larval recruitment
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2022 ◽  
Vol 8 ◽  
Author(s):  
Mizuki Horoiwa ◽  
Takashi Nakamura ◽  
Hideaki Yuasa ◽  
Rei Kajitani ◽  
Yosuke Ameda ◽  
...  

The estimation of larval dispersal on an ecological timescale is significant for conservation of marine species. In 2018, a semi-population outbreak of crown-of-thorns sea star, Acanthaster cf. solaris, was observed on a relatively isolated oceanic island, Ogasawara. The aim of this study was to assess whether this population outbreak was caused by large-scale larval recruitment (termed secondary outbreak) from the Kuroshio region. We estimated larval dispersal of the coral predator A. cf. solaris between the Kuroshio and Ogasawara regions using both population genomic analysis and simulation of oceanographic dispersal. Population genomic analysis revealed overall genetically homogenized patterns among Ogasawara and other Japanese populations, suggesting that the origin of the populations in the two regions is the same. In contrast, a simulation of 26-year oceanographic dispersal indicated that larvae are mostly self-seeded in Ogasawara populations and have difficulty reaching Ogasawara from the Kuroshio region within one generation. However, a connectivity matrix produced by the larval dispersal simulation assuming a Markov chain indicated gradual larval dispersal migration from the Kuroshio region to Ogasawara in a stepping-stone manner over multiple years. These results suggest that the 2018 outbreak was likely the result of self-seeding, including possible inbreeding (as evidenced by clonemate analysis), as large-scale larval dispersal from the Kurishio population to the Ogasawara population within one generation is unlikely. Instead, the population in Ogasawara is basically sustained by self-seedings, and the outbreak in 2018 was also most likely caused by successful self-seedings including possible inbreeding, as evidenced by clonemate analysis. This study also highlighted the importance of using both genomic and oceanographic methods to estimate larval dispersal, which provides significant insight into larval dispersal that occurs on ecological and evolutionary timescales.


2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Kristina L. Remple ◽  
Nyssa J. Silbiger ◽  
Zachary A. Quinlan ◽  
Michael D. Fox ◽  
Linda Wegley Kelly ◽  
...  

AbstractWork on marine biofilms has primarily focused on host-associated habitats for their roles in larval recruitment and disease dynamics; little is known about the factors regulating the composition of reef environmental biofilms. To contrast the roles of succession, benthic communities and nutrients in structuring marine biofilms, we surveyed bacteria communities in biofilms through a six-week succession in aquaria containing macroalgae, coral, or reef sand factorially crossed with three levels of continuous nutrient enrichment. Our findings demonstrate how biofilm successional trajectories diverge from temporal dynamics of the bacterioplankton and how biofilms are structured by the surrounding benthic organisms and nutrient enrichment. We identify a suite of biofilm-associated bacteria linked with the orthogonal influences of corals, algae and nutrients and distinct from the overlying water. Our results provide a comprehensive characterization of marine biofilm successional dynamics and contextualize the impact of widespread changes in reef community composition and nutrient pollution on biofilm community structure.


