Detection of p34cdc2- and cyclin B-like proteins in Dunaliella tertiolecta (Chlorophyceae)

p34cdc2 and cyclin B are two key proteins in the eukaryotic cell cycle control machinery. They thus could be important cell cycle markers for studies of environmental effects on cell cycle progression and on growth rate of marine phytoplankton. From July 1993 to March 1995, we used commercially available antibodies to examine the presence of their homologs in a marine phytoplankton species, Dunaliella tertiolecta Butcher. A p34cdc2-like protein was detected on the Western blots, with an apparent molecular mass as expected (34 kDa). Anti-cyclin B detected a protein of 63 kDa, a size similar to that of cyclin B in other organisms. The two proteins decreased from the exponential to the stationary growth phase. As determined on the Western blots, their abundance only changed slightly during the cell cycle, being slightly more abundant prior to cell division. Immunofluorescence performed for a partially synchronized culture showed that the fraction of the cell population that was positively stained by anti-p34cdc2 was highest at the time when the culture was mainly in the late G1 or early S phase, and in the late G2 or early M phase, respectively. The fraction was low when the culture was mainly in the S phase. Although further characterization is required to verify their identities, these two growth phase-related proteins appear to be p34cdc2 and cyclin B homologs, which may be useful in studying the cell cycle and growth rates of phytoplankton.     

Water-soluble extracts of the diatom Thalassiosira rotula induce aberrations in embryonic tubulin organisation of the sea urchin Paracentrotus lividus

Eggs and embryos of the sea urchin Paracentrotus lividus were used as a model to study the effect at the cellular level of potential anti-mitotic compounds extracted from the diatom Thalassiosira rotula. Eggs and embryos incubated in a water-soluble diatom extract, corresponding to 5 × 10⁶ and 10⁷ cells ml⁻¹, were totally blocked (i.e. cell division was blocked) at the one-cell stage. At lower concentrations (2.5 and 1.25 × 10⁶ cells ml⁻¹), the first mitotic division was inhibited in 32 ± 26% and 25 ± 3.5% of the zygotes, respectively, demonstrating the dose-dependent effect of diatom extracts on sea urchin development. Immunofluorescence dyes, specific for DNA and α-tubulin subunits, were used to stain nuclei and microtubules in sea urchin embryos during various phases of development. Images with the confocal laser scanning microscope showed that tubulin was not organised in filaments at the sperm aster and cortex levels, and that the pronuclei were not fused in embryos incubated soon after fertilisation with water-soluble diatom extracts corresponding to 10⁷ cells ml⁻¹. At lower diatom-extract concentrations (4 × 10⁶ cells ml ⁻¹), fusion of the pronuclei occurred but the mitotic spindle was not formed. Microtubules were clearly de-polymerised and the chromatin appeared globular and compacted at the centre of the cell. A similar structure was observed for sea urchin embryos incubated with 0.1 mM colchicine, a potent anti-mitotic compound. When sea urchin embryos were incubated in water-soluble diatom extracts at different times prior to the first mitotic division, microtubules appeared de-polymerised at each step, from pronuclear fusion to telophase, and cell division was blocked. At the histological level, embryos incubated with 4 × 10⁶ cells ml⁻¹ diatom extract showed nuclear fragmentation without cytokinesis. The possible use of sea urchin embryos as a bioassay to test for other unknown compounds with cytotoxic activity in phytoplankton species is discussed. Received: 7 May 1998 / Accepted: 9 December 1998     

海胆胚胎不同发育期P-糖蛋白（P-glycoprotein）药物外排功能的研究

通过研究添加维拉帕米(Verapamil,VER)后,灭蝇胺(Cyromazine)和杀虫丹(Ethiofencarb)对海胆胚胎致死中浓度(LC50)的变化,探讨了不同发育期海胆胚胎P-糖蛋白(P-glycoprotein,P-gp)的功能.结果表明:灭蝇胺和杀虫丹对海胆胚胎的平均LC50分别为2.50mg·L-1和3.50mg·L-1,在加入0.75μmol·L-1P-gp抑制剂VER后,其LC50平均降低40%～42%,说明海胆胚胎P-gp具有药物外排作用.药物浓度可影响P-gp功能,随药物浓度的升高,P-gp外排功能逐渐减弱,甚至达到饱和.实验同时通过分子模拟方法研究了灭蝇胺和杀虫丹的分子结构特征,实验和理论结果均证实了这两种药物分子为海胆胚胎P-gp的底物.     

