Open Estuaries Research Articles

Influence of prey abundance and abiotic factors on the long-term home-range and movement dynamics of spotted grunter Pomadasys commersonnii in an intermittently open estuary

Long-term home-range and movement dynamics of spotted grunter Pomadasys commersonnii and the distribution of their dominant prey, the sandprawn Callichirus kraussi, were investigated in the intermittently open East Kleinemonde Estuary, South Africa. In addition, the effects of fish length, diel cycle, season and other abiotic factors on home range and area use were examined. Nine adult spotted grunter (326–489 mm total length) were tagged with acoustic transmitters, and their movements were studied by manual tracking on six consecutive days and nights during each of five tracking sessions from March to November 2004. In addition, movement patterns were recorded by stationary data-logging receivers. Kernel home ranges (95% utilised distribution) varied in size (mean: 76 797 m2 , range: 26 296–165 321 m2), but were all located in the lower one-third of the 3.6 km-long estuary. There was no effect of season, the diel cycle or fish length on the home-range estimates. However, the distribution of prey corresponded with the home-range distribution of tagged fish. Although sandprawn distribution was highly variable within and among transects and depth classes, sandprawns were most abundant in the lower region of the estuary, which corresponded to the home-range distribution of spotted grunter. Spatial distribution of prey appears to be a dominant factor influencing home-range parameters of this species within an intermittently open estuary.

A preliminary fish survey of the estuaries on the southeast coast of South Africa, Kayser’s Beach – Kei Mouth: a comparative study

A basic ichthyofaunal and physico-chemical survey of estuaries on the southeast coast of South Africa from Kayser’s Beach to Kei Mouth was undertaken during September and October 1996. Twenty-eight (28) estuaries have been identified along this stretch of coastline, and these were grouped into three types: small ( 10 ha) predominantly closed estuaries, and predominantly open estuaries. Multivariate analyses revealed significant differences between estuarine types both in terms of their physico-chemical characteristics and fish communities. These features were consistent with those reported in other parts of the south and southeast coast. Overall, predominantly closed estuaries had a lower species diversity than predominantly open estuaries and smaller systems had a lower species diversity than moderate to large systems. Although differences were observed between estuarine types, most systems provided important habitat for a number of estuarine-dependent marine species as well as resident species, which were often recorded in high numbers. Many of these species were also endemic, which further emphasises the importance of these estuaries in maintaining ichthyofaunal diversity in the region. This survey represents one of the few fish surveys undertaken along this little-studied section of coastline. Keywords: ichthyofauna, estuarine survey, fish habitat, southeast coast

Shoreline change and sea level rise at the Muni-Pomadze coastal wetland (Ramsar site), Ghana

Lagoon-wetland systems are common along low-lying coastlines. They provide rich species habitats, multiple ecosystem services and socio-economic activities. They are particularly susceptible to the impacts of sea level rise (SLR), especially in less developed countries (LDCs) where economic and development constraints limit adaptation. The Muni-Pomadze lagoon is one of five coastal Ramsar sites in Ghana and one of many along the country’s coastline. It is an intermittently closed lagoon with extreme seasonal hydrological and physico-chemical variation. Field observation, digital mapping and GIS analysis of the shoreline has enabled an understanding of coastal change and SLR at the lagoon. From 1972 to 2014 the high water mark has shifted landwards with an average retreat rate of 0.22 m/year. Evidence of erosion and sediment washover indicate loss of and a shift landward of the sand barrier separating the lagoon from the ocean. Creation of an inundation map for a one-meter rise of sea level reveals fragementation and breaching of the barrier and an increasingly permanent connection to the ocean. A more open lagoon system stabilises hydrological and physico-chemical conditions, leading to increases in biodiversity and aquatic productivity. The lagoon currently has no consideration of SLR in its management plan. The results of this analysis and the limited development of the Muni-Pomadze lagoon support a no intervention approach to coastal management that allows SLR to transform the closed lagoon to an open estuary. A similar approach at comparable coastal wetland systems in Ghana and in other LDCs could prove an effective management option.

