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  • 1
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    Seaweed farming pressure affects seagrass and benthic macroalgae dynamics in Chwaka Bay (Zanzibar, Tanzania) (2021)
    Springer Berlin Heidelberg
    Details
    Publication Date: 2023-08-01
    Description: Farming of Eucheuma denticulatum is a major activity in Zanzibar affecting seagrass ecosystems primarily through shading and trampling. The aim of this study was to test the impacts of shading and trampling during seaweed farming on seagrass meadows composed by Halophila stipulacea and Thalassia hemprichii and their associated benthic macroalgae. Areas covered by these species were selected for the building of seaweed farms in three treatments: seaweed farm plots (with shading and trampling effects), trampling plots (with trampling effects only), and control plots (with no shading or trampling effects). Reduction of light within the plots was recorded over 9 weeks. Percentage cover of seagrasses and macroalgae and shoot density of seagrasses were measured over 12 weeks to assess the impact of shading and trampling by seaweed farming activities. Light was significantly reduced in the seaweed farm plots by 75 to 90% by the end of a seaweed growth cycle. H. stipulacea, despite its capacity for rapid growth, was significantly affected by the combination of shading and trampling under the seaweed farm treatment, while the climax seagrass species T. hemprichii was unaffected. Due to the decline in H. stipulacea, benthic macroalgae cover increased in the seaweed farm treatment, suggesting a change in seagrass community dynamics. In contrast, trampling had a negative effect on the benthic macroalgae as an isolated disturbance, which suggests that seagrasses are more resistant to trampling than macroalgae and would likely dominate the benthic macrophyte community under these conditions.
    Description: Leibniz-Zentrum für Marine Tropenforschung
    Description: Universität Bremen (DE)
    Description: Deutsche Forschungsgemeinschaft (DFG)
    Keywords: ddc:631 ; Thalassia hemprichii ; Halophila stipulacea ; Eucheuma denticulatum ; Shading ; Trampling
    Language: English
    Type: doc-type:article
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    CITATION GEO-LEO
  • 2
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    Morphological and Physiological Responses of Enhalus acoroides Seedlings Under Varying Temperature and Nutrient Treatment (2020)
    Frontiers Media
    Details
    Publication Date: 2020-05-15
    Electronic ISSN: 2296-7745
    Topics: Biology
    Published by Frontiers Media
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    PAPER CURRENT
  • 3
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    Rising Temperature Is a More Important Driver Than Increasing Carbon Dioxide Concentrations in the Trait Responses of Enhalus acoroides Seedlings (2021)
    Molecular Diversity Preservation International
    Details
    Publication Date: 2021-03-18
    Description: Increasing temperature and CO2 concentration are among the most important factors affecting marine ecosystems under climate change. We investigated the morphological, biochemical, and physiological trait responses of seedlings of the tropical seagrass Enhalus acoroides under experimental conditions. Trait responses were greater under temperature effects than increasing CO2 concentration. Seedlings under rising temperatures showed enhanced leaf growth, lower leaf nutrient content, and stimulated down-regulating mechanisms in terms of photo-physiology. Increasing CO2 concentrations did not show any significant effects independently. There was a significant interaction for some of the trait responses considered, such as leaf number and carbon content in the roots, and trends of higher starch concentrations in the leaves and lower rETRmax under combined enriched CO2 and high temperature, even though none of these interactions were synergistic. Understanding the single and interactive trait responses of seagrass seedlings to increasing temperature and CO2 concentration is of importance to determine the relative responses of early life stages of seagrasses, which may differ from adult plants, in order to form a more holistic view of seagrass ecosystem health under climate change.