2021 ◽  
Author(s):  
◽  
Joseph Marlow

<p>Coral reefs are among the most diverse ecosystems on the planet, yet they are also sensitive to anthropogenic disturbances that can degrade these systems. On many degraded reefs, large increases in bioeroding sponge abundance have occurred. On healthy reefs these sponges contribute to species diversity and habitat complexity, however there is growing concern that their proliferation on degraded reefs could lead to a state of net-erosion. In the Southeast Asian Indo-Pacific, the ecology of bioeroding sponges in relation to coral degradation has been poorly studied compared to other coral reef regions. This thesis aims to increase our understanding of the ecology of these sponges in the Wakatobi region of Indonesia, and their likely trajectory if reefs continue to degrade in the region.  My first research chapter aimed to identify the common bioeroding sponge species of the Wakatobi. This was achieved through in-water surveys, and subsequent spicule and phylogenetic analysis. This resulted in the identification of eight commonly occurring Wakatobi bioeroding sponge species, two of which are described for the first time. The assemblage composition was distinctly different from the only other bioeroding sponge study in Indonesian waters (Calcinai et al. 2005), highlighting the need for more clionaid taxonomic information from the region.  Having identified the common bioeroding sponge species in the region, my second chapter assessed the major environmental drivers of the abundance and assemblage composition of these sponges. Abundance surveys were conducted at 11 reef sites characterised by different environmental conditions and states of reef health. Bioeroding sponges occupied 8.9% of suitable substrate, and differences in abundance and assemblage composition were primarily attributed to differences in the availability of dead substrate. However, abundance was lowest at a sedimented and turbid reef, despite abundant dead substrate availability. This indicates a limited resilience in some species to conditions associated with terrestrial run-off and that not all forms of reef degradation are beneficial for bioeroding sponges. The capacity to increase spatial occupation of degraded reefs is also dependent upon larval recruitment and my third chapter was a two year recruitment study using in situ experimental calcareous blocks. Recruitment occurred rapidly and consistently with bioeroding sponges recruiting to approximately 70% of experimental blocks and exhibiting a preference for settlement on uncolonised dead calcareous substrates. The importance of substrate settlement cues and extent of larval dispersal appeared to differ between species, indicative of different recruitment mechanisms. Any significant increase in the availability of exposed calcareous substrate (e.g. following a mass coral bleaching event) is therefore likely to result in widespread increases in bioeroding sponge recruitment.  Surveys conducted in my second research chapter revealed that two of the three locally abundant zooxanthellate bioeroding species were absent from a highly turbid reef, Sampela. My fourth research chapter investigated whether this was due to light limitation by examining the photoacclimatory capabilities of the Symbiodinium photosymbionts of Cliona aff. viridis n. sp. A. PAM chlorophyll fluorometry was employed in a 25 day shading experiment and Symbiodinium of C. aff. viridis n. sp. A demonstrated an ability to photoacclimate to extreme light reduction and recover quickly when conditions returned to normal. My results demonstrate that the absence of this species at Sampela is not due to light limitation but possibly due to other stressors associated with turbidity, e.g. suspended sediment.  My final chapter was an assessment of the environmental drivers of rates of bioerosion in Spheciospongia cf. vagabunda, a common species in the Wakatobi. Erosion rates were determined from changes in dry-weight of calcareous substrates with attached grafts of S. cf. vagabunda after a year deployment across seven reef sites. The average bioerosion rate was 12.0 kg m⁻² sponge tissue yr⁻¹ (± 0.87 SE), but differed between sites and was negatively correlated with settled sediment depth. Bioerosion by this species can play a significant part in the carbonate budget on reefs where it is abundant (up to 20% of available substrate on some reefs in the Wakatobi) but is likely reduced on highly sedimented reefs.  In summary, the Wakatobi bioeroding sponge assemblage is diverse and overall, both adult abundance and recruitment are primarily driven by the availability of dead calcareous substrates. Therefore, further coral mortality and a subsequent rise in the availability of dead substrate in the region is likely to result in increased abundance of bioeroding sponges. However, not all forms of reef degradation will benefit these sponges; turbid and sedimented reefs will likely constitute stressful habitats for some bioeroding sponge species and assemblages in these environments will be comprised of fewer more resilient species.</p>


