The influence of seasonal salinity and turbidity maximum variations on the nursery function of the Loire estuary (France)

In the Loire estuary which is a macrotidal estuary, the river flow and tides induce large seasonal variations in salinity gradients and in location and density of the turbidity maximum. These characteristics influence colonization patterns developed by juveniles of euryhaline fish populations (structure, distribution, density) and the dynamics of benthic communities which constitute their food resources. In some hydrological conditions, the upstream limit of the nursery function may be controlled by the turbidity maximum which induces anoxic conditions: reduction in densities or mass mortalities may be observed.     

FISH CONSERVATION IN SOUTH AFRICAN ESTUARIES: PRESSURES,PROBLEMS AND PROSPECTS

Summary

A review of the conservation status of fish in the estuarine environment around the South African coastline reveals that some species face serious problems associated either with habitat destruction, and its associated biological, physical and chemical components or exploitation. The 65 species considered fall into three categories; truly estuarine species, which are dependent on estuaries for their entire life; marine species dependent on estuaries during the juvenile phase of their life cycle; and marine species whose juveniles occur mainly in estuaries but are also found at sea. Included in the first two categories are 14 species of fish which are on the South African Red Data list. These comprise one species which is endangered, five which are vulnerable and eight which are rare. All groups are considered in relation to factors in estuaries which are affecting their populations. A conservation strategy is suggested for certain estuarine types or for specific estuaries which could ensure the survival of the entire range of estuarine faunas.     

Turbellaria from intertidal flats and salt-marshes in the estuaries of the south-western part of the Netherlands

A list of 91 species of Turbellaria from intertidal flats and saltmarshes in the estuaries of the south-western part of the Netherlands is given.     

Variation in fish density,assemblage composition and relative rates of predation among mangrove,seagrass and coral reef habitats

We tested the hypothesis for several Caribbean reef fish species that there is no difference in nursery function among mangrove, seagrass and shallow reef habitat as measured by: (a) patterns of juvenile and adult density, (b) assemblage composition, and (c) relative predation rates. Results indicated that although some mangrove and seagrass sites showed characteristics of nursery habitats, this pattern was weak. While almost half of our mangrove and seagrass sites appeared to hold higher proportions of juvenile fish (all species pooled) than did reef sites, this pattern was significant in only two cases. In addition, only four of the six most abundant and commercially important species (Haemulon flavolineatum, Haemulon sciurus, Lutjanus apodus, Lutjanus mahogoni, Scarus iserti, and Sparisoma aurofrenatum) showed patterns of higher proportions of juvenile fish in mangrove and/or seagrass habitat(s) relative to coral reefs, and were limited to four of nine sites. Faunal similarity between reef and either mangrove or seagrass habitats was low, suggesting little, if any exchange between them. Finally, although relative risk of predation was lower in mangrove/seagrass than in reef habitats, variance in rates was substantial suggesting that not all mangrove/seagrass habitats function equivalently. Specifically, relative risk varied between morning and afternoon, and between sites of similar habitat, yet varied little, in some cases, between habitats (mangrove/seagrass vs. coral reefs). Consequently, our results caution against generalizations that all mangrove and seagrass habitats have nursery function.     

番橄榄实生育苗技术初探

对番橄榄实生育苗技术进行初步研究。结果表明,番橄榄育苗不宜使用果实直接播种,应采用成熟种子进行容器袋育苗,这样既有利于提高种子发芽率,又可避免移栽时苗木受损伤;遮荫度30%、空气相对湿度80%~90%有利于种子发芽和幼苗生长。     

Distribution and ecology of anthozoa in the estuarine region of the rivers Rhine,Meuse and Scheldt

Data on the ecology and distribution in the estuarine region of the rivers Rhine, Meuse and Scheldt are given for ten species of Anthozoa. These data have been correlated with several environmental variables, but especially salinity. Communication nr. 142 of the Delta Institute for Hydrobiological Research.     

Dolphin sympatric ecology

Interspecific associations between two or more species of the family Delphinidae have been reported by many scientists, but the sympatric ecology of such dolphin associations has not been studied in great detail. A few field investigations have been conducted on this subject in different parts of the world on species such as bottlenose dolphins (Tursiops spp.), short-beaked common dolphins (Delphinus delphis), and killer whales (Orcinus orca). Sympatric dolphins seem to use different strategies to co-exist when resources appear to be limited, including dietary divergence (different prey preference, slightly diverse diet, different feeding time) and/or different habitat use (shallow versus deep waters, flat areas versus submarine canyons and escarpments, different travel routes). This paper presents a review of some well-studied dolphin species found in sympatry and discusses the nature of habitat and resource partitioning as well as studies on aggressive behaviour displayed by species living in the same habitat.     

