Manuel J. Zetina-Rejón

Trophic structure and flows of energy in the Huizache-Caimanero lagoon complex on the Pacific coast of Mexico

Abstract The Huizache–Caimanero coastal lagoon complex on the Pacific coast of Mexico supports an important shrimp fishery and is one of the most productive systems in catch per unit area of this resource. Four other less important fish groups are also exploited. In this study, we integrated the available information of the system into a mass-balance trophic model to describe the ecosystem structure and flows of energy using the E copath approach. The model includes 26 functional groups consisting of 15 fish groups, seven invertebrate groups, macrophytes, phytoplankton, and a detritus group. The resulting model was consistent as indicated by the output parameters. According to the overall pedigree index (0.75), which measures the quality of the input data on a scale from 0 to 1, it is a high quality model. Results indicate that zooplankton, microcrustaceans, and polychaetes are the principal link between trophic level (TL) one (primary producers and detritus) and consumers of higher TLs. Most production from macrophytes flows to detritus, and phytoplankton production is incorporated into the food web by zooplankton. Half of the flow from TL one to the next level come from detritus, which is an important energy source not only for several groups in the ecosystem but also for fisheries, as shown by mixed trophic impacts. The Huizache–Caimanero complex has the typical structure of tropical coastal lagoons and estuaries. The TL of consumers ranges from 2.0 to 3.6 because most groups are composed of juveniles, which use the lagoons as a nursery or protection area. Most energy flows were found in the lower part of the trophic web.

Climate Change Effects on Aquatic Ecosystems and the Challenge for Fishery Management: Pink Shrimp of the Southern Gulf of Mexico

Ecosystems that change through time impose new scientific challenges for fisheries management advice. We present a case study to illustrate our view on how to face such challenges. The Pink Shrimp fishery in the Southern Gulf of Mexico has collapsed. Annual yields were about 24,000 metric tons during the mid-1950s to early 1970s; currently, they are about 1,200 metric tons. Overfishing was assumed as the main cause, but single-species models failed to provide the advice necessary for recovery. An inverse relationship between stock abundance and temperature was demonstrated, and a decline in recruitment and primary production (since 1970s) was observed. We constructed a trophic model for the ecosystem using Ecopath with Ecosim, incorporating the annual mean anomaly of the Atlantic Multidecadal Oscillation as a climate change index to force primary production. Signals were propagated throughout the food web, and biomasses were simulated for the period of 1956 to 2011. Ecosystem changes were estimated with t...

Functional and Structural Food Web Comparison of Terminos Lagoon, Mexico in Three Periods (1980, 1998, and 2011)

Terminos Lagoon has a high diversity of species and habitats and is the largest coastal lagoon in the southern Gulf of Mexico. It has been a natural protected area since 1994, but in recent decades, environmental changes have modified its biological communities and habitats. In this study, we construct three trophic models for the periods 1980, 1998, and 2011 using the Ecopath with Ecosim approach to evaluate the status of the ecosystem. Based on model outputs, we compare functional indicators and perform a structural analysis of the food web. We found significant changes in the biomasses of trophic compartments and in other functional indicators. The global productivity of the ecosystem was the main ecosystem indicator that changed over time. The structural analysis included a collection of centrality indices which measure the number, strength, and distance (in terms of number of links) of linkages between each trophic compartment and all other compartments, as indicators of the relative importance of each compartment in overall energy flows. Structure was also assessed by identifying the number and composition of subgroups connected by strong trophic linkages. Certain compartments from lower trophic levels, such as seagrasses, microcrustaceans, meiobenthos, and echinoderms had the higher values of centrality measures in the three periods analyzed. Substructures were relatively stable between periods, confirming that a reduction in productivity was the main ecosystem indicator that changed over time. Some trophic compartments were recurrent in substructures, revealing their key role in the food web structure regardless of changes in productivity. This analysis suggests that those compartments must be prioritized in conservation scenarios because the loss of those species would change the ecosystem structure impacting severely its biological productivity.

