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Animals have a deep evolutionary relationship with microbial symbionts, such that individual microbes or an entire microbial community can diverge alongside the host. Here, we explore these host-microbe relationships in Echinometra, a sea urchin genus that speciated with the Isthmus of Panama and throughout the Indo-West Pacific. We find that the eggs from five Echinometra species generally associate with a species-specific bacterial community and that the relatedness of these communities is largely congruent with host phylogeny. Microbiome divergence per million years was higher in more recent speciation events than in older ones. We, however, did not find any bacterial groups that displayed co-phylogeny with Echinometra. Together, these findings suggest that the evolutionary relationship between Echinometra and their microbiota operates at the community level. We find no evidence suggesting that the associated microbiota is the evolutionary driver of Echinometra speciation. Instead, divergence between Echinometra and their microbiota is likely the byproduct of ecological, geographic, and reproductive isolations. [ABSTRACT FROM AUTHOR]

Four closely related Echinometra species exist in the Indo-Pacific region, but little is known about their population genetics in Taiwan, an area rich in marine biodiversity. Echinometra dominates the Douziping coral reef off Liuqiu Island, where urchin barrens are also present. To understand the relationship between Echinometra species and urchin barrens, we investigated the genetic diversity of Echinometra species in Taiwan by using a nondestructive DNA extraction method on the spines of sea urchins. Mitochondrial DNA results showed that E. sp. C is the dominant species in Taiwan, with relatively high interspecific genetic distance. The E. sp. C is the only species in Douziping, and its population is expanding in accordance with the significantly low R2 value, the significantly negative Fu's Fs values, and mismatch distribution analysis results. Gene flow estimates between the urchin populations in Taiwan and those in the neighbouring waters of Okinawa suggested that the Kuroshio Current could play an important role in Echinometra dispersal. This implies strongly connectivity between these populations. This study reports the first case of E. sp. C-associated urchin barrens in the tropics. [ABSTRACT FROM AUTHOR]

Introduction: The Persian Gulf is home to a diverse range of marine life, including various species of fish, crustaceans, mollusks, and echinoderms. This study investigates the potential therapeutic properties of venoms from echinoderms in the Persian Gulf, specifically their ability to inhibit cholinesterases (Acetylcholinesterase and butyrylcholinesterase) and act as antioxidants. Methods: Four venoms from two echinoderm species, including the spine, gonad, and coelomic fluids of sea urchins, as well as brittle star venoms, were analyzed using various methods, including LD[sub 50] determination, protein analysis, antioxidant assays, GC-MS for secondary metabolite identification, and molecular docking simulations. Results and discussion: The study's results revealed the LD[sub 50] of the samples as follows: 2.231 ± 0.09, 1.03 ± 0.05, 1.12 ± 0.13, and 6.04 ± 0.13 mg/mL, respectively. Additionally, the protein levels were 44.037 ± 0.002, 74.223 ± 0.025, 469.97 ± 0.02, and 104.407 ± 0.025 µg/mL, respectively. SDS-PAGE and total protein studies indicated that at least part of the venom was proteinaceous. Furthermore, the study found that the brittle star samples exhibited significantly higher antioxidant activity compared to other samples, including the standard ascorbic acid, at all tested concentrations. GC-MS analysis identified 12, 23, 21, and 25 compounds in the samples, respectively. These compounds had distinct chemical and bioactive structures, including alkaloids, terpenes, and steroids. Conclusion: These venoms displayed strong cholinesterase inhibitory and antioxidant activities, likely attributed to their protein content and the presence of alkaloids, terpenes, and steroids. Notably, the alkaloid compound C7 was identified as a promising candidate for further research in Alzheimer's disease therapy. In conclusion, echinoderms in the Persian Gulf may hold significant potential for discovering novel therapeutic agents. [ABSTRACT FROM AUTHOR]

Sea urchins have long been an important component of gleaning invertebrate fisheries and are valued for their highly nutritious gonads. Sea urchin fisheries are often unreported and unregulated, despite increasing indications of overexploitation. Data on the post-harvest utilization of sea urchins are limited, particularly in the Indo-Pacific region. This study at 12 sites across four regions in Indonesia (Sulawesi, Moluccas, Nusa Tenggara, Papua) aimed to provide an overview of sea urchin utilization in eastern Indonesia. Data were collected from July to September 2020 using a questionnaire with a snowballing sampling method. There were 187 respondents (62.6% male and 37.4% female) ranged in age from 3-76 years old, and most had been collecting sea urchins for more than five years. Respondents mostly collected the sea urchins from coral reef or seagrass habitats. Four genera (Tripneustes, Diadema, Echinometra and Echinothrix) were identified. Mean catch ranged from 32 (Makassar) to 169 (Maluku Tengah) individual sea urchin per collection. Most respondents knew local names for sea urchins, especially those they collected. Almost 70% respondents used their catch mainly for home consumption, and only 4.8% respondents mainly selling their catch. Most urchins sold were whole or crudely de-spined, typically fetching IDR 500-1000 each. Additional post-harvest processing before sale included removing the gonads from the test and/or cooking, with a unit price of IDR 5,000-25,000/product. Commonly consumed raw, urchins were sometimes cooked (mostly barbecued). These data indicate a need for efforts towards socio-ecologically appropriate sea urchin conservation and fisheries management to address the widespread indications of increasing exploitation levels and declining sea urchin populations. [ABSTRACT FROM AUTHOR]

Shifts in microbial communities represent a rapid response mechanism for host organisms to respond to changes in environmental conditions. Therefore, they are likely to be important in assisting the acclimatization of hosts to seasonal temperature changes as well as to variation in temperatures across a species' range. The Persian/Arabian Gulf is the world's warmest sea, with large seasonal fluctuations in temperature (20℃ ‐ 37℃) and is connected to the Gulf of Oman which experiences more typical oceanic conditions (<32℃ in the summer). This system is an informative model for understanding how symbiotic microbial assemblages respond to thermal variation across temporal and spatial scales. Here, we elucidate the role of temperature on the microbial gut community of the sea urchin Echinometra sp. EZ and identify microbial taxa that are tightly correlated with the thermal environment. We generated two independent datasets with a high degree of geographic and temporal resolution. The results show that microbial communities vary across thermally variable habitats, display temporal shifts that correlate with temperature, and can become more disperse as temperatures rise. The relative abundances of several ASVs significantly correlate with temperature in both independent datasets despite the >300 km distance between the furthest sites and the extreme seasonal variations. Notably, over 50% of the temperature predictive ASVs identified from the two datasets belonged to the family Vibrionaceae. Together, our results identify temperature as a robust predictor of community‐level variation and highlight specific microbial taxa putatively involved in the response to thermal environment. [ABSTRACT FROM AUTHOR]

Global change has resulted in oceans that are warmer, more acidic, and lower in oxygen. Individually any one of these stressors can have numerous negative impacts on marine organisms, and in combination they are likely to be particularly detrimental. Understanding the interactions between these factors is important as they often covary, with warming promoting hypoxia, and hypoxia co-occurring with acidification. Few studies have examined how all three factors interact to affect organismal performance, and information is particularly sparse for tropical organisms. Here we documented a strong relationship between high temperatures, low dissolved oxygen (DO), and low pH in and around a tropical bay. We used these field values to inform two multi-stressor experiments. Each experimental factor had two levels, one representing current average conditions and the other representing current extreme conditions experienced in the area. We used sea urchin righting response as a measure of organismal performance for an important reef herbivore. In the first experiment 2-h exposures to a fully factorial combination of temperature, DO, and pH showed that righting success was significantly depressed under low oxygen. To more fully understand the impacts of pH, we acclimated sea urchins to control and low pH for 7 days and subsequently exposed them to the same experimental conditions. Sea urchins acclimated to control pH had significantly reduced righting success compared to animals acclimated to low pH, and righting success was significantly depressed under hypoxia and high temperature, compared to normoxia and ambient temperature. These results show that short, 2 h exposures to the temperature and DO extremes that are already experienced periodically by these animals have measurable detrimental effects on their performance. The positive impact of reduced pH is evident only over longer, 7 days durations, which are not currently experienced in this area.