Time scales of change in the San Francisco Bay benthos

Results from multi-year investigations in the San Francisco Bay estuary show that large abundance fluctuations within benthic macroinvertebrate populations reflect both (1) within-year periodicity of reproduction, recruitment, and mortality that is not necessarily coincident with seasonal changes of the environment (e.g., the annual temperature cycle), and (2) aperiodic density changes (often larger than within-year fluctuations) following random perturbations of the environment.Density peaks of the small, short-lived estuarine invertebrates that comprise the vast majority of individuals in the bay's relatively homogeneous benthic community normally occur between spring and autumn depending on the species, in large part a reflection of reproductive periodicity. However, because mild winters permit reproductive activity in some of the common species throughout much of the year, other factors are important to within-year density fluctuations in the community. Seasonally predictable changes in freshwater inflow, wind and tidal mixing, microalgal biomass, and sediment erosion/deposition patterns all contribute to observed seasonal changes in abundance. For example, the commonly observed decline in abundance during winter reflects both short-lived species that die after reproducing and the stress of winter conditions (e.g., inundation by less saline, sediment-laden water and the decline in both planktonic and benthic algal biomass — a direct source of food for the shallow-water benthos). On the other hand, data from several studies suggest that observed recruitment and mortality may in fact be the migration of juveniles and adults to and from study sites. For example, the common amphipod Ampelisca abdita apparently moves from shallow to deep water, or from up-estuary to down-estuary locations, coincident with periods of high river runoff in winter. Growth of individuals within the few studied species populations is also highly seasonal, and appears to be coincident with seasonal increases in the abundance of planktonic and/or benthic microalgae.Two multi-year studies have shown that, in addition to within-year periodicity, major restructuring of the benthic community can occur as a result of anomalous (usually climate-related) perturbations of the benthic habitat. For example, during wet years freshwater-intolerant species disappear from the upper part of the estuary and from shallow areas of the bay. During a two-year drought these same species colonized the extreme upper end of the estuary in large numbers. Other aperiodic perturbations include localized instances of sediment erosion or deposition and algal mat accumulations that greatly depress abundance. Additionally, there is evidence (observations that the clam Macoma balthica establishes large populations only when the amphipod A. abdita is not abundant) that species interactions can contribute greatly to interannual variations. Thus, while community composition may change little over the long term, year-to-year predictability of species abundances is low.     

Intertidal zonation of animals and plants on rocky shores in the Bristol Channel and Severn Estuary–the northern shores

The vertical distribution of common species of macroalgae and fauna on rocky shores extending through the length of the estuary is described. In the west, the shores are fully marine and exposed to Atlantic waves. In an eastward direction, greater shelter and an increasing tidal range occur along a gradient of salinity and turbidity. The flora and fauna change along this gradient. No single biological feature signals a transition from the Bristol Channel to the Severn Estuary but four arbitrary regions are recognized: a 'marine' section eastwards to Swansea, a 'transitional' section between Swansea and Cardiff, an 'estuarine' section up to Newnham, and the tidal river Severn.     

Routine metabolism of juvenile spot, Leiostomus xanthums (Lacépède), as a function of temperature, salinity and weight

Routine oxygen consumption rates of juvenile spot, Leiostomus xanthums , were measured over a range of temperatures, salinities and fish weights. As predicted, Q O₂ increased with temperature and decreased with body weight. However, Q O₂ decreased with decreasing salinity and did not show the expected minimum at isosmotic concentrations. The data are best described by the relationship: log₁₀ Q O₂ (mg O₂ g⁻¹ h⁻¹) = 0.129 log_lo salinity (%0) + 1.604 log₁₀ temperature (°C)-0.1401og₁₀(g)-2.767.     

Characterization of Scale Abnormalities in Pinfish, Lagodon rhomboides, from Biscayne Bay, Florida

Correlations between marine habitat degradation and the prevalence of abnormalities and diseases in populations can provide a starting point for understanding the effects of changes in environmental conditions on marine organisms. The present study characterized the features of scale disorientation (SD), a common morphological anomaly encountered in pinfish, Lagodon rhomboides, in Biscayne Bay, Florida (U.S.A.). Scale disorientation consisted of discrete patches of scales rotated dorsally or ventrally away from the normal scale position without any projection of the scales outwards from the body surface. The direction of scale growth within the patches varied from normal to a minor misalignment to a complete reversal of direction. The severity of SD, defined as the percentage of body surface area affected, varied from 1 to 34% with a mean of 9.3%. Affected fish monitored in the laboratory demonstrated a proportional growth of SD areas such that the percentage of body surface affected did not change as the fish grew. Scale disorientation was more prevalent in the northern region of the bay, an area known to be more contaminated. Scales from SD areas exhibited significantly abnormal morphology with larger average focus diameter, smaller size, more elongate shape and fewer radii relative to normal scales. Experimental removal of scales demonstrated that normal scales regrew in normal orientation and morphology while those from SD areas regrew in abnormal orientations and morphologies. Experiments in which fish were exposed to acute and chronic injuries indicated that these physical traumas were insufficient to directly induce formation of scale disorientations typical of those seen in the wild. Observations of pinfish in the laboratory revealed that SD areas can appear spontaneously in normal juvenile and adult fish. These new SD areas developed relatively rapidly, did not require prior scale loss and remained stable in size after first appearance. Although the etiology of SD remains unknown, the significant difference in prevalence of this syndrome between regions of Biscayne Bay having different levels of sediment contaminants suggests that environmental factors may be important in development of SD.     

