Impact of climate variability on an east Australian bay

The climate along the subtropical east coast of Australia is changing significantly. Rainfall has decreased by about 50 mm per decade and temperature increased by about 0.1 °C per decade during the last 50 years. These changes are likely to impact upon episodes of hypersalinity and the persistence of inverse circulations, which are often characteristic features of the coastal zone in the subtropics and are controlled by the balance between evaporation, precipitation, and freshwater discharge. In this study, observations and results from a general ocean circulation model are used to investigate how current climate trends have impacted upon the physical characteristics of the Hervey Bay, Australia. During the last two decades, mean precipitation in Hervey Bay deviates by 13% from the climatology (1941–2000). In the same time, the river discharge is reduced by 23%. In direct consequence, the frequency of hypersaline and inverse conditions has increased. Moreover, the salinity flux out of the bay has increased and the evaporation induced residual circulation has accelerated. Contrary to the drying trend, the occurrence of severe rainfalls, associated with floods, leads to short-term fluctuations in the salinity. These freshwater discharge events are used to estimate a typical response time for the bay.     

Assessment of spatial variation in carbon utilization by benthic and pelagic invertebrates in a temperate South African estuary using stable isotope signatures

Stable isotope analyses (δ¹³C and δ¹⁵N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ¹³C values of Zostera capensis and surface sediments near the salt marsh, the δ¹³C and δ¹⁵N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ¹³C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ¹³C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ¹⁵N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ¹³C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.     

黄河口大型底栖动物群落结构特征及其与环境因子的耦合分析

为探究复杂环境下的河口大型底栖生物群落结构特征,研究了黄河口及其毗邻海域内14个站位的底栖生物群落结构及其与主要环境因子的耦合关系。研究结果表明调查海域底栖生物群落组成和结构的空间异质性较高。底栖生物优势度不明显,优势物种集中于河口附近站位。生物多样性随离河口距离增加而增加,物种丰富度和生物多样性指数等的高值区均出现在远离河口的渤海湾和渤海中部站位,低值区位于近河口站位。对底栖生物群落的非参数多维排序(nMDS)和等级聚类分析显示,底栖生物群落结构相似性较低。丰度/生物量曲线(ABC曲线)分析显示,黄河口底栖生物群落整体上处于稳定状态,但近河口和莱州湾中西部站位受到干扰影响,群落结构不稳定。研究还表明生物量大的底栖生物(软体动物)倾向于向重金属含量较高的站位聚集。综合沉积物化学、预测毒性和底栖生物群落结构变化的评价结果可知,远离黄河口的沉积物环境质量普遍较好,而河口附近的沉积物环境质量较差。     

Influence of allochthonous organic matter on bacterioplankton biomass and activity in a eutrophic,sub-tropical estuary

Heterotrophic bacterial and phytoplankton biomass, production, specific growth rates, and growth efficiencies were studied in the Northern region of the Cananéia–Iguape estuarine system, which has recently experienced an intense eutrophication due to anthropogenic causes. Two surveys were carried out during spring and neap tide periods of the dry season of 2005 and the rainy season of 2006. This region receives large freshwater inputs with organic seston and phosphate concentrations that reach as high as 1.0 mg l⁻¹ and 20.0 μM, respectively. Strong decreasing gradients of seston and dissolved inorganic nutrients were observed from the river/estuary boundary to the estuary/coastal interface. Gradients were also observed in phytoplankton and bacterial production rates. The production rates of phytoplankton were 5.6-fold higher (mean 8.5 μg C l⁻¹ h⁻¹) during the dry season. Primary production rates (PP) positively correlated with salinity and euphotic depth, indicating that phytoplankton productivity was light-limited. On the other hand, bacterial biomass (BB) and production rates (BP) were 1.9- and 3.7-fold higher, respectively, during the rainy season, with mean values of up to 40.4 μg C l⁻¹ and 7.9 μg C l⁻¹ h⁻¹, respectively. Despite such a high BP, bacterial abundance remained <2 × 10⁶ cells ml⁻¹, indicating that bacterial production and removal were coupled. Mean specific growth rates ranged between 0.9 and 5.5 d⁻¹. BP was inversely correlated with salinity and positively correlated with temperature, organic matter, exopolymer particles, and particulate-attached bacteria; this last accounted for as much as 89.6% of the total abundance. During the rainy season, BP was generally much higher than PP, and values of BP/PP > 20 were registered during high freshwater input, suggesting that under these conditions, bacterial activity was predominantly supported by allochthonous inputs of organic carbon. In addition, BB probably represented the main pathway for the synthesis of high-quality (low C:N) biomass that may have been available to the heterotrophic components of the plankton food web, particularly nanoheterotrophs.     

