Morphology of gametes in sea urchins from Peter The Great Bay,Sea of Japan

The fine structure of the gametes in six sea urchin species of the Sea of Japan was studied. The sperm in Strongylocentrotus nudus, S. intermedius, Echinocardium cordatum, Scaphechinus mirabilis, Sc. griseus and Echinarachnius parma are species-specific. The conical head and symmetrically disposed ring-shape mitochondrion are common to regular sea urchin sperm cells. S. nudus is characterized by the bulb-shaped head of the sperm; S. intermedius, by a bullet-shaped one. The sperm spearhead and small amount of post-acrosome material are common to irregular sea urchins; the sperm width: length ratio varies for different species, with the highest for Sc. mirabilis. The sperm of Sc. griseus is characterized by two lipid drops in the middle part of sperm. Asymmetrical mitochondrion disposal is usual for E. parma. Actin filaments are found in the postacrosome material in the sperm of heart-shaped sea urchins. The differences in the fine structure of sperm in cosmopolitan species Ech. cordatum inhabiting the Sea of Japan and coastal areas of the Northeast Atlantic may bear record to the complex existence of species Ech. cordatum. The fine structure of sperm is unique for each of the studied families, Strongylocentrotidae, Scutellidae, and Loveniidae. The eggs of all the species are characterized by vitelline and jelly-like membranes. The vitelline membrane is formed by cytoplasm protrusions; the area between them is filled with fibrillar material. The jelly-like membrane is formed by fibrillar material associated with apical parts of microvilli of the vitelline membrane. The irregular sea urchins Sc. griseus, Sc. mirabilis and E. parma are characterized by chromatophores situated in the jelly-like membrane, with the highest abundance in Sc. mirabilis.     

Distribution Patterns of Strongylocentrotus Sea Urchins along the Coast of Eastern Kamchatka

The distribution patterns of three sea urchin species of the genus Strongylocentrotus in relation to depth, type of substrate, surf action, and to some hydrological parameters were studied along the coast of eastern Kamchatka and in adjacent waters in 1984–1996. The sea urchin Strongylocentrotus polyacanthus dominated the open coast on rocky subintertidal sites with increased surf action and standard oceanic salinity. S. droebachiensis prevailed in shoals with lower salinity, higher water temperature and lower turbulence (enclosed and semienclosed bays). S. pallidus dominated at depths corresponding to the position of the cold intermediate layer deeper than 30–50 m with normal oceanic salinity and lower temperature.     

Positive Darwinian selection in gamete recognition proteins of Strongylocentrotus sea urchins

Gamete recognition proteins commonly experience positive Darwinian selection and evolve more rapidly than nonreproductive proteins, but the selective forces responsible for their adaptive diversification remain unclear. We examined the patterns of positive selection in the cognate interacting pair of proteins formed by sperm bindin and its egg receptor (EBR1) and in two regions of the sea urchin sperm receptor for egg jelly suREJ3 gene (exons 22 and 26) among four species of Strongylocentrotus sea urchins (S. purpuratus, S. droebachiensis, S. pallidus and S. franciscanus). The signatures of selection differed at each reproductive protein. A strong signal of positive selection was detected at bindin in all lineages even though the species compared had highly variable gamete traits and experience different intensities and forms of sexual selection and sexual conflict in nature. Weaker selection was observed at EBR1 but the small region studied precluded a clear understanding of the extent of sexual conflict between bindin and the EBR1 protein. At the suREJ3 locus, diversifying selection was observed in exon 22 but not exon 26, suggesting that these regions experience different selective pressures and evolutionary constraints. Positive selection was also detected within S. pallidus at suREJ‐22 because of the presence of 12 amino acid replacement mutations segregating at frequencies >0.10. Our results suggest that sexual conflict may be the predominant evolutionary mechanism driving the rapid diversification of reproductive proteins between, and polymorphism within, strongylocentrotid sea urchins.     

