Bioerosion Processes Research Articles

Variation of the diet of the sea urchin (Diadema mexicanum (Diadematoida: Diadematidae)) according to its size in the Eastern Tropical Pacific

Introduction: The sea urchin Diadema mexicanum, due to its bioerosion activity, is considered of ecological importance. This phenomenon could negatively or positively affect coral reef ecosystems. The bioerosion process varies according to the abundance and size of the sea urchin.
 Objective: Juvenile organisms possess different metabolic needs compared to adults, so knowing their stomach content according to size allows us to quantify the selection of substrate bioeroded.
 Methods: To determine this, D. mexicanum individuals were collected in 12 sites from January 2009 to September 2010 along the Eastern Tropical Pacific coast. The stomach content was categorized in Carbonated Fraction (CF), Non-Carbonated Fraction (NCF), and Organic Matter (OM). Stomach content was analyzed according to a) juvenile (< 2.5 cm) or adult (> 2.5 cm) stage and b) locality.
 Results: Juveniles presented the following stomach content average percentages: 20.7 % OM, 12 % NCF and 67.9 % CF; and adults: 11.4 % OM, 14.8 % NCF and 73.8 % CF. Based on a Wilcoxon test and a Kendall linear regression, the following results were obtained. The carbonated fraction in the stomach increased by 0.47 units on average for every cm of growth (p < 0.05). OM consumed by D. mexicanum increases only 0.05 units for every cm of growth (p < 0.05). We found a difference of stomach content depending on the site (p < 0.05) and life stage (p < 0.05). Localities like Huatulco and Coco presented significant differences that could be related to local oceanographic conditions.
 Conclusions: We relate these changes of the stomach fractions to the necessity of the juvenile sea urchins for nutrients to maintain their growth. The amount of OM is crucial for the development of early stages, meaning that there is a difference in substrate selection associated with growth.

New insights into endolithic palaeocommunity development in mobile hard substrate using CT imaging of bioeroded clasts from the Pliocene (Almería, SE Spain).

Bioeroded carbonate clasts from a Pliocene shallow-marine succession of Almería (SE Spain, Betic Cordillera) were analysed with computed tomography (CT). This revealed the detailed 3D architecture of bioerosion structures hidden within and allowed for their ichnotaxonomic identification (14 ichnospecies of 5 ichnogenera) and quantification. Borings are produced by worms, mostly polychaetes and sipunculids dominated, followed by bivalves and lastly by sponges. The crosscutting relationship between the borings and their preservation characteristics points to a complex colonization history of the clasts with repeated bioerosive episodes interrupted by physical disturbances, including overturning and abrasion of the clasts followed by their recolonization. Our findings facilitated paleoenvironmental interpretation and can be compared to analogous modern-day ecological succession. The sharp dominance of worm borings - early successional species - may be related to frequent, periodic, physical disturbance that possibly prevented the cobble-dwelling macroboring community from being overtaken by sponges - late successional taxa. CT, hand sample and petrographic observations detected, aside from borings, other irregularly shaped pores which are interpreted to be generated by diagenetic processes including dolomitization, silicification and dissolution, representing an intraparticle moldic and moldic enlarged porosity. Boring porosity crosscutting the diagenetically altered grains suggests the later occurrence of bioerosion processes. Irregular shapes ranging from roughly spherical, elongate sub-polyhedral to amoeboid resemble morphologies produced by modern sponges. Moldic pores possibly acted as primary domiciles for boring sponges, which infested, altered and enlarged pre-existing pores as they grew (as happens in the modern), providing an example of how biological and non-biological processes interacted and together influenced endolithic palaeocommunity development.