Field observations in a small subtropical estuary during and after a rainstorm event

In Australia, a large majority of small subtropical estuaries are narrow, elongated and meandering channels with large width to depth ratio and cross-sections which deepen and widen towards the mouth. Up to date, episodic rainstorm events in such small systems were rarely documented, and this study presents a field data set collected during and immediately after a rainstorm. A number of hydrodynamic and physio-chemical parameters were recorded simultaneously at several longitudinal locations for 12 h. The field measurements demonstrated a significant flushing of the estuarine zone, caused primarily by the rainfall runoff from the nearby shopping malls and roadways. Some strong vertical stratification of the water column was observed at all sampling locations, and the depth-averaged salinity data exhibited a dome-shaped intrusion curve. A solution of the salt dispersion equation provided some agreement with the freshwater flushing conditions during the wet weather.     

Climate variability and planktonic communities: The effect of an extreme event (severe drought) in a southern European estuary

As a consequence of climate change, flood and drought events are increasing in frequency throughout the world. Nevertheless, knowledge of the effects on zooplankton estuarine communities is still scarce. The present study aimed to examine zooplankton ecology over two contrasting environmental conditions: regular years and extreme dry years, in a shallow temperate southern European estuary, the Mondego Estuary (Portugal). Monthly samples were carried out during three consecutive years: 2003 characterized as a regular temperate year concerning precipitation and river flow, and an extremely dry period during 2004–2005. The spatial and temporal structure of the biological data was evaluated by a three-mode principal component analysis (PCA), which allowed us to distinguish three distinct ecological areas based on their biological composition and their relationship with hydrologic parameters. The severe drought in 2004–2005 was responsible for spatial shifts in the estuary regarding zooplankton community and interannual variability, with an increase in abundance and diversity during the period of low freshwater flow. This freshwater flow regime influenced the composition of the zooplankton community at the most upstream section of Mondego estuary (zone 3), with a replacement of the freshwater community by one predominantly dominated by estuarine organisms. The occurrence of such estuarine community contributed to the increase in zooplankton abundance which is ascribed to the estuarine species Acartia tonsa. The comparison with previous data obtained for this estuarine ecosystem, demonstrated the occurrence of a different scenario at times of high freshwater flow, being defined the existence of two sub-estuarine systems, the north and south arm, presenting the south one the highest values of abundance.     

Trophic structure and production in the macrobenthos of a temperate Australian estuary