Distribution of benthic diatom communities in a permanently open temperate estuary in relation to physico-chemical variables

The spatial and temporal patterns in benthic diatom community structure in temperate permanently open estuaries are poorly understood. In this study, we used a combination of multivariate and diversity indices to elucidate environmental factors associated with diatom community structure in the Kowie Estuary, South Africa. Benthic diatom samples were collected from three sites corresponding to the upper, middle and lower reaches of the estuary on four occasions over the period early spring 2012 to winter 2013. Among the 89 benthic diatoms observed, Entomoneis paludosa (W Smith) Reimer, Nitzschia reversa W Smith, Nitzschia closterium (Ehrenberg) W Smith, Pleurosigma elongatum W Smith, P. salinarum (Grunow) Grunow, Staurosira elliptica (Schumann) DM Williams & Round, Surirella brebissonii Krammer & Lange-Bertalot, and Surirella ovalis Brébisson were the numerically dominant species. Principal component analysis demonstrated that the diatom community structure was determined by a variety of factors including nutrient (ammonia, nitrate) concentrations, hydrology (e.g., water depth and flow) and pH. Hierarchical cluster analysis revealed the absence of any distinct spatial patterns, although distinct benthic diatom communities were recorded during the different sampling periods. The species richness was highest in the middle reach, decreasing from early spring to summer in all reaches. The results of the study provide important insights into the various factors that structure benthic diatom community composition within a permanently open temperate southern African estuary.

Meiobenthic communities in permanently open estuaries and open/closed coastal lagoons of Uruguay (Atlantic coast of South America)

This study aimed to determine if estuarine meiofaunal communities of Uruguay (South America) vary between permanently open estuaries and open/closed coastal lagoons, or if they respond to the sediment composition. In Uruguay, estuaries and coastal lagoons vary in the degree of connectivity to the sea and in the sediment composition; sediments in estuaries are characterized by fine-medium sands but sediments vary from lagoon to lagoon (either fine-medium or coarse sand). Taxa richness (total = 16) showed less temporal variability in lagoons than in estuaries, due to patterns of presence/absence of the less abundant taxa. However, no major response to habitat was found in the most abundant groups: polychaetes (6% of total fauna) were on average 5% more abundant in lagoons than in estuaries. Some level of zonation, within estuaries and lagoons, was found in the most abundant groups, nematodes (63% of total fauna) and copepods (15%) in response to medium and fine sands. In addition, sediment type modulated seasonal patterns in the frequency of presence/absence in ostracods, polychaetes and oligochaetes. For instance, in polychaetes and ostracods the increase in the frequency of absences, occurring from summer to winter, was stronger in lagoons and estuaries dominated by fine sands. The lagoon habitat appears to ameliorate the effects of unfavourable (winter) conditions in less abundant meiofaunal taxa. In summary, sediment fractions explain spatial patterns in the average abundance of organisms (e.g. nematodes) as well as the seasonal changes in frequency of presence/absence (e.g. polychaetes).

FROM OPEN ESTUARY TO MEANDERING RIVER IN A GREENHOUSE WORLD: AN ECOLOGICAL CASE STUDY FROM THE MIDDLE EOCENE OF HELMSTEDT, NORTHERN GERMANY

