Alberto M. Arias

Spatial and temporal variation of the nekton and hyperbenthos from a temperate european estuary with regulated freshwater inflow

The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary.

Heavy metals in organisms of the River Guadalquivir estuary: possible incidence of the Aznalcóllar disaster

On the 25 April 1998, the giant holding pool of the Aznalcóllar mine, owned by the Canadian-Swedish Company Boliden Ltd burst its banks; 5 million cubic meters (6.7 million cubic yards) of sludge poured into the nearby River Guadiamar, which is a tributary of the River Guadalquivir (the main river of the south Iberian Peninsula). Within hours of the accident, approximately 2.5 Hm3 of acidic water with high concentrations of metals, especially Zn, had entered the River Guadalquivir. A biomonitoring program has been carried out to evaluate the incidence of this spill on the fauna of the River Guadalquivir. Six sampling stations within the estuary of were established and six species of molluscs (Crassostrea angulata, Scrobicularia plana), crustaceans (Palameon longirostris, Uca tangeri, Melicertus kerathurus) and fish (Liza ramada) were chosen for analysis. In the Portuguese oyster, Crassostrea angulata, Cd and Cu concentrations were above the maximum allowed by the Spanish legislation for bivalves for human consumption (60 micrograms.g-1 wet wt. for Cu and 1.0 microgram.g-1 wet wt. for Cd). The crustaceans Palaemon longirostris and Uca tangeri, also showed values above the legal limits for Cu (20 micrograms.g-1 wet wt.). An increase of the Zn levels was observed, as Zn concentrations in C. angulata were higher than those reported 30 years ago. The heavy metal concentrations in some of the organisms collected in the River Guadalquivir were higher than in the Bay of Cadiz or the Mediterranean Sea (clean sites), showing that this estuary was subjected to a heavy metal load. One month after the accident, concentrations of Zn were higher in C. angulata and in Palaemon longirostris compared with levels recorded on the 25 April. Nevertheless, some organisms did not show a clear tendency during the sampling period, probably due to the fluctuations of environmental (salinity, temperature) and physiological variables that affect bioaccumulation.

Total and inorganic arsenic in the fauna of the Guadalquivir estuary: environmental and human health implications.

To evaluate the impact on fauna of the release of toxic waste from the tailings dam operated by the Boliden Apirsa S.L company at Aznalcóllar, Seville (Spain) a study was carried out of total and inorganic arsenic contents in 164 samples from six different estuary species, including molluscs, crustaceans and fish, collected at six sampling stations distributed along the estuary and mouth of the River Guadalquivir. The contents found, expressed in micrograms per gram wet weight, were as follows. Total arsenic: Crassostrea angulata--giant cupped oyster (2.44 +/- 0.45); Scrobicularia plana--peppery furrow (2.50 +/- 0.73); Palaemon longirostris--delta prawn (1.33 +/- 0.54); Uca tangeri--AfroEuropean fiddler crab (1.76 +/- 0.08); Melicertus kerathurus--shrimp (3.60 +/- 1.92); and Liza ramada--mullet (0.65 +/- 0.38). Inorganic arsenic: C. angulata (0.09 +/- 0.02); S. plana (0.38 +/- 0.23); P. longirostris (0.04 +/- 0.01); U. tangeri (0.22 +/- 0.03); M. kerathurus (0.03 +/- 0.01); and L. ramada (0.03 +/- 0.03). The levels of total As are comparable to those obtained by other authors. With respect to inorganic arsenic, only S. plana and U. tangeri present high levels of inorganic arsenic. This may be due to the fact that these organisms live in estuary sediments, reservoirs of inorganic arsenic, and ingest particles of sediments during feeding. Because of the lack of information for this area concerning previous levels of total and inorganic arsenic in the species analysed, it was not possible to establish the impact on the fauna of the River Guadalquivir estuary of the toxic spill resulting from the failure of the mine tailings dam at Aznalcóllar. With respect to the implications to human health as a result of consumption of species from the Guadalquivir estuary, only with the species Scrobicularia plana, as a high consumption of this mollusc might, in some cases, exceed the maximum tolerable intake for inorganic arsenic indicated by the FAO/WHO. Consumption of the liver of L. ramada does not appear to present problems to human health.