Towards reef restoration in Zihuatanejo, Guerrero, México: lessons learned

Introduction: Coral reef structures in Zihuatanejo, Guerrero are well-preserved. The coverage of living corals, near 60 % at several locations, makes them comparable to other coral reefs in the states of Oaxaca, Jalisco, and Nayarit and with high potential to promote their conservation.
 Objective: To present the outcome of 12 years of research in coral communities from Zihuatanejo, Guerrero, as a justifying argument for the current conservation efforts in the area.
 Methods: We developed a baseline on the conservation status of the reef structures, bioerosion processes and the source of major natural and anthropogenic impacts. We assessed the genetic diversity of the coral zooxanthellae symbionts, the outcome of a technique of coral transplantation to recover the coverage of living corals and the local ecological knowledge to involve local inhabitants to promote conservation.
 Results: At least five coral reefs remain exposed to a medium-low level of impact by bioerosion and anthropization. Coral transplantation experiments made in the area showed records of transplant survival nearing 90 %. Although the warming of the sea surface temperature that occurred during the El Niño of 2015-2016 caused coral bleaching and mortality in several coral populations in this area, there were no affectations attributed to this phenomenon in other locations. This response was not related to the level of exposure to anthropogenic impacts, and the presence of thermal resistant zooxanthellae was assessed using molecular tools, confirming the existence of zooxanthellae of the genus Durusdinium. The analysis of local ecological knowledge of the inhabitants of Zihuatanejo showed that they keep elaborate knowledge on the ecology of coral reefs. This is complemented with scientific knowledge that will encourage community participation in conservation strategies.
 Conclusions: A long-term multidisciplinary strategy is required for coral reef conservation that encompasses: 1) assessing the role of the overall holobiont in the thermal resistance of corals from this area and 2) establishing restoration strategies of coral reefs that include the local knowledge about marine ecology, for the establishment of coral reef protection and management schemes put in place by local inhabitants.

Climate Change and The Persistence of Coral-Reef Development in Upwelling Zones

Upwelling exerts a major control on coral-reef development in the eastern tropical Pacific (ETP). Upwelling zones exhibit conditions that are detrimental to coral growth, such as low sea-surface temperatures and high levels of turbidity. During the late Holocene, the reefs in the strongly upwelling Gulf of Panamá (GoP) and the weakly upwelling Gulf of Chiriquí (GoC) experienced a climate-driven hiatus in coral growth and reef development, and strong upwelling exacerbated this hiatus in the GoP. Strong upwelling in the GoP is now acting as a buffer against thermal stress, providing a refuge from climatic warming, whereas corals in the GoC are highly vulnerable to increased thermal stress. Using ecological surveys and paleoecological data, we quantified calcification and bioerosion processes for the reefs in these two gulfs to develop carbonate-budget models. We determined the reef-accretion potential (RAP) for reefs in each gulf to project their capacity to keep pace with current and predicted future rates of sea-level rise. On average, reefs in the GoP exhibited an average RAP of 5.5 mm yr-1, which would be enough to keep pace with future rates of sea-level rise if CO2 emissions were reduced under representative concentration pathways (RCPs) 2.6 and 4.5. In contrast, reefs in the GoC exhibited an average RAP of only 0.3 mm yr-1, which is not even enough to keep pace with contemporary rates of sea-level rise in Panamá (1.4 mm yr-1). Furthermore, even if the reefs in either gulf could achieve 100% coral cover, none of them has the capacity to keep pace with RCP 8.5. Although the GoP should support reef development in the near future, reducing greenhouse-gas emissions will be essential to ensure the persistence of accreting reefs and promote the recovery of those vulnerable to net erosion.

