Upper thermal threshold of Lepidurus arcticus (Branchiopoda, Notostraca) in lakes on the southern outreach of its distribution range

The Arctic tadpole shrimp Lepidurus arcticus has a circumpolar distribution and the Scandes (Fennoscandian Mountains) marks its southernmost limit in Europe. Within this area, 391 natural and 88 regulated lakes with L. arcticus have been identified, of which 87% are above the treeline. The lakes hosting L. arcticus decrease in altitude from south to north, which results from its temperature preferences. The majority of the locations are at a lower lake air temperature than 11°C which is equivalent to a water temperature near 14°C. This is assumed to be near the upper thermal threshold for L. arcticus. In lakes that exceed this average summer water temperature (1 July – 15 September), sustainable populations seem to be rare. In warmer lakes, life cycle mismatches are assumed to explain the absence of L. arcticus, most likely by affecting the embryo and juvenile stages. The distribution appears to be dichotomous, with one large northern area north of 65°N and one separated southern “island”. Only two locations of L. arcticus are known for the area between latitudes 62.88 and 64.39°N. In this part of the Scandes, the lakes are likely too warm to host L. arcticus as most of them are situated below 700 m a.s.l. This may also be the case in the northernmost region, north of 70°N, where only 11 populations are recorded. Most of the lakes in this area typically occurs below 400 m a.s.l. L. arcticus populations are sensitive to fish predation, and dense fish populations may be another stressor limiting its distribution. In contrast to water bodies in the High Arctic where L. arcticus only exists in shallow, fishless ponds, in the Scandes they co-exist with fish in 97% of the findings. Global warming has already modified the environment of the Scandes, and populations of L. arcticus are at threat in many of the small and shallow water bodies at low altitudes.

Impact of the local environmental variability on the patterns of coral recruitment on Indo-Pacific reefs

<p>Coral reefs are threatened by a range of human activities at both local and global scales. The result of these impacts has resulted in a worldwide decline in the coral reef ecosystems. Corals are the principle reef builders and the maintenance of their populations is fundamental for healthy reef ecosystems. Local environmental factors are critically important in shaping coral populations, particularly at the post-settlement phase, when young coral colonies are most vulnerable to disturbances. In this context, understanding the environmental factors that drive coral recruitment and affect coral survivorship in the early life history stages is vital to effectively manage coral reefs. In this thesis I began by investigating the effect of abiotic and biological factors on coral recruitment and juvenile coral life history stages using settlement panels deployed in the Wakatobi Marine National Park (SE Sulawesi, Indonesia). My objectives were to assess the spatio-temporal variability in coral recruitment rates and juvenile abundance. I used a modelling approach to identify the environmental factors that affected the distribution and abundance patterns of corals. Then, I focused on the main environmental factors, identified from previously published research, affecting coral recruitment. I conducted a caging experiment to assess the impact of fish predation on coral juveniles. Finally, I analysed the development of the benthic community and the interactions between corals and benthic organisms in the first two years of colonisation of artificial bare surfaces. I found high spatial and temporal variability in recruitment rates over seven years of data, values were lower than on other Indo-Pacific reefs and ranged from 9.6 (±8.21 SE) to 317.19 (±12.76 SE) rec. m⁻²; while juvenile abundance ranged from 4.2 (±1.49 SE) to 33 (±6.36 SE) juv. m⁻². The local characteristics of the sites, such as coral cover, influenced the distribution of coral colonies in early life history stages; furthermore differences in coral density between the two life history stages (juvenile and recruits) were consistent over time. However, no single or combination of factors adequately explained abundance patterns for either recruits or juveniles. Fish predation did not appear to be the main cause of coral post-settlement mortality in the Wakatobi and it affected only 10.8% of the coral juveniles in the experiment. In contrast, 58.51% of the coral juveniles were found to be overgrown by algae and other invertebrates, however only turf and green encrusting algae affected coral survivorship. Coral colony abundance and the number of interactions with other benthic organisms, especially crustose coralline algae (CCA) and sponges, increased over time on panels and they were different between the front and back side of the panels, which was attributed to differences in light and predation regimes. Coral recruitment was higher on older benthic communities, although none of the known coral recruitment promoters, such as CCA, or competitors, such as turf algae, were correlated with coral abundance. My results show that changes in coral populations between the recruit and juvenile stages are likely driven by small-scale processes. The site characteristics determine the final patterns, which vary over time following temporal fluctuations in environmental factors. The effect of the interactions between algae and sponges with coral recruits and their influence on juvenile survivorship suggests these organisms having a role in coral recruitment success and highlight their importance as a focus for reef management. Furthermore, the use of long term studies allowed a better understanding of the high variability present in coral recruitment and the trends of the recruitment process, which are useful information for conservative purposes.</p>