    Electronic ISSN: 2076-3417
    Topics: Natural Sciences in General
    Published by Molecular Diversity Preservation International
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    PAPER CURRENT
  • 4
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    Species-Specific Trait Responses of Three Tropical Seagrasses to Multiple Stressors: The Case of Increasing Temperature and Nutrient Enrichment (2020)
    Frontiers Media
    Details
    Publication Date: 2020-11-05
    Electronic ISSN: 1664-462X
    Topics: Biology
    Published by Frontiers Media
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    PAPER CURRENT
  • 5
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    A trait-based framework for seagrass ecology: Trends and prospects (2023)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: In the last three decades, quantitative approaches that rely on organism traits instead of taxonomy have advanced different fields of ecological research through establishing the mechanistic links between environmental drivers, functional traits, and ecosystem functions. A research subfield where trait-based approaches have been frequently used but poorly synthesized is the ecology of seagrasses; marine angiosperms that colonized the ocean 100M YA and today make up productive yet threatened coastal ecosystems globally. Here, we compiled a comprehensive trait-based response-effect framework (TBF) which builds on previous concepts and ideas, including the use of traits for the study of community assembly processes, from dispersal and response to abiotic and biotic factors, to ecosystem function and service provision. We then apply this framework to the global seagrass literature, using a systematic review to identify the strengths, gaps, and opportunities of the field. Seagrass trait research has mostly focused on the effect of environmental drivers on traits, i.e., “environmental filtering” (72%), whereas links between traits and functions are less common (26.9%). Despite the richness of trait-based data available, concepts related to TBFs are rare in the seagrass literature (15% of studies), including the relative importance of neutral and niche assembly processes, or the influence of trait dominance or complementarity in ecosystem function provision. These knowledge gaps indicate ample potential for further research, highlighting the need to understand the links between the unique traits of seagrasses and the ecosystem services they provide.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: other
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    PAPER (OCEANREP)
  • 6
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    Density of Tripneustes gratilla in different seagrass meadows in Changuu Island (Unguja Island, Zanzibar Archipelago, Tanzania) (2022)
    PANGAEA
    Details
    Publication Date: 2023-12-18
    Description: To assess the sea urchin distribution across the seagrass species, we measured the sea urchin density in three monospecific meadows (T. ciliatum, C. serrulata and H. uninervis) and two mixed meadows (dominated by T. hemprichii and by S. isoetifolium) in the study site. We selected three patches per meadow type. Each patch was 25 square meters, delimited with a transect tape. We counted the number of sea urchins at high tide, and divided this number by the surface of the patch to calculate sea urchin density per square meter of meadow (individuals per square meter).
    Keywords: Area; Biodiversity mapping; BIOMAP; Calculated, see abstract; Counted; grazing; Number; seagrass traits; sea urchin; Site; Species; Tripneustes gratilla; tropical seagrass; Unguja_Island_Changuu2; Zanzibar Archipealgo, Tanzania
    Type: Dataset
    Format: text/tab-separated-values, 90 data points
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    DATA PANGAEA
  • 7
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    Seagrass canopy height and leaf area in Changuu Island (Unguja Island, Zanzibar Archipelago, Tanzania) (2022)
    PANGAEA
    Details
    Publication Date: 2023-12-18
    Description: We measured seagrass leaf area and canopy height. We took six biomass cores in random points in the study site Changuu Island. We then measured with a ruler the canopy height (centimeters) as the length of the leaves (from meristem to the tip of the leaf) of each seagrass species in each core. For T. ciliatum, we measured the length of the stem separately and coupled it to the corresponding shoot. Stem and leaf lengths were then summed to obtain canopy height. The length (centimeters) and width (centimeters) of each leaf was measured with a ruler and then multiplied to calculate the leaf area per species (squared centimeters). Special case for T. ciliatum: Some of the datapoints show no data for leaf lenght and width for this species. In these cases, the shoot has been overgrazed and therefore there was no leaf material to measure, and only the stem length was measured.
    Keywords: Calculated, see abstract; Core; CORE; grazing; Identification; Number; Ruler tape; Seagrass, canopy height; Seagrass, leaf area; Seagrass, leaf length; Seagrass, leaf width; seagrass traits; sea urchin; Site; Species; Thalassodendron ciliatum, stem length; tropical seagrass; Unguja_Island_Changuu1; Zanzibar Archipealgo, Tanzania
    Type: Dataset
    Format: text/tab-separated-values, 19385 data points
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    DATA PANGAEA
  • 8
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    Seagrass leaf carbon, nitrogen and phosphorus content and their ratios in Changuu Island (Unguja Island, Zanzibar Archipelago, Tanzania) (2022)
    PANGAEA
    Details
    Publication Date: 2023-12-18
    Description: We measured the % carbon (C), nitrogen (N) and phosphorus (P) content of seagrass leaves. We took three seagrass leaf samples in five meadows of each seagrass species (T. ciliatum, T. hemprichii, H. uninervis, S. isoetifolium, C. serrulata) in Changuu Island and transported them in a cooled container to the Institute of Marine Sciences (Stone Town, Zanzibar). The leaves were cleaned of epiphytes and rinsed with distilled water. We separated the second leaf of each shoot for the measurement, dried them in the oven at 60 degrees for 48 hours, and ground them to a fine powder with mortar and pestle. The samples were then transported to the Leibniz Centre of Tropical Marine Research in Bremen (Germany). Carbon and nitrogen % content was measured in a Euro EA 3000 (EuroVector) analyzer. For the determination of the % phosphorous content of the leaves, we used an alkaline persulphate oxidation method (Koroleff, 1983). We transferred 1 mg of ground sample into a vial and added 4.5 ml of distilled water and 0.5 ml of Oxisolv reagent (Merck). The vials were closed and placed in the oven for one hour at 120 °C. After letting the samples cool down at room temperature, they were centrifuged at 4700 rpm for ten minutes. Three mL of supernatant were placed into another vial and 0.0626 mL of ascorbic acid reagent were added. After mixing, 0.0626 mL of molybdate mix-reagent was added. After a reaction time of 10 minutes, the samples were transferred to a 1 cm macrocuvette. We then measured absorbance at 880 nm in a Shimadzu UV-1700 UV-VIS dual-beam photometer for the % P determination. Finally, we calculated the ratios between C, N and P: C:N.
