Adjacent Oceanic Areas Research Articles

The genus Bradleya Hornibrook, 1952 (Crustacea: Ostracoda) in South America and adjacent oceanic areas, with description of a new bradleyine genus.

The ostracod genus Bradleya Hornibrook is an important taxon of Cenozoic assemblages, occurring practically in all oceanic regions. The wide distribution both in shallow and deep waters turns Bradleya interesting for studies involving phylogeny and paleoceanography. The present work aims at the study of fossil and recent species in South America and adjacent regions, based on bibliographic review and the restudy of samples from the Brazilian continental margin, the Navidad Formation (lower Miocene) and El Peral Beds (meso-upper Miocene), both cropping out in the Central Chile. The chronostratigraphic, (paleo)bathymetric and (paleo)zoogeographic distribution of the species is reviewed and updated. The bridge composition was studied in all species recorded and revealed to be important taxonomic character. The taxa identified were gathered into three morphological groups: two proposed previously (i.e., the dictyon-group and the arata-group) and a new one in the present work (i.e., the normani-group). The dictyon-group and the arata-group gather deep-sea species, while the normani-group is predominantly neritic, including most of the species of Brazilian margin. Bradleya victorjarai sp. nov. is proposed for the Miocene of Chile, and Bradleya ybate (Bergue et al.) is reassigned to Rigracythere gen. nov. Questionable or misidentified species ascribed to Bradleya are briefly discussed.

Potassic Volcanism Induced by Mantle Upwelling Through a Slab Window: Evidence From Shear Wave Splitting Analyses in Central Java

AbstractTo delineate the mantle flow fields in the vicinity of a previously proposed slab window and the possible roles that they may play in the formation of potassic volcanism in Central Java, we conduct shear wave splitting analyses using both local S and teleseismic XKS waves (including SKS, SKKS, and PKS) recorded by 121 onshore stations and two ocean bottom seismometers (OBSs). The XKS fast orientations from the OBSs are trench normal and in accord with previous subslab anisotropy measurements. In the eastern part of Central Java, the XKS and local S fast orientations from the onshore stations are mostly trench‐parallel; in contrast, in the western part of Central Java, the XKS fast orientations are trench‐normal while the local S measurements are spatially varying. The observations can be attributed to four flow systems including (a) subslab trench normal mantle flow in areas away from the trench which is entrained by the Australian Plate, (b) trench normal flow that goes into the mantle wedge from the subslab area through a slab window beneath the western part of the study area, (c) trench‐parallel subslab flow near the trench beneath the eastern part of the study area which is driven by slab‐rollback, and (d) dominantly trench‐parallel flow system in the mantle wedge reflecting the horizontal component of the escaped flow system through the slab window. We propose that the vertical component of the escaped flow is responsible for the formation of the potassic volcanoes in the adjacent oceanic area.

Nearshore to Offshore Trends in Plankton Assemblage and Stable Isotopes in Reefs of the West Philippine Sea

Coral reefs are typified by their benthic components, and reef diversity and productivity are traditionally ascribed to the symbiotic association between corals and zooxanthellae, and other macroalgal forms. Less understood is the role of plankton and adjacent pelagic areas in contributing to reef productivity. Half of the reef benthos are filter or particle feeders, while a significant proportion of reef fishes are planktivorous. These organisms can serve as bridges between adjacent oceanic areas to the reef proper, and the pelagic and benthic realm. Here, we investigate the plankton trophic dynamics in two reef systems in the West Philippine Sea. Physico-chemical data, phytoplankton and mesozooplankton samples were collected from stations spanning offshore to reef areas per site. These were subjected to microscopic and stable isotope analysis to determine variability in plankton distribution, phytoplankton and zooplankton interactions, and gain insights into the trophic dynamics and productivity of reefs. Results showed distinct variations in plankton biomass and assemblage from offshore to reef areas, as well as between the reef systems. Phytoplankton distributions pointed toward filtering out of cells across the fore reef and reef flat areas, while mesozooplankton distributions could be mediated more by other factors. Isotopic signatures of δ13C and δ15N indicated the influence of different nutrient sources for phytoplankton and that mesozooplankton relied only partly on phytoplankton for food in most areas of the reefs. The mesozooplankton likely also obtain food from other sources such as the microbial and detrital pathways. More in-depth spatio-temporal studies on these bentho-pelagic interactions are recommended, which can provide more robust estimates of the trophic dynamics of these reefs that are situated in important fishing grounds and key biodiversity areas.

