32 research outputs found
"Ecological interactions between abalone, urchins, and benthic habitat in a temperate reef ecosystem : implications for ecosystems based management"
Material type influences the abundance but not richness of colonising organisms on marine structures
Urbanisation of coastal areas and growth in the blue economy drive the proliferation of artificial structures in marine environments. These structures support distinct ecological communities compared to natural hard substrates, potentially reflecting differences in the materials from which they are constructed. We undertook a meta-analysis of 46 studies to compare the effects of different material types (natural or eco-friendly vs. artificial) on the colonising biota on built structures. Neither the abundance nor richness of colonists displayed consistent patterns of difference between artificial and natural substrates or between eco-friendly and standard concrete. Instead, there were differences in the abundance of organisms (but not richness) between artificial and natural materials, that varied according to material type and by functional group. When compared to biogenic materials and rock, polymer and metal supported significantly lower abundances of total benthic species (in studies assessing sessile and mobile species together), sessile invertebrates and corals (in studies assessing these groups individually). In contrast, non-indigenous species were significantly more abundant on wood than metal. Concrete supported greater abundances of the general community, including habitat-forming species, compared to wood. Our results suggest that the ecological requirements of the biological community, alongside economic, logistic and engineering factors should be considered in material selection for multifunctional marine structures that deliver both engineering and ecological (enhanced abundance and diversity) benefits
The effects of an invasive habitat modifier on the biotic interactions between two native herbivorous species and benthic habitat in a subtidal rocky reef ecosystem
Range expanding species can have major
impacts on marine ecosystems but experimental field
based studies are often lacking. The urchin Centrostephanus
rodgersii has recently undergone a southerly
range expansion to the east coast of Tasmania,
Australia. We manipulated densities of C. rodgersii
and algal regrowth in urchin barrens habitat to test
effects of the urchin on biotic interactions between two
native herbivores, black-lip abalone (Haliotis rubra)
and another urchin (Heliocidaris erythrogramma), and
their benthic habitat. After 13 months, removals of
only C. rodgersii resulted in overgrowth of barrens
habitat by algae and sessile invertebrates. Densities of
abalone increased (?92 %) only in patches from
which C. rodgersii was removed and algal regrowth
allowed. In contrast, densities of H. erythrogramma
increased in all treatments (?45, ?28, ?25 %) in
which C. rodgersii was removed, irrespective of the
algal regrowth manipulations. These results suggest
that C. rodgersii has a negative influence on the
densities of abalone through competition for food and
on densities of H. erythrogramma through competition
for preferred habitat. Densities of abalone (?65 %)
but not H. erythrogramma (?25 %), were lower in the
patches from which C. rodgersii and canopy algae
regrowth were removed relative to patches from which
only C. rodgersii was removed (?92 and ?28 %,
respectively). These results suggest that C. rodgersii
overgrazing of canopy-algae results in loss of structural
complexity which could increase abalone susceptibility
to predation, cause abalone to seek shelter
in cryptic microhabitats and/or prevent their return to
patches where canopy algae are absent. The ongoing
spread of C. rodgersii and expansion of barrens habitat
in eastern Tasmania will continue to negatively affect
populations of these two native herbivores and their
associated fisheries at a range of spatial scales. This
example shows that habitat modifying species which
become highly invasive can have disproportionate
negative impacts on the structure and dynamics of the
recipient community
Effects of a Range-Expanding Sea Urchin on Behaviour of Commercially Fished Abalone
BACKGROUND: Global climate change has resulted in a southerly range expansion of the habitat modifying sea urchin Centrostephanus rodgersii to the east coast of Tasmania, Australia. Various studies have suggested that this urchin outcompetes black-lipped abalone (Haliotis rubra) for resources, but experiments elucidating the mechanisms are lacking. METHODOLOGY/PRINCIPAL FINDINGS: We outline a new framework involving experimental manipulations and Markov chain and Pareto modelling to examine the effects of interspecific competition between urchins and abalone and the effect of intraspecific competition in abalone, assessed as effects on behaviour. Manipulations of abalone densities had no detectable effect on urchin behavioural transitions, movement patterns or resightability through time. In contrast, additions of urchins resulted in abalone shifting microhabitats from exposed to sheltered positions, an increase in the proportion of mobile abalone, and declines in abalone resightability through time relative to controls without the urchins. Our results support the hypothesis of asymmetrical competitive interactions between urchins and abalone. CONCLUSIONS/SIGNIFICANCE: The introduction of urchins to intact algal beds causes abalone to flee and seek shelter in cryptic microhabitat which will negatively impact both their accessibility to such microhabitats, and productivity of the abalone fishery, and will potentially affect their growth and survival, while the presence of the abalone has no detectable effect on the urchin. Our approach involving field-based experiments and modelling could be used to test the effects of other invasive species on native species behaviour
