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Effects of hydrographic conditions of ponds on juvenile fish assemblages in the Kakum mangrove system, Ghana
... The patterns of occurrence of fish fauna in these mangrove ponds are not clear with respect to the prevailing hydrodynamic conditions associated with tidal stages. In the case of adjoining mangrove systems, Levy et al. (2015) established to some extent the water depth preferences for different sizes of fish that may be associated with tidal stages. ...
... This suggests that these species are more tolerant to low dissolved oxygen content and high turbidity conditions that characterised the pond, as well as able to cope with the more variable hydrographic and hydrodynamic conditions that prevail in the channels. This finding is in line with that of Levy et al. (2015), with S. melanotheron and species of Mugilidae as the most abundant in mangrove tidal ponds of the same study area. S. melanotheron being an estuarine species and euryhaline in nature may explain its widespread occurrence within the estuarine mangrove system. ...
... However, with <3% of the individuals belonging to the Mugilidae found to be utilising the pond during the study period, the main mangrove water channel may be the best location for the mullets within the study area. It is also worth noting that the level of occurrence in the pond by mullets in this study is much lower than the findings of Levy et al. (2015). Nonetheless, the number still represents approximately twice as many individuals found in the mangrove channel during this study, compared with that of all the ponds studied in Levy et al. (2015). ...
This study assessed the effects of tidal stages and habitat conditions on nekton assemblage and distribution in the Kakum River estuarine mangrove system in the Central Region of Ghana. Teleosts and crustaceans were sampled using pole seine and cast net from a tidal mangrove pond and a channel, and characterised using morphometry and ecological guilds concept. In total, 1 146 specimens were collected, with 35 species from 19 families represented. The most abundant species encountered were Liza spp. (Mugilidae; 36%), Sarotherodon melanotheron (Cichlidae; 16%), Elops lacerta (Elopidae; 6%) and Sardinella aurita (Clupeidae; 5%), which exhibited pronounced spatial distribution. Sarotherodon melanotheron showed preference for ponds with minimal water flow and depth, Sardinella aurita occurred only in deeper sections of the mangrove channel with significant flow velocity, and Elops lacerta in the pond and all channel stations. Mugilids were found exclusively in the channel, whereas Palaemonidae (Macrobrachium macrobrachion and M. vollenhoveni) occurred in specific locations in the channel, with species- specific preferences for tidal stages. Most species encountered were identified to be predominantly marine migrants with bentophagous feeding habit. Site selection and tidal stages were found to affect the occurrence and distribution of fishes over a tidal cycle and interactively influence species diversity.
... The Kakum Estuary in the Central Region and the Pra Estuary in the Western Region are two such estuaries that have been studied over the years. Previous studies on the Kakum Estuary and mangrove forest mostly sought to characterize and quantify biodiversity (Adotey, 2015;Aheto, Aduomih & Obodai, 2011;Aheto et al., 2014;Okyere, 2010;Sackey, Kpikpi & Imoro, 2011), while some assessed quality of water and sediments (Dzakpasu & Yankson, 2015;Fianko, Osae, Adomako, Adotey & Serfor-Armah, 2007;Koranteng-Addo, Bentum, Awuah & Owusu-Ansah, 2011;Levy, Asare, Yankson & Wubah, 2015;Okyere & Nortey, 2018). Few published literature are available on the ecological parameters of mangroves (see FoN, 2014) and estuarine water quality (Donkor, Bonzongo, Nartey & Adotey, 2006;Okyere, 2015;Okyere & Nortey, 2018) at Pra Estuary, although other works looked at issues concerning conservation of the estuary (FoN, 2015(FoN, , 2016(FoN, , 2017Kankam & Robadue, 2013). ...
Mangrove forests provide a variety of valuable uses and resources for inhabitants of coastal communities. This study was aimed at assessing the health of mangrove forests at the estuaries of Kakum and Pra using multi criteria approach involving social, biological, chemical and physical factors. The study was conducted from March 2017 to August 2018. Socioeconomic data were gathered from 136 respondents through field surveys in ten communities around the two estuaries while remote sensing and Geographic Information System (GIS) were used to characterize mangrove cover change between the period 2005-2017. Species inventory, structural parameters, litter production and soil analyses were estimated in four study plots of sizes 0.25 ha within each mangrove forest whereas physico-chemical parameters of estuarine water were measured in situ. It was observed that coastal inhabitants harvested fuel wood, timber (poles), crabs, periwinkles and tilapia from these mangrove forests. Mangrove area at Kakum reduced by 41.58 % while that of Pra increased by 12.54 %, from 2005 to 2017. A total of 23 and 20 plants species, including five and three true mangroves were encountered at the Kakum and Pra mangrove forests, respectively. The mangrove species had low structural developments in terms of size and height. Annual litter production rate was lower at the Kakum mangrove forest (9.60 t ha-1 y-1) than at the Pra mangrove forest (10.72 t ha-1 y-1). The estuaries and mangrove sediments were of moderate quality. On the basis of computed mangrove health indices (MHI), the overall health of the Kakum mangrove forest was bad, whereas the Pra mangrove forest was moderately healthy. There is the pressing need for stakeholders to institute stringent management measures for sustainable conservation of both forests.
... This mangrove is part of wetland plays an important role for the fishery production of adjacent neritic waters by exporting organic and inorganic nutrients whereas root habitats provide abundant food for the fishes (Nagelkerken et al. 2000;Carr and Adams 1973). Study on the fish assemblage in the mangrove ecosystem had been reported in many parts of the world such as Ghana (Levy et al. 2015) and Brazil (Castellanos-Galindo and Krumme 2014). In Malaysia, limited study has been conducted on mangrove fishes from the east coast of Peninsular Malaysia such as Chong et al. (2010) who identified mangrove fishes in Bachok, Kelantan. ...