This study investigates the biomechanics, behavior, and distribution of urchin species in Mo’orea, French Polynesia to understand how they withstand hydrodynamic forces. Field surveys examined the flow distribution of four species:E. mathaei, Tripneustes gratilla, Diadema savignyiandEchinotrix calamaris. Flow tests were conducted on twoEchinometra mathaeisubspecies to measure spine angle under no flow and heavy flow conditions. Short spine urchin species were found in significantly higher flows than were long spine urchin species. Experimental findings revealed thatE. mathaeitype B temporarily adopts a more streamlined shape in response to increasing flow velocity, whileE. mathaeitype A does not. Understanding the streamlining behavior and other strategies for surviving hydrodynamic conditions is necessary in order to examine these organisms’ role in their environment.

The island of Mo’orea in French Polynesiafunctions as a model system to study the biologicaland ecological concept of niche differentiation,whereby two or more species are forced into differenthabitats so as to avoid competition with each other.In the waters surrounding this island, two speciesof sea urchin within the genus Echinometra livein distinctly different habitats. Previous studiesdocument Echinometra sp. A located exclusivelyon the fringing reef and Echinometra mathaeilocated exclusively on the barrier reef. This studyinvestigated three short-term factors (availablespace, nutrient supply, and predation) that mightbe influencing this spatial distribution. None ofthese factors appear to be causing the separation ofE. sp. A and E. mathaei. In fact, they all support thedistributional findings of this study that showednon-mutually exclusive distribution data on the tworeef types.

The island of Mo’orea in French Polynesia functions as a model system to study the biological and ecological concept of niche differentiation, whereby two or more species are forced into different habitats so as to avoid competition with each other. In the waters surrounding this island, two species of sea urchin within the genus Echinometra live in distinctly different habitats. Previous studies document Echinometra sp. A located exclusively on the fringing reef and Echinometra mathaei located exclusively on the barrier reef. This study investigated three short-term factors (available space, nutrient supply, and predation) that might be influencing this spatial distribution. None of these factors appear to be causing the separation of E. sp. A and E. mathaei. In fact, they all support the distributional findings of this study that showed non-mutually exclusive distribution data on the two reef types.

The complete mitogenome of Echinometra sp. EZ has been described and fully annotated in this study. Phylogenetic analysis of cytochrome c oxidase subunit I (COI) from six Echinometra species confirms that our sample is E. sp. EZ. The mitogenome is 15,698 bp in length and contains 13 protein-coding genes, 22 tRNAs, 2 rRNAs, and a non-coding region with an identical organization to other Echinoidea. The E. sp. EZ mitogenome shared ∼99.1% identity to the published Echinometra mathaei mitogenome, differing by 147 SNPs. The E. sp. EZ mitogenome will serve as a resource that can be applied to disentangling the Echinometra species complex and to future population genetic studies of this ecologically important sea urchin species.

The sexual system and sexual dimorphism of the shrimp Arete indicus are described. The following were measured for all shrimp under stereomicroscope to the nearest ±0.01 mm: carapace length (CL), merus length (ML) and carpus length (CrL) of the largest of the first pair of chelipeds, pleural width of the second abdominal segment (PW), and propodus length (PL) of the second (larger) pair of chelipeds. Sex determinations were based on presence of the appendix masculina on the base of the endopod of the second pleopods. With a view to determine whether or not a linear relationship exists between the CL, PL, ML, CrL and PW, the allometric model y = axb was used. A correlation was found between CL and ML in both sexes of Arete indicus. The status of allometry differed among various body parts of both sexes, and degree of allometry differed among various body parts between the sexes. According to ANCOVA, PW, PL, and ML of females are not larger than that of males at any given body size. The CL of Arete indicus females was not larger than the males. Due to observation a few of males with tiny appendices masculina, also based on earlier literature worked on Arete indicus, we believe this species is partially protandric. [ABSTRACT FROM AUTHOR]

Four recently-diverged species of Indo-Pacific sea urchins, belonging to the genus Echinometra, occur most abundantly and sympatrically along the coast of Okinawa Island, southern Japan. Among them, the two most distinct species--Echinometra sp. A (Ea) and Echinometra mathaei (Blainville, 1825) (Em)--were examined for potential hybridization through a series of cross-fertilization and hybrid raising experiments. Compared to conspecifk crosses, fertilization rates in both heterospecific crosses were very low, even at a very high concentration of sperm. At limited sperm concentration, where conspecifk crosses achieved near 100% fertilization, heterospecific crosses had <3% fertilization success. This strong block to fertilization in either heterospecific cross indicates the presence of a protein-binding system for gamete recognition. A significantly lower survival rate in larvae, juveniles, and adults does indicate a postzygotic isolating mechanism that is strong enough to limit hybrid survival, but is not complete, and did in fact cause some amount of developmental incompatibility or hybrid inviability. In adults, Em (ova) x Ea (sperm) was largest in live weight, followed by Ea (ova) x Em (sperm), Ea x Ea, and Em x Em, in that order. Other growth performances, such as test sizes, gonad weight, and gonad index of hybrids and their conspecifics, also followed the same trend as live weight. Phenotypic color patterns of the hybrids were maternally inherited, while other characters (spine length, morphology of tubefoot and gonad spicules, pedicellaria valve length, and gamete sizes) were intermediate. Ova and sperm of the F, hybrids were fertile in backcrosses, minimizing the possibility that hybrid infertility is a postzygotic isolating mechanism. Nevertheless, intensive surveys failed to find individuals with such hybrid characteristics, suggesting a very low presence or complete absence of natural hybrids in the field. This strongly suggests that pre- and postzygotic isolating mechanism(s) are isolating these species. Among these mechanisms, strong gametic incompatibility and probably microhabitat separation, differences in spawning times, gamete competition, or other factors appear to be important for maintaining genetic integrity of these two species. [ABSTRACT FROM AUTHOR]

We have studied the sensitivity to cryoprotecting agents of different embryos of the local sea urchin, Echinometra lucunter which is the species used for embryo-larval bioassays in Brazil. We have located significant differences between both species sensitivity to cryoprotecting agents; while for P. lividus propylene glycol was the less toxic compound for most development stages, whereas for E. lucunter is was the most toxic and the least toxic was Dimethyl sulfoxide. There is a significant difference between development stages as well; in the case of P. lividus , the blastula embryo was the most resistant to the cryoprotecting agents, meanwhile for E. lucunter, it was the fertilized oocyte. This is a very promising result, a really early embryo that is not extremely sensitive to Me 2 SO. Our next aim is to develop a cryopreservation protocol for E. lucunter early embryos and test them in an embryo-larval bioassay. [ABSTRACT FROM AUTHOR]

Background: Fluorochrome staining is among the most widely used techniques to study growth dynamics of echinoderms. However, it fails to detect fine-scale increments because produced marks are commonly diffusely distributed within the skeleton. In this paper we investigated the potential of trace element (manganese) labeling and subsequent cathodoluminescence (CL) imaging in fine-scale growth studies of echinoderms. Results: Three species of sea urchins (Paracentrotus lividus, Echinometra sp. and Prionocidaris baculosa) were incubated for different periods of time in seawater enriched in different Mn2+ concentrations (1 mg/L; 3 mg/L; 61.6 mg/L). Labeling with low Mn2+ concentrations (at 1 mg/L and 3 mg/L) had no effect on behavior, growth and survival of sea urchins in contrast to the high Mn2+ dosage (at 61.6 mg/L) that resulted in lack of skeleton growth. Under CL, manganese produced clearly visible luminescent growth fronts in these specimens (observed in sectioned skeletal parts), which allowed for a determination of the average extension rates and provided direct insights into the morphogenesis of different types of ossicles. The three species tend to follow the same patterns of growth. Spine growth starts with the formation of microspines which are simultaneously becoming reinforced by addition of thickening layers. Spine septa develop via deposition of porous stereom that is rapidly (within less than 2 days) filled by secondary calcite. Development of the inner cortex in cidaroids begins with the formation of microspines which grow at ~3.5 μm/day. Later on, deposition of the outer polycrystalline cortex with spinules and protuberances proceeds at ~12 μm/day. The growth of tooth can be rapid (up to ~1.8 mm/day) and starts with the formation of primary plates (pp) in plumula. Later on, during the further growth of pp in aboral and lateral directions, secondary extensions develop inside (in chronological order: lamellae, needles, secondary plate, prisms and carinar processes), which are increasingly being solidified towards the incisal end. Interradial growth in the ambital interambulacral test plates exceeds meridional growth and inner thickening. Conclusions: Mn2+ labeling coupled with CL imaging is a promising, low-cost and easily applicable method to study growth dynamics of echinoderms at the micro-length scale. The method allowed us to evaluate and refine models of echinoid skeleton morphogenesis. [ABSTRACT FROM AUTHOR]

