Marta Pérez | Universidad de Jaén (original) (raw)
Papers by Marta Pérez
Journal of Pediatrics, 2005
To determine the neurodevelopmental outcome of prematurely born newborns with magnetic resonance ... more To determine the neurodevelopmental outcome of prematurely born newborns with magnetic resonance imaging (MRI) abnormalities.A total of 89 prematurely born newborns (median age 28 weeks postgestation) were studied with MRI when stable for transport to MRI (median age, 32 weeks postgestation); 50 newborns were studied again near term age (median age, 37 weeks). Neurodevelopmental outcome was determined at 18 months adjusted age (median) using the Mental Development Index (Bayley Scales Infant Development II) and a standardized neurologic exam.Of 86 neonatal survivors, outcome was normal in 51 (59%), borderline in 22 (26%), and abnormal in 13 (15%). Moderate/severe MRI abnormalities were common on the first (37%) and second (32%) scans. Abnormal outcome was associated with increasing severity of white matter injury, ventriculomegaly, and intraventricular hemorrhage on MRI, as well as moderate/severe abnormalities on the first (relative risk [RR] = 5.6; P = .002) and second MRI studies (RR = 5.3; P = .03). Neuromotor abnormalities on neurologic examination near term age (RR = 6.5; P = .04) and postnatal infection (RR = 4.0; P = .01) also increased the risk for abnormal neurodevelopmental outcome.In premature newborns, brain abnormalities are common on MRI early in life and are associated with adverse neurodevelopmental outcome.
The effects of fish farming on a seagrass (Posidonia oceanica) meadow at Fornells Bay, Minorca (B... more The effects of fish farming on a seagrass (Posidonia oceanica) meadow at Fornells Bay, Minorca (Balearic Islands) were studied. Changes in plant and meadow features (e.g. shoot morphology, shoot density, biomass, rhizome growth, nutrient and soluble sugars concentrations…) in three stations along a transect from a disturbed (organic pollution due to fish cultures) to an undisturbed site were assessed. The fish culture had ceased in 1991; however, seagrass decline, already reported in a previous study for the period 1988–1990, was still taking place at the time of sampling (July 1994). Differences between stations were very clear; the station closest to the fish cages showed reduced shoot density, shoot size, underground biomass, sucrose concentration and photosynthetic capacities. In contrast, shoots from the most polluted station showed higher P-concentration in tissues and higher epiphyte biomass than the other two. Since water conditions had recovered completely by the time of the sampling mission, it is proposed that the persistence of the seagrass decline was due to the excess organic matter remaining in the sediment.Les effets de l'élevage de poissons en cages flottantes sur un herbier de Posidonia oceanica ont étéétudiés dans la baie de Fornells (Minorque, îles Baléares). Des modifications dans les caractéristiques de la plante et de l'herbier (morphologie et densité des faisceaux, biomasse, croissance des rhizomes, teneurs en nutriments et en sucres solubles) sont observées en trois stations d'une radiale allant d'une zone polluée (par la matière organique due aux élevages de poissons) à une zone non polluée. Bien que l'élevage ait cessé en 1991, la dégradation notée en 1988–1990 s'est poursuivie jusqu'au moment de l'échantillonage décrit ici (juillet 1994). Les différences entre les stations sont très nettes : la proximité des cages est associée aux plus faibles valeurs de densité et taille des faisceaux, biomasse, teneur en saccharose et taux photosynthétique, tandis que dans cette même zone polluée, la concentration du phosphore dans les tissus et la biomasse des épiphytes sont maximales. La colonne d'eau ayant retrouvé son état initial après la disparition des élevages, la persistance de la dégradation pourrait être liée à des modifications du sédiment dont la teneur en matière organique est restée très élevée.
