Browsing by Author "Hernandez, Ignacio"
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- Effects of nutrient enrichment on seagrass population dynamics: evidence and synthesis from the biomass-density relationshipsPublication . Cabaco, Susana; Apostolaki, Eugenia T.; Garcia-Marin, Patricia; Gruber, Renee; Hernandez, Ignacio; Martinez-Crego, Begona; Mascaro, Oriol; Perez, Marta; Prathep, Anchana; Robinson, Cliff; Romero, Javier; Schmidt, Allison L.; Short, Fred T.; van Tussenbroek, Brigitta I.; Santos, RuiThe available data from experimental and descriptive studies on seagrass biomass and density responses to nutrient enrichment were analysed to assess the intraspecific mechanisms operating within seagrass populations and whether biomass-density relationships can provide relevant metrics for monitoring seagrasses. The response of shoot biomass and density to nutrient enrichment was dependent on the type of study; the short-term positive response of biomass and density in experimental studies reveals context-specific nutrient limitation of seagrasses. The long-term negative response of descriptive studies probably results from ecosystem-scale events related to nutrient enrichment such as increased turbidity, algal blooms, epiphyte loads and anoxia. Most seagrass species analysed lie in the nonthinning part of the theoretical biomass-density curves. A simultaneous increase in biomass and decrease in density, evidence of self-thinning, were only observed in 4 of 28 studies. The analysis of both the static and the dynamic biomass-density relationships revealed that the slopes increase under nutrient enrichment. Surprisingly, the species-specific slopes (log B-log D) were higher than one, revealing that the B/D ratio, that is, the average shoot biomass, increases with density in all seagrass species analysed. Nutrient enrichment further enhanced this effect as biomass-density slopes increased to even higher values. The main drivers behind the increasing biomass-density slopes under nutrient enrichment were the increase in shoot biomass at densities above a species-specific threshold and/or its decrease below that threshold. Synthesis. Contrasting short- and long-term responses of both biomass and density of seagrasses to nutrient enrichment suggest that the former, positive ones result from nutrient limitation, whereas the later, negative ones are mediated by whole ecosystem responses. In general, shoot biomass of seagrasses increases with density, and nutrient enrichment enhances this effect. Experimental testing of facilitation processes related to clonal integration in seagrasses needs to be done to reveal whether they determine the low incidence of self-thinning and the intriguing biomass-density relationships of seagrass species. The increasing slopes and decreasing intercepts of the species-specific dynamic biomass-density relationships of seagrasses and the decreasing coefficients of variation of both biomass and density constitute relevant, easy-to-collect metrics that may be used in environmental monitoring.
- Increased vulnerability of Zostera noltii to stress caused by low light and elevated ammonium levels under phosphate deficiencyPublication . Brun, Fernando G.; Olive, Irene; Malta, Erik-jan; Vergara, Juan J.; Hernandez, Ignacio; Lucas Perez-Llorens, J.The effects of light and ammonium levels on net production, fluorescence parameters and non-structural carbohydrates of the seagrass Zostera noltii under different phosphate conditions were studied. A fully factorial design was used with light (low/high levels), ammonium supply and phosphate preculture conditions of the plants as the experimental variables. Both ammonium supply and low light caused negative and synergistic effects on net production, while ammonium toxicity was more severe at high light levels; in this case, it was independent of the non-structural carbohydrate (sucrose and starch) content. Preculturing of plant with added phosphate alleviated the ammonium toxicity, and also attenuated the negative production balance of plants grown at low light levels. The results indicated that phosphate preculture ameliorated the plant's short-term response against the assayed stressors (low light, high ammonium) significantly. An overall consumption of non-structural carbohydrates in response to environmental stressors was recorded throughout the experiment, indicating the importance of carbon and phosphorus reserves to cope with adverse conditions. ln addition, phosphate deficiency increased the vulnerability of plants, which could have negative ecological consequences for seagrass species thriving under phosphate deficiency conditions, or in developing seagrass transplantation programs.