The sampling programme was conducted to determine the diversity and abundance in fish assemblages from June 2011 to July 2012 using gill and trawl nets and traps. A total of 13,132 individuals of fishes comprising 116 species and 50 families were recorded. Family Siganidae had the highest family abundance recorded with 43.0%. Siganus javus was determined as the most abundant species with a percentage value of 38.8%. Ninety species were caught and considered to be commercially valuable. Four species were recorded as vulnerable in the IUCN Red List, which were Hippocampus spinosissimus, Hippocampus trimaculatus , Himantura uarnak, and Pegasus laternarius; while Himantura walga, Favonigobius melanobranchus, Favonigobius rechei. Epinephelus coioides , and Epinephelus diachanthus were listed as near threatened. Overall values of diversity, richness and evenness indices were found to be 2.60, 12.12 and 0.55, respectively. Estimates from these indices were an indication of high fish species composition, richness, and evenness in the population of fishes in Setiu wetlands. It is recommended that government should gazette the Setiu Wetlands as a state park in Terengganu for future planning.
... Mangroves are open ecosystems that straddle the land and the sea, from freshwater to seawater, providing diverse habitats for plant and animal species (Li and Less 1997). They are one of the most productive ecosystems in the world and provide a variety of ecological and societal goods and services (Liu et al. 2014), such as nursing fishes (Levy et al. 2015), maintaining biodiversity (Thornton and Johnstone 2015), and absorbing pollution (Debenay et al. 2015). Despite their ecological relevance, mangroves that grow along the latitudinal extremes of their distribution in subtropical and tropical environments are extremely vulnerable to low temperature (Ellis et al. 2006). ...
IntroductionUnderstanding how mangroves respond to rare cold events has implications for both restoration and conservation under climate change scenarios. This study investigated the responses of photosynthesis and activities of key enzymes involving carbon and nitrogen metabolism at different ages of Kandelia obovata to a rare cold event in the winter of 2010. Methods
This study took place on Ximen Island, Zhejiang Province, China. We measured the physiological recovery of 2–3-, 5–6-, 9–10- and 54–55-year-old K. obovata trees after freezing injury in February and March in 2011 and 2012, respectively. ResultsChilling injury index and electrolyte leakage of K. obovata increased with increasing tree age in the winter of 2010, and electrolyte leakage in K. obovata at different ages in the winter of 2010 was far higher than that in the winter of 2011. The rare cold events significantly changed the recoveries of the leaf net photosynthetic rate (Pn) and stomatal conductance (Gs); ratios of chlorophyll a/chlorophyll b (Chl a/Chl b); contents of total soluble sugar (TSS), sucrose, free amino acid (FAA), and soluble protein; and activities of sucrose phosphate synthase (SPS), endopeptidase, and carboxypeptidase in K. obovata at different ages. These effects were mainly due to changes in the physiological mechanism in the 2-year-old trees. A clear decrease in Pn of the 2-year-old trees was observed in February 2011, as exemplified by reductions in ratios of Chl a/Chl b and chlorophyll/carotenoid (Chl/Car), as well as inhibition of the levels of TSS and FAA (osmotic substances). During recovery in 2011 and 2012, the activities of SPS and sucrose synthase (SS) were responsible for sucrose synthesis after the rare cold events in 2011, but only SPS activity was one of the main factors contributing to the metabolism of stachyose to sucrose without cold damage in 2012. Carboxypeptidase played a more important role than endopeptidase during protein hydrolysis after the rare cold events. Conclusions
The results suggest that the recovery of photosynthetic capacity in K. obovata was changed after a rare cold event, which is associated with pigment components and activities of SS, SPS, and carboxypeptidase, especially the seedlings.
This study aims at stimulating the scientific community towards a better understanding of fish community ecology in relation to physico-chemical determinants in unmanaged coastal wetlands relevant for informed decision-making on ecosystem functioning and management in the tropical context. We investigated the diversity, size distribution and food habits of the fish community and the abiotic environmental conditions of the Kakum Estuary wetland in Ghana (5o 6' N; 1o 18'W) from July 2009 to February 2010. Eighteen species belonging to 18 genera and 12 families of marine, brackishwater and freshwater fishes were sampled. The poecilid Aplocheilichthys spilauchen (43.31%), the cichlid Sarotherodon melanotheron (18.12%) and the freshwater shrimp Macrobrachium macrobrachion (12.37%) were dominant. Fish communities in pools in the wetland were quite close in diversity (H' ranged from 2.2 to 2.7) and highly similar (Cs > 0.6) possibly as a result of the prevailing similar environmental conditions. Smaller individuals of the cichlids Tilapia zillii, Hemichromis fasciatus and S. melanotheron measuring 2.0-3.9 cm TL, and marine species such as Elops lacerta and Liza falcipinnis measuring 6.0-7.9 cm TL constituted between 60% and 80% of the populations, suggesting the wetland as nursery and feeding grounds for the fishes. Examination of stomach contents showed that the communities included detritivorous, planktivorous, insectivorous, omnivorous and piscivorous species. It is strongly recommended to restrict fishing in the wetland during the wet season to avoid exploitation of juvenile fishes which use the wetland as nursery and feeding grounds during that period.
