The population dynamics of Halecium petrosum and Halecium pusillum (Hydrozoa, Cnidaria), epiphytes of Halimeda tuna in the nortwestern Mediterranean

Halecium petrosum and Halecium pusillum on the alga Halimeda tuna from Tossa de Mar, northeastern Spain, were studied. Asexual reproduction of H. petrosum, by stolonisation, occurred throughout the year except for July and August. Asexual reproduction of H. pusillum, by planktonic propagules, occurred throughout the year. Sexual reproduction was limited to the autumn in H. petrosum and spring in H. pusillum. The growth rates of colonies of both species were rapid but declined with increased size. Mean colony size over two consecutive two week periods increased approximately five-fold and three-fold for H. petrosum, and six-fold and four-fold for H. pusillum. Mortality was estimated to be high for both species, especially in summer. The maximum life span of colonies (ramets) of both species was estimated to be only eight weeks. Consequently most colonies do not reproduce sexually. The absence of reproduction of H. petrosum in summer, when the turnover of algal thalli was greatest, probably contributed to the summer decline in its abundance. In both species the genet (clone) survives for unknown, possibly very long, periods by asexual reproduction which facilites colonisation of other substrata.

Fecal pellets collection as a method for assessing egesta of the marine cave-dwelling mysid Hemimysis speluncula

Egesta of a cave-dwelling mysid (Hemimysis speluncola Ledoyer, 1963) was studied in a submarine cave of Medes Islands, NW Mediterranean by in situ fecal pellet collecting. Fecal pellet production and gut fullness of mysids during incubation experiments are used to estimate mysid egestion rates. Intrinsic factors related with the natural history of this species such as population structure, density of mysids, daily rhythms and pellet decomposition rates are tested for their influence on the egestion rate. The effects of methodological artifacts, such as the stress induced by both incubation and preservation procedures, are also studied. An average mysid egests about 2.5 pellets per day into the cave. The time of day is the main factor affecting egestion. The highest deposition rate is between 2 to 4 hours after sunrise when about 38 % of the total daily pellet production becomes egested. Fecal pellet morphology changes with mysid demographic classes: immature mysids produce slender and thick pellets, whereas mature mysids produce only thick pellets. Immature classes show higher percentages of full guts than mature ones. Mysid density in the incubators does not affect the results on gut fullness, but it causes a decrease in the number of pellets collected after incubation. Coprorhexia seems to be the only plausible process to explain this paradox. The incubation procedure does not increase deposition rate significantly. Time of incubation is critical because the half-life of fecal pellets is about 2.5 hours. Fixation with liquid nitrogen decreases gut fullness and also deposition rates. Higher values are obtained with 70 % ethanol and 5 % formalin solutions which show very similar results for both gut fullness and pellet deposition rates. Nevertheless, ethanol is not suitable as fixative because it enhances the opacity of the body. Several suggestions are given in order to optimize the reliability of further in situ experiments for evaluation of egesta of Hemimysis speluncola in submarine caves.

Temporal variation of the biomass and structure of Caulerpa prolifera (Forsskal) Lamouroux meadows in the Mar Menor lagoon (SE Spain).

The temporal changes in the structure, biomass and C, N and P content of meadows of Caulerpa prolifera (Forsskal) Lamouroux in the Mar Menor coastal lagoon (SE Spain) are described over the period from November 1986 to March 1989. C. prolifera meadows showed a unimodal pattern of vegetative development with maximum biomass values (168-173 g d.w. m-2) reached in summer and maintained during autumn, and minimum biomass values (0-57 g d.w. m-2) during late winter and early spring. Leaf area index values changed between 0.37-0.40 m2 m-2 in January-February and 2.60-7.06 m2 m-2 in July. The seasonality in the biomass and structure of the meadow was mainly related to the vegetative development of the secondary fronds. Carbon and phosphorus content of the thallus (32.5-34.8% d.w. and 0.065-0.069% d.w., respectively) had no seasonality, but nitrogen content showed a bimodal annual pattern with higher values in spring and fall (>2.5% d.w.) than in summer and winter (<2.5% d.w.).

Morphometric relationhip in the Chaetognath Sagitta setosa Muller 1847: within population versus between population variability.

Sagitta setosa is a neritic Chaetognath exhibiting a discontinuous geographic distribution. To assess the influence of its discontinuous geographic distribution on morphometric variability between isolated populations, we conducted a biometric study of S. setosa from three different locations: Goteborg and Plymouth (North Atlantic) and Barcelona ( Western Mediterranean). Out results do indicate some disparity between the populations that is reflected not in size differences, largely determined by water temperature, but in shape (body proportions).