Tropical climates reached their northernmost expansion during the early Paleogene greenhouse phase, supporting a paratropical biota as far north as the southern shore of the ancient North Sea. There, relative sea-level fluctuations led to the formation of transgressive-regressive sequences, exposed in open-cast lignite mines in the area of Helmstedt (Lower Saxony, Germany), which record environmental changes at the marine-terrestrial interface. We studied an example from the middle Eocene of the Helmstedt Mine from which we reconstruct ecological successions from open estuary to meandering river environments, which represent vegetation at the Paleogene climatic optimum. In the absence of vertebrate and shelly fossils, environmental interpretations are made exclusively on plant matter in the sediment. Vegetational reconstructions are based mainly on quantitative palynological analyses, supported by paleobotanical and organic-petrographical evidence and confirmed by Principal Component Analysis. Diverse dinocyst assemblages in conjunction with Ophiomorpha-type bioturbation indicate open estuarine conditions. These are succeeded by mangrove, represented by pollen of Rhizophora, Avicennia, Nypa and the form species Psilodiporites iszkaszentgoergyi, and marsh environments, indicated by pollen of Restionaceae, Sparganiaceae/Typhaceae and fern spores. Subsequent lowland mire forests are characterized by a dominance of either the Tricolporopollenites cingulum group (Fagaceae) or triporate pollen of the Triporopollenites robustus/rhenanus complex (Myricaceae/Betulaceae). Within this landscape coexists a meandering river system, represented by channel lag and point-bar deposits of the active channel and by the clastic to lignitic sedimentary fill of an abandoned channel.

Global patterns and predictors of fish species richness in estuaries.

1. Knowledge of global patterns of biodiversity and regulating variables is indispensable to develop predictive models. 2. The present study used predictive modelling approaches to investigate hypotheses that explain the variation in fish species richness between estuaries over a worldwide spatial extent. Ultimately, such models will allow assessment of future changes in ecosystem structure and function as a result of environmental changes. 3. A comprehensive worldwide data base was compiled of the fish assemblage composition and environmental characteristics of estuaries. Generalized Linear Models were used to quantify how variation in species richness among estuaries is related to historical events, energy dynamics and ecosystem characteristics, while controlling for sampling effects. 4. At the global extent, species richness differed among marine biogeographic realms and continents and increased with mean sea surface temperature, terrestrial net primary productivity and the stability of connectivity with a marine ecosystem (open vs. temporarily open estuaries). At a smaller extent (within a marine biogeographic realm or continent), other characteristics were also important in predicting variation in species richness, with species richness increasing with estuary area and continental shelf width. 5. The results suggest that species richness in an estuary is defined by predictors that are spatially hierarchical. Over the largest spatial extents, species richness is influenced by the broader distributions and habitat use patterns of marine and freshwater species that can colonize estuaries, which are in turn governed by history contingency, energy dynamics and productivity variables. Species richness is also influenced by more regional and local parameters that can further affect the process of community colonization in an estuary including the connectivity of the estuary with the adjacent marine habitat, and, over smaller spatial extents, the size of these habitats. In summary, patterns of species richness in estuaries across large spatial extents seem to reflect from global to local processes acting on community colonization. The importance of considering spatial extent, sampling effects and of combining history and contemporary environmental characteristics when exploring biodiversity is highlighted.

Spatial and temporal patterns in the distribution of large bivalves in a permanently open temperate estuary: implications for management

To inform management, baseline ecological studies in estuaries must be implemented at spatial scales that accommodate both environmental gradients and likely anthropogenic pressures. We describe fine-scale spatial patterns in the abundances and size structure of large infaunal bivalves inhabiting shallow sand habitats in the lower reaches of a relatively undisturbed, permanently open, temperate estuary. Sampling over 3 years at 19 sites during the autumn, when freshwater influence was minimal, revealed that Soletellina alba, Wallucina assimilis and Paphies elongata were consistently the most abundant of nine species present. Although most abundant near the ocean entrance, S. alba was distributed widely and shells of differing lengths, and presumably ages, were present at most sites, suggesting that this species recruited continuously throughout the study area when conditions were appropriate. In contrast, W. assimilis and P. elongata occurred only near or in the entrance channel of the Nornalup Inlet in areas where seagrass rhizomes may grow and where oceanic influences caused relatively turbulent conditions, respectively. Sediment structure appeared to exert only a moderate and intermittent influence on the bivalve assemblage at some sites where particularly large grain sizes occurred. This study provides important baseline information on the distribution and abundance of large bivalves in this estuary. These species are likely to be important in the trophic ecology of this system and are potential indicators of disturbance and ecosystem health.