In order to enhance ecological knowledge for coastal and mangrove ecosystem conservation in Ghana, the study documents the taxonomic groups of benthic macrofauna and fish assemblages in an urban mangrove swamp as its fundamental objective with emphasis on their composition, richness and diversity. This is because benthic and fish fauna of mangrove habitats are amongst the least studied biota in Ghana. Fish and benthos sampling was undertaken from five randomly selected pools within a mangrove stand during the wet and dry seasons using pole-seine net (7 m long and 1.5 m depth, with stretched mesh size of 5 mm) and an Ekman grab (15 cm × 15 cm dimensions), respectively. All samples were preserved in 10% formalin for laboratory analysis. The results indicated a more diverse macrozoobenthic community in the wet (H¹ = 1.8) than dry season (H¹ = 1.5) . Overall, five out of a total of 13 genera found are intolerant to pollution and four moderately tolerant, while four comprising polychaetes and the midge Chironomus, are pollution tolerant. This suggests that the mangrove habitat is less polluted. A grand total of 917 fish specimens, belonging to 15 species and nine families, were encountered for both seasons (371 and 546 specimens for wet and dry seasons, respectively). The black-chinned tilapia, Sarotherodon melanotheron, was the dominant fish species in the wet season, accounting for 54.2% of the total fish caught, whilst the grey mullets, Mugil babanensis and Mugil curema, were the dominant species in the dry season, with a combined total of 51.4% of the fish population. However, over 70% of these dominant fish species from both seasons were juveniles providing a strong justification for the observation that the mangrove habitats are nursery grounds for fish inhabiting adjacent riverine, estuarine and inshore marine habitats. Considering this relevance of mangroves and the ongoing conversion attempts of mangrove habitats to other land uses, a concerted mangroves conservation effort is strongly advocated.
Organic carbon (OC), total nitrogen (TN) and stable carbon and nitrogen isotopic compositions were meas-ured in suspended particulate matter (SPM) and sur-face sediment along estuaries of Mandovi and Zuari rivers, two small mountainous river systems in western India during wet and dry seasons, to characterize the sources of organic matter (OM) in these systems. Unlike major rivers, SPM concentrations increase sea-ward with a general trend of decreasing particulate organic carbon (POC) in these rivers, mostly due to the presence of estuarine turbidity maximum (ETM) lo-cated downstream of the estuaries. POC and particu-late nitrogen (PN) were higher in the Mandovi than in the Zuari estuary. Except during wet season in the Mandovi, POC/PN and δ 15 N were altered by biogeo-chemical processes in both the estuaries and are not in-dicators of source organic matter. PN/POC and δ 13 C org indicated the dominance of terrestrial plant-derived OM and terrestrial soil-derived OM respectively, in the Mandovi and Zuari estuaries during wet season. The δ 13 C org versus salinity plot indicated increasing propor-tions of marine OM seaward in both estuaries during dry season. OC and TN in the sediments of both estuar-ies were much lower than in the overlying suspended matter. The mean δ 13 C org in the sediment and SPM were similar in both the seasons in Mandovi and only during wet season in Zuari estuary. Uniform mean val-ues of δ 13 C org in the lower estuary and bay of Zuari in-dicated efficient mixing of sediments during wet season. Sediments with relatively high δ 13 C org and low δ 15 N in the upper estuary of Zuari were related to anthropo-genic contamination by sewage effluents during dry season. It is estimated that each river contributed at least ~20% terrestrial organic carbon (TOC) to the coastal system during wet season and received similar quantity of TOC during dry season. Since there are more than 10,000 small rivers originating from mon-soon-dominated and/or mountainous regions globally, it must be appreciated that their total TOC contribu-tion to the coastal system must be substantial. Introduction RIVERS transport sediment as bed load and in suspension, and bed load is usually <10% of the total load 1 . Milliman and Meade 2 , and Degens et al. 3 estimated the annual global river discharge reaching the seas and oceans at 13.5 × 10 15 and 16 × 10 15 g respectively. Data gathered by the SCOPE/UNEP International Carbon Project indi-cate that the particulate organic carbon (POC) in world rivers varied between 1% and 8% of the total suspended matter (TSM). Rivers with low TSM concentrations (<15 mg/l) exhibit the highest relative POC contents, whereas those with high TSM concentrations (500– 1500 mg/l) display the lowest relative POC contents 4 . Although POC from major rivers is mostly from alloch-thonous sources, the sources of POC in the medium (<200 km length) and minor (<100 km length) rivers 5 are yet to be precisely determined. Since there are numerous small mountainous rivers (more than 10,000), Milliman and Syvitski 6 suggested that the sediment contribution from them is grossly underestimated and more research is needed to appreciate their role in discharging sediment. Except the Indus and Narmada–Tapi rivers, all other rivers bringing sediment load to the coastal eastern Ara-bian Sea are moderate and minor-sized and originate in mountainous regions 5 . Run-off from these rivers is high during wet season (monsoon) and negligible during dry (non-monsoon) season. Circulation in the estuaries of these rivers is dominated by tidal and wind-driven currents during dry season. In view of the contrasting seasonal hydrodynamic conditions in these tropical rivers, the river estuaries are expected to show relatively high sus-pended particulate matter (SPM) and reduced production during wet season, and autotrophic production and active biological and geochemical processes during dry season. Here we report organic carbon (OC), total nitrogen (TN)
Mangrove forests prominently occupy an intertidal boundary position where the effects of sea level rise will be fast and well visible. This study in East Africa (Gazi Bay, Kenya) addresses the question of whether mangroves can be resilient to a rise in sea level by focusing on their potential to migrate towards landward areas. The combinatory analysis between remote sensing, DGPS-based ground truth and digital terrain models (DTM) unveils how real vegetation assemblages can shift under different projected (minimum (+9 cm), relative (+20 cm), average (+48 cm) and maximum (+88 cm)) scenarios of sea level rise (SLR). Under SLR scenarios up to 48 cm by the year 2100, the landward extension remarkably implies an area increase for each of the dominant mangrove assemblages except for Avicennia marina and Ceriops tagal, both on the landward side. On the one hand, the increase in most species in the first three scenarios, including the socio-economically most important species in this area, Rhizophora mucronata and C. tagal on the seaward side, strongly depends on the colonisation rate of these species. On the other hand, a SLR scenario of +88 cm by the year 2100 indicates that the area flooded only by equinoctial tides strongly decreases due to the topographical settings at the edge of the inhabited area. Consequently, the landward Avicennia-dominated assemblages will further decrease as a formation if they fail to adapt to a more frequent inundation. The topography is site-specific; however non-invadable areas can be typical for many mangrove settings.
