Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

New sequencing technologies and analytical capabilities have stimulated the study of microbial communities from specific environments, enabling researchers to understand the complexity of those systems. The 16S rRNA gene has proved very useful in describing the diversity and characterization of marine microbial communities, particularly of uncultivated organisms. The development of new sequencing techniques has contributed to the exponential increase in the number of reported 16S rRNA sequences as barcodes for microorganisms, forcing a review of concepts and methods for the taxonomic classification of these organisms. Manipulation and analysis of large amounts of genetic information have prompted the development of specific databases, specialized algorithms, and computational tools to compare thousands of such sequences and make a taxonomic assignment. Complete 16S rRNA sequences are thus needed for accurate and reproducible taxonomy assignment in the study of marine bacterial communities. 

Coastal lagoons are very sensitive to anthropogenic impacts and sedimentary records may provide valuable temporal reconstructions of the environmental changes in the lagoon, the coastal zone, and the catchment area. The Alvarado Lagoon (Veracruz, southwestern gulf of Mexico) belongs to an extensive complex of wetlands recognized as a Ramsar site. However, its catchment basin has one of the highest deforestation rates in Mexico due to the transformation of lowlands for agriculture and grazing, thus causing siltation of the surrounding aquatic bodies. To evaluate the impact of land use change on Alvarado Lagoon, sediment fluxes and provenance were reconstructed by studying the elemental composition (determined by X-ray fluorescence spectrometry) of a sediment core dated radiometrically (210Pb, 137Cs, 239,240Pu). The sedimentary record showed an acceleration of the sediment accumulation rate during more than 134 ± 17 years; however, the changes in elemental composition during the past 40 years (i.e., 1972–2011) indicated the incorporation of continental weathered sediments and an increment of sediment accumulation of circa 470%, in coincidence with the period of higher deforestation and siltation. The recent increase in sediment accumulation rates and changes in geochemical features are attributed to erosion caused by land use changes in the Alvarado Lagoon drainage basin. 

The reproductive biology of the massive coral Pavona gigantea has been studied along Mexico’s Pacific coast, but basic aspects such as its relation to local environmental variables and its variation on a mesoscale level have not been addressed. The reproductive cycle of P. gigantea was monitored monthly over a two-year period (2010–2012) at four sites along the coast of Oaxaca (southwestern Mexico). Except for one hermaphroditic colony, P. gigantea was gonochoric and exhibited asynchronous development. The data suggest that, in the study area, the species may reproduce seasonally, with minor interannual differences (May–September 2010, April–August 2011, April–May 2012). There were spatial and temporal variations in the percentage of reproductively active colonies and the presence of mature sex cells. A multiple regression analysis revealed that the percentage of reproductively active colonies was significantly explained (69.6%) by mesoscale variations in environmental variables such as sea surface temperature, photosynthetically active radiation, diffuse attenuation coefficient, percentage of lunar illumination, and photoperiod, the latter being the most relevant variable in the model. The data suggest that temporal mesoscale variations can exert a meaningful influence on coral reproduction in the study area. 

Sedimentation and burial affect a variety of habitats worldwide, especially within coastal marine systems. In the Mediterranean, seagrasses like Cymodocea nodosa are commonly subjected to sedimentation and, although the response of C. nodosa has been documented, few studies have included macrofaunal responses. We used a manipulative field experiment to examine the effects of a single small-scale, pulse burial event on benthic invertebrate macrofauna. Burial did not affect the total abundance, richness, or diversity of higher taxa nor the live abundance or diversity after 5 days. However, live higher taxa richness decreased by day 3. After 5 days, such decrease reversed and partial recovery seemed to occur. Almost 2 months later, three of the buried plots remained with some additional sedimentation, but the other three had lost their sediment. We compared faunal metrics of buried plots between days 5 and 54 and found greater diversity on day 54, providing evidence that macrofaunal recovery apparent 5 days after burial seemed to persist. Although we likely underestimated the effects and can only be conservative with our conclusions, taken together our results suggest small-scale, pulse burial events can have some negative effects on the C. nodosa-associated benthic macrofaunal community, but the community can recover within a few weeks.

The Sagua la Grande River is the largest of northern Cuba. The socioeconomic development in this region during the last 100 years has caused changes in its natural conditions, such as an increase in Hg levels. In 1981, a chlor-alkali plant with mercury-cell technology was built on the river bank and has released several contaminants to the environment. Sedimentation along the river and the nearby coastal zone was reconstructed using the radionuclides 210Pb, 226Ra, 137Cs, and 239,240Pu in sediment cores. The changes in sediment accumulation were related to important changes in the river basin after 1950, such as the channeling of the river in 1955 and the construction of the Alacranes Dam in 1972. Maximum sediment accumulation rates were attributed to large floods in 1933, 1948, and 1985 (Hurricane Kate). The 210Pb chronology allowed the reconstruction of Hg pollution during the last four decades. In the locations with greatest fluvial influence, Hg concentrations increased since the early 1980s exceeding the Effects Range-Median (0.71 mg kg–1). The accumulated Hg inventories released from the plant were one order of magnitude larger than those due to other sources. These results show the impact of Hg releases from this industry on the estuary, especially in the coastal zone close to the river mouth. 

