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Sea cages, seaweeds and seascapes: Causes and consequences of spatial links between aquaculture and ecosystems
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.ORCID iD: 0000-0001-5814-5905
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aquaculture is of growing importance in the global seafood production. The environmental impact of aquaculture will largely depend on the type of environment in which the aquaculture system is placed. Sometimes, due to the abiotic or biotic conditions of the seascape, certain aquaculture systems tend to be placed within or near specific ecosystems, a phenomenon that in this thesis is referred to as aquaculture system - ecosystem links. The exposed ecosystems can be more or less sensitive to the system specific impacts. Some links are known to be widespread and especially hazardous for the subjected ecosystem such as the one between the shrimp aquaculture and the mangrove forest ecosystem. The aim of this thesis was to identify and investigate causes and consequences of other spatial links between aquaculture and ecosystems in the tropical seascape.

Two different aquaculture system - ecosystem links were identified by using high resolution satellite maps and coastal habitat maps; the link between sea cage aquaculture and coral reefs, and the one between seaweed farms and seagrass beds. This was followed by interviews with the sea cage- and seaweed farmers to find the drivers behind the farm site selection. Many seaweed farmers actively choose to establish their farms on sea grass beds but sea cage farmers did not consider coral reefs when choosing location for their farms. The investigated environmental consequences of the spatial link between sea cage aquaculture and coral reefs were considerable both on the local coral reef structure, and coral associated bacterial community. Furthermore, coral reef associated fish are used as seedlings and feed on the farms, which likely alter the coral food web and lower the ecosystem resilience. Unregulated use of last resort antibiotics in both fish- and lobster farms were also found to be a wide spread practice within the sea cage aquaculture system, suggesting a high risk for development of antibiotic resistant bacteria. The effects of seaweed farms on seagrass beds were not studied in this thesis but have earlier been shown to be rather substantial within the borders of the farm but less so outside the farm.

Further, a nomenclature is presented to facilitate the discussion about production system - ecosystem links, which may also be used to be able to incorporate the landscape level within eco-certifying schemes or environmental risk assessments. Finally - increased awareness of the mechanisms that link specific aquaculture to specific habitats, would improve management practices and increase sustainability of an important and still growing food producing sector - the marine aquaculture.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2017. , p. 45
Keywords [en]
Spatial links, Aquaculture, Coral Reefs, Seagrass, Seascape
National Category
Fish and Aquacultural Science
Research subject
Marine Ecotoxicology
Identifiers
URN: urn:nbn:se:su:diva-141009ISBN: 978-91-7649-787-6 (print)ISBN: 978-91-7649-788-3 (electronic)OAI: oai:DiVA.org:su-141009DiVA, id: diva2:1087222
Public defence
2017-05-24, Vivi Täckholmssalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-04-28 Created: 2017-04-06 Last updated: 2017-05-09Bibliographically approved
List of papers
1. Spatial correlation and potential conflicts between sea cage farms and coral reefs in South East Asia
Open this publication in new window or tab >>Spatial correlation and potential conflicts between sea cage farms and coral reefs in South East Asia
2015 (English)In: Aquaculture, ISSN 0044-8486, E-ISSN 1873-5622, Vol. 448, p. 418-426Article in journal (Refereed) Published
Abstract [en]

In the South China and Java Seas, cage farming is a recent regional activity, which since the year 2000 has experienced an annual growth of 29%. The region holds the highest diversity of marine life, which is partly or completely dependent on coral reefs. The increasingly growing coastal human population in the area relies on ecosystem goods and services provided by the reefs that are threatened by anthropogenic activities. Sea cage farming is one of the stressors negatively impacting coral reefs by being point sources of nutrients and other effluents. To date no systematic information is available on the physical location of marine farms in relation to the coral reefs. Little is known about the distance where impact from the farms can be detected on nearby coral reefs. The present survey aimed to fill this gap by assessing to what extent marine cage farms in South East Asia are placed in the vicinity of the reefs and at which distance stress indicators from the farms are observed. We used Google Earth satellite images to investigate the extension and spatial distribution of sea cage aquaculture in relation to the presence of coral reefs. The stress indicators were locally assessed in Central Vietnam by recording turf algal overgrowth, coral mortality, live coral and branching coral cover at increasing distances from the farms. We found that 90% of sea cage farms throughout the region clustered closer than 5 km from coral reefs and 50% of them closer than 1 km from reefs. In Taiwan, 71% of the cages were located within 100m from a reef. This pattern is nonrandom and could not be explained by the natural distribution of coral reefs; only 5% of the Vietnamese coast harbors coral reefs, and sea cage farms are present in these areas only. This indicates that the farms require similar conditions as the reefs including clear and shallow waters and protection against storms and wave action. We found that turf algal overgrowth decreased at 287 m +/- 54 m, dead coral at 1446m +/- 154 m, live coral cover increased at 566 +/- 221 m and branching corals increased at 867 m +/- 140 m from the cage farms. We conclude that proximity to coral reefs should be considered when planning future developments of sea cage aquaculture, and recommend that distances of at least 1.5 km should be kept. Statement of relevance: Consider coral reefs when planning sea cage aquaculture site.

Keywords
Google Earth, Marine cage aquaculture, Coral reefs, South East Asia, Spatial planning
National Category
Agricultural Science, Forestry and Fisheries Biological Sciences
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-121485 (URN)10.1016/j.aquaculture.2015.06.024 (DOI)000360189000054 ()
Available from: 2015-10-13 Created: 2015-10-05 Last updated: 2017-04-18Bibliographically approved
2. Causes and consequences of spatial links between sea cage aquaculture and coral reefs in Vietnam
Open this publication in new window or tab >>Causes and consequences of spatial links between sea cage aquaculture and coral reefs in Vietnam
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(English)Manuscript (preprint) (Other academic)
Keywords
Sea cage aquaculture, Coral reef, Vietnam, Spatial planning, Trashfish
National Category
Biological Sciences
Research subject
Ecotoxicology
Identifiers
urn:nbn:se:su:diva-140999 (URN)
Available from: 2017-03-28 Created: 2017-03-28 Last updated: 2017-04-18Bibliographically approved
3. Habitat preference for seaweed farming – a case study from Zanzibar, Tanzania
Open this publication in new window or tab >>Habitat preference for seaweed farming – a case study from Zanzibar, Tanzania
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(English)Manuscript (preprint) (Other academic)
Keywords
Seagrass, Aquaculture, Mariculture, Algae, Eucheuma denticulatum and Kappaphycus alvarezii
National Category
Agricultural Sciences Fish and Aquacultural Science
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-141000 (URN)
Available from: 2017-03-28 Created: 2017-03-28 Last updated: 2017-04-18Bibliographically approved
4. Antibiotic use on Vietnamese fish and lobster sea cage farms and implications for the coral reef environment and human health
Open this publication in new window or tab >>Antibiotic use on Vietnamese fish and lobster sea cage farms and implications for the coral reef environment and human health
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(English)Manuscript (preprint) (Other academic)
Keywords
Antibiotics, Fungia fungites, Bacillus niabensis, Sea cage aquaculture
National Category
Fish and Aquacultural Science
Research subject
Marine Ecotoxicology
Identifiers
urn:nbn:se:su:diva-141004 (URN)
Available from: 2017-03-28 Created: 2017-03-28 Last updated: 2017-04-18Bibliographically approved

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