F. Páez-Osuna

Eutrophication and macroalgal blooms in temperate and tropical coastal waters: nutrient enrichment experiments with Ulva spp.

Receiving coastal waters and estuaries are among the most nutrient-enriched environments on earth, and one of the symptoms of the resulting eutrophication is the proliferation of opportunistic, fast-growing marine seaweeds. Here, we used a widespread macroalga often involved in blooms, Ulva spp., to investigate how supply of nitrogen (N) and phosphorus (P), the two main potential growth-limiting nutrients, influence macroalgal growth in temperate and tropical coastal waters ranging from low- to high-nutrient supplies. We carried out N and P enrichment field experiments on Ulva spp. in seven coastal systems, with one of these systems represented by three different subestuaries, for a total of nine sites. We showed that rate of growth of Ulva spp. was directly correlated to annual dissolved inorganic nitrogen (DIN) concentrations, where growth increased with increasing DIN concentration. Internal N pools of macroalgal fronds were also linked to increased DIN supply, and algal growth rates were tightly coupled to these internal N pools. The increases in DIN appeared to be related to greater inputs of wastewater to these coastal waters as indicated by high δ15N signatures of the algae as DIN increased. N and P enrichment experiments showed that rate of macroalgal growth was controlled by supply of DIN where ambient DIN concentrations were low, and by P where DIN concentrations were higher, regardless of latitude or geographic setting. These results suggest that understanding the basis for macroalgal blooms, and management of these harmful phenomena, will require information as to nutrient sources, and actions to reduce supply of N and P in coastal waters concerned.

The environmental impact of shrimp aquaculture and the coastal pollution in Mexico

The moderated, but continual development of the shrimp aquaculture in Mexico, in conjuction with municipal and agriculture effluents, in the last decade has created the first symptoms of negative environmental impacts, due mainly to the discharge of nutrients and organic matter into adjacent coastal waters. Similarly, the increasing impairment of coastal water quality resulting from the discharge of domestic, agricultural and industrial wastes into coastal waters has affected the aquaculture profitability in certain areas. The cumulative impact of the main anthropogenic sources of nutrients in the Mexican coastal states was estimated in 190 088 ton N yr−1 and 51 831 ton P yr−1. The input from shrimp aquaculture is only 1.5% and 0.9% of the main sources of nitrogen and phosphorus. This last input, though small, is related to local and adverse effects on coastal ecosystems. The introduction of management measures to mitigate the adverse environmental impacts of shrimp aquaculture development has now become necessary and urgent.

Fluxes and mass balances of nutrients in a semi-intensive shrimp farm in north-western Mexico

Fluxes of suspended solids, chlorophyll a and nutrients (phosphorus, nitrate, nitrite and ammonia) were estimated in a semi-intensive shrimp farm in north-west Mexico for two consecutive cycles of production encompassing both the dry and wet seasons. A mass balance model was developed for nitrogen and phosphorus and fluxes estimated included shrimp feed, fertilization, shrimp stocked, harvest, macrofauna associated, water exchange, filling and drainage. Of the total nitrogen and phosphorus input to the ponds, 35.5% and 6.1% were recovered in 1822 kg ha−1 of shrimp harvested. Volatilization of ammonia and adsorption by sediments of phosphorus constituted 27.4% and 63.5%, respectively; the estimated environmental losses of nitrogen and phosphorus per t of shrimp produced were 28.6 kg and 4.6 kg, respectively. Assuming that all the shrimp farms in Sinaloa (Mexico), operate according to the model, the farms could represent a load corresponding to the untreated sewage generated by 56 200-192 750 and 43 500-149 170 people in terms of nitrogen and phosphorus discharged annually.

Nutrients, phytoplankton and harmful algal blooms in shrimp ponds: a review with special reference to the situation in the Gulf of California

Abstract The present work is a first attempt to document the latest reports on the occurrence of algal blooms in shrimp farm ponds worldwide. Particular emphasis is placed on discussing the relation of algal blooms with nutrients, with special reference to the northwest of Mexico. Typically, shrimp pond waters are enriched with organic matter and nutrients whose concentrations depend mostly on the management (i.e. higher stocking densities, water use, food and fertilizers). Generally, more intensive culture systems produce higher loads of nutrients in their discharge (e.g. N and P). Nitrogen and P concentrations vary in pond waters; N/P ratio ranges from 1.1 to 67 with values being more frequently between 1.1 and 6.8. Such variations are closely related with the cycling and supply of nutrients in the ponds. In shrimp farms located in NW Mexico, phytoplankton abundance varies widely, having a higher abundance in advanced stages of the culture cycle. In the most common pond types (intensive and semi-intensive), Synechocystis diplococcus (cyanobacteria) was the dominant species (>88.9%), followed by Peridinium trochoideum ( Scrippsiella trochoidea ) and eventually Prorocentrum minimum and Gymnodinium spp. (dinoflagellates). The numerous occurrences of large blooms of dinoflagellates and other functional groups such as cyanobacteria, diatoms, chlorophytes and flagellates mean economic losses for farm industry on account of shrimp mortality or growth diminution due to poisoning, anoxic or mucus production effects, in which shrimp were mortality provoked in different regions: in China, the dinoflagellates Alexandrium tamarense ( Gonyaulax tamarensis ) and Gymnodinium ; in Malaysia, the raphidophyte Hornellia ( Chattonella ) and the dinoflagellate Pyrodinium bahamense var. compressum ; in Vietnam, the diatom Nitzchia navis - varingica ; in Ecuador, the dinoflagellate Gyrodinium instriatum ; and in NW Mexico the cyanobacteria S. diplococcus , Schizothrix calcicola , and the dinoflagellates P. minimum , and lastly Gymnodinium catenatum from supply waters.