Update on crustaceans known from the Amazonian continental shelf and adjacent oceanic areas

Abstract The major biodiversity on the planet is present in coastal and oceanic environments, despite this, on the northern continental shelf of Brazil, data on most of the marine groups still are deficient, especially in areas deeper than 20 m and in the continental slope area. This lack of data is aggravated by high fisheries exploitation, which causes a decline in large, abundant populations, even leading them to threat of extinction. Among that marine biodiversity, no group has a larger morphological variety than crustaceans. In this scenario, knowledge about the local biodiversity, its richness and seasonality, is essential for a qualified fisheries management. The Amazon continental shelf has one of the largest shrimp fisheries in the country, and due to the ecological and economic importance that crustaceans have in the region, a detailed study on their diversity is necessary. In this article, we use data collected in the Revizee Program. We identified 91 species: crabs (32.97%), shrimp (28.57%), anomurans (10.99%), soft crabs (10.99%), lobsters (9.89%), stomatopods (4.40%) and isopods (2.20%). The State of Amapá had fewer species () compared to Pará (). The data analysis shows there is a lack of knowledge about the real biodiversity present on the Amazon continental shelf.

Coupled Interannual Variability of Wind and Sea Surface Temperature in the Caribbean Sea and the Gulf of Mexico

AbstractThis work describes dominant patterns of coupled interannual variability of the 10-m wind and sea surface temperature in the Caribbean Sea and the Gulf of Mexico (CS&GM) during the period 1982–2016. Using a canonical correlation analysis (CCA) between the monthly mean anomalies of these fields, four coupled variability modes are identified: the dipole (March–April), transition (May–June), interocean (July–October), and meridional-wind (November–February) modes. Results show that El Niño–Southern Oscillation (ENSO) influences almost all the CS&GM coupled modes, except the transition mode, and that the North Atlantic Oscillation (NAO) in February has a strong negative correlation with the dipole and transition modes. The antisymmetric relationships found between the dipole mode and the NAO and ENSO indices confirm previous evidence about the competing remote forcings of both teleconnection patterns on the tropical North Atlantic variability. Precipitation in the CS and adjacent oceanic and land areas is sensitive to the wind–SST coupled variability modes from June to October. These modes seem to be strongly related to the interannual variability of the midsummer drought and the meridional migration of the intertropical convergence zone in the eastern Pacific. These findings may eventually lead to improving seasonal predictability in the CS&GM and surrounding land areas.

Composition, richness and taxonomic diversity of Polychaete assemblages from La Paz Bay and adjacent oceanic areas of the Southern Gulf of California

In the present study, the composition and structure of the assemblages of polychaetes of La Paz Bay and adjacent oceanic areas of the Gulf of California was analyzed. A total of 56 species belonging to 39 genera and 22 families were collected from eight stations sampled during the spring of 2006 at 31 to 208 m depth. Onuphidae (14 species), Paraonidae (7 species) and Spionidae (6 species) were the best represented families. The highest number of species and individuals (mean= 13 species station−1; 76.7 ind. 0.1 m−2) was found in stations located in the Gulf shelf while inside of La Paz Bay, the fauna was less abundant and diverse (mean= 9 species station−1; 47.0 ind. 0.1 m−2). Differences in species composition defined two main faunal groups, which were linked by their spatial distribution: assemblage Aricidea (Acmira) simplex – Aglaophamus verrilli inside the Bay, and assemblage Paraexogone molesta – Cirrophorus furcatus – Prionospio dubia in the Gulf shelf. The composition and structure of the fauna was mainly associated with the sediment type (Rho= 0.48; p=0.06): muddy habitats inside the bay and sandy bottoms in the Gulf. Only 11 out of the 39 identified genera (28.2%) had more than two species, and only seven of the 23 families (30.4%) had two or more species. This taxonomic heterogeneity caused a wide variability in the “average taxonomic distance” of every pair of individuals at each station (64.69 to 89.58). Therefore, the distribution patterns of the taxonomic diversity values between the sites inside La Paz Bay (mean= 79.45) and those found outside, in the Gulf (mean= 79.77), were similar.

