Chemical and microbiological studies of sea-surface films in the Southern Gulf of California and off the West Coast of Baja California

Sea-surface films and the corresponding 10-cm subsurface waters were sampled on three cruises to the eutrophic and oligotrophic waters in the Gulf of California and off the west coast of Baja California. The following constituents and properties were measured: NH₄⁺, NO₂⁻, NO₃⁻, PO₄³⁻, SiO₃²⁻, urea, ATP and Chl-a; dissolved and particulate organic carbon and nitrogen; lipid, protein and carbohydrate; total viable and nitrifying bacteria; simulated in situ bacterial heterotrophy; microplankton and simulated in situ primary productivity; surface potential and film pressures; ultraviolet absorption; and film-formation rates using surface potential and chemical methods.Mean enrichment factors (film concentration/10-cm concentration) for the three cruises were: 1.1–2.4 for the soluble inorganic nutrients, dissolved organic carbon, nitrogen, urea, carbohydrate, and lipid; 1.3–2.0 for ATP, Chl-a, microplankton and bacteria; and 1.1–3.7 for particulate carbon and nitrogen and both dissolved and particulate protein. Particulate and dissolved carbon and nitrogen were the only constituents never depleted in the films relative to the subsurface waters. Systematic, significant correlations between the various chemical and biological parameters measured were few, reflecting the complexity of processes which form and maintain surface films.Protein, carbohydrate and lipid carbon accounted for 15–114% (mean = 50%) of the total particulate organic carbon and 14–42% (mean = 28%) of the total dissolved organic carbon in both the films and 10-cm waters. Lipid was not the major identified constituent of films, averaging 18% of the particulate organic carbon and 2.5% of the dissolved organic carbon. There was more protein relative to carbohydrate in film samples compared to 10-cm water; there was also more protein relative to carbohydrate in particulate compared to dissolved mater. Microplankton plus bacterial carbon averaged 16% of the particulate organic carbon in films and 19% in 10-cm waters.     

Microplastic pollution in urban streams across New Zealand: concentrations,composition and implications

ABSTRACT

Microplastic pollution in aquatic systems has been reported globally at an alarming rate, with an increasing number of documented negative biological consequences. Research on microplastic pollution in freshwaters has barely begun in New Zealand, and few studies from smaller lotic systems such as streams exist globally. We investigated the extent of microplastic pollution within urban streams across New Zealand and determined if microplastic concentrations were related to human population density and urbanisation of streams. Fifty-two streams were surveyed across five urban agglomerations in January 2019. Microplastics were found in samples from all sites at densities ranging from <1 to 44?items/m³. This concentration range was comparable to global data but lower than reported in another recent New Zealand study, probably due to differences in sampling methodology. Microplastic pollution was similar across all urban centres, and neither length of urbanised catchment nor urban proportion of the stream were significant predictors of microplastic concentrations. These findings suggest microplastic pollution in New Zealand streams are comparable to larger aquatic systems globally, and that smaller urban streams are significant transport pathways for microplastics. We also recommend standardising microplastic sampling methods to a greater extent in the future, to improve comparability across studies.     