2021 ◽  
Author(s):  
◽  
Joseph Marlow

<p>Coral reefs are among the most diverse ecosystems on the planet, yet they are also sensitive to anthropogenic disturbances that can degrade these systems. On many degraded reefs, large increases in bioeroding sponge abundance have occurred. On healthy reefs these sponges contribute to species diversity and habitat complexity, however there is growing concern that their proliferation on degraded reefs could lead to a state of net-erosion. In the Southeast Asian Indo-Pacific, the ecology of bioeroding sponges in relation to coral degradation has been poorly studied compared to other coral reef regions. This thesis aims to increase our understanding of the ecology of these sponges in the Wakatobi region of Indonesia, and their likely trajectory if reefs continue to degrade in the region.  My first research chapter aimed to identify the common bioeroding sponge species of the Wakatobi. This was achieved through in-water surveys, and subsequent spicule and phylogenetic analysis. This resulted in the identification of eight commonly occurring Wakatobi bioeroding sponge species, two of which are described for the first time. The assemblage composition was distinctly different from the only other bioeroding sponge study in Indonesian waters (Calcinai et al. 2005), highlighting the need for more clionaid taxonomic information from the region.  Having identified the common bioeroding sponge species in the region, my second chapter assessed the major environmental drivers of the abundance and assemblage composition of these sponges. Abundance surveys were conducted at 11 reef sites characterised by different environmental conditions and states of reef health. Bioeroding sponges occupied 8.9% of suitable substrate, and differences in abundance and assemblage composition were primarily attributed to differences in the availability of dead substrate. However, abundance was lowest at a sedimented and turbid reef, despite abundant dead substrate availability. This indicates a limited resilience in some species to conditions associated with terrestrial run-off and that not all forms of reef degradation are beneficial for bioeroding sponges. The capacity to increase spatial occupation of degraded reefs is also dependent upon larval recruitment and my third chapter was a two year recruitment study using in situ experimental calcareous blocks. Recruitment occurred rapidly and consistently with bioeroding sponges recruiting to approximately 70% of experimental blocks and exhibiting a preference for settlement on uncolonised dead calcareous substrates. The importance of substrate settlement cues and extent of larval dispersal appeared to differ between species, indicative of different recruitment mechanisms. Any significant increase in the availability of exposed calcareous substrate (e.g. following a mass coral bleaching event) is therefore likely to result in widespread increases in bioeroding sponge recruitment.  Surveys conducted in my second research chapter revealed that two of the three locally abundant zooxanthellate bioeroding species were absent from a highly turbid reef, Sampela. My fourth research chapter investigated whether this was due to light limitation by examining the photoacclimatory capabilities of the Symbiodinium photosymbionts of Cliona aff. viridis n. sp. A. PAM chlorophyll fluorometry was employed in a 25 day shading experiment and Symbiodinium of C. aff. viridis n. sp. A demonstrated an ability to photoacclimate to extreme light reduction and recover quickly when conditions returned to normal. My results demonstrate that the absence of this species at Sampela is not due to light limitation but possibly due to other stressors associated with turbidity, e.g. suspended sediment.  My final chapter was an assessment of the environmental drivers of rates of bioerosion in Spheciospongia cf. vagabunda, a common species in the Wakatobi. Erosion rates were determined from changes in dry-weight of calcareous substrates with attached grafts of S. cf. vagabunda after a year deployment across seven reef sites. The average bioerosion rate was 12.0 kg m⁻² sponge tissue yr⁻¹ (± 0.87 SE), but differed between sites and was negatively correlated with settled sediment depth. Bioerosion by this species can play a significant part in the carbonate budget on reefs where it is abundant (up to 20% of available substrate on some reefs in the Wakatobi) but is likely reduced on highly sedimented reefs.  In summary, the Wakatobi bioeroding sponge assemblage is diverse and overall, both adult abundance and recruitment are primarily driven by the availability of dead calcareous substrates. Therefore, further coral mortality and a subsequent rise in the availability of dead substrate in the region is likely to result in increased abundance of bioeroding sponges. However, not all forms of reef degradation will benefit these sponges; turbid and sedimented reefs will likely constitute stressful habitats for some bioeroding sponge species and assemblages in these environments will be comprised of fewer more resilient species.</p>