Net Heterotrophy in the Amazon Continental Shelf Changes Rapidly to a Sink of CO2 in the Outer Amazon Plume

The Amazon continental shelf and adjacent oceanic area were sampled for inorganic and organic carbon parameters in order to improve data coverage and understanding of carbon cycling dynamics within this important region. Seasonal coverage of the Amazon plume on the French Guiana continental shelf further north, was provided by CO2 monitoring using a merchant ship sailing from France to French Guiana (2006-2016). Salinity ranged from 1 to 36 (transects in April 2013, and May 2014). At salinity below 10, strong outgassing was observed with fugacity of CO2 (fCO2) over 2000 atm. This region displayed net heterotrophy, fueled by organic matter with terrestrial origin, as shown by 13C and 15N values of suspended particles. A 13C cross shelf average of -31‰ was measured during May 2014, contrasting with oceanic values in excess of -20‰. The reactivity of this terrestrial material resulted in the local production of dissolved inorganic and organic carbon as well as fluorescent humic compounds. Further offshore, the dilution of freshwater by ocean waters created a sink for CO2, enhanced by biological activity. The strongest CO2 drawdowns, associated with high chlorophyll a concentrations, were observed on the French Guiana continental shelf in the outer Amazon plume, with fCO2 values below 150 uatm. Here, a CO2 sink was present almost throughout the year, with a seasonal maximum of -9.2 mmol CO2 m-2d-1 observed in June 2015. However, both the CO2 and salinity distributions could vary significantly within a few days, confirming the presence of many eddies in this region. The Amazon continental shelf hence behaved as a transition zone between an inshore source of CO2 to the atmosphere and an offshore sink. Some marine phytoplankton production was detected but occurred mainly close to the French Guiana shelf. A mean net CO2 outgassing of 44 ± 43.6 mmol m-2d-1 was estimated for the area. Quantifying the CO2 flux for the entire Amazon shelf area led to a revised annual estimate of the net ocean carbon export of 2.86 1012 mol C from the region.

Modulation of sea surface temperature warming in the Bay of Biscay by Loire and Gironde Rivers

AbstractThe influence of Loire and Gironde River discharges over the sea surface temperature (SST) in the eastern Bay of Biscay (0.6º–36.6ºW, 44.2º–47.8ºW) was analyzed by means of two complementary databases (MODIS and OISST1/4). The area influenced by river plume showed a different SST when compared with the adjacent oceanic area for the months when the plume attains its highest extension (December, January, and February). Ocean was observed to warm at a rate of approximately 0.3ºC dec−1 while temperature at the area influenced by the rivers cooled at a rate of −0.15ºC dec−1 over the period 1982–2014. The mere presence of a freshwater layer is able to modulate the warming observed at adjacent ocean locations since the coastal area is isolated from the rest of the Bay. This nearshore strip is the only part of the Bay where changes in SST depend on North Atlantic Oscillation (NAO) but not on North Atlantic SST represented by the Atlantic Multidecadal Oscillation (AMO). These different cooling‐warming trends are even more patent over the last years (2002–2014) under atmospheric favorable conditions for plume enhancement. River runoff increased at a rate on the order of 120 m3s−1dec−1 over that period and southwesterly winds, which favor the confinement of the plume, showed a positive and significant trend both in duration and intensity. Thus, the coastal strip has been observed to cool at a rate of −0.5°C dec−1.

Seawater temperature changes associated with the North Brazil current dynamics

This study used hydrographic data (CTD and ADCP) collected along the north Brazilian continental shelf and the adjacent oceanic area (the north Brazilian zone) and 13 years of monthly data of sea surface temperatures (SSTs) obtained from the Tropical Rainfall Measuring Mission satellite microwave images. In July and August 2001, the core of the North Brazil Current (NBC) with a velocity exceeding 1.2 m s−1 in the upper 150 m was observed near the break of the north Brazilian continental shelf. The satellite and in situ SSTs from the same time indicate that relatively cold waters (<27.5 °C) extended throughout the NBC region where the vertical distribution of temperature displayed a rise of the 26 °C isotherm to near the surface on transects where the NBC was more intense. These observations indicated that the NBC plays an important role in temperature changes in the water column near and/or over the north Brazilian continental shelf margin even at times when, theoretically, the NBC may be expected to be less intense (April–May) and warm waters dominate the area. The distribution of accumulated temperature change reveals that the NBC may contribute to possible nutrient upwelling of the bottom boundary layer along the continental shelf to surficial areas and offshore following the NBC deflection or merely into the North Atlantic.

