Mussel reefs on soft sediments: a severely reduced but important habitat for macroinvertebrates and fishes in New Zealand

Green-lipped mussels (Perna canaliculus) formed extensive reefs on soft sediments in sheltered embayments around northern New Zealand until overfishing and/or increased sediment input caused their virtual disappearance by 1980. To determine the role of mussel reefs as habitat for other animals, we located remnant soft-sediment reefs in five locations and compared the density, biomass, productivity and composition of mobile macroinvertebrate communities, and the density of small fishes associated with mussels, with fauna in the surrounding soft sediments. The mussel reefs had a distinct assemblage of macroinvertebrates, which had 3.5 times the density, 3.4 times the biomass and 3.5 times the productivity of surrounding areas. The density of small fishes was 13.7 times higher than in surrounding areas. These results show that soft-sediment mussel reefs support an abundant and productive fauna, highlighting the probable large loss of productivity associated with the historical decline in mussel habitat and the consequent desirability of restoration efforts.     

Development of passive sampling devices for bioavailable contaminants of current and emerging concern: Waitemata Harbour case study

Bioavailable contaminant concentrations are an important component in assessing environmental effects as they directly affect ecosystem health. Shellfish contaminant monitoring programmes have traditionally filled this requirement but are being phased out in some jurisdictions. Passive sampling devices (PSDs) have the potential to replace shellfish monitoring; however, there are still knowledge gaps to address before this can occur. This study assessed the suitability of three different PSDs in providing the required information to replace shellfish monitoring. PSDs were deployed at three historic mussel monitoring sites with different levels of urban influence in the Waitemata Harbour, Auckland, New Zealand. Contaminants of interest were urban heavy metals, plus current and emerging organic contaminants. PSDs provided extremely low detection limits and, for some contaminants, very strong correlations to shellfish. PSDs can currently complement shellfish in monitoring, but it is premature to make conclusions as to the suitability of PSDs in replacing shellfish monitoring until more information is available.     

Numerical simulation of larval shrimp dispersion in the Northern Region of the Gulf of California

The trajectories of shrimp larvae in the northern part of the Gulf of California were studied from a Lagrangian point of view using a three-dimensional numerical model. The advection of particles was carried out over fortnightly periods starting at spring and neap tides. The northernmost region of the gulf has important shrimp fisheries and nursery areas have been located off the coast of Baja California at San Felipe (SF) and off the Sonora coast at Santa Clara (SC). Though the reproduction zone is believed to be south of these nursery areas, there is much that remains unknown about the zone and the routes used by shrimps to reach these areas. Passive and active simulations of shrimp larvae drift were carried out in order to study the possible areas of shrimp spawning and their migratory routes. The active migration schemes were based on assumptions that the larvae can be advected only: (1) during the day, (2) at night or (3) when the currents flow in the northward direction toward the nursery areas. It was found that the larvae in Santa Clara and San Felipe came from different production zones. No differences were found between the spring and neap tide scenarios except for the diurnal migration experiments. The distance traveled by shrimp larvae was always less than 40–50 km, except in the cases when the larvae selected the appropriate direction to the nursery areas when the larvae travel 140 km to SC and 95 km to SF.     

Zooplankton succession during extraordinary drought–flood cycles: A case study in a South American floodplain lake

We examined the zooplankton abundance and composition of Laguna Grande, a floodplain wetland of the Lower Paraná Basin (Argentina), during an extraordinary drought–flood cycle that affected both the environment and the biological conditions of the lake. Low waters were characterised by remarkably high conductivities and pH values, and high phytoplankton and bacterioplankton abundances with cyanobacterial blooms, while high waters showed opposite features. In relation to zooplankton, the mean abundances of all the taxonomic groups (rotifers, cladocerans, copepods, ciliates, and heterotrophic nanoflagellates) were slightly higher at low waters. Major changes were observed in the specific composition of metazooplankton: the euryhaline species assemblage that dominated in the dry warm period was replaced by several oligohaline littoral and planktonic species characteristic of the Paraná River Basin, when the water level rose. Mean species richness values at high waters doubled those of low waters and were directly correlated to water depth. Most of the rotifers of the genus Brachionus and the cladoceran Moina micrura switched from parthenogenetic to sexual reproduction during low waters, as a response to a harsh environment and crowding. We suggest that the main changes in the environmental conditions in this eutrophic floodplain lake are driven by the hydrology, which regulates the zooplankton succession. The herein described shifts in the zooplankton structure and dynamics of Laguna Grande over an extraordinary drought–flood cycle contribute to the understanding of the processes that might occur under the scenarios predicted by climate change models.     

Larval fish assemblages,environment and circulation in a semienclosed sea (Gulf of California,Mexico)

Fish larvae and hydrographic data collected in the Gulf of California (GC) in December 2002 are used to describe larval fish assemblages (LFAs) and to explore their relationships with environmental variables (temperature, salinity, dissolved oxygen, fluorescence maximum, ?$?$ and superficial chlorophyll a). The Bray–Curtis dissimilarity index defined three LFAs, distributed in areas with distinctly different environmental conditions. The affinity of most of the species with the environmental characteristics of their areas of distribution could be interpreted as an indication that spawning occurred inside those areas. Particle tracking in current fields from a 3D numerical model and connectivity matrices are used to assess larval retention in the LFA areas. The technique is well suited for seas like the GC that have well-defined circulation patterns. On time scales around 30 days, retention (from 56% to 73% of the particles) occurred (1) for the North LFA in the Upper GC, (2) for the Channel-Center LFA in the anticyclone over the Northern GC and in Ballenas Channel, and (3) for the South LFA in the eddy over San Pedro Mártir basin and in the shallow zone off the peninsula. Therefore, the Lagrangian analysis revealed that the observed LFAs have a permanency long enough to allow fish larvae to remain in a favorable environment until they develop motility. The main particle export path (less than 26% of the particles) was from the North to the South LFA, following the anticyclonic main flow and coinciding with the gradient in species number and larval abundance.     