Epipsammic Diatom <I>Cocconesis</I> sp. as New Bioeroder in Scleractinian Coral

Highlight Research The endolithic bioeroders were identified. Cocconeis sp. was new for the science of euendolithic bioeroder of Scleractinian coral. SEM revealed Cocconeis sp. etch and bore of coral skeleton. Pennate diatom was present on coral cavities. Abstract Laminar coral, Montipora, contributes to the coral reef ecosystem. The laminar life form is usually used by juvenile reef biota to shelter and prey. In an intertidal area, such as Pantai Kondang Merak, these corals are susceptible to erosion caused by mechanical and biological forces. Strong current or other anthropogenic activity may break coral colonies into pieces. Also, some grazers from reef fish and bioeroder potentially weaken coral structures. This study aimed to find the effect of biological agents from Bacillariophyceae, such as Cocconeis diatom, on the bioerosion process in laminar coral, e.g., Montipora. Ten montiporid corals from Pantai Kondang Merak were observed to find bio-eroding activities. Each coral colony was divided into 12 parts and photographed to record signs of bio-erosion on coral surface. While observing microborers, a 2x2 cm of the coral surface was observed using Scanning Electron Microscopy (SEM). SEM revealed that a frustule of Cocconeis sp. was found inside aragonite laminar coral from Pantai Kondang Merak. Cocconeis naturally grows on the coasts of tropical oceans as benthic organisms. They are reported as living attached to many substrates’ surfaces and within the substrate as euendolith. This study revealed that Cocconeis sp. lived inside the coral skeleton as micro bioeroder by attaching their valve in coral aragonite. Further work needs more observations of another potential euendolith diatom living inside the coral and to build new information on their mechanism of bio-eroding process in more detail.

54 years of microboring community history explored by machine learning in a massive coral from Mayotte (Indian Ocean)

Coral reefs are increasingly in jeopardy due to global changes affecting both reef accretion and bioerosion processes. Bioerosion processes dynamics in dead reef carbonates under various environmental conditions are relatively well understood but only over a short-term limiting projections of coral reef evolution by 2100. It is thus essential to monitor and understand bioerosion processes over the long term. Here we studied the assemblage of traces of microborers in a coral core of a massive Diploastrea sp. from Mayotte, allowing us to explore the variability of its specific composition, distribution, and abundance between 1964 and 2018. Observations of microborer traces were realized under a scanning electron microscope (SEM). The area of coral skeleton sections colonized by microborers (a proxy of their abundance) was estimated based on an innovative machine learning approach. This new method with 93% accuracy allowed analyzing rapidly more than a thousand SEM images. Our results showed an important shift in the trace assemblage composition that occurred in 1985, and a loss of 90% of microborer traces over the last five decades. Our data also showed a strong positive correlation between microborer trace abundance and the coral bulk density, this latter being particularly affected by the interannual variation of temperature and cumulative insolation. Although various combined environmental factors certainly had direct and/or indirect effects on microboring species before and after the breakpoint in 1985, we suggest that rising sea surface temperature, rainfall, and the loss of light over time were the main factors driving the observed trace assemblage change and decline in microborer abundance. In addition, the interannual variability of sea surface temperature and instantaneous maximum wind speed appeared to influence greatly the occurrence of green bands. We thus stress the importance to study more coral cores to confirm the decadal trends observed in the Diploastrea sp. from Mayotte and to better identify the main factors influencing microboring communities, as the decrease of their abundance in living massive stress tolerant corals may have important consequences on their resilience.

Natural photosynthetic microboring communities produce alkalinity in seawater whereas aragonite saturation state rises up to five

Bioerosion, resulting from microbioerosion or biogenic dissolution, macrobioerosion and grazing, is one the main processes involved in reef carbonate budget and functioning. On healthy reefs, most of the produced carbonates are preserved and accumulate. But in the context of global change, reefs are increasingly degraded as environmental factors such as ocean warming and acidification affect negatively reef accretion and positively bioerosion processes. The recent 2019 SROCC report suggests that if CO2 emissions in the atmosphere are not drastically reduced rapidly, 70%–99% of coral reefs will disappear by 2,100. However, to improve projections of coral reef evolution, it is important to better understand dynamics of bioerosion processes. Among those processes, it was shown recently that bioeroding microflora which actively colonize and dissolve experimental coral blocks, release significant amount of alkalinity in seawater both by day and at night under controlled conditions. It was also shown that this alkalinity production is enhanced under ocean acidification conditions (saturation state of aragonite comprised between 2 and 3.5) suggesting that reef carbonate accumulation will be even more limited in the future. To better understand the conditions of production of alkalinity in seawater by boring microflora and its possible consequences on reef resilience, we conducted a series of experiments with natural rubble maintained under natural or artificial light, and various saturation states of aragonite. We show here that biogenic dissolution of natural reef rubble colonized by microboring communities dominated by the chlorophyte Ostreobium sp., and thus the production of alkalinity in seawater, can occur under a large range of saturation states of aragonite, from 2 to 6.4 under daylight and that this production is directly correlated to the photosynthetic activity of microboring communities. We then discuss the possible implications of such paradoxical activities on reef resilience.