SEQUENTIAL REPRODUCTION BY DIFFERENT TYPES OF SPECIMENS OF THE ESTUARINE SPONGE,HALICHONDRIA SP., WITH AN EMPHASIS ON REPRODUCTION OF POSTLARVAL SPECIMENS

Young specimens of Halichondria sp., recently developed from larvae (postlarval specimens), engage in sexual reproduction; and reproductive activity increases with specimen size. Reproduction by such specimens takes place primarily during a period after breeding by the parental generation has declined. This fact suggests that environmental conditions are favorable for reproduction for an extended period of time and that reproduction is to a large extent under endogenous control.     

Seasonal cycles of zooplankton from San Francisco Bay

The two estuarine systems composing San Francisco Bay have distinct zooplankton communities and seasonal population dynamics. In the South Bay, a shallow lagoon-type estuary, the copepods Acartia spp. and Oithona davisae dominate. As in estuaries along the northeast coast of the U.S., there is a seasonal succession involving the replacement of a cold-season Acartia species (A. clausi s.l.) by a warm-season species (A. californiensis), presumably resulting from the differential production and hatching of dormant eggs. Oithona davisae is most abundant during the fall. Copepods of northern San Francisco Bay, a partially-mixed estuary of the Sacramento-San Joaquin Rivers, organize into discrete populations according to salinity distribution: Sinocalanus doerrii (a recently introduced species) at the riverine boundary, Eurytemora affinis in the oligohaline mixing zone, Acartia spp. in polyhaline waters (18–30\%), and neritic species (e.g., Paracalanus parvus) at the seaward boundary. Sinocalanus doerrii and E. affinis are present year-round. Acartia clausi s.l. is present almost year-round in the northern reach, and A. californiensis occurs only briefly there in summer-fall. The difference in succession of Acartia species between the two regions of San Francisco Bay may reflect differences in the seasonal temperature cycle (the South Bay warms earlier), and the perennial transport of A. clausi s.l. into the northern reach from the seaward boundary by nontidal advection.Large numbers (>10⁶ m^–3) of net microzooplankton (>64 µm), in cluding the rotifer Synchaeta sp. and three species of tintinnid ciliates, occur in the South Bay and in the seaward northern reach where salinity exceeds about 5–10 Maximum densities of these microzooplankton are associated with high concentrations of chlorophyll. Meroplankton (of gastropods, bivalves, barnacles, and polychaetes) constitute a large fraction of zooplankton biomass in the South Bay during winter-spring and in the northern reach during summer-fall.Seasonal cycles of zooplankton abundance appear to be constant among years (1978–1981) and are similar in the deep (>10 m) channels and lateral shoals (<3 m). The seasonal zooplankton community dynamics are discussed in relation to: (1) river discharge which alters salinity distribution and residence time of plankton; (2) temperature which induces production and hatching of dormant copepod eggs; (3) coastal hydrography which brings neritic copepods of different zoogeographic affinities into the bay; and (4) seasonal cycles of phytoplankton.     

Improved sustainable maintenance for mid-water coral nursery by the application of an anti-fouling agent

The ‘gardening concept’ for reef restoration focuses on coral colonies farming in mid-water nurseries before their transplantation onto denuded reef areas. Nurseries situated in a nutrient-enriched environment significantly curtail nursery time, but extend labor, as nursery construction and farmed corals must be frequently cleaned from competing fouling organisms. Mass farming of corals calls, therefore, for efficient and cheap maintenance methodologies, which we here tested by employing Aqua-guard M250, an anti-fouling agent used in the fish farming industry. We found that this anti-fouling paint, while reducing fouling organisms on nursery components during the crucial phase of coral ramets' development from nubbins and small fragments sizes to colony sizes suitable for transplantation, is not toxic to maricultured coral fragments that staged more than 2 cm away from the paint. Applying small quantities of such antifouling paint to coral nurseries, while restricting its use to nursery components that are not in direct contact with farmed coral material, reduces fouling coverage and cleaning procedures by 90%.     

Integrating spatial and temporal variability into the analysis of fish food web linkages in Tijuana Estuary

Our understanding of fish feeding interactions at Tijuana Estuary was improved by incorporating estimates of spatial and temporal variability into diet analyses. We examined the stomach contents of 7 dominant species (n=579 total fish) collected between 1994 and 1999. General feeding patterns pooled over time produced a basic food web consisting of 3 major trophic levels: (1) primary consumers (Atherinops affinis, Mugil cephalus) that ingested substantial amounts of plant material and detritus; (2) benthic carnivores (Clevelandia ios, Hypsopsetta guttulata, Gillichthys mirabilis, and Fundulus parvipinnis) that ingested high numbers of calanoid copepods and exotic amphipods (Grandidierella japonica); and (3) piscivores (Paralichthys californicus and Leptocottus armatus) that often preyed on smaller gobiids. Similarity-based groupings of individual species' diets were identified using nonmetric multidimensional scaling to characterize their variability within and between species, and in space and time. This allowed us identify major dietary shifts and recognize events (i.e., modified prey abundance during 1997–98 El Ni no floods) that likely caused these shifts.