The soft-bottom fauna of Gunnamatta Bay, Port Hacking, N.S.W., was sampled to estimate the abundance, trophic structure and net production of the macrobenthos. The samples were classified into groups from spatially distinct strata, the groups differing in species abundance and diversity and in the identity of the dominant species. The composition and community structure of the fauna was generally similar to that in other sheltered embayments on the southeastern coast of Australia. Estimated production values were low for an estuary, ranging from 10 kJ m^?2 year^?1 in an intertidal stratum of well sorted sand to 210–450 kJ m^?2 year^?1 in shallow subtidal strata with an admixture of silt. Estimated net production over all strata was 160 kJ m^?2 year^?1. Polychaetes dominated production, providing 45% of the total; crustaceans provided 20%, and molluscs and echinoderms 12% each. Detritus-feeders were dominant in most strata: the bivalve Theora fragilis, the polychaetes Australonereis ehlersi and Notomastus torquatus, and the urchin Echinocardium cordatum were major contributors to overall biomass and to net production. Substantial biomass and net production was also contributed by the suspension-feeding bivalve Corbula vicaria and a carnivorous crab Ceratoplax cf. glaberrimus. Overall, detritus-feeders contributed 61% of estimated net production, carnivores 32% and suspension-feeders 7%. Production estimated for carnivores was higher than could be supported by the non-carnivore populations, suggesting that some of the species considered to be carnivores have additional feeding modes. Excessive harvesting of bivalves by humans is suggested as the main reason for the low biomass of, and therefore low production by, suspension feeders.     

The biology of the catfish Cnidoglanis macrocephalus (Plotosidae) in an Australian estuary

This paper describes the age structure, growth, diet and aspects of gonadal development in the cobbler, Cnidoglanis macrocephalus (Valenciennes), in the large Swan estuary in south-western Australia between August 1982 and June 1984. Analysis of otolith annuli showed that while the 0+ to 3+ age classes were regularly represented in monthly samples, the 4+ and more particularly the 5+ and 6+ were much less abundant. The weighted means for the back calculated lengths at the end of the first to fourth years of life were 181 mm (≡ 26 g), 314 mm (≡ 156 g), 418 mm (≡ 410 g) and 518 mm (≡ 833 g) respectively. The mean length at the end of the second year of life was similar to the minimum legal size for capture by commercial fishermen (320 mm). The von Bertlanffy growth curve calculated from the back calculated lengths was L_t = 917 [1 − e^{−0·20(t + 0·11)}]. The relative weight of mulluscs, crustaceans and polychaetes in the intestine varied markedly between small and large fish, apparently reflecting differences in the size of these prey. The large mean diameter of mature eggs ( ) was correlated with a low mean absolute fecundity (2078). Trends shown by egg size, gonadosomatic index and time of appearance of spent females indicate that spawning takes place between October and December. The attainment of sexual maturity is both age- and size-dependent. Although sexually maturing and occasionally spent fish were found in the lower estuary, meristic values, commercial catch statistics and other data indicate that the cobbler found in the Swan estuary are part of a population which typically spawns at sea.     

Heavy metals in a contaminated Australian estuary—Dispersion and accumulation trend

Very high concentrations of Zn, Pb, Cu and Cd occur in the muddy bottom sediments of Lake Macquarie, a saline coastal lagoon in southeastern Australia. The trace metals emanate from industrial sources, especially a lead-zinc smelter, at the northern end of the lake. Individual metal concentrations decrease progressively away from the source area but at differing rates; Zn is most mobile and Cd appears to be deposited first. They approach natural background levels in the southern part of the lake. Mn shows a reverse trend but Ni, Co, Ag and Fe rarely rise above background levels.Shallow cores in the lake bed penetrated a metal enriched surface zone 15–35 cm thick underlain by uncontaminated sediments with natural (background) metal concentrations. Sedimentation rates determined from radiocarbon ages on shells in the cores mainly range between 0·15 and 0·5 mm yr^?1. Over the 85 years since industrialization commenced, less than 5 cm of mud has accumulated on the lake bed. Bioturbation is invoked to account for the depth to which the sediment has been enriched in heavy metals.     

Impact of vehicles on benthic macrofauna on a subtropical sand beach

Our study aimed to identify possible relationships between the structure of the benthic macrofauna and the intense use of vehicles in Cassino Beach. Physical changes in the sediment were identified, with high compaction in the sector most affected by the vehicles, especially during the summer. The benthic macrofauna was significantly affected by vehicles, with lower densities observed in the most impacted sector, mainly in the summer, unlike the control sector, where higher densities were observed during the pre-summer and summer. We concluded that the vehicle traffic changes the physical environment of the beach and consequently affects the benthic community in the face of this disturbance. We conclude that the benthic macrofauna is highly impacted by vehicle traffic at Cassino Beach, mainly in the period with the highest traffic, and alternatives are needed for this impact, helping to recover this ecosystem.     