Plankton and seston size spectra estimated by the LOPC and ZooScan in the Abrolhos Bank ecosystem (SE Atlantic)

The biomass size spectrum provides valuable information about the functioning of plankton systems. We evaluated hydrographic and bathymetric influences on biomass size spectra and on vertical distributions of plankton and seston above the Abrolhos Bank and in adjacent oceanic areas off Eastern Brazil. We used both in situ Laser Optical Particle Counter (LOPC) and preserved plankton samples analyzed with a ZooScan system to determine seston and plankton abundances, size distributions, and biomasses. Shelf stations, including those on the Abrolhos Bank, had higher particle concentrations and mesozooplankton biomasses than the vertically stratified oceanic stations. The latter were influenced by cold, nutrient-rich South Atlantic Central Water (SACW) below the mixed layer, particularly toward the south of the study area. Small particles (<1mm) were more abundant above and within the pycnocline, whereas large particles (>1mm) had a more heterogeneous vertical distribution, but were more abundant above the pycnocline, especially at the oceanic stations. Calanoid copepods usually dominated the mesozooplankton biomass spectra, but were accompanied by cyclopoids, appendicularians, and ostracods, the latter being particularly abundant during nighttime stations on the Abrolhos Bank. Both LOPC and ZooScan data showed significant differences in NBSS slopes and intercepts between shelf and oceanic stations. The higher intercepts and steeper slopes over the shelf are characteristic of higher productivity. The shallower slopes and presence of more biomass in larger particles indicate a more important contribution of large organisms and higher energy transfer efficiencies at the open ocean stations. Our results highlight the importance of the Abrolhos Bank for pelagic production in an otherwise oligotrophic ocean.

Hook selectivity as a mitigating measure in the catches of the stingray Pteroplatytrygon violacea (Bonaparte, 1832) (Elasmobranchii, Dasyatidae)

Hook selectivity, sex ratio of catches and relative abundance (Catch Per Unit Effort – CPUE) were assessed for the pelagic stingray Pteroplatytrygon violacea (Bonaparte, 1872), caught by longline gear in the southwestern Atlantic Ocean over the continental slope and adjacent oceanic area. The catches were carried out at depths of 200–4000 m by research cruises in 2002 and 2003, from Cabo Frio (22°52′S) to Laguna (28°28′S); and by hook selectivity experiments from 2004 to 2008, from Itajaí (26°54′S) to Tramandaí (29°59′S). Hook selectivity experiments indicated higher catches of stingrays with ‘J’ hooks (9/0, 10° offset) commonly used by the pelagic longline fleet than with ‘circle’ hooks (18/0, 10° offset). ‘circle’ hooks reduce the longline by-catches of this species. Most of the stingrays caught were males (6 : 1). One female aborted mid-term embryos at the time of capture. CPUE was highest between spring and autumn and lowest during winter.

Cloud-to-ground lightning over Mexico and adjacent oceanic regions: a preliminary climatology using the WWLLN dataset

