Runoff from acid sulfate soils (ASS) has large negative environmental and economic impacts on est... more Runoff from acid sulfate soils (ASS) has large negative environmental and economic impacts on estuarine ecosystems. Oysters display reduced abundance, growth rate and shell thickness when exposed to ASS runoff, yet the molecular underpinnings of their responses have not been explored. We hypothesized that the proteomes of wild Sydney rock oysters, Saccostrea glomerata, would differ between populations that are recurrently exposed to and that are unaffected by runoff from ASS. We used two-dimensional electrophoresis to compare protein abundances in the gills of S. glomerata collected from two sites close to (acidified) and two sites away from (reference) major ASS outflow drains in a south-east Australian estuary. Approximately 5 % of the proteome was differentially expressed between oysters from acidified and reference sites, with 5 protein spots more abundant and one less abundant at the sites close to drains. Another protein spot was present only in oysters from reference sites. This study has provided the first screening of spatial variation in the protein expression of S. glomerata with respect to discharge from ASS. Altered protein expression may underpin short-term inducible responses to ASS runoff, or genetic resistance acquired through recurrent exposure of populations to the stressor.
Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed ... more Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed abundance and have fewer smaller individuals than unaffected populations, despite having similar recruitment levels to unaffected sites during dry periods. We examined how the timing and duration of exposure to ASS runoff influences the growth and survival of successfully settled oysters. We predicted that among 6-month-old oysters, growth and survival would be (1) lower among individuals continuously exposed to ASS-acidified waters than those that are episodically exposed, and (2) most negatively affected during rainfall events, which enhance transport of ASS runoff to estuaries. Six-month-old Sydney rock oysters, Saccostrea glomerata, were deployed at ASS-affected and unaffected sites within each of two south-east Australian estuaries. After 10 weeks, oysters were transplanted within and across sites in an estuary and maintained in situ for another 10 weeks. Oysters that remained for 20 weeks at ASS-affected sites grew at just over half the rate of oysters at reference sites. Oysters transplanted from acidified to reference sites grew more than oysters transplanted from reference to acidified sites or oysters that remained at reference sites. Unexpectedly, overall oyster mortality was low. Greater rainfall, and hence a lower pH, is likely to have accounted for the greater impact of acidification on growth during the second 10 weeks. Where oysters recruit to a 6-month age cohort, they may be able to tolerate subsequent, moderate, acidification events. Reduced growth during acidification periods may be offset by positive growth during intervening dry periods.
Short-term experiments exposing calcifying organisms to acidification have revealed altered growt... more Short-term experiments exposing calcifying organisms to acidification have revealed altered growth and strength of their exoskeletons. We tested the hypothesis that multi-generational exposure to sustained estuarine acidification from runoff from acid sulfate soils (ASS) would (1) reduce the shell strength of sessile or relatively immobile wild benthic invertebrates and (2) as a consequence render these invertebrates that rely on armour for anti-predator defence more susceptible to generalist benthic predators. First, we compared the force required to break the exoskeletons of Saccostrea glomerata, Bembicium auratum and Heloecius cordiformis between replicate south-east Australian mangrove forests close to (acidified) and away from (reference) major ASS outflow drains. Second, we assessed differences in the susceptibility of oysters from acidified and reference forests to predation by the generalist muricid gastropod, Morula marginalba. Mollusc shells were significantly weaker at ASS-affected than at reference sites but the strength of crab carapaces was not influenced by acidification. Oysters from acidified sites were consumed by M. marginalba at a faster rate than oysters from reference sites in choice and no-choice experiments because M. marginalba required less time to drill through weaker shells. Many other predators, such as crabs, are generalist feeders that consume prey at rates inversely proportional to their shell strength. Hence, in the absence of effects of acidification on the ability of these predators to consume prey, molluscs at acidified sites may also be more susceptible to other such predators. This study highlights how human stressors can rapidly alter predator-prey interactions that have evolved over many years.
Runoff from acid-sulphate soils (ASS) is increasingly threatening the structure and function of e... more Runoff from acid-sulphate soils (ASS) is increasingly threatening the structure and function of estuarine ecosystems worldwide. Along the east coast of Australia, sulphuric acid is known to affect the growth and survival of mangrove saplings, but impacts of ASS runoff on the structure and function of established mangrove trees are unclear. Pneumatophores, the aerial roots produced by some species of mangrove, are critical sites of gas exchange, allowing these species to persist in waterlogged soils. They also provide physical structure in estuarine sediments, facilitating communities of algae, invertebrates and, at high tide, fish. We tested the hypotheses that Avicennia marina pneumatophores would be less abundant, shorter, thinner and weaker close to major ASS outflow drains. Sampling at sites close to and away from drains within each of two estuaries of New South Wales, Australia, showed no effect of exposure to runoff on pneumatophore density or thickness. Pneumatophores were, however, shorter (~2 cm) and weaker (up to 2-fold) at ASS-affected than reference sites. Although the reduced length and strength of pneumatophores at acidified sites may limit the number of epifaunal molluscs they can support, the persistence of dense pneumatophores indicates that the capacity for their facilitation of invertebrates and fish remains.