Marine Ecology, 1994
Abstract. Cymodocea nodosa is a relatively small seagrass species which is common in the Mediterr... more Abstract. Cymodocea nodosa is a relatively small seagrass species which is common in the Mediterranean. An intensive survey on its growth and production was carried out in a dense, monospecific stand located in a semi-estuarine embayment. Data on leaf appearance and growth, shoot recruitment and death, rhizome growth, above- and belowground biomass, and nutrient content in the different parts of the plant were obtained over 2 years. All these variables showed a clear seasonality. In general, maximum growth and production occurred in early summer (July), and maximum biomass was reached between July and September. Biomass, shoot density, growth and production showed clear minima in winter.
Aquatic Botany, 1994
We examine here the growth plasticity (as the variability in leaf growth and production, and shoo... more We examine here the growth plasticity (as the variability in leaf growth and production, and shoot mortality rate) and stand structure (rhizome, root and shoot biomasses and nutrient contents, and shoot age structure), of the Mediterranean seagrass Cymodocea nodosa (Ucria) Aschers. growing across an existing gradient of nutrient supply in shallow water (from 2 μM soluble reactive phosphorus at nutrient-rich, to 0.08 μM at nutrient-poor sites). Phosphorus concentrations in plant tissues increased strongly (three-fold in leaves, and ten-fold in rhizomes and roots) from nutrient-poor to nutrient-rich sites. Leaf phosphorus concentrations at nutrient-poor sites were only half of those required for balanced seagrass growth, indicating the importance of phosphorus in limiting C. nodosa growth at the nutrient-poor sites. Phosphorus-limited plants allocated a greater proportion of the limiting resource (32% of the P standing stock, compared with about 10% at nutrient-sufficient sites), and a greater proportion of the produced biomass (about 40% of the biomass, compared with about 15% of the biomass at nutrient-sufficient sites), to root development, thereby increasing their capacity to acquire phosphorus from the sediment at the expense of impaired shoot growth and size. Resources were relocated as nutrient shortage ameliorates towards nutrient-rich sites, yielding a reduction in the relative allocation to below-ground biomass (which represented about 80% and 50% of the biomass at nutrient-poor and nutrient-rich sites, respectively). Shoot growth at the nutrient-rich site exceeded that at sites receiving intermediate and low nutrient loadings by two-fold and three-fold, respectively, yet the biomass of plants growing under high nutrient supply was almost half of that of the plants receiving intermediate nutrient loading. Thos was due to reduced shoot density at the nutrient-rich site, resulting from higher shoot mortality at higher nutrient concentrations, which suggests a shift from phosphorus as the limiting resource towards limitation by light or oxygen supply to the roots. Depsite their lower biomass, the fast growth of plants at the nutrient-rich site allowed them to support similar leaf production to plants receiving intermediate nutrient supply, and twice the phosphorus incorporation rate of those plants. The observed differences in population dynamics across the gradient in nutrient supply demonstrate the power of comparative analyses of seagrass stands as an additional approach to examine the importance of nutrient supply in controlling seagrass growth and productivity.
Marine Pollution Bulletin, 2001
The spatial extent and timing of the impact of fish farms on the distribution and performance of ... more The spatial extent and timing of the impact of fish farms on the distribution and performance of a Posidonia oceanica meadow were examined in an embayment of the south-eastern coast of Spain (Hornillo Bay, Murcia). Changes in seagrass distribution were determined using available seagrass mapping (from 1988, i.e., before the onset of aquaculture activities and 1998) and by successive sampling in 1994 and 1998. Environmental variables (light attenuation coefficient, water-column dissolved nutrients and organic content of sediments) together with plant performance (shoot biomass, leaf growth rate, photosynthetic activity, carbohydrate reserves, the number of leaves per shoot, epiphyte loads and herbivore pressure) were measured in plants affected by organic discharges, and were compared with those found in reference healthy plants over an annual growth cycle. Since the onset of fish farm activity, 11.29 ha of P. oceanica meadow has been completely lost and 9.86 ha significantly degraded, thus resulting in a total affected area which accounts for about 53% of the former meadow, or 7-fold the fish farming area. Unequal propagation of seagrass die-off or degradation reflects the relevance of local factors such as depth and hydrodynamism on the true extent of fish farm impact. Water transparency decreases and dissolved nutrient and organic content of sediments increases in the vicinity of cages compared to distant reference stations, thus supporting the notion of environmental gradients caused by the organic release from cages, which spreads outwards. Shoot size, leaf growth rate and the number of leaves per shoot in plants close to the fish farm decreased. Moreover, low leaf growth and low rhizome carbohydrate concentration (always relative to that found in an undisturbed area) indicated carbon budget imbalances. Since light reduction in the affected area was only modest (31% of light reaching the sea surface, while at the same depth this figure was 39% at the reference site), and light availability was well above the minimum requirement estimated for this species, neither this factor nor epiphyte overgrowth (epiphyte load was lower in the affected area) seem to explain such carbon imbalances or the observed meadow regression. Alternatively, the high herbivore pressure found in the affected zone suggests that overgrazing is one of the main causes of decreasing shoot sizes and hence of carbon imbalance, reduced growth and shoot mortality. The impact of fish farms on seagrasses, therefore, seems to be highly variable and depends on complex interactions between a large number of processes.