Embryonic development and morphological characteristics of Japanese devil stinger Inimicus japonicus during early life stage were investigated. Larvae were hatched out 50 h after fertilization at temperature 21°C. Total length of the newly hatched larva was 4.03 mm, the mouth of the larva opened at 3 days after hatching (DAH), and the yolk sac of the larva disappeared at 5 DAH. After hatching, the pectoral fin first developed, then the tail fin, dorsal fin, anal fin and pelvic fin continuously developed, and all fins formed completely at 15 DAH. The metamorphosis was complete at 25 DAH, and the body color and habit of the metamorphosed individuals were different from the larvae. At 30 DAH, the morphology and habit of the juveniles were the same to adults. In order to determine the suitable salinity for larviculture of I. japonicus, salinity tolerance at different early developmental stages was compared in terms of the survival activity index (SAI) and mean survival time (MST). The results indicated that salinity tolerance varied with development stages. The optimum salinity range for newly hatched larvae was 10-25‰. Larvae showed low tolerance to low salinity (5‰) before the mouth opened, and the suitable salinities for the larvae with open mouth, yolk-sac larvae, post yolk-sac larvae were 10-15‰. The flexion larvae showed a wider salinity tolerance with range of 5-20‰. After metamorphosis, the juveniles showed a preferable adaptability of salinities of 15-20‰. The SAI and MST of individuals at various stages under different salinity conditions were positively correlated.
A total of 53 species of juvenile fish were caught over a 2 yr study period in 2 mangrove lined estuaries in Moreton Bay, eastern subtropical Australia. Comparing juvenile fish communities among mangrove forests, seagrass beds and mudflats identified significant differences in species richness and abundances of juveniles. Seagrass communities comprised distinct species of resident and nonresident fish species of little economic importance. Mangrove forests and mudflats had many shared species (but mangrove forests were dominated by smaller or younger juveniles in greater abundances; Laegdsgaard unpubl. data). Mudflat habitats appear to be transition zones between juvenile and adult habitats. Only 4 species were exclusive to seagrass whereas 27 species were exclusive to the mangrove/mudflat habitat. Juveniles of 7 of the 10 commercially harvested fish species in Moreton Bay were found in greatest numbers in mangrove forests. Salinity, temperature and turbidity were similar in all habitats so could not account for differences in habitat choice of juvenile fish. Most juvenile fish in mangroves during summer were nonresidents and species richness and abundance were highest in summer and lowest in winter. There were significant differences among sites and years in the numbers of species and individuals; however, the trends were similar and demonstrated clearly that mangrove sites within Moreton Bay play a more important role and have greater potential as nursery habitats than do adjacent habitats. Preferential selection of mangrove habitats by juvenile fish, particularly commercial species, indicates a need for conservation.
Deforestation of mangrove forests is common occurrence worldwide. We examined fish assemblage
composition in three mangrove creek systems in Tanzania (East Africa), including two creeks where the
upper parts were partly clear-cut of mangrove forest due to the construction of solar salt farms, and one
creek with undisturbed mangrove forest. Fish were caught monthly for one year using a seine net (each
haul covering 170 m2) within three locations in each creek, i.e. at the upper, intermediate and lower
reaches. Density, biomass and species number of fish were lower in the upper deforested sites compared
to the mangrove-fringed sites at the intermediate and lower parts in the two creeks affected by deforestation,
whereas there were no differences among the three sites in the undisturbed mangrove creek
system. In addition, multivariate analyses showed that the structure of fish assemblages varied between
forested and clear-cut sites within the two disturbed creeks, but not within the undisturbed creek. Across
the season, we found no significant differences except for a tendency of a minor increase in fish densities
during the rainy season. At least 75% of the fishes were juveniles and of commercial interest for coastal
fisheries and/or aquaculture. Mugil cephalus, Gerres oyena and Chanos chanos were the most abundant
species in the forested sites. The dominant species in the clear-cut areas were M. cephalus and Elops
machnata, which were both found in relatively low abundances compared to the undisturbed areas. The
conversion of mangrove forests into solar salt farms not only altered fish assemblage composition, but
also water and sediment conditions. In comparison with undisturbed areas, the clear-cut sites showed
higher salinity, water temperature as well as organic matter and chlorophyll a in the sediments. Our
results suggest that mangrove habitat loss and changes in environmental conditions caused by salt farm
developments will decrease fish densities, biomass and species numbers as well as alter the overall fish
assemblage composition in the salt farm area but not downstream in the creek.
A stratified study of microhabitat use by grey mullet on the island of Minorca (Balearic archipelago, western Mediterranean) showed that the distribution of all the species was dramatically affected by salinity. Sites with a salinity level under 15 were positively selected in spring and summer by those species whose growth performance was the best in oligomesohaline water (Liza ramado and Mugil cephalus) but also by a species whose growth was not affected by salinity (Chelon labrosus). Liza aurata concentrated in polyhaline and euhaline sites, where growth was improved, a pattern also exhibited by Liza saliens. Both species avoided fresh water sites all year round. As a consequence, community structure was correlated with salinity. The above reported electivity patterns often disappeared in autumn, when most grey mullets migrate off-shore.
Fish were sampled by fyke nets for a year over diel cycles and a seasonal cycle in a subtropical mangrove creek of northern Taiwan. A total of 30 fish species belonging to 18 families were captured; Gobiidae and Mugilidae were the most diverse families. The fish assemblage was dominated by a small number of small-sized and commercially important species. Total fish number and biomass were highly variable and showed little seasonal differences. However, species richness and diversity were significantly higher in fall than in winter-spring. An ordination analysis demonstrated that monthly changes in species composition followed a gradual pattern and showed a clear seasonal cycle. A combination of water temperature and salinity best explained the monthly changes in species composition. Pearson correlations indicated that water temperature was positively correlated, and salinity was negatively correlated, with the species richness and diversity. There were no significant diel differences in total fish number and species richness. However, biomass and diversity were significantly higher at night than during the day. Classification and ordination analyses showed that there were distinct 'day' and 'night' assemblages in winter-spring and fall, but not in summer. Our results suggest that a seasonal cycle was more important than diel cycles in structuring temporal changes in the fish assemblage of a subtropical mangrove creek.