Impact of freshwater influx on microzooplankton mediated food web in a tropical estuary (Cochin backwaters – India)

The diversity, abundance and biomass of microzooplankton in Cochin backwaters were studied for the first time during pre-summer monsoon to peak of summer monsoon (April–July 2003) to understand the impact of large freshwater influx. Microzooplankton abundance and biomass were highest during pre-summer monsoon (av. 3817 ind. L⁻¹ and 146 μg C L⁻¹) that declined with the onset (av. 2052 ind. L⁻¹ and 45 μg C L⁻¹) and peak (av. 409 ind. L⁻¹ and 10 μg C L⁻¹) summer monsoon. Species diversity, richness and evenness of microzooplankton also showed similar trends as that of abundance and biomass. Grazing experiment showed that microzooplankton consumes 43 ± 1% of the daily phytoplankton standing stock during the high saline condition (27.5). Low abundance of microzooplankton during summer monsoon period (1/8 of the pre-summer monsoon value) along with the concomitant occurrence of low mesozooplankton (1/8 times of pre-summer monsoon value) suggests that there could be a general lack of planktonic grazers. This would result in a weak transfer of primary and bacterial carbon to higher trophic levels, eventually leaving behind much unconsumed basic food in the estuary during summer monsoon. Thus a major portion of the primary carbon either settles down or gets transported to the coastal regions during monsoon. High flushing of Cochin backwaters also facilitates faster removal of primary producers to the coastal regions during monsoon.     

Scale-dependent effects of nutrient loads and climatic conditions on benthic and pelagic communities in the Gulf of Finland

Eutrophication and climate change are ranked among the most serious threats to the stability of marine ecosystems worldwide. The effects of nutrient loads and climatic conditions vary in direction, magnitude and spatial extent. To date the factors that are behind the scale-specific spatial and temporal variability are poorly known. In this study we assessed how variability in nutrient loads and climatic conditions at local, gulf and regional scales explained the spatial patterns and temporal trends of zooplankton and benthic invertebrates in the Gulf of Finland. In general both local and gulf scale environmental variability had an important effect on benthic invertebrate species and the variability was mainly due to local nutrient loading, gulf scale temperature and salinity patterns. Zooplankton species were equally affected by environmental variability at all spatial scales, and all nutrient load and climatic condition variables contributed to the models. The combination of variables at all spatial scales did not explain the substantially larger proportion in invertebrate variability than variables at any individual scale. This suggests that large-scale pressures such as nutrient loads and change of climatic conditions may define broad patterns of distribution but within these patterns small-scale environmental variability significantly modifies the response of communities to these large-scale pressures.     

Spatial and temporal variability in particle-bound pesticide exposure and their effects on benthic community structure in a temporarily open estuary

Spatial and temporal variations in particle-bound pesticide contamination, natural environmental variables, and benthic abundance were measured during the dry summer season within a temporarily open estuary (Lourens River). This study focused on the effect of particle-associated pesticides on the dynamics of the benthic community (including epi-benthic, hyper-benthic, and demersal organisms) by comparing two runoff events, differing in their change in pesticide concentration and environmental variables. The two chosen sites were situated within the upper and middle reaches of the estuary and differ significantly in salinity (p = 0.001), flow (p = 0.5), temperature (p < 0.001) and particulate organic carbon in the sediment (p < 0.001). Generally higher particle-bound pesticides were found in the upper reaches.     