Impact of the local environmental variability on the patterns of coral recruitment on Indo-Pacific reefs

<p>Coral reefs are threatened by a range of human activities at both local and global scales. The result of these impacts has resulted in a worldwide decline in the coral reef ecosystems. Corals are the principle reef builders and the maintenance of their populations is fundamental for healthy reef ecosystems. Local environmental factors are critically important in shaping coral populations, particularly at the post-settlement phase, when young coral colonies are most vulnerable to disturbances. In this context, understanding the environmental factors that drive coral recruitment and affect coral survivorship in the early life history stages is vital to effectively manage coral reefs. In this thesis I began by investigating the effect of abiotic and biological factors on coral recruitment and juvenile coral life history stages using settlement panels deployed in the Wakatobi Marine National Park (SE Sulawesi, Indonesia). My objectives were to assess the spatio-temporal variability in coral recruitment rates and juvenile abundance. I used a modelling approach to identify the environmental factors that affected the distribution and abundance patterns of corals. Then, I focused on the main environmental factors, identified from previously published research, affecting coral recruitment. I conducted a caging experiment to assess the impact of fish predation on coral juveniles. Finally, I analysed the development of the benthic community and the interactions between corals and benthic organisms in the first two years of colonisation of artificial bare surfaces. I found high spatial and temporal variability in recruitment rates over seven years of data, values were lower than on other Indo-Pacific reefs and ranged from 9.6 (±8.21 SE) to 317.19 (±12.76 SE) rec. m⁻²; while juvenile abundance ranged from 4.2 (±1.49 SE) to 33 (±6.36 SE) juv. m⁻². The local characteristics of the sites, such as coral cover, influenced the distribution of coral colonies in early life history stages; furthermore differences in coral density between the two life history stages (juvenile and recruits) were consistent over time. However, no single or combination of factors adequately explained abundance patterns for either recruits or juveniles. Fish predation did not appear to be the main cause of coral post-settlement mortality in the Wakatobi and it affected only 10.8% of the coral juveniles in the experiment. In contrast, 58.51% of the coral juveniles were found to be overgrown by algae and other invertebrates, however only turf and green encrusting algae affected coral survivorship. Coral colony abundance and the number of interactions with other benthic organisms, especially crustose coralline algae (CCA) and sponges, increased over time on panels and they were different between the front and back side of the panels, which was attributed to differences in light and predation regimes. Coral recruitment was higher on older benthic communities, although none of the known coral recruitment promoters, such as CCA, or competitors, such as turf algae, were correlated with coral abundance. My results show that changes in coral populations between the recruit and juvenile stages are likely driven by small-scale processes. The site characteristics determine the final patterns, which vary over time following temporal fluctuations in environmental factors. The effect of the interactions between algae and sponges with coral recruits and their influence on juvenile survivorship suggests these organisms having a role in coral recruitment success and highlight their importance as a focus for reef management. Furthermore, the use of long term studies allowed a better understanding of the high variability present in coral recruitment and the trends of the recruitment process, which are useful information for conservative purposes.</p>

The Impacts of Predation and Habitat Degradation on Coral Reef Sponge Assemblages in SE Sulawesi, Indonesia