The effect of aquaculture practices on the benthic macroinvertebrate community of a lagoon system in the Bay of Cádiz (southwestern Spain)

Monthly quantitative Ekman-Birge grab sampling was used to characterize and compare the composition and structure of the benthic macroinvertebrate community inhabiting semi-enclosed polyculture lagoons (SPL) (three sampling sites) and enclosed monoculture ponds (EMP) (two sampling sites) of a lagoonal system of the Bay of Cádiz. The two areas differed considerably in habitat characteristics and aquaculture management. The SPL area was characterized by low rates of water exchange, low fish densities, and the presence of a macroalgal cover. In the EMP area, there was a complete exchange of water daily (by pumping) and a supply of food pellets, density of fish was high, and no vegetative cover was present. There were considerable differences in species composition between habitats with different culture methods: 11 of the 21 most abundant species were exclusive to one or the other. Several epibenthic species were abundant in the polyculture lagoon but were low in density or were absent in monoculture ponds. Some infaunal species, on the other hand, were more abundant in the monoculture ponds. Univeriate measures of community structure (abundance and biomass, Margalef’s species richness, Shannon-Wiener diversity, and Pielou’s evenness indices) did not indicate significant differences between the SPL and EMP areas. Conversely, the abundance-biomass comparison (ABC) method indicated that, on average, the macrobenthic community was moderately disturbed in the SPL and undisturbed in the EMP areas. Multidimensional scaling (MDS) ordination and hierarchical cluster analysis (Bray-Curtis similarity measure) revealed the occurrence of two main benthic assemblages that corresponded to the aquaculture methods. The different rates of water exchange for the two aquaculture practices seem to have contributed to differences in the composition and structure of the benthic communities.

Ichthyoplankton of a shallow coastal inlet in south-west Spain: Factors contributing to colonization and retention

Abstract The ichthyoplankton of a shallow inlet was sampled for 13 months using conical tide-strained nets. The utilization of this habitat by the young stages of different fish species is analysed. Temporal and spatial distributions are discussed in relation to environmental cycles and gradients, and to feeding rhythms. A total of 110 971 individuals, belonging to 39 species and 19 families of teleosts, was collected. The postlarval stage was the most represented in the samples. Ichthyoplankton density peaked during late winter and early spring. Density was higher during flood tide, resulting in a net input of postlarvae from the bay to the inner inlet. This ecosystem functions primarily as a nursery ground for coastal pelagic spawners and, secondarily, as a spawning area for some benthic egg spawners and pouch-brooder species. Most postlarvae migrate from their spawning area (open sea) to the inlet probably cued by a decreasing gradient of water temperature and salinity, and an increasing gradient of water turbidity and suitable food concentration. The attraction of postlarvae towards the inlet mouth probably results from a combination of biotic (availability of suitable food) and abiotic (temperature, salinity and turbidity) factors. Passive transport contributes to the subsequent penetration and retention of the postlarvae within the shallow, flood-dominated inlet. Vertical migrations observed among some planktonic fish stages were related to light periods and feeding activity rather than tidal phases, and cannot act as a retention mechanism.

Distribution and production ofChironomus salinarius (Diptera: Chironomidae) in a shallow coastal lagoon in the Bay of Cádiz

The abundance, generation time and production ofChironomus salinarius larvae in a lagoon fish-pond system in the Bay of Cádiz were studied by taking monthly samples at 3 sites during 1991 and 1992. Numerical abundance and biomass of larvae showed considerable spatial, seasonal and interannual variation (ANCOVAs,P<0.001). The maximum mean annual density was 7048 larvae m−2, and corresponded to a biomass of 3.08 g dry weight (DW) m−2. It was recorded at the site with the lowest rate of water renewal. Seasonal patterns were similar at all sites, with main annual peaks of abundance and biomass in autumn-early winter. Chironomid density was positively related to the biomass of benthic macroalgae (P<0.001). The population studied was multivoltine with a probable average of five generations per year, with overlapping cohorts and a predominance of third- and fourth-instar larvae. Estimates of annual production ranged between 72.2 g DW m−2 yr−1 at the site with the lowest rate of water renewal in 1991 and 0.1 g DW m−2 yr−1 at the site with the highest rate of water renewal in 1992. Mean annual production and the production/biomass ratio for the system was estimated to be 16.8 g DW m−2 yr−1 and 12.7, respectively. Possible factors leading to the observed density fluctuations are discussed, as well as possible sources of error in production estimates.

Macrobenthic community structure in estuarine pollution assessment on the Gulf of Cádiz (SW Spain): Is the Phylum-level Meta-analysis approach applicable?