The complete mitogenome of Echinometra sp. EZ has been described and fully annotated in this study. Phylogenetic analysis of cytochrome c oxidase subunit I (COI) from six Echinometra species confirms that our sample is E. sp. EZ. The mitogenome is 15,698 bp in length and contains 13 protein-coding genes, 22 tRNAs, 2 rRNAs, and a non-coding region with an identical organization to other Echinoidea. The E. sp. EZ mitogenome shared ∼99.1% identity to the published Echinometra mathaei mitogenome, differing by 147 SNPs. The E. sp. EZ mitogenome will serve as a resource that can be applied to disentangling the Echinometra species complex and to future population genetic studies of this ecologically important sea urchin species. [ABSTRACT FROM AUTHOR]

Background: Marine organisms produce a variety of compounds with pharmacological activities, including anticancer effects. They contain several secondary metabolites with interesting biological activities. This study attempted to find cytotoxicity of Hexane, Dichloromethane and Butanol partitions of Holothuria leucospilota and Echinometra mathaei. Materials and Methods: H. leucospilota and E. mathaei were collected from Persian Gulf. The animals were extracted by maceration with methanol-ethyl acetate (1:1). The H. leucospilota extract was partitioned by Kupchan method to hexane, dichloromethane, butanol, and water partitions. The cytotoxic activity of the extracts was investigated against HeLa (cervical cancer) and human umbilical vein endothelial cells cell lines by mitochondrial tetrazolium test assay after 72 h. Results: The cell survivals of HeLa cell were decreased by increasing the concentration of extracts. A significant reduction in cell viability at the doses of 30 (μg/ml) of dichloromethane (DCM) partition, 0.3, 3, and 30 (μg/ml) of ButOH partitions of sea cucumber, and 0.5 (μg/ml) of E. mathaei was observed. The median growth inhibitory concentration value of Hex, DCM, ButoH, and water partitions were 0.301, 0.21, 2.29, and 0.229 μg/ml, respectively. Conclusion: This study reveals that different partitions of H. leucospilota and total extract of E. mathaei have cytotoxic activity against cancer cell lines. More study is necessary to find the active metabolites in the more active partitions.

Long-term changes in macroalgal cover, spatial variation between macroalgal communities, and relationships with environmental variables and benthic groups were assessed in coral reefs along the Caribbean coast of Panama. Sampling was conducted in two regions: Western and Central. Data collected between 2000 and 2012 showed a continuous increase in macroalgal abundance, although patterns differed according to region and site. There were differences in macroalgal communities between regions, as well as within regions between different wave-exposure levels. There were also differences between sites within regions exposed to the same level of wave action. Multivariate analysis found that wave exposure along with herbivore density ( Echinometra viridis ) and sedimentation were the variables that explained most of the variability between communities. Other variables such as Echinometra lucunter and Diadema antillarum densities, fish density, productivity, and live coral cover had significant relationships with community structure, but explained less of the variability. [ABSTRACT FROM AUTHOR]

Echinometra viridis previously was considered a cryptic species unable to control the development and growth of macroalgae on coral reefs. Its role as a herbivore was seen as minor compared to other grazers present on the reef. However, the present disturbed state of some reefs has highlighted the role played by this sea-urchin. Combining field data with experiments on the Caribbean coast of Panama, we demonstrate that the current community organization on disturbed coral reefs in the Mesoamerican Caribbean is largely due to the action of E. viridis . It is the most abundant sea-urchin species, together with two others ( Diadema antillarum and Echinometra lucunter ). Field data also indicate that the relationship between its density and the abundance of macroalgae is stronger and it is more negative in impact than those of the other two. However, the niche this urchin exploits most efficiently is confined to leeward reefs with low levels of sedimentation. Outside these habitats, their populations are not decisive in controlling macroalgal growth. Grazing experiments showed that E. viridis consumes more fresh macroalgae per day and per weight of sea-urchin, and is a more effective grazer than D. antillarum or E. lucunter . E. viridis showed food preferences for early-successional turf macroalgae ( Acanthophora spicifera ), avoiding the less palatable late-successional and fleshy macroalgae ( Lobophora variegata , Halimeda opuntia ). However, it becomes a generalist herbivore feeding on all varieties of macroalgae when resources are scarce. H. opuntia is the macroalga that most resists E. viridis activity, which may explain its wide distribution. [ABSTRACT FROM AUTHOR]

Rising atmospheric CO2 concentrations will significantly reduce ocean pH during the 21st century (ocean acidification, OA). This may hamper calcification in marine organisms such as corals and echinoderms, as shown in many laboratory-based experiments. Sea urchins are considered highly vulnerable to OA. We studied an Echinometra species on natural volcanic CO2 vents in Papua New Guinea, where they are CO2-acclimatized and also subjected to secondary ecological changes from elevated CO2. Near the vent site, the urchins experienced large daily variations in pH (>1 unit) and pCO2 (>2000 ppm) and average pH values ( pHT 7.73) much below those expected under the most pessimistic future emission scenarios. Growth was measured over a 17-month period using tetracycline tagging of the calcareous feeding lanterns. Average-sized urchins grew more than twice as fast at the vent compared with those at an adjacent control site and assumed larger sizes at the vent compared to the control site and two other sites at another reef near-by. A small reduction in gonad weight was detected at the vents, but no differences in mortality, respiration, or degree of test calcification were detected between urchins from vent and control populations. Thus, urchins did not only persist but actually 'thrived' under extreme CO2 conditions. We suggest an ecological basis for this response: Increased algal productivity under increased pCO2 provided more food at the vent, resulting in higher growth rates. The wider implication of our observation is that laboratory studies on non-acclimatized specimens, which typically do not consider ecological changes, can lead to erroneous conclusions on responses to global change. [ABSTRACT FROM AUTHOR]

Trophic cascades caused by a reduction in predators of sea urchins have been reported in Indian Ocean and Caribbean coral reefs. Previous studies have been constrained by their site-specific nature and limited spatial replication, which has produced site and species-specific understanding that can potentially preclude larger community-organization nuances and generalizations. In this study, we aimed to evaluate the extent and variability of the cascade community in response to fishing across ~23° of latitude and longitude in coral reefs in the southwestern Indian Ocean. The taxonomic composition of predators of sea urchins, the sea urchin community itself, and potential effects of changing grazer abundance on the calcifying benthic organisms were studied in 171 unique coral reef sites. We found that geography and habitat were less important than the predator-prey relationships. There were seven sea urchin community clusters that aligned with a gradient of declining fishable biomass and the abundance of a key predator, the orange-lined triggerfish ( Balistapus undulatus). The orange-lined triggerfish dominated where sea urchin numbers and diversity were low but the relative abundance of wrasses and emperors increased where sea urchin numbers were high. Two-thirds of the study sites had high sea urchin biomass (>2,300 kg/ha) and could be dominated by four different sea urchin species, Echinothrix diadema, Diadema savignyi, D. setosum, and Echinometra mathaei, depending on the community of sea urchin predators, geographic location, and water depth. One-third of the sites had low sea urchin biomass and diversity and were typified by high fish biomass, predators of sea urchins, and herbivore abundance, representing lightly fished communities with generally higher cover of calcifying algae. Calcifying algal cover was associated with low urchin abundance where as noncalcifying fleshy algal cover was not clearly associated with herbivore abundance. Fishing of the orange-lined triggerfish, an uncommon, slow-growing by-catch species with little monetary value drives the cascade and other predators appear unable to replace its ecological role in the presence of fishing. This suggests that restrictions on the catch of this species could increase the calcification service of coral reefs on a broad scale. [ABSTRACT FROM AUTHOR]

