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Thermal Tolerance of two ecosystem engineers of East African mangroves : forecasting the effects of climate change on ecosystem functionality
No full textRapid climate change has a strong impact on marine ecosystems, through warming, acidification, hypoxia and salinisation of sea water. Marine ectotherms are mostly affected by changes in temperature, which directly influence oxygen availability and their ability to utilise oxygen and so can have potential cascading effects on their overall fitness. As a consequence, understanding the thermal response of organisms, particularly ecosystem engineers, is crucial to forecasting the effects of climate warming on ecosystem functionality. Here we focus on the thermal tolerance of two mangrove ecosystem engineers inhabiting the eulittoral of East African and South African mangrove forests, the crabs Perisesarma guttatum (Sesarmidae) and Uca urvillei (Ocipodidae). In order to assess their sensitivity to acute temperature fluctuations across a wide latitudinal gradient, we studied the thermal window of a Kenyan and a South African population of each species using intermittent flow-throw respirometry. Metabolic rate was measured in the laboratory along a temperature ramp procedure of 1°C × h-1 between 17-27 °C in water and in air, as these species experience both conditions. The results showed a stenothermic response for both species in water, with a pronounced latitudinal effect, the South African populations being adapted to lower temperatures than the Kenyan ones. Both species showed a different response in air, where the thermal window was wider, highlighting a better tolerance to temperature change in air than in water. This suggests that oxygen limitation is the driving parameter in determining the limits of thermal tolerance. These results suggest that these subtropical mangrove populations are vulnerable to long-term increases in temperature, particularly because of reduced oxygen content in water as it warms. This is likely to lead to a loss of fitness with serious consequences for overall mangrove ecosystem functioning
Thermal Tolerance of two ecosystem engineers of East African mangroves: forecasting the effects of climate change on ecosystem functionality
No full textRapid climate change has a strong impact on marine ecosystems, through warming, acidification, hypoxia and salinisation of sea water. Marine ectotherms are mostly affected by changes in temperature, which directly influence oxygen availability and their ability to utilise oxygen and so can have potential cascading effects on their overall fitness. As a consequence, understanding the thermal response of organisms, particularly ecosystem engineers, is crucial to forecasting the effects of climate warming on ecosystem functionality. Here we focus on the thermal tolerance of two mangrove ecosystem engineers inhabiting the eulittoral of East African and South African mangrove forests, the crabs Perisesarma guttatum (Sesarmidae) and Uca urvillei (Ocipodidae). In order to assess their sensitivity to acute temperature fluctuations across a wide latitudinal gradient, we studied the thermal window of a Kenyan and a South African population of each species using intermittent flow-throw respirometry. Metabolic rate was measured in the laboratory along a temperature ramp procedure of 1°C × h-1 between 17-27 °C in water and in air, as these species experience both conditions. The results showed a stenothermic response for both species in water, with a pronounced latitudinal effect, the South African populations being adapted to lower temperatures than the Kenyan ones. Both species showed a different response in air, where the thermal window was wider, highlighting a better tolerance to temperature change in air than in water. This suggests that oxygen limitation is the driving parameter in determining the limits of thermal tolerance. These results suggest that these subtropical mangrove populations are vulnerable to long-term increases in temperature, particularly because of reduced oxygen content in water as it warms. This is likely to lead to a loss of fitness with serious consequences for overall mangrove ecosystem functioning
Thermal tolerance of key-note macrofaunal species: a method to forecast the impact of climate change on African Mangrove systems
No full textThe principle of oxygen limitation of thermal tolerance in ectotherm (OLTT) theorises that the higher limits of an organism’ thermal niche are directly linked to its capability of maintaining an adequate provision of oxygen to its tissues. Initially inferred for marine ectotherms, the decline of thermal resistance due to inefficient tissue oxygenation, as expected by the OLTT, was shown also in terrestrial species. air-breathing ectotherms, however, showed wide thermal tolerances, since they could take advantage of the higher oxygen availability in air than in water. Here we tested the educated guess that bimodal species, such as intertidal invertebrates, could better cope with acute thermal stresses with respect to truly marine species, by taking advantage from air-breathing. Using intermittent flow-throw respirometry, we measured the metabolic rate of the rocky intertidal crab P. marmoratus along a temperature ramp procedure of 1°C × h-1 between 17-27 °C. We demonstrated that the oxygen consumption rates showed by P. marmoratus during aquatic and aerial respirations show the typical temperature-dependant exponential raise in water, while in air the aerobic metabolism remain unaltered. Our results demonstrate the ability of bimodal intertidal ectotherms to exploit both the aquatic and the aerial phases. This ability has to be taken into account in climate warming scenarios predicting about their present and future distribution and biology
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Thermal response of mangrove macrobenthos: explaining processes in endangered coastal systems
No full textRapid climate change has a strong impact on marine ecosystems, through warming, acidification and hypoxia of sea water. Marine ectotherms are mostly affected by changes in temperature, which directly influences oxygen availability and the ability to utilize oxygen affecting their overall fitness. As a consequence, understanding the thermal response of organisms is crucial to forecast the effects of climate change on ecosystem functionality.