Mangroves, the only woody halophytes living at the confluence of land and sea, have been heavily used traditionally for food, timber, fuel and medicine, and presently occupy about 181 000 km2 of tropical and subtropical coastline. Over the past 50 years, approximately one-third of the world's mangrove forests have been lost, but most data show very variable loss rates and there is considerable margin of error in most estimates. Mangroves are a valuable ecological and economic resource, being important nursery grounds and breeding sites for birds, fish, crustaceans, shellfish, reptiles and mammals; a renewable source of wood; accumulation sites for sediment, contaminants, carbon and nutrients; and offer protection against coastal erosion. The destruction of mangroves is usually positively related to human population density. Major reasons for destruction are urban development, aquaculture, mining and overexploitation for timber, fish, crustaceans and shellfish. Over the next 25 years, unrestricted clear felling, aquaculture, and overexploitation of fisheries will be the greatest threats, with lesser problems being alteration of hydrology, pollution and global warming. Loss of biodiversity is, and will continue to be, a severe problem as even pristine mangroves are species-poor compared with other tropical ecosystems. The future is not entirely bleak. The number of rehabilitation and restoration projects is increasing worldwide with some countries showing increases in mangrove area. The intensity of coastal aquaculture appears to have levelled off in some parts of the world. Some commercial projects and economic models indicate that mangroves can be used as a sustainable resource, especially for wood. The brightest note is that the rate of population growth is projected to slow during the next 50 years, with a gradual decline thereafter to the end of the century. Mangrove forests will continue to be exploited at current rates to 2025, unless they are seen as a valuable resource to be managed on a sustainable basis. After 2025, the future of mangroves will depend on technological and ecological advances in multi-species silviculture, genetics, and forestry modelling, but the greatest hope for their future is for a reduction in human population growth.
This review places the life-history styles of fishes associated with South African estuaries in a global context and presents a classification system incorporating all the major life-history categories for estuary-associated fish species around the world. In addition, it documents the early life histories of the major fish groups in South African estuaries, with particular emphasis on the differing modes of estuarine utilization by marine, estuarine and freshwater taxa.
This review details factors influencing the ichthyofaunal community structure in South African estuaries. The availability of fish for recruitment into an estuary depends primarily upon the distributional range of euryhaline marine and estuarine species, with tropical and temperate taxa showing marked abundance trends. Within a particular biogeographic region, however, estuarine type and prevailing salinity regime have a major influence on the detailed ichthyofaunal structure that develops. There is an increasing preponderance of marine fish taxa when moving from a freshwater-dominated towards a seawater-dominated type of system, and a decline in species diversity between subtropical estuaries in the north-east and cool temperate systems in the south-west. Similar declines in fish species diversity between tropical and temperate estuaries in other parts of the world are highlighted.
Fish assemblages in estuaries adjust constantly in response to changing seasons, salinities, turbidities, etc. Despite persistent fluctuations in both the biotic and abiotic environment, the basic ichthyofaunal structure appears to have an underlying stability and to be predictable in terms of the response of individual species to specific conditions. This stability seems to be governed by factors such as the dominance of eurytopic taxa within estuarine assemblages and the robust nature of food webs within these systems. The predictability arises from factors such as the seasonality associated with estuarine spawning cycles and juvenile fish recruitment patterns. These patterns, together with a well-documented resilience to a wide range of physico-chemical and biotic perturbations, appear to be an underlying feature of fish assemblages in estuaries around the world.
In contrast to marine fish species, estuary-associated taxa have received little conservation attention. Apart from the designation of protected areas, the main direct means of conserving estuary-associated fish stocks include habitat conservation and controls over fishing methods, effort, efficiency and seasonality. Of these, the conservation of fish habitats, the most important, because healthy aquatic environments invariably support healthy fish populations. The use of estuarine sanctuaries for fish conservation is briefly reviewed, as well as the legislation governing the USA National Estuarine Research Reserve System (NERRS) and the Australian Marine and Estuarine Protected Area (MEPA) system. It is concluded that South Africa requires an expansion of the existing Estuarine Protected Area (EPA) network, as well as the upgrading of selected 'estuarine reserves' where fishing is permitted, into 'estuarine sanctuaries' where no exploitation of biological resources is allowed.
Daytime sampling of mangrove and seagrass (Halophila/Halodule community) habitats every 7 wk at Alligator Creek, Queensland, Australia, over a period of 13 mo (February 1985–February 1986) using two types of seine net, revealed distinct mangrove and seagrass fish and crustacean faunas. Total abundance of fish and relative abundance of small and large fish also varied between habitats and seasonally. Post-larval, juvenile and small adult fish captured with a small seine-net (3 mm mesh) were significantly more abundant (4 to 10 times) in the mangrove habitat throughout the 13 mo of sampling. Mangrove fish abundance showed significant seasonality, greatest catches being recorded in the warm, wet-season months of the year. Relative abundances of larger fish (captured in a seine net with 18 mm mesh) in the two habitats varied throughout the year, but did not show a seasonal pattern. At the same site, small crustaceans were significantly more abundant in the mangroves in all but one dryseason sample. Similar comparisons for three riverine sites, sampled less frequently, in the dry and wet seasons of 1985 and 1986, respectively, showed that in general mangrove habitats had significantly more fish per sample, although the relative abundance of fish in mangroves and other habitats changed with season. Crustacean catches showed a similar pattern, except that densities among sites changed with season. Fish and crustacean abundance in mangroves varied among sites, indicating that estuaries differ in their nursery-ground value. The juveniles of two commercially important penaeid prawn species (Penaeus merguiensis and Metapenaeus ensis) were amongst the top three species of crustaceans captured in the study, and both were significantly more abundant in the mangrove habitat. By contrast, mangroves could not be considered an important nursery for juveniles of commercially important fish species in northern Australia. However, based on comparisons of fish catches in other regions, the results of the present study indicate the importance of mangroves as nursery sites for commercially exploited fish stocks elsewhere in South-East Asia.