Aquatic Botany, 1994
Carbon, nitrogen and phosphorus accumulation in the belowground parts of the seagrass Posidonia o... more Carbon, nitrogen and phosphorus accumulation in the belowground parts of the seagrass Posidonia oceanica (L.) Delile are presented. Including all the dead parts of the plant (roots, leaf bases, rhizomes and the organic matter in the sediment), values as high as 71 kg C m−2, 0.8 kg N m−2 and 0.03 kg P m−2 were found. Accumulation rates are estimated between 19–191 g C m−2 year−1, 0.2–2.3 g N m−2 year−1 and 0.009–0.09 g P m−2 year−1.
Marine Pollution Bulletin, 2001
The spatial extent and timing of the impact of fish farms on the distribution and performance of ... more The spatial extent and timing of the impact of fish farms on the distribution and performance of a Posidonia oceanica meadow were examined in an embayment of the south-eastern coast of Spain (Hornillo Bay, Murcia). Changes in seagrass distribution were determined using available seagrass mapping (from 1988, i.e., before the onset of aquaculture activities and 1998) and by successive sampling in 1994 and 1998. Environmental variables (light attenuation coefficient, water-column dissolved nutrients and organic content of sediments) together with plant performance (shoot biomass, leaf growth rate, photosynthetic activity, carbohydrate reserves, the number of leaves per shoot, epiphyte loads and herbivore pressure) were measured in plants affected by organic discharges, and were compared with those found in reference healthy plants over an annual growth cycle. Since the onset of fish farm activity, 11.29 ha of P. oceanica meadow has been completely lost and 9.86 ha significantly degraded, thus resulting in a total affected area which accounts for about 53% of the former meadow, or 7-fold the fish farming area. Unequal propagation of seagrass die-off or degradation reflects the relevance of local factors such as depth and hydrodynamism on the true extent of fish farm impact. Water transparency decreases and dissolved nutrient and organic content of sediments increases in the vicinity of cages compared to distant reference stations, thus supporting the notion of environmental gradients caused by the organic release from cages, which spreads outwards. Shoot size, leaf growth rate and the number of leaves per shoot in plants close to the fish farm decreased. Moreover, low leaf growth and low rhizome carbohydrate concentration (always relative to that found in an undisturbed area) indicated carbon budget imbalances. Since light reduction in the affected area was only modest (31% of light reaching the sea surface, while at the same depth this figure was 39% at the reference site), and light availability was well above the minimum requirement estimated for this species, neither this factor nor epiphyte overgrowth (epiphyte load was lower in the affected area) seem to explain such carbon imbalances or the observed meadow regression. Alternatively, the high herbivore pressure found in the affected zone suggests that overgrazing is one of the main causes of decreasing shoot sizes and hence of carbon imbalance, reduced growth and shoot mortality. The impact of fish farms on seagrasses, therefore, seems to be highly variable and depends on complex interactions between a large number of processes.