Chemical defenses in Sacoglossan Opisthobranchs: Taxonomic trends and evolutionary implications

Sacoglossan sea slugs (Mollusca: Opisthobranchia) are one of the few groups of specialist herbivores in the marine environment. Sacoglossans feed suctorially on the cell sap of macroalgae, from which they 'steal' chloroplasts (kleptoplasty) and deterrent substances (kleptochemistry), retaining intracellularly both host plastids and chemicals. The ingested chloroplasts continue to photosynthesize for periods ranging from a few hours or days up to 3 months in some species. Shelled, more primitive sacoglossans feed only on the siphonalean green algal genus Caulerpa, and they do not have functional kleptoplasty. The diet of sacoglossans has radiated out from this ancestral food. Among the shell-less Plakobranchidae (=Elysiidae), the more primitive species feed on other siphonales (families Derbesiaceae, Caulerpaceae, Bryopsidaceae and Codiaceae) and fix carbon, while the more 'advanced' species within the Plakobranchidae and Limapontioidae have a more broad dietary range. Most of these 'advanced' species are unable to fix carbon because the chloroplasts of their food algae are mechanically disrupted during ingestion. Mesoherbivores are likely to be eaten if they live on palatable seaweeds, their cryptic coloration and form not always keeping them safe from predators. Sacoglossans prefer to live on and eat chemically defended seaweeds, and they use ingested algal chemicals as deterrents of potential predators. The most ancestral shelled sacoglossans (Oxynoidae) and some Plakobranchidae such as Elysia translucens, Thuridilla hopei and Bosellia mimetica have developed a diet-derived chemical defense mechanism. Oxynoids and Thuridilla hopei are able to biomodify the algal metabolites. However, the Plakobranchidae Elysia timida and E. viridis, together with Limapontioidea species, are characterized by their ability to de novo synthesize polypropionate metabolites. A whole analysis of kleptoplasty and chemical defenses in sacoglossans may offer a better understanding of the ecology and evolution of these specialized opisthobranchs. In this paper we summarize some of the latest findings, related mainly to Mediterranean species, and offer a plausible evolutionary scenario based on the biological and chemical trends we can distinguish in them.

Sedimen-water nutrient fluxes: Preliminary results of in situ measurements in Alfaques Bay, Ebro River Delta.

Sediment-water exchanges of oxygen, ammonium, nitrate, total dissolved nitrogen, phosphate and total dissolved phosphorus were measured by means of an in situ incubator of 7 1 volume and 700 cm2 base area. The incubations lasted for three hours and were done over a whole season on different kinds of sediments in Alfaques Bay. We present some preliminary results on: i) methodological aspects, ii) spatial and temporal variability of fluxes, and iii) estimates of contribution of benthic nutrient regeneration relative to total nutrient loading of the Bay. Oxygen uptake averaged 1700 mmo1 m-2 h-1 (range 200-3500); no differences were found between sandy and muddy sediments. The release of ammonia from the sediment averaged 70 mmo1 m-2 h-1 and was higher in muddy sediments than in sandy ones. Very low to null nitrate and nitrite fluxes and only small fluxes of organic nitrogen were detected. We conclude that ammonium release from sediment is the major path of nitrogen regeneration. Some sediments removed dissolved reactive phosphorus (DRP) from the water and released dissolved organic phosphorus (DOP). Additional manipulative experiments revealed DRP release under particular conditions (turbulence, anoxia). From these data, we estimate that at least 50% of the nitrogen requirements of phytoplankton in the area may be supplied by benthic remineralization.

Spatial distribution and biomass of aquatic rooted macrophytes and their relevance in the metabolism of a Mediterranean coastal lagoon

This work aims to characterise the current autotrophic compartment of the Albufera des Grau coastal lagoon (Menorca, Balearic Islands) and to assess the relationship between the submerged macrophytes and the limnological parameters of the lagoon. During the study period the submerged vegetation was dominated by the macrophyte Ruppia cirrhosa, which formed dense extensive meadows covering 79% of the surface. Another macrophyte species, Potamogeton pectinatus, was also observed but only forming small stands near the rushing streams. Macroalgae were only occasionally observed. Macrophyte biomass showed a clear seasonal trend, with maximum values in July. The biomass of R. cirrhosa achieved 1760 g DW m-2, the highest biomass ever reported for this species in the literature. The seasonal production-decomposition cycle of the macrophyte meadows appears to drive the nutrient dynamics and carbon fluxes in the lagoon. Despite the significant biomass accumulation and the absence of a washout of nutrients and organic matter to the sea, the lagoon did not experience a dystrophic collapse. These results indicate that internal metabolism is more important than exchange processes in the lagoon.