Estimation of foraging on the sea urchin <Emphasis Type="Italic">Strongylocentrotus droebachiensis</Emphasis> (Echinoidea: Echinoida) by the red king crab <Emphasis Type="Italic">Paralithodes camtschaticus</Emphasis> (Malacostraca: Decapoda) in coastal waters of the Barents Sea

A new method for the estimation of foraging on the sea urchin Strongylocentrotus droebachiensis (O.F. Müller, 1776) by the red king crab Paralithodes camtschaticus (Tilesius, 1815) is proposed. This method uses the reconstruction of the size, number, and biomass of eaten sea urchins, based on fragments of their teeth and tests from the crab’s digestive tract. Data obtained by this method suggest that in shallow waters of the Barents Sea (Kola Bay, Dal’nezelenetskaya Bay) adult, most often, female and immature crabs predominantly consume juvenile sea urchins. The weight of sea urchins daily eaten by one adult red king crab was 0.2–8.0% of its body weight for sexually mature crabs and 3.0–28.0% for immature specimens. Damage inflicted to the S. droebachiensis population as a result of the crab feeding activity was estimated to be at least 10% of the sea urchin biomass in Dal’nezelenetskaya Inlet and at least 30% in Kola Bay.     

Survivorship, development, and DNA damage in echinoderm embryos and larvae exposed to ultraviolet radiation (290-400 nm)

Laboratory experiments utilizing ecologically relevant irradiances of ultraviolet radiation (UVR) known to occur in shallow Gulf of Maine waters were conducted on the planktonic embryos and larvae of two common benthic echinoids; the green sea urchin Strongylocentrotus droebachiensis and the sand dollar Echinarachnius parma. Significant decreases in survivorship were observed in freshly fertilized embryos of both species with greater mortality in E. parma that was associated with the absence of UVR-absorbing compounds, the mycosporine-like amino acids. Experiments on blastula, gastrula, and prism larval stages of S. droebachiensis also showed significant decreases in survivorship, delays in development, and abnormal embryos and larvae associated with exposure to UVR. Additionally, all developmental stages of S. droebachiensis experimentally exposed to UVR resulted in significant increases in DNA damage, measured as cyclobutane pyrimidine dimer photoproducts. The observed delays in early cleavage and subsequent developmental stages for S. droebachiensis are correlated with DNA damage. It is postulated that cell cycle arrest at critical checkpoints after DNA damage, mediated by a suite of cell cycle genes, is a component of the observed UVR induced developmental delays.     

Simultaneous cloning of multiple nuclear genes by pooling PCR products of variable size: a cost‐effective method of improving efficiency in large‐scale genetic analyses

I present a simple approach to overcome the high cost and low efficiency of cloning polymerase chain reaction (PCR) products for individuals in wide‐scale population genetic analyses. The methodology reduces the number of cloning reactions per individual by engineering a suite of genetic markers that differ in size and pooling these PCR products prior to cloning. Alleles from each gene are then recovered by screening transformed bacterial colonies and identifying the inserts corresponding to each gene based on size. I demonstrate the utility of this technique by presenting the results I obtained from cloning four nuclear genes in 118 individuals from three species of sea urchins (Strongylocentrotus purpuratus, S. droebachiensis and S. pallidus). Of the 472 different PCR products I cloned, I recovered at least one allele for 432 of them (91.5%) by screening between 16 and 32 bacterial colonies for each individual. There existed a bias with respect to recovery efficiency: the two largest fragments (1130–800 bp) were recovered 100% of the time, while the two smaller fragments (580–650 bp) were recovered in 85.6% and 81.4% of the experiments, respectively. I discuss the promise of this application for wide‐scale genetic analyses.     

