| 1. |
- Cossa, Damboia, et al.
(author)
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Drones and machine-learning for monitoring dugong feeding grounds and gillnet fishing
- 2023
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In: Marine Ecology Progress Series. - 0171-8630 .- 1616-1599. ; 716, s. 123-136
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Journal article (peer-reviewed)abstract
- Fishing provides an important food source for humans, but it also poses a threat to many marine ecosystems and species. Declines in wildlife populations due to fishing activities can remain undetected without effective monitoring methods that guide appropriate management actions. In this study, we combined the use of unmanned aerial vehicle-based imaging (drones) with machine-learning to develop a monitoring method for identifying hotspots of dugong foraging based on their feeding trails and associated seagrass beds. We surveyed dugong hotspots to evaluate the influence of gillnet fishing activities on dugong feeding grounds (Saco East and Saco West) at Inhaca Island, southern Mozambique. The results showed that drones and machine-learning can accurately identify and monitor dugong feeding trails and seagrass beds, with an F1 accuracy of 80 and 93.3%, respectively. Feeding trails were observed in all surveyed months, with the highest density occurring in August (6040 ± 4678 trails km−2). There was a clear overlap of dugong foraging areas and gillnet fishing grounds, with a statistically significant positive correlation between fishing areas and the frequency of dugong feeding trails. Dugongs were found to feed mostly in Saco East, where the number of gillnet stakes was 3.7 times lower and the area covered by gillnets was 2.6 times lower than in Saco West. This study highlights the clear potential of drones and machine-learning to study and monitor animal behaviour in the wild, particularly in hotspots and remote areas. We encourage the establishment of effective management strategies to monitor and control the use of gillnets, thereby avoiding the accidental bycatch of dugongs.
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| 2. |
- Barcelona, Aina, et al.
(author)
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The role epiphytes play in particle capture of seagrass canopies
- 2023
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In: Marine Environmental Research. - 0141-1136 .- 1879-0291. ; 192
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Journal article (peer-reviewed)abstract
- Seagrass epiphytic communities act as ecological indicators of the quality status of vegetated coastal environments. This study aims to determine the effect leaf epiphytes has on the sediment capture and distribution from outside sources. Thirteen laboratory experiments were conducted under a wave frequency of 0.5 Hz. Three epiphyte models were attached to a Zostera marina canopy of 100 plants/m2 density. The sediment deposited to the seabed, captured by the epiphytic leaf surface, and remaining in suspension within the canopy were quantified. This study demonstrated that the amount of epiphytes impacts on the sediment stocks. Zostera marina canopies with high epiphytic areas and long effective leaf heights may increase the sediment captured on the epiphyte surfaces. Also, reducing suspended sediment and increasing the deposition to the seabed, therefore enhancing the clarity of the water column. For largest epiphytic areas, a 34.5% increase of captured sediment mass is observed. The sediment trapped on the leaves can be 10 times greater for canopies with the highest epiphytic areas than those without epiphytes. Therefore, both the effective leaf length and the level of epiphytic colonization are found to determine the seagrass canopy ability at distributing sediment.
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| 3. |
- Cossa, Damboia, et al.
(author)
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Hidden cost of pH variability in seagrass beds on marine calcifiers under ocean acidification
- 2024
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In: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 915
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Journal article (peer-reviewed)abstract
- Coastal ecosystems experience large environmental variability leading to local adaptation. The key role of variability and adaptation in modulating the biological sensitivity to ocean acidification is increasingly acknowledged. Monitoring and understanding the ecological niche at the right spatio-temporal scale is key to understand the sensitivity of any organism and ecosystems. However, the role of the variability in relevant carbonate chemistry parameters as a driver is often overlooked. For example, the balance between photosynthesis and respiration over the day/night cycle is leading to high pH/pCO2 variability in seagrass beds. We hypothesized that (i) the calcifying larvae of the sea urchin Echinus esculentus exposed to seagrass-driven variability would have some physiological mechanisms to respond to such variability; and (ii) these mechanisms would reach their limit under ocean acidification. We compared the presence and absence of the seagrass Zostera marina in flow through mesocosms fed with seawater with 4 pHs. The carbonate chemistry was monitored and biological response of a sea urchin larvae was documented over 3 weeks. Growth and net calcification rates were measured twice a day to encompass diurnal variability. Our results show that larvae growth rate significantly decreased with decreasing average pHT in both absence and presence of seagrass. Moreover, sea urchin larvae showed a slower growth rate in presence of seagrass, only visible in the lowest pH conditions. In addition, larvae raised in presence of seagrass, maximized calcification during the day, and lower their calcification during the night. In contrast, no significant difference was observed between day and night for the net calcification rate in larvae raised in absence of seagrass. Our results demonstrate the limit of local adaptation to the present range of variability under ocean acidification conditions. It also demonstrates that photosynthetic ecosystems such as seagrass may not play a role of refuge against future ocean acidification.