Here we focus on the thermal tolerance of adult males, females and gravid females, of two mangrove ecosystem engineers inhabiting the East African mangroves, the amphibious crabs Perisesarma guttatum (Sesarmidae) and
Uca urvillei (Ocipodidae). In order to assess their sensitivity to acute temperature fluctuations across a wide latitudinal gradient, we studied the thermal window of Kenyan and South African populations of both species. The metabolic rate, haemolymph oxygen saturation and heart rate were measured in the laboratory along a temperature ramp (17-37 °C) in water and in air. Additionally, we characterized the environmental temperature range which the animals are subjected to and compared this to their relative body temperatures. In order to evaluate the species sensitivity, we fit the environmental data with the thermal model constructed by our experiments. The results show different responses for sex in both species and particularly a stenothermic response in water compared to air, with a pronounced latitudinal effect, with the South African populations better adapted to lower temperatures than the Kenyan ones. Females with eggs show a higher metabolic rate than males and females with no eggs, representing the most vulnerable adult life stage. The results suggest that these subtropical mangrove populations are vulnerable to long-term increases in temperature, particularly because of reduced oxygen content in water as it warms. This is likely to lead to a loss of fitness with serious consequences for the persistence of such populations and the overall mangrove ecosystem functioning
Bacterial symbionts in East African mangrove crabs
No full textMangrove communities are highly productive ecosystems releasing large amounts of organic matter to adjacent coastal waters. Organisms in the mangrove ecosystems have to cope with different stresses like high salinity, periodic tidal flows, anoxic niches in soil and fluctuating thermal regimes. Moreover, mangrove soil and sediments present high contents of lignin-derived tannins and polyphenols that plants produce to preserve the tissues from microbial pathogens. Despite the harsh conditions a large animal biomass characterizes the mangrove ecosystem mainly represented by the true burrowing crabs sesarmids and ocipodids (Crustacea, Brachyura) that play an important role in the ecosystem functioning as ecosystem engineers (Kristensen and Alongi 2006). How the mangrove crabs cope with the harsh conditions of the ecosystem, especially how they manage the high C/N ratio of their diet are intriguing questions. It has been hypothesized that mangrove crabs can take advantage of an associated symbiotic microbiome (Thongtham and Kristensen 2005) that may complement nutritional deficiencies like occurs in other arthorpods (Moran and Dale 2006). The aim of this study was to evaluate the diversity of microbial symbionts associated to two representative mangrove crab species, Uca urvillei (ocipodids) and Perisesarma guttatum (sesarmids), collected from two different populations in a Kenyan and in a South African mangrove forests. The bacterial community associated to different crab organs and tissues such as gill, hindgut, gonads and eggs was characterized by sequencing PCR-amplified 16S rRNA genes following separation by denaturing gradient gel electrophoresis. Rather highly diverse bacterial communities have been associated to all the organs examined. A range of novel taxa showing low sequence identity with previously identified bacteria have been found associated to all crabs organs. rRNA gene sequences related to sulfur- oxidizing bacteria have been identified in the gills suggesting the chemolithoautotrophy may play a role in the maintenance of the crab metacommunity. In hindgut tissues sequences related to nitrifying and denitrifying bacteria were found supporting the hypothesis of a complex nitrogen cycle occurring in the gut
Are mangrove crabs true intertid al ectotherms? Different thermal strategies to cope with climate change
No full textTropical intertidal ecosystems such as mangrove forests are particularly vulnerable to climate change since they are at the interface between the marine and terrestrial environments. Crabs are the most important ecological engineers among macrobenthos species in that ecosystem.
They undertake different adaptive strategies to occupy several niches along a terrestrial-marine gradient. Sesarmid crabs, such as Perisesarma guttatum, are exposed to tidal cycles and since they are not a burrowing species, they have to cope with cycling exposition to water and air. Ocypodid crabs, such as Uca urvillei, are burrowers and active only during day low tides. At high tide, they burrow into their holes until the next ebb tide. Through direct observations in the field, we examined the use of time and space of these species and the thermal exposition at low tide, by recording en vironmental temperature. Body temperature was also measured to assess the thermal niche of the animals. Observations indicate that different strategies are employed by each species.