2021 ◽  
Author(s):  
◽  
Ingrid Sally Sigrid Knapp

<p>Anthropogenic pressures, direct and indirect, have left no coral reef untouched. Those that remain in a near-pristine condition are remote islands and atolls removed from the majority of direct impacts, but even these are still subjected to the pressures of global climate change to which they are demonstrating a higher resilience than those which are already severely compromised. These near-pristine systems should be protected, managed and studied to better understand how they function and hopefully ensure the future of coral reefs. Unfortunately a number of the remote atolls and islands in the Pacific were modified or used by the US military during WWII, which altered these systems in unknown ways and threatened their surrounding reefs. Palmyra Atoll in the Central Pacific for example had its lagoons dredged and blocked to create more landmass for building, along with the creation of a channel through the reef to allow boat access into the lagoons making them susceptible to introduced species. Fortunately the surrounding reefs at Palmyra are still in a near-pristine condition with high densities of scleractinian corals, however the lagoon fauna is now predominantly sponges. Sponges in high enough densities can have considerable impacts on semi-enclosed bodies of water through their high filtering capabilities and could even threaten native species through competition if they were to extend onto non-lagoon reefs. Therefore, the broad aim of this thesis was to understand the ecology of the sponges in the lagoons at Palmyra and determine their potential impacts on the atoll directly and indirectly. To answer these questions I collected sponge assemblage data across the lagoons at both shallow and deep depths and sampled those species found on the reefs, which were surprisingly entirely different from the lagoon species. I then modelled a suite of environmental predictors to ascertain whether environmental conditions might be maintaining the sponges in the lagoon. To further examine whether the sponges were capable of extending onto the reef I also looked at larval recruitment patterns and assessed the temporal stability with semi-permanent quadrats. The initial surveys revealed the presence of at least two introduced species: Haliclona caerulea (Hechtel 1965) and Gelliodes fibrosa (Wilson 1925). Molecular tools were then employed to confirm the identification and attempt to ascertain the introduction pathway of H. caerulea. Finally, to assess the potential impact of the sponges on the water column I calculated the filtration rates of all the morphologies in the lagoon and extrapolated to the time required to clear all the available water in the lagoon as well as the removal rates of dissolved organic carbon and oxygen.  Overall the lagoons appear to have undergone a phase-shift from a coral to sponge dominated system. However, the direct threat of the sponges extending onto the adjacent near-pristine reef currently seems negligible as they appear to be relatively “stable” (sponge mortality and recruitment are in equilibrium) and maintained in the lagoons by the environmental conditions, despite larval production. Sponge diversity changed over depths but the total number of species was consistent with other atoll systems despite the military modifications, with the most prominent sponge being a Hawaiian endemic species: Iotrochota protea (de Laubenfels 1950). The introduction of H. caerulea, a Caribbean sponge is thought to have occurred to Palmyra via Hawaiʻi; however, the molecular data also revealed further cryptic speciation at both the species and order levels, suggesting greater species diversity at Palmyra than previously believed. Finally, the indirect impacts of the sponges on the water column also appear to be small and with limited future risks to the reef organisms, as recruitment and mortality are currently in equilibrium and therefore unlikely to increase dramatically in percentage cover. Globally sponges can play important functional roles in semi-enclosed bodies of water and in summary, despite the sponges being the most dominant fauna on the hard substrate in the lagoons, they appear to pose little threat to the atoll and the adjacent reefs either directly or indirectly despite the confirmed introduction of non-endemic species. However, it must be noted that the time since the modification (70 years) is not that long in an evolutionary sense, so the sponges may still have the potential to extend onto the reef, particularly if there are any dramatic changes to the environmental conditions on the outer reefs. Therefore, to detect whether the sponges are extending onto the reef I propose, as a future management tool, the use of I. protea as an indicator species. The use of multidisciplinary approaches to answer important ecological questions with respect to the potential for sponges to have negative impacts on the nonlagoon reefs proved to be essential in understanding whether the modifications to the lagoons and the subsequent dominance of sponges could be threatening one of the last few remaining near-pristine reef systems in the world.</p>