Bioconstruction and Bioerosion in the Northern Adriatic Coralligenous Reefs Quantified by X-Ray Computed Tomography

The northern Adriatic continental shelf hosts several coralligenous reefs rising from the sedimentary bottom and characterized by three main benthic assemblages, respectively, dominated by algal turfs, encrusting calcareous rhodophyte (ECRs) or erect sponges. Bioconstruction and bioerosion processes have been investigated using recruitment travertine limestone tiles deployed in a random site for each main benthic assemblages off Chioggia, 6.1–14.4 km offshore and 20.2–25.4 m depth. Tiles were retrieved after 3 and 12 years and analyzed by X-ray computed tomography (CT), allowing for non-destructively identifying and quantifying deposited and eroded limestone. The main builders were ECRs, serpulids, bryozoans, barnacles, and the bivalves Anomia ephippium, while the most effective borers were sponges from the genus Cliona and the bivalve Rocellaria dubia. The deposition of limestone after 12 years was greater at the site MR08 dominated by ECRs (12.52 ± 2.22 kg m–2), intermediate at the site P213 dominated by erect sponges (4.20 ± 1.24 kg m–2), and lower in the site P204 dominated by algal turfs (2.20 ± 0.72 kg m–2). At MR08, the deposition rate did not vary much over time (from 1.295 ± 0.270 to 1.080 ± 0.198 kg m–2 a–1), while in the other two sites, it significantly slowed down after the first survey period: from 0.952 ± 0.199 to 0.350 ± 0.103 kg m–2 a–1 at P213, and from 1.470 ± 0.462 to 0.203 ± 0.058 kg m–2 a–1 at P204. The amount of eroded limestone increased with the exposure time, with no significant differences among sites, from 1.13 ± 0.29 to 10.39 ± 1.14 kg m–2 on average at 3 and 12 years, respectively. The bioerosion rate also increased with the exposure time and was slightly higher at MR08 (from 0.682 ± 0.208 to 1.105 ± 0.088 kg m–2 a–1), mostly eroded by Cliona rhodensis in addition to C. viridis, compared to P204 (from 0.267 ± 0.078 to 0.676 ± 0.172 kg m–2 a–1) and P213 (from 0.179 ± 0.065 to 0.816 ± 0.171 kg m–2 a–1). Overall, bioconstruction has overcome the bioerosion processes in 3 years. In 12 years, the estimated net balance was essentially nil at all sites. Combining field experiment and CT analysis, this study provides the first quantification of the bioerosion and bioconstruction processes in the northern Adriatic coralligenous reefs, a fundamental step toward their conservation.

Taphonomy and Diagenesis of Human Bone in Underwater Archaeology: A Review of the Current Status and the Proposal of Post-Mortem Submersion Interval (PMSI) as a Potential Forensic Application