Aportació al coneixement de la brioflora aquàtica de l'alta muntanya pirinenca

Hemos estudiado la brioflora acuática de diversas localidades de los Pirineos Centrales y Orientales, situadas por encima de 1600 m de altitud. En las aguas corrientes abundan Hygrohypnum sp. pl., Schistidium alpicola var. rivulare, Cratoneuron commutatum, Pbilonotis sp. pl., Bryum pseudotriquetrum, Scapania undulata y Marsupella emarginata var. aquatica. En las aguas remansadas y en los lagos abundan Blindia acuta, Jungermanma exsertifolia ssp. cordi/olia, Chiloscyphus polyantbos y, en los márgenes Pbilonotis seriata. Todas estas especies han desarrollado características morfológicas de adaptación al medio y se trata de especies muy diferentes de las que dominan en la montaña media y en el llano. Es destacable la presencia de briófitos en las riberas de los ibones, a muy poca profundidad, donde han de soportar el hielo de 7 a 9 meses.

El género Mastogloia en los sistemas acuáticos del litoral mediterraneo español

Desde 1979 se ha estudiado la flora de diatomeas bentónicas de 60 ecosistemas acuáticos del litoral mediterráneo español. En este trabajo se resumen las observaciones realizadas sobre las especies del género Mastogloia Thwaites presentes en estos puntos. Se han identificado 18 especies y 4 variedades; 15 de las cuales se citan por primera vez de nuestras aguas epicontinentales. Los datos sobre la distribución de las frecuencias relativas (%) de cada uno de los táxones del género Mastogloia han permitido la tipificación de las localidades estudiadas. Esta clasificación está de acuerdo con la obtenida a partir de los datos sobre la mineralización de las aguas (LOPEZ, 1981b).

Catálogo de las algas bentónicas (con exclusión de las diatomeas) de la costa catalana

Aquest treball és un intent d´actualitzar i sistematitzar les dades algològiques que es posseeixen referents al nostre país. Aquestes dades han estat obtingudes de la bibliografia existent, incloent-hi també nombroses observacions personals inèdites. La sistemàtica utilitzada ha estat, bàsicament, la proposada per PARKE i DIXON (1976). La distribució geogràfica de les espècies s'especifica en funció del reticle UTM. En aquest moment són 403 (28 Cyanophyta, 220 Rhodophyta, 69 Phaeophyta, 85 Chlorophyta i 1 Chrysophyta) les espècies que es coneixen a les costes del Principat.

El fitoplàncton dels aiguamolls de Ca l'Estany de Tordera (Barcelona)

Els aiguamolls de Ca l'Estany de Tordera (Maresme, Catalunya) són sistemes força fluctuants, lligats al règim del riu La Tordera. Han estat determinades un total de 71 espècies i varietats en el fìtoplàncton, de les que són descrites les seves variacions estacional i de comunitat segons les localitats.

Sobre dos supuestas protofitas

Durante algún tiempo conservé la descripción y la figura de un curioso objeto, encontrado entre algas de agua dulce y que creí una clorofícea de muy especiales caracteres. Al contemplar por primera vez polen de mimosa, vi en el campo del microscopio innumerables ejemplares de mi extraordinaria «alga», cuya identidad quedaba así inequívocamente definida...

Contribución al conocimiento del género Platymonas (Volvocales)

En el curso de mis investigaciones sobre la microflora acuática he sido favorecido con el hallazgo de dos nuevas especies de volvocales clamidomonadáceas, pertenecientes a un grupo interesante por muchos conceptos, seguramente rico en formas, pero que ha sido relativamente poco estudiado...

Materiales para una flora de las algas del NE de España. I. Zygnemales

Posteriormente a la publicación de mi primera contribución a la flora algológica de nuestras aguas dulces (1944), he dado preferencia a la preparación de trabajos de carácter local y ecológico, por entender que éstos podían conducir más rápidamente al planteamiento, y quizá a la resolución, de problemas de interés superior al puramente taxonómico. Pero el estudio de muchos centenares de muestras de algas, procedentes de localidades dispersas de Cataluña y de comarcas limítrofes, ha ido prosiguiendo independientemente, permitiendo reunir una cantidad considerable de datos inéditos. Eáta nota es la primera de una serie de contribuciones taxonómicas a nuestra flora algológica, que tendrán como base el material no utilizado en otros trabajos de limnología regional o local.

Los métodos para la investigación de las comunidades acuáticas adnadas y especialmente las formadas por organismo microscópicos (perifiton, pecton)

Esta nota se refiere a los métodos de estudio de las agrupaciones de organismos que se desarrollan sobre las superficies libres de los objetos sumergidos en el agua. Se trata de un tipo de comunidad que forma una capa o almohadilla continua sobre el substrato, que puede alcanzar un grueso considerable y precipita a menudo depósitos minerales en su espesor. Otras veces, la presencia de tal comunidad no puede apreciarse a simple vista, por su escasa altura y pequenez de los organismos que la constituyen. El mismo tipo de comunidad puede desarrollarse sobre substrato suelto o movedizo limo, arcilla, gyttja , en forma de lámina continua aplicada sobre el fondo...