Carlos Neira

MECHANISMS GENERATING MODIFICATION OF BENTHOS FOLLOWING TIDAL FLAT INVASION BY A SPARTINA HYBRID

Many coastal habitats are being substantially altered by introduced plants. In San Francisco Bay, California, USA, a hybrid form of the eastern cordgrass Spartina alterniflora is rapidly invading open mudflats in southern and central sections of the Bay, altering habitat, reducing macrofaunal densities, and shifting species composition. The invasion has resulted in significant losses of surface-feeding amphipods, bivalves, and cirratulid polychaetes, while subsurface feeding groups such as tubificid oligochaetes and capitellid polychaetes have been unaffected. In the present paper, we document the causes and mechanisms underlying the changes observed. Through a series of in situ manipulative experiments we examined the influence of hybrid Spartina canopy on a range of physical, chemical, and biological properties. The hybrid Spartina canopy exerted a strong influence on the hydrodynamic regime, triggering a series of physical, chemical, and biological changes in the benthic system. Relative to tidal flats, water velocity was reduced in hybrid patches, promoting deposition of fine-grained, organic-rich particles. The resulting changes in the sediment environment included increased porewater sulfide concentrations and anoxia, which led to poor survivorship of surface feeders such as bivalves, amphipods, and polychaetes. These are key taxa that support higher trophic levels including migratory shorebirds that feed on tidal flats. Altered flow in the Spartina canopy further contributed to changes in barnacle recruitment and resuspension of adult benthic invertebrates. Increased crab-induced predation pressure associated with Spartina invasion also contributed to changes in benthic invertebrate communities. Our results suggest that multiple physical, chemical, biotic, and trophic impacts of the Spartina invasion have resulted in substantial changes in benthic communities that are likely to have important effects on the entire ecosystem.

Meiofauna and sedimentary organic matter off Central Chile: response to changes caused by the 1997–1998 El Niño

Quantitative surveys of metazoan meiofauna were carried out in an upwelling region off Central Chile (36oS). During May 1997 and May 1998, coinciding with the onset and end of El Nino, five benthic stations (respectively 27, 34, 64, 88, and 120 m depth), from the middle of Concepcion Bay to the edge of the adjacent continental shelf, were sampled. The sedimentary organic matter biopolymeric fraction (proteins, carbohydrates and lipids) and chloroplastic pigments were also assessed. Total meiofauna abundance and biomass increased significantly between sampling dates at the mid-bay and inner shelf sites, from 1474 ± 354 to 5035 ± 291 individuals 10 cm–2 and from 2618 ± 332 to 5241 ± 903 individuals 10 cm–2, respectively. The relative importance of copepods in the top 2 cm increased at all sites (except in the bay mouth). During May 1998, meiofauna, especially nematodes, penetrated deeper in the bay, as well as in the inner and middle shelf sediments. Changes observed in meiobenthos structure among sites and periods were attributed to the higher oxygenation of bottom waters during the summer of 1998 (i.e. El Nino conditions). This was most evident at sites such as the mid bay, where during non-El Nino years, oxygen-deficient conditions prevail. A decrease of organic matter quantity and quality, related to low primary productivity conditions in 1998 (El Nino), apparently caused few changes in meiofauna structure. A positive correlation between Thioploca and the meiofauna biomass was observed in May 1997, whereas in May 1998 no relationship was found.

Spatial distribution of copper in relation to recreational boating in a California shallow-water basin

The overall effect of the number of boats on the copper (Cu) levels in the water column and sediment, along with their spatial variability within Shelter Island Yacht Basin (SIYB), San Diego Bay, California was examined. We identified a horizontal gradient of increasing dissolved Cu and Cu in sediment from outside to the head of SIYB which was coincident with the increasing number of boats. Spatial models of Cu distribution in water and sediment indicated the presence of ‘hotspots’ of Cu concentration. From outside to the head of SIYB, dissolved Cu ranged from 1.3 μ g L−1 to 14.6 μ g L−1 in surface water, and 2.0 μ g L−1 to 10.2 μ g L−1 in bottom water. Cu in sediment exceeded the Effect Range Low of 34 mg kg−1 (i.e. where adverse effects to fauna may occur), with a peak concentration of 442 mg kg−1 at the head of the basin. Free Cu++ in surface water was several orders of magnitude higher than in sediment porewater. High-resolution data of Cu species together with probability maps presented in this paper will allow managers to easily visualise and localise areas of impaired quality and to prioritise which areas should be targeted to improve Cu-related conditions.