On barriers to hybridization between Strongylocentrotus droebachiensis (O.F. Müller) and S. Pallidus (G.O. Sars)

Strongylocentrotus droebachiensis (O. F. Müller) and Strongylocentrotus pallidus (G. O. Sars) occur together over much of their ranges in both the Atlantic and Pacific Oceans and remain distinct species, but no strong barrier to genetic exchange has been found in a study in the San Juan Islands. Co-occurrence of embryos of both species in the plankton indicates similar times of spawning. Ova of S. droebachiensis are fertilized by sperm of S. pallidus but the reciprocal cross gives a percent fertilization near zero. Hybrids of both crosses are viable with pigmentation resembling S. pallidus in the larval stage and S. droebachiensis in the adult stage. Ova of first generation female hybrids are more readily fertilized by sperm of S. pallidus, so that gene flow through female hybrids is more likely to be from S. droebachiensis to S. pallidus than the reverse. Male hybrids were not tested. S. droebachiensis and S. pallidus from deeper waters have lower fecundity than shallow water S. droebachiensis, which suggests that in the deeper waters individuals are food limited. The hypothesis that S. pallidus uses the sterile male technique to reduce reproductive output of S. droebachiensis is considered and rejected.     

Consumers of sea urchins,<Emphasis Type="Italic"> Paracentrotus lividus</Emphasis> and<Emphasis Type="Italic"> Arbacia lixula</Emphasis>, in shallow Mediterranean rocky reefs

Underwater observations on fish and asteroid consumers (i.e. predators and scavengers) of sea urchins, Paracentrotus lividus and Arbacia lixula, were carried out at several locations in shallow Mediterranean rocky reefs. Observations conducted in the marine reserve of Torre Guaceto (Adriatic Sea) revealed that sparid fishes, Diplodus sargus and D. vulgaris, are the main fish predators of small (<1 cm in test diameter) and medium (1–4 cm) sea urchins, whereas the labrids Coris julis and Thalassoma pavo preyed only upon small sea urchins. Large D. sargus were able to prey upon small and medium, and occasionally large (>4 cm) sea urchins, whereas medium and small Diplodus preyed mainly upon small sea urchins. The number of sea urchins preyed upon by fishes was negatively related to sea urchin size for both species. P. lividus appeared to be subject to higher predation levels than A. lixula. The scavenger guild comprised 11 fish species, with D. sargus, D. vulgaris, Coris julis and Chromis chromis accounting for about 80% of scavenger fishes. Observations performed at several locations in the Mediterranean on the predatory asteroid Marthasterias glacialis revealed that only 3% of the detected individuals were preying upon sea urchins. Due to the importance of sea urchins for assemblage structure and functioning of Mediterranean rocky reef ecosystems, these results may have also important implications for management of fishing activities.Communicated by H.-D. Franke     

Scanning electron microscope studies of the surface of the sea urchin egg

Summary The surface of the egg of the two sea urchin species,Strongylocentrotus droebachiensis andS. pallidus, was studied with SEM. Clear differences were observed between the two species, in both the number and form of the microvilli. The changes in the egg surface which follow insemination are described.     

Behavioral ecology of Strongylocentrotus droebachiensis (Muller) (Echinodermata: Echinoidea)

Summary Field observation indicated that extensive aggregation behavior occurs in Strongylocentrotus droebachiensis, an important echinoid herbivore in rocky subtidal zones of northern New England. The relationship of this behavior to the behavioral ecology of this species was investigated. Laboratory studies indicated that urchins are chemically sensitive to the stimuli of food and other urchins. Quantitative field experiments with tagged animals and transects showed the existence of two types of aggregations: feeding and nonfeeding, which appear to be pervasive phenomena in the biology of S. droebachiensis.It is concluded that, depending upon their hunger state, urchins shuttle between feeding aggregations in exposed locations and non-feeding aggregations located in relatively sheltered areas (where they spend most of their time). Individuals of S. droebachiensis aggregate actively through response to other urchins in the form of chemotaxis. The aggregative behavior may be maintained for its selective value in terms of defense from predation and, to lesser extents, facilitation of feeding and breeding.     

