Uxío Labarta

Coastal upwelling, primary production and mussel growth in the Rías Baixas of Galicia

The Rías Baixas are four flooded tectonic valleys located on the northwest Iberian Peninsula that support a mussel production of about 250 × 106 kg y−1 from 3337 mussel rafts. Mussel production in this region is the highest in Europe and one of the most intensive in the world, giving employment to 9000 people directly and 20000 indirectly. The causes of this high mussel production are discussed through the analysis of published and some unpublished information. The interaction between coastal upwelling and the circulation patterns in the Rías, which channel the 3-dimensional variability of the open ocean into a 2-dimensional system, promotes a massive response in the productivity of phytoplankton populations inside the Rías, even during weak upwelling events along the coast. Coastal upwelling in the area typically occurs between March–April and September–October. The mean value of gross primary production during the whole upwelling season is ∼1.4 g C m−2 d−1, although high sporadic values of ∼4 g C m−2 d−1 may occur during upwelling relaxation events, when phytoplankton export to the coastal shelf is restricted. Mussel growth occurs mainly during the upwelling season. It is estimated that mussel harvest extracts ∼10% of the primary production. The phytoplankton response to upwelling provides food of high quality (f ∼0.5) that determines high absorption efficiency (∼0.6), whereas the characteristics of the Rías maintains the seston concentration at levels (0.5 – 1.3 mg TPM l−1 and <5 mg Chl a m−3) below the threshold of pseudo-faeces production. The physiological behaviour of mussels indicates that the high yield of mussel culture in the Rías of Galicia is a consequence of the particular characteristics of the seston.

Biomass production and variation in the biochemical profile (total protein, carbohydrates, RNA, lipids and fatty acids) of seven species of marine microalgae

Abstract Seven species of marine microalgae ( Pavlova lutheri, Isochrysis galbana, Tetraselmis suecica , Chaetoceros calcitrans, Phaeodactylum tricornutum, Rhodomonas sp. and Heterosigma akashiwo ) were harvested at three phases in the growth curve and biochemical composition (total protein, carbohydrates, RNA, lipids and fatty acids) was determined. Carbohydrate and lipid contents increased with the development of the culture, while protein levels increased in the later phases of the culture in the case of diatoms and Rhodomonas sp. and decreased in I. galbana, P. lutheri and T. suecica . Saturated fatty acids and, to a lesser extent, monoethylenic fatty acids represent between 70 and 100% of the total fatty acids. Polyunsaturated fatty acids reached their highest values in the exponential phase in Rhodomonas sp. (30.99%), in an early stationary phase in P. tricornutum (19.58%) and C. calcitrans (9.06%) and in a late stationary phase in I. galbana (12.89%), P. lutheri (4.24%) and T. suecica (18.58%). RNA levels never exceeded 2.5%. The daily production was calculated for each batch culture in three growth phases and was compared with the production of a semicontinuous culture maintained in the exponential phase. Rhodomonas sp., C. calcitrans and P. tricornutum showed a lower daily production under semicontinuous culture than in batch cultures, while I. galbana, P. lutheri, T. suecica and H. akashiwo showed the opposite. The daily production of each of the biochemical components also varied with the species.

Evaluation of live microalgal diets for the seed culture of Ruditapes decussatus using physiological and biochemical parameters.

Abstract The nutritional quality of several microalgal diets used in the seed culture of the little-neck clam, Ruditapes decussatus , was evaluated in the present study. The live diets tested were Isochrysis galbana , clone T-ISO, Tetraselmis suecica and Phaeodactylum tricornutum . Criteria used in the evaluation of the diets were acceptability, digestibility, growth and biochemical composition. The highest growth rate was registered in the seed fed the T. suecica diet, followed by the seed fed I. galbana , while the lowest one was obtained in the seed fed P. tricornutum . Food ingestion rates were higher in the seed fed Tetraselmis . This fact would partly explain the higher growth observed with this diet. The limited nutritional value of Phaeodactylum could be related to the low digestibility of its cell wall, the degree of acceptability of this diet being similar to or even higher than that of the other two. The low protein content of Tetraselmis seems to indicate that R. decussatus shows a low requirement for proteins, which can be spared by carbohydrate, an abundant component in the cells of Tetraselmis . Lipid needs of this bivalve also seem to be rather low.