Echinometra mathaei is a common echinoid on tropical reefs and where abundant plays an important role in the control of algal communities. Despite high prevalence of E. mathaei on southern Persian/Arabian Gulf reefs, their abundance and distribution is poorly known. Spatial and temporal patterns in population abundance were examined at 12 sites between breakwater and natural reef habitats in Dubai (UAE) every 3 months from 2008 to 2010. Within the breakwater habitat, densities were greatest at shallow wave-exposed sites, and reduced with both decreasing wave-exposure and increasing depth. Interestingly, E. mathaei were significantly more abundant on exposed breakwaters than natural reef sites, presumably due to differences in habitat structure and benthic cover. Population abundances differed seasonally, with peak abundances during summer (July–September) and lower abundances in winter (December–February). Seasonal fluctuations are likely the result of peak annual recruitment pulses coupled with increased fish predation from summer to winter. [ABSTRACT FROM AUTHOR]

Ocean acidification, a process caused by the continuous rise of atmospheric CO levels, is expected to have a profound impact on marine invertebrates. Findings of the numerous studies conducted in this field indicate high variability in species responses to future ocean conditions. This study aimed at understanding the effects of long-term exposure to elevated pCO conditions on the performance of adult Echinometra sp. EE from the Gulf of Aqaba (Red Sea). During an 11-month incubation under high pCO (1,433 μatm, pH 7.7) and control (435 μatm, pH 8.1) conditions, we examined the urchins' somatic and gonadal growth, gametogenesis and skeletal microstructure. Somatic and gonadal growths were exhibited with no significant differences between the treatments. In addition, all urchins in the experiment completed a full reproductive cycle, typical of natural populations, with no detectable impact of increased pCO on the timing, duration or progression of the cycle. Furthermore, scanning electron microscopy imaging of urchin tests and spines revealed no signs of the usual observed effects of acidosis, such as skeletal dissolution, widened stereom pores or non-smoothed structures. Our results, which yielded no significant impact of the high pCO treatment on any of the examined processes in the urchins studied, suggest high resistance of adult Echinometra sp. EE to near future ocean acidification conditions. With respect to other findings in this area, the outcome of this study provides an example of the complicated and diverse responses of echinoids to the predicted environmental changes. [ABSTRACT FROM AUTHOR]

Abstract: Echinoid–habitat relations are complex and bi-directional. Echinoid community structure is affected by the habitat structural and environmental conditions; while at the same time, echinoids may also act as ‘reef engineers’, able to alter marine environments on a wide geographic scale. In particular, echinoids play a major role in bioerosion and herbivory on coral reefs. Through feeding, echinoids reduce algal cover, enabling settlement and coral growth. However, at the same time, they also remove large parts of the reef hard substrata, gradually leading to reef degradation. Here, we compared coral and macroalgal abundance, echinoid community structure and species-specific rates of echinoid herbivory and bioerosion on reefs subjected to different intensities of oceanic exposure. Spatio-temporal variations in coral and macroalgal cover were monitored, and populations of the four most abundant echinoid species on the coral reefs of Zanzibar – Diadema setosum (Leske), Diadema savignyi (Michelin), Echinometra mathaei (de Blainville) and Echinothrix diadema (Linnaeus) – were compared between the Island's eastern exposed reefs and western sheltered ones. To account for the effect of management in the context of reef exposure, we included marine protected areas (MPAs) of both types of reef categories (i.e. sheltered and exposed) in our comparison. Coral and macroalgal cover presented a conspicuous contrasting pattern across exposed and sheltered sites. While coral dominance and lack of macroalgae were prominent on sheltered reefs, an opposite trend of low coral cover and moderate–high macroalgal cover were found on exposed reefs. Bioerosion was also significantly higher on exposed reefs than on sheltered ones (4.2–13 and 1.2–3.9kg CaCO3 m−2 year−1, respectively). The highest rates, recorded on Pongwe, with almost 7kg CaCO3 m−2 year−1, are among the highest echinoid bioerosion rates known to date. Management had a substantial effect on habitat and echinoid community structure, as coral cover was significantly higher, macroalgal cover lower, and echinoid densities generally reduced on MPAs regardless of exposure intensity. Our findings suggest that exposed reefs are susceptible to markedly higher degrees of echinoid bioerosion; however, adequate management measures can significantly reduce these rates, consequently altering the reef's trajectory for degradation. [Copyright &y& Elsevier]

Marine organisms exhibit substantial life-history diversity, of which egg size is one fundamental parameter. The size of an egg is generally assumed to reflect the amount of energy it contains and the amount of per-offspring maternal investment. Egg size and energy are thought to scale isometrically. We investigated this relationship by updating published datasets for echinoderms, increasing the number of species over those in previous studies by 62%. When we plotted egg energy versus egg size in the updated dataset we found that planktotrophs have a scaling factor significantly lower than 1, demonstrating an overall trend toward lower energy density in larger planktotrophic eggs. By looking within three genera, Echinometra, Strongylocentrotus, and Arbacia, we also found that the scaling exponent differed among taxa, and that in Echinometra, energy density was significantly lower in species with larger eggs. Theoretical models generally assume a strong tradeoff between egg size and fecundity that limits energetic investment and constrains life-history evolution. These data suggest that the evolution of egg size and egg energy content can be decoupled, possibly facilitating response to selective factors such as sperm limitation which could act on volume alone. [ABSTRACT FROM AUTHOR]

The Upper Pliocene Hopegate Formation has been the least attractive limestone unit for paleontological investigation in the Cenozoic of Jamaica due to its extreme lithification and dolomitization, despite the scientific appeal of it being a rare example of a Pliocene raised reef in the Caribbean. Preservation of invertebrate macrofossils is commonly moldic. Hitherto, few named macrofossils from the unit have been published. New and extensive exposures of the Hopegate Formation have become available since 2002 as the main north coast road has been re-engineered in central north Jamaica. Echinoids were previously unknown from this formation, but at least seven taxa are now recognized, namely, Eucidaris tribuloides (Lamarck), Echinometra viridis A. Agassiz, regular echinoids spp. indet., Echinoneus sp. cf. E. cyclostomus Leske, Schizaster sp. cf. S. doederleini (Chesher), Meoma? sp. and Brissus sp. cf. B. unicolor (Leske). The identifiable genera are typical of modern shallow water environments of the Caribbean. With the exception of Meoma? and Brissus, these nominal genera have also been identified from the coeval Bowden Formation, a deeper water deposit with a mixed allochthonous/autochthonous echinoderm fauna. In contrast to the Bowden Formation, which has yielded numerous fragmentary, but well preserved, echinoderm specimens, the Hopegate Formation has yielded only rare, poorly preserved echinoid tests and rarer fragments. [ABSTRACT FROM AUTHOR]