Does Hybridization Increase Evolutionary Rate? Data from the 28S-rDNA D8 Domain in Echinoderms

The divergent domain D8 of the large ribosomal RNA is very variable and extended in vertebrates compared to other eukaryotes. We provide data from 31 species of echinoderms and present the first comparative analysis of the D8 in nonvertebrate deuterostomes. In addition, we obtained 16S mitochondrial DNA sequences for the sea urchin taxa and analyzed single-strand conformation polymorphism (SSCP) of D8 in several populations within the species complex Echinocardium cordatum. A common secondary structure supported by compensatory substitutions and indels is inferred for echinoderms. Variation mostly arises at the tip of the longest stem (D8a), and the most variable taxa also display the longest and most stable D8. The most stable variants are the only ones displaying bulges in the terminal part of the stem, suggesting that selection, rather than maximizing stability of the D8 secondary structure, maintains it in a given range. Striking variation in D8 evolutionary rates was evidenced among sea urchins, by comparison with both 16S mitochondrial DNA and paleontological data. In Echinocardium cordatum and Strongylocentrotus pallidus and S. droebachiensis, belonging to very distant genera, the increase in D8 evolutionary rate is extreme. Their highly stable D8 secondary structures rule out the possibility of pseudogenes. These taxa are the only ones in which interspecific hybridization was reported. We discuss how evolutionary rates may be affected in nuclear relative to mitochondrial genes after hybridization, by selective or mutational processes such as gene silencing and concerted evolution.     

Herbivory and patch dynamics on rocky reefs in temperate Australasia: The roles of fish and sea urchins

Sea urchins are widely considered to be the major grazers in temperate subtidal systems, with herbivorous fish being browsers of minor importance. This paper reviews spatial and temporal patterns in these herbivores on rocky reels in temperate Australasia, with the aim of assessing their relative impacts on patch structure and dynamics. Herbivorous fishes are widespread and make up a significant numerical component the reel fish fauna. Sea urchins are also abundant, but not all geographic locations support actively grazing species. Both fish and sea urchins exhibit distinct patterns of distribution among depth strata. Within depth strata, all herbivores are restricted to (sea urchins) or forage preferentially in (fish) particular habitat patches, causing a mosaic of different feeding activities. These patches are either related to specific features of the habitat (e.g. Kelp patches, topography) or behavioural interactions. Foraging by sea urchins and demersal-nesting damselfishes is intense and persistent, whereas in the kelp-feeding fish Odax cyanomelas, foraging reaches greatest intensity at predictable locations during a few months of every year. Many fish and sea urchins consume some algae in preference to others. However, feeding preferences may determine the nature of the impact only in fishes. For sea urchins, preference may occasionally determine the order in which algae are consumed, but at high densities they consume all available macroalgae. Impacts of both types of herbivore on the abundance of algae have been recorded. Some sea urchins (e.g. Evechinus chloroticus, Centrostephanus rodgersii) appear to severely modify biogenic habitat structure by maintaining ‘barrens’ (areas devoid of macroalgae) over long periods. In contrast to this, the effects of fishes may be more transitory (e.g. seasonal impact of Odax cyanomelas on brown algae) or occur at smaller spatial scales (e.g. nest sites maintained by male Parma victoriae) Herbivorous and other fishes appear to respond to spatial patterns in algal distributions, rallier than having it major impact upon them. The relative effects of fish and sea urchins on the long-term dynamics of kelp forests are unknown, hut temporal patterns in herbivore abundance and behaviour, and algal demography arc urgent targets for research.     

Dynamics of Fish Colonization of an Experimental Artificial Reef in Peter the Great Bay,Sea of Japan

An experimental artificial reef (AR) was built in Peter the Great Bay (Sea of Japan) to compensate for the biotope of Zostera destroyed by sea urchins. After eight years, the number of fish species on the AR increased from 5 to 18 and the fish biomass increased from 3.07 up to 37.1 g/m². Nonmigrating species (Opisthocentrus, young-of-the-year rockfishes, elegant sculpin) formed the bulk of the population; and migrant species (flounders, frog and great sculpins, sea raven) made up the greater portion of the biomass (up to 34 g/m²). Cage reefs are recommended to compensate for destroyed habitats, particularly Zostera beds.Original Russian Text Copyright ¢ 2005 by Biologiya Morya, Markevich.     