Diagenesis is the collective word for the physical, biological, and chemical processes that bones undergo in the post-mortem period, until their physical destruction or fossilization. In forensic anthropology, the analysis of macroscopic and microscopic bone alterations, alongside the taphonomy of the soft tissues of a body, has proven valuable for the estimation of the time-of-death, or Post-Mortem Interval (PMI), of skeletonized individuals. To date, bone alterations have been mostly researched in terrestrial settings, such as exposed or buried skeletal remains, but here the scientific literature regarding human bones submerged underwater has been reviewed. It features 20 publications in the last 42 years, of which 9 are reviews, 8 are studies on ancient material and 3 are experimental studies. Future research on analysis of microscopic diagenetic parameters of submerged bones, together with the refinement of the correlation with time of the slightly better known macroscopic underwater alterations, will prove valuable for the estimation of a Post-Mortem Submersion Interval (PMSI) in both forensic and archaeological contexts, because bones have always been and still are regularly recovered underwater. The concurrent estimation of both PMI and PMSI of bones recovered underwater will add vital information to criminal investigations. Diagenetic parameters have been identified in Histological Index, protein content, porosity and crystallinity of bioapatite. They are depicted with the analytic techniques currently available to assess their presence and magnitude, and to relate them to the diagenetic processes of bioerosion, abrasion, and encrustation, but also to the extremes of dissolution or fossilization.

Actuotaphonomic model of the mollusk fauna of Laguna de Mandinga, Veracruz, Mexico

Introduction: The taphonomic attributes of a faunal assemblage provide information about which agents affect both, the distribution and preservation of ancient or newly-formed biogenic materials, during their depositional and post-depositional processes.
 Thus, actuotaphonomy is a valuable tool to the reconstruction of fossil communities, as it establishes analogies between observable processes in the present and those that happened in the past.
 Objective:The taphonomic attributes of a marginal marine environment were analyzed, in order to assess the origin of fragmentation, bioerosion and incrustation processes and the role of these characteristics in the deterioration of current sediment accumulations of mollusks (gastropods and bivalves), to generate an actuotaphonomic model that could be applyable to analogous ecosystems to Laguna de Mandinga (Mandinga Lagoon), in Veracruz, Mexico.
 Methods: The material came from a shell-remain accumulation called "El Conchal". A batch of 1,697.9 g was processed, selecting 1,165 complete specimens, of which 5 genera of bivalves and 4 genera of gastropods were identified. Results: The taphonomic analysis showed that fragmentation and bioerosion have a medium attribute, which may be due to energy, constant rework and exhumation of the remains at the lagoon's water-sediment interface; three biogeneous agents were identified: Entobia isp, Oichnus and Caulostrepsi, being Caulostrepsi the less abundant. The incrustation showed of poor degree since the ecosystem intrinsic conditions did not allow many encrusting organisms to grow properly, however, these organisms are represented by calcareous tubes of serpulid polychaetes, bryozoans with calcareous skeleton and barnacles.

Biological consequences of an outbreak of growth anomalies on Isopora palifera at the Cocos (Keeling) Islands

Growth anomalies (GAs), a tumour-like disease affecting scleractinian corals, have been reported across the major reef systems of the Indo-Pacific and wider Atlantic regions, predominantly affecting Acropora and Porites species. In 2018, GAs were observed for the first time on Isopora palifera, an important observation from the isolated Cocos (Keeling) Islands in the East Indian Ocean, as the species is a key reef building coral at the atoll. In this study, the local distribution and abundance of GAs was quantified to determine if this occurrence could be classified as an outbreak, and the effects of this disease on I. palifera on reproductive potential and growth was described using histological and geochemical analysis. Growth anomalies were documented at 75% of sites and affected approximately one third of the I. palifera colonies examined. This disease compromises the biological and reproductive functioning of the host, as evidenced by a significant reduction in the density of oocytes, mesenteries, polyps, and zooxanthellae in infected tissues in comparison to healthy tissue. Furthermore, geochemical analysis indicates changes to key trace elements may be the result of bioerosion processes by infecting bacteria and the reprecipitation of calcite. The results of this study indicate the division of energy to the rapid skeletal development that characterises the disease, may have occurred at the detriment of the future reproductive potential of the population.

