Luís Chícharo

Ecohydrology as a new tool for sustainable management of estuaries and coastal waters

Throughout the world, estuaries and coastal waters have experienced degradation. Present proposed remedial measures based on engineering and technological fix are not likely to restore the ecological processes of a healthy, robust estuary and, as such, will not reinstate the full beneficial functions of the estuary ecosystem. The successful management of estuaries and coastal waters requires an ecohydrologybased, basin-wide approach. This necessitates changing present practices by official institutions based on municipalities or counties as an administrative unit, or the narrowly focused approaches of managers of specific activities (e.g., farming and fisheries, water resources, urban and economic developments, wetlands management and nature conservationists). Without this change in thinking and management concept, estuaries and coastal waters will continue to degrade, whatever integrated coastal management plans are implemented. To help in this process of change there is a need to (1) develop a profound understanding of the effects of biota and biotic processes on mediating estuary response to changing hydrology, sediment and nutrient flux and of the biota on hydrology at the river basin scale, and (2) to develop science-based remediation measures at the river basin scale, with elements of ecohydrology and phytotechnology at their core, to strengthen the ability of the biota to sustain and adapt to human-induced stresses.

RNA:DNA Ratio and Other Nucleic Acid Derived Indices in Marine Ecology

Some of most used indicators in marine ecology are nucleic acid-derived indices. They can be divided by target levels in three groups: 1) at the organism level as ecophysiologic indicators, indicators such as RNA:DNA ratios, DNA:dry weight and RNA:protein, 2) at the population level, indicators such as growth rate, starvation incidence or fisheries impact indicators, and 3) at the community level, indicators such as trophic interactions, exergy indices and prey identification. The nucleic acids derived indices, especially RNA:DNA ratio, have been applied with success as indicators of nutritional condition, well been and growth in marine organisms. They are also useful as indicators of natural or anthropogenic impacts in marine population and communities, such as upwelling or dredge fisheries, respectively. They can help in understanding important issues of marine ecology such as trophic interactions in marine environment, fish and invertebrate recruitment failure and biodiversity changes, without laborious work of counting, measuring and identification of small marine organisms. Besides the objective of integrate nucleic acid derived indices across levels of organization, the paper will also include a general characterization of most used nucleic acid derived indices in marine ecology and also advantages and limitations of them. We can conclude that using indicators, such RNA:DNA ratios and other nucleic acids derived indices concomitantly with organism and ecosystems measures of responses to climate change (distribution, abundance, activity, metabolic rate, survival) will allow for the development of more rigorous and realistic predictions of the effects of anthropogenic climate change on marine systems.

Changes in a temperate estuary during the filling of the biggest European dam

This study aimed to determine whether and how the disruption of river flow, during the filling of the Alqueva dam, influenced the variability of abiotic and biotic factors in the Guadiana estuary, particularly the abundance and distribution of anchovy eggs. River inflow was found to be the most important factor in determining abiotic and biotic variability in the Guadiana estuary. Seasonal patterns were obscured by long periods of low inflow (mid April to early December 2002), which caused marked changes in the estuary. The estuarine turbidity maximum zone was displaced towards the upper estuary, to at least 38 km from the river mouth, 8 to 16 km upstream from previous records. The dynamics of nutrient stoichiometry was also affected. In the upper and middle estuary, P was more potential limiting than N and potential Si limitation was only frequent on the coast, with direct and/or indirect influence in changing phytoplankton dynamics and composition. Previously, the upper estuary alternated between potential P limitation during winter, Si limitation during spring and mid summer and N limitation during mid summer and autumn. The flooding of vast areas in the catchment of the dam probably caused the increase of DSi concentrations, as well as maximal N and P loadings. The abundance of larval stages of anchovy decreased, putatively because estuarine productivity has also decreased. In April 2002 there was an uncontrolled discharge from the Alqueva dam, which reduced the abundance of anchovy eggs by 99.99%. It is suggested that dam managers should mimic, as much as possible, the natural river flow, in order to minimize the impact on downstream ecosystems. Management efforts should not be restricted to the areas upstream of the dam, but should also encompass the estuary and adjacent coastal area.

