The effects of manipulating microhabitat size and variability on tropical seawall biodiversity: field and flume experiments
Loke, L.H.L.; Bouma, T.J.; Todd, P.A. (2017). The effects of manipulating microhabitat size and variability on tropical seawall biodiversity: field and flume experiments. J. Exp. Mar. Biol. Ecol. 492: 113-120. https://dx.doi.org/10.1016/j.jembe.2017.01.024 In: Journal of Experimental Marine Biology and Ecology. Elsevier: New York. ISSN 0022-0981; e-ISSN 1879-1697, more |  |
| Author keywords | Coastal defences; Ecological engineering; Habitat complexity; Hydrodynamics; Microhabitat; Seawalls |
| Authors | | Top | - Loke, L.H.L.
- Bouma, T.J., more
- Todd, P.A.
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| Abstract | Previous studies have shown that concrete tiles on seawalls that incorporate microhabitat size variability (i.e.complexity) can increase species richness compared to unmodified seawalls. In a recent study, we showedthat manipulating complexity at the 4–28 mm scale can have an effect on seawall community compositionand that the type of structural component (microhabitats such as pits and grooves) can influence assemblage diversityindependently of their complexity. It is not known, however, whether these effects will be exhibited at alarger scale; in other words,will the positive relationship be present if the size range of components on concretetiles is enlarged (8–56mm). Therefore, in the present study,we examine: (1) the effects of changing the scale ofstructural manipulation on species richness and, (2) the hydrodynamic properties (i.e. velocity of flow over thewhole tile) of different designs.We doubled the size of all x, y and z dimensions to create 400 × 400 × 64 mmconcrete tiles (up from 200 × 200 × 32 mm in the previous study) with two different basic designs: ‘Pits’ and‘Grooves’. These were deployed for one year at two island sites off Singapore’smainland alongwith ‘Granite control’tiles so that we could assess what the existing seawall would host within the same timeframe. Resultsshowed that the ‘complex’ tiles supported greater richness (S) than ‘simple’ ones, suggesting that the sizerange tested here (8–56mm) is relevant to tropical intertidal communities. Flume experiments revealed similarwave amplitude values over the surfaces of all tile types, including the granite controls, suggesting that intertidalorganisms are unlikely to colonise the tiles differentially as a result of cm-scale hydrodynamic differences, i.e. thedominant mechanism underlying this ‘complexity-diversity’ relationship is unlikely to be due to differences inflow velocities over a 400 × 400 mm tile surface but, rather, is related to resource (e.g. refuge) availability.These results help identify the “scale of effect” of topographic complexity which can be directly integrated intoecological engineering designs to increase biodiversity on tropical seawalls. |
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