Spatially Variable Effects of Artificially-Created Physical Complexity on Subtidal Benthos

Abstract

In response to the environmental damage caused by urbanization, Nature-based Solutions (NbS) are being implemented to enhance biodiversity and ecosystem processes with mutual benefits for society and nature. Although the field of NbS is flourishing, experiments in different geographic locations and environmental contexts have produced variable results, with knowledge particularly lacking for the subtidal zone. This study tested the effects of physical complexity on colonizing communities in subtidal habitats in two urban locations: (1) Plymouth, United Kingdom (northeast Atlantic) and (2) Tel Aviv, Israel (eastern Mediterranean) for 15- and 12-months, respectively. At each location, physical complexity was manipulated using experimental tiles that were either flat or had 2.5 or 5.0 cm ridges. In Plymouth, biological complexity was also manipulated through seeding tiles with habitat-forming mussels. The effects of the manipulations on taxon and functional richness, and community composition were assessed at both locations, and in Plymouth the survival and size of seeded mussels and abundance and size of recruited mussels were also assessed. Effects of physical complexity differed between locations. Physical complexity did not influence richness or community composition in Plymouth, while in Tel Aviv, there were effects of complexity on community composition. In Plymouth, effects of biological complexity were found with mussel seeding reducing taxon richness, supporting larger recruited mussels, and influencing community composition. Our results suggest that outcomes of NbS experiments are context-dependent and highlight the risk of extrapolating the findings outside of the context in which they were tested.

Complexity–biodiversity relationships on marine urban structures: reintroducing habitat heterogeneity through eco-engineering

“…This requires identifying the key stressors to species, under a given set of environmental conditions, and identifying those aspects of complexity that successfully mitigate these [ 6 , 21 ]. Adding random habitat complexity to build structures, without knowledge of key environmental stressors to target species, is likely to lead to suboptimal outcomes [ 21 , 28 ]. For example, if the goal of an intervention is to improve water quality, crevice and swimthrough panels that have protective surfaces that bolster the cover of oysters might be selected.…”

“…Interestingly, however, the rockpool panel, which most positively influenced species richness and abundance on the mid shore, was over-represented at the high, but not the low shore of this site. Irrespective, the stronger effects of complexity at low- than mid- or high-intertidal elevations add to growing evidence that benefits of marine eco-engineering are highly context-dependent [ 21 , 28 , 55 ].…”

“…water-retaining feature, pits, holes [ 6 ], but see [ 8 , 23 ] for examples simultaneously manipulating two types of complexity). Despite the positive effects of complexity that have been described at seascape and landscape scales [ 3 ], these interventions have produced effects on biodiversity ranging from highly positive to neutral [ 6 , 21 , 28 ] and on individual functional groups of organisms that range from positive to negative [ 21 ].…”

Effect of habitat topography on the structure and diversity of benthic communities across five marinas from the southwestern Atlantic Ocean

“…Complex habitats are expected to ameliorate conditions when implemented in the intertidal zone, reducing the stress caused by high temperature and desiccation during low tides and then increasing diversity (Vozzo et al, 2021,). This is not the case for communities from the subtidal zone, as those studied here, where habitat complexity is probably not interfering in temperature and other physical parameters of water, resulting in no biodiversity benefits (O'Shaughnessy et al, 2021).…”

“…Even not affecting the physical conditions (O'Shaughnessy et al, 2021), habitat complexity can still provide protection against predators . In our study, where increasing habitat topography affected the abundance of sessile organisms, we observed an increased abundance of ascidians (except for Styela plicata), arborescent bryozoans, hydrozoans, and polychaetes lacking calcareous tubes (mainly Branchioma luctuosum).…”