Flux of nutrients in the Gulf of California: Geostrophic approach

Continental margins exert a strong influence on global biogeochemical cycles; however there have been relatively few attempts to quantify either the magnitude or nature of temporal variability in material fluxes. At present here are no reports on nutrient fluxes at the mouth of the Gulf of California (GC) so further information is needed to provide estimated values from direct measurements. From 1995–1999 during five cruises covering all seasons, seawater samples were collected and measured the nutrient content from the surface to the bottom (some deeper than 2500 m) from a repeated hydrographic sections at the mouth of the GC. This chemical and physical database is unique because it covers an area with important biogeochemical signs, which has been detected as one of the highest in primary productivity of the world oceans. These sections are perpendicular to the coastlines of the Mexican states of Baja California Sur (BCS) and Sinaloa. In this section, the most dynamic area was the surface waters in February 1999 with strong geostrophic currents and temperatures of 20 ± 1.5 °C; salinity 35.091 ± 0.156; pH 8.16 ± 0.13; phosphate 0.85 ± 0.42 μM, nitrate + nitrite 2.35 ± 2.94 μM, and ammonia 2.00 ± 1.25 μM (average ± standard deviation).Geostrophic velocities were computed from high-resolution CTD sections across the entrance to the GC. During winter and spring, the outflow occurred near BCS and the inflow occurred either through the center of the section and/or along the Sinaloa coast. Both inflow and outflow cores were 45 km wide and extended deeper than 700 m. Summer and fall showed a complex pattern, alternating cores of inflow and outflow but with inflow along Sinaloa on all cruises. The maximum flow into the Gulf occurs during May in the center of the section while outflow was concentrated along BCS. Mascarenhas et al. [Mascarenhas, A., Castro, R., Collins, C.A., Durazo, R., 2004. Seasonal variation of geostrophic velocity and heat flux at the entrance to the Gulf of California, Mexico. Journal Geophysical Research, 2124.] calculated the section mean geostrophic velocity that was composed of two alternating cores of inflow and outflow. The two cores that were adjacent to either coast were broader and contained the highest inflow (0.40 m s^− 1) and outflow (− 0.25 m s^− 1) velocities, supporting the general idea of inflow along the Sinaloa and an outflow along BCS.The highest nutrient fluxes occur during El Niño conditions in November 1997 with outflows as high as 54.5 Tg yr^− 1 for Phosphate, 43.0 Tg yr^− 1 for Nitrate and 31.7 Tg yr^− 1 for Ammonia, this values were at least three times higher than in February 1999.     

Effective ecosystem-based management must encourage regulatory compliance: A Gulf of California case study

The Northern Gulf of California is an area important for small-scale fisheries in terms of economic activity and food security, but widespread non-compliance with fisheries regulations impedes effective management of resources and conservation efforts. Where a previous study evaluated quantitatively a theoretical situation in which all regulations are perfectly followed, this article compares a suite of recently proposed ecosystem-based management (EBM) policies against the expected benefits of full enforcement of current regulations. Policies evaluated include no-take marine protected areas (MPAs), breeding period closures, changes in hook size and fishing effort, and gear-specific spatial closures. No-take MPAs yield ecological benefits over a wide range of MPA sizes and characteristics, but do not increase overall catch. Seasonal closures are effective at reducing overfishing for the depleted leopard grouper (Mycteroperca rosacea); changing the hook size of artisanal longlines does not increase catch of either the target species or the assemblage, and gear-specific fishery closures for crab traps near Puerto Peñasco are effective at reducing overfishing of blue crab (Callinectes bellicosus and C. arcuatus). In general, full enforcement of existing regulations outperforms these EBM policies in terms of conservation benefits, but it may be less palatable to stakeholders as it requires major reductions in catch.     

Nutrient fluxes in a semi-arid microtidal mangrove wetland in the Gulf of California

Nutrient (C, N and P) fluxes were monitored in a microtidal semi-arid mangrove system, which links a semi-enclosed shallow coastal lagoon with the Gulf of California. We assessed the role of the mangrove ecosystem as a nutrient sink/source and determined how mangrove litterfall rates, tidal regime and climate factors influence these fluxes. Despite high seasonal differences in DOC, POC, N-NO₃⁻ and TP levels, nutrient concentrations were only marginally influenced by either hydrological variables or the concentration of these fractions in the adjacent lagoon. The carbon budget appeared to be balanced throughout the study. Retention rates in the mangrove system were related to litterfall rates. Export of DIN was observed mainly in the wet season due to the low nitrogen assimilation efficiency of the system. Import of organic nitrogen was related to the high retention efficiency of particulate organic nitrogen. Phosphorus fractions were imported and retained in the mangrove supporting previous findings that mangroves are phosphorus sinks. Finally, through a simple meta-analysis we tested the quantitative importance of main variables (tidal flow, tidal elevation, tidal range, rainfall, mangrove catchment area, litterfall) controlling mangrove nutrient dynamics. Although results suggest that generalizations can be made about factors regulating nutrient export from mangroves, the lack of statistical significance highlights the relative importance of the local environment for the magnitude of nutrient exchange in mangroves. Future research should focus on finding mechanistic models to explain these general patterns, taking into account the main biogeochemical processes and their roles in coastal ecosystem ecology.     