Movements and residency of juvenile white steenbras Lithognathus lithognathus in a range of contrasting estuaries

Acoustic telemetry was used to assess estuarine area use and movements of an overexploited, endemic fishery species in three South African estuaries; two permanently open systems with contrasting salinity gradients and an intermittently open system. Forty juvenile white steenbras Lithognathus lithognathus (215–379 mm FL) were surgically equipped with acoustic transmitters and tracked for up to 355 days. Tagged fish exhibited high levels of site fidelity and long-term residency within each estuary. Most of their time was spent in the lower reaches of all three estuaries and hypersalinity restricted movements into the upper reaches of the freshwater-deprived estuary. All tagged fish exhibited a distinct diel movement pattern. Most individuals (91%) in the two permanently open estuaries also exhibited a tidal-associated pattern, which comprised mainly small-scale (tens to hundreds of metres) transverse movements between deep channels and shallow banks. Observed behaviour was consistent across a range of estuary sizes, types and physico-chemical conditions. This study has identified critical habitats for juvenile white steenbras across a range of estuarine environments. Estuarine management initiatives need to consider these critical habitats, in order to enhance abundance of juveniles and ultimately recruitment to the marine (adult) population.

Utilization of organic matter by invertebrates along an estuarine gradient in an intermittently open estuary

In intermittently open estuaries, the sources of organic matter sustaining benthic invertebrates are likely to vary seasonally, particularly between periods of connection and disconnection with the ocean and higher and lower freshwater flows. This study investigated the contribution of allochthonous and autochthonous primary production to the diet of representative invertebrate species using stable isotope analysis (SIA) during the austral summer and winter (2008, 2009) in an intermittently open estuary on the south-eastern coast of Australia. As the study was conducted towards the end of a prolonged period of drought, a reduced influence of freshwater/terrestrial organic matter was expected. Sampling was conducted along an estuarine gradient, including upper, middle and lower reaches and showed that the majority of assimilated organic matter was derived from autochthonous estuarine food sources. Additionally, there was an input of allochthonous organic matter, which varied along the length of the estuary, indicated by distinct longitudinal trends in carbon and nitrogen stable isotope signatures along the estuarine gradient. Marine seaweed contributed to invertebrate diets in the lower reaches of the estuary, while freshwater/terrestrial organic matter had increased influence in the upper reaches. Suspension-feeding invertebrates derived large parts of their diet from freshwater/terrestrial material, despite flows being greatly reduced in comparison with non-drought years.

Recruitment of fish larvae and juveniles into two estuarine nursery areas with evidence of ebb tide use

Recruitment of larvae and early juveniles, against the ebb tide in the shallower, slower-flowing marginal areas of two permanently open estuaries in the Eastern Cape, South Africa was observed. To determine tidal, diel and seasonal variations of larval and juvenile fish recruitment, fyke nets were used during a 24-hour cycle over two years from December 2010 to October 2012. On either side of each estuary bank, two fyke nets with mouth openings facing opposite directions (i.e. one net facing the incoming or outgoing tide and the other facing the opposing direction) were used to sample fishes. The aims of this study were to determine if 1) on the flood tide, were the nets facing the incoming tide collecting more larvae and early juveniles recruiting into the estuarine nursery area, than the nets facing the opposing direction and 2) on the ebb tide, were the nets facing the sea, and hence the opposing direction of the outgoing ebb tide, collecting more fishes recruiting into the nursery against the ebb tide, than the nets facing the outgoing ebb tide? Larval and juvenile fish CPUE, species diversity and richness varied seasonally between estuarine systems and between diel and tidal conditions. Highest catches were recorded on the flood tide, which coincided with sunrise in the Swartkops Estuary. Greatest catches of larvae and early juveniles were observed during the ebb tide at night in the Sundays Estuary. On the ebb tide, higher catches of several dominant species and several commercially important fishery species, occurred in the fyke nets which faced the sea, indicating the early developmental stages of these fish species are not necessarily being lost from the nursery. These larvae and juveniles are actively swimming against the ebb tide in the shallower, slower-flowing marginal areas facilitating recruitment against ebb flow.