The ecological role of the vaquita, Phocoena sinus, in the ecosystem of the Northern Gulf of California

From an ecosystem management perspective, analysis of the functional roles of species is a challenge. It is valuable to determine which species are irreplaceable within a given community based on their contribution to the system’s organization. This study relates the emergent functional and structural indices of biological groups estimated from a trophic model of the Northern Gulf of California to identify the roles of these groups in the ecosystem context, with a particular focus on the role of the vaquita, an endemic porpoise in critically endangered status. The simulation of removing each group allowed the analysis of the removal’s functional effect on the ecosystem’s global attributes and organization (based on Ulanowicz’s ascendency concept). Groups from lower trophic levels (TL) were more related to complexity indicators, suggesting their contribution to the organization and structure of energy flows in the food web. Groups from intermediate TL had higher values of structural indexes, indicating their function in the control of flows throughout the network. The vaquita along with other marine mammals, aquatic birds, and some species of fish with a high TL contribute in a similar way to the order (for example, ascendency/capacity-of-development ratio) of the system, showing a relatively high value of ascendency (contribution of the group to the organization inherent to the ecosystem) and the change in ecosystem ascendency when they were removed. The vaquita, like marine and coastal birds, plays a small role in the ecosystem. But like them, it does contribute substantially to ecosystem organization. This study thus provides information potentially useful for management in understanding the species’ role and in reducing uncertainty in decision-making.

The food sources of Selene peruviana (actinopterygi: perciformes: carangidae) in the southern Gulf of California

Background. The food and feeding habits of a fish are important for understanding not only the fish biology but also the role played by the species in the ecosystem. The Peruvian moonfish (known also as Pacific moonfish), Selene peruviana (Guichenot, 1866), is a relatively abundant species, with its biology poorly known along the Mexican Pacific zone. Therefore, the aim of this study was to determine the principal food items of the Peruvian moonfish by using stable isotopes and the stomach content analysis. Materials and methods. We analyzed stomachs of 204 moonfish collected by a shrimp fishing boat along the coast of Nayarit and south of Sinaloa, Mexico from September to March, within 2006-2007. We also took 11 muscle samples of moonfish and some organisms being potential prey items for stable isotope analysis. Examining the stomach contents we determined the most important prey species using the geometric index of importance. We also determined the feeding strategy of this predator using Amundsen plots and Levins index and finally we calculated the trophic position. We also determined the principal preys using stable isotopes analy- sis along with mixing models, and based on those values we calculated the trophic position. Results. The stomachs of Selene peruviana contained chiefly engraulid fishes and crustaceans. The stable iso- topes analysis (SIA) helped to identify partly digested material as representing crustaceans of the family Portunidae. The trophic position found by both methods was between 3.7 and 3.9 and we also determined that this fish tended to feed near the coast. Conclusion. Selene peruviana is an opportunistic predator that consumes preys that are abundant in the zone. The stable isotopes analysis proved to be an efficient tool supplementing the stomach content analysis and helping to identify also partly digested items.

Temporal shifts in functional traits of the fish community in Terminos Lagoon (Mexico) in three periods (1980, 1998 and 2011)

The trophic structure of the fish community ecosystem in the Terminos Lagoon (southern Gulf of Mexico) has shown a range of functional changes. The description of the heterogeneity of functional traits in a biological community allows the identification of the relevant functions in an ecosystem. An analysis was conducted of the functional traits (trophic level, reproductive and trophic guild, habitat, estuary use, essential habitat, salinity tolerance, body shape, mouth type, caudal fin type, and maximum length) of the fish community of the lagoon for three different years (1980, 1998 and 2011). We developed a new index to analyze the variation of functional diversity called the functional traits diversity index (FADI). This index takes into account the abundance of traits and emphasizes less common traits (i.e., those that are less redundant). The functional redundancy was different in the three periods studied. The FADI value for 1998 was the highest and was outside of the expected probability distribution, indicating a greater abundance of species with unique functional traits. A principal components analysis was performed to assess the relative contribution of functional traits to the overall variance of functional diversity over the three periods. We found that the trophic level, body shape, and mouth type were the most influential traits in the functional diversity changes. The environmental changes were correlated with the variability of the functional structure. Depth was the most influential environmental variable in the principal component analysis. The results indicate a reorganization of the functional structure of the fish community in the Terminos Lagoon. The FADI was helpful in explaining these changes observed throughout the three periods studied.