Acid sulphate soils (ASS), which occur on floodplains worldwide, pose a significant threat to est... more Acid sulphate soils (ASS), which occur on floodplains worldwide, pose a significant threat to estuarine ecosystems. In laboratory and field experiments, naïve calcifying organisms that are exposed for even short periods (1e2 mo) to runoff from ASS suffer 80% mortality and slowed growth. Based on these observations we expected that sampling of wild oyster, gastropod and crab populations at sites close to and away from drains discharging ASS runoff would reveal more depauperate populations, of sparser and smaller-sized individuals at the more acidified sites. Sampling within three estuaries of New South Wales, Australia, confirmed that the oyster Saccostrea glomerata and gastropods (primarily Bembicium auratum) were less abundant at ASS-affected than reference sites. Nevertheless, crab abundances did not differ between the acidified and reference sites and impacts to bivalves and gastropods were far smaller than predicted. Although at ASS-affected sites gastropod populations were dominated by smaller individuals than at reference sites, oyster populations were skewed towards larger individuals. Even at ASS-affected sites, oyster and gastropod abundances were within the range encountered in estuaries that are not influenced by ASS runoff. Behaviour, long-term physiological acclimation or genetic selection may be responsible for differences in the responses of wild and naïve macroinvertebrates to acidification. Alternatively, wild populations may exhibit some recovery between the rainfall events that transport ASS runoff into estuaries, despite the persistently lower pH near outflow drains. Irrespective, this study suggests that at the population level, calcifying organisms display a certain degree of natural resistance to recurrent disturbance from ASS runoff.
Constructed wetlands, especially mangroves, have been studied for their usefulness in sewage trea... more Constructed wetlands, especially mangroves, have been studied for their usefulness in sewage treatment but the effects of mangrove vegetation and a sewage load on mangrove macrofauna have been given little attention. Ocypodid crabs are important components of mangrove forests and constitute good bioindicators of the functioning of the ecosystem as a whole. In constructed mangrove mesocosms, three vegetation treatments (bare substratum, and Avicennia marina and Rhizophora mucronata seedlings) were subjected to 0, 20, 60 and 100% sewage loads from a nearby hotel. The physiological condition of introduced Uca annulipes and Uca inversa was evaluated in terms of their RNA/DNA ratio after one, five and twelve months, and used as an indicator of ecological function in the system. Crab condition in 0% sewage load was similar to that of wild crabs throughout, suggesting no significant effects of the mesocosms on their RNA/DNA ratio. Overall, both species coped well with the administered sewage loads, suggesting good ecological function in the system. Both species manifested similar patterns in RNA/DNA ratio, being more affected by seasonal fluctuations than by sewage load and vegetation presence and type. Higher RNA/DNA ratios were recorded in the long compared to the short rainy season. Sewage enhanced crab condition in the bare substratum and R. mucronata treatments, especially after one year, probably as a result of enhanced food availability. Uca inversa may be more sensitive to sewage pollution than U. annulipes. In A. marina, no difference in crab condition was observed between sewage loads, and this mangrove yielded the best reduction in sewage impacts. Our results support the usefulness of constructed mangrove areas in sewage treatment, especially if planted with A. marina and inhabited by physiologically healthy ocypodid crabs to enhance the system’s performance.
Estuarine and nearshore marine areas are vital habitats for several fish and benthic invertebrate... more Estuarine and nearshore marine areas are vital habitats for several fish and benthic invertebrates. The shore crab Carcinus maenas (Crustacea: Brachyura: Portunidae) inhabits a variety of coastal, estuarine and lagoon habitats. At low tide, habitat structural complexity may be most important for crabs in the intertidal, providing refuge from predation and desiccation. The quality of different vegetated and nonvegetated estuarine and rocky shore habitats in SW Portugal and SW England was evaluated for intertidal C. maenas populations. We estimated population density, size–structure, and potential growth (RNA/DNA ratios) to investigate habitat quality. Vegetated estuarine habitats supported higher crab densities, than nonvegetated estuarine and rocky shore habitats. Investigation of population size–structure revealed that all habitats seem important recruitment and nursery areas although estuarine habitats in SW Portugal appeared to support higher densities of new recruits than equivalent habitats in SW England. Significant variation was found in RNA/DNA ratios among habitats. Ratios were highest in the rocky shore suggesting a high quality habitat where growth potential is high. We speculate that competition from other top-predators (Pachygrapsus spp.) rather than low habitat quality may limit the occurrence of C. maenas in intertidal rocky shore habitats in SW Portugal. In estuarine environments RNA/DNA ratios were significantly higher in the vegetated than in the nonvegetated estuarine habitats in SW Portugal but not in SW England, suggesting geographic differences in the extent to which highly structure habitats represent high quality. Our results challenge the current paradigm that structured habitats are necessarily those of higher quality for C. maenas.