The frequency of connection of coastal water bodies to the ocean predicts Carcinus maenas invasion

Semi‐enclosed coastal water bodies range from permanently open estuaries to lagoons that are periodically isolated from the ocean. The proportion of time these are connected to the ocean may influence biological invasions by determining recruitment opportunities, environmental conditions, and available biogenic habitats. Along the south coast of New South Wales, Australia, we tested whether the abundance and persistence of the nonnative crab, Carcinus maenas, varies among coastal water bodies according to the proportion of time their entrance is open to the ocean. In quarterly sampling over 2 yr in 14 estuaries and lagoons varying in the percentage of time they were closed to the ocean from 0–100% crab presence and abundance was correlated with the proportion of time the entrances were open. Crabs were absent from lagoons with entrances closed to the ocean > 60% of the time and consistently detected in open estuaries. Crab abundance increased with the connectivity of coastal water bodies to the ocean and was influenced by habitat availability. In water bodies where conditions supported mangroves, this habitat contained higher abundances of crabs than seagrass, saltmarsh, oyster habitat, or bare substrate. Entrance morphology initially predicts the likelihood of the crabs' arrival by influencing their population connectivity between estuaries or lagoons and the open coast, and the probability of establishment by influencing abiotic conditions. Entrance morphology may also affect crab abundance by influencing the available habitats. Hence, the geomorphology of semi‐enclosed coastal water bodies should be considered when managing marine bioinvasions.

A sediment record of barrier estuary behaviour at the mesoscale: Interpreting high-resolution particle size analysis

At present, limited understanding of mesoscale (years–decades–centuries) back-barrier lagoon, barrier estuary behaviour is a critical shortcoming for resource managers and decision makers. In this paper, high-resolution particle size analysis of a sediment core from an intermittently open and closed barrier estuary is utilised to reconstruct a history of back-barrier environmental change at mesoscale temporal resolution. Sediments from Pescadero Marsh, California, were analysed for their particle size distribution at consecutive 2-mm intervals down-core. Site selection, informed by a time series of maps and aerial photographs coupled with a robust core chronology, ensured that the particle size data primarily reflect changing hydrodynamics of the back-barrier area over the European–American era (1850 to the present). Following more traditional plotting of particle size data and summary statistics, and statistical analysis of particle size end-members, visual analysis and categorisation of particle size distribution curves (PSDCs) provide an effective basis for the identification of recurring modal sizes and subpopulations. These particle size windows (PSWs) are interpreted as reflecting different modes of sediment transport and deposition, i.e., suspension and saltation loads, the varying prominence of which is interpreted as being modified by barrier integrity. When considered together, the down-core mean particle size (MPS) trend and individual PSDCs offer considerable insight into mesoscale system behaviour at subannual resolution over multiple years. This behaviour is expressed in the recurrence of characteristic barrier estuarine environments (closed lagoon, tidal lagoon, tidal marsh, and open estuary) and the overall barrier regime, and their persistence over the last c. 150years. Subannual and multiannual fluctuations in back-barrier environmental configuration are seen to be superimposed on a longer-term quasi-stable barrier regime, demonstrating the value of the applied methodology with regard to bridging the estuarine evolution (long-term, stratigraphic) and process (short-term, geomorphic) knowledge bases. The documented behaviour suggests a level of innate morphological resilience in the system over the long term despite episodic disturbance by high-energy storms. Such empirical demonstrations of resilient behaviour in coastal environments are rare at the mesoscale.

