Laura Airoldi

Oyster Reefs at Risk and Recommendations for Conservation, Restoration, and Management

Native oyster reefs once dominated many estuaries, ecologically and economically. Centuries of resource extraction exacerbated by coastal degradation have pushed oyster reefs to the brink of functional extinction worldwide. We examined the condition of oyster reefs across 144 bays and 44 ecoregions; our comparisons of past with present abundances indicate that more than 90% of them have been lost in bays (70%) and ecoregions (63%). In many bays, more than 99% of oyster reefs have been lost and are functionally extinct. Overall, we estimate that 85% of oyster reefs have been lost globally. Most of the worlds remaining wild capture of native oysters (> 75%) comes from just five ecoregions in North America, yet the condition of reefs in these ecoregions is poor at best, except in the Gulf of Mexico. We identify many cost-effective solutions for conservation, restoration, and the management of fisheries and nonnative species that could reverse these oyster losses and restore reef ecosystem services.

THE EFFECTS OF SEDIMENTATION ON ROCKY COAST ASSEMBLAGES

Sedimentation is a widespread and increasing process on most rocky coasts. The literature on its effects is reviewed and support is found for the general conclusion that sedimen- tation is an important ecological factor for hard bottom organisms. Sediments deeply affect the composition, structure and dynamics of rocky coast assemblages, and increased sediment load as a consequence of anthropogenic activities can be a threat to their diversity and functioning. Sediments that accumulate on rocky substrata are important agents of stress and disturbance. They can cause burial, scour and profound modifications to the characteristics of the bottom surface, and interact with other important physical and biological processes. The effects of sedi- mentation are complex, because they involve both direct outcomes on settlement, recruitment, growth or survival of individual species and indirect outcomes through mediation of competitive and/or predator-prey interactions. Not all species and assemblages are equally affected by sedi- mentation and responses vary over space and time, depending on the characteristics of the depo- sitional environment, life histories of species and the stage of development of individuals and assemblages, and in relation to variable physical factors, including hydrodynamics, light intens- ity and bottom topography. Recent studies have much improved our ability to detect and under- stand the effects of sedimentation on rocky coast assemblages. However, little is still known about the underlying mechanisms. Overall, our present ability to make generalisations and pre- dictions is limited by a paucity of quantitative and experimental research, and by the scant atten- tion devoted to measuring the regime of perturbation by sediments and responses of organisms at relevant spatial and temporal scales. Predicting the magnitude of the effects that different sed- imentation regimes have on rocky coast organisms and the critical levels above which detrimen- tal effects become manifest remains a key issue for the ecology of rocky coasts and a challenge for future studies.

Roles of disturbance, sediment stress, and substratum retention on spatial dominance in algal turf

A common assumption of ecological theories addressing the causes of spatial dominance and stability in natural communities is that organisms have trade-offs between resistance to disturbance, environmental tolerance, and competitive abilities, i.e., that different species or groups of species dominate under different regimes of disturbance and stress. A multifactorial field experiment was conducted from June 1994 to October 1995 in a turf-dominated macroalgal assemblage on a rocky subtidal shore south of Livorno (western Mediterranean, Italy) to test the hypothesis that variable patterns of disturbance and stress influence the differential success of species, and to identify functional characteristics resulting in persistent monopolization of space. The experiment, which included manipulation of the depositional environment, was designed specifically to test whether patterns of recovery following abrasion or removal of the biota differed among patches of different sizes, produced at different times of the...

Integrating abundance and functional traits reveals new global hotspots of fish diversity

