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Identifying reef fish nursery habitats on subtropical rocky reefs in the Southwestern Atlantic
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.ORCID iD: 0000-0003-1222-2033
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Availability of nursery habitats can potentially limit adult populations of reef fish. Suitable nursery habitats are often shallow and located close to shore, and in many cases overlap with anthropogenic stressors and human activities. For proper management of reef fish communities it is therefore important to identify these habitats and minimize conflicts of habitat use in time and space. To identify potential spatial and temporal patterns of nursery habitat use, the reef fish communities on subtropical rocky reefs in the South western Atlantic were surveyed with under water visual census. Surveys were performed in summer and winter months during two years, along a depth gradient on marginal reefs and in seasonal Sargassum macroalgal beds. No clear patterns in total juvenile abundance and distribution were distinguished between seasons, although some families occurred in significantly higher abundances in summer months (Haemulidae and Sparidae). There were large variances in juvenile abundance between the two surveyed summers, with low total abundance in the summer of 2017, which could be linked to weak upwelling in the area and hampered growth of Sargassum. Similar to in other locations globally, climatic events that affect biomass of Sargassum may hence have large effects on fish recruitment also in the South western Atlantic. In general, shallow areas in sheltered bays had higher abundances of juvenile fish, especially when Sargassum was present in these locations. Spatial patterns of acanthurids and labrid scarinae, were more homogenous compared to those of tropical reefs in the South western Atlantic, where Sargassum beds harbor significantly more juveniles than other habitats. We suggest that fish in sub-tropical rocky reef environments in the South western Atlantic have access to less habitat diversity and complex substrate to use as nursery areas, and thus shallow, sheltered and vegetated habitats are critical for many species. Additionally, those habitats are also the most threatened by human uses demanding proper management.

National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-165463OAI: oai:DiVA.org:su-165463DiVA, id: diva2:1283797
Available from: 2019-01-29 Created: 2019-01-29 Last updated: 2019-02-11Bibliographically approved
In thesis
1. Identification and implications of fish nurseries in tropical and subtropical seascapes
Open this publication in new window or tab >>Identification and implications of fish nurseries in tropical and subtropical seascapes
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Many species of reef fish reside in specific nursery habitats as juveniles. Seagrass meadows, and mangroves are examples of well-recognized nursery habitats, but only recently canopy-forming seaweeds have been found to provide important habitats for some fish species in the tropics. Availability of nurseries can have effects on the abundance and spatial distribution of adult fish, which is why it is important to recognize key nursery habitats for proper management. Information on reef fish nurseries is largely lacking in the South Western Atlantic (SWA), while information in the Western Indian Ocean (WIO) and elsewhere is more extensive. However, more information on the  consequences of nursery availability on adult fish populations is needed. This thesis studies nursery habitat use of reef fish on tropical and subtropical reefs in the SWA and in seagrass and reef systems in the WIO. The hypothesis that seagrass and canopy-forming macroalgae meadows function as a nursery habitat for reef fish is tested in the SWA. The aim of this thesis is also to understand distribution patterns of fish arising from the arrangement of the seascape, using a seascape ecology approach, linking patterns to non-reef nursery habitat use (mangroves and seagrass systems). Results showed that spatial and temporal patterns of juvenile reef fish abundance were weak on rocky, subtropical reefs in the SWA (Paper I), while there was a stronger preference for certain habitats on SWA tropical biogenic reefs, especially seaweed beds dominated by Sargassum (Paper II). The widely accepted paradigm that seagrass meadows function as nursery habitats for reef fish was not supported by the results from the study site in the tropical SWA (Paper II). This may be related to habitat availability in the seascape. In the SWA, seagrass meadows are spatially small, fragmented and less complex, compared to in the WIO, where they display high structural complexity and cover large areas. At the WIO study site (Bazaruto Archipelago), the juvenile fish assemblage in the seagrass meadows encompassed a number of reef fish species from a range of trophic groups and families, as well as resident seagrass species (Paper III). Key variables and extent of spatial scales that structure ontogenetic migrations were identified in both seagrass and reef habitats. Fish distribution patterns in the seagrass seascape was strongly influenced by seascape configuration and distance to adjacent habitats, highlighting that not all seagrass meadows are equally productive as nursery habitats. Variables important for distribution patterns of fish were identified, which in most cases were species-specific, and related to life history and functional traits of species. Effects of two small protected areas on the fish assemblage was also linked to geographical placement of reserves in the seascape. Likewise, the adult fish community composition on the reefs was found to be structured by the spatial arrangement of nursery habitats in the seascape, and presence of stretches of sand acting as isolating barriers (Paper IV). Nursery fish species were less abundant on reefs far from nurseries, resulting in differences in community and functional group composition along distance gradients in the seascape. Depending on functional traits of the nursery fish assemblage, seagrass and mangroves can enhance certain ecological functions on reefs. Both community structure and ecosystem functioning may therefore change depending on nursery habitat availability, highlighting the need to adopt a holistic seascape approach in management.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University, 2019. p. 48
National Category
Ecology
Research subject
Marine Biology
Identifiers
urn:nbn:se:su:diva-165468 (URN)978-91-7797-606-6 (ISBN)978-91-7797-607-3 (ISBN)
Public defence
2019-03-15, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 13:00 (English)
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Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Submitted. Paper 4: Manuscript.

Available from: 2019-02-20 Created: 2019-01-29 Last updated: 2019-02-15Bibliographically approved

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