1. Pollution of mangrove ecosystems puts their future and that of local communities at risk. Only... more 1. Pollution of mangrove ecosystems puts their future and that of local communities at risk. Only the use of informed and integrative approaches will successfully maintain and restore these valuable ecosystems. 2. Biochemical indicators of organism physiological condition have been widely used to evaluate habitat quality and for early detection of the impact of stressors. Mangrove crabs may be useful bioindicators of the quality of mangrove habitats, as they are characteristic and ecologically important organisms in mangrove environments. 3. The physiological condition (evaluated by the RNA/DNA ratio) of Perisesarma guttatum (Grapsidae) and Uca annulipes (Ocypodidae) was assessed to determine its potential as an indicator of habitat quality in one polluted and two relatively unpolluted Mozambican mangroves, during the rainy and dry seasons. 4. Both species showed seasonal effects on RNA/DNA ratio, but only U. annulipes was significantly affected by pollution. RNA/DNA ratio of U. annulipes may thus be a useful indicator of pollution and seasonality in mangrove habitats. There was a synergistic negative effect of the rainy season and pollution on the RNA/DNA ratio of U. annulipes. Due to higher DNA, rather than lower RNA contents, the RNA/DNA ratio of P. guttatum was always significantly lower than that of U. annulipes. 5. The knowledge gathered in this study can be used in integrative strategies, policies and programmes aiming to sustain, maintain and restore mangrove areas, and for the evaluation of mangrove habitat quality.
Cannibalism is a potentially important factor in the regulation of populations in a range of habi... more Cannibalism is a potentially important factor in the regulation of populations in a range of habitats. The intensity of this biotic factor may be determined by both intra and interspecific interactions. Cancer pagurus and Porcellana platycheles are two co-occurring decapods on Atlantic rocky shores. In laboratory mesocosms, we investigated intra and intersize class cannibalistic and interspecific predatory behaviours in those species. We addressed the effects of prey and predator densities, food, starvation, alternative prey and habitat type. No agonistic behaviour was noted in P. platycheles, suggesting a non-aggressive co-existence between gregarious individuals. Predation of C. pagurus on P. platycheles was intense, possibly accounting for the spatial segregation observed in the natural environment. Cannibalism among C. pagurus juveniles was low and only on vulnerable prey (i.e. at moulting), suggesting a non-aggressive co-existence among juveniles. However, intersize class cannibalism in C. pagurus was intense (ontogenetic shift), possibly reflecting the juvenile-adult segregation in the natural environment. Prey and predator densities, food and habitat type strongly influenced this behaviour. Possible interference among cannibals was noted, with lower prey consumption at high predator density. Food supply alone had more effect on cannibalistic rate than did alternative prey (P. platycheles) and predator starvation. structurally complex habitats (small pebble and Fucus serratus habitats) yielded higher prey survival than the sandy habitat, and the behaviours of both prey and cannibals reflected the small-scale spatial distribution of individuals in the wild. Intersize class cannibalism and interspecific agonistic relationships may account for the intertidal distribution of crab species at low tide.
Post-settlement processes can regulate the size and structure of marine invertebrate and fish pop... more Post-settlement processes can regulate the size and structure of marine invertebrate and fish populations. Faster growth and better physiological condition generally increase the survival potential of early juveniles, being usually associated with structurally complex habitats. Successive cohorts of early juvenile Carcinus maenas were followed in sandy and seagrass (Zostera noltii) habitats in the Mira Estuary, Portugal, to estimate growth and physiological condition (evaluated by RNA/DNA ratio) of juvenile populations. Mean cohort growth was similar in both habitats. However, in the sandy habitat, population size structure progressed to cohorts of larger carapace width (CW) and the RNA/DNA ratio was always higher than in the Z. noltii habitat. In this habitat, cohorts of low CW prevailed throughout and RNA/DNA ratio only increased after ∼5.0mmCW. Higher densities characterising seagrass areas may result in higher competition for resources, limiting growth and condition and leading to dispersal to less populated habitats. Larger juveniles had the best physiological condition, especially early in the season. Seagrass habitats do not necessarily yield enhanced growth rates and physiological condition of early juvenile crabs in relation to sandy areas. Knowledge of such trends is vital to understand distribution and abundance patterns of fish and marine invertebrate populations.
The current conceptual model of reinvasion and settlement for estuarine brachyuran crabs in mesot... more The current conceptual model of reinvasion and settlement for estuarine brachyuran crabs in mesotidal systems is that megalopae undergo selective tidal stream transport, in an upstream direction, and settle by the end of the flood tide. Recent studies on recruitment processes of Carcinus maenas (L.) have reported a clear decoupling between supply, as larval influx, and settlement events in the lower Mira Estuary (SW Portugal). We investigated, at high temporal resolution, whether overestimation of planktonic abundances and/or deviations of megalopal responses from the conceptual model were responsible for such decoupling. Daily settlement of megalopae was analyzed using regression and spectral analyses to identify periodicities and correlated with tidal amplitude. Hydrological parameters and supply, net flux and hourly concentration of megalopae in the plankton were addressed as factors influencing short, intermediate and long-term settlement, through 50 h sampling series. Supply and surface net flux levels of megalopae were similar and clearly decoupled from settlement on bottom-deployed collectors. Both hourly planktonic concentration and settlement patterns of megalopae fitted the conceptual model at high temporal resolution, with some deviations in terms of light intensity influences. Furthermore, our results suggest that processes preventing settlement and capable of overriding the influence of light intensities—such as turbulence—may explain the decoupling between supply and settlement of shore crab megalopae in the lower Mira Estuary.