Patterns in Larval Fish Diversity, Abundance, and Distribution in Temperate South African Estuaries

Estuaries are important nursery areas for fishes worldwide but large-scale studies of spatial patterns of use are lacking. This study presents data on larval fish diversity, abundance and distribution within and among a range of temperate estuary types, spanning 25 systems sampled from 1998 to 2008 in South Africa. A standardized boat-based plankton towing technique was used. Estuary type and physico-chemical conditions played a defining role in the trends observed. Estuary resident Clupeidae and Gobiidae dominated the mid-channel larval catch, particularly the preflexion stages in permanently and intermittently open estuaries and in estuarine lakes. Permanently open estuaries were also characterized by high numbers of larvae and early juveniles of marine migrant fishes. Density was higher in warmer months (spring and summer), which coincides with peak spawning in coastal habitats coupled with zooplankton maxima in the warm-temperate region. A strong seasonal component was also evident in larval fish catches in cool-temperate systems, but this peak coincided with late winter rainfall. River inflow provides a strong influence on food availability and larval survival. Species richness and diversity was higher in estuaries with either extensive habitat variability and/or a strong, natural good supply of river flow. This was particularly evident in the higher numbers of marine migrant larvae in these systems. Freshwater deprived estuaries also displayed high species diversity due to the higher incidence of marine straggler species. Characterization of salinity into zones provided a valuable means to understand distribution and abundance dynamics. Mesohaline zones had the highest density of larval fishes, providing ideal food patches. A select suite of species dominate the larval fish assemblages in the various estuary types studied. These patterns persist but species abundance and rank may vary interannually based on productivity and larval fish survival.

Macrofaunal patterns and animal–sediment relationships in Uruguayan estuaries and coastal lagoons (Atlantic coast of South America)

Estuaries vary considerably in geomorphology, hydrology and in the properties of sediments. Structure of benthic communities may respond to the interaction of these estuarine characteristics, resulting in between site differences. This work evaluated several hypothetical scenarios to explain variation in macrofaunal communities in permanently open estuaries and open/closed coastal lagoons of the coast of Uruguay, South America. Of particular relevance were three hypothetical scenarios: (1) that sediment characteristics, temperature or conductivity may explain variation in fauna between estuarine habitat types (estuaries vs. lagoons), (2) that fauna may not vary between habitat types, but may vary among sites in response to environmental variables and (3) that fauna differed between habitat types but patterns were not clearly being mediated by the measured environmental variables. Scenario 1 was discarded because none of the observed environmental variables showed a significant habitat effect. Patterns of species richness differed between lagoons and estuaries in accordance with scenario 3; richness was higher in open/closed lagoons than in estuaries. The abundance of three important infaunal species supported scenario 2: these species varied considerably among sites in response to the proportion of different sand fractions. Fine sands, common in all estuaries and in a lagoon, were characterised by polychaetes (Laeonereis acuta and Alitta succinea) whereas coarse sands, found in two lagoons were characterised by a bivalve, Erodona mactroides. Another three species responded to sediment but did not show clear site to site variation in abundance. Lagoons differ from estuaries in their higher site to site variation in sediment composition and in the diversity of community variants: lagoons may therefore increase regional diversity as compared to estuaries. We conclude that sediment type played a strong role in explaining variations in macrofaunal abundance among estuaries and lagoons.

Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

Summary Quantitative tools to describe biological communities are important for conservation and ecological management. The analysis of trophic structure can be used to quantitatively describe communities. Stable isotope analysis is useful to describe trophic organization, but statistical models that allow the identification of general patterns and comparisons between systems/sampling periods have only recently been developed. Here, stable isotope‐based Bayesian community‐wide metrics are used to investigate patterns in trophic structure in five estuaries that differ in size, sediment yield and catchment vegetation cover (C3/C4): the Zambezi in Mozambique, the Tana in Kenya and the Rianila, the Betsiboka and Pangalanes Canal (sampled at Ambila) in Madagascar. Primary producers, invertebrates and fish of different trophic ecologies were sampled at each estuary before and after the 2010–2011 wet season. Trophic length, estimated based on δ15N, varied between 3·6 (Ambila) and 4·7 levels (Zambezi) and did not vary seasonally for any estuary. Trophic structure differed the most at Ambila, where trophic diversity and trophic redundancy were lower than at the other estuaries. Among the four open estuaries, the Betsiboka and Tana (C4‐dominated) had lower trophic diversity than the Zambezi and Rianila (C3‐dominated), probably due to the high loads of suspended sediment, which limited the availability of aquatic sources. There was seasonality in trophic structure at Ambila and Betsiboka, as trophic diversity increased and trophic redundancy decreased from the prewet to the postwet season. For Ambila, this probably resulted from the higher variability and availability of sources after the wet season, which allowed diets to diversify. For the Betsiboka, where aquatic productivity is low, this was likely due to a greater input of terrestrial material during the wet season. The comparative analysis of community‐wide metrics was useful to detect patterns in trophic structure and identify differences/similarities in trophic organization related to environmental conditions. However, more widespread application of these approaches across different faunal communities in contrasting ecosystems is required to allow identification of robust large‐scale patterns in trophic structure. The approach used here may also find application in comparing food web organization before and after impacts or monitoring ecological recovery after rehabilitation.

Influence of habitat structure and mouth dynamics on avifauna of intermittently-open estuaries: A study of four small South African estuaries

Habitat composition was a major factor in determining waterbird species composition and abundance, particularly the area of floodplain and vegetated channel in four intermittently open estuaries (IOEs) in the warm-temperate coastal biogeographical region of South Africa. Average bird densities on the four estuaries varied from 0.5 to 4.2 birds per hectare, and community composition differed significantly between estuaries. However, the considerable variation in abundance of macrophytes did not have a detectable effect on waterbirds. Under closed mouth conditions, piscivorous birds dominated the avifauna. Each estuary's avifauna responded differently in terms of changes in feeding guild composition when the mouth opened. Bird abundance changed immediately after breaching, but not consistently. Diversity was significantly higher under open-mouth conditions for three of the four estuaries, and species composition was significantly different from that under closed-mouth conditions at all four estuaries. Changes in mouth dynamics as a result of climate change, water abstraction and artificial breaching could lead to significant changes in estuarine fauna.

The effects of artificial sandbar breaching on the macrophyte communities of an intermittently open estuary

Artificial sandbar opening of intermittently open estuaries is a practice utilised worldwide to improve water quality, fishing, and recreational amenities and to prevent the flooding of adjacent properties. Breaching causes the water level to drop drastically, exposing plants to two water level extremes. With some exceptions, estuarine communities are adversely affected by this practice. Although breaching can happen naturally, artificial breaching is on the rise, and the impact of manipulating water levels on estuarine communities needs to be investigated. In this work, we described the breaching cycles of the Massaguaçu River Estuary and proposed flooding scenarios for the estuary's macrophyte banks based on our data. We calculated the relationship between plant distribution and flooding conditions and used our calculations to predict the estuary community's composition depending on the water level at breaching time. We discovered a strong relationship between plant distribution and flooding conditions, and we predicted that the estuarine community would be markedly different between flooding scenarios. Low frequency flooding scenarios would be related to submerged macrophytes and, as the flooding frequency increases, macrophytes would be replaced by amphibious plants, and eventually by the arboreal stratus. Therefore, we concluded that an increase in artificial breaching cycles would have a detrimental impact on the estuary community.