Estuarine Coastal and Shelf Science, 1997
The Mediterranean seagrassPosidonia oceanicaaccumulates large quantities of organic debris as roo... more The Mediterranean seagrassPosidonia oceanicaaccumulates large quantities of organic debris as roots, rhizomes and leaf sheaths are progressively buried forming a bioconstruction called ‘ matte ’. The organic material remains with little morphological alteration for millennia. Several strata from these accumulations in variousP. oceanicameadows were sampled. Radiocarbon dating of samples yielded a range of 0–3370 years before present. From these data, accretion rates averaging 0·175 cm year−1(range: 0·061–0·414) were inferred. Significant differences between sites were found. Accretion rates showed significant differences between matte strata (i.e. with time), but no defined patterns were appreciated. Such differences were not coherent across sites. It is concluded that accretion rates are mainly controlled by local factors.Analysis of carbon, nitrogen and phosphorous in the organic debris showed that there was not a net release during the process of matte construction; in some sites, nitrogen and phosphorus concentration remained constant throughout the matte profile, while in the other sites, their concentration increased significantly with age. This confirms the role ofP. oceanicameadows as sinks for biogenic elements.
Marine Biology, 1991
Experimental nutrient (N, P, and N+P) additions to shallow (ca. 1 m)Cymodocea nodosa (Ucria) Asch... more Experimental nutrient (N, P, and N+P) additions to shallow (ca. 1 m)Cymodocea nodosa (Ucria) Aschers. stands growing in patches and in a continuous meadow in a Mediterranean Bay (Alfacs Bay, NE Spain) in 1988 demonstrated mid-summer growth to be strongly P-limited, as suggested by the high N:P ratios (>35) in unmanipulated plants. P additions resulted in increased leaf P content, reduced N:P ratios, and enhanced shoot growth and turnover in both populations. These effects promoted in turn a stand response, leading to increased biomass and, therefore, increased areal productivity in the plots receiving P. The stand response was largely attributable to a doubling of shoot density, indicating enhanced rhizome growth and branching.
Journal of Pediatrics, 2005
To determine the neurodevelopmental outcome of prematurely born newborns with magnetic resonance ... more To determine the neurodevelopmental outcome of prematurely born newborns with magnetic resonance imaging (MRI) abnormalities.A total of 89 prematurely born newborns (median age 28 weeks postgestation) were studied with MRI when stable for transport to MRI (median age, 32 weeks postgestation); 50 newborns were studied again near term age (median age, 37 weeks). Neurodevelopmental outcome was determined at 18 months adjusted age (median) using the Mental Development Index (Bayley Scales Infant Development II) and a standardized neurologic exam.Of 86 neonatal survivors, outcome was normal in 51 (59%), borderline in 22 (26%), and abnormal in 13 (15%). Moderate/severe MRI abnormalities were common on the first (37%) and second (32%) scans. Abnormal outcome was associated with increasing severity of white matter injury, ventriculomegaly, and intraventricular hemorrhage on MRI, as well as moderate/severe abnormalities on the first (relative risk [RR] = 5.6; P = .002) and second MRI studies (RR = 5.3; P = .03). Neuromotor abnormalities on neurologic examination near term age (RR = 6.5; P = .04) and postnatal infection (RR = 4.0; P = .01) also increased the risk for abnormal neurodevelopmental outcome.In premature newborns, brain abnormalities are common on MRI early in life and are associated with adverse neurodevelopmental outcome.
