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Sustainable Urban Development: solutions to promote the biological and conservation value of marine urban structures

Final Report Summary - MARURBE (Sustainable urban development: solutions to promote the biological and conservation value of marine urban structures)

Urbanisation is one of the leading causes for habitat and species loss in coastal waters, yet mitigating the effects of urban structures (UMS) on marine life is not a top priority in marine conservation science. Marurbe outlines a new approach for sustainable management of UMS, by acquiring and disseminating ecological knowledge on factors promoting the growth of desired assemblages on UMS.

Specific goals included:

1) enhancing the potential of species with high conservation value to grow on UMS,
2) monitoring the spread of invasive/nuisance species on UMS,
3) examining the ecological footprint of UMS on coastal systems.

In order to provide guidelines for promoting the biological/ecological value of UMS we tested factors facilitating the growth of desirable native species on them, using the canopy-forming alga Cystoseira barbata as model species. We documented the ongoing loss of this species in rocky habitats in the study region in relation to both anthropogenic and natural disturbances. We estimated natural recovery potential by monitoring recruitment, survival and growth patterns of C. barbata recruits, and tested the potential of UMS as suitable substrata for this species.

Transplantation and settlement experiments on substrata of different orientations, composition and complexity demonstrated that Cystoseira can grow on UMS and that most materials commonly used for their construction will equally sustain Cystoseira, and that surfaces with medium levels of small-scale complexity might be advantageous for settlement of the species, provided they are not subsequently disturbed. Long term success may be influenced by key factors including wave exposure, competition with opportunistic species and herbivorous pressure, which seem to be magnified in certain UMS.

Marurbe also analysed effects of UMS on the establishment and spread of invasive/nuisance species. Tunicates were chosen as model species due to their widespread occurrence and considerable impacts on human activities. Surveys and field sampling were carried out throughout the northern Adriatic Sea coastlines, recording the community composition and abundance of ascidians and other dominant space occupiers. Through comparisons between UMS and natural reefs we tested if ascidians assemblages on UMS include a greater proportion of invasive species than natural reefs. Results suggest that invasive and cryptogenic species dominate UMS, while native ones occupy natural habitats almost exclusively, supporting the notion that UMS are not surrogates to natural rocky habitats, thus the strong dominance of invasive ascidians on UMS functions de-facto as barriers for natural spread of native species, disturbing natural corridors. Few if any studies have explored the ecological footprint of UMS on coastal system.

In the second year of the project, we experimentally examined local changes in sedimentary environments and associated assemblages related to the production of detritus originating from UMS. We analysed the effects of detritus from the two most dominant organisms on UMS (Ulva spp., and Mytilus galloprovincialis) on surrounding sedimentary environments. We predicted different effects of these taxa related to different nature of organic material and the provision of shell material associated with mussel deposition. Detritus originated from Ulva spp. and mussels had different effects on both composition and distribution of macrofauna in the sediments, suggesting that mounds of detritus produced by organisms dominating UMS can differently affect adjacent native soft-bottom assemblages. We expect these effects to have significant impacts when scaled up in areas of intense coastal development.

Marurbe demonstrated that it is possible to enhance the ecological and conservation value UMS by careful management. This concept could be applied to any ecosystem by customising it to local conservation needs, making it potentially applicable for any urbanised marine environment.