Journal of Experimental Marine Biology and Ecology, Jan 1, 2007
Settlement patterns of decapod crustaceans are influenced by size, shape and nature of substrates... more Settlement patterns of decapod crustaceans are influenced by size, shape and nature of substrates, as well as by species-specific behaviour patterns. Hog's hair filter material is one of the most commonly used artificial substrates in the study of settlement rates. However, the use of hog's hair collectors in settlement studies poses several problems: movement restriction of settled animals, relatively long and complicated laboratory processing time, and cost and decreasing availability. Despite widely used, no consistent investigation has focused on the influence of size and shape of hog's hair collectors on rates of benthic settlement. A first experiment was set to investigate the effects of collector patchiness on settlement abundances of Carcinus maenas megalopae. Benthic hog's hair collectors of different sizes were deployed intertidally in the lower Mira Estuary. Settlement was addressed as ind collector−1 and ind m−2 in relation to collector' surface area and perimeter:area ratio. Results showed that collector patchiness significantly influenced settlement response of C. maenas megalopae, which differed according to settlement intensity and measure. Megalopae settlement responded to lower scales of habitat patchiness at high than at low intensity. Settlement as ind collector−1 generally increased, while as ind m−2 generally decreased, with increasing collector' surface area (decreasing perimeter: area ratio). A second experiment investigated the efficiency of plastic grass, as a new type of artificial surface, in estimating settlement patterns of C. maenas megalopae, and compared it with that of hog's hair. Collectors of both types were deployed daily and intertidally in the lower Mira Estuary. Settlement showed the same pattern and intensity on both collector types. Plastic grass collectors constitute a good alternative to those of hog's hair, possessing several advantages over them.
Crabs are amongst the most conspicuous and ecologically important organisms inhabiting nearshore ... more Crabs are amongst the most conspicuous and ecologically important organisms inhabiting nearshore environments. Their complex life cycle and bioindicator capacity makes them good models for the study of distribution and abundance patterns of marine fish and benthic invertebrate populations. Such knowledge is essential for explaining species occurrence and demographic patterns, predicting the success of biological indicators and controls, as well as for conservation and management purposes of exploited populations and ecosystems. In this study, the impacts of specific environmental constraints at different life phases of estuarine and coastal crabs on population structure and physiological condition were evaluated and related to habitat quality. During settlement and recruitment events, the patchiness of artificial substrates significantly influenced settlement estimation, and strong water currents might have resulted in a decoupling pattern between supply and settlement. Estuarine sandy habitats presented higher quality for early recruits than seagrass ones. In fact, vegetated habitats were not of higher quality for crab populations than non-vegetated and rocky-shore ones. Adult-juvenile cannibalism showed potential to structure intertidal crab assemblages, especially under shortage of food and refuge. Interestingly, mangrove crabs were more affected by climatic season than by pollution, and coped well with several combinations of vegetation and sewage load. Specific constraints of different life stages, individually and in combination, must be considered for full understanding distribution and abundance patterns of crab populations. Furthermore, the relative importance of a specific constraint is likely to change throughout ontogenesis, and the mechanisms by which it interacts with other environmental variables and processes, sometimes synergistically, have also to be considered. This study constitutes an extension to the knowledge on population structure and physiological condition of coastal and estuarine crabs and other marine invertebrate and fish species, and on their use as indicators of ecological status of habitats and ecosystems.
The abundance of the wiskered sole Monochirus hispidus in the Sado Estuary showed a marked season... more The abundance of the wiskered sole Monochirus hispidus in the Sado Estuary showed a marked seasonal pattern, the highest densities occurred in spring and summer. The density of this species was mainly related, non-linearly, to depth, water transparency and percentage of gravel, fine sand and mud in the sediment. Monochirus hispidus fed mainly on crustaceans and polychaets. Significant differences were found between the proportions of prey items eaten and total length class; larger fish consumed more decapods and polychaets. The von Bertalanffy growth equation coefficients differed between sexes. The asymptotic length L1 obtained for females was higher compared to males, while the growth coefficient (K) was higher for males. Individuals with mature gonads were found between March and September, but the main spawning period of M. hispidus in the Sado Estuary was from March to June.
Runoff from acid sulfate soils (ASS) has large negative environmental and economic impacts on est... more Runoff from acid sulfate soils (ASS) has large negative environmental and economic impacts on estuarine ecosystems. Oysters display reduced abundance, growth rate and shell thickness when exposed to ASS runoff, yet the molecular underpinnings of their responses have not been explored. We hypothesized that the proteomes of wild Sydney rock oysters, Saccostrea glomerata, would differ between populations that are recurrently exposed to and that are unaffected by runoff from ASS. We used two-dimensional electrophoresis to compare protein abundances in the gills of S. glomerata collected from two sites close to (acidified) and two sites away from (reference) major ASS outflow drains in a south-east Australian estuary. Approximately 5 % of the proteome was differentially expressed between oysters from acidified and reference sites, with 5 protein spots more abundant and one less abundant at the sites close to drains. Another protein spot was present only in oysters from reference sites. This study has provided the first screening of spatial variation in the protein expression of S. glomerata with respect to discharge from ASS. Altered protein expression may underpin short-term inducible responses to ASS runoff, or genetic resistance acquired through recurrent exposure of populations to the stressor.
Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed ... more Oyster populations periodically exposed to runoff from acid sulfate soils (ASS) are of depressed abundance and have fewer smaller individuals than unaffected populations, despite having similar recruitment levels to unaffected sites during dry periods. We examined how the timing and duration of exposure to ASS runoff influences the growth and survival of successfully settled oysters. We predicted that among 6-month-old oysters, growth and survival would be (1) lower among individuals continuously exposed to ASS-acidified waters than those that are episodically exposed, and (2) most negatively affected during rainfall events, which enhance transport of ASS runoff to estuaries. Six-month-old Sydney rock oysters, Saccostrea glomerata, were deployed at ASS-affected and unaffected sites within each of two south-east Australian estuaries. After 10 weeks, oysters were transplanted within and across sites in an estuary and maintained in situ for another 10 weeks. Oysters that remained for 20 weeks at ASS-affected sites grew at just over half the rate of oysters at reference sites. Oysters transplanted from acidified to reference sites grew more than oysters transplanted from reference to acidified sites or oysters that remained at reference sites. Unexpectedly, overall oyster mortality was low. Greater rainfall, and hence a lower pH, is likely to have accounted for the greater impact of acidification on growth during the second 10 weeks. Where oysters recruit to a 6-month age cohort, they may be able to tolerate subsequent, moderate, acidification events. Reduced growth during acidification periods may be offset by positive growth during intervening dry periods.
Short-term experiments exposing calcifying organisms to acidification have revealed altered growt... more Short-term experiments exposing calcifying organisms to acidification have revealed altered growth and strength of their exoskeletons. We tested the hypothesis that multi-generational exposure to sustained estuarine acidification from runoff from acid sulfate soils (ASS) would (1) reduce the shell strength of sessile or relatively immobile wild benthic invertebrates and (2) as a consequence render these invertebrates that rely on armour for anti-predator defence more susceptible to generalist benthic predators. First, we compared the force required to break the exoskeletons of Saccostrea glomerata, Bembicium auratum and Heloecius cordiformis between replicate south-east Australian mangrove forests close to (acidified) and away from (reference) major ASS outflow drains. Second, we assessed differences in the susceptibility of oysters from acidified and reference forests to predation by the generalist muricid gastropod, Morula marginalba. Mollusc shells were significantly weaker at ASS-affected than at reference sites but the strength of crab carapaces was not influenced by acidification. Oysters from acidified sites were consumed by M. marginalba at a faster rate than oysters from reference sites in choice and no-choice experiments because M. marginalba required less time to drill through weaker shells. Many other predators, such as crabs, are generalist feeders that consume prey at rates inversely proportional to their shell strength. Hence, in the absence of effects of acidification on the ability of these predators to consume prey, molluscs at acidified sites may also be more susceptible to other such predators. This study highlights how human stressors can rapidly alter predator-prey interactions that have evolved over many years.
Runoff from acid-sulphate soils (ASS) is increasingly threatening the structure and function of e... more Runoff from acid-sulphate soils (ASS) is increasingly threatening the structure and function of estuarine ecosystems worldwide. Along the east coast of Australia, sulphuric acid is known to affect the growth and survival of mangrove saplings, but impacts of ASS runoff on the structure and function of established mangrove trees are unclear. Pneumatophores, the aerial roots produced by some species of mangrove, are critical sites of gas exchange, allowing these species to persist in waterlogged soils. They also provide physical structure in estuarine sediments, facilitating communities of algae, invertebrates and, at high tide, fish. We tested the hypotheses that Avicennia marina pneumatophores would be less abundant, shorter, thinner and weaker close to major ASS outflow drains. Sampling at sites close to and away from drains within each of two estuaries of New South Wales, Australia, showed no effect of exposure to runoff on pneumatophore density or thickness. Pneumatophores were, however, shorter (~2 cm) and weaker (up to 2-fold) at ASS-affected than reference sites. Although the reduced length and strength of pneumatophores at acidified sites may limit the number of epifaunal molluscs they can support, the persistence of dense pneumatophores indicates that the capacity for their facilitation of invertebrates and fish remains.
Acid sulphate soils (ASS), which occur on floodplains worldwide, pose a significant threat to est... more Acid sulphate soils (ASS), which occur on floodplains worldwide, pose a significant threat to estuarine ecosystems. In laboratory and field experiments, naïve calcifying organisms that are exposed for even short periods (1e2 mo) to runoff from ASS suffer 80% mortality and slowed growth. Based on these observations we expected that sampling of wild oyster, gastropod and crab populations at sites close to and away from drains discharging ASS runoff would reveal more depauperate populations, of sparser and smaller-sized individuals at the more acidified sites. Sampling within three estuaries of New South Wales, Australia, confirmed that the oyster Saccostrea glomerata and gastropods (primarily Bembicium auratum) were less abundant at ASS-affected than reference sites. Nevertheless, crab abundances did not differ between the acidified and reference sites and impacts to bivalves and gastropods were far smaller than predicted. Although at ASS-affected sites gastropod populations were dominated by smaller individuals than at reference sites, oyster populations were skewed towards larger individuals. Even at ASS-affected sites, oyster and gastropod abundances were within the range encountered in estuaries that are not influenced by ASS runoff. Behaviour, long-term physiological acclimation or genetic selection may be responsible for differences in the responses of wild and naïve macroinvertebrates to acidification. Alternatively, wild populations may exhibit some recovery between the rainfall events that transport ASS runoff into estuaries, despite the persistently lower pH near outflow drains. Irrespective, this study suggests that at the population level, calcifying organisms display a certain degree of natural resistance to recurrent disturbance from ASS runoff.
