Aggression among sea urchins on Caribbean coral reefs

The existence and nature of intra- and interspecific aggression were examined for five species of sea urchins inhabiting Caribbean coral reefs. The studies took place in the San Blas Islands of Panama and involved the following species: Echinometra lucunter (Linnaeus), E. viridis Agassiz, Diadema antillarum Phillipi, Lytechinus williamsi Chesher, and Eucidaris tribuloides (Lamarck). An intruder was placed next to an undisturbed resident and the behaviors and responses of both individuals were followed. All pairwise combinations of resident species and intruder species were tested except for combinations involving D. antillarum as intruder.

For E. viridis and E. lucunter, agonistic interactions occurred commonly (46–79% of trials) between conspecifics and congeners. Almost all of the agonistic encounters involved pushing. Additionally, biting occurred in 8–25 % of the trials. Residents were most often the aggressors and usually succeeded in retaining their location. Intruders only succeeded in forcing residents out of their positions if the intruder was equal to or larger in size than the resident. Surveys of an undisturbed population of E. viridis during the daytime indicated that 16% of the individuals were engaged in intraspecific agonistic interactions at any one time.

D. antillarum exhibited biting behavior against both species of Echinometra in 23–24% of the trials. Biting attacks against L. williamsi and E. tribuloides occurred rarely. L. williamsi only once demonstrated pushing behavior and never was observed biting another sea urchin. E. tribuloides occasionally exhibited pushing and biting behaviors, both as residents and as intruders, and was twice observed biting Echinometra.

These studies suggest that two kinds of agonistic interactions may commonly occur among Caribbean reef-dwelling sea urchins: (1) intraspecific and interspecific aggression among Echinometra, and (2) predatory/aggressive attacks against Echinometra by D. antillarum. The former may result in greater dispersion of Echinometra relative to food and shelter resources and control the spatial distribution and concentration of Echinometra grazing pressure within an area. The attacks by D. antillarum may result in the restriction to, or higher densities of, Echinometra in crevices and rugose microhabitats that provide shelter from the larger-bodied D. antillarum.     

Hydrology and Changes in the Nutrients and Phytoplankton Levels in Goat Island Bay,Northern New Zealand

A survey of the phytoplankton and nutrient levels in Goat Island Bay, northern New Zealand was carried out in 1981–82 and the data compared with an earlier survey in 1966–69. The contribution of nutrients from the inflowing creek was also measured. The only significant change was a doubling of the dissolved nitrate levels in the sea, which appeared to be related to increased nitrate levels in the freshwater creek. It is suggested that the increase is due to an increase in the farming and recreational use of the catchment area. The standing crops of phytoplankton in the bay showed no correlation with nutrient levels, but there were significant correlations with the radiation received.     

Bacterial Populations (First Record) at Two Shallow Hydrothermal Vents of the Mexican Pacific West Coast

Thermophilic and metal-oxidizing bacteria were identified in shallow hydrothermal vents on the western Mexican coast. The role of these bacteria in biomineralization processes observed in the vents is explained, and the effect of the vents on biodiversity of prokaryotes is discussed. Research was done at two shallow hydrothermal vent sites: Bahía Concepción (BC) in the Baja California Peninsula and Punta Mita (PM), on the central Pacific coast. Temperature at the sediments proximal to the vents was similar, but the redox potentials (0.5 V in BC and ?0.3 V in PM) and pH (6.2 in BC and as low as 4.5 in PM) differed. The composition of the discharged water ranged from nearly seawater to lower-salinity fluids, and the gas phase was mainly CO₂ at BC and N₂ and CH₄ at PM. The study focuses on the biogeochemical processes related to the different species of bacteria present in the studied sites, which are involved in the anaerobic oxidation of methane (AOM), seawater sulfate reduction, and metal oxidation. The detected bacterial lineages represented typical deep vent species, which disproves a previous hypothesis that proposed that different consortia were populating deep and shallow hydrothermal vents. The results obtained here show that the main parameter affecting the bacterial groups present in shallow vents was the redox potential: gamma-, delta-, and epsilon proteobacteria as well as Bacteriodetes are present under the oxidizing conditions of BC, and Thermotogae, Aquificae, and Planctomycetes are present in PM. Sunlight abundance favored the prevalence of halophilic and Chlorofleaxae bacteria in both areas.     