Abstract: Atmospheric carbon dioxide (pCO2) has risen from approximately 280 to 400ppm since the Industrial Revolution, due mainly to the combustion of fossil fuels, deforestation, and cement production. It is predicted to reach as high as 900ppm by the end of this century. Ocean acidification resulting from the release of anthropogenic CO2 has been shown to impair the ability of some marine calcifiers to build their shells and skeletons. Here, we present the results of ocean acidification experiments designed to assess the effects of an increase in atmospheric pCO2 from ca. 448 to 827ppm on calcification rates of the tropical urchin Echinometra viridis. Experiments were conducted under the urchin''s winter (20°C) and summer (30°C) water temperatures in order to identify seasonal differences in the urchin''s response to ocean acidification. The experiments reveal that calcification rates decreased for urchins reared under elevated pCO2, with the decline being more pronounced under wintertime temperatures than under summertime temperatures. These results indicate that the urchin E. viridis will be negatively impacted by CO2-induced ocean acidification that is predicted to occur by the end of this century. These results also suggest that impact of CO2-induced ocean acidification on urchin calcification will be more severe in the winter and in cooler waters. [Copyright &y& Elsevier]

Two reef margin species of tropical sea urchins, Echinometra sp. C (Ec) and Echinometra oblonga (Eo), occur sympatrically on Okinawa intertidal reefs in southern Japan. Hybridization between these species was examined through a series of cross-fertilization experiments. At limited sperm concentrations, where conspecific crosses reached near 100% fertilization, both heterospecific crosses showed high fertilization rates (81%-85%). The compatibility of the gametes demonstrated that if gamete recognition molecules are involved in fertilization of these species, they are not strongly species-specific. We found that conspecific crosses reached peak fertilization levels much faster than did heterospecific crosses, indicating the presence of a prezygotic barrier to hybridization in the gametes. Larval survival, metamorphosis, and juvenile and adult survival of hybrid groups were nearly identical to those of their parent species. Hybrids from crosses in both directions developed normally through larval stages to sexually mature adults, indicating that neither gametic incompatibility nor hybrid inviability appeared to maintain reproductive isolation between these species. In adults, Ec×Ec crosses gave the highest live weight, followed by Eo (ova)×Ec (sperm), Ec (ova)×Eo (sperm), and Eo×Eo. Other growth performance measures (viz., test size, Aristotle's lantern length, and gonad index) of hybrid groups and their parental siblings showed the same trends. The phenotypic color patterns of the hybrids were closer to the maternal coloration, whereas spine length, tube-foot and gonad spicule characteristics, pedicellaria valve length, and gamete sizes showed intermediate features. Adult F hybrids were completely fertile and displayed high fertilization success in F backcrosses, eliminating the likelihood that hybrid sterility is a postzygotic mechanism of reproductive isolation. Conversely, intensive surveys failed to find hybrid individuals in the field, suggesting the lack or rarity of natural hybridization. This strongly suggests that reproductive isolation is achieved by prezygotic isolating mechanism(s). Of these mechanisms, habitat segregation, gamete competition, differences in spawning times, gametic incompatibility or other genetic and non-genetic factors appear to be important in maintaining the integrity of these species. [ABSTRACT FROM AUTHOR]

Predators are important for regulating adult sea urchin densities. Here, we employ remote underwater video cameras to record diurnal predation on tethered sea urchins at Lizard Island on the Great Barrier Reef (GBR). We identified four fish predators of adult sea urchins ( Balistoides viridescens, Balistapus undulatus, Lethrinus atkinsoni and Choerodon schoenleinii). Predator activity appeared to be site-specific. Balistoides viridescens and B. undulatus (f: Balistidae) were the two most important predators of Echinometra mathaei with the former handling E. mathaei significantly faster (mean 0.7 min) than B. undulatus (5.2 min). Balistoides viridescens also successfully preyed on 70 % of detections, while C. schoenleinii, B. undulatus and L. atkinsoni preyed on just 33, 17 and <1 %, respectively. Additionally, B. viridescens were behaviourally dominant among predator species and were observed as aggressors in 30 encounters with B. undulatus and 8 encounters with L. atkinsoni. In only one encounter was B. viridescens the recipient of any aggression (from B. undulatus). In terms of relative vulnerability, of the three sea urchin species examined, E. mathaei were more vulnerable to predation than Diadema setosum or Echinothrix calamaris, with mean handling times of 1.2, 4.8 and 10.3 min, respectively. Balistoides viridescens and B. undulatus both appear to be able to play an important role as predators of sea urchins on the relatively intact coral reefs of Lizard Island. However, B. viridescens emerge as the most efficient predator in terms of handling speed and the proportion of detections preyed upon. They were also the behaviourally dominant predator. This preliminary study of the predators of sea urchins on the GBR highlights the potential significance of relatively scarce but functionally important species. [ABSTRACT FROM AUTHOR]

Egg size is one of the fundamental parameters in the life histories of marine organisms. However, few studies have examined the relationships among egg size, composition, and energetic content in a phylogenetically controlled context. We investigated the associations among egg size, composition, and energy using a comparative system, geminate species formed by the closure of the Central American Seaway. We examined western Atlantic (WA) and eastern Pacific (EP) species in three echinoid genera, Echinometra, Eucidaris, and Diadema. In the genus with the largest difference in egg size between geminates (Echinometra), the eggs of WA species were larger, lipid rich and protein poor compared to the smaller eggs of their EP geminate. In addition, the larger WA eggs had significantly greater total egg energy and summed biochemical constituents yet significantly lower egg energy density (energy-per-unit-volume). However, the genera with smaller (Eucidaris) or no (Diadema) differences in egg size were not significantly different in summed biochemical constituents, total egg energy, or energy density. Theoretical models generally assume a strong tradeoff between egg size and fecundity that limits energetic investment and constrains life history evolution. We show that even among closely-related taxa, large eggs cannot be assumed to be scaled-up small eggs either in terms of energy or composition. Although our data comes exclusively from echinoid echinoderms, this pattern may be generalizable to other marine invertebrate taxa. Because egg composition and egg size do not necessarily evolve in lockstep, selective factors such as sperm limitation could act on egg volume without necessarily affecting maternal or larval energetics. [ABSTRACT FROM AUTHOR]

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Understanding diel patterns in sea urchin activity is important when assessing sea urchin populations and when interpreting their interactions with predators. Here we employ a combination of surveys and a non-invasive tethering technique to examine these patterns in an intact coral reef system on the Great Barrier Reef (GBR). We also assess local scale variation in relative diurnal predation pressure. Surveys revealed that sea urchins were active and exposed at night. Echinometra mathaei and Echinothrix calamaris were the most abundant species with significantly higher night densities (0.21 and 0.03 ind. m, respectively), than daytime densities (0.05 and 0.001, respectively). Bioassays revealed that exposed adult E. mathaei (the most abundant sea urchin species) were 30.8 times more likely to be eaten during the day than at night when controlling for sites. This observation concurs with widely held assumptions that nocturnal activity is a risk-related adaptive response to diurnal predation pressure. Despite relatively intact predator communities on the GBR, potential predation pressure on diurnally exposed E. mathaei assays was variable at a local scale and the biomass of potential fish predators at each site was a poor predictive measure of this variation. Patterns in predation appear to be more complex and variable than we may have assumed. [ABSTRACT FROM AUTHOR]

Abstract: Sedimentation can provide indirect benefits to the survival of macroalgae in areas with potentially high grazing pressure. Field studies were performed in an embayment with extensive urchin barrens but also with locally persistent fucoid beds, on the coast of Kagoshima, south-western Japan, to elucidate the physical and biological processes responsible for the maintenance of the beds. Rocky subtidal reefs devoid of fine sediment were almost completely barren and dominated by sea urchins (primarily Echinometra sp. A), while fucoid algae (predominantly Sargassum duplicatum) densely populated cobble sites overlaid with a thin layer of fine sediment (medium grain size: 0.15–0.25mm). Quadrat samplings in areas intermixed with urchin barrens and sand flats as well as experimental addition of sediment suggested that Echinometra sp. was readily excluded from hard substratum overlaid with even only a thin layer of fine sediment. Quadrat surveys and a transplant experiment conducted at the border area between a cobble bed with a thin cover of fine sediment and a sediment-free boulder one indicated that sea urchins (mainly composed of Echinometra sp. and Diadema spp.) rarely invaded the sediment-covered bed to graze. Wave measurements at the entrance (8m deep) of the embayment over a 3.5-year period showed that the study area had long-term extremely calm conditions (84% of significant wave heights <0.1m) and seasonal or transient moderate disturbances due to relatively high waves (significant wave height: 0.8–1.3m). However, the 2-year time series of root-mean-square wave orbital velocity estimates at different sites consistently suggested that the wave-action intensities at urchin barrens were still too high for deposition of fine sediments which occurred in more wave-sheltered persistent fucoid area. Nearly 2-year investigations on sediment level change and on cobble substrates together with overlying sediment in the fucoid area suggested that the absence of fatal sediment inundation and maintenance of the thin overlying sediment layer (mean thickness