Analyses of organic matter content, organic carbon, nitrogen, sulfur and granulometric variables were performed on 101 surface sediment samples from Ubatuba Bay in order to investigate the spatial distribution of organic matter, its origin and the relationships among its components. The samples were obtained with a manual corer, from water depths between 1 and 15m during 5 cruises of the R/V "Veliger II'', two months apart. Pearson correlation, regression and Principal Component Analysis (PCA) statistical methods were used to analyze the data. Strong correlations between organic matter and fine sediment fractions were obtained. The PCA revealed at least two main sample groups that reflect the different environmental conditions prevalent in the bay. There is a simple linear relationship between organic carbon content and the organic matter content determined by the calcination technique. Taking into account that the analysis of organic matter content is less expensive and less time consuming than the analysis of organic carbon, the present method of estimation can be useful when fast evaluation of the organic carbon content is needed for samples from similar environments.
Mechanical properties of materials, such as Young's modulus, shear modulus and linear viscoelastic damping, are experimentally measured with a thin-film cantilever shaker. The experimental apparatus consists of a bimorph piezoelectric transducer acting as an actuator to generate base excitation to the cantilever, which is analogous to earthquake causing building vibration. The motion of the cantilever is monitored by a pair of fiber optics to measure the displacements of the fixed end and the sample. Linear viscoelastic properties of the material are measured from the resonant frequencies of the vibrating cantilever. Young's modulus and shear modulus are measured from bending and torsion resonant peaks, respectively. For high loss materials, loss tangent of the materials is obtained from the Lorenzian curve fit around the resonant peak. Material properties at various frequencies are measured by changing the length of the specimens. Furthermore, by introducing crack-like defects, the measured resonances, which may be viewed as a measure of effective moduli, are able to be adopted to locate the crack via the method of system identification.
IntroductionThreats, Costs and BenefitsRehabilitation and RestorationClimate Change and Sea Level Rise
In order to clarify the mechanisms determining fish distribution patterns in a mangrove system on Iriomote Island, in southern Japan, fish assemblage structures were determined by visual observation, along with food abundance and environmental factors, in an area of mangrove roots on the banks, and a bare sand area at the center, within downstream, midstream and upstream portions of a branch creek from the Urauchi River. The fish assemblage structures differed significantly between the area types, with the mangrove-root area supporting a more diverse and abundant fish fauna. A canonical correspondence analysis revealed that the
relationships between fish distribution and their food abundance differed among trophic groups. Benthic crustacean or plant feeders were positively associated with their prey i.e. crabs and macroalgae—in other words, these trophic groups were abundant in downstream and/or midstream mangrove-root areas in which their prey were also particularly abundant. However, zooplankton feeders did not show such relationships, their abundance being positively associated with fine sediment particles (characteristic of areas with weak water movement). These results suggested that food availability is a major factor determining the distribution patterns of benthic crustacean feeders and plant feeders, whereas for zooplankton feeders other factors, such as sheltering effects against water current and/or predators, may be more significant.
Behaviors, activity budgets, and spatial locations of reef-associated schoolmaster snapper (Lutjanus apodus) and non-reef-associated checkered puffer (Sphoeroides testudineus) were cataloged in mangrove forests in Caribbean Honduras to see how and where they spent their time and whether this changed as they grew. For schoolmasters, swimming was the most common behavior, while checkered puffers spent the majority of their time resting. Both remained completely within (as opposed to outside) the mangrove roots and in the lower half of the water column most of the time. However, as the size of the fish increased there was a clear decrease in the time spent both within the root system and closer to the substrate; the larger fish spent more time higher up in the water column and outside the root system. This was observed in both the schoolmaster and the puffer; the schoolmaster subsequently moves to reefs while the puffer does not. Coupled with limited feeding, the results suggest a primarily protective function for mangroves.
Abundances and size-frequency distributions of common epibenthic fish and crustaceans were compared among 3 depth zones (1-35, 35-70, 71-95 cm) of the Rhode River, a subestuary of Chesapeake Bay, USA. In the absence of submerged aquatic vegetation (SAV), inter- and intraspecific size segregation occurred by depth from May to October, 1989-1992. Small species (Palaemonetes pugio, Crangon septemspinosa, Fundulus heteroclitus, F. majalis, Rhithropanopeus harrisii, Apeltes quadracus, Gobiosoma bosci) were most abundant at water depths < 70 cm. Furthermore, the proportion of small individuals decreased significantly with depth for 7 of 8 species, with C. septemspinosa being the exception, exhibiting no size change with increasing depth. These distributional patterns were related to depth-dependent predation risk. Large species (Callinectes sapidus, Leiostomus xanthurus, and Micropogonias undulatus), known predators of some of the small species, were often most abundant in deep water (> 70 cm). In field experiments, mortality of tethered P. pugio (30 to 35 mm), small F. heteroclitus (40 to 50 mm), and small C. sapidus (30 to 70 mm) increased significantly with depth. We hypothesize that predation risk was size-dependent, creating the observed intra- and interspecific size differences among depth zones. For C. septemspinosa, burial may modify this size-dependency and create the unusual absence of intraspecific size increase with depth. Historically, P. pugio and Fundulus spp, (and other small species) were not restricted to shallow (< 70 cm) waters and were abundant in deeper SAV beds, which provided a structural refuge from predators. Since the recent demise of SAV in Chesapeake Bay, our results indicate many small species have shifted their distributions and now utilize primarily shallow water as an alternate refuge habitat.