A new computational growth model for sea urchin skeletons

A new computational model has been developed to simulate growth of regular sea urchin skeletons. The model incorporates the processes of plate addition and individual plate growth into a composite model of whole-body (somatic) growth. A simple developmental model based on hypothetical morphogens underlies the assumptions used to define the simulated growth processes. The data model is based on a Delaunay triangulation of plate growth center points, using the dual Voronoi polygons to define plate topologies. A spherical frame of reference is used for growth calculations, with affine deformation of the sphere (based on a Young-Laplace membrane model) to result in an urchin-like three-dimensional form. The model verifies that the patterns of coronal plates in general meet the criteria of Voronoi polygonalization, that a morphogen/threshold inhibition model for plate addition results in the alternating plate addition pattern characteristic of sea urchins, and that application of the Bertalanffy growth model to individual plates results in simulated somatic growth that approximates that seen in living urchins. The model suggests avenues of research that could explain some of the distinctions between modern sea urchins and the much more disparate groups of forms that characterized the Paleozoic Era.     

Evolutionary modification of specification for the endomesoderm in the direct developing echinoid <Emphasis Type="Italic">Peronella japonica</Emphasis>: loss of the endomesoderm-inducing signal originating from micromeres

We investigated the inductive signals originating from the vegetal blastomeres of embryos of the sand dollar Peronella japonica, which is the only direct developing echinoid species that forms micromeres. To investigate the inductive signals, three different kinds of experimental embryos were produced: micromere-less embryos, in which all micromeres were removed at the 16-cell stage; chimeric embryos produced by an animal cap (eight mesomeres) recombined with a micromere quartet isolated from a 16-cell stage embryo; and chimeric embryos produced by an animal cap recombined with a macromere-derived layer, the veg1 or veg2 layer, isolated from a 64-cell stage embryo. Novel findings obtained from this study of the development of these embryos are as follows. Micromeres lack signals for endomesoderm specification, but are the origin of a signal establishing the oral–aboral (O–Ab) axis. Some non-micromere blastomeres, as well as micromeres, have the potential to form larval skeletons. Macromere descendants have endomesoderm-inducing potential. Based on these results, we propose the following scenario for the first step in the evolution of direct development in echinoids: micromeres lost the ability to send a signal endomesoderm induction so that the archenteron was formed autonomously by macromere descendants. The micromeres retained the ability to form larval spicules and to establish the O–Ab axis.     

A New Ichnospecies of Arthrophycus from the Upper Cambrian-Lower Tremadocian of Northwest Argentina: Implications for the Arthrophycid Lineage and Potential in Ichnostratigraphy

A new ichnospecies of Arthrophycus Hall 1852, A. minimus , is described from Upper Cambrian-Lower Tremadocian, shallow-marine strata of northwest Argentina. This new ichnospecies consists of small, long, regularly annulated hypichnial elements displaying subcircular to squarish cross-section and a ventral median groove. Side branches are occasionally present, but palmate, fan-like structures and scribbling patterns are absent. We adopt a relatively narrow diagnosis of Arthrophycus , suggesting that roughly annulated, cylindrical structures should not be included in this ichnogenus, unless other diagnostic features (i.e., squarish cross-section, median groove, zipper-like annulations) are also present. Arthrophycus is a common ichnotaxon in Ordovician-Silurian shallow-marine siliciclastic environments. Post-Paleozoic occurrences are removed from Arthrophycus . Arthrophycus has been proposed as a biostratigraphic index fossil in Ordovician-Silurian rocks. The presence of A. minimus in the Santa Rosita Formation of northwest Argentina indicates that Arthrophycus ranges at least from the Upper Cambrian-Lower Tremadocian with probable representatives in the Lower Cambrian and, therefore, its biostratigraphic utility is extended. Arthrophycus minimus represents the first Cambrian occurrence exhibiting not only fine, diagnostic morphologic features, but also the classical Arthrophycus behavioral pattern in dense monoichnospecific assemblages. The exploratory behavioral pattern displayed by A. minimus is simpler than that of the younger ichnospecies, particularly A. brogniartii, A. alleghaniensis, and A. lateralis . This is consistent with the basal position of A. minimus within the arthrophycid lineage.     

