Influence of Algal Farming on Fish Assemblages

Bergman, Kajsa C; Svensson, Sara; Öhman, Marcus

doi:10.1016/s0025-326x(01)00168-0

Cited by 42 publications

(64 citation statements)

References 28 publications

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“…The lack of effects on total abundance and diversity, which contrasts previous findings (e.g. Russell 1983, Bergman et al 2001, is probably accounted for by the relative short term of this study (11 wk), where the decrease of one structurally important habitat component (seagrass shoots) compared to controls was compensated for by the addition of another (farmed algae). However, the abundance of sea urchins was 4 times higher in farm plots compared to controls.…”

Section: Effects Of Farmingcontrasting

confidence: 99%

“…Since this figure also includes remnant patches between plots, the actual cover underneath farmed plots was much lower. This undoubtedly affects the habitat structural complexity, and although the farmed algae seem to counter-balance part of this change (Bergman et al 2001, Eklöf et al 2006, it will certainly affect the structure of associated communities (Bergman et al 2001, Eklöf et al 2005, this study). For some taxa, e.g.…”

Section: Implications For Ecosystem Structure and Functionmentioning

confidence: 75%

“…By altering habitat and involuntary spreading farmed algae to adjacent areas, seaweed farming seems to affect many components of natural communities e.g. bacteria (Johnstone & Ólafs-son 1995), meiofauna (Ólafsson et al 1995), benthic macrofauna (Eklöf et al 2005), fish (Bergman et al 2001) and scleractinian corals (Russell 1983). However, as environmental impacts are still disputed (see e.g.…”

Section: Introductionmentioning

confidence: 99%

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Effects of tropical open-water seaweed farming on seagrass ecosystem structure and function

Eklöf¹,

Henriksson

Kautsky³

2006

Mar. Ecol. Prog. Ser.

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Seaweed farming is often depicted as a sustainable form of aquaculture, but suspected habitat alterations and spread of algae outside farms have rendered speculations on the actual degree of sustainability. We conducted an experimental field study on Unguja Island (Zanzibar, Tanzania) to investigate the effects of off-bottom seaweed farming on a tropical seagrass ecosystem, using 1.5 × 2.5 m experimental farm plots. After 11 wk, above-ground seagrass biomass was 40% lower than in control plots, owing to a combination of lower shoot density, shoot length and leaf growth rate. Since the biomass was constant between Day 15 and 75 in the farm (F) treatment, but increased by 67 vs. 48% in the 2 controls (control treatment [C] and stick-and-line control treatment [CSL]), the effect exerted by the farm was a lack of potential biomass increase rather than an actual decrease. The effect was transplanted to associated organisms both in terms of lower seagrass epiphyte cover and changes in the abundance of 2 dominating epifauna taxa (>1 cm): sea urchins and sponges. Furthermore, the F treatment caused an accumulation of seagrass leaf litter, but did not affect sediment organic matter (SOM) content. The mechanisms behind these effects were not explicitly tested, but algal shading, emergence stress and mechanical abrasion were identified as likely contributors. Interestingly, the effects were largely restricted to 1 of the 2 seagrass species present, Enhalus acoroides, while the other, Thalassia hemprichii, remained more or less unaffected. This may be due to reduced interspecific competition or species-specific differences in morphology and stress tolerance, and could in the long-term have implications for (amongst others) associated fish communities. Although seaweed farming at the current level is less detrimental than, for example, intensive shrimp farming, and therefore should be seen as a strong option for future aquaculture developments, intensive farming on seagrasses should be avoided or at least minimized by, for example, implementing other farming methods. The risk of ecosystem-level changes in large-scale and uncontrolled farm enterprises warrants a holistic and integrated coastal management approach which considers all aspects of the tropical seascape including human societies and natural resource use.KEY WORDS: Environmental effects · Seagrass ecosystems · Seaweed farming · Aquaculture · Algae · Eucheuma denticulatum Resale or republication not permitted without written consent of the publisher

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Section: Effects Of Farmingcontrasting

confidence: 99%

Section: Implications For Ecosystem Structure and Functionmentioning

confidence: 75%

Section: Introductionmentioning

confidence: 99%

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Effects of tropical open-water seaweed farming on seagrass ecosystem structure and function

Eklöf¹,

Henriksson

Kautsky³

2006

Mar. Ecol. Prog. Ser.