Fossichnus solus and Oichnus simplex, two peculiar ichnospecies in modern benthic foraminifera from a polluted area in SW coast of Sardina, Italy

The modern benthic foraminiferal tests collected from a coastal area of south-western Sardinia (Portoscuso-Portovesme) that is heavily polluted by industrial activity reveal intense and widespread bioerosional structures induced by diversified microborers. A large number of the foraminifera reveals microscopic round holes (1-60 μm in diameter) and roundish concavities (25x40 μm in external diameter) on their surface that belong, respectively, to the ichnospecies Oichnus simplex Bromley, 1981, and Fossichnus solus Nielsen et al., 2003. These traces just occur in the tests of the foraminifera which are heavily infested by microendolithic cyanobacteria, algae and fungi suggests comparable ethological behaviour between the ichnospecies Fossichnus and Oichnus and the microbial euendoliths that are ascribed to individual biological taxa. The greater occurrence of F. solus and O. simplex in the high-Mg foraminiferal porcelanaceous tests than in the low-Mg foraminiferal hyaline tests reveals that the bioerosional processes seem to be related to the Mg/Ca ratio, as well as to morphological structures of the taxa

Four New Records of Eunicidae (Annelida: Polychaeta) from the Western Philippines Islands

During December 2010, an expedition was conducted to the Philippines Islands aiming to collect coastal polychaetes in the area. Among the abundant material, 593 individuals belonging to the family Eunicidae (Annelida; Polychaeta) were found and studied, and their identification yielded seven species. Four of them were new records to Philippines, enlarging the list of eunicid polychaetes of the country from 32 to 36 species; moreover, two of the species new for these islands were also new records to South China Sea. Additionally, the taxonomic status of one of them is modified, by transferring it from genus Eunice Cuvier, 1817 to Leodice Lamarck, 1818. Eunicids are especially abundant and diverse in benthic environments of tropical seas, were they act mainly as predators and scavengers or as herbivores. Some species are important in coral reefs because their boring abilities make them key organisms in the bioerosion processes. In this respect, knowledge on the composition of their communities is of capital for the understanding of ecological structure of the system.

Boring worms (Sipuncula and Annelida: Polychaeta): their early impact on Eastern Tropical Pacific coral reefs

The form, condition, and survival of coral reefs depends on the balance between construction and destruction. Natural processes such as bioerosion can cause this balance to lean towards destruction, threatening these ecosystems. Polychaetes and sipunculids are members of the boring community; however, knowledge of their identity and role in the bioerosive process and their capacity to remove calcium carbonate (CaCO3) in the coral reefs of the Eastern Tropical Pacific (ETP) is scarce. To tackle this problem, 5 experimental units of Pocillopora spp. branches were deployed in 4 reef zones (back-reef, reef-flat, reef-front, reef-slope) at 2 reefs (La Azufrada, Playa Blanca) for 2 time periods (P1: 6 mo, P2: 9 mo; n = 80) in Gorgona National Natural Park, Colombia. All worms (polychaetes and sipunculids) were identified and net removal and bioerosion rate were determined. In total, 137 worms were found: 64.2% in La Azufrada and 35.8% in Playa Blanca. There were no significant effects of reef, reef-zone, or duration of exposure (6 vs. 9 mo) for either net removal of CaCO3 or bioerosion rate. Irrespective of reef or exposure duration, average net removal was 0.022 and 0.027 g during P1 and P2, and 0.032 and 0.018 g at La Azufrada and Playa Blanca, respectively. Average bioerosion rate, also irrespective of reef or exposure duration, was 2.553 and 2.011 g kg-1 yr-1 for P1 and P2, and 2.839 and 1.807 g kg-1 yr-1 at La Azufrada and Playa Blanca, respectively. The trend between periods was opposite for net removal and bioerosion rate, which indicates a decelerating impact of worms on the coral substrate as time passes. We suggest that, regardless of the small size of the boring worms, their role in CaCO3 removal is very important. The information provided here—species involved and amounts removed—is key in understanding the bioerosion process in ETP coral reefs.