Abstract Macrobenthic species abundances and biomasses were determined at twelve stations from three estuarine areas of the Gulf of Cadiz (SW Spain). They are subject to different sources of pollution: urban effluents (Bay of Cadiz), agricultural/urban sewages (Barbate River Estuary) and mining/industrial sewages (Odiel River Estuary). Different univariate and multivariate techniques were used in the assessment of the community disturbance status. At the Species-level, inferences from Gray and Pearson’s graphics together with multivariate MDS ordinations provided a reliable picture of the severity of the community disturbance at the twelve sampling sites. At the Phylum-level, the meta-analysis of “production” also gave a reliable disturbance status for all the stations when new samples were introduced in the MDS analysis one by one. These results suggest a more general applicability of the Phylum-level meta-analysis, provided that the original NE Atlantic data ordination remains unmodified.

DISTRIBUTION AND PRODUCTION OF MICRODEUTOPUS GRYLLOTALPA (AMPHIPODA: AORIDAE) IN A SHALLOW COASTAL LAGOON IN THE BAY OF CADIZ, SPAIN

ABSTRACT The spatial and temporal fluctuations of density, life cycle, and production of Microdeutopus gryllotalpa in a seminatural lagoon system were studied by taking monthly samples at 3 sites during 1991 and 1992. Its numerical abundance and biomass, which showed considerable spatial and temporal variation, were positively related to the biomass of benthic macroalgae and water salinity (stepwise multiple regression analysis, P 17°C) than for the rest of the year (0.026 mm d-1; T < 17°C). The population studied was multivoltine, with overlapping cohorts and a possible maximum of 5 generations per year. Using the size-frequency method, the mean annual production and production/biomass ratio for the system were estimated to be 22.42 g DW (13.49 g AFDW) m-2 yr-1 and 12.8 (11.7), respectively. These results indicated that in warm temperate lagoons secondary production for species such as M. gryllotalpa may be high, despite its moderate mean biomass.

Initial effects of the toxic waste spill (Aznalcóllar mine accident) on the aquatic macrofauna of the Guadalquivir Estuary

The initial effects of the toxic waste spill in April 1998 at the Aznalcóllar mine (SW Spain) on the nektonic community of the Guadalquivir Estuary were examined at three sampling sites using univariate and multivariate techniques. Since studied communities showed a considerable seasonal trend, only seasonally homogenous periods were compared to analyse effects of the spill: May-August 1997 (before spill) and May-August 1998 (after spill). Results of both techniques (two-way nested ANOVA and ANOSIM tests, P > 0.05) indicated that there was no significant difference between the nektonic community of the estuary before and after the spill (monthly number of species, abundance, biomass and similarity among samples). Conversely, an unusually high density was observed at the outer sampling site immediately after the spill for species typical of more stagnant estuarine habitats. This feature seems to indicate that the fauna in the estuarine area through which the untreated water penetrated into the main course may have been disturbed. Results also suggest that this initial sudden input of fresh water to the estuary could have enhanced the effects of an increased river flow (a drop in the salinity). Nevertheless, longer temporal series of data, especially for permanent estuarine inhabitants, are recommended before conclusions can be drawn on the effects of the toxic waste spill on estuarine communities.

Freshwater scarcity effects on the aquatic macrofauna of a European Mediterranean-climate estuary

In the Mediterranean-climate zone, recurrent drought events and increasing water demand generally lead to a decrease in freshwater input to estuaries. This water scarcity may alter the proper function of estuaries as nursery areas for marine species and as permanent habitat for estuarine species. A 12-year data set of the aquatic macrofauna (fish, decapod and mysid crustaceans) in a Mediterranean estuary (Guadalquivir estuary, South Spain) was analysed to test if water scarcity favours the nursery function of regional estuaries to the detriment of permanent estuarine inhabitants. Target species typically displayed a salinity-related distribution and estuarine salinisation in dry years resulted in a general upstream community displacement. However, annual densities of marine species were neither consistently higher in dry years nor estuarine species during wet years. Exceptions included the estuarine mysid Neomysis integer and the marine shrimp Crangon crangon, which were more abundant in wet and dry years, respectively. High and persistent turbidity, a collateral effect of water scarcity, altered both the structural (salinity-related pattern) and functional (key prey species and predator density) community characteristics, chiefly after the second drought period of the analysis. The observed high inter-year environmental variability, as well as species-specific effects of water scarcity, suggests that exhaustive and long-term sampling programmes will be required for rigorously monitoring the estuarine communities of the Mediterranean-climate region.