Conservation of vaquita marina in the Northern Gulf of California

Vaquita marina, a small species of porpoise endemic to the Northern Gulf of California in Mexico, is the world's most endangered cetacean species. With the purpose of preserving vaquita, the Mexican government launched PACE-Vaquita in 2008. This voluntary program offers an innovative schedule of compensations: as in a payment-for-conservation program, PACE-Vaquita compensates for temporary reductions in fishing effort; as in a program to accelerate technology adoption, PACE-Vaquita compensates for switching to vaquita-safe fishing methods; and as in a buyback program, PACE-Vaquita compensates fishermen for a permanent exit from fisheries. This paper seeks the factors explaining fishermen's participation in PACE-Vaquita during its first year of operation. Analysis is carried out through a multinomial logit specification on a data set collected one week after the enrollment deadline. This paper shows that fishermen with skills in alternative economic activities more likely quit fishing, and fishermen with relatively less productive vessels more likely switched to vaquita-safe fishing methods. Discussion of public policy implications is provided.     

Late Pleistocene-Holocene Paleoceanography and Ventilation of the Gulf of California

Sediment cores collected in 1990 from the Gulf of California have been studied using stable isotope and radiocarbon techniques to reconstruct the climate and ventilation histories since the last glacial maximum. Benthic foraminiferal δ¹⁸O from core tops in a water depth range of 145 to 1442 m increases by about 2% with increasing depth. This is consistent with a composite temperature profile constructed from several hydrocasts in the various gulf basins. However, the δ¹⁸O water/salinity relationship is not sufficiently linear in gulf locations or in nearby open Pacific Geochemical Ocean Sections Study (GEOSECS) stations to be useful in solving paleotemperature equations. Of the most common benthic foraminifera, only Planulina ariminensis has δ¹³C that is consistent with the measured δ¹³C of ΣCO₂. Several cores in the depth range 500 to 900 m have the laminated Holocene and Bolling/Allerod sediments, and the nonlaminated glacial age and Younger Dryas sediments that are typical of the gulf and other locations such as Santa Barbara Basin. The best of those, Jumbo Piston Core (JPC) 56 from 818 m water depth on the western margin of Guaymas Basin, was sampled for intensive study. Oxygen isotope ratios in benthic and planktonic foraminifera show little evidence for deglacial temperature oscillations. Carbon isotope ratios are generally lower during warm epochs, but the most striking result is strongly lowered benthic and planktonic δ¹³C about 9500 years ago. This may reflect water column oxidation of locally released methane. Neither benthic δ¹³C in depth section nor paired benthic and planktonic ¹⁴C data in JPC56 are consistent with increased intermediate water ventilation during the glacial maximum and Younger Dryas. Likewise, ¹⁴C data from 5 pairs of foraminifera from the Okhotsk Sea fail to support better ventilation in that basin during the last glacial maximum. This revised version was published online in August 2006 with corrections to the Cover Date.     

The cycling and oxidation pathways of organic carbon in a shallow estuary along the Texas Gulf Coast