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| 4. |
- Eggertsen, Linda, 1981-, et al.
(author)
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Where is the grass greenest? Influence of seascape structure and marine protected areas on fish distribution patterns in a seagrass-dominated landscape
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In: Ecography. - 0906-7590 .- 1600-0587.
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Journal article (peer-reviewed)abstract
- Tropical seagrass beds are critical habitats for many resident- and nursery fish species. While numerous studies have explored factors that structure reef fish assemblages, few have investigated the relative influence of multiple factors at fine- and large spatial scales as well as MPAs on seagrass fish. To understand which are the most important factors structuring fish assemblages in tropical seagrass beds, and how this is related to life history of species, we investigated fish distribution patterns at 20 sites in 13 different seagrass beds across the Bazaruto Archipelago, Mozambique. Using boosted regression tree modelling, we assessed the influence of fine-scale variables (seagrass meadow characteristics) and seascape variables (distance to adjacent habitats) on abundance of four nursery taxa (Lutjanus fulviflamma, Lethrinus spp., Scarus ghobban and Gerres spp.) and two resident species (Pelates quadrilineatus and Leptoscarus vaigiensis). We found that seascape variables were generally more important than seagrass characteristics, and that the influence of different variables was highly taxon-specific. Fish distribution patterns in seagrass-dominated seascapes were related to life history traits of the species; nursery fish taxa were negatively correlated with distance to adult habitats, while resident species occurred in higher abundances far from reefs. Proximity to mangroves was important for taxa that utilised mangroves in addition to seagrass as nurseries. Most seascape variables influenced fish abundances on a large spatial scale (km). The influence of protected areas was taxon-specific, with stronger effects on resident species than on nursery species, with geographical placement shadowing potential effects of protection on fish abundance. Our results indicate that protection efforts in seagrass-dominated seascapes can have varying impacts on fish distribution, depending on the geographical location of the reserve. This highlights the importance of considering seascape arrangement and the ecology of targeted species for conservation and marine spatial planning in seagrass-dominated systems.
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| 5. |
- Eggertsen, Linda, 1981-, et al.
(author)
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Where the grass is greenest in seagrass seascapes depends on life history and simple species traits of fish
- 2022
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In: Estuarine, Coastal and Shelf Science. - : Academic Press. - 0272-7714 .- 1096-0015. ; 266
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Journal article (peer-reviewed)abstract
- Tropical seagrass meadows are critical habitats for many fish species, yet few studies have investigated the influence of multiple scale-dependent factors and marine protected areas on seagrass fish species of differing life histories. We assessed the influence of fine-scale seagrass meadow characteristics and seascape-scale variables on the abundance of fish in a seagrass-dominated seascape in the Bazaruto Archipelago, Mozambique, particularly examining patterns of nursery- vs. resident species as well as mobile- vs. sedentary species. We found that fish distribution patterns in this seagrass-dominated seascape were dependent on species’ life history characteristics; nursery taxa showed lower abundance in seagrass meadows further from adult reef habitats, while resident species within seagrass meadows occurred in higher abundances far from reefs. For taxa utilizing both mangroves and seagrass meadows as nursery habitat, proximity to mangroves was an important factor. Fish abundances were generally influenced by variables at the seascape scale (km), while sedentary species were predominantly influenced by area variables, and smaller seascapes (<500 m in radius) better explained distribution patterns. The influence of marine protected areas was taxon-specific, with the strongest effects of protection on resident species. Our results indicate that protection efforts in seagrass-dominated seascapes can have varying impacts on fish distribution, depending on the life history of the species present, and the geographical placement of the reserve within the seascape. Further, we suggest that simple species attributes can be utilised to describe generalized abundance patterns of fish in seagrass seascapes.
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