Constructed wetlands, especially mangroves, have been studied for their usefulness in sewage trea... more Constructed wetlands, especially mangroves, have been studied for their usefulness in sewage treatment but the effects of mangrove vegetation and a sewage load on mangrove macrofauna have been given little attention. Ocypodid crabs are important components of mangrove forests and constitute good bioindicators of the functioning of the ecosystem as a whole. In constructed mangrove mesocosms, three vegetation treatments (bare substratum, and Avicennia marina and Rhizophora mucronata seedlings) were subjected to 0, 20, 60 and 100% sewage loads from a nearby hotel. The physiological condition of introduced Uca annulipes and Uca inversa was evaluated in terms of their RNA/DNA ratio after one, five and twelve months, and used as an indicator of ecological function in the system. Crab condition in 0% sewage load was similar to that of wild crabs throughout, suggesting no significant effects of the mesocosms on their RNA/DNA ratio. Overall, both species coped well with the administered sewage loads, suggesting good ecological function in the system. Both species manifested similar patterns in RNA/DNA ratio, being more affected by seasonal fluctuations than by sewage load and vegetation presence and type. Higher RNA/DNA ratios were recorded in the long compared to the short rainy season. Sewage enhanced crab condition in the bare substratum and R. mucronata treatments, especially after one year, probably as a result of enhanced food availability. Uca inversa may be more sensitive to sewage pollution than U. annulipes. In A. marina, no difference in crab condition was observed between sewage loads, and this mangrove yielded the best reduction in sewage impacts. Our results support the usefulness of constructed mangrove areas in sewage treatment, especially if planted with A. marina and inhabited by physiologically healthy ocypodid crabs to enhance the system’s performance.
Estuarine and nearshore marine areas are vital habitats for several fish and benthic invertebrate... more Estuarine and nearshore marine areas are vital habitats for several fish and benthic invertebrates. The shore crab Carcinus maenas (Crustacea: Brachyura: Portunidae) inhabits a variety of coastal, estuarine and lagoon habitats. At low tide, habitat structural complexity may be most important for crabs in the intertidal, providing refuge from predation and desiccation. The quality of different vegetated and nonvegetated estuarine and rocky shore habitats in SW Portugal and SW England was evaluated for intertidal C. maenas populations. We estimated population density, size–structure, and potential growth (RNA/DNA ratios) to investigate habitat quality. Vegetated estuarine habitats supported higher crab densities, than nonvegetated estuarine and rocky shore habitats. Investigation of population size–structure revealed that all habitats seem important recruitment and nursery areas although estuarine habitats in SW Portugal appeared to support higher densities of new recruits than equivalent habitats in SW England. Significant variation was found in RNA/DNA ratios among habitats. Ratios were highest in the rocky shore suggesting a high quality habitat where growth potential is high. We speculate that competition from other top-predators (Pachygrapsus spp.) rather than low habitat quality may limit the occurrence of C. maenas in intertidal rocky shore habitats in SW Portugal. In estuarine environments RNA/DNA ratios were significantly higher in the vegetated than in the nonvegetated estuarine habitats in SW Portugal but not in SW England, suggesting geographic differences in the extent to which highly structure habitats represent high quality. Our results challenge the current paradigm that structured habitats are necessarily those of higher quality for C. maenas.
1. Pollution of mangrove ecosystems puts their future and that of local communities at risk. Only... more 1. Pollution of mangrove ecosystems puts their future and that of local communities at risk. Only the use of informed and integrative approaches will successfully maintain and restore these valuable ecosystems. 2. Biochemical indicators of organism physiological condition have been widely used to evaluate habitat quality and for early detection of the impact of stressors. Mangrove crabs may be useful bioindicators of the quality of mangrove habitats, as they are characteristic and ecologically important organisms in mangrove environments. 3. The physiological condition (evaluated by the RNA/DNA ratio) of Perisesarma guttatum (Grapsidae) and Uca annulipes (Ocypodidae) was assessed to determine its potential as an indicator of habitat quality in one polluted and two relatively unpolluted Mozambican mangroves, during the rainy and dry seasons. 4. Both species showed seasonal effects on RNA/DNA ratio, but only U. annulipes was significantly affected by pollution. RNA/DNA ratio of U. annulipes may thus be a useful indicator of pollution and seasonality in mangrove habitats. There was a synergistic negative effect of the rainy season and pollution on the RNA/DNA ratio of U. annulipes. Due to higher DNA, rather than lower RNA contents, the RNA/DNA ratio of P. guttatum was always significantly lower than that of U. annulipes. 5. The knowledge gathered in this study can be used in integrative strategies, policies and programmes aiming to sustain, maintain and restore mangrove areas, and for the evaluation of mangrove habitat quality.