<p>Coral reefs across the globe are in decline due to multiple threats including overexploitation, pollution, coastal development, climate change and ocean acidification. Much research has focused on the effects of these threats on hard corals while their impacts on other important benthic invertebrate groups have been overlooked. Sponges are a diverse and abundant component of coral reef communities in the Indo-Pacific that play important functional roles on reefs including nutrient cycling, linking primary and secondary production, reef bioerosion and spatial competition. Consequently, changes in the abundance and distribution patterns of sponges can affect overall reef ecosystem function. Understanding the factors that control sponge distribution patterns is therefore essential for the successful prediction and mitigation of the effects of current threats to reef systems. Sponge distributions are known to be affected by a number of abiotic factors such as wave action, sedimentation and water flow, but the role of biological factors such as predation and competition is less clear. The primary aim of my thesis was to determine the effects of predation on the distribution and abundance of sponge assemblages in the Wakatobi Marine National Park (WMNP), SE Sulawesi, Indonesia. My first objective (chapter 2) was to identify the major spongivores in the Wakatobi using surveys and behavioural observations of key invertebrate (nudibranchs and starfish) and vertebrate taxa (fish). I then adopted a statistical modelling approach (chapter 3) to examine associations between sponges and a suite of abiotic and biological factors, including spongivore abundance, across nine sites in the WMNP. The results of this analysis showed that although sponge assemblage composition was weakly associated with spongivore abundance, sedimentation is more likely to have a greater impact on sponge abundance and distribution patterns. I found that degraded sites were characterized by low diversity sponge assemblages dominated by a single sediment tolerant species Lamellodysidea herbacea. In order to explore the relationship between sponges and spongivore abundance further, I used an experimental approach (chapter 4), establishing a caging experiment to examine the effect of excluding predators on reef slope sponge assemblages. The caging experiment did not reveal any effects of predator exclusion on sponge abundance or diversity. In the last data chapter (chapter 5), I focus on sub-lethal predation effects on sponges and examine the extent and impact of partial predation on the Indo-Pacific giant barrel sponge Xestospongia testudinaria. Video observations of fish predation and measurements of barrel sponge regeneration rates were used to model the impacts of predation on barrel sponges. In summary, a combination of observational, modelling and experimental approaches were used in order to determine the impact of fish predation on Indo-Pacific sponge assemblages. Spongivory does not appear to have a major influence on the abundance and distribution of reef sponges but is an important trophic link in reef ecosystems. Ecologically important sponge species, such as the giant barrel sponge X. testudinaria, are exposed to intensive partial predation and future changes in predation intensity could have consequences for the fitness of these species. Finally, my work suggests that changes on reefs such as increases in sedimentation could produce a shift from coral dominated to lower diversity sponge dominated communities.</p>

The Impacts of Predation and Habitat Degradation on Coral Reef Sponge Assemblages in SE Sulawesi, Indonesia

<p>Coral reefs across the globe are in decline due to multiple threats including overexploitation, pollution, coastal development, climate change and ocean acidification. Much research has focused on the effects of these threats on hard corals while their impacts on other important benthic invertebrate groups have been overlooked. Sponges are a diverse and abundant component of coral reef communities in the Indo-Pacific that play important functional roles on reefs including nutrient cycling, linking primary and secondary production, reef bioerosion and spatial competition. Consequently, changes in the abundance and distribution patterns of sponges can affect overall reef ecosystem function. Understanding the factors that control sponge distribution patterns is therefore essential for the successful prediction and mitigation of the effects of current threats to reef systems. Sponge distributions are known to be affected by a number of abiotic factors such as wave action, sedimentation and water flow, but the role of biological factors such as predation and competition is less clear. The primary aim of my thesis was to determine the effects of predation on the distribution and abundance of sponge assemblages in the Wakatobi Marine National Park (WMNP), SE Sulawesi, Indonesia. My first objective (chapter 2) was to identify the major spongivores in the Wakatobi using surveys and behavioural observations of key invertebrate (nudibranchs and starfish) and vertebrate taxa (fish). I then adopted a statistical modelling approach (chapter 3) to examine associations between sponges and a suite of abiotic and biological factors, including spongivore abundance, across nine sites in the WMNP. The results of this analysis showed that although sponge assemblage composition was weakly associated with spongivore abundance, sedimentation is more likely to have a greater impact on sponge abundance and distribution patterns. I found that degraded sites were characterized by low diversity sponge assemblages dominated by a single sediment tolerant species Lamellodysidea herbacea. In order to explore the relationship between sponges and spongivore abundance further, I used an experimental approach (chapter 4), establishing a caging experiment to examine the effect of excluding predators on reef slope sponge assemblages. The caging experiment did not reveal any effects of predator exclusion on sponge abundance or diversity. In the last data chapter (chapter 5), I focus on sub-lethal predation effects on sponges and examine the extent and impact of partial predation on the Indo-Pacific giant barrel sponge Xestospongia testudinaria. Video observations of fish predation and measurements of barrel sponge regeneration rates were used to model the impacts of predation on barrel sponges. In summary, a combination of observational, modelling and experimental approaches were used in order to determine the impact of fish predation on Indo-Pacific sponge assemblages. Spongivory does not appear to have a major influence on the abundance and distribution of reef sponges but is an important trophic link in reef ecosystems. Ecologically important sponge species, such as the giant barrel sponge X. testudinaria, are exposed to intensive partial predation and future changes in predation intensity could have consequences for the fitness of these species. Finally, my work suggests that changes on reefs such as increases in sedimentation could produce a shift from coral dominated to lower diversity sponge dominated communities.</p>