Status of the Guadiana Estuary (south Portugal) during 1996-1998: An ecohydrological approach

The aims of this study were to monitor basic hydrological and ecological characteristics of the Guadiana Estuary (1996-1998) before the construction of the Alqueva dam. This work was carried out to determine how environmental factors affect seasonal and tidal variations of plankton populations in the estuary. The available information on the subcatchment of the estuary (e.g., urban, agricultural and forested areas) was integrated into a geographic information system-based software program. Mean monthly river flow varied markedly on a seasonal and yearly basis. River flow near Mértola (ca 50 km upstream from the mouth) reached 3400 2 10 6 m 3 in winter and decreased to 42 2 10 6 m 3 in summer. With respect to nutrients, nitrogen to phosphorus ratios indicated some limitation by phosphorus, except at the end of summer, when nitrogen limitation appeared. During this period, cyanobacterial blooms usually occurred in the upper/middle estuary. Estuarine Turbidity Maximum may significantly influence the retention of zooplankton in the estuary. The fish larval life cycle, especially sensitive to environmental alterations, showed high ratios of ribonucleic to desoxyribonucleic acids indicating good physiological condition. It was concluded that an ecohydrological approach, allowing integration of different elements from the cellular to the habitat level into a geographic information system, can contribute to a better understanding of the processes that influence the aquatic biota of the estuary. The approach will be a useful assessment tool for monitoring the estuary following dam completion.

Effects of environmental conditions on planktonic abundances, benthic recruitment and growth rates of the bivalve mollusc Ruditapes decussatus in a Portuguese coastal lagoon

Abstract Controlling environmental parameters for the early stages of marine invertebrates have received little attention, particularly in field studies. This study involves measurement of abundances and growth rates of the bivalve Ruditapes decussatus Linnaeus 1758 during its planktonic larval and early benthic life stages in a coastal lagoon: Ria Formosa, Portugal. Measured abundances were compared with tidal amplitude, water temperature, salinity, wind velocity and direction, and a food availability indicator (chlorophyll a). Data were obtained on abundance and prodissoconch length of the larvae, measured two to three times per week, and of post-larval stages individuals that had settled in artificial collectors over 10 months. Larval and juvenile cohorts were identified using size-frequency distributions and larval ages estimated by larval shell growth lines. Data were fitted to linear, exponential, and Laird–Gompertz growth models. Larval growth rates best matched a linear model: 3.78±0.55 per day, r 2 =0.75, p r 2 =0.98, p

A comparison of direct macrofaunal mortality using three types of clam dredges

The white clam Spisula solida is harvested along the entire coast of Portugal using mechanical dredges. In this study, the total direct mortality of the macrobenthic community caused by three types of clam dredges (north dredge—ND, traditional dredge—TD, and the metallic grid dredge—GD) used in the S. solida fishery was determined and compared. The relationship between mortality and catching efficiency for each type of dredge was also assessed. Our results showed significant differences for total direct mortality between the ND and both the GD and TD dredges. This difference was largely attributed to the mortality of animals that died in the dredge track as a direct result of the physical damage inflicted by the dredge passing. It was also found that the damage to uncaught individuals is directly related to gear efficiency. The lower catching efficiency of the ND (64%) led to a higher proportion of damaged individuals being left in the dredge path, when compared with the more efficient GD (98%) and TD (90%) dredges. Short and long-term implications of the impact of dredging on the composition of benthic communities are discussed. From fisheries management and ecological points of view, there are obvious advantages to introduce into the bivalve dredge fisheries more efficient and selective dredges in order to reduce the number of damaged individuals and by-catch, and consequently decreasing the impact on the macrobenthic communities.