Cannibalism is a potentially important factor in the regulation of populations in a range of habi... more Cannibalism is a potentially important factor in the regulation of populations in a range of habitats. The intensity of this biotic factor may be determined by both intra and interspecific interactions. Cancer pagurus and Porcellana platycheles are two co-occurring decapods on Atlantic rocky shores. In laboratory mesocosms, we investigated intra and intersize class cannibalistic and interspecific predatory behaviours in those species. We addressed the effects of prey and predator densities, food, starvation, alternative prey and habitat type. No agonistic behaviour was noted in P. platycheles, suggesting a non-aggressive co-existence between gregarious individuals. Predation of C. pagurus on P. platycheles was intense, possibly accounting for the spatial segregation observed in the natural environment. Cannibalism among C. pagurus juveniles was low and only on vulnerable prey (i.e. at moulting), suggesting a non-aggressive co-existence among juveniles. However, intersize class cannibalism in C. pagurus was intense (ontogenetic shift), possibly reflecting the juvenile-adult segregation in the natural environment. Prey and predator densities, food and habitat type strongly influenced this behaviour. Possible interference among cannibals was noted, with lower prey consumption at high predator density. Food supply alone had more effect on cannibalistic rate than did alternative prey (P. platycheles) and predator starvation. structurally complex habitats (small pebble and Fucus serratus habitats) yielded higher prey survival than the sandy habitat, and the behaviours of both prey and cannibals reflected the small-scale spatial distribution of individuals in the wild. Intersize class cannibalism and interspecific agonistic relationships may account for the intertidal distribution of crab species at low tide.
Post-settlement processes can regulate the size and structure of marine invertebrate and fish pop... more Post-settlement processes can regulate the size and structure of marine invertebrate and fish populations. Faster growth and better physiological condition generally increase the survival potential of early juveniles, being usually associated with structurally complex habitats. Successive cohorts of early juvenile Carcinus maenas were followed in sandy and seagrass (Zostera noltii) habitats in the Mira Estuary, Portugal, to estimate growth and physiological condition (evaluated by RNA/DNA ratio) of juvenile populations. Mean cohort growth was similar in both habitats. However, in the sandy habitat, population size structure progressed to cohorts of larger carapace width (CW) and the RNA/DNA ratio was always higher than in the Z. noltii habitat. In this habitat, cohorts of low CW prevailed throughout and RNA/DNA ratio only increased after ∼5.0mmCW. Higher densities characterising seagrass areas may result in higher competition for resources, limiting growth and condition and leading to dispersal to less populated habitats. Larger juveniles had the best physiological condition, especially early in the season. Seagrass habitats do not necessarily yield enhanced growth rates and physiological condition of early juvenile crabs in relation to sandy areas. Knowledge of such trends is vital to understand distribution and abundance patterns of fish and marine invertebrate populations.
The current conceptual model of reinvasion and settlement for estuarine brachyuran crabs in mesot... more The current conceptual model of reinvasion and settlement for estuarine brachyuran crabs in mesotidal systems is that megalopae undergo selective tidal stream transport, in an upstream direction, and settle by the end of the flood tide. Recent studies on recruitment processes of Carcinus maenas (L.) have reported a clear decoupling between supply, as larval influx, and settlement events in the lower Mira Estuary (SW Portugal). We investigated, at high temporal resolution, whether overestimation of planktonic abundances and/or deviations of megalopal responses from the conceptual model were responsible for such decoupling. Daily settlement of megalopae was analyzed using regression and spectral analyses to identify periodicities and correlated with tidal amplitude. Hydrological parameters and supply, net flux and hourly concentration of megalopae in the plankton were addressed as factors influencing short, intermediate and long-term settlement, through 50 h sampling series. Supply and surface net flux levels of megalopae were similar and clearly decoupled from settlement on bottom-deployed collectors. Both hourly planktonic concentration and settlement patterns of megalopae fitted the conceptual model at high temporal resolution, with some deviations in terms of light intensity influences. Furthermore, our results suggest that processes preventing settlement and capable of overriding the influence of light intensities—such as turbulence—may explain the decoupling between supply and settlement of shore crab megalopae in the lower Mira Estuary.
Journal of Experimental Marine Biology and Ecology, Jan 1, 2007
Settlement patterns of decapod crustaceans are influenced by size, shape and nature of substrates... more Settlement patterns of decapod crustaceans are influenced by size, shape and nature of substrates, as well as by species-specific behaviour patterns. Hog's hair filter material is one of the most commonly used artificial substrates in the study of settlement rates. However, the use of hog's hair collectors in settlement studies poses several problems: movement restriction of settled animals, relatively long and complicated laboratory processing time, and cost and decreasing availability. Despite widely used, no consistent investigation has focused on the influence of size and shape of hog's hair collectors on rates of benthic settlement. A first experiment was set to investigate the effects of collector patchiness on settlement abundances of Carcinus maenas megalopae. Benthic hog's hair collectors of different sizes were deployed intertidally in the lower Mira Estuary. Settlement was addressed as ind collector−1 and ind m−2 in relation to collector' surface area and perimeter:area ratio. Results showed that collector patchiness significantly influenced settlement response of C. maenas megalopae, which differed according to settlement intensity and measure. Megalopae settlement responded to lower scales of habitat patchiness at high than at low intensity. Settlement as ind collector−1 generally increased, while as ind m−2 generally decreased, with increasing collector' surface area (decreasing perimeter: area ratio). A second experiment investigated the efficiency of plastic grass, as a new type of artificial surface, in estimating settlement patterns of C. maenas megalopae, and compared it with that of hog's hair. Collectors of both types were deployed daily and intertidally in the lower Mira Estuary. Settlement showed the same pattern and intensity on both collector types. Plastic grass collectors constitute a good alternative to those of hog's hair, possessing several advantages over them.