Alginate degradation by bacteria isolated from the gut of sea urchins and abalones

Degradation of alginate and its constituents, polymannuronate (polyM) and polyguluronate (polyG), by gut bacteria isolated from sea urchins and abalones in the northern part of Japan, were investigated. Bacterial counts in the guts of sea urchin S. intermedius, were 10⁵ to 10⁸ CFU/g, and in abalone H. discus hannai, counts ranged from 10⁶ to 10⁹ CFU/g. More than 80% of total 600 isolates were found to have alginolytic activity. The alginolytic bacteria were predominantly fermentative, but some differences were observed in their substrate specificity as well as between the flora in the gut of sea urchins and the abalones. Seventy percent of the alginolytic bacteria from the sea urchins showed no degrading preference for polyM or polyG blocks, and were able to degrade both the substrates simultaneously. Most of the alginolytic bacteria (96.6%) from sea urchins belonged to the genus Vibrio. The majority of alginolytic bacteria (68.0% on average) from abalones only degraded polyG and they were predominantly non-motile fermenters. From these results, it appeared that a different type of association exists between alginolytic gut microflora and the marine algal feeders with respect to the level of contribution by bacteria to the host's digestion of alginate. Correspondence to: T. Sawabe     

Externally visible fluorochrome marks and allometries of growing sea urchins

Externally visible, growing calcitic structures can be marked using fluorochromes. Such marks are useful for field recapture studies in ecology, evolution, and aquaculture as well as for studies on mechanisms of growth and development. We marked 2‐month‐old sea urchins (Strongylocentrotus droebachiensis) with the fluorochromes calcein, calcein blue, and tetracycline by batch‐marking via immersion. Neither growth nor survival was affected by marking. Marks were externally visible on the skeletal plates, demipyramids, and spines of 100% of the marked sea urchins up to 63 d post‐marking. After 342 d, marks were still externally visible on 100% of calcein‐marked, 98% of calcein blue‐marked, and 22% of tetracycline‐marked sea urchins. Marks were brightest on calcein‐marked and faintest on tetracycline‐marked sea urchins, in correspondence to the fluorochrome dose. Growth marks in the aboral oculogenital ring, followed for 333 d, showed that genital plate growth in the hoop direction was greatest adjacent to the anal suture and that both the oculogenital ring and periproct grew less than isometrically. Internal marks (not externally visible) were subsequently seen on 99% of the demipyramids at 342 d post‐marking. Such fluorochrome marks on demipyramids have previously been used to measure aboral and oral‐end demipyramid growth to allometrically calibrate diametrical growth rates of field sea urchins. We found that although aboral demipyramid marks were always clear, 13% of marks on the oral end were obscured. However, we show that measuring only aboral end growth is sufficient for allometric calibration. In a separate experiment, multiple marks of the above three fluorochromes plus alizarin complexone, administered by injection to larger (12.9–37.1 mm diameter) sea urchins, persisted internally for at least 2 years. Multi‐color, internally and externally visible, persistent marks will enhance experimental designs in laboratory, field, and common garden experiments.     

流速对光棘球海胆行为和生长的影响

海胆在海藻床生态系统结构和功能调控中发挥重要作用。深入理解流速对海胆摄食和生长的影响具有重要的生态学研究价值。研究了长时间(49 d)不同流速(2 cm/s, 10 cm/s和20 cm/s)对光棘球海胆幼胆(Mesocentrotus nudus,壳径：约20 mm)摄食行为、摄食量和生长的影响,以评估不同流速下,海胆摄食行为和生长的差异。实验结果表明,流速对光棘球海胆的存活无显著影响,但显著影响其生长。2 cm/s下海胆的壳径和体重显著大于10和20 cm/s。在实验开始后的第2周和第3周,2 cm/s下海胆的体重和壳径已显著高于20 cm/s。流速显著影响光棘球海胆的摄食量(P<0.001)和觅食行为(20 cm/s,P=0.004),但口器咬合行为未受显著影响(P=0.113)。管足附着时间在流速为10 cm/s和20 cm/s下显著长于其在2 cm/s。同样的,相较于2 cm/s(P=0.02)和10 cm/s(P=0.03),20 cm/s的流速可显著削弱光棘球海胆的翻正行为。综上,高流速(20 cm/s)通过影响海胆管足活动削弱其觅食行为(而非摄食行为),进而降低其...     