Species richness has dominated our view of global biodiversity patterns for centuries. The dominance of this paradigm is reflected in the focus by ecologists and conservation managers on richness and associated occurrence-based measures for understanding drivers of broad-scale diversity patterns and as a biological basis for management. However, this is changing rapidly, as it is now recognized that not only the number of species but the species present, their phenotypes and the number of individuals of each species are critical in determining the nature and strength of the relationships between species diversity and a range of ecological functions (such as biomass production and nutrient cycling). Integrating these measures should provide a more relevant representation of global biodiversity patterns in terms of ecological functions than that provided by simple species counts. Here we provide comparisons of a traditional global biodiversity distribution measure based on richness with metrics that incorporate species abundances and functional traits. We use data from standardized quantitative surveys of 2,473 marine reef fish species at 1,844 sites, spanning 133 degrees of latitude from all ocean basins, to identify new diversity hotspots in some temperate regions and the tropical eastern Pacific Ocean. These relate to high diversity of functional traits amongst individuals in the community (calculated using Rao’s Q), and differ from previously reported patterns in functional diversity and richness for terrestrial animals, which emphasize species-rich tropical regions only. There is a global trend for greater evenness in the number of individuals of each species, across the reef fish species observed at sites (‘community evenness’), at higher latitudes. This contributes to the distribution of functional diversity hotspots and contrasts with well-known latitudinal gradients in richness. Our findings suggest that the contribution of species diversity to a range of ecosystem functions varies over large scales, and imply that in tropical regions, which have higher numbers of species, each species contributes proportionally less to community-level ecological processes on average than species in temperate regions. Metrics of ecological function usefully complement metrics of species diversity in conservation management, including when identifying planning priorities and when tracking changes to biodiversity values.

The effectiveness of coral reefs for coastal hazard risk reduction and adaptation

The world’s coastal zones are experiencing rapid development and an increase in storms and flooding. These hazards put coastal communities at heightened risk, which may increase with habitat loss. Here we analyse globally the role and cost effectiveness of coral reefs in risk reduction. Meta-analyses reveal that coral reefs provide substantial protection against natural hazards by reducing wave energy by an average of 97%. Reef crests alone dissipate most of this energy (86%). There are 100 million or more people who may receive risk reduction benefits from reefs or bear hazard mitigation and adaptation costs if reefs are degraded. We show that coral reefs can provide comparable wave attenuation benefits to artificial defences such as breakwaters, and reef defences can be enhanced cost effectively. Reefs face growing threats yet there is opportunity to guide adaptation and hazard mitigation investments towards reef restoration to strengthen this first line of coastal defence.

Recovery of marine animal populations and ecosystems

Many marine populations and ecosystems have experienced strong historical depletions, yet reports of recoveries are increasing. Here, we review the growing research on marine recoveries to reveal how common recovery is, its magnitude, timescale and major drivers. Overall, 10-50% of depleted populations and ecosystems show some recovery, but rarely to former levels of abundance. In addition, recovery can take many decades for long-lived species and complex ecosystems. Major drivers of recovery include the reduction of human impacts, especially exploitation, habitat loss and pollution, combined with favorable life-history and environmental conditions. Awareness, legal protection and enforcement of management plans are also crucial. Learning from historical recovery successes and failures is essential for implementing realistic conservation goals and promising management strategies.

Effects of sedimentation on subtidal macroalgal assemblages: an experimental study from a mediterranean rocky shore

Abstract The effects of sedimentation on the development and structure of macroalgal assemblages were investigated from June 1992 to December 1993 on a rocky subtidal shore South of Livorno (Ligurian Sea). Experimental procedures were specifically designed to address: (1) which species recruit in patches of bare rock under different sedimentation rates; (2) whether small-scale variations of sediment deposition influence the local diversity of the assemblage; (3) whether the effects of sedimentation are independent from the time of the year when succession begins. Depositional environment was manipulated in the field by means of transparent Plexiglas panels which on average reduced the amount of sediment sinking over the algal assemblage by 35%. Possible effects on the penetration of light and flow microenvironment were assessed. Small-scale variations of sedimentation rates significantly influenced the local structure and diversity of the algal assemblage. Such effects were particularly evident during the recolonisation of patches of bare rock and were dependent upon the time at which succession was initiated. The erect algae were the ones more affected by depositional environment and showed different responses to the experimental reduction of sediment supplies. All the plots were quantitatively dominated by a filamentous turf mostly consisting of Polysiphonia setacea , whose growth was potentially enhanced by reduced sedimentation rates. At the end of the experiments, the overall diversity and evenness of the assemblage were lower in treatments with lessened sediment supplies. It is suggested that small-scale spatial variability of the depositional environment may affect the within-habitat diversity of algal assemblages either through direct effects on individual species or on their propagules, and through indirect effects mediated by competitive outcomes.