Trace fossils formed by heart urchins - a study of Scolicia and related traces

Cretaceous and Tertiary traces belonging to the ichnogenera Scolicia, Subphyllochorda and Taphrhelminthopsis are described and analysed functionally. Resting traces continuous with Subphyllochorda are described for the first time and interpreted as the work of heart urchins. The new ichnogenus Cardioichnus is erected for them. The preservation and complexity of some specimens of these ichnogenera allows for a detailed comparison with heart urchin morphology. Subphyllochorda is interpreted as a burrow produced by heart urchins and Scolicia as either burrows or sea floor furrows. The traces here assigned to Taphrhelminthopsis are probably casts of washed-out Subphyllochorda burrows. Palaeozoic traces previously referred to 'Scolicia' sensu lato are, in the main, much simpler than the Mesozoic and Tertiary traces and should be transferred to other ichnogenera.     

The contribution of the facultative feeding period to echinoid larval development and size at metamorphosis: a comparative approach

Planktotrophic invertebrate larvae have two dissociable stages during development, a facultative feeding period, whose length is determined by the amount of maternal provisioning in the egg, and an obligate feeding period, whose length is determined by the quantity of exogenous energy needed to reach metamorphic competence. Here we set out to experimentally test the impact of feeding during the facultative feeding period at two food concentrations (limiting and nonlimiting) on larval development time and juvenile quality. We used two closely related subtropical sand dollar species that differ in the quantity of maternal investment for these comparisons: Leodia sexiesperforata (large egg, long facultative feeding period) and Mellita tenuis (small egg, short facultative feeding period). We found that feeding during the facultative period accelerates development to metamorphosis only in M. tenuis and only at the high food ration. Feeding during the facultative feeding period had no effect on development time for M. tenuis at a food limiting concentration and for L. sexiesperforata at either food concentration. Furthermore, we found feeding during the facultative period to significantly increase quantity of carbohydrates and lipids at metamorphosis only for M. tenuis in nonlimiting food concentration. Thus, our data reveal a two-fold benefit of the facultative feeding period for a poorly provisioned species under high food conditions but little effect on a well-provisioned species. We discuss our results in reference to McEdward's [McEdward, L.R., 1997. Reproductive strategies of marine benthic invertebrates revisited: facultative feeding by planktotrophic larvae. Am. Nat. 150, 48-72] facultative feeding model.     

盾皮鱼类下颌板在中国的首次报道

记述了产自云南省华宁县盘溪地区一打得组一新的节甲鱼类化石,似扁平华宁鱼（Ｈｕａｎｉｎｇｉｃｈｔｈｙｓ ｏｍａｌｏｄｅｓ ｇｅｎ． ｅｔ　ｓｐ． ｎｏｖ．）。化石为一完整的下颌板,这是我国首次记述的盾皮鱼类下颌骨化石。根据与下颌板一起产出的竹节石化石和地层对比,产出化石的地层时代为晚泥盆世早期（Ｆｒａｓｎｉａｎ）。该类鱼的生境为浅海深水的盆地相或开放海环境。     

Chemical host detection and differential attraction in a parasitic pea crab infecting two echinoids