Impacts of UV-B radiation on short-term cultures of sea urchin coelomocytes

Three specialized cell types constitute the heterogeneous population present in the coelomic cavity fluid of sea urchins. The list includes: phagocytes, which undergo a stress-induced petaloid-filopodial transition, white or red amoebocytes and vibratile cells. As a whole, they act as the immune defense system of the sea urchin and respond to environmental and experimental challenge triggering specific stress markers. Here we extended our studies on coelomocytes short-term cultures by describing the morphology and occurrence of each cell type and analyzing their response to UV-B radiation at the biochemical level and with respect to DNA damage. The effects of different doses, ranging from 500 to 2,000 J/m², on cells, which were then cultured in vitro for 1–6 h were tested. As early as 1 h after irradiation we found an increase in the levels of the heat shock protein70 (hsp) stress marker. A peak at 1,000 J/m² corresponding to a 3.4-fold hsp70 increase over the levels of control coelomocytes was observed. Concurrently, we found an increase in the number of apoptotic nuclei detected by Hoechst staining, which varied from 7.1 to 15.6% in cells that were exposed to 500 and 2,000 J/m², respectively. On the basis of our findings we confirm sea urchin coelomocytes as a sensitive cell culture system for environmental studies and propose their use for the analysis on the effects of UV-B radiation. Physical and Chemical Impacts on Marine Organisms, a Bilateral Seminar Italy-Japan held in November 2004. This paper is dedicated to the memory of Aurelia Koros, Ph. D., University of Pittsburg, who committed her scientific life to the study of natural killer cell antigens expressed in small lung carcinoma cells and sea urchin coelomocytes.     

Ein mimetisches Kollektiv — Beobachtungen an Fischschwärmen,die Seeigel nachahmen

In the Indian Ocean, the fish Siphamia argentea usually lives in small groups within the interradial spaces of the sea urchin Astropyga radiata. The fish has a colouration similar to that of the sea urchin and is thus protected from predators both by camouflage and the physical barrier of the sea urchin's spines. If the fish do not keep to the interradial spaces, the urchin can prick them with its spines. When the fish groups become too large, there is not enough space for them in these protected interradial spaces. Individuals which cannot be accomodated, form a dense group around the sea urchin which resembles a large urchin. Such dense groups are also known to occur in the fish Plotosus anguillaris where the individuals actually touch each other. The relationship between fish and sea urchin is described and discussed as an example of collective mimetic behaviour. This is the first record of collective mimetic behaviour in a marine environment. It is difficult to decide whether this is mimicry or mimese, as detailed research on the predators of both the sea urchin and the fish has not been carried out.     

Profitability and sustainability of edible sea urchin fishery in Sardinia (Italy)

Sea urchin (Paracentrotus lividus) fishery is intensively practiced in several areas of the Mediterranean basin. In Sardinia, as well as other Mediterranean countries, sea urchin is a basic ingredient for several dishes due to the delicacy of its gonads (roe), and demand is constantly increasing. Restrictions have been implemented in order to minimise the risk of overexploitation, however, these measures might jeopardize economic convenience in sea urchin harvesting. This paper estimates economic convenience within the edible sea urchin fishery in Sardinia. It aims to determine whether both profitability and sustainability, in terms of the preservation of sea urchin stock, can be guaranteed by actual policy regulation. We found high variability in terms of captures and profitability among firms, and a considerable degree of this variability is the result of technological differences between fishing methods. Analysis also suggests that a slight increase in allowed captures should generate a more than proportional increase in profits. This evidence gives some useful suggestions for improving the efficacy of policies in affecting the economic and environmental sustainability of the Mediterranean sea urchin fishery.     

Response of embryos of the sea urchin Strongylocentrotus purpuratus to aqueous petroleum waste includes the expression of a high molecular weight glycoprotein

The present study investigated the sublethal effects of the largest aqueous waste associated with offshore oil development, produced water (PW), on sea urchin embryo development. PW inhibited normal gastrulation in purple sea urchin (Strongylocentrotus purpuratus) embryos exposed at the hatching stage. The exposed embryos did not form complete archenterons, and secondary mesenchyme cells exhibited an unusual behavior with respect to the wall of the blastocoelic cavity. In addition, an abundance of extracellular matrix was observed in the blastocoelic cavities in the embryos exposed to higher concentrations of PW. An inhibition of the development of embryos through the pluteus stage was observed as a result of PW exposure. This was manifested by inhibition of normal spicule formation with concomitant abnormal pluteus morphology. To determine if a biochemical stress response occurs as a result of PW exposure, embryos at the early gastrula stage were exposed to PW for 2 h, followed by an additional 1 h in 3H-leucine and PW. These embryos expressed a 253 kDa protein as observed by one-dimensional SDS (sodium dodecyl sulfate) polyacrylamide gel electrophoresis and autoradiography. This protein could occasionally be observed in gels stained for protein, and was glycosylated as demonstrated by staining with periodic acid Schiff (PAS). The 70 to 73 kDa heat-shock proteins previously described in sea urchin embryos (and other organisms) as a result of stress were not synthesized as a result of PW exposure. Heat shock did not induce synthesis of the 253 kDa glycoprotein. Combined