Nutrient loading and macrophyte growth in Wilson Inlet,a bar-built southwestern Australian estuary

Wilson Inlet is a ‘bar-built’ estuary, open to the ocean only when a sandbar has been breached after river flow. estimates are presented of phosphorus and nitrogen loadings from rivers, losses to the ocean, and amounts present in estuarine components during a particular year. Following bar opening, a volume of water equivalent to 35% of estuarine volume at the time was lost, providing a major loss of dissolved nutrients from the estuary. While the bar was open (51 days) water was displaced through river flow, but there was little tidal exchange. There was net retention of phosphorus (about 60% of river input) and some loss of nitrogen (less than 15%).Much of the nutrient held in the estuary was in surface sediments, but concentrations have shown little change with time and are similar to other southwestern estuaries. In contrast there have been massive increases in the biomass of Ruppia megacarpa Mason in recent years; this constitutes more than 90% of plant biomass. The nutrient bank in this plant is large compared to the water column, and amounts recycled through plant material greatly exceeded riverine loading in the year of the study. Tissue N concentrations were relatively high and constant, tissue P relatively low and seasonally variable, suggesting P limitation of plant biomass.Estimates of nutrient loading from streams showed relatively higher nutrient inputs from catchments cleared for agriculture. These are in higher rainfall areas, have high drainage densities, large proportions of sandy soils and are subjected to phosphatic fertilizer application.     

Comparison of benthic and pelagic suspension feeding in shallow water habitats of the Northeastern Baltic Sea

Combining field experiments with the biomass distribution data of dominant suspension feeders we compared the benthic and pelagic suspension feeding rates in shallow non-tidal brackish water coastal habitats. We found that pelagic grazing exceeded benthic grazing in almost all cases, on average from 14 to 4819 times depending on the site. Benthic grazing rates were related to site-specific environmental parameters and showed no relationship with water chlorophyl a (Chl a ) content, whereas pelagic grazing rates varied both spatially and temporally and were related to water Chl a content. Our results indicate that in several shallow coastal habitats, pelagic suspension feeding substantially exceeds benthic suspension feeding. This suggests that pelagic recycling is higher than the amounts of energy redirected from pelagic to benthic food webs by benthic suspension feeders. These results increase our knowledge of the energy flows in coastal ecosystems.     

Phosphate adsorption and desorption in a tropical estuary (Maracaibo system)

The Maracaibo Estuary is of particular interest because of its location in the tropics, its large size (over 12,000 km²), the economic importance of its underlying hydrocarbon deposits and its increasing rate of pollution. Sediments from this estuary were studied in order to characterise their capacity to adsorb and desorb phosphorus. Considerable variability in capacity for phosphate sorption was found among the seventeen samples studied. This variability can be attributed first to the differences among the samples in total P content and, secondly, to their differences in free iron content. Also, it appears that P retention contributes to the control of P concentration in the water and therefore the sediments serve as a buffer in controlling P eutrophication in the estuary.     

Seasonal occurrence and growth of benthic algae in the Patos Lagoon estuary, Brazil

The seasonal occurrence of 94 benthic algal species, including Cyanophyta, was observed on a monthly basis over one year in the Patos Lagoon estuary (32°S, 52°W), Brazil, and showed three patterns of algal periodicity. An aseasonal group of 46 species was present throughout the year and two groups of 24 species each occurred either during summer and fall or winter and spring. The seasonal growth of 55 green, brown and red algae was correlated with monthly variations of salinity, water temperature, daylength and light radiation energy, which were measured daily in the estuary. Summer/fall peak growth was observed in 15 algae most of which correlated significantly with high salinities alone or in combination with other factors during this period. Growth peak of 11 species in winter/spring was principally a function of low water temperatures alone or together with a reduced light regime.Both periodicity of benthic algae and their seasonal growth, as a more sensitive measure of their floristic affinity, demonstrated the presence of cool temperate and tropical elements in this flora typical for warm temperate biogeographic regions. Correlations between seasonal variation of algal growth and selected environmental parameters aided in the evaluation of causal factors for algal seasonality.