Crabs are amongst the most conspicuous and ecologically important organisms inhabiting nearshore ... more Crabs are amongst the most conspicuous and ecologically important organisms inhabiting nearshore environments. Their complex life cycle and bioindicator capacity makes them good models for the study of distribution and abundance patterns of marine fish and benthic invertebrate populations. Such knowledge is essential for explaining species occurrence and demographic patterns, predicting the success of biological indicators and controls, as well as for conservation and management purposes of exploited populations and ecosystems. In this study, the impacts of specific environmental constraints at different life phases of estuarine and coastal crabs on population structure and physiological condition were evaluated and related to habitat quality. During settlement and recruitment events, the patchiness of artificial substrates significantly influenced settlement estimation, and strong water currents might have resulted in a decoupling pattern between supply and settlement. Estuarine sandy habitats presented higher quality for early recruits than seagrass ones. In fact, vegetated habitats were not of higher quality for crab populations than non-vegetated and rocky-shore ones. Adult-juvenile cannibalism showed potential to structure intertidal crab assemblages, especially under shortage of food and refuge. Interestingly, mangrove crabs were more affected by climatic season than by pollution, and coped well with several combinations of vegetation and sewage load. Specific constraints of different life stages, individually and in combination, must be considered for full understanding distribution and abundance patterns of crab populations. Furthermore, the relative importance of a specific constraint is likely to change throughout ontogenesis, and the mechanisms by which it interacts with other environmental variables and processes, sometimes synergistically, have also to be considered. This study constitutes an extension to the knowledge on population structure and physiological condition of coastal and estuarine crabs and other marine invertebrate and fish species, and on their use as indicators of ecological status of habitats and ecosystems.
The abundance of the wiskered sole Monochirus hispidus in the Sado Estuary showed a marked season... more The abundance of the wiskered sole Monochirus hispidus in the Sado Estuary showed a marked seasonal pattern, the highest densities occurred in spring and summer. The density of this species was mainly related, non-linearly, to depth, water transparency and percentage of gravel, fine sand and mud in the sediment. Monochirus hispidus fed mainly on crustaceans and polychaets. Significant differences were found between the proportions of prey items eaten and total length class; larger fish consumed more decapods and polychaets. The von Bertalanffy growth equation coefficients differed between sexes. The asymptotic length L1 obtained for females was higher compared to males, while the growth coefficient (K) was higher for males. Individuals with mature gonads were found between March and September, but the main spawning period of M. hispidus in the Sado Estuary was from March to June.
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to recurrent disturbance from ASS runoff.
2. Biochemical indicators of organism physiological condition have been widely used to evaluate habitat quality and for early detection of the impact of stressors. Mangrove crabs may be useful bioindicators of the quality of mangrove habitats, as they are characteristic and ecologically important organisms in mangrove
environments.
3. The physiological condition (evaluated by the RNA/DNA ratio) of Perisesarma guttatum (Grapsidae) and Uca annulipes (Ocypodidae) was assessed to determine its potential as an indicator of habitat quality in one polluted and two relatively unpolluted Mozambican mangroves, during the rainy and dry seasons.
4. Both species showed seasonal effects on RNA/DNA ratio, but only U. annulipes was significantly affected by pollution. RNA/DNA ratio of U. annulipes may thus be a useful indicator of pollution and seasonality in mangrove habitats. There was a synergistic negative effect of the rainy season and pollution on the RNA/DNA ratio of U. annulipes. Due to higher DNA, rather than lower RNA contents, the RNA/DNA ratio of P. guttatum was always significantly lower than that of U. annulipes.
5. The knowledge gathered in this study can be used in integrative strategies, policies and programmes aiming to sustain, maintain and restore mangrove areas, and for the evaluation of mangrove habitat quality.
species at low tide.
compared to males, while the growth coefficient (K) was higher for males. Individuals with mature gonads were found between March and September, but the main spawning period of M. hispidus in the Sado Estuary was from March to June.
to recurrent disturbance from ASS runoff.
2. Biochemical indicators of organism physiological condition have been widely used to evaluate habitat quality and for early detection of the impact of stressors. Mangrove crabs may be useful bioindicators of the quality of mangrove habitats, as they are characteristic and ecologically important organisms in mangrove
environments.
3. The physiological condition (evaluated by the RNA/DNA ratio) of Perisesarma guttatum (Grapsidae) and Uca annulipes (Ocypodidae) was assessed to determine its potential as an indicator of habitat quality in one polluted and two relatively unpolluted Mozambican mangroves, during the rainy and dry seasons.
4. Both species showed seasonal effects on RNA/DNA ratio, but only U. annulipes was significantly affected by pollution. RNA/DNA ratio of U. annulipes may thus be a useful indicator of pollution and seasonality in mangrove habitats. There was a synergistic negative effect of the rainy season and pollution on the RNA/DNA ratio of U. annulipes. Due to higher DNA, rather than lower RNA contents, the RNA/DNA ratio of P. guttatum was always significantly lower than that of U. annulipes.
5. The knowledge gathered in this study can be used in integrative strategies, policies and programmes aiming to sustain, maintain and restore mangrove areas, and for the evaluation of mangrove habitat quality.
species at low tide.
compared to males, while the growth coefficient (K) was higher for males. Individuals with mature gonads were found between March and September, but the main spawning period of M. hispidus in the Sado Estuary was from March to June.