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.     

On the role of the unresolved eddies in a model of the residual currents in the central strait of Georgia,B.C.: Research Note

Abstract

A depth‐independent numerical model of the Juan de Fuca/Strait of Georgia system reproduces the broad structure of the observed depth‐averaged residual circulation in the Central Strait of Georgia but underestimates its magnitude (Marinone and Fyfe, 1992). Here we present some new calculations based on a re‐parameterization of the unresolved eddies in terms of “statistical dynamical tendencies” instead of the previous eddy‐viscosity treatment. With the new parameterization, the simulated time‐mean flow is closer to the observed circulation both in structure and magnitude. While not specifically designed to do so, the new parameterization also leads to a modest improvement in the low‐pass filtered component of the flow. Based on these results, the depth‐averaged residual currents in the region are conjectured to involve a four‐way balance between the hitherto ignored effect of “statistical dynamical tendencies” and conventional tidal, atmospheric and buoyancy forcing.     

新疆东天山图拉尔根大型铜镍矿床硫化物珠滴构造的特征及其对通道式成矿的指示

东天山图拉尔根岩浆铜镍硫化物矿床中产出一种不常见的硫化物珠滴状构造。这些硫化物珠滴粒度在5~20mm左右,是由磁黄铁矿、镍黄铁矿、黄铜矿等硫化物矿物组成的斑杂状硫化物集合体。野外观察发现硫化物珠滴具有各种几何形态,产出在稀疏浸染状硫化物和无矿化的辉石岩之间的部位。对图拉尔根杂岩体中发育的24个硫化物珠滴的统计结果显示,平缓厚层状矿化部位的硫化物珠滴呈水平方向拉长,陡倾薄层状矿化部位的硫化物珠滴呈陡倾拉长,珠滴的拉长方向和矿体的延伸方向一致。这表明在含矿母岩浆上升就位到中上地壳的过程中,硫化物珠滴受到熔浆流动的控制,因而其形态可以很好地指示通道式成矿硫化物熔体运动的方向。 硫化物珠滴的矿相学和电子探针数据表明其具有向地性特征,即磁黄铁矿和镍黄铁矿先结晶,沉淀在下部; 珠滴上部为后结晶的黄铜矿和其它富铜硫化物。这种元素分布可能对贯入块状硫化物矿石同样适用。碲化物和铋化物在硫化物珠滴中的含量明显高于其在早结晶的浸染状硫化物中的含量,表明富Te和Bi等元素及挥发份的熔体是在岩浆演化后期开始富集结晶的。     

Seasonal changes in larval fish assemblages in a semi-enclosed sea (Gulf of California)

The northern Gulf of California (NGC) is characterized by seasonal hydrography and circulation (cyclonic in summer and anticyclonic in winter), by intense tidal mixing in the midriff archipelago region (MAR), and by coastal upwelling on the eastern side from autumn to spring. We examined changes in larval fish assemblages (LFAs) in relation with hydrography and circulation during both phases of the seasonal circulation, as indicators of changes in the pelagic ecosystem. A canonical correspondence analysis defined LFAs (r>0.70), which were related with: (i) the coastal current on the mainland shelf, (ii) the central eddy and (iii) the MAR. In the early cyclonic phase, when the temperature and stratification were increasing and the coastal current was starting, demersal (Gobulus crescentalis, Lythrypnus dalli) and mesopelagic species (Benthosema panamense) dominated the NGC. The highest larval abundance was in the Current LFA area and the lowest in the MAR LFA area. In the mature cyclonic phase, the larval abundance increased in the NGC and species characteristic of eastern boundary current systems such as Opisthonema libertate and Engraulis mordax displaced the demersal species and became dominant, together with B. panamense in the Current LFA area; the latter species dominated in the Eddy LFA area. In the early anticyclonic phase, the direction of the coastal current reversed and the temperature and larval abundance decreased. E. mordax and B. panamense larvae continued dominating the NGC with higher abundance in the MAR than in the Current and Eddy LFA areas. In the mature anticyclonic phase, E. mordax larvae dominated in the Current and the Eddy LFA areas with the highest abundance in the former, while M. productus larvae (an eastern boundary current species) dominated in the Eddy LFA area. Results showed that in the NGC, the dramatically seasonal and predictable hydrographic and circulation features trigger the seasonal spawning of the dominant species. The biological richness of the coastal current area, in both circulation phases, suggested that this area has an important role in the pelagic ecosystem functionality of the NGC.     

Pigmente phototropher Bakterien in Seesedimenten und ihre Bedeutung für die Seenforschung

Sediments of shallow lakes contain besides plankton pigments as well pigments of purple non-sulfur and purple sulfur bacteria. A thin-layer chromatographic method was developed for the separation of the most important pigments of purple bacteria beside plankton pigments. The new method was examined in three different lakes for a stratigraphic analysis of bacteria pigments beside plankton pigments and the results were discussed subsequently.