Coastal wetlands are transition zones between terrestrial marine and aquatic habitats; consequently they exhibit relatively unique habitat and species diversity. Estuaries, deltas, and lagoons are among the most biologically productive but least understood ecosystems in the world. In the recent past, the world’s coastal wetlands have been drained and destroyed by conversion to agricultural land, or by industrial and urban development. Wetlands have often been overlooked or misunderstood, but scientists and coastal managers are learning that these ecosystems provide essential services. Such services include the storage of runoff, denitrification and detoxification of polluted water, prevention of shoreline erosion, and they serve as important breeding and feeding grounds for fish, shellfish, and birds. Ghana’s 550 km of coastline includes over one hundred estuaries and lagoons. These coastal wetlands are on the boundary of two major migration corridors for waterbirds: the East Atlantic Flyway and the Mediterranean Flyway. Studies by the Save the Sea Shore Birds ‐ Project and the Ghana Wildlife Society dating back to the early 1980s, have shown that significant numbers of waterbirds use Ghana coastal wetlands as staging areas and wintering grounds. At least 15 species of waterbirds occur here in internationally important populations (Ntiamoa-Baidu 1991). Five coastal lagoons and their watersheds along the Ghana coast have been proposed as Ramsar sites (internationally important wetlands) under the Convention on Wetlands of International Importance (Ramsar Convention). In 1992, the government of Ghana received support from the Global Environment Facility (GEF) for the protection of these sites (Muni-Pomadze, Densu delta, Sakumo, Songor, and Keta) under the Coastal Wetlands Management Project (CWMP), which is implemented by the Ghana Wildlife Department. The CWMP seeks to preserve the ecological integrity of these five coastal wetlands, and to enhance the socio-economic benefits that these wetlands provide to the local communities (Ntiamoa-Baidu and Gordon 1991; Piersma and Ntiamoa-Baidu 1995). To fulfil the CWMP’s goals, baseline information on the ecological health and integrity of these wetland ecosystems is required before sound management decisions can be made. Toward that end, the CWMP has implemented a series of baseline ecological studies aimed at characterizing the current status of these
This aper examines the status of the tilapia fishery in Fosu Lagoon at Cape Coast, inthe Central Region of GLana (5°07’ N,1°6’ W). The blackchin tilaia, Sarotherodon melanotheron (Rüppel), constitutes about 90 % by weight of the total fish catch, and the annual yield of 452—664 kg/ha is apreciably higher than those reported for other tropical lagoons. Variations in the CPUE (0·30—0·96 kg/man-h) were related to fluctuations in the water level of the lagoon. Using the ELEFAN method, estimates of the growth and mortality parameters, based on length-frequency data were: Loo = 16·1 cm TL, K = 0·82/ yr, Z = 4·95/yr, M = 1·90/yr and F = 3·05/yr. The growth estimates and the maturity-length ratio suggest that the population is stunted. The mean length at first capture(Lcso) was estimated to be 6·2 cm TL. Although the present rate of exploitation (E= 0·62) appears high, an analysis of the relative yield-er-recruit (Y/R) and highrecruitment shows that this exploitation rate can be maintained by the Egoon population. Recruitment occurs throughout the year with two peaks, and this probably ensures the sustenance of the high yield.
The population changes of nine species of fish from a mangrove swamp near Port Harcourt, Nigeria, including species of Tilapia, Sarotherodon, Aplocheilichthys, Porogobius and Yongeichthys are described. The most important factor affecting the fish populations is salinity.
Juvenile mugilid fishes, Liza falcipinnis, L. dumerilii, Mugil bananensis and M. curema, which enter the Elmina Lagoon in the Cape Coast District of Ghana, have a similar diet comprising mainly bacteria, diatoms, blue-green/green algae, protozoans, detritus and particulate organic matter. No seasonal changes in the diet and feeding activity were observed. The relative gut length (intestine to standard length ratio) and diet showed no significant changes with size of fish in all the species. All four species were diurnal feeders, but their peak feeding times differed. Interspecific competition for food was possibly limited by species preferences for substrate particles of particular size range and differences in feeding chronology.
Conducted in subtropical coastal waters of eastern Hong Kong, this study provides information on species compositions of juvenile fish communities in several mangrove and non-mangrove habitats, and evaluated the influences of water temperature, salinity, turbidity, sediment organic matter (SOM), water depth, and sediment grain size on fish assemblages. In total, 85,427 fish belonging to 76 species from more than 29 families were collected. Fish densities were higher in mangrove mudflats than in non-mangrove habitats, but only a few of the dominant species were significantly more abundant in mangrove than in non-mangrove habitats. Fish assemblages in mangrove and non-mangrove mudflats were quite similar. Fish compositions were influenced by environmental factors including the SOM and water depth, but not by the presence of mangroves. The present study suggests that the nursery function of mangroves is both site- and species-specific. Compared to shallow mudflats with and without mangroves, deep-water sandy beaches may be less suitable for juvenile fish because of their low SOM content and high piscivorous fish abundances. More studies need to be conducted before definitive conclusions can be made on the nursery function of mangroves in Hong Kong and subtropical Asia.
Sediment traps with 0.5 and 1.15 m2 apertures which are capable of collecting 12–25 samples at programmed intervals, typically weekly or bi-monthly, during one continuous semi- to interannual deployment have been developed. They utilize a number of new synthetic materials and stable metallic components which ensure reliable, long-lasting performance at any oceanic depth. The key component of the trap is a set of sequentially rotating samplers which is driven by a microprocessor-controlled electronic stepping motor. The electronic power controller controls sampler exchange with a high degree of flexibility and precision, as well as independently recording the executed sampling events. Each sampling bottle is sealed from ambient water during the time samples are stored before recovery. After continuous improvement and modification during 29.5 deployment-years of application in deep ocean experiments since 1982, we are convinced that these sediment traps can provide a relatively large quantity of settling particles in time-series with high experimental reliability.