Fatty acid profiles of Mytilus galloprovincialis (Lmk) mussel of subtidal and rocky shore origin

Fatty acid profiles of seeds of the mussel Mytilus galloprovincialis originating from two habitats (rocky shore and subtidal) were compared after transfer to the same habitat (subtidal). The objective was to study the initial levels of different fatty acids of metabolic importance and, furthermore, the variability of these fatty acids over the experimental period. The results show that of all fatty acids identified in both seed groups, the polyunsaturated fatty acids (PUFA) is the group with highest percentage. Within this group, the C20:5n-3 and C22:6n-3 fatty acids show the highest levels. Additionally, the mussels of subtidal origin presented higher initial levels than the rocky shore mussels with regard to fatty acids characterised by energetic-type functions, such as the C14:0, C16:0, and the C20:5n-3 fatty acids, among others. Fatty acids characterised by structural-type functions, e.g. C18:0, C22:6n-3 and non-methylene interrupted dienoic (NMID) with 20 and 22 carbons in rocky shore mussels presented higher levels than those of the subtidal mussels. However, it has not been ruled out that aside from influences relating to the functional aspects of the different fatty acids, the initial differences were also associated with the quantitative and qualitative differences of the available food in both habitats. Nevertheless, 22 days into the experiment (in the majority of cases) the initial differences disappear in the different fatty acids with metabolic importance. On the basis of these results, the influence that mussel origin could exercise on the variability of the fatty acid profiles of recognised metabolic importance is discussed.

Evolution of fatty acid profiles of subtidal and rocky shore mussel seed (Mytilus galloprovincialis, Lmk.). Influence of environmental parameters

Abstract In the present study fatty acid profiles of Mytilus galloprovincialis mussel seeds originating from two habitats with different environmental conditions (rocky shore and subtidal) were compared after transfer to the same environmental habitat (subtidal). The aim of the research was to investigate the influence of various environmental parameters on the relative percentage of fatty acids. The study was based in the Arosa Ria, Northwest Spain, between 27th November 1995 and 3rd July 1996. The location of the mussels suspended from the raft, the rope density (1.6 kg m −1 ) and cultivation depth (1.5–5.0 m) were common parameters for both mussel groups. Our results show that during the first 36 days of the experimental period the mussel origin participated significantly in the model explaining the variance of various fatty acids of physiological importance in marine bivalves, namely the acids 18:0, 16:1 n −7, 18:1 n −9, 18:1 n −7, 18:2 n −6, 18:3 n −3, 18:4 n −3, 20:2NMID1, 20:5 n −3 and 22:6 n −3. In addition, other environmental parameters related to food availability, such as the ratio chl- a /POM and TPM, only participated in the explanation of two and three of these acids, respectively. In contrast, 50 days into the experiment the mussel origin did not participate in the model of variance of the fatty acids studied, and the ratio chl- a /POM participated significantly in the model explaining the variance of 11 of the total (16) selected fatty acids studied. Moreover, the coefficients were only positive in the fatty acids of known energetic importance in marine bivalves, namely the acids 14:0, 16:1 n −7, 18:1 n −7, 20:5 n −3 and the ratio PUFAs n −3/ n −6. The influence that mussel origin and various environmental parameters could exercise on the variability of diverse fatty acids of both mussel groups is discussed.

Effect of condition index on allometric relationships of clearance rate in Mytilus galloprovincialis Lamarck, 1819

The allometric relationships between clearance rate (CR) and length and CR and weight show considerable variability in the literature. Nonetheless, they have...

Metabolism of the mussel Mytilus galloprovincialis from two origins in the Ría de Arousa (north-west Spain)

Mussel seed Mytilus galloprovincialis (Bivalvia: Mytilidae) from two origins (rocky shore and collector ropes) was cultivated on a raft in the Ria de Arousa (north-west Spain), from seeding to thinning out, for 226 d (November 1995-July 1996) and two aspects of metabolism, oxygen consumption rate (VO 2 ) and ammonia excretion rate (VNH 4 -N) were studied in situ. The model derived from multiple analysis of oxygen consumption accounted for 91.9% of the variance, based on dry weight of the mussels and the environmental factors quality of food (organic content) and mainly chlorophyll-a. Seed origin also showed significant influence. The seasonal pattern of the oxygen consumption can be attributed mainly to the variation of chlorophyll-a, which showed a higher range of values in the spring months. Origin of seed did not show a homogeneous effect on oxygen consumption throughout the cultivation period. Collector rope mussels showed higher oxygen consumption values at the beginning of the cultivation period and after the first 15 d, but the rocky shore mussels showed a higher oxygen consumption between days 22 and 110. Energy-conserving patterns and lower condition index at the onset of the experiment for rocky shore mussels could explain these initial differences. Multiple analysis on the variation of ammonia excretion rate provided a model that accounted for 72.6% of the variance based on dry weight of mussels, seed origin and the environmental parameters chlorophyll-a and total particulate matter. The rocky shore mussels showed a significantly higher excretion values for most of the cultivation period, although there was no constant tendency throughout. High excretion values were recorded between January and March, whilst for the rest of the cultivation period values were low. The O:N index was higher in collector rope mussels for most of the cultivation period, which may suggest a more favourable energy metabolism and/or a more appropriate nutritional state for these specimens.