Abstract. This work constitutes the first climatological study of lightning over Mexico and adjacent oceanic areas for the period 2005–2009. Spatial and temporal distributions of cloud to ground lightning are presented and the processes that contribute to the lightning variability are analysed. The data are retrieved from the World Wide Lightning Location Network (WWLLN) dataset. The current WWLL network includes 40 stations which cover much of the globe and detect very low frequency radiation ("spherics") associated with lightning. The spatial distribution of the average yearly lightning over the continental region of Mexico shows the influence of orographic forcing in producing convective clouds with high lightning activity. However, a very high number of strikes is also observed in the States of Tabasco and Campeche, which are low-lying areas. This maximum is related to the climatological maximum of precipitation for the country and it may be associated with a region of persistent low-level convergence and convection in the southern portion of the Gulf of Mexico. The maps of correlation between rainfall and lightning provide insight into the microphysical processes occurring within the clouds. The maritime clouds close to the coastline exhibit similar properties to continental clouds as they produce very high lightning activity. The seasonal cycle of lightning registered by WWLLN is consistent with the LIS/OTD dataset for the selected regions. In terms of the annual distribution of cloud-to-ground strikes, July, August and September exhibit the highest number of strikes over continental Mexico. The diurnal cycle indicates that the maximum number of strikes over the continent is observed between 6 and 9 p.m. LT. The surrounding oceanic regions were subdivided into four distinct sectors: Gulf of Mexico, Caribbean, Sub-tropical Pacific and Tropical Pacific. The Gulf of Mexico has the broadest seasonal distribution, since during winter lightning associated with mid-latitude systems also affects the region. The diurnal distribution of lightning for the Gulf of Mexico exhibits the highest number of strokes at 9 a.m. The Caribbean seasonal distribution is slightly biased towards early fall, with a clear maximum observed during October. The diurnal distribution of lightning over the Caribbean is quite uniform with a slight increase near midnight. The Subtropical Pacific has the narrowest seasonal distribution, associated with the convection observed during the "North American Monsoon", with the maximum number of strikes during August and September. In contrast, the Tropical Pacific has a broader seasonal cycle, associated with convection in the Inter-Tropical Convergence Zone (ITCZ), starting in May and lasting till October. In both adjacent Pacific regions, the strikes present a maximum in the early morning, the time of the highest frequency of land breeze.

Artisanal fisheries in La Paz Bay and adjacent oceanic area (Gulf of California, Mexico)

We analyzed the artisanal fishery capture data for La Paz Bay (Baja California Sur, Mexico) from 1998 to 2005. Capture data were related to the reproductive cycle of each species. Complete fishing records for 18 species of commercial importance belonging to eight families were identified. The most frequently captured species in La Paz Bay was the Pacific red snapper Lutjanus peru, with 43% of the total capture. This species was followed in importance by the spotted rose snapper Lutjanus guttatus, other groupers (Serranidae), and the jacks (Carangidae), with 18.8%, 15%, and 7.3% of the capture, respectively. Other commercial species captured in smaller amounts included the yellowfin tuna Thunnus albacares, the California flounder (or California halibut) Paralichthys californicus, the flathead mullet Mugil cephalus, the goliath grouper Epinephelus itajara, and different species of mojarra (Gerreidae). With few exceptions, catches outside the bay were higher than in the inner bay. All species were caught throughout the year regardless of their reproductive season. We recommend the implementation of fishery regulations for La Paz Bay, especially in the case of the Pacific red snapper, since it is the most exploited. Currently, overexploitation and possible local shortage of species may occur at any time and without warning in the near future. Aside from fishery management, an attractive option for increasing the supply of marine resources in the area is to use the inner bay for marine fish farming.

Reconstructing ancient environments from detailed stratigraphic distributions of dinoflagellate cysts: providing a palaeobathymetric and related sequence framework for the Valanginian to Aptian of the northwestern Australian margin

The environmental effects upon the lateral distribution of Early Cretaceous microplankton assemblages and the differentiation of shallow and deeper-water assemblages have not been studied extensively in the Australian region (Helby et al, 1987). For this study, Valanginian to Early Aptian assemblages from the Carnarvon Basin and adjacent oceanic areas were investigated to clarify the nature of environmental controls – particularly bathymetry – on species distribution.

Simulation capability of tropical and extratropical seasonal climate anomalies over South America

An ensemble of 20 extended integrations of the atmospheric model CSIRO Mark 2, forced with the sea-surface temperature observed during the 1986–1998 period, was performed to analyze the simulation capability of seasonal climate anomalies over South America and adjacent oceanic areas. Variations of the simulation skill within the region and during the experimental period were assessed through standard statistical measures and compared to the signal-to-noise ratio distribution. Before the skill assessment, model systematic errors were thoroughly evaluated. The results confirm that the simulation skill is very high in tropical oceanic areas, and decreases rapidly towards middle and high latitudes. Model performance at mid and high atmospheric levels is substantially better than at low levels. Relatively high simulation capability was found over the Pacific Ocean between the equator and the Antarctic coast, which is coherent with the presence of three relative maximums in the signal-to-noise ratio, similar to the increase of the forced variance found by several authors over much of the Pacific–North American pattern region. Rainfall rate and second-order moments associated with the cyclonic activity and the meridional eddy fluxes of heat and humidity are better simulated in a narrow strip parallel to the SPCZ and extending further southeast into mid latitudes of the continent. The simulation skill noticeably improves during the warm and cold ENSO phases, in correspondence with an intensification of the signal-to-noise ratio, and useful rainfall anomaly simulations can be obtained over the Amazonas and Rio de la Plata river basins.