2021 ◽  
Author(s):  
◽  
Ingrid Sally Sigrid Knapp

<p>Anthropogenic pressures, direct and indirect, have left no coral reef untouched. Those that remain in a near-pristine condition are remote islands and atolls removed from the majority of direct impacts, but even these are still subjected to the pressures of global climate change to which they are demonstrating a higher resilience than those which are already severely compromised. These near-pristine systems should be protected, managed and studied to better understand how they function and hopefully ensure the future of coral reefs. Unfortunately a number of the remote atolls and islands in the Pacific were modified or used by the US military during WWII, which altered these systems in unknown ways and threatened their surrounding reefs. Palmyra Atoll in the Central Pacific for example had its lagoons dredged and blocked to create more landmass for building, along with the creation of a channel through the reef to allow boat access into the lagoons making them susceptible to introduced species. Fortunately the surrounding reefs at Palmyra are still in a near-pristine condition with high densities of scleractinian corals, however the lagoon fauna is now predominantly sponges. Sponges in high enough densities can have considerable impacts on semi-enclosed bodies of water through their high filtering capabilities and could even threaten native species through competition if they were to extend onto non-lagoon reefs. Therefore, the broad aim of this thesis was to understand the ecology of the sponges in the lagoons at Palmyra and determine their potential impacts on the atoll directly and indirectly. To answer these questions I collected sponge assemblage data across the lagoons at both shallow and deep depths and sampled those species found on the reefs, which were surprisingly entirely different from the lagoon species. I then modelled a suite of environmental predictors to ascertain whether environmental conditions might be maintaining the sponges in the lagoon. To further examine whether the sponges were capable of extending onto the reef I also looked at larval recruitment patterns and assessed the temporal stability with semi-permanent quadrats. The initial surveys revealed the presence of at least two introduced species: Haliclona caerulea (Hechtel 1965) and Gelliodes fibrosa (Wilson 1925). Molecular tools were then employed to confirm the identification and attempt to ascertain the introduction pathway of H. caerulea. Finally, to assess the potential impact of the sponges on the water column I calculated the filtration rates of all the morphologies in the lagoon and extrapolated to the time required to clear all the available water in the lagoon as well as the removal rates of dissolved organic carbon and oxygen.  Overall the lagoons appear to have undergone a phase-shift from a coral to sponge dominated system. However, the direct threat of the sponges extending onto the adjacent near-pristine reef currently seems negligible as they appear to be relatively “stable” (sponge mortality and recruitment are in equilibrium) and maintained in the lagoons by the environmental conditions, despite larval production. Sponge diversity changed over depths but the total number of species was consistent with other atoll systems despite the military modifications, with the most prominent sponge being a Hawaiian endemic species: Iotrochota protea (de Laubenfels 1950). The introduction of H. caerulea, a Caribbean sponge is thought to have occurred to Palmyra via Hawaiʻi; however, the molecular data also revealed further cryptic speciation at both the species and order levels, suggesting greater species diversity at Palmyra than previously believed. Finally, the indirect impacts of the sponges on the water column also appear to be small and with limited future risks to the reef organisms, as recruitment and mortality are currently in equilibrium and therefore unlikely to increase dramatically in percentage cover. Globally sponges can play important functional roles in semi-enclosed bodies of water and in summary, despite the sponges being the most dominant fauna on the hard substrate in the lagoons, they appear to pose little threat to the atoll and the adjacent reefs either directly or indirectly despite the confirmed introduction of non-endemic species. However, it must be noted that the time since the modification (70 years) is not that long in an evolutionary sense, so the sponges may still have the potential to extend onto the reef, particularly if there are any dramatic changes to the environmental conditions on the outer reefs. Therefore, to detect whether the sponges are extending onto the reef I propose, as a future management tool, the use of I. protea as an indicator species. The use of multidisciplinary approaches to answer important ecological questions with respect to the potential for sponges to have negative impacts on the nonlagoon reefs proved to be essential in understanding whether the modifications to the lagoons and the subsequent dominance of sponges could be threatening one of the last few remaining near-pristine reef systems in the world.</p>