Optimizing the initial cultivation stages of kelp Ecklonia radiata for restoration
Restoration of kelp forests typically relies on transplanting sporophylls to new locations and has limited application in regions with low remnant kelp cover. Cultivated kelp requires fewer sporophylls and is a potential alternative and sustainable source of transplants for large‐scale restoration projects. Naturally sourced fertile sporophylls, however, are still required as ‘seed’ stock in cultivation practices, thus optimizing cultivation methods is important to minimize this dependency on wild stocks. To assist in optimizing the early‐stage cultivation methods for restoring beds of the laminarian kelp Ecklonia radiata, we first tested the effects of sporophyll transport, storage, and dehydration on zoospore release. We then tested for effects of inoculum storage temperature on zoospore abundance, and lastly for media sterilization and inoculum concentration effects on both zoospore settlement and resulting gametophyte densities. Our results show, to maximize zoospore release, sporophylls should be transported dry and inoculated within three hours. Inoculum can be stored at 4°C without affecting zoospore abundance and should be added to sterilized media at lower concentrations to reduce settled zoospore density and improve post‐settlement survival of the gametophyte stage. This study provides practical recommendations for optimizing the initial cultivation procedures of E. radiata. To develop a full life‐cycle cultivation protocol for kelp restoration purposes, future research should focus on optimizing sporophyte production, out‐planting and transplanting techniques
Identifying key factors for transplantation success in the restoration of kelp (Ecklonia radiata) beds
Kelp beds are a defining feature of temperate reefs worldwide, playing a fundamental role as ecosystem engineers and primary producers. Overgrazing by the native sea urchin Heliocidaris erythrogramma has driven a phase shift from kelp beds of Ecklonia radiata to barrens across much of Port Phillip Bay, Victoria. Here we present the results of a transplant experiment, which took juvenile E. radiata sporophytes from a source reef and attached them with silicon tubing to basalt tiles. Following an initial localized cull, we monitored the development and survival of individual E. radiata to investigate the drivers of loss during transplantation, including disturbance (control vs. procedural control), receiving environment (kelp canopy vs. no canopy), and translocation site (within vs. between reefs). We also investigated the role of holdfast reattachment and developmental stage on kelp survival. 69% of the kelp transplants survived over the 17 weeks, with no increased loss resulting from transplantation to a reef 41 km away. We observed high survival of transplants in the absence of ongoing urchin exclusion. Furthermore, the provision of a canopy is not necessary and may result in adverse impacts on survival and development of juvenile sporophyte transplants presumably through competition for light. Individuals at the collection location (controls) were unlikely to survive to maturity suggesting their removal for transplanting is likely to have minimal impact on the kelp population of the donor reef. The methods used could be feasibly upscaled for rehabilitating or restoring kelp beds both in Port Phillip Bay and elsewhere
Eco-engineered mangroves provide complex but functionally divergent niches for estuarine species compared to natural mangroves
There is growing demand for novel coastal protection approaches that also provide co-benefits such as enhanced biodiversity. Rock-fillets, which are used to stabilise eroding banks in estuaries, can be colonised by mangroves, and may provide habitat for estuarine fauna. However, it is unknown whether hybrid mangrove/rock-fillet habitats are functionally equivalent to natural mangroves, for estuarine fauna. To determine whether hybrid mangrove habitats are functionally equivalent to natural mangroves, we used δ13C and δ15N stable isotope analyses to describe the isotopic niche space and overlap of estuarine species in these two habitats across three estuaries in NSW, Australia. Using a Bayesian standard ellipse analysis of isotopic niche area, over half the 12 species observed had larger isotopic niche areas in natural mangroves compared to hybrid habitats, however there were no clear patterns for species between habitats. Natural mangroves and hybrid rock-fillet habitats were isotopically distinct for all species sampled (low proportional overlap, 0–19%) suggesting they are not, at present, wholistically functionally equivalent. Estuarine communities from the two habitat types, however, had similar isotopic niches. Hybrid communities displayed a broader range of δ13C values compared to natural mangroves, suggesting mangrove/rock-fillet habitats have a more diverse range of basal food sources. These findings demonstrate the potential for defence solutions to provide unique co-benefits by supporting food webs, but also that natural habitats provide unique ecosystem services that should be protected and rehabilitated where possible. Future modelling and monitoring of habitat utilisation and species performance could provide further insight into the co-benefits and trade-offs of hybrid habitats