Ecological characterization of dredged and non-dredged bivalve fishing areas off south Portugal

Macro and meiobenthic communities of two fishing areas (Vilamoura and Lagos) in the western part of south Portugal (Algarve coast) were analysed. Both locations had been under severe dredge-fishing impact until four years previously. Vilamoura has since continued to be dredged, while fishing activity in Lagos was stopped in 1995 as a response to overfishing. For each location, three replicate areas were analysed at depths of 7–9 m. In each of these areas, 18 quadrats for macrofauna and 12 cores for meiofauna were randomly sampled by SCUBA divers during September 1999. The Shannon–Weiner diversity index was higher for meiofauna in the fished area, whereas macrofauna diversity was higher in the recently non-fished area. Bray–Curtis dissimilarity between the two areas was 87·82%. Major differences were found between Ampeliscidea, Amphiura mediterranea , Spisula solida , Haustoriidae, Nemertinea and Diogenes pugilator populations at the two sites. There was higher abundance but lower biomass of potential macrofaunal scavengers in the fished area, and carnivore biomass was also higher in this area. Deposit-feeders dominated meiofauna abundance in both study areas. The community structure of the continuously fished area was dominated by small, opportunistic, short-lived species while the community structure of the recently non-fished area was dominated by more fragile and long-living sessile organisms.

Does the nutritional condition limit survival potential of sardine Sardina pilchardus (Walbaum, 1792) larvae off the north coast of Spain? RNA/DNA ratios and their variability

The aim of this study was to determine the nutritional condition of Sardina pilchardus larvae and the percentage of larvae that were starving at the time of capture. The survey was conducted, during the spawning season, in April and May of 1991 and 1992, off the northern coast of Spain. An accepted fluorimetric technique was used to determine the concentrations of both RNA and DNA and to calculate RNA/DNA ratio for each larva. RNA/DNA ratios were related to the zooplankton biomass (>53 μm). Low percentages of starving larvae (RNA/DNA ratio less than 1.3) were registered, ranging from 0% to 2.5%. Results based on the mean and variance of individual larval growth rates showed that predation pressure was not increasing from 1991 to 1992. Based on the presence of sardine larvae in good condition together with low predation, a high recruitment was expected. However, the 1993 recruitment, from 1992 spring spawning, was very poor. This was associated mainly with unfavourable advection from the nursery area. Moreover, even low levels of starvation, such as registered, operating over long time periods could have considerable consequences for larval mortality.

Diel variation of the RNA/DNA ratios in Crassostrea angulata (Lamarck) and Ruditapes decussatus (Linnaeus 1758) (Mollusca: Bivalvia)

The aim of this study was to investigate the effect of time of day on RNA/DNA ratios among fed and starved Crassostrea angulata and Ruditapes decussatus juveniles. Sampling to investigate the day and night condition of juveniles was carried out for 48 h. A highly sensitive method for nucleic acid quantification was applied to bivalves. The results suggest that there is some variation in nucleic acid quantities with the time of the day. For the two species analysed, the RNA/DNA ratio was particularly high during the night and was higher in the fed animals. The results seem to indicate that there is some endogenous rhythm in the production of RNA. If there are diel changes in RNA/DNA ratios, it follows that average RNA/DNA ratios can be unrepresentative if there is any day or night bias in sampling.

Estimation of the life history parameters of Mytilus galloprovincialis (Lamarck) larvae in a coastal lagoon (Ria Formosa south Portugal)

Abstract The life history parameters of early stages of marine invertebrates, particularly field estimations, have received relatively little attention. The aim of this research was to estimate in situ abundance and growth of Mytilus galloprovincialis planktonic larvae. Plankton samples were filtered through gauze of 63 μm mesh and identified, counted and measured using an inverted microscope. Short-term fluctuations in Mytilus galloprovincialis larvae abundance and environmental parameters (water temperature, salinity, wind velocity direction, tidal amplitude and chlorophyll a ) were monitored (two to three times a week). Larval cohorts were identified using size–frequency distributions and age estimates compared with larval shell growth lines. Data were fitted to the linear, exponential, von Bertalanffy and Laird–Gompertz growth models. Larval growth adjusted better to the Laird–Gompertz model (0.525±0.073 μm d −1 ; r 2 =0.768; P