    Keywords: Atomic weight; Biodiversity mapping; BIOMAP; Calculated, see abstract; Carbon; Carbon/Nitrogen ratio; Carbon/Phosphorus ratio; Determined according to Koroleff (1983); Element analyser Euro EA 3000; grazing; Nitrogen; Number; Phosphorus; Seagrass, leaf carbon; Seagrass, leaf nitrogen; Seagrass, leaf phosphorus; seagrass traits; sea urchin; Site; Species; tropical seagrass; Unguja_Island_Changuu2; Zanzibar Archipealgo, Tanzania
    Type: Dataset
    Format: text/tab-separated-values, 630 data points
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    DATA PANGAEA
  • 9
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    Seagrass abundance in Changuu Island (Unguja Island, Zanzibar Archipelago, Tanzania) (2022)
    PANGAEA
    Details
    Publication Date: 2023-12-18
    Description: We mapped the seagrass meadows in the study area to calculate the total area covered by each seagrass species and the extent of the overgrazing of T. gratilla. The mapping was performed in low tide with a Garmin GPSmap 78s and a transect tape, making a total of six transects parallel to the coast and 20 perpendicular to the coast to form a grid. We recorded patches of seagrass species directly in the GPS by marking the change in the benthic communities along each transect. The meadows were categorized by species and further sub-categorized as overgrazed or not-overgrazed. A meadow was defined as overgrazed when the shoots in the meadow were lacking leaves and meristems except for sparsely distributed ungrazed individual shoots. All data points were transferred to the software Quantum GIS (Version 2.10.1 Pisa). We constructed polygons over the seagrass meadows with the data and the plug-in Open Layers and calculated the total cover area per seagrass species (square meters) and the percentage of the total covered by each seagrass species.
    Keywords: Calculated, see abstract; Garmin GPSmap 62sc (GPS); grazing; Seagrass, cover; seagrass traits; sea urchin; Site; Species; Status; tropical seagrass; Unguja_Island_Changuu3; Zanzibar Archipealgo, Tanzania
    Type: Dataset
    Format: text/tab-separated-values, 30 data points
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    DATA PANGAEA
  • 10
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    Gut content of Tripneustes gratilla in Changuu Island (Unguja Island, Zanzibar Archipelago, Tanzania) (2022)
    PANGAEA
    Details
    Publication Date: 2023-12-18
    Description: To determine the gut content of T. gratilla, we sampled 10 sea urchins along a transect parallel to the coastline and transported them to the Institute of Marine Sciences (Stone Town, Zanzibar). The urchins were collected upon encounter along the transect with the rule of not collecting urchins from the same seagrass patch. This rule was applied to avoid bias towards specific seagrass species. For this analysis, we weighed the sea urchins, measured their diameter to the nearest millimeter with a ruler, and stored them in a 90% ethanol solution. For the gut content analysis, the sea urchins were opened and the content from the whole digestive tract was extracted. The gut content was placed in a Petri dish, and then transferred to a 250 µm mesh to remove the sediment. After the sediment removal, we weighed the gut content fresh weight. Approximately 1 gram (fresh weight) was taken as a sub-sample from the gut content and placed in a new Petri dish to observe under the magnifying glass. Each sample was compared to an example of seagrass material that was prepared specifically for identification after the grazing and digestion process of each species. We imitated this effect by grinding the seagrass species to a similar size and storing them in 90% ethanol solution. Using this method, we could separate the gut contents into the different seagrass species. Contents were then dried in the oven at 60 degrees for 24 hours to obtain their dry weight, and percentage of each seagrass species in the gut was calculated.
    Keywords: Biodiversity mapping; BIOMAP; grazing; Gut content, dry mass; Gut content, wet mass; Identification; Seagrass in gut, dry mass; seagrass traits; sea urchin; see description in data abstract; Site; Species; Tripneustes gratilla, diameter; Tripneustes gratilla, gut content, dry mass; Tripneustes gratilla, gut content, wet mass; Tripneustes gratilla, weight; tropical seagrass; Unguja_Island_Changuu2; Zanzibar Archipealgo, Tanzania
    Type: Dataset
    Format: text/tab-separated-values, 750 data points
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    DATA PANGAEA
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