The distribution of benthic amphipod crustaceans in Indonesian seas

Amphipod crustaceans are an essential component of tropical marine biodiversity. However, their distribution and biogeography have not been analysed in one of the world’s largest tropical countries nested in the Coral Triangle, Indonesia. We collected and identified amphipod crustaceans from eight sites in Indonesian waters and combined the results with data from 32 additional sites in the literature. We analysed the geographic distribution of 147 benthic amphipod crustaceans using cluster analysis and the ‘Bioregions Infomaps’ neural network method of biogeographic discrimination. We found five groups of benthic amphipod crustaceans which show relationships with sampling methods, depth, and substrata. Neural network biogeographic analysis indicated there was only one biogeographic region that matched with the global amphipod regions and marine biogeographic realms defined for all marine taxa. There was no support for Wallaces or other lines being marine biogeographic boundaries in the region. Species richness was lower than expected considering the region is within the Coral Triangle. We hypothesise that this low richness might be due to the intense fish predation which may have limited amphipod diversification. The results indicated that habitat rather than biogeography determines amphipod distribution in Indonesia. Therefore, future research needs to sample more habitats, and consider habitat in conservation planning.

Inducible responses to antagonistic predation risks are not in a dilemma: Evidences from multi-traits and transcriptome of Ceriodaphnia

Inducible defenses of prey are evolved under diverse and variable predation risks. In the co-evolution of prey and multiple predators with antagonistic selection pressures, whether inducible defense responses of prey will fall into a dilemma and its underlying mechanism are still unclear. Based on the antagonistic predation pressure from invertebrate predator Chaoborus larvae and vertebrate predator fish, we studied multi-traits and transcriptome of the freshwater crustacean Ceriodaphnia cornuta under multiple predation risks. Our results showed that Chaoborus larvae predation risks altered the expression of genes encoding cuticle protein and changed the biosynthesis of steroid hormone, cutin, suberine, and wax, promoting Ceriodaphnia to express horns and grow larger at a late development stage, whereas fish predation risks mainly triggered responses in genes encoding ribosome and pathways of unsaturated fatty acids biosynthesis, cysteine and methionine metabolism, resulting in a smaller individual size and earlier reproduction. The inducible responses on transcription and individual traits both revealed that predator unique responses are dominant and the antagonistic responses are the least. Besides, Pearson correlations between different predator unique responses are extremely weak. Furthermore, the unique individual traits triggered by different predators can be expressed simultaneously. These results indicated that Ceriodaphnia can avoid the dilemma by performing predator unique responses and diverse inducible responses are favored in the co-evolution of zooplankton and multiple predators.