2021 ◽  
Author(s):  
◽  
Lauren Marion Fletcher

<p>Over the past decade, several species of non-indigenous ascidian have had adverse effects in the marine environment and on associated industries. The colonial ascidian Didemnum vexillum is a recent successful invader in temperate marine communities worldwide, proving problematic to mussel aquaculture in New Zealand. At the inception of this thesis, control strategies to manage the threat from Didemnum to mussel aquaculture were implemented in the absence of information on the biological processes underpinning the species’ invasion success. Background information on Didemnum presented in Chapter 2 recognises this paucity of information on several key biological attributes as well as negative impacts of this species. The ability to obtain larvae and culture colonies in the laboratory was a crucial first step. Thus, Chapter 3 presents laboratory experiments that describe the first successful methods to induce spawning in adult Didemnum colonies, as well as techniques for the successful settlement and metamorphosis of the larvae produced, and for laboratory culture of juveniles. Chapters 4 to 6 address key aspects of the biological characteristics of Didemnum that relate to its invasiveness and spread. The recruitment and reproductive development of Didemnum were assessed over a 20-month period at two locations in central New Zealand. Results indicated that the reproductive season for Didemnum in New Zealand (at least 9 months) is considerably longer than previously believed, with recruitment patterns strongly correlated with seasonal water temperature fluctuations at each location. Secondly, the natural dispersal ability of Didemnum was assessed using a weight-of-evidence approach that combined laboratory and field studies. Larval competency trials revealed that > 70 % of larvae were able to settle and undergo metamorphosis following an artificial settlement delay of 2 hours. Larval viability decreased with increasing delay duration; however 10 % of larvae remained viable following a 36 hour delay. These findings were supported by a field-based study documenting larval recruitment at distances up to 250 m from source populations. Exponential decay models indicated that, given favourable conditions, larval dispersal distances greater than 1 km were theoretically possible, which is a much greater distance than previously assumed. Lastly, the impacts of Didemnum on cultured New Zealand green-lipped mussels (Perna canaliculus) were investigated. At the level of invasiveness experienced in a field experiment, only small mussel size classes were vulnerable to direct Didemnum impacts, with negative effects restricted to fouling-related displacement of mussels as opposed to reduced size or condition. However, at the greater levels of invasiveness evident at other places and times, Didemnum impacts have the potential to be considerably larger. As such, the ability to predict invasiveness, and hence impacts, is critical for stakeholders. However, for reasons discussed in the thesis, making reliable specific predictions of invasiveness is difficult. Despite such limitations, it is clear that an understanding of a species’ basic biological attributes can still greatly assist with management decisions, as highlighted throughout the chapters in this thesis. My research findings have led to a better awareness of commercial impacts and potential spread of this species. Simultaneously, my research also highlights the limitations inherent in inferring invasiveness from other situations (e.g. places, times, and related species); there is a need to specifically evaluate a species’ biological attributes and invasive behaviour when introduced into a novel environment.</p>


2021 ◽  
Author(s):  
◽  
Lauren Marion Fletcher

<p>Over the past decade, several species of non-indigenous ascidian have had adverse effects in the marine environment and on associated industries. The colonial ascidian Didemnum vexillum is a recent successful invader in temperate marine communities worldwide, proving problematic to mussel aquaculture in New Zealand. At the inception of this thesis, control strategies to manage the threat from Didemnum to mussel aquaculture were implemented in the absence of information on the biological processes underpinning the species’ invasion success. Background information on Didemnum presented in Chapter 2 recognises this paucity of information on several key biological attributes as well as negative impacts of this species. The ability to obtain larvae and culture colonies in the laboratory was a crucial first step. Thus, Chapter 3 presents laboratory experiments that describe the first successful methods to induce spawning in adult Didemnum colonies, as well as techniques for the successful settlement and metamorphosis of the larvae produced, and for laboratory culture of juveniles. Chapters 4 to 6 address key aspects of the biological characteristics of Didemnum that relate to its invasiveness and spread. The recruitment and reproductive development of Didemnum were assessed over a 20-month period at two locations in central New Zealand. Results indicated that the reproductive season for Didemnum in New Zealand (at least 9 months) is considerably longer than previously believed, with recruitment patterns strongly correlated with seasonal water temperature fluctuations at each location. Secondly, the natural dispersal ability of Didemnum was assessed using a weight-of-evidence approach that combined laboratory and field studies. Larval competency trials revealed that > 70 % of larvae were able to settle and undergo metamorphosis following an artificial settlement delay of 2 hours. Larval viability decreased with increasing delay duration; however 10 % of larvae remained viable following a 36 hour delay. These findings were supported by a field-based study documenting larval recruitment at distances up to 250 m from source populations. Exponential decay models indicated that, given favourable conditions, larval dispersal distances greater than 1 km were theoretically possible, which is a much greater distance than previously assumed. Lastly, the impacts of Didemnum on cultured New Zealand green-lipped mussels (Perna canaliculus) were investigated. At the level of invasiveness experienced in a field experiment, only small mussel size classes were vulnerable to direct Didemnum impacts, with negative effects restricted to fouling-related displacement of mussels as opposed to reduced size or condition. However, at the greater levels of invasiveness evident at other places and times, Didemnum impacts have the potential to be considerably larger. As such, the ability to predict invasiveness, and hence impacts, is critical for stakeholders. However, for reasons discussed in the thesis, making reliable specific predictions of invasiveness is difficult. Despite such limitations, it is clear that an understanding of a species’ basic biological attributes can still greatly assist with management decisions, as highlighted throughout the chapters in this thesis. My research findings have led to a better awareness of commercial impacts and potential spread of this species. Simultaneously, my research also highlights the limitations inherent in inferring invasiveness from other situations (e.g. places, times, and related species); there is a need to specifically evaluate a species’ biological attributes and invasive behaviour when introduced into a novel environment.</p>


