Shading impacts by coastal infrastructure on biological communities from subtropical rocky shores

Abstract

Summary1. Artificial shading has been highlighted as an important human disturbance, affecting both productivity and community organization. However, studies of shading have been poorly explored from an environmental impact perspective. 2. We compared community structure on subtropical rocky shores in areas shaded by human constructions with those in unshaded areas. We then implemented a manipulative field experiment to determine the effects of shading on the macrobenthic community, biofilm biomass and larval recruitment. 3. Shading consistently affected the biological community of rocky shores. The biomass and cover of macroalgae and the size of most sedentary grazers were smaller in shaded habitat. In the infralittoral fringe, we recorded a shift in dominance from macroalgae in unshaded habitats to invertebrate filter feeders in shaded ones. In a similar way, the community from the mesolittoral was also affected by shading but not at all locations. 4. Experimental manipulation of shading led to a total loss of macroalgae from the infralittoral fringe and no community replacement over a period of 220 days. In the mesolittoral, oysters became more abundant in shaded conditions, while barnacles decreased in abundance. Larval recruitment was also affected, with oysters and barnacles recruiting more in shaded habitats. 5. Synthesis and applications. We demonstrate a clear impact of shading by artificial humanmade structures on patterns and processes regulating biodiversity on rocky shores and thus consequences for coastal ecosystem functioning. We argue that shading by artificial coastal structures, such as those proposed in the port expansion in our study site in south-eastern Brazil, is potentially underestimated. Our work emphasizes the importance of careful evaluations of artificial structures in order to promote sustainable coastal development. As a result, we do not recommend the proposed expansion by suspended structures of the port of São Sebastião, as the consequent shading will negatively affect the biodiversity and ecosystem functioning of the Arac ß a Bay and surrounding areas.

Co-occurring morphologically distinct algae support a diverse associated fauna in the intertidal zone of Araçá Bay, Brazil

“…This is crucial to diversity maintenance not only in the local scale (among patches), but also in larger scales (regional diversity), with broad implications to conservation, especially today with the anthropogenic threat that most coastal systems have been facing, such as the Araçá Bay. The expansion of São Sebastião Harbor may lead not only to a homogenization of conditions, which may result on the survivor of only few resistant species, but will also preclude algae survivorship through light limitation caused by the suspended platforms (Pardal-Souza et al 2017). As a consequence, following the decrease of diversity of macroalgae species, we may also expect a great loss of diversity of associated organisms, since they are closely related to their hosts.…”

“…Recently, the Araçá Bay system has being threatened by the plan of expansion of São Sebastião Harbor (for details check Pardal-Souza et al 2017), which would lead to irreversible damages to this ecosystem. Although the plan consists in covering the bay with suspended platforms, a recent study conducted in the area has shown that the limitation of light imposed by the platforms may lead to significant changes in the structure of sessile and mobile community, reducing the occurrence of macroalgae (Pardal-Souza et al 2017).…”

The outsized trophic footprint of marine urbanization

“…; Pardal‐Souza et al . ). These communities, forming on human‐made habitats, can achieve densities of up to 270 kg m −2 in a single year (Figure ; Rajagopal et al .…”

“…One general but rarely recognized effect of marine urbanization is that most artificial structures increase the proportion of shaded and vertical-facing substrata compared to natural habitats (Dafforn et al 2015;Firth et al 2015). Floating platforms, barges, piers, pontoon, seawalls, or port quays decrease access to direct sunlight, thereby reducing the ability of autotrophic organisms to colonize the available space and promoting the formation of dense communities of filter-feeding sessile invertebrates (eg barnacles, mussels, ascidians, polychaetes; Dafforn et al 2015;Firth et al 2015;Pardal-Souza et al 2017). These communities, forming on human-made habitats, can achieve densities of up to 270 kg m −2 in a single year ( Figure 1; Rajagopal et al 1991) and can alter the natural trophic pyramid.…”

Efeitos de estressores múltiplos no impacto da acidificação oceânica na biota marinha

“…Algumas regiões costeiras têm sofrido progressivamente com a redução de pH (Waldbusser et al, 2011), que pode ocorrer simultaneamente ao sombreamento do ambiente consequente da construção de portos, marinas, píeres (Shaffer, 1999;Roca et al, 2014), pontes (Struck et al, 2004) e sistemas de aquicultura (ostras; Forrest et al, 2009;Bulmer et al, 2012). Distúrbios na disponibilidade de luz impactam drasticamente a estrutura das comunidades em zonas costeiras (Pardal-Souza et al, 2017), afetando não somente espécies fotossintetizantes (Benham et al, 2016), como também a composição de espécies de invertebrados bentônicos (Glasby 1999;Struck et al, 2004). Nestes ambientes, crustáceos apresentam importante papel ecológico nas teias tróficas (Shaffer et al, 1995;Laidre & Greggor, 2015) e no fluxo de energia do ecossistema (Robertson, 1986;Kristensen, 2008), sendo impactados por condições ambientais estressantes, que podem alterar aspectos fisiológicos (Vernberg & Vernberg, 1972;Dissanayake & Ishimatsu, 2011;Madeira et al, 2014) e comportamentais (Dissanayake & Ishimatsu, 2011).…”