The silverside Odontesthes bonariensis is a euryhaline species native of South America and represents a very important fishing resource for the Plata Basin (Argentina and Uruguay). This study compares the Sr:Ca ratio of water as well as the Sr:Ca ratio and morphometry of the sagittal otolith of the silverside present in different environments (one salt lake, two freshwater dams, one lagoon, and one estuary) in order to evaluate the use of these variables as markers of habitat. The pattern of the Sr:Ca ratio in the water agrees with the one found in the otoliths, showing a positive relationship with the conductivity of the water. Univariate and multivariate analyses of variance indicated significant differences (P < 0.05) among the localities studied for the morphometric indices. The discriminant function analysis provided a high percentage of correctly classified individuals for the saltwater environment (100%) and the lentic water bodies and estuary (60–80%), circularity and form factor being the most relevant morphometric variables. These results indicate that the Sr:Ca ratio and otolith morphometry are good markers of habitat for this important resource.

The world tuna fishing fleet is dominated by purse seine boats. Purse seine sets are sometimes unsuccessful in capturing fish; these unsuccessful attempts are known as null sets. Null sets have been widely documented and the numbers indicate that they happen in large proportions. In Mexico, the tuna fishery represents the second most important fishery by volume and value. The frequency of occurrence of null sets during the period 2000–2013 was analyzed to identify the regions, periods, and oceanographic conditions (e.g., ENSO) related to them. Null sets on free-swimming fish schools and between June and July had a higher relative representation. The region with highest relative occurrence was the mouth of the Gulf of California (between August and October). A positive correlation was observed between the occurrence of null sets on free-swimming fish schools and the Multivariate El Niño Index. The maximum values of occurrence of null sets were related to those months in which the water column structure presented changes. Comprehension of this phenomenon (null sets) and its relation to natural events is of importance for the fishery, as there could be repercussions for the economy and management of the resource.

The Cuban Countercurrent (CCC), along with the Yucatan Current, forms part of the Yucatan Basin circulation system, but it has not been well described and its connection to the system of currents in the Caribbean Sea has not been studied. Based on altimetry data (1993–2009) and the MERCATOR three-dimensional assimilation model (2007–2009), the CCC was observed flowing ~1000 km from the eastern Yucatan Channel to Jamaica and to have a width of ~150 km. Off southern Cuba, the mean velocity was 0.20 m s–1 at the surface and 0.05 m s–1 at 1000 m depth. The CCC transported ~3.5 Sv when it passed through the Yucatan Channel towards the Caribbean Sea, where ~1.6 Sv was recorded south of Cuba. During its annual cycle, the CCC weakened from December to February (0–250 m) and in the summer its magnitude intensified slightly, reaching 0.35 m s–1 in August, due to the increase in water temperature of the Atlantic warm pool. Consequently, the sea level rose in the center of the Yucatan Basin and the pressure gradient increased along the Cuban coast, producing an increase in zonal velocity (0.1 m s–1) and transport (2–3 Sv; r = 0.90). Its connection to the Caribbean current system demonstrated the importance of its study. 

The historical development of Peru’s sardine (Sardinops sagax) fishery between 1978 and 2005 is described from fishery indicators (landings and effort) and environmental indicators (Pacific Decadal Oscillation [PDO] index, Southern Oscillation Index, and Sea Surface Temperature Anomaly) in order to observe the spatial and temporal variations of the fishery. During this period, the fishery indicators showed that excessive fishing pressure caused the drastic decline in abundance, as demonstrated by the low catch levels in recent years. Regarding the environmental indicators, a positive relationship with sardine landing anomalies was observed; however, the PDO index had a significant positive correlation (rPearson = 0.50; P = 0.0005; n = 45) in comparison with the other indices. The results of this study show that the effects of overfishing and adverse environmental conditions strongly impacted the Peruvian sardine population, with the consequent collapse of the fishery. 

Historical information was collected on vessel groundings in the Parque Nacional Sistema Arrecifal Veracruzano (Veracruz Reef System National Park, PNSAV) during the periods 1902–1945 and 1970–2010 to generate specific pressure indicators associated with these events. Information on 126 vessel groundings was gathered, and the cause, specific location, season, and type of vessel were analyzed. Three indicators were generated: stranding pressure, annual pressure, and pressure per site. The highest number of vessel groundings occurred in 1925 and on the Anegada de Adentro reef, the most impacted in both periods. The most common causes of strandings were human error and northerly winds (Nortes). Small vessels were the ones that impacted the most against the reefs. The indicators showed that despite technological advances, pressure caused by groundings in PNSAV continues to occur at a medium level. These indicators are relevant for the management of the area in view of the imminent expansion of the port of Veracruz, which will likely lead to increased vessel traffic and a potential increase in vessel groundings.