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“…This also corroborates previous studies (Priyadarshana et al 2001). Among the benefits of high macroalgal cover are provision of structural complexity (Diehl 1992), which, in turn, can affect fish abundance and diversity (Bergman et al 2001), microhabitat types (Adams et al 2004) and positive effects on predator-prey interactions (Flynn & Ritz 1999). The percentage of vegetation cover was correlated to indices at both levels of spatial resolution, whereas the abundance of Phaeophyta was strongly correlated to 3 or more indices on both spatial levels, highlighting both the importance of vegetation in general, but, in parti cular, the strong positive effects of canopy-forming macro algae (Fernandez et al 2009) in providing tertiary structure.…”

Section: Discussionmentioning

confidence: 99%

“…Such variables, e.g. measures of structural complexity of the reef matrix (Steele 1999) or aspects of the vegetation (Bergman et al 2001), vary substantially, on the order of metres (Flynn & Ritz 1999), and can affect abundance of fishes at similar spatial scales. Variables operating at smaller grain sizes can be upscaled, i.e.…”

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confidence: 99%

Identification of discrete and ecologically relevant types of ichthyo-habitat at two spatial scales for process-based marine planning

Jung

Swearer²

2011

Aquat. Biol.

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One objective of marine planning is the protection of biodiversity. The majority of planning strategies are based on descriptive methodologies, i.e. detecting and managing diversity hotspots. The disadvantage of such approaches is the lack of explanatory power in elucidating what facilitates the variation in diversity. The present study proposes an alternative approach: planning based on ecological processes. Correlations between 24 variables of the biophysical habitat and 4 ecological indices of fish assemblage composition were established. Variables strongly correlated to at least 1 index (adjusted r 2 > 0.6) were regarded as likely drivers of variation and used as a basis for cluster analyses to classify discrete, ecologically relevant habitat types. Variables were quantified at 2 spatial scales: individual transects (at scales of 10s of meters) and whole reefs (at scales of 100s of meters to kilometers). Habitat variables at the reef scale were not strongly correlated to ecological indices as often as variables at the transect scale. Aspects of vegetation and habitat complexity correlated strongly to most indices. In all approaches, high capacity habitat, i.e. habitat containing high values of habitat variables positively correlated to diversity indices, was defined by high abundance of Phaeophyta and high structural complexity of the reef itself. High capacity habitat was spatially confined. All cluster analyses yielded similar spatial patterns of habitat types. The statistical methodology used in the present study -identifying distinct and ecologically relevant habitat types and habitat with high capacity to support high diversity -be a useful approach for identifying candidate areas for protection in marine conservation planning. KEY WORDS: Process-based management · Diversity · Fishes · Rocky reefs · HabitatResale or republication not permitted without written consent of the publisher Aquat Biol 12: 187-196, 2011 (Anderson & Millar 2004). Habitat variables operate at different spatial scales or grain sizes (Wiens 1989, Arias-Gonzalez et al. 2008, and it can be difficult to detect their respective effect when such variables are assessed at an inappropriate grain size (Underwood & Chapman 1998). The grain size for some habitat variables is the reef itself. Such variables include the size of the reef (MacNeil et al. 2009), effects of the surrounding matrix, e.g. distance to other reefs or other distinct habitats, or the reef perimeter, potentially facilitating edge effects (Dorenbosch et al. 2005). These habitat variables can affect fish assemblages at spatial scales of kilometres (Dorenbosch et al. 2006).Other habitat variables can be analysed at smaller grain sizes, i.e. 'patch' or 'transect' scales. Such variables, e.g. measures of structural complexity of the reef matrix (Steele 1999) or aspects of the vegetation (Bergman et al. 2001), vary substantially, on the order of metres (Flynn & Ritz 1999), and can affect abundance of fishes at similar spatial scales. Variables operating at smaller...

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Extensive spread of farmed seaweeds causes a shift from native to non-native haplotypes in natural seaweed beds

et al. 2015

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Influence of Algal Farming on Fish Assemblages

Cited by 42 publications

References 28 publications

Effects of tropical open-water seaweed farming on seagrass ecosystem structure and function

Effects of tropical open-water seaweed farming on seagrass ecosystem structure and function

Identification of discrete and ecologically relevant types of ichthyo-habitat at two spatial scales for process-based marine planning

Extensive spread of farmed seaweeds causes a shift from native to non-native haplotypes in natural seaweed beds

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