European intertidal salt marshes are important nursery sites for juvenile fish and crustaceans. Due to the increasing threat of habitat loss, the seasonal changes of salt marsh fish communities need to be understood in order to appreciate the ecological and economic importance of the saltmarsh habitat. This study was the first in Great Britain to investigate the seasonal changes of salt marsh fish communities and the variation in community structure between closely located marsh habitats. Between February 2007 and March 2008, five marshes on three estuaries of the Essex coastline were sampled using flume nets to block off intertidal creeks at high tide. Fourteen fish species were caught. The community overall was dominated by three species that made up 91.6% of the total catch: the common goby Pomatoschistus microps (46.2% of the total catch), juvenile herring Clupea harengus (24.3%), and juvenile and larval sea bass Dicentrarchus labrax (21.2%). Cluster analysis demonstrated clear seasonal patterns, with some community structures unique to specific marshes or estuaries. The marsh fish community shifts from a highly diverse community during spring, to a community dominated by D. labrax and P. microps in autumn, and low diversity during winter months. Gravimetric stomach content analysis of fish community identified three main trophic guilds; macroinvertivores, planktivores and omnivores. The macroinvertivore feeding guild contained D. labrax and P. microps, the two most frequently occurring species. This investigation demonstrates the importance of British salt marshes as nursery habitats for commercial fish species.
Mangroves are defined by the presence of trees that mainly occur in the intertidal zone, between land and sea, in the (sub) tropics. The intertidal zone is characterised by highly variable environmental factors, such as temperature, sedimentation and tidal currents. The aerial roots of mangroves partly stabilise this environment and provide a substratum on which many species of plants and animals live. Above the water, the mangrove trees and canopy provide important habitat for a wide range of species. These include birds, insects, mammals and reptiles. Below the water, the mangrove roots are overgrown by epibionts such as tunicates, sponges, algae, and bivalves. The soft substratum in the mangroves forms habitat for various infaunal and epifaunal species, while the space between roots provides shelter and food for motile fauna such as prawns, crabs and fishes. Mangrove litter is transformed into detritus, which partly supports the mangrove food web. Plankton, epiphytic algae and microphytobenthos also form an important basis for the mangrove food web. Due to the high abundance of food and shelter, and low predation pressure, mangroves form an ideal habitat for a variety of animal species, during part or all of their life cycles. As such, mangroves may function as nursery habitats for (commercially important) crab, prawn and fish species, and support offshore fish populations and fisheries. Evidence for linkages between mangroves and offshore habitats by animal migrations is still scarce, but highly needed for management and conservation purposes. Here, we firstly reviewed the habitat function of mangroves by common taxa of terrestrial and marine animals. Secondly, we reviewed the literature with regard to the degree of interlinkage between mangroves and adjacent habitats, a research area which has received increasing attention in the last decade. Finally, we reviewed current insights into the degree to which mangrove litter fuels the mangrove food web, since this has been the subject of longstanding debate. Yes Yes
Three hypotheses to discern the strong positive association between juvenile fish and mangrove habitat were tested with field and laboratory experiments. Artificial mangrove structure in the field attracted slightly more juvenile fish than areas without structure. Artificial structure left to accumulate fouling algae attracted four-times the total number of juvenile fish than areas without structure or areas with clean structure. Community composition of fish attracted to structure with fouling algae was different when compared with areas with no structure or clean structure; five species were attracted by structure with fouling algae whilst two species were associated with structure regardless of fouling algae. Algae were linked to increased food availability and it is suggested that this is an important selection criteria for some species. Other species were apparently attracted to structure for different reasons, and provision of shelter appears to be important. Predation pressure influenced habitat choice in small juvenile fish in laboratory experiments. In the absence of predators, small juveniles of four out of five species avoided shelter but when predators were introduced all species actively sought shelter. Large fish were apparently less vulnerable to predators and did not seek shelter when predators were added to their tank. Feeding rate was increased in the mangrove habitat for small and medium-sized fish compared with seagrass beds and mudflats indicating increased food availability or foraging efficiency within this habitat. Larger fish fed more effectively on the mudflats with an increased feeding rate in this habitat compared with adjacent habitats. The most important aspect of the mangrove habitat for small juvenile fish is the complex structure that provides maximum food availability and minimises the incidence of predation. As fish grow a shift in habitat from mangroves to mudflat is a response to changes in diet, foraging efficiency and vulnerability to predators.
Effects of changing environments of riverside mangroves, coastal land uses, and water quality on fish communities were studied in Bangphra and Thaprik creeks, Trat Bay, Thailand. Regression analysis revealed that fish species richness in the wet season had a negative relationship with water transparency, nitrate, and phosphate and a positive relationship with zooplankton. In the dry season, species richness had a negative relationship with nitrate and phosphate and a positive relationship with salinity, pH, and zooplankton. Abundances and species richness of fish declined over distance from downstream to upstream in both creeks. Riparian mangroves and water quality also declined with distance upstream in both creeks. Results from one-way analysis of variance and Tukey's HSD test revealed that the highest zooplankton volume with the lowest amounts of nitrate and phosphate were observed at the downstream station in both creeks in each season. Low zooplankton volume with high amounts of nitrate and phosphate were found at the midstream and upstream stations of the creeks. The midstream and upstream stations of Bangphra Creek had low to moderate abundance of mangroves along the riversides, whereas shrimp farms were mainly found along the riversides at the midstream and upstream stations of Thaprik Creek. Correlation analysis results of land-use types and the significant habitat factors were discussed. This study found that mangrove degradation, shrimp farming, and residential and agricultural areas altered water quality and the health of fish habitats, causing the decreases in fish abundance and species richness.
Use of food resources by detritivorous fish in floodplains: A synthesis
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