The cycling and oxidation pathways of organic carbon were investigated at a single shallow water estuarine site in Trinity Bay, Texas, the uppermost lobe of Galveston Bay, during November 2000. Radio-isotopes were used to estimate sediment mixing and accumulation rates, and benthic chamber and pore water measurements were used to determine sediment-water exchange fluxes of oxygen, nutrients and metals, and infer carbon oxidation rates. Using ⁷Be and ²³⁴Th_XS, the sediment-mixing coefficient (D_b) was 4.3 ± 1.8 cm² y⁻¹, a value that lies at the lower limit for marine environments, indicating that mixing was not important in these sediments at this time. Sediment accumulation rates (S_a), estimated using ¹³⁷Cs and ²¹⁰Pb_XS, were 0.16 ± 0.02 g cm⁻² y⁻¹. The supply rate of organic carbon to the sediment-water interface was 30 ± 3.9 mmol C m⁻² d⁻¹, of which ∼10% or 2.9 ± 0.44 mmol C m⁻² d⁻¹was lost from the system through burial below the 1-cm thick surface mixed layer. Measured fluxes of O₂ were 26 ± 3.8 mmol m⁻² d⁻¹ and equated to a carbon oxidation rate of 20 ± 3.3 mmol C m⁻² d⁻¹, which is an upper limit due to the potential for oxidation of additional reduced species. Using organic carbon gradients in the surface mixed layer, carbon oxidation was estimated at 2.6 ± 1.1 mmol C m⁻² d⁻¹. Independent estimates made using pore water concentration gradients of ammonium and C:N stoichiometry, equaled 2.8 ± 0.46 mmol C m⁻² d⁻¹. The flux of DOC out of the sediments (DOC_efflux) was 5.6 ± 1.3 mmol C m⁻² d⁻¹. In general, while mass balance was achieved indicating the sediments were at steady state during this time, changes in environmental conditions within the bay and the surrounding area, mean this conclusion might not always hold. These results show that the majority of carbon oxidation occurred at the sediment-water interface, via O₂ reduction. This likely results from the high frequency of sediment resuspension events combined with the shallow sediment mixing zone, leaving anaerobic oxidants responsible for only ∼10–15% of the carbon oxidized in these sediments.     

The Gulf of California: Review of ecosystem status and sustainability challenges

The Gulf of California is unique because of its geographical location and conformation. It hosts diverse ecosystems and important fisheries that support industry and provide livelihood to coastal settlements. It is also the site of interests and problems, and an intense interaction among managers, producers, and conservationists. In this report, we scrutinize the abiotic (hydrography, climate, ocean circulation, and chemistry) and biotic (phyto- and zooplankton, fish, invertebrates, marine mammals, birds, and turtles) components of the marine ecosystem, and some particular aspects of climate variability, endemisms, harmful algal blooms, oxygen minimum layer, and pollution. We also review the current conditions and conflicts around the main fisheries (shrimp, small and large pelagic fishes, squid, artisanal and sportfishing), the most important human activity in the Gulf of California. We cover some aspects of management and conservation of fisheries, especially the claimed overexploitation of fish resources and the ecosystems, and review proposals for creating networks of marine protected areas. We conclude by identifying main needs for information and research, particularly the integration of data bases, the implementation of models and paleoreconstructions, establishment of monitoring programs, and the evaluation of fishing impacts and management actions.     

The Tamayo transform fault in the mouth of the Gulf of California

The Tamayo transform fault is located at the north end of the East Pacific Rise where it enters the Gulf of California. This paper presents bathymetric, seismic reflection, magnetic, and gravity data from a detailed survey of the transform fault. The dominant feature of the offset region is a bathymetric ridge trending 120°, parallel to the predicted transform plate boundary. This transform ridge is associated with a large (600 ) positive magnetic anomaly, and a very small positive free-air gravity anomaly. Magnetic and gravity models indicate either a basalt or serpentinite composition for the ridge, but cannot distinguish between these possibilities. At its eastern end, the modern zone of strike-slip motion is in a narrow valley south of the transform ridge. The transform plate margin appears to pass through a saddle in the transform ridge and meet the western spreading center segment in the trough north of the transform ridge. On the basis of this survey and previous work, the history of the Tamayo from continental breakup to the present has been reconstructed. Initial rifting occurred along a trend of 130° at approximately 3.5 m.y.b.p. Once the transform fault was free of the constraints imposed by continent-continent and continent-oceanic lithospheric interaction, the trend of the transform fault rotated counter-clockwise. This rotation resulted in a leaky transform fault and intrusion of a large continuous transform ridge. Further adjustments in the spreading center/transform fault plate boundary configuration have given rise to an incipient zone of rifting cutting across the transform ridge and emplacement of diapiric structures.Contribution of the Scripps Institution of Oceanography, new series.     