Monthly samples were taken from November 2004 to October 2005 in the Los Frailes reef, BCS, Mexico. The objective was to determine the feeding habits of the pufferfish, Arothron meleagris, as well as possible variations in feeding patterns due to size and/or sex. We captured 101 specimens, with all stomachs contained food. The index of relative importance (IRI) was used to determine the main items; which were non-identified organic matter (NIOM) (30.44%), Echinometra vanbrunti (26.25 %), Porifera (12.63 %), Pocillopora spp. (11.84%), Bryozoa (5.37 %) and Porites spp. (4.83 %). Levin's index indicated a low trophic niche breadth (Bi= 0.12) and allowed us to determine that A. meleagris is a specialist predator with strong preferences towards certain food types. The Morisita-Horn index showed a high trophic overlap between sexes (Cλ=0.78), seasons (hot and cold Cλ=0.95) and among sizes (small and medium Cλ=0.94; small and large Cλ=0.74; medium and large Cλ=0.83). [ABSTRACT FROM AUTHOR]

Do changes in food resources lead to evolutionary changes in phenotypic plasticity or in different constant phenotypes? I addressed this question by studying plasticity of larval feeding arms for “geminate species pairs” in three echinoid genera. These closely related species were geographically isolated when the Panamanian Isthmus raised 2.8–3.1 million years ago, creating two different food level environments: high but variable food levels in the eastern Pacific versus chronically low food levels in the western Caribbean. I reared larvae of geminate species in different replicated food environments for 10 days postfertilization, collected morphological measurements of individual arm and body lengths, and calculated degrees of plasticity of relative arm length for each species. In contrast to previous studies with temperate echinoids, there was no significant plasticity of arm length in either the Pacific or Caribbean species considered here. Caribbean species, however, had significantly longer relative arm lengths than Pacific species, regardless of food levels. These results suggest that historical changes in food levels have led to the evolution of constant rather than plastic differences between Pacific and Caribbean echinoids. The evolution of plasticity may be limited by the timing of reproduction or by egg size in this system. [ABSTRACT FROM AUTHOR]

The peculiar limpet-like morphology of the genus Colobocentrotus is unique among the regular echinoids. This shape has been interpreted as an adaptation to life in areas of extreme wave exposure. In this study the attachment strength of C. atratus is compared with that of three sympatric species, Echinometra mathaei, Heterocentrotus trigonarius and Stomopneustes variolaris, which have more typical echinoid morphology and live in different microhabitats. For each species, the adhesion of individual sea urchins was measured as well as the tenacity of single tube foot and the mechanical properties of the tube foot stems. Colobocentrotus always presented the highest measured values, although not always significantly different from those of the other species. Of the mechanical properties of the stem measured, the stem extensibility was the only property that was significantly different among species. In general the stems of all the species studied became more extensible and more difficult to break with increasing strain rate, providing an adaptative advantage to the sea urchin when subjected to rapid loads such as waves. In terms of single tube foot tenacity, C. atratus tube feet attached with a tenacity (0.54 MPa) two times higher than the one of E. mathaei, H. trigonarius and S. variolaris (0.21–0.25 MPa). Individual sea urchins of the four species, however, attached with a similar strength (0.2–0.26 MPa). The calculation of safety factors showed that it is the very high number of adoral tube feet of C. atratus and not the overall shape of the animal that allows this species to withstand very high water velocities. However, C. atratus streamlined morphology may be a functional adaptation to reduce the impact of other hydrodynamic forces (such as wave impingement forces) or to cope with other selective environmental stresses (such as dessication), and thus to inhabit extremely exposed areas of the intertidal. [ABSTRACT FROM AUTHOR]

Hypoxia-inducible factor-1 (HIF-1) is now recognized as a possible target for cancer treatment. This transcription factor is responsible for the overexpression of several genes favouring cancer cell survival and inducing neo-angiogenesis. Echinomycin has recently been described to inhibit HIF-1 DNA binding and transcriptional activity. In this work, it is shown that echinomycin strongly inhibits the activity of HIF-1 under hypoxic conditions, and also interferes with the activity of other transcription factors. These results demonstrate the lack of specificity of this molecule. Moreover, it is demonstrated that echinomycin induces an increase in HIF-1 activity under normoxic conditions, parallel to an increase in the expression of HIF-1 target genes. This effect is caused by an increase in HIF-1α protein level, resulting from an increase in the transcription of the HIF-1A gene in the presence of a low concentration of echinomycin. Transfection experiments with HIF-1α promoter constructs revealed the presence of an Sp1 binding element responsive to echinomycin. Furthermore, echinomycin enhanced Sp1 activity, as measured by the use of a specific reporter system. These findings show, for the first time, that echinomycin has a dual effect on HIF-1 activity under normoxic and hypoxic conditions, demonstrating that this molecule cannot be used in cancer treatment. [ABSTRACT FROM AUTHOR]

Abstract: Four closely related species of sea urchins belonging to the genus Echinometra, Echinometra sp. A (Ea), E. mathaei (Em), E. sp. C (Ec), and E. oblonga (Eo), occur sympatrically but in different microhabitats on Okinawan coral reefs. Feeding rates and absorption efficiencies of the four species were investigated in the laboratory by feeding sea urchins ad libitum a diet prepared from turf algae and agar over a 7-day period. Feeding rates differed significantly among the four species of Echinometra (Ea>Em≈Ec>Eo). Absorption efficiencies of protein and lipid did not differ significantly among the four species. Carbohydrate, a major nutrient component in the diet, was absorbed by the four species at significantly different efficiencies (Eo>Ec≈Em>Ea), which resulted in similar interspecific differences in absorption efficiencies of dry matter, total organic matter, and energy. The amount of nutrients absorbed from the diet was directly related to the feeding rate, indicating that the increase in absorption efficiency was not sufficient to completely compensate for low feeding rate. The interspecific difference in physiological performance in relation to feeding and absorption is consistent with taxonomic differentiation among the four species. [Copyright &y& Elsevier]

The article presents a study which examines the feeding ecology of the four species of sea urchin Echinometra in Okinawa Island, Japan. The study focuses on the distribution, food availability and gut contents of the species at five different sites on the Okinawan coral reefs. The study indicates that the availability of major plants in the field was generally proportional to their abundance in the gut. It is also indicated that benthic grazing was the primary feeding mode of Echinometra living on rock platforms while drift feeding was pronounced when macrophytes were abundant in the habitat or surroundings.