The effects of fish farming on a seagrass (Posidonia oceanica) meadow at Fornells Bay, Minorca (B... more The effects of fish farming on a seagrass (Posidonia oceanica) meadow at Fornells Bay, Minorca (Balearic Islands) were studied. Changes in plant and meadow features (e.g. shoot morphology, shoot density, biomass, rhizome growth, nutrient and soluble sugars concentrations…) in three stations along a transect from a disturbed (organic pollution due to fish cultures) to an undisturbed site were assessed. The fish culture had ceased in 1991; however, seagrass decline, already reported in a previous study for the period 1988–1990, was still taking place at the time of sampling (July 1994). Differences between stations were very clear; the station closest to the fish cages showed reduced shoot density, shoot size, underground biomass, sucrose concentration and photosynthetic capacities. In contrast, shoots from the most polluted station showed higher P-concentration in tissues and higher epiphyte biomass than the other two. Since water conditions had recovered completely by the time of the sampling mission, it is proposed that the persistence of the seagrass decline was due to the excess organic matter remaining in the sediment.Les effets de l'élevage de poissons en cages flottantes sur un herbier de Posidonia oceanica ont étéétudiés dans la baie de Fornells (Minorque, îles Baléares). Des modifications dans les caractéristiques de la plante et de l'herbier (morphologie et densité des faisceaux, biomasse, croissance des rhizomes, teneurs en nutriments et en sucres solubles) sont observées en trois stations d'une radiale allant d'une zone polluée (par la matière organique due aux élevages de poissons) à une zone non polluée. Bien que l'élevage ait cessé en 1991, la dégradation notée en 1988–1990 s'est poursuivie jusqu'au moment de l'échantillonage décrit ici (juillet 1994). Les différences entre les stations sont très nettes : la proximité des cages est associée aux plus faibles valeurs de densité et taille des faisceaux, biomasse, teneur en saccharose et taux photosynthétique, tandis que dans cette même zone polluée, la concentration du phosphore dans les tissus et la biomasse des épiphytes sont maximales. La colonne d'eau ayant retrouvé son état initial après la disparition des élevages, la persistance de la dégradation pourrait être liée à des modifications du sédiment dont la teneur en matière organique est restée très élevée.
Marine Ecology, 1994
Abstract. Cymodocea nodosa is a relatively small seagrass species which is common in the Mediterr... more Abstract. Cymodocea nodosa is a relatively small seagrass species which is common in the Mediterranean. An intensive survey on its growth and production was carried out in a dense, monospecific stand located in a semi-estuarine embayment. Data on leaf appearance and growth, shoot recruitment and death, rhizome growth, above- and belowground biomass, and nutrient content in the different parts of the plant were obtained over 2 years. All these variables showed a clear seasonality. In general, maximum growth and production occurred in early summer (July), and maximum biomass was reached between July and September. Biomass, shoot density, growth and production showed clear minima in winter.
Aquatic Botany, 1994
We examine here the growth plasticity (as the variability in leaf growth and production, and shoo... more We examine here the growth plasticity (as the variability in leaf growth and production, and shoot mortality rate) and stand structure (rhizome, root and shoot biomasses and nutrient contents, and shoot age structure), of the Mediterranean seagrass Cymodocea nodosa (Ucria) Aschers. growing across an existing gradient of nutrient supply in shallow water (from 2 μM soluble reactive phosphorus at nutrient-rich, to 0.08 μM at nutrient-poor sites). Phosphorus concentrations in plant tissues increased strongly (three-fold in leaves, and ten-fold in rhizomes and roots) from nutrient-poor to nutrient-rich sites. Leaf phosphorus concentrations at nutrient-poor sites were only half of those required for balanced seagrass growth, indicating the importance of phosphorus in limiting C. nodosa growth at the nutrient-poor sites. Phosphorus-limited plants allocated a greater proportion of the limiting resource (32% of the P standing stock, compared with about 10% at nutrient-sufficient sites), and a greater proportion of the produced biomass (about 40% of the biomass, compared with about 15% of the biomass at nutrient-sufficient sites), to root development, thereby increasing their capacity to acquire phosphorus from the sediment at the expense of impaired shoot growth and size. Resources were relocated as nutrient shortage ameliorates towards nutrient-rich sites, yielding a reduction in the relative allocation to below-ground biomass (which represented about 80% and 50% of the biomass at nutrient-poor and nutrient-rich sites, respectively). Shoot growth at the nutrient-rich site exceeded that at sites receiving intermediate and low nutrient loadings by two-fold and three-fold, respectively, yet the biomass of plants growing under high nutrient supply was almost half of that of the plants receiving intermediate nutrient loading. Thos was due to reduced shoot density at the nutrient-rich site, resulting from higher shoot mortality at higher nutrient concentrations, which suggests a shift from phosphorus as the limiting resource towards limitation by light or oxygen supply to the roots. Depsite their lower biomass, the fast growth of plants at the nutrient-rich site allowed them to support similar leaf production to plants receiving intermediate nutrient supply, and twice the phosphorus incorporation rate of those plants. The observed differences in population dynamics across the gradient in nutrient supply demonstrate the power of comparative analyses of seagrass stands as an additional approach to examine the importance of nutrient supply in controlling seagrass growth and productivity.