Recent sedimentary history of anthropogenic impacts on the Culiacan River Estuary, northwestern Mexico: geochemical evidence from organic matter and nutrients.

210Pb geochronology and sediment profiles of carbon, phosphorus and nitrogen were used to study time dependent changes in nutrients fluxes to Culiacan River Estuary. Results indicate that the release of urban sewage and agriculture wastes transported through Culiacan River has produced historically increased carbon, phosphorus and nitrogen fluxes to the study area. C:N:P elemental ratios showed that increments in the nutrients input begins simultaneously for C, N and P in 1948 with the clearing of the catchment for agriculture; although excess of nutrients input increased most importantly around the 1970s to roughly follow the rapidly growing population of Culiacan City. C/N ratios, delta13C and delta15N suggested that nutrient enrichment is mostly influenced by sewage delivered through Culiacan River.

Trace metal concentrations in relation to season and gonadal maturation in the oyster Crassostrea iridescens

Abstract The gonadal development and the concentrations of six trace metals (Cd, Cu, Fe, Mn, Ni and Zn) associated with the gonadal and somatic (nogonadal) tissue throughout the reproductive cycle of the oyster Crassostrea iridescens (Hanley) have been studied. The metal concentration in this oyster in both tissues exhibited significant seasonal variations. The minimum Cd, Cu, Fe, Ni and Zn concentrations in the gonadal tissue are related to periods of maximum gonadic development. In contrast, Mn shows a maximum in the gonad and whole tissue that is correlated positively with the maturation of the organism. This last result suggests that Mn may perform some function during the gonadic maturation or prespawning. In addition, this element (in somatic and whole soft tissue) was correlated negatively with body size. A general conclusion is that the reproductive state and body size in C. iridescens exerts an important influence on the accumulation (and variability) of these trace metals, which may influence interpretations with respect to low chronic or short-term contamination.

Discharge of Nutrients from Shrimp Farming to Coastal Waters of the Gulf of California

This work deals with phosphorus (P) and nitrogen (N) loads resulting from shrimp farming in the NW coast of Mexico and a mass balance model for N and P is presented. Using such a model and the feed coefficients obtained in the NW region, nutrient loads for all shrimp farms in each state were estimated. The P and N loads from NW Mexican shrimp farming in 1993 were ca 345 and 1209 tons, and for 1998 were predicted to be 834 and 2903 tons, respectively. These loads correspond to 0.7 and 1.3% for 1993, and 1.7 and 3.1% for 1998, of the total sources of P and N in the region on the adjacent coastal waters. The contribution estimated of nutrients for 1998 via agriculture (2 6714 tons of P and 53476 tons of N) corresponds to 54.9 and 57.7%, and the municipal sources (1730 tons of P and 3806 tons of N) have an intermediate position with 3.6 and 4.1% of the total sources of P and N, respectively. The total nutrient load from aquaculture is small in comparison with other nutrient sources, however, local and adverse effects on coastal ecosystems can be of significance and subject to restrictions.

Trace metals in the Mexican shrimp Penaeus vannamei from estuarine and marine environments.

Trace-metal concentrations (Fe, Mn, Ni, Cu, Co, Cd, Cr, and Zn) were measured in estuarine postlarvae, juveniles, and marine adults of the shrimp Penaeus vannamei collected along the Pacific coast of Mexico. With the exception of Fe, the trace-metal concentrations fell within the ranges of similar organisms collected elsewhere. Size-dependent relationships were observed only for Ni, Fe, and Zn and varied depending on the element considered. Small individuals had higher concentrations of Fe and Ni than larger individuals. For Zn, the opposite tendency occurred. This may reflect different metabolic requirements of young and old shrimps.

Selected trace metals in oysters (Crassostrea iridescens) and sediments from the discharge zone of the submarine sewage outfall in Mazatlán Bay (southeast Gulf of California): chemical fractions and bioaccumulation factors

Concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the soft tissue of Crassostrea iridescens and the associated surface sediments (bulk and bioavailable metal concentrations) from an area influenced by a sewage outfall in Mazatlán Bay (southeast Gulf of California), were determined by atomic absorption spectrophotometry. Significant spatial differences in metal concentrations in both the bulk and bioavailable forms in the sediments were identified. An enrichment of Cu, Ni, Pb and Zn in sites located on a south-north transect was detected indicating a dominant influence of the sewage outfall toward the north. C. iridescens accumulated more Zn, Cu, Ni, Fe, Cd; and less Mn, Cr and Pb than were bioavailable in the sediments, as measured using conventional extraction analysis. The degree of enrichment and the bioavailable metal concentrations in the sediments of the south portion of Mazatlán Bay is discussed. The potential ability of C. iridescens as a biomonitor of metallic pollutants is postulated.

Comparative bioavailability of trace metals using three filter-feeder organisms in a subtropical coastal environment (Southeast Gulf of California)

To evaluate the relative bioavailability of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the coastal waters of one selected site in Mazatlán Harbor, different filter feeder organisms, an oyster (Crassostrea corteziensis), a mussel (Mytella strigata) and a barnacle (Fistulobalanus dentivarians), were sampled during 1 year. Seasonal and interspecific variations in some metal concentrations were evident, especially for Cd, Ni, Pb and Zn. In contrast with Fe, Pb and Zn, the concentrations of Cd varied accordingly in both bivalves. Even though the organisms live in the same site and have a common feeding mechanism, accumulated body Cd concentrations were different. Mussels concentrated significantly higher levels of Ni than the other organisms, while barnacles were better concentrators of Cd, Pb and Zn. A relationship existed between the concentrations of Cd, Fe and Zn in the soft tissues of the two bivalves, which is useful in monitoring studies when only one species occurs.