Mechanisms of host detection and host choice are important for mobile parasites or symbionts that frequently move among host individuals. The parasitic pea crab Dissodactylus primitivus is an ectoparasite exploiting asymmetrically two spatangoid echinoid hosts, Meoma ventricosa and Plagiobrissus grandis. The entire life cycle takes place on M. ventricosa, while only adults colonize P. grandis, the host where female's fecundity is the greatest. Dissodactylus primitivus frequently exhibits host-switching, a behaviour that raises the question of host detection. To test if adult crabs are able to detect potential hosts and are attracted to the host where their fitness is greater, crab olfactory responses were investigated using a Y-tube. We first showed that D. primitivus are attracted by olfactory cues of M. ventricosa, versus those of a non-host echinoid species, Clypeaster rosaceus sharing the same habitat. This attractiveness was not due to a yellowish water-soluble substance secreted by the host. We then showed that the chemical attraction to the two hosts was different according to the origin of the crabs. Crabs coming from M. ventricosa were more attracted to this host than to P. grandis, a pattern compatible with an imprinting phenomenon. However, crabs collected from P. grandis were equally attracted to both host species, as if imprinting was lost after host change. We propose that the pattern of D. primitivus host detection could be intermediate between the behaviour of specialist and generalist symbionts.     

Milankovitch 41 000-year cycles in lithofacies and molluscan content in the tropical Middle Miocene Nyalindung Formation, Jawa, Indonesia

Nine cyclothems based on changes in sedimentary facies and molluscan fossil associations are identified in the Middle Miocene (± 12 Ma) lower part of Nyalindung Formation, Cijarian River section, Sukabumi, West Jawa Province, Indonesia. Molluscan associations were studied in 75 blocks collected through the succession; 47 species of autochthonous molluscs, belonging to 38 genera, were separated from the blocks. Five molluscan associations were recognized through comparison of these species with their closest living analogues. A sedimentary cycle consists of two conformable lithologic units: in ascending order, a gravelly shellbed or gravelly/conglomeratic sandstone and a muddy fine to medium-grained sandstone. The exception is the basal cycle, which has an intercalation of limestone. The systematic change in the molluscan fossil associations within individual cycles indicates that lithological changes correspond to changes in water depth with an amplitude of about 30 m. The short time period represented by the section and the thin units (many not more than 2 m thick) indicates that the main cause of the cyclicity was orbitally induced climate change, representing Milankovitch-scale cycles of 41 000 years. This appears to be the first time Milankovitch sea-level cycles have been reported from the tropical regions of the Earth.     

New bacilli from shallow hydrothermal vents of Panarea Island (Italy) and their biotechnological potential

Aims: To characterize bacilli isolated from shallow hydrothermal vents of Panarea Island (Italy) and evaluate their biotechnological potential. Methods and Results: Fifteen isolates were characterized by culture and molecular methods. Eleven isolates were thermophilic, six isolates were alkalophilic and four of them were haloalkalophilic. After 16S rRNA gene sequencing, four strains, exhibiting sequence similarity below 95% with deposited strains, may represent novel species of bacilli. One strain was strictly related to Geobacillus subterraneus, but shared phenotypic characteristics for which it could be considered a new strain of this species. Four strains were affiliated with different Bacillus spp. Most isolates produced gelatinase, lipases and amylase, and some were mercury tolerant. Exopolysaccharides (EPS) production was tested adding different sugars (glucose, sucrose, trehalose, fructose, ribose, xylose and mannose, 1% w/v) as a carbon source in a minimal medium. The highest EPS yield (185 mg l^?1) was reached by strain 1A70 utilizing ribose as a carbon source. Conclusions: Novel strains of Geobacillus and indigenous ribotypes of Bacillus with biotechnological potential inhabit shallow vents of Panarea Island. Significance and Impact of the Study: New strains of thermophilic bacilli from Panarea are producers of useful biomolecules for industrial purposes as well as environmental and biotechnological applications.     