U. urvillei exhibit a broad use of space and time and experience a wide variation in temperature during their feeding, displaying and
homing activities. They consistently visit their burrows, and increase the frequency of visits with the incoming tide. In contrast, P. guttatum, show a restricted use of space, occupying consistently shaded areas and maintaining a very low activity pattern. Body temperature shows clear patterns of thermoregulation for P. guttatum and none for U. urvillei.
Haemolymph oxygen saturation for the former is, nevertheless, very low in air compared to the one of U. urvillei. Moreover, with the incoming tides U. urvillei close the burrows, avoiding water inundation and thriving in air during high tide. We describe two life strategies of two species that occupy similar habitats, but display different physiological and behavioural strategies to thermal stress. These differences might underline the role of these species in the mangrove system for coping with climate induced environmental changes
An ontogenetic approach to the thermal response of mangrove macro-benthos: explaining processes in endangered coastal systems under global change
No full textRapid climate change has a strong impact on marine ecosystems, through warming, acidification, hypoxia and salinisation of sea water. Marine ectotherms are mostly affected by changes in temperature, which directly influence oxygen availability and their ability to utilize oxygen with potential cascading effects on their overall fitness. As a consequence, understanding the thermal response of organisms, especially in ecosystem engineers, is crucial to forecasting the effects of climate warming on ecosystem functionality. Here we focus on the thermal tolerance of two mangrove ecosystem engineers inhabiting the eulittoral zone of East African and South African mangrove forests, the crabs Perisesarma guttatum (Sesarmidae) and Uca urvillei (Ocipodidae). In order to assess their sensitivity to acute temperature fluctuations across a wide latitudinal gradient, we studied the thermal window of a Kenyan and a South African population of each species at different life stages: eggs, larvae (zoea) and adults. The metabolic rates were measured in the laboratory along a temperature ramp procedure of 1°C × h-1 between 17-37°C. The measures were performed in air and water for the adults and eggs, as these two stages experience both conditions, and just in water for the larvae. For the adults we used an intermittent flow-throw respirometry and for eggs and larvae a closed respiratory micro-chamber.
Preliminary results show different thermal response for adults of both species at different latitudinal range, while results for eggs and larvae are still on progress.
Further analysis have to be conducted in order to draw a complete and clarifying scenario on thermal biology of these species as oxygen saturation in adult haemolymph and heart rate in eggs and larvae.
Evaluate the thermal niche of different life stage of bimodal breather marine ectotherms are important because we could retrieve information about their plasticity and so their vulnerability facing current environmental change. Sensitiveness of macrobenthos is crucial to understand ecological dynamics in mangrove ecosystem functioning
Thermal Response of Mangrove Macrobenthos: Measurement of Population Fitness in Endangered Coastal Systems
No full textClimate change has a strong impact on marine ecosystems, through warming, acidification and hypoxia of seas. Marine ectotherms are mostly affected by changes in temperature, which directly influences their overall fitness. Understanding the thermal response of organisms is therefore crucial to forecast the effects of climate change on ecosystem functionality. Here we focus on the thermal tolerance of adult males, females and gravid females, of two mangrove ecosystem engineers inhabiting the East African mangroves, the crabs Perisesarma guttatum and Uca urvillei. To assess their sensitivity to acute temperature fluctuations across a wide latitudinal gradient, we studied the thermal window of Kenyan and South African populations of both species. The metabolic rate, haemolymph oxygen saturation were measured in the laboratory along a temperature ramp (17-37 °C) in water and in air. Additionally, we characterised the environmental temperature range which the animals are subjected to and compared this to their relative body temperatures measuring their spatio-temporal use in the field. To evaluate the species sensitivity to temperature, we fit these data with the thermal model constructed by our experiments. The different thermal regimes found show different life strategies in the use of time and space. A stenothermic response in water compared to air, with a pronounced latitudinal effect was established, with the South African populations better adapted to lower temperatures than the Kenyan ones. Females with eggs show a higher metabolic rate than males and females with no eggs, representing the most vulnerable adult life stage. The results suggest that these subtropical mangrove populations are vulnerable to long-term increases in temperature, particularly because of reduced oxygen content in water as it warms. This is likely to lead to a loss of fitness with serious consequences for the persistence of such populations and the overall mangrove ecosystem functioning
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