Long-term modifications of coastal defences enhance marine biodiversity

Abstract

SUMMARYRealization that hard coastal infrastructures support lower biodiversity than natural habitats has prompted a wealth of research seeking to identify design enhancements offering ecological benefits. Some studies showed that artificial structures could be modified to increase levels of diversity. Most studies, however, only considered the short-term ecological effects of such modifications, even though reliance on results from short-term studies may lead to serious misjudgements in conservation. In this study, a sevenyear experiment examined how the addition of small pits to otherwise featureless seawalls may enhance the stocks of a highly-exploited limpet. Modified areas of the seawall supported enhanced stocks of limpets seven years after the addition of pits. Modified areas of the seawall also supported a community that differed in the abundance of littorinids, barnacles and macroalgae compared to the controls. Responses to different treatments (numbers and size of pits) were speciesspecific and, while some species responded directly to differences among treatments, others might have responded indirectly via changes in the distribution of competing species. This type of habitat enhancement can have positive long-lasting effects on the ecology of urban seascapes. Understanding of species interactions could be used to develop a rule-based approach to enhance biodiversity.

Biodiversity surveys and stable isotope analyses reveal key differences in intertidal assemblages between tropical seawalls and rocky shores

“…Currently, a multitude of techniques to improve various physical factors of seawalls, for example topo-graphic complexity, slope angle, and elevation, have been attempted (Moreira et al 2007, Chapman & Blockley 2009, Firth et al 2013, Browne & Chapman 2014, Ido & Shimrit 2015, Martins et al 2016). Very few, however, have been targeted directly at recruiting a high abundance and diversity of native algal species (e.g.…”

Patchiness in habitat distribution can enhance biological diversity of coastal engineering structures

“…To test the effect of patchiness on gastropod diversity, 20 plots (25 × 25 cm 2 ) were haphazardly marked at mid‐shore level (approximately 1.50–1.90 m above lowest astronomical tide) of each site, where barnacles, limpets and littorinids are present, and randomly assigned to four treatments ( n = 5): control (no pits added), low, intermediate and high levels of microhabitat patchiness (Figure ). Comparisons of controls and treatments were used to confirm that all the three species, M. neritoides , T. striatus and P. candei , responded positively to the experimental addition of pits (see Martins et al, ). To ensure that the sizes of experimental pits were suitable for the majority of the individuals, the total number and size of pits were established a priori according to previous observational and experimental studies in the area (Martins et al, , ).…”

“…This study builds on previous findings (Martins et al, ; ) to test whether spatial variability (patchiness) in the distribution of microhabitats (pits) can affect snail behaviour and be used as a means to enhance diversity in coastal defence structures.…”

“…Moreover, the contrasting response of limpets and littorinids to microhabitat size had community‐wide cascading effects, leading, in the longer term, to the establishment of very distinct assemblages. Martins et al () also noted that though many individual littorinids were often found aggregating in a single pit, limpets were generally found alone (one individual limpet per pit). This pattern suggests that inter‐ and intraspecific competition (for pits) is higher for limpets than among littorinids.…”

“…This has included the addition of simple topographic features such as pits, grooves, cracks or water‐retaining structures (Browne & Chapman, ; Chapman & Blockley, ; Coombes et al, ; Dafforn et al, ; Dafforn, Mayer‐Pinto, Morris, & Waltham, ; Evans et al, ; Firth, Browne, Knights, Hawkins, & Nash, ; Firth, Mieszkowska, et al, ; Firth, Schofield, White, Skov, & Hawkins, ; Firth, Thompson, et al, , ; Martins, Thompson, Neto, Hawkins, & Jenkins, ; Morris, Chapman, Firth, & Coleman, ; Morris et al, ; Strain et al, for a review). In order to further increase their ecological value, we need to understand how modifications made to coastal defence structures might affect species coexistence with potential long‐lasting effects (Martins, Jenkins, Neto, Hawkins, & Thompson, ).…”