Variação sazonal da estrutura de massas de água na plataforma continental do Amazonas e área oceânica adjacente

Este trabalho analisa as informacoes de temperatura e salinidade obtidas a partir de tres cruzeiros oceanograficos realizados na area da Plataforma Continental do Amazonas e regiao oceânica adjacente. Os dados foram coletados em diferentes periodos do ano, correspondendo a distintas situacoes de aporte de aguas continentais: minima descarga do rio Amazonas (outubro/1997), maxima descarga fluvial (maio/1999), e durante o periodo de transicao (maxima para minima) descarga do rio (agosto/2001). Os resultados permitiram descrever a variacao sazonal da distribuicao tridimensional das quatro massas de agua encontradas: Agua Costeira (AC), Agua Tropical (AT), Agua Central do Atlântico Sul (ACAS) e Agua Intermediaria da Antartica (AIA). Os resultados sugerem que o cisalhamento eolico age sobre a distribuicao temporal das aguas superficiais (AC e AT), enquanto que a distribuicao das massas d'agua de subsuperficie (ACAS e AIA) e influenciada pela variabilidade sazonal da Corrente Norte do Brasil (CNB) e pela presenca de vortices anticiclonicos na regiao de retroflexao da CNB. Os transectos verticais indicam que a ACAS sofre uma expansao de cerca de 70 m (49oW) e de 220m (50oW) durante o periodo de transicao das descargas fluviais, que corresponde a epoca de maxima acao da CNB e da Contra-corrente Norte Equatorial (CCNE).

Annual life cycle of the copepod Eucalanus inermis at a coastal upwelling site off Mejillones (23�S), northern Chile

Eucalanus inermis is an abundant species in the eastern tropical and subtropical South Pacific, including the oceanic and coastal waters off Chile and Peru. Its annual life cycle was studied through a time-series sampling (weekly intervals) during 2002, at a fixed coastal station at an upwelling site (Mejillones Bay, 23°S) off northern Chile. The more-or-less continuous occurrence and abundance of naupliar and copepodid stages indicated that the species reproduces during most of the year, with two peaks: one during the austral spring and the other during the summer. Thereafter, an abrupt decline in the population was observed during winter. The abundances of E. inermis copepodids and nauplii were positively correlated with sea surface temperature, suggesting temperature-dependent development and growth during the spring–summer period. Three cohorts could be distinguished during one annual cycle, with generation times >30 days. The estimate of mean weight-specific daily growth (0.12 day−1) is lower than that of other species in the area, but it is consistent with a slower development rate. The distribution of this copepod is associated with the equatorial subsurface waters characterized by low-oxygen content ( 200 m depth), probably in a lethargic mode, within the oxygen minimum zone in the adjacent oceanic area.

Fish larvae abundance and distribution in the central Gulf of California during strong environmental changes (1997–1998 El Niño and 1998–1999 La Niña)

Abstract The pelagic ecosystem of the Gulf of California was affected by the 1997–1998 El Nino warming event and the 1998–1999 La Nina cooling. Larval fish abundance and distribution were analyzed in the central Gulf during El Nino (November 1997 and March 1998) and La Nina (November 1998 and March 1999). Mean sea-surface temperature (SST) differed significantly between El Nino and La Nina ( P 0.05 ) , with variations up to 4 ∘ C . The lowest zooplankton biomass and larval abundance were recorded during El Nino, when species with tropical–subtropical affinity dominated. The Bray–Curtis Dissimilarity Index defined two persisting station groups. The oceanic group, located south of Islas Angel de la Guarda and Tiburon, was strongly co-dominated by Benthosema panamense, Engraulis mordax, and Vinciguerria lucetia larvae in November 1997, whereas larvae of these species together with Triphoturus mexicanus, Sardinops caeruleus, and Scomber japonicus larvae co-dominated in November 1998. Abundances of these last two species were drastically reduced during El Nino. Larval Diogenichthys laternatus, B. panamense, V. lucetia, and T. mexicanus co-dominated the oceanic station group in March 1998, but were less prominent in March 1999, except for V. lucetia, which co-dominated with E. mordax larvae. This situation was associated with the peak of maximum intensity of the La Nina. The second station group, located in the vicinity of Big Islands, was dominated by B. panamense larvae in both Novembers and by E. mordax larvae in both Marches; in both cases this probably was more reflective of high larval abundance in the adjacent oceanic area than a preferential habitat in the Big Islands vicinity. Results suggest that the fish larvae abundance and distribution were altered in different ways by the environmental changes caused by the 1997–1998 El Nino and 1998–1999 La Nina.