Marine Pollution Bulletin, 2001
The spatial extent and timing of the impact of fish farms on the distribution and performance of ... more The spatial extent and timing of the impact of fish farms on the distribution and performance of a Posidonia oceanica meadow were examined in an embayment of the south-eastern coast of Spain (Hornillo Bay, Murcia). Changes in seagrass distribution were determined using available seagrass mapping (from 1988, i.e., before the onset of aquaculture activities and 1998) and by successive sampling in 1994 and 1998. Environmental variables (light attenuation coefficient, water-column dissolved nutrients and organic content of sediments) together with plant performance (shoot biomass, leaf growth rate, photosynthetic activity, carbohydrate reserves, the number of leaves per shoot, epiphyte loads and herbivore pressure) were measured in plants affected by organic discharges, and were compared with those found in reference healthy plants over an annual growth cycle. Since the onset of fish farm activity, 11.29 ha of P. oceanica meadow has been completely lost and 9.86 ha significantly degraded, thus resulting in a total affected area which accounts for about 53% of the former meadow, or 7-fold the fish farming area. Unequal propagation of seagrass die-off or degradation reflects the relevance of local factors such as depth and hydrodynamism on the true extent of fish farm impact. Water transparency decreases and dissolved nutrient and organic content of sediments increases in the vicinity of cages compared to distant reference stations, thus supporting the notion of environmental gradients caused by the organic release from cages, which spreads outwards. Shoot size, leaf growth rate and the number of leaves per shoot in plants close to the fish farm decreased. Moreover, low leaf growth and low rhizome carbohydrate concentration (always relative to that found in an undisturbed area) indicated carbon budget imbalances. Since light reduction in the affected area was only modest (31% of light reaching the sea surface, while at the same depth this figure was 39% at the reference site), and light availability was well above the minimum requirement estimated for this species, neither this factor nor epiphyte overgrowth (epiphyte load was lower in the affected area) seem to explain such carbon imbalances or the observed meadow regression. Alternatively, the high herbivore pressure found in the affected zone suggests that overgrazing is one of the main causes of decreasing shoot sizes and hence of carbon imbalance, reduced growth and shoot mortality. The impact of fish farms on seagrasses, therefore, seems to be highly variable and depends on complex interactions between a large number of processes.
Aquatic Botany, 1994
Carbon, nitrogen and phosphorus accumulation in the belowground parts of the seagrass Posidonia o... more Carbon, nitrogen and phosphorus accumulation in the belowground parts of the seagrass Posidonia oceanica (L.) Delile are presented. Including all the dead parts of the plant (roots, leaf bases, rhizomes and the organic matter in the sediment), values as high as 71 kg C m−2, 0.8 kg N m−2 and 0.03 kg P m−2 were found. Accumulation rates are estimated between 19–191 g C m−2 year−1, 0.2–2.3 g N m−2 year−1 and 0.009–0.09 g P m−2 year−1.