Effects of commercial enrichment diets on the nutritional value of the rotifer (Brachionus plicatilis)

Abstract The rotifer, Brachionus plicatilis, pre-fed on bakers yeast, was enriched for 6 h with three commercial products from Artemia Systems S.A., namely Protein Selco (microcapsules), Dry Selco (microparticles) and Super Selco (an emulsion containing high levels of n−3 HUFA). The biochemical composition (protein, carbohydrate, total lipid, lipid classes and fatty acids) and dry weight of the rotifers before and after the enrichment experiments were studied. Two of the enrichers, Dry Selco and Super Selco, are rich in lipid but poor in protein and carbohydrate. Protein Selco contains lipid as well as protein and carbohydrate. The biochemical composition and the dry weight of the rotifers were changed after 6 h of enrichment. The percentage of protein and lipid increased with all of the three enrichers and the percentage of carbohydrate decreased slightly. Rotifer dry weight increased in rotifers enriched on Protein Selco. Phospholipids, sterol esters + waxes, triacylglycerols and free fatty acids increased after the enrichment with the three enrichers while sterols slightly decreased when the rotifers were fed on Protein Selco. The fatty acid content of the rotifers increased after the enrichment with all of the enrichers and this increase was particularly apparent in the case of n−3 HUFAs (20:5n−3) and 22:6n−3).

Fatty Acid Composition of Ruditapes decussatus Spat Fed on Different Microalgae Diets

The fatty acid composition of the Ruditapes decussatus spat fed on three different microalgal diets during 4 weeks was determined. The fatty acid pattern of each diet was also analysed. The diets used were Isochrysis galbana, clone T-ISO, Tetraselmis suecica, and Phaeodactylum tricornutum. The fatty acid composition of the spat was usually well correlated with that of the diet supplied. Major differences among spat cultures were found in 14:0, 16:0, 16:1n-9, 16:1n-7, 18:1n-9, 18:2n-6, 18:3n-3, 18:4n-3, 20:5n-3, 22:5n-6 and 22:6n-3 fatty acids. These differences were correlated with the particular fatty acid content of each diet supplied. It has been shown that R. decussatus spat have a very low capacity to elongate and desaturate linolenic acid to n-3 PUFA, so when 20:5n-3 or 22:6n-3 were not present in the diet, they were also absent, at least in measurable amounts, in the clams. The absence of any of the “essential” fatty acids, 20:5n-3 in T-ISO or 22:6n-3 in Tetraselmis, did not limit spat growth, so their role as “essential” fatty acids might be a matter for discussion. Finally, the nutritive value of each diet was discussed in terms of its fatty acid composition.

Energy, biochemical substrates and growth in the larval development, metamorphosis and postlarvae of Ostrea edulis (L.)

This study investigates the larval development, metamorphosis and postlarval stage of O. edulis, evaluating growth, energy acquisition processes and the role assigned to the different biochemical substrates from a standpoint of both energy and structure. During the premetamorphic stage the highest growth rates correspond to organic weight, with a total energy gain of 46.1%. However, during the metamorphosis process the greatest rates correspond to inorganic weight, with negative growth rates for organic weight, the total energy loss being 51.5% of the energy content existing at the beginning of metamorphosis. In the post-larva greater growth rates are observed in dry weight. In this stage an energetic catabolism continues to be produced, although much less than in the previous stage (10.7%). The energetic data of larval and post-larval development of O. edulis showed a simultaneous negative curvilinear catabolism of lipids, carbohydrates and proteins. With respect to ash, adjustment is a positive curvilinear catabolism. With regard to organic weight, a negative linear adjustment is observed. Lipids were the main source of energetic metabolism of O. edulis throughout development, but there is also a significant protein catabolism rate. It was shown that the energy necessary to deposit 1 g of shell during the development of larval and post-larval in O. edulis is 15.04 kJ (3.59 kcal). Shell formation theories can explain the destination of at least part of the protein component, which, more than an energetic contribution could be interpreted as a structural contribution to shell formation, a process which reaches a high growth rate (measured in terms of inorganic weight and/or size) during the metamorphosis and post-metamorphosis stages analysed in this work, stages which coincide with increased protein catabolism.