This study investigates the influence of mesograzer prior exposure to toxic metabolites on palatability of the marine cyanobacterium, Lyngbya majuscula. We examined the palatability of L. majuscula crude extract obtained from a bloom in Moreton Bay, South East Queensland, Australia, containing lyngbyatoxin-a (LTA) and debromoaplysiatoxin (DAT), to two groups: (1) mesograzers of L. majuscula from Guam where LTA and DAT production is rare; and (2) macro- and mesograzers found feeding on L. majuscula blooms in Moreton Bay where LTA and DAT are often prevalent secondary metabolites. Pair-wise feeding assays using artificial diets consisting of Ulva clathrata suspended in agar (control) or coated with Moreton Bay L. majuscula crude extracts (treatment) were used to determine palatability to a variety of consumers. In Guam, the amphipods, Parhyale hawaiensis and Cymadusa imbroglio; the majid crab Menaethius monoceros; and the urchin Echinometra mathaei were significantly deterred by the Moreton Bay crude extract. The sea hares, Stylocheilus striatus, from Guam were stimulated to feed by treatment food whereas S. striatus collected from Moreton Bay showed no discrimination between food types. In Moreton Bay, the cephalaspidean Diniatys dentifer and wild caught rabbitfish Siganus fuscescens were significantly deterred by the crude extract. However, captive-bred S. fuscescens with no known experience with L. majuscula did not clearly discriminate between food choices. Lyngbya majuscula crude extract deters feeding by most mesograzers regardless of prior contact or association with blooms. [ABSTRACT FROM AUTHOR]

Abstract: Hybridization between Echinometra sp. A (Ea) and Echinometra mathaei (Em) was examined through cross fertilization and rearing experiments to evaluate the aquaculture potential of hybrids. Mean performance traits of fertilization, larval survival, metamorphosis, and recovery of juveniles Em (ova)×Ea (sperm) and Ea (ova)×Em (sperm) hybrids were not significantly different from each other but were significantly lower than either of their conspecific controls, Ea×Ea and Em×Em. Percent survival from metamorphosis to 3-month-old juveniles at recovery was approximately 63% for hybrids and approximately 74% for parents. Postzygotic isolating mechanisms were not large enough to cause developmental incompatibility or hybrid survival. Growth of postmetamorphic hybrids was significantly higher than that of conspecific controls. After culture for 2 years, the mean weight gained by Ea×Ea, Em×Ea, Ea×Em, Em×Em was 41.1±0.8, 50.5±0.4, 49.8±0.3, and 34.3±0.2 g, respectively. Both reciprocal hybrids, Em×Ea and Ea×Em had significantly faster growth than the superior parent (Ea×Ea) and inferior parent (Em×Em). Other growth parameters such as final weight, weight gain (%), specific growth rate (SGR) (%/day) and test size had the same trends as weight gain. Production of gonads was significantly lower in slow-growing Em×Em (7.5±0.1 g) than the fast-growing Ea×Ea (9.1±0.4 g). Reciprocal hybrids contained significantly larger amount of gonads (12.1±0.1 g in Em×Ea and 11.9±0.2 g in Ea×Em) than conspecific controls. Gonad production showed an increase of 45% in F1 hybrids (mean of both hybrids) over mid parents and an increase of 34%, 63% and 47% in F1 hybrid of Em×Ea and 31%, 60%, and 44% in F1 hybrid of Ea×Em over the superior (Ea×Ea), inferior (Em×Em) and mid parents, respectively. Survival was similar in Em×Em (87%) and Ea×Ea (86%), followed by Em×Ea (79%), and Ea×Em (78%). Despite this, survival was lower in the reciprocal hybrids; the values are very close to their conspecific controls. Therefore, body growth, gonad production and survival indicate hybrids in either direction were viable in laboratory conditions and showed parental heterosis. Mean heterosis for final body weight, weight gain, percent weight gain and test size of Em×Ea and Ea×Em hybrids was not differed significantly between hybrid groups, but a significant difference in heterosis for SGR values of Em×Ea and Ea×Em was found. Mean heterosis for gonad weight and gonad index of Em×Ea (1.5±0.03 and 1.1±0.02) and Ea×Em (1.4±0.06 and 1.1±0.03) was not significantly different. The superiority of these growth traits of the hybrid groups over their parental values indicates positive heterosis (hybrid vigor). Hence hybrids in both directions appear to have considerable potential for use in aquaculture. [Copyright &y& Elsevier]

Reproduction in the widely distributed tropical sea urchinEchinometra mathaei(de Blainville) was examined in three Kenyan reef lagoons that differed in substrate cover andE.mathaeipopulation density. Histological examination of the gonads and gonad index measurements for 3 years showed a seasonal reproductive cycle with gametogenesis commencing in July, when temperature and light are at their lowest, and spawning commencing in December and peaking in February to May, when temperature and light reach their annual maxima. Monthly gonad indices correlated significantly with seawater temperature and light intensity. Male urchins had mature gametes for a longer period (8 months) than females (6 months), possibly an adaptive strategy that increases the probability of fertilization. Lunar periodicity was not observed, as male and female gonads were full of gametes on all days of the lunar cycle during the period of spawning. The peak in spawning activity coincides with the peak in phytoplankton abundance, which could ensure high food availability for the planktonic larvae. Gonad weights were significantly higher relative to urchin weight at the reef having the largest mean sizes and lowest population of urchins, indicating availability of food resources for growth and reproduction.E.mathaeiat the reef with the highest density had the smallest urchins and high relative gonad sizes, indicative of a tradeoff between growth and reproduction when food is limited. [ABSTRACT FROM AUTHOR]

Conspecific sperm precedence occurs when females are exposed to sperm from males of multiple species, but preferentially use sperm of a conspecific. Conspecific sperm precedence and its mechanisms have been documented widely in terrestrial species, in which complex female behaviors or reproductive tract morphologies can allow many opportunities for female choice and sperm competition, however, the opportunity for conspecific sperm precedence in free spawning marine invertebrates has been largely ignored. Two sea urchin species, Echinometra oblonga and E. sp. C, have high levels of interspecific fertilization in no-choice lab crosses, but no natural hybrids have been found. We performed competitive fertilization assays to test for conspecific sperm precedence and found that eggs of both species showed a marked preference for conspecific sperm when fertilized with heterospecific sperm mixtures. Strong rejection of heterospecific sperm would not have been predicted from no-choice assays and helps explain the lack of natural hybrids. We also found significant variation in hybridization success among crosses. Conspecific sperm precedence in free spawning invertebrates shows that the simple surfaces of eggs and sperm provide ample opportunity for egg choice and sperm competition even in the absence of intricate behavior or complex reproductive morphologies. [ABSTRACT FROM AUTHOR]

Abstract: Interspecific and intraspecific morphological and fertilization variations were studied in three sibling species of Echinometra (known as sp. B, C and D) found off the coast of Okinawa, Japan. Eggs from C and D were readily fertilized by sperm from all three color morphs of B when the sperm concentrations were high, but no fertilization was observed when sperm of the former were mixed with eggs from the latter. Under limiting sperm concentrations, however, both C and D were incapable to fertilize reciprocally with B. In contrast, crossing between C and D produced fertilization membrane at high and limiting sperm concentrations in both directions. Interspecific crosses between B vs. C and B vs. D clearly showed that these combinations were reproductively isolated in contrast to that observed for crossing between C and D. Interestingly, intraspecific fertilization of B showed considerable morphological variation in addition to variability in fertilization success. Intraspecific fertilization and morphological variations may occur due to a number of genetic and/or non-genetic factors. While the underlying cause(s) remain to be elucidated, the results of the present study suggest that B is now speciating very slowly. [Copyright &y& Elsevier]

Although eyes are generally considered necessary for image resolution, a diffuse photoreceptive system with directional sensitivity may also have this ability. Two species of the echinoid genus Echinometra were tested for spatial vision by examining their ability to locate and move towards targets of different sizes. The echinoids were significantly oriented (P<0.0001) towards a target with an angular width of 33° (0.3 sr) but were not oriented to targets with angular widths of 26° and 16°. This ability is probably due to the blocking of off-angle light by the spines, which have approximately the correct spacing for the observed resolution. Spatial vision is advantageous for echinoids of this genus because they leave and return to small dark shelters. This first demonstration of spatial vision in an echinoderm sheds further light on the complex optical structures and photobehaviors found in this phylum. [ABSTRACT FROM AUTHOR]