Variation among females in egg lipid content and developmental success of echinoderms from McMurdo Sound,Antarctica

Egg lipid and protein content of different females of Antarctic echinoderms in McMurdo Sound, Antarctica, were measured to assess variation among females and developmental success. Egg triacylglycerol content of the Antarctic sea urchin Sterechinus neumayeri, when less than 70 ng, correlated with embryos that failed to develop past the 4-day-old blastula stage. In contrast asteroids (Odontaster meridionalis, O. validus, Acodontaster hodgsoni) all produced eggs that developed normally, even with variable egg lipid content. This difference might be related to dietary sources for more herbivorous sea urchins compared to more omnivorous and predatory asteroids. Low egg lipid content, with resulting poor embryonic survivorship, suggests that herbivorous sea urchins may be under unusual levels of nutritional stress in McMurdo Sound during the time frame studied (2004–2005). This nutritional stress might be related to the presence of large icebergs, known to have reduced primary production in the Ross Sea area.     

The influence of diet on the oxygen uptake of the sea urchins,Tripneustes ventricosus and Strongylocentrotus droebachiensis

• 1.1. The influence of different natural foods on the rate of oxygen uptake of two species of sea urchins was examined.
• 2.2. The rate of oxygen uptake of specimens of Tripneustes ventricosus was greater in those fed with the brown alga, Saryassum sp., than in those fed with the angiosperm, Thalassia testudinum.
• 3.3. When specimens of Strongylocentrotus droebachiensis were fed following a period of food deprivation, the increase in the rate of oxygen uptake was higher in individuals fed with the brown alga, Nereocystis luetkeana, than in individuals fed with the angiosperm, Zostera marina. This difference is attributed to a higher specific dynamic action resulting from a greater rate of food absorption in urchins fed with N. luetkeana.

     

Effects of different UV radiation on photoprotective pigments and antioxidant activity of the hot‐spring cyanobacterium Leptolyngbya cf. fragilis

UV‐induced synthesis/accumulation of photoprotective pigments and antioxidant activity were investigated in the hot‐spring cyanobacterium Leptolyngbya cf. fragilis. The results indicated that UV radiation may induce biosynthesis of carotenoids, allophycocyanin, phycoerythrin, and scytonemin while phycocyanin degrades in response to longtime UV radiation. Moreover, pigment composition of L. cf. fragilis was significantly altered with increasing UV radiation times, probably due to destruction and resynthesis of accessory pigments as an adaptation strategy to UV stress. The in vitro antioxidant analysis of different extracts of UV treated cyanobacteria exhibited concentration‐dependent antioxidant activity. Ethyl acetate extract of 72 h UV treatment showed maximum total antioxidant activity (IC50 = 71.73 ± 5.3 μg mL^?1) followed by ethyl acetate control (non‐UV irradiated) extract (IC50 = 109.43 ± 2.76 μg mL^?1). This is the first report for the UV‐induced synthesis of photoprotective pigments and their antioxidant activity in L. cf. fragilis.     

Destruction of kelp-beds by sea-urchins: A cyclical phenomenon or irreversible degradation?

A stable kelp bed ecosystem in St. Margaret's Bay, Nova Scotia (Canada), had as its main producersLaminaria longicruris andL. digita. Most algal production was exported as detritus, but there was a moderate population of herbivores, mainly the sea urchinsStrongylocentrotus droebachiensis. These were eaten by crabs,Cancer irroratus and by lobsters,Homarus americanus. Lobsters also preyed on crabs. Beginning in 1968, sea urchins became locally abundant and overgrazed the kelp beds, converting large areas to urchindominated barren grounds. Almost all kelp beds in St. Margaret's Bay (140 km²) have now been destroyed. During the same period, lobster biomass decreased, and the hypothesis was put forward that reduction in lobster predation led to increased urchin abundance and kelp bed destruction. Evidence is presented for the hypothesis that urchin-dominated barren grounds are a new, stable configuration of the ecosystem, and that a long-term decrease in primary and secondary productivity of these coastal waters can be expected.