Fish larvae abundance and distribution in the central Gulf of California during strong environmental changes (1997–1998 El Niño and 1998–1999 La Niña)

The pelagic ecosystem of the Gulf of California was affected by the 1997–1998 El Niño warming event and the 1998–1999 La Niña cooling. Larval fish abundance and distribution were analyzed in the central Gulf during El Niño (November 1997 and March 1998) and La Niña (November 1998 and March 1999). Mean sea-surface temperature (SST) differed significantly between El Niño and La Niña ( P < 0.05 ) , with variations up to 4 ∘ C . The lowest zooplankton biomass and larval abundance were recorded during El Niño, when species with tropical–subtropical affinity dominated. The Bray–Curtis Dissimilarity Index defined two persisting station groups. The oceanic group, located south of Islas Angel de la Guarda and Tiburón, was strongly co-dominated by Benthosema panamense , Engraulis mordax , and Vinciguerria lucetia larvae in November 1997, whereas larvae of these species together with Triphoturus mexicanus , Sardinops caeruleus , and Scomber japonicus larvae co-dominated in November 1998. Abundances of these last two species were drastically reduced during El Niño. Larval Diogenichthys laternatus , B. panamense, V. lucetia , and T. mexicanus co-dominated the oceanic station group in March 1998, but were less prominent in March 1999, except for V. lucetia , which co-dominated with E. mordax larvae. This situation was associated with the peak of maximum intensity of the La Niña. The second station group, located in the vicinity of Big Islands, was dominated by B. panamense larvae in both Novembers and by E. mordax larvae in both Marches; in both cases this probably was more reflective of high larval abundance in the adjacent oceanic area than a preferential habitat in the Big Islands vicinity. Results suggest that the fish larvae abundance and distribution were altered in different ways by the environmental changes caused by the 1997–1998 El Niño and 1998–1999 La Niña.

Ichthyoplankton distribution off the Peninsula de Mejillones, Chile (23° S, 71° W), under variable hydrographic conditions during the austral summer and winter of the 1997 El Niño

This paper identifies the larval fish community distribution, emphasizing non-commercial species, in the coastal zone and the adjacent oceanic area off the Peninsula de Mejillones (23° S, 71° W) during the 1997 El Nino. We performed one survey in the austral summer (January) and one in the austral winter (July). In January, cold, upwelled water dominated the area off the Peninsula de Mejillones with a cold-water filament extending 60 nm offshore. In July, warm Subtropical Surface Waters affected the area. We identified a total of 56 taxa, which included taxa from different adult habitats (coastal, epipelagic, epi-mesopelagic and mesopelagic). The most abundant species were Engraulis ringens (18% and 21%), Bathylagus sp. (4% and 5%), Diogenichthys laternatus(12% and 39%), Lampanyctus parvicauda (9% and 2%), Triphoturus mexicanus (14% and 3%) and Vinciguerria spp. (21% and 23%), in January and July, respectively. A multidimensional scaling (MDS) ordination and similitude dendograms revealed changes in the larval fish community structure influenced by hydrographic conditions. The rank correlations between the assemblage similarity matrix and the physical variables matrix indicate the importance of the distance from shore and production processes (represented by chlorophyll-a) on the assemblage distributions. Off the Mejillones' coast, there is a complex spatial and temporal hydrographic system where ichthyoplankton of coastal and oceanic fish species coexist. Despite both short-term and longer-term disruptive oceanographic processes (e.g., mesoscale filaments, El Nino events), it seems that the numerically dominant species persist in the area due to their various behavioral strategies and physiological adaptations.