Governance and effects of marine reserves in the Gulf of California,Mexico

We trace the evolution, governance, and effects of three marine reserve (no-take zones) initiatives in the Gulf of California, Mexico: Loreto Bay National Park, Puerto Peñasco, and San Pedro Mártir Island Biosphere Reserve. Preliminary monitoring results, although highly variable, are encouraging for conservation and fisheries management. However, open access situations and differing conceptions among local stakeholders and government concerning access rights to fishing grounds, coupled with limited support for surveillance and lags between local and government institutional arrangements and interests, are the main constraints for the success of these and future reserves in the region. We discuss the main social–ecological feedbacks at play and the implications of our findings within a regional context.     

Thermohaline variability and geostrophic circulation in the southern portion of the Gulf of California

Data from seven oceanographic cruises in the southern Gulf of California from 1997 to 2002 are used to describe the thermohaline variability and the geostrophic circulation. Baroclinic patterns exhibited spatial and temporal variability. A deepening of isotherms at the center of the section was evident in February 1999, suggesting anticyclonic flow. In May 1998 and November 1997, cyclonic flow was suggested by shoaling of isotherms at the center of the section. Other cruises showed alternating cores of flow into and out of the Gulf (August 1998, September 1997 and October 2002). Neither a seasonal nor a spatial pattern in geostrophic flows was apparent, suggesting that the exchange of waters between the cyclonic flow of Pescadero basin and the interior of the Gulf is complex. Relatively high salinities were recorded during most of the cruises indicating that Gulf of California Water (GCW) was present most of the year. Higher salinities were observed during winter and spring, although during summer, relatively high and low salinities were both observed as surface and subsurface cores. Temperature and salinity characteristics of California Current waters were observed only in August 1995 when they reached as far north as Cerralvo Island at ∼50 dbar. During El Niño conditions in November 1997, a mixed layer (∼70 dbar) and deepening of the thermocline (∼50 dbar) characterized anomalous conditions; during this cruise an asymmetric salinity pattern was observed with low salinities characteristic of Tropical Surface waters at the center and east of the section, while maximum salinities (34.9<S<35.0) and Gulf waters were located in an 80 km wide core next to the Baja California Sur shelf as far north as San Jose Island.     

Subsidies in the jumbo squid fishery in the Gulf of California,Mexico

This paper investigates the effects of fuel subsidies and value added tax refunds on the operation of two types of firms associated with the jumbo squid (Dosidicus gigas) fishery in Mexico: (a) firms with ships that catch shrimp and squid in different periods of the year and (b) firms that deploy outboard-motor boats to catch squid year-round. The cost-benefit ratios of the policies are analyzed for 2008–2015, both with and without subsidy-related income. Additionally, the net cash surplus is calculated. The elimination of subsidies may affect jobs related to vessel operations in the squid fishery and may also encourage the voluntary retirement of shrimp ships. This effect is less evident in the case of the smaller boats. Strategies aimed at improving the landed squid prices are nonetheless suggested.     

Coastal residents' literacy about seawater desalination and its impacts on marine ecosystems in California

This article examines coastal residents' awareness and knowledge about impacts of seawater desalination on marine ecosystems Carlsbad, California. The paper explores to what extent sociodemographics, motivational factors, and information use shape public awareness and self-assessed and factual knowledge. Data was collected using a mail survey (n=330) from a random sample of residents in Carlsbad. Both self-assessed and factual knowledge about the desalination plant and its impacts on marine ecosystem were low, with only two of 11 factual questions answered correctly by more than 50% of respondents. Gender, frequency of ocean use, and use of distinct information sources correlated positively with greater factual knowledge. Education, age, time of residency in local community, membership in an NGO, and place attachment to marine areas did not increase factual knowledge. Findings also demonstrate that knowledge shaped attitudes towards the seawater desalination plant as greater knowledge about marine impacts reduced support.     