- Influence of irradiance, dissolved nutrients and salinity on the colour and nutritional characteristics of Gracilariopsis longissima (Rhodophyta)Publication . Bermejo, Ricardo; Macias, Manuel; Sanchez-Garcia, Fini; Love, Robyn; E, Varela-Álvarez; Hernandez, IgnacioColour is immediately perceived by the consumer and crucial for food product attractiveness. In this study, the possibility of obtaining different colour morphotypes in the rhodophyte Gracilariopsis longissima using short cultivation protocols (i.e. 9 days) was explored. In a first factorial experiment, the effects of salinity (25‰, 35‰ and 45‰), irradiance (60 and 270 μmol photons m− 1 s − 1 ) and nutrient conditions (N and P enrichment, no enrichment) on the growth, pigment concentration and colour of G. longissima were assessed. The results indicated that growth rate and phycocyanin were influenced by the three variables, whereas the concentration of other pigments (chlorophyll a, carotenoids and phycoerythrin) was significantly influenced by irradiance and nutrient conditions. The colour, defined as the Red, Green, Blue (RGB) signal from the photographed thalli, was mainly affected by irradiance and nutrient conditions. In a second experiment, four culture conditions yielding contrasting colour morphotypes and growth rates were repeatedly scaled up in the experiment to get enough biomass and to analyze nutritional properties (lipids, proteins, tissue N and P). The colour morphotypes and the corresponding culture conditions selected were: i) dark red; high salinity, low irradiance, nutrient enrichment; ii) light red; medium salinity, high irradiance, nutrient enrichment; iii) brownish; low salinity, low irradiance; no enrichment; and iv) green-yellowish; low salinity, high irradiance, no enrichment. These conditions caused marked differences in the nutritional properties of the thalli. The light red colour showed the best nutritional characteristics. Overall, G. longissima was not a suitable source of omega 3, but can be a source of Fe (0.34–0.53 mg g− 1 DW) and K (103–161 mg g− 1 DW), and its K:Na ratio can be enhanced under increasing salinity. The fast ecophysiological response, and its wide tolerance to environmental conditions, makes this species an excellent candidate for the development of short cultivation protocols.
- Marine forests of the Mediterranean-Atlantic Cystoseira tamariscifolia complex show a southern Iberian genetic hotspot and no reproductive isolation in parapatryPublication . Bermejo, Ricardo; Chefaoui, Rosa M.; Engelen, Aschwin H.; Buonomo, Roberto; Neiva, J.; Ferreira-Costa, Joana; Pearson, Gareth; Marba, Nuria; Duarte, Carlos M.; Airoldi, Laura; Hernandez, Ignacio; Guiry, Michael D.; Serrao, Ester A.Climate-driven range-shifts create evolutionary opportunities for allopatric divergence and subsequent contact, leading to genetic structuration and hybrid zones. We investigate how these processes influenced the evolution of a complex of three closely related Cystoseira spp., which are a key component of the Mediterranean-Atlantic seaweed forests that are undergoing population declines. The C. tamariscifolia complex, composed of C. tamariscifolia s.s., C. amentacea and C. mediterranea, have indistinct boundaries and natural hybridization is suspected. Our aims are to (1) infer the genetic structure and diversity of these species throughout their distribution ranges using microsatellite markers to identify ancient versus recent geographical populations, contact zones and reproductive barriers, and (2) hindcast past distributions using niche models to investigate the influence of past range shifts on genetic divergence at multiple spatial scales. Results supported a single, morphologically plastic species the genetic structure of which was incongruent with a priori species assignments. The low diversity and low singularity in northern European populations suggest recent colonization after the LGM. The southern Iberian genetic hotspot most likely results from the role of this area as a climatic refugium or a secondary contact zone between differentiated populations or both. We hypothesize that life-history traits (selfing, low dispersal) and prior colonization effects, rather than reproductive barriers, might explain the observed genetic discontinuities.