Daya Predasi Ikan Lemon (Labidochromis caeruleus) dan Ikan Kapiat (Barbonymus schwanenfeldii) Terhadap Larva Nyamuk Aedes aegypti

Dengue hemorrhagic fever (DHF) is a vector-borne disease that still happens every year in Indonesia. This disease is caused by the dengue virus and transmitted by the Aedes aegypti as its vector. One of the biological vector controls that can be implemented is using fish as a predator of mosquito larvae, such as using Electric Yellow Cichlid fish (Labidochromis caeruleus) and Tinfoil Barb fish (Barbonymus schwanenfeldii). This study aimed to determine the difference in predation capacities of Electric Yellow Cichlid and Tinfoil Barb on Ae. aegypti larvae. This research is quasiexperimental with a completely randomized design (CRD) with Post Test Only research design. One aquarium with three liters of water containing one fish is given 25 Ae. aegypti larvae. Testing of each fish species is carried out in five replications. Fish predation was observed every 30 seconds until all larvae were eaten. The result showed that Electric Yellow Cichlid could prey on 25 larvae in an averagetime of 5.7 minutes, while Tinfoil Barb spent 11.6 minutes. The results of the Friedman test showed that there was a significant time difference in preying time of Electric Yellow Cichlid and Tinfoil Barb. It’s concluded that Electric Yellow Cichlid was more effective as an Ae. aegypti larvae predator.

Alteration of the feeding behavior of an omnivorous fish, Scardinius acarnanicus (Actinopterygii: Cypriniformes: Cyprinidae), in the presence of fishing lights

Fishing with light is an old and common practice yielding a substantial catch volume globally. Despite the popularity of the method and the efforts to improve it, there is a lack of field studies on the effects of light on the feeding preferences of the attracted fishes. A previous report suggested that purse seine fishing lights can differentiate the feeding preferences of the approaching fishes, such as Atherina boyeri Risso, 1810 in Lake Trichonis (Greece). The presently reported study aims to verify these findings by investigating the diet of the endemic Scardinius acarnanicus Economidis, 1991. The feeding behavior of S. acarnanicus was studied from 2016 to 2019 through gut content analysis, in specimens from Lake Trichonis that came from purse seining with light and specimens caught without light. The same investigation was carried out comparatively in specimens taken by gillnets from two nearby lakes (lakes Ozeros and Amvrakia), where S. acarnanicus is present, but no fishing with light is exercised. The stomach content analysis conducted on 699 S. acarnanicus specimens revealed the intense effect of light on its diet resulting in the alteration of its feeding habits towards fish predation and especially Atherina boyeri. On the contrary, the specimens taken with the use of gillnets, from the three lakes, showed a typical omnivorous feeding behavior. The findings of the presently reported study support the assumption that the elevated concentration of fish close to fishing lights alters the feeding behavior of certain species making them predators. Considering that fishing with light is practiced worldwide, this could be of great ecological significance to the ichthyofauna not only of inland waters but also of marine areas, affecting perhaps several commercial species.

Alteration of the feeding behavior of an omnivorous fish, Scardinius acarnanicus (Actinopterygii: Cypriniformes: Cyprinidae), in the presence of fishing lights

Fishing with light is an old and common practice yielding a substantial catch volume globally. Despite the popularity of the method and the efforts to improve it, there is a lack of field studies on the effects of light on the feeding preferences of the attracted fishes. A previous report suggested that purse seine fishing lights can differentiate the feeding preferences of the approaching fishes, such as Atherina boyeri Risso, 1810 in Lake Trichonis (Greece). The presently reported study aims to verify these findings by investigating the diet of the endemic Scardinius acarnanicus Economidis, 1991. The feeding behavior of S. acarnanicus was studied from 2016 to 2019 through gut content analysis, in specimens from Lake Trichonis that came from purse seining with light and specimens caught without light. The same investigation was carried out comparatively in specimens taken by gillnets from two nearby lakes (lakes Ozeros and Amvrakia), where S. acarnanicus is present, but no fishing with light is exercised. The stomach content analysis conducted on 699 S. acarnanicus specimens revealed the intense effect of light on its diet resulting in the alteration of its feeding habits towards fish predation and especially Atherina boyeri. On the contrary, the specimens taken with the use of gillnets, from the three lakes, showed a typical omnivorous feeding behavior. The findings of the presently reported study support the assumption that the elevated concentration of fish close to fishing lights alters the feeding behavior of certain species making them predators. Considering that fishing with light is practiced worldwide, this could be of great ecological significance to the ichthyofauna not only of inland waters but also of marine areas, affecting perhaps several commercial species.