Bioerosion in massive porites at reef flat area of the south Java Sea

Scleractinian coral as the main builder of the reef contributes to building a complex reef framework through produce growing aragonite in their skeleton. In shallow water area (reef flat) the reef constructional process will be equal with erosional one, can be caused by mechanical damage such as storm or water motion and biological way (bioerosion). This research focused on the biological agent that influence on bioerosion process on massive Porites. 3 types of bioerosion they were grazing, boring, and etching. We monitored 10 massive Porites coral that was abundant at Pantai Kondang Merak, where each coral colony was segmented into 12 parts and then photographed to record data grazing and boring in massive Porites coral, while for etching was observed using Scanning Electron Microscopy (SEM). The result showed the number of bioerosion from grazing was 581 and boring was 1,155. The etching process was dominated by cyanobacteria Planobola macrogata that live inside of coral skeleton. The grazing process caused by parrotfish and triggerfish, boring caused by polychaetes, bivalves, and sponge. Bioerosion process not only weakening reef structures but also increase habitat complexity of reef-associated biota and expand coral occupy in space with natural propagation.

In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat.

Coral reef resilience depends on the balance between carbonate precipitation, leading to reef growth, and carbonate degradation, for example, through bioerosion. Changes in environmental conditions are likely to affect the two processes differently, thereby shifting the balance between reef growth and degradation. In cold-water corals estimates of accretion-erosion processes in their natural habitat are scarce and solely live coral growth rates were studied with regard to future environmental changes in the laboratory so far, limiting our ability to assess the potential of cold-water coral reef ecosystems to cope with environmental changes. In the present study, growth rates of the two predominant colour morphotypes of live Lophelia pertusa as well as bioerosion rates of dead coral framework were assessed in different environmental settings in Norwegian cold-water coral reefs in a 1-year in situ experiment. Net growth (in weight gain and linear extension) of live L. pertusa was in the lower range of previous estimates and did not significantly differ between inshore (fjord) and offshore (open shelf) habitats. However, slightly higher net growth rates were obtained inshore. Bioerosion rates were significantly higher on-reef in the fjord compared to off-reef deployments in- and offshore. Besides, on-reef coral fragments yielded a broader range of individual growth and bioerosion rates, indicating higher turnover in live reef structures than off-reef with regard to accretion–bioerosion processes. Moreover, if the higher variation in growth rates represents a greater variance in (genetic) adaptations to natural environmental variability in the fjord, inshore reefs could possibly benefit under future ocean change compared to offshore reefs. Although not significantly different due to high variances between replicates, growth rates of orange branches were consistently higher at all sites, while mortality was statistically significantly lower, potentially indicating higher stress-resistance than the less pigmented white phenotype. Comparing the here measured rates of net accretion of live corals (regardless of colour morphotype) with net erosion of dead coral framework gives a first estimate of the dimensions of both processes in natural cold-water coral habitats, indicating that calcium carbonate loss through bioerosion amounts to one fifth to one sixth of the production rates by coral calcification (disregarding accretion processes of other organisms and proportion of live and dead coral framework in a reef). With regard to likely accelerating bioerosion and diminishing growth rates of corals under ocean acidification, the balance of reef accretion and degradation may be shifted towards higher biogenic dissolution in the future.

The sea urchin Paracentrotus lividus as a bioeroder of plastic

It is increasingly recognised that plastic pollution of the marine environment is highly dynamic in nature. Larger plastic items are fragmented or eroded into smaller and smaller pieces as its moves through marine ecosystems and small particles can be fouled or flocculate into larger aggregates. Whilst physical processes play a major part in photo- and oxidative degradation of plastic debris, biological process may also contribute to the breakdown of larger plastic items into smaller particulates, yet this has not been studied well to date. Here, we demonstrate the potential for the sea urchin Paracentrotus lividus to act as bioeroders of macroplastics. We found that urchins readily graze on a plastic surface, with this grazing activity generating microplastics, when held in experimental systems together. On average each urchin produced 91.7 (±33.8 pieces) smaller plastic pieces (118–15,797 μm) from one macroplastic item over a ten day period. This plastic fragmentation by the urchins grazing activity was strongly influenced by the additional availability of natural food and by the presence of fouling of the macroplastic surface. Fragmentation of macroplastic by urchins dropped by 97% when urchins were exposed to virgin plastic in the presence of natural food (kelp). However, when macroplastic was biofouled urchins acted to fragment this plastic irrespective of the presence of additional food. The majority of fragments produced were negatively buoyant due to both the biofouling process and indeed the fouling by faecal matter, sinking to the bottom of the exposure systems. This smaller size range of plastic would then bioavailable to a much wider suite of species than the original macroplastic item; hence this bioerosion process has the potential to contribute to the transfer plastic fragments through benthic food webs.