Assessing the coastal protection services of natural mangrove forests and artificial rock revetments
Coastal flooding and erosion cause significant social and economic impacts, globally. There is a growing interestin using natural habitats such as mangroves to defend coastlines. The protective services of mangroves, however,have not been assessed in the same rigorous engineering and socio-economic terms as rock revetments, andtherefore are often overlooked by coastal managers. We used field measurements, a social science survey andeconomic valuation to compare the coastal protection services of mangroves and rock revetments, at five locationsacross Victoria, Australia. The results showed, in sheltered locations, both mangroves and rock revetmentsattenuated waves, however, the wave attenuation (per metre) of rock revetments was greater than mangroves, attwo of the five locations. Only a small proportion of the survey respondents had observed flooding or erosion intheir suburb but most agreed that mangroves provide important coastal protection benefits. Coastal landownersvisited areas with mangroves more often than the public but were less likely to worry about the links between climatechange and coastal erosion and flooding, or to agree that the coast was well protected with existing artificialcoastal infrastructure, than other respondents. There were much higher up-front costs associated with buildingrock revetments, than planting mangroves, but rock revetments required less land than mangroves. Mangrovescovered a larger area and averted more damages than rock revetments. Coastal managers and policy makerswill have more success in advocating for nature-based solutions for coastal protection, if they are implementedin locations where they are eco-engineering and socio-economically acceptable options for climatechange adaptation
Developing a nature-based coastal defence strategy for Australia
Australia’s rapid coastal population growth coupled with the increased risk of hazards driven by climate change creates an urgent need to start adaptation planning for the future. The most common solutions for protecting the coast (seawalls, breakwaters) are expensive and non-adaptive (i.e., they need to be rebuilt, upgraded and maintained in response to a changing climate). There is international precedence for the development of nature-based solutions (i.e., the integration of natural habitats such as coastal vegetation and biogenic reefs) as a cost-effective and sustainable approach to shoreline protection from erosion and flooding. The development of nature-based approaches has been supported by large interdisciplinary teams to inform policy and decision-making. Nature-based coastal defence is currently not a tool widely used in Australia. Key to their wider implementation is: (1) improved scientific knowledge; (2) effective governance; and (3) social acceptance. Recently implemented pilot trials need to inform industry-accredited guidelines that can be integrated into coastal management and government policy
Increasing microhabitat complexity on seawalls can reduce fish predation on native oysters
Increasingly, urbanised coastlines are being armoured by shoreline protection structures, such as seawalls. Seawalls typically lack the complex microhabitats and protective spaces of natural shorelines and consequently organisms that settle on them may be particularly susceptible to predation. We tested whether the addition of complex microhabitats to seawalls enhances the survivorship of oysters, key habitat-forming species on intertidal shores, by reducing the intensity of predation. At two sites in Sydney Harbour, we compared the magnitude and sources of mortality of juvenile oysters among (1) flat tiles, without crevices or ridges; (2) complex tiles, with 2.5 cm high ridges, separated by crevices; and (3) complex tiles, with 5 cm high ridges, separated by crevices. We also compared predatory fish visitation and feeding among sites and treatments using GoPro® cameras. The abundance and feeding of predatory fish was much greater at one of the study sites than the other, but at neither site differed among treatments. At the site with greater predatory fish abundances, survivorship of juvenile oysters was 50% greater on the 5 cm complex tiles than flat tiles, and on complex tiles approximately 300% greater in crevices than on ridges. Of the dead oysters, almost all were cracked, indicative of fish predation. In contrast, at the site with fewer predatory fish, there were no detectable differences in oyster survivorship between treatments. These results suggest that the addition of complex habitat to seawalls could be an effective strategy in reducing fish predation pressure on juvenile oysters at sites with abundant predatory fish. A greater understanding of the site-specific pressures is required to enhance the abundances of desirable species and functions on seawalls