because of its negative interaction with humans. Climatic conditions that favor enhanced reproduction by P. noctiluca and probably also determine optimal conditions for the formation of blooms are characterized by mild winters, low rainfall, high temperature, and high-atmospheric pressure. The Medusa Project in Catalonia aims to understand the spatiotemporal dynamics of the jellyfish populations in the NW Mediterranean Sea by undertaking daily sampling during summer (May to September) of 243 beaches, covering more than 500 km of coast. Data on beach strandings along the Spanish Catalan coast revealed that jellyfish occur in greatest concentrations along the northern Catalan coast and on beaches located close to marine canyons. The arrival of P. noctiluca to the coast depends firstly on the offshore production of jellyfish. Oceanographic structures like fronts, which enhance and maintain high levels of biological production and provide ideal conditions for feeding, growth, and reproduction of the jellyfish are present in the NW Mediterranean. The weakening of the front results in large numbers of P. noctiluca being driven into the coast by southeast winds. In the NW Mediterranean Sea P. noctiluca exert top-down control over a variety of prey including fish eggs and possibly the invasive ctenophore Mnemiopsis leidyi. P. noctiluca is also responsible for the majority of the stings incurred by bathers along the Catalan coast. Finally, we recommend that similar sampling programs should be done elsewhere to better understand changes in the distribution, abundance, and blooming patterns of dangerous jellyfish species.

Short-term physical and biological variability in the shelf-slope region of the NW mediterranean during the spring transition period

Abstract The present paper reports on temporalmesoscale (weeks) changes in physical and biological coupling in the cross-frontal area off the coast of Catalonia in Spain (NW Mediterranean) during the spring transition period. The effect of short-term physical variability on the spatio-temporal heterogeneity of phytoplankton biomass and in the area of overlap of the larvae of fish species dwelling on the shelf and slope is discussed. Our results indicate that the region off the Catalan coast is a dynamically active area during the spring transition period. Short-term spatio-temporal variability in the frontal system brought about significant changes in the extension of shelf and slope waters, giving rise to major changes in the spatial distribution patterns of chlorophyll and fish larvae. The relationship between integrated chlorophyll, surface chlorophyll and DCM (Deep Chlorophyll Maximum) showed important variability in a short time period. The area of overlap of the larvae of shelf and slope fish species was broad when the front was located offshore, compared to nearly complete segregation of shelf and oceanic fish larvae when the front moved inshore near the coast.

Clues from the recent past to assess recruitment of Mediterranean small pelagic fishes under sea warming scenarios

Knowledge of the effect of environmental variables on the early life history of fishes is essential to assess the effect of future environmental changes on the recruitment of commercial species. We investigate the effect of sea warming on two small pelagic fishes (Engraulis encrasicolus and Sardinella aurita) in the NW Mediterranean Sea based on the analysis of ichthyoplankton data collected in two surveys of contrasting conditions: the exceptionally warm summer of 2003, which may be indicative of conditions under future climate change scenarios, and the summer of 2004, with temperatures within the climatic average for the period 2000-2012. We use fine-resolution environmental variables measured locally and Generalized Additive Models to assess the influence of environment on these two summer-spawning small pelagic fishes. We show that sea surface temperature is the main environmental factor explaining abundance, but other factors (food availability and water currents) have additional roles tuning the effect of temperature. In the hot summer of 2003 we observed a decline of local egg production of anchovy and an increase of larval advection from the colder Gulf of Lions compared to 2004. Round sardinella spawning was higher in 2003 than in 2004 and extended over a wider area, but larvae viability was compromised by the lower availability of trophic resources. We hypothesize that future changes in environmental forcing on these two co-occurring summer spawning species will determine differential larval survival, with cascading effects on the upper trophic levels which feed on these species, including negative impacts on their fisheries.

Early development of eye and retina in lanternfish larvae.

The morphological characteristics of the eyes and the retinae of lanternfish larvae of Lampanyctus crocodilus, Benthosema glaciale, and Myctophum punctatum were analyzed in pre-flexion, flexion, and post-flexion stages. Pre-flexion larvae of L. crocodilus, the species with the shallowest depth distribution, had spherical eyes located antero-laterally on a strongly laterally-compressed head, suggesting a forward binocular visual field. B. glaciale and M. punctatum larvae live deeper in the water column and had eyes elongated in the dorsal-ventral plane. The eyes of B. glaciale were prominent, projecting slightly outward from a laterally-compressed head, suggesting a strongly laterally-directed visual field. M. punctaum had stalked elongated eyes projecting from a dorso-ventrally flattened head. The eyes can be freely rotated allowing lateral, anterior and dorsally-directed vision. A prominent choroidal gland was situated beneath the ventral portion of the eye in M. punctatum and B. glaciale, while a smaller gland was present in the dorsal and ventral portions of the eye of L. crocodilus. In pre-flexion stage larvae, the retina of all three species was differentiated with numerous rod photoreceptors in the peripheral retinal areas and fewer cone photoreceptors mainly distributed in the central retina. This distribution suggests concomitant enhancement of scotopic sensitivity in the vertical visual plane and improved photopic acuity in the lateral and forward visual directions. The concurrent development of cones and rods, as observed in the pre-flexion stage of myctophid larvae, is consistent with meeting the special demands of visual planktivory in sub-surface waters. During larval development a gradual increase of ROS length was also accompanied by a progressive loss of cones that were almost totally absent in post-flexion larvae. This can be interpreted as an adaptive response to an impending deep mesopelagic adult life.