Impact of an experimental eutrophication on the processes of bioerosion on the reef: One Tree Island, Great Barrier Reef, Australia

The components of bioerosion were investigated during ENCORE (The Effect of Nutrient Enrichment on Coral Reefs) over 2years of controlled additions of dissolved inorganic nitrogen and phosphorus. The study was carried out at One Tree Island, southern Great Barrier Reef, Australia. Rates of microbioerosion and external erosion by grazing were significantly higher at the enriched sites than at the control sites. Rates of accretion by coralline algae were also significantly higher at enriched sites. In contrast, rates of macroboring were not significantly different between enriched and control sites.This study highlights the importance of improving water quality on the reef to reduce rates of bioerosion given that quantities of dead coral substrates have recently substantially increased as a result of coral bleaching (Hughes et al., 2015) and several Crown of Thorns plagues (Fabricius et al., 2010; De'ath et al., 2012), on the Great Barrier Reef.

A geological perspective on the degradation and conservation of western Atlantic coral reefs.

Continuing coral-reef degradation in the western Atlantic is resulting in loss of ecological and geologic functions of reefs. With the goal of assisting resource managers and stewards of reefs in setting and measuring progress toward realistic goals for coral-reef conservation and restoration, we examined reef degradation in this region from a geological perspective. The importance of ecosystem services provided by coral reefs-as breakwaters that dissipate wave energy and protect shorelines and as providers of habitat for innumerable species-cannot be overstated. However, the few coral species responsible for reef building in the western Atlantic during the last approximately 1.5 million years are not thriving in the 21st century. These species are highly sensitive to abrupt temperature extremes, prone to disease infection, and have low sexual reproductive potential. Their vulnerability and the low functional redundancy of branching corals have led to the low resilience of western Atlantic reef ecosystems. The decrease in live coral cover over the last 50 years highlights the need for study of relict (senescent) reefs, which, from the perspective of coastline protection and habitat structure, may be just as important to conserve as the living coral veneer. Research is needed to characterize the geological processes of bioerosion, reef cementation, and sediment transport as they relate to modern-day changes in reef elevation. For example, although parrotfish remove nuisance macroalgae, possibly promoting coral recruitment, they will not save Atlantic reefs from geological degradation. In fact, these fish are quickly nibbling away significant quantities of Holocene reef framework. The question of how different biota covering dead reefs affect framework resistance to biological and physical erosion needs to be addressed. Monitoring and managing reefs with respect to physical resilience, in addition to ecological resilience, could optimize the expenditure of resources in conserving Atlantic reefs and the services they provide.

Impact and colonization dynamics of the bivalve Rocellaria dubia on limestone experimental panels in the submerged Roman city of Baiae (Naples, Italy)

The present study describes the role of the bivalve Rocellaria dubia Pennant, 1777 in the bioerosion process of submerged limestone artificial panels. The research was carried out in the central Mediterranean sea, in the Underwater Archaeological Park of Baiae (Naples, Italy). During the three year experimental period, the panels were submerged at 5 m depth and sequentially removed after 12, 24 and 36 months. R. dubia boreholes strongly affected stone material. The rate of bioerosion increased over time. After 36 months settlement still occurred with hundreds of boreholes and the shells were up to 13 mm in length. The results obtained concerning the impact of R. dubia on the experimental panels help to evaluate the bioerosive role of this species on submerged calcareous archaeological structures.