Distribution and dynamics of epibiota on hard structures for coastal protection

Hard structures for protection against erosion of shores are some of the most common human-made constructions in coastal areas. Nevertheless, little is known as to how marine organisms respond to their presence. The composition and distribution of intertidal epibiota at different positions around different types of defence structures (groynes and breakwaters) at three stations along the Emilia Romagna coast (Italy) were analysed. Sampling covered a range of scales: meters (distance among replicate plots), hundreds of meters (distance among replicate areas) and tens of kilometres (distance among stations). The colonisation and dynamics of conspicuous species over 1 year, following maintenance works on two structures, were also quantified. Assemblages on defence structures were characterised by a notably low richness of species, by strong spatial dominance of mussels and green ephemeral algae, and by high rates of colonisation. Abundance of mussels, Enteromorpha intestinalis and filamentous algae differed significantly among nearby areas within stations. Mussels were significantly less abundant along the landward side of breakwaters compared with all other positions on both groynes and breakwaters. Overall, however, fewer differences, than expected, were observed in the distribution of species at different positions around groynes and breakwaters, probably as a consequence of the low complexity of the colonising assemblages. Possible factors explaining the patterns of distribution observed are discussed, including the roles of harvesting of mussels and frequent maintenance works on the structures. The implications of the low richness of species observed in terms of management of defence structures and other human-made constructions are discussed.

EFFECTS OF DISTURBANCE, LIFE HISTORIES, AND OVERGROWTH ON COEXISTENCE OF ALGAL CRUSTS AND TURFS

Coexistence of species is generally attributed to the interacting roles of competition, predation, and disturbance. Overgrowth is considered to be an important mechanism of competition for space, and species are often ranked in hierarchies based on their abilities to overgrow. In some marine habitats, however, encrusting algae dominate primary substrata despite a dense permanent cover of epiphytes, suggesting that factors other than competition could be important in influencing their distributions. The spatial relationships and competitive interactions between encrusting algae and overgrowing filamentous, turf-forming algae were investigated on a subtidal rocky reef (Mediterranean Sea, Italy). Quantitative observations and field experiments were done from 1992 to 1998: (1) to investigate the relative patterns of distribution and abundance of crusts and turf and how they differed across space and time, (2) to test whether spatial relationships between crusts and turf were influenced by various characteristics of the substratum and by disturbance from wave action, (3) to investigate spatial and temporal patterns of recruitment and the mechanisms by which crusts colonize space, and (4) to test whether crusts and turf compete for space. Crusts were always among the first colonizers of available bare rock and were subsequently overgrown by turf. Despite variations in spatial and temporal recruitment of crusts, this pattern was never reversed. Covers of crusts and turf were not significantly affected by disturbance. There was some evidence for competition, but this did not result in the local exclusion of either crusts or turf. Despite extensive and persistent cover of turf, encrusting algae were abundant and were able to live, grow, and reproduce beneath the turf over long periods with little adverse effect. Similarly, crusts did not limit the distribution of turf, although they slowed its rate of growth. The capabilities of turf and crusts to overgrow and tolerate overgrowth, respectively, were identified as the major determinants of the structure of this two-layered assemblage and the probable basis of the success of these species in coexisting as the dominant algal forms. Overgrowth was not equivalent to competitive subordination and displacement, emphasizing the need for caution when interpreting competitive abilities from observed patterns of overgrowth. Overall, results suggested that, in some habitats, tolerance may be more important than competition in maintaining coexistence of species and influencing community structure.

Marine urbanization: an ecological framework for designing multifunctional artificial structures

Underwater cities have long been the subject of science fiction novels and movies, but the “urban sprawl” of artificial structures being developed in marine environments has widespread ecological consequences. The practice of combining ecological principles with the planning, design, and operation of marine artificial structures is gaining in popularity, and examples of successful engineering applications are accumulating. Here we use case studies to explore marine ecological engineering in practice, and introduce a conceptual framework for designing artificial structures with multiple functions. The rate of marine urbanization will almost certainly escalate as “aquatourism” drives the development of underwater accommodations. We show that current and future marine developments could be designed to reduce negative ecological impacts while promoting ecosystem services.