Maternal factors and the evolution of developmental mode: Evolution of oogenesis in Heliocidaris erythrogramma

 Evolutionary change in developmental mode in sea urchins is closely tied to an increase in maternal provisioning. We examined the oogenic modifications involved in production of a large egg by comparison of oogenesis in congeneric sea urchins with markedly different sized oocytes and divergent modes of development. Heliocidaris tuberculata has small eggs (95 μm diameter) and the ancestral mode of development through feeding larvae, whereas H. erythrogramma has large eggs (430 μm diameter) and highly modified non-feeding lecithotrophic larvae. Production of a large egg in H. erythrogramma involved both conserved and divergent mechanisms. The pattern and level of vitellogenin gene expression is similar in the two species. Vitellogenin processing is also similar with the gonads of both species incorporating yolk protein from coelomic and hemal stores into nutritive cells with subsequent transfer of this protein into yolk granules in the developing vitellogenic oocyte. Immunocytology of the eggs of both Heliocidaris species indicates they incorporate similar levels of yolk protein. However, H. erythrogramma has evolved a highly divergent second phase of oogenesis characterised by massive deposition of non-vitellogenic material including additional maternal protein and lipid. Maternal provisioning in H. erythrogramma exhibits recapitulation of the ancestral vitellogenic program followed by a novel oogenic phase with hypertrophy of the lipogenic program being a major contributor to the increase in egg size. Received: 12 August 1998 / Accepted: 25 November 1998     

Physical forces experienced by echinoid eggs in the oviduct during spawning: comparison of the geminate pair Echinometra vanbrunti and Echinometra lucunter

During spawning, eggs of echinoids are released from the gonad and traverse a narrow oviduct-gonopore complex before being released into the water surrounding the spawning female. As the eggs traverse the oviduct-gonopore complex, a velocity gradient develops within the fluid formed by the eggs. This velocity gradient imposes a shear stress on the eggs that ranges from a maximal value at the walls of the oviduct-gonopore complex and declines linearly to zero at the center of the complex. In addition to shear stress, the eggs of some echinoids also experience strain. Strain is imposed on the eggs in situations where the diameter of the egg is greater than the diameter of the oviduct-gonopore complex. Both shear stress and strain have the potential to damage echinoid eggs during spawning and are likely selective pressures acting on the physical properties of protective extracellular layers, which surround the eggs of these organisms. The amounts of shear stress and strain experienced by eggs of a geminate pair of echinoids, Echinometra vanbrunti and E. lucunter, are calculated. Calculations of shear stress based on the mean spawning rates and dimensions of the oviduct-gonopore complexes of specimens collected during this study ranged up to 30 Pa for E. vanbrunti and up to 17 Pa for E. lucunter. To obtain conservative estimates of shear stress, these calculations were repeated incorporating a spawning rate that was reduced by one order of magnitude below the mean rate measured for both species. These calculations yielded shear stresses that ranged up to 13 and 6 Pa for E. vanbrunti and E. lucunter, respectively. The diameter of the oviduct-gonopore complex of echinoids increases linearly with the diameter of the tests of the adults. Because the diameter of the oviduct-gonopore complex influences the amount of shear stress experienced by eggs of echinoids, shear stress calculations were repeated incorporating the full range of potential diameters of the oviduct-gonopore complexes from data in the literature. Using the mean spawning rates obtained from each species, the amount of shear stress experienced by eggs ranged up to 32 Pa for E. vanbrunti and up to 398 Pa for E. lucunter. When the mean spawning rates were reduced by one order of magnitude, the amount of shear stress experienced by E. vanbrunti eggs ranged up to 14 Pa and up to 140 Pa for the eggs of E. lucunter. The eggs of E. vanbrunti do not experience strain during spawning because the diameter of the its eggs is smaller than the diameter of its oviduct-gonopore complex at all stages of adult growth. In contrast, the diameter of the eggs of E. lucunter is larger than the diameter of the oviduct-gonopore complex at small adult sizes and the eggs of this species experience true strains ranging up to 1.2. These results indicate that there are substantial differences in the amounts of physical forces that the eggs of echinoids experience during spawning both within species at different stages of adult growth and between species. Different amounts of shear stress and strain experienced by eggs among echinoid species may select for differences in the mechanical properties of protective extracellular layers that surround them.