Simulation of tides,residual flow and energy budget in the Gulf of California

With the application of a two-dimensional nonlinear hydrodynamical-numerical semi-implicit model, the principal tides M₂, S₂, K₂, N₂, K₁, P₁ and O₁ were studied. Energy budgets of the semi-diurnal M₂ and S₂ were calculated separately. The linear sum of these budgets was compared with the tidal energy budget obtained when these two tidal constituents interact. Since a quadratic form for the bottom friction was used, remarkable differences were found. The results show that in the area of the Colorado River delta, the dissipation of tidal energy is very strong. Intense tidal currents were observed in the same region and over the Salsipuedes Sill. Energy budgets calculated for forcing waves of different periods, but of the same amplitude, were used to estimate the principal periods of resonance. Although the topography of the Gulf is very complex, the model reproduced observed sea-surface elevation and current patterns. To study spring tide conditions, the above seven tidal constituents were simulated. Estimates of residual currents reveal the presence of several intense cyclonic and anticyclonic gyres. Over the Salsipuedes Sill, residual currents of the M₂ tide reach values of more than 15 cm s⁻¹. Horizontal distributions of dissipation rates of tidal energy and of kinetic energy were also obtained.     

Seasonal and annual variability in particle fluxes in the Gulf of California: A response to climate forcing

A six-year time series of sediment trap samples is used to document seasonal and interannual changes in particle fluxes in Guaymas Basin, Gulf of California. Sedimentation in this region of the Gulf of California is dominated by two seasonally varying components: biogenic silica during the late fall–spring and lithogenic material during the summer. This variability in sediment fluxes is a direct response to the seasonally reversing monsoon climate in this region. In addition, this seasonal variability in particle flux to the seafloor combined with the lack of bioturbation results in the formation of sediment laminae or varves in Guaymas Basin. Observed interannual differences in the magnitude of sediment fluxes appear to be related to ENSO. These findings indicate that biogenic sediment fluxes, and hence primary productivity, are higher during non-ENSO years in the central Gulf of California. A decrease in the carbonate: opal flux ratio from 1991 to 1996 indicates that diatoms became an increasingly important component of the plankton during this period and further supports our findings that productivity in Guaymas Basin is higher during non-ENSO years.     

Segmentation and disruption of the East Pacific Rise in the mouth of the Gulf of California

Analysis of new multibeam bathymetry and all available magnetic data shows that the 340 km-long crest of the East Pacific Rise between Rivera and Tamayo transforms contains segments of both the Pacific-Rivera and the Pacific-North America plate boundaries. Another Pacific-North America spreading segment (Alarcon Rise) extends 60 km further north to the Mexican continental margin. The Pacific-North America-Rivera triple junction is now of the RRR type, located on the risecrest 60 km south of Tamayo transform. Slow North America-Rivera rifting has ruptured the young lithosphere accreted to the east flank of the rise, and extends across the adjacent turbidite plain to the vicinity of the North America-Rivera Euler pole, which is located on the plate boundary. The present absolute motion of the Rivera microplate is an anticlockwise spin at 4° m.y.^–1 around a pole located near its southeast corner; its motion has recently changed as the driving forces applied to its margins have changed, especially with the evolution of the southern margin from a broad shear zone between Rivera and Mathematician microplates to a long Pacific-Rivera transform. Pleistocene rotations in spreading direction, by as much as 15° on the Pacific-Rivera boundary, have segmented the East Pacific Rise into a staircase of en echelon spreading axes, which overlap at lengthening and migrating nontransform offsets. The spreading segments vary greatly in risecrest geomorphology, including the full range of structural types found on other rises with intermediate spreading rates: axial rift valleys, split shield volcanoes, and axial ridges. Most offsets between the segments have migrated southward, but within the past 1 m.y. the largest of them (with 14–27 km of lateral displacement) have shown dueling behavior, with short-lived reversals in migration direction. Migration involves propagation of a spreading axis into abyssal hill terrain, which is deformed and uplifted while it occupies the broad shear zones between overlapping spreading axes. Tectonic rotation of the deformed crust occurs by bookshelf faulting, which generates teleseismically recorded strike-slip earthquakes. When reversals of migration direction occur, plateaus of rotated crust are shed onto the rise flanks.