The 1997–98 El Niño event was the most severe on record, resulting in record elevated water temperatures across much of the world's tropical ocean regions. This event triggered extensive bleaching of coral reefs world-wide, but little information is available on the impact of this major global event on the non-coral invertebrates associated with reef systems. Here, we report the results of a 6 yr (1995–2000) survey of the echinoderm assemblage from 4 coral reef systems in Bahia, Brazil; the 1997–98 El Niño event occurred in the middle of the survey, allowing impact and recovery to be assessed. At each location, 3 contrasting reef habitats were sampled (intertidal emergent reef tops, coastal reef walls, offshore shallow-bank reefs), with all echinoderm species being identified and enumerated. The El Niño event had a dramatic and consistent impact on the echinoderm assemblage, with a sharp post-El Niño decrease in the number of species from all habitats. However, declines in diversity continued into subsequent years, with the local extinction of the majority of echinoderm species by 2000. In contrast, echinoderm density peaked in 1998, due to opportunistic increases in urchin populations (Diadema antillarum and Echinometra lacunter) across the studied reef systems. Multivariate analysis confirmed a marked change in echinoderm assemblage composition between 1997 and 1998 for all reef habitats, with no evidence of recovery to a pre-El Niño assemblage in the 2 subsequent years. The stresses associated with the El Niño event, in the case of Bahia increases in water temperature and ultraviolet light reaching the reef (reduced cloud cover and turbidity), appear to have had a lethal impact on the majority of reef echinoderm species with no evidence of recovery over 2 yr following El Niño. Increases in urchins are most likely due to migration of individuals onto the reef from deeper areas to exploit the reduced competition and potential increasing algal food resource. The study highlights that El Niño can have severe impacts on reef systems additional to the effect on corals. [ABSTRACT FROM AUTHOR]

This paper presents novel spatial distribution and abundance patterns of ecomorphs of Echinometra sp. nov A and E. sp. nov C (hereafter referred to as E. sp. A and E. sp. C, and collectively as Echinometra spp.). Echinometra spp. were surveyed on the Nukubuco Reef, to determine the within-reef variations in size-frequency and density at several spatial scales [between positions (east versus west), zones (crest versus flat), sites and quadrats]. The scales of variation were greatest for both species between positions and zones. Echinometra sp. A was more readily found on the calmer flats while E. sp. C preferred the high-energy crests. The distribution of ecomorphs of Echinometra spp. varied between habitats (position x zone). Echinometra sp. A ecomorphs were more abundant on all locations and showed different size-class distributions compared with E. sp. C. Greater urchin numbers were observed on both zones of the eastern position than the western position. Echinometra sp. A showed marginal aggregation pattern while E. sp. C showed a stronger tendency to cluster. [ABSTRACT FROM AUTHOR]

In the tropical sea urchin Echinometra mathaei, pigment cells are just detectable before the onset of gastrulation, owing to an early accumulation of red pigment granules. Taking advantage of this feature, behavior of pigment cells was studied in relation to the processes of gastrulation. Before the initiation of primary invagination, pigment cells were arranged in a hemi-circle in the dorsal half of the vegetal plate. Inward bending of the vegetal plate first occurred at the position occupied by pigment cells, while the bending was not conspicuous in the ventral half of the blastopore. Rhodamine–phalloidin staining showed that actin filaments were abundant at the apical corticies of pigment cells. It was also found that the onset of gastrulation was considerably delayed in the NiCl2-treated embryos, in which pigment cells were drastically reduced in number. It is notable that the NiCl2-treated embryos began to gastrulate on schedule if they contained a number of pigment cells in spite of treatment. This shows that pigment cells are the bottle cells that trigger the onset of gastrulation. In the embryos devoid of pigment cells, a short stub-like gut rudiment formed in a delayed fashion, and several secondary mesenchyme cells (SMC) appeared at the tip of the rudiment and elongated gradually until its tip reached the apical plate. This observation suggests that the SMC that pull the gut rudiment upward are not pigment cells but blastocoelar cells, because pigment cells change their fate to blastocoelar cells upon NiCl2-treatment. [ABSTRACT FROM AUTHOR]

The characteristics of the sedimentary grains produced by the sea urchin Echinometra mathaei were described from two reef sites: a fringing Acropora-dominated reef at La Reunion island (Indian Ocean) and a barrier Porites-dominated reef at Moorea island (French Polynesia). The composition of the sediment produced by Echinometra was determined from SEM observations. The size and shape of the particles were measured by using image analysis method. The grain diameters range between a few micrometres and 2 mm, with a large predominance (more than 80 %) of particles smaller than 400 μm. The grain size distribution is dependent on the nature of the grazed substratum. Echinometra individuals collected at La Reunion on branching Acropora colonies produce a higher proportion of particles smaller than 200 μm compared to those collected at Moorea on massive Porites colonies. At Moorea, more grains having a diameter comprised between 200 and 500 μm are produced. The microstructure of coral substrata affects the mean particle diameter, which is 192,17 μm for a Acropora substratum and 244,69 μm for a Porites substratum. Since the sediment derived from Acropora erosion is finer, the proportion of suspended material that is exported from the reef is greater at La Reunion than at Moorea. We estimate that, for similar erosion rates and hydrodynamic conditions, the production of sands by Echinometra mathaei is higher and the retention of this erosional sediment more effective on reefs dominated by massive Porites than on Acropora-dominated reefs. This result is in accordance with the proportions of suspension-moving grains that have been previously measured on Moorea and La Reunion reefs. This study highlighted the effect of coral communities on the production of particles related to the bioerosion and on the sedimentary budget. [Copyright &y& Elsevier]

The behavior and differentiation processes of pigment cells were studied in embryos of a tropical sea urchin Echinometra mathaei, whose egg volume was one half of those of well-known sea urchin species. Owing to earlier accumulation of pigments, pigment cells could be detected in the vegetal plate even before the onset of gastrulation, distributed dorsally in a hemi-circle near the center of the vegetal plate. Although some pigment cells left the archenteron during gastrulation, most of them remained at the archenteron tip. At the end of gastrulation, pigment cells left the archenteron and migrated into the blastocoele. Unlike pigment cells in typical sea urchins, however, they did not enter the ectoderm, and stayed in the blastocoele even at the pluteus stage. It is of interest that the majority of pigment cells were distributed in the vicinity of the larval skeleton. Aphidicolin treatment revealed that eight blastomeres were specific to pigment cell lineage after the eighth cleavage, one cell cycle earlier than that in well-known sea urchins. The pigment founder cells divided twice, and the number of pigment cells was around 32 at the pluteus stage. It was also found that the differentiation of pigment cells was blocked with Ni2+, whereas the treatment was effective only during the first division cycle of the founder cells. [ABSTRACT FROM AUTHOR]

Bioerosion is one of the most important structuring forces in coral reef communities. The bioerosion impact of several species of fish, sponges and sea urchins have been estimated in the Caribbean; however, there is no information for one important species, the red sea urchin Echinometra viridis. This species can be found in high densities in many localities. In this study, bioerosion rates for E. viridis were estimated in two patch reefs off La Parguera, southwest Puerto Rico, using the population size-class distribution, average densities, and the CaCO3 content in fecal pellets produced over 24 h. Average densities of urchins along four depth intervals were estimated using 40-m transect lines and 1-m2 quadrats. Average size and size-structure distribution were estimated by measuring the diameter of 180–220 urchins haphazardly collected at each of the four depth intervals. The ignition–loss method was used to estimate the daily rate of bioerosion. Fecal pellets produced by the urchins over a 24 h period were collected in buckets, rinsed in fresh water, dried for 24 h at 70°C, and then burned in a furnace at 550°C, first to eliminate organics, and then at 1000°C until constant weight to determine the amount of calcium carbonate (CaCO3) in the fecal pellets. HCl (10%) was then added to the remainder of the sample to test for presence of CaCO3.Average individual CaCO3 bioerosion rates were estimated at 0.181±0.104 g day-1. Average densities (0.77–62.0 ind. m-2), size (2.01–2.44 cm) and average bioerosion rates (0.114–4.14 kg m-2 year-1) were significantly higher in shallow areas (1–3 m) in both reefs. Bioerosion rates were low compared to those reported for parrotfish, endolithic sponges and the black sea urchin D. antillarum, but they were higher than those reported for other small-sized sea urchins in the Caribbean and the Indo-Pacific. [ABSTRACT FROM AUTHOR]