2021 ◽  
Author(s):  
Viviana Brambilla ◽  
Andrew Baird ◽  
Miguel Barbosa ◽  
Inga Dehnert ◽  
Joshua S Madin ◽  
...  

Niche construction is the process through which organisms modify environmental states in ways favourable to their own fitness. Here, we test experimentally whether scleractinian corals can be considered niche constructors. In particular, we demonstrate a positive feedback involved in corals building structures which facilitate recruitment. Coral larval recruitment is a key process for coral reef persistence. Larvae require low flow conditions to settle from the plankton, and hence the presence of colony structures that can break the flow is expected to facilitate coral recruitment. Here, we show an increase in settler presence on artificial tiles deployed in the field along a gradient of coral-built structural complexity. Structural complexity had a positive effect on settlement, with an increase of 15,71% of settler presence probability along the range of structural complexity considered. This result provides evidence that coral built structural complexity creates conditions that facilitate coral settlement, while demonstrating that corals meet the criteria for ecological niche construction.


2021 ◽  
Vol 8 ◽  
Author(s):  
Romuald N. Lipcius ◽  
Yi Zhang ◽  
Jingyi Zhou ◽  
Leah B. Shaw ◽  
Junping Shi

Restoration of native oyster (Crassostrea virginica) populations in Chesapeake Bay shows great promise after three decades of failed attempts. Population models used to inform oyster restoration had integrated reef habitat quality, demonstrating that reef height determines oyster population persistence and resilience. Larval recruitment drives population dynamics of marine species, yet its impact with reef height and sediment deposition upon reef restoration is unknown. To assess the influence of reef height, sediment deposition and larval supply, we adapted a single-stage population model to incorporate stage structure using a system of four differential equations modeling change in juvenile density (J), and changes in volume of adults (A), oyster shell reef (R), and sediment (S) on an oyster reef. The JARS model was parameterized with empirical data from field experiments. Larval supply included larvae from the natal population and from outside populations. The stage-structured model possessed multiple non-negative equilibria (i.e., alternative stable states). Different initial conditions (e.g., oyster shell reef height) resulted in different final states. The main novel findings were that the critical reef height for population persistence and resilience was jointly dependent on sediment input and larval supply. A critical minimum larval supply was necessary for a reef to persist, even when initial sediment deposition was zero. As larval supply increased, the initial reef height needed for reef persistence was lowered, and oyster reef resilience was enhanced. A restoration oyster reef with higher larval influx could recover from more severe disturbances than a reef with lower larval influx. To prevent local extinction and assure a positive population state, higher levels of larval supply were required at greater sediment concentrations to overcome the negative effects of sediment accumulation on the reef. In addition, reef persistence was negatively related to sediment deposited on a reef prior to larval settlement and recruitment, implying that restoration reefs should be constructed immediately before settlement and recruitment to minimize sediment accumulation on a reef before settlement. These findings are valuable in oyster reef restoration because they can guide reef construction relative to larval supply and sediment deposition on a reef to yield effective and cost-efficient restoration strategies.


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