Marine Pollution Bulletin, 2001
The spatial extent and timing of the impact of fish farms on the distribution and performance of ... more The spatial extent and timing of the impact of fish farms on the distribution and performance of a Posidonia oceanica meadow were examined in an embayment of the south-eastern coast of Spain (Hornillo Bay, Murcia). Changes in seagrass distribution were determined using available seagrass mapping (from 1988, i.e., before the onset of aquaculture activities and 1998) and by successive sampling in 1994 and 1998. Environmental variables (light attenuation coefficient, water-column dissolved nutrients and organic content of sediments) together with plant performance (shoot biomass, leaf growth rate, photosynthetic activity, carbohydrate reserves, the number of leaves per shoot, epiphyte loads and herbivore pressure) were measured in plants affected by organic discharges, and were compared with those found in reference healthy plants over an annual growth cycle. Since the onset of fish farm activity, 11.29 ha of P. oceanica meadow has been completely lost and 9.86 ha significantly degraded, thus resulting in a total affected area which accounts for about 53% of the former meadow, or 7-fold the fish farming area. Unequal propagation of seagrass die-off or degradation reflects the relevance of local factors such as depth and hydrodynamism on the true extent of fish farm impact. Water transparency decreases and dissolved nutrient and organic content of sediments increases in the vicinity of cages compared to distant reference stations, thus supporting the notion of environmental gradients caused by the organic release from cages, which spreads outwards. Shoot size, leaf growth rate and the number of leaves per shoot in plants close to the fish farm decreased. Moreover, low leaf growth and low rhizome carbohydrate concentration (always relative to that found in an undisturbed area) indicated carbon budget imbalances. Since light reduction in the affected area was only modest (31% of light reaching the sea surface, while at the same depth this figure was 39% at the reference site), and light availability was well above the minimum requirement estimated for this species, neither this factor nor epiphyte overgrowth (epiphyte load was lower in the affected area) seem to explain such carbon imbalances or the observed meadow regression. Alternatively, the high herbivore pressure found in the affected zone suggests that overgrazing is one of the main causes of decreasing shoot sizes and hence of carbon imbalance, reduced growth and shoot mortality. The impact of fish farms on seagrasses, therefore, seems to be highly variable and depends on complex interactions between a large number of processes.
Estuarine Coastal and Shelf Science, 1997
The Mediterranean seagrassPosidonia oceanicaaccumulates large quantities of organic debris as roo... more The Mediterranean seagrassPosidonia oceanicaaccumulates large quantities of organic debris as roots, rhizomes and leaf sheaths are progressively buried forming a bioconstruction called ‘ matte ’. The organic material remains with little morphological alteration for millennia. Several strata from these accumulations in variousP. oceanicameadows were sampled. Radiocarbon dating of samples yielded a range of 0–3370 years before present. From these data, accretion rates averaging 0·175 cm year−1(range: 0·061–0·414) were inferred. Significant differences between sites were found. Accretion rates showed significant differences between matte strata (i.e. with time), but no defined patterns were appreciated. Such differences were not coherent across sites. It is concluded that accretion rates are mainly controlled by local factors.Analysis of carbon, nitrogen and phosphorous in the organic debris showed that there was not a net release during the process of matte construction; in some sites, nitrogen and phosphorus concentration remained constant throughout the matte profile, while in the other sites, their concentration increased significantly with age. This confirms the role ofP. oceanicameadows as sinks for biogenic elements.
Marine Biology, 1991
Experimental nutrient (N, P, and N+P) additions to shallow (ca. 1 m)Cymodocea nodosa (Ucria) Asch... more Experimental nutrient (N, P, and N+P) additions to shallow (ca. 1 m)Cymodocea nodosa (Ucria) Aschers. stands growing in patches and in a continuous meadow in a Mediterranean Bay (Alfacs Bay, NE Spain) in 1988 demonstrated mid-summer growth to be strongly P-limited, as suggested by the high N:P ratios (>35) in unmanipulated plants. P additions resulted in increased leaf P content, reduced N:P ratios, and enhanced shoot growth and turnover in both populations. These effects promoted in turn a stand response, leading to increased biomass and, therefore, increased areal productivity in the plots receiving P. The stand response was largely attributable to a doubling of shoot density, indicating enhanced rhizome growth and branching.