Pest Control in Agricultural Plantations Using Image Processing

Monocropped plantations are unique to India and a handful of countries throughout the globe. Essentially, the FOREST approach of growing coffee along with in India has enabled the plantation to fight many outbreaks of pests and diseases. Mono cropped Plantations are under constant threat of pest and disease incidence because it favours the build up of pest population. To cope with these problems, an automatic pest detection algorithm using image processing techniques in MATLAB has been proposed in this paper. Image acquisition devices are used to acquire images of plantations at regular intervals. These images are then subjected to pre-processing, transformation and clustering. I. Introduction Today there are more than 250 organic pesticides and thousands of formulations. The coffee industry unfortunately relies on these poisons to protect the plant and berries from insect attack and disease spread. In some advanced countries aerial spraying of these hazardous chemicals is carried out to save on labour costs. Most, coffee farmers advocate the use of BROAD SPECTRUM pesticides. These are more dangerous than systemic pesticides because they act on many insects both beneficial and harmful. There is every chance that these chemicals can easily drift or get washed or leached by heavy showers and reach groundwater or open estuaries there by contaminating the earth's precious water reserve. However, the cultivation of these crops for optimum yield and quality produce is highly technical. A lot of research has been done on greenhouse agro systems And more generally on protected crops to control pests and diseases by biological means instead of pesticides. Research in agriculture is aimed towards increase of productivity and food quality at reduced expenditure and with increased profit, which has received importance in recent time. A strong demand now exists in many countries for non -chemical control methods for pests or diseases. However no automatic methods are available which precisely and periodically detect the pests on plants. In fact, in production conditions, greenhouse staff periodically observes plants and search for pests. This manual method is time consuming. With the recent advancement in image processing pattern recognition techniques, it is possible to develop an autonomous system for disease classification of crops. In this paper, we focus on early pest detection. First, this implies to regularly observe the plants. Disease images are acquired using cameras or scanners. Then the acquired image has to be processed to interpret the image contents by image processing methods. The focus of this paper is on the interpretation of image for pest detection.

하구 환경관리를 위한 관리구역 경계 설정방안

실질적인 하구환경의 관리를 위해서는 관리구역, 즉 하구역이 먼저 정의되어야 한다. 그러나 하구역의 경계를 설정할 수 있는 과학적 자료의 부족으로 인해 아직까지 체계적인 경계설정 방법이 제시되지 못하고 있다. 본 연구는 하구의 물리화학적 특성 등의 과학적 자료와 더불어 지리 지형적 특성 및 이용개발 특성 등을 종합적으로 고려하여 체계적으로 하구역 경계를 설정하는 방법을 제안하였다. 하구를 하구순환의 유지여부에 따라 열린 하구와 닫힌 하구로 구분하고, 각 유형에 속한 개별 하구에 대해 물리화학, 지리지형학 및 이용개발 특성을 고려하여 하구수역의 경계를 설정한 후에 하구수역에 영향을 미치는 하구육역의 경계를 설정하는 순차적인 방법이다. 이 방법에 따라 국내 274개 하구역의 경계를 시범적으로 설정해본 결과 각 하구별로 가용한 자료의 수준과 지역 특성의 차이를 합리적으로 고려한 하구역 경계 설정이 가능한 것으로 나타났다. Definition of estuary and its administrative boundaries is needed for the practical management of estuarine environment. However, the majority of Korean estuaries are lack of scientific data required for defining the administrative boundaries. For this reason, a systematic way to set the boundaries has not been developed so far. This study proposed adaptive and comprehensive criteria in defining the boundary of an estuary based on the available data which includes physiochemical, geographical and topographical characteristics and regional data such as land uses and socio-economic conditions. An estuary boundary is defined with a sequential manner. First of all, according to the estuarine circulation pattern, 463 estuaries in Korea were classified into open estuaries and closed estuaries. Then an individual belonging to each type of estuary is defined an water zone boundary considering the physiochemical, geographical and topographical characteristics and land uses. Finally, a land zone boundary is set along the catchment. According to the proposed criteria, we have delineated 274 estuarine management zones in Korea on a trial basis and found that it was possible to set a boundary reasonably considering the difference of level of available data and regional characteristics in each estuary.