Comments on and implications of a steady-state in coastal marine ecosystems

Coastal ecosystems can be thought of as being established by a number of physico-geochemical drivers, e.g. geochemistry and bathymetry of the basins, climate, tidal and freshwater flows, natural and anthropogenic inputs of nutrients and toxins, all of which exert an influence on the resulting communities of organisms. Depending on the interactions among the major drivers, ecosystems may occur on both large and small scales and be basin-wide or within basins. For individual and separate ecosystems to exist with some permanence in time, e.g. reach a steady-state, they also have to be ‘defended’. Defences are mechanisms that counter changes to maintain the status quo. We argue, and present evidence to support the notion, that the defence mechanisms are inextricably tied to primary production and the biogeochemical cycling of organic matter and provide buffers that mitigate potentially adverse impacts by trace toxins. Colloid pumping, production of complexing ligands and sulfide formation are some of the mechanisms that control trace substances. Current methods for assessing ecosystems do not address the issue of steady-state, nor do they take account of defence activities, e.g. buffering. Therefore, they cannot assess the ‘robustness’ of ecosystems or their ability to resist change, for good or bad. Also, defence mechanisms may, for a time, mask future potentially serious impacts, suggesting that monitoring efforts with limited budgets should consider the measurement of the inputs into ecosystems as well as the immediate or short-term result of the inputs.

Nitrogen sediment fluxes in an upwelling system off central Chile (Concepción Bay and adjacent shelf) during the 1997-1998 El Niño

Se analizaron los flujos de compuestos nitrogenados desde los sedimentos en dos areas representativas de condiciones costeras y de plataforma (Bahia Concepcion y plataforma adyacente, respectivamente). Durante el periodo de muestreo las aguas de fondo presentaron un anomalamente alto contenido de oxigeno disuelto, coincidente con el evento El Nino 1997-1998. De ambos sitios, se incubaron testigos de sedimento intactos para determinar los flujos totales de NH4+. Ademas se determino la concentracion de NH4+, NO3- y NO2- en el agua intersticial para estimar los flujos difusivos de compuestos nitrogenados en la interfase agua-sedimento. Los flujos de NH4+ totales variaron entre 0,55 y 2,18 mmol m-2 dia-1 al interior de la bahia y entre 1,84 a 2,14 mmol m-2 dia-1 en la plataforma. Se observaron flujos difusivos de NO3- en direccion a los sedimentos al interior de la bahia en Marzo de 1998 (-17 x 10-2 mmol m-2 dia-1) y en la plataforma en Noviembre de 1997 (-2,7 x 10-2 mmol m-2 dia-1) asociados a los flujos difusivos de NH4+ mas bajos, coincidiendo esto con la mayor gradiente de Eh en los sedimentos superficiales. Ademas, los bajos flujos de NH4+ medidos en comparacion con mediciones previas, sugieren la influencia de un ambiente menos reductor, generado a su vez por la disminucion del flujo de material organico particulado y por el aumento de las concentraciones de oxigeno disuelto en las aguas del fondo. Estas condiciones fueron generadas probablemente por el evento El Nino. Tambien, con relacion a reportes previos se registro un incremento en los coeficientes de irrigacion (DI). Todo esto sugiere que durante este periodo los flujos de otros compuestos nitrogenados podrian haber adquirido relevancia con relacion a los flujos de NH4+

Differences in meiofauna communities with sediment depth are greater than habitat effects on the New Zealand continental margin: implications for vulnerability to anthropogenic disturbance

Studies of deep-sea benthic communities have largely focused on particular (macro) habitats in isolation, with few studies considering multiple habitats simultaneously in a comparable manner. Compared to mega-epifauna and macrofauna, much less is known about habitat-related variation in meiofaunal community attributes (abundance, diversity and community structure). Here, we investigated meiofaunal community attributes in slope, canyon, seamount, and seep habitats in two regions on the continental slope of New Zealand (Hikurangi Margin and Bay of Plenty) at four water depths (700, 1,000, 1,200 and 1,500 m). We found that patterns were not the same for each community attribute. Significant differences in abundance were consistent across regions, habitats, water and sediment depths, while diversity and community structure only differed between sediment depths. Abundance was higher in canyon and seep habitats compared with other habitats, while between sediment layer, abundance and diversity were higher at the sediment surface. Our findings suggest that meiofaunal community attributes are affected by environmental factors that operate on micro- (cm) to meso- (0.1–10 km), and regional scales (> 100 km). We also found a weak, but significant, correlation between trawling intensity and surface sediment diversity. Overall, our results indicate that variability in meiofaunal communities was greater at small scale than at habitat or regional scale. These findings provide new insights into the factors controlling meiofauna in these deep-sea habitats and their potential vulnerability to anthropogenic activities.

Salinity and its variability in the Lagoon of Venice, 2000–2009

Yearly averages computed from monthly and bimonthly salinity data collected between 2000 and 2009 from 13 broadly spaced stations in the Venice Lagoon were analysed in view of 30 min data collected semi-continuously during 2009 at nine similarly located stations. Data from all stations and all years indicate that, based on yearly averages, the lagoon may be divided along its major (long) axis into three areas: 1) a northern, freshwater impacted area (S = 32 PSU of low, tidally-caused, variability, and 3) an intermediate zone. Salinity changes are closely associated with rainfall events, and the incoming freshwater is consistently distributed throughout the lagoon by tidal action. Much variability is simply a result of the forward and backward motion of the tides and is not caused by a salinity change in the water itself. The consistency of the 2000–2009 data and the historical (to 1961) watershed record support the hypothesis that the Venice Lagoon has been and is currently at steady-state with respect to its salinity distribution. As such, it is conducive to the development of (at least) three separate ecosystems.

Polychlorinated biphenyls (PCBs) in recreational marina sediments of San Diego Bay, southern California

Polychlorinated biphenyl (PCB) concentrations were determined in surface sediments from three recreational marinas in San Diego Bay, California. Total PCB concentrations ranged from 23 to 153, 31-294, and 151-1387ngg-1 for Shelter Island Yacht Basin (SIYB), Harbor Island West (HW) and Harbor Island East (HE), respectively. PCB concentrations were significantly higher in HE and PCB group composition differed relative to HW and SIYB, which were not significantly different from each other in concentration or group composition. In marina sediments there was a predominance (82-85%) of heavier molecular weight PCBs with homologous groups (6CL-7CL) comprising 59% of the total. In HE 75% of the sites exceeded the effect range median (ERM), and toxicity equivalence (TEQ dioxin-like PCBs) values were higher relative to those of HW and SIYB, suggesting a potential ecotoxicological risk.

Scientific Considerations for the Assessment and Management of Mine Tailings Disposal in the Deep Sea

Deep-sea tailing disposal (DSTD) and its shallow water counterpart, submarine tailings disposal (STD), are practiced in many areas of the world, whereby mining industries discharge processed mud- and rock waste slurries (tailings) directly into the marine environment. Pipeline discharges and other land-based sources of marine pollution fall beyond the regulatory scope of the London Convention and the London Protocols (LC/LP). However, guidelines have been developed (Papua New Guinea) to improve tailing waste management frameworks in which mining companies can operate. DSTD can impact ocean ecosystems in addition to other sources of stress, such as from fishing, pollution, energy extraction, tourism, eutrophication, climate change and, potentially in the future, from deep-seabed mining. Environmental management of DSTD may be most effective when placed in a broader context, drawing expertise, data and lessons from multiple sectors (academia, government, society, industry and regulators) and engaging with international deep-ocean observing programs, databases and stewardship consortia. Here, the challenges associated with DSTD are identified, along with possible solutions, based on the results of a number of robust scientific studies. Also highlighted are the key issues, trends of improved practice and techniques that could be used if considering DSTD, such as increased precaution if considering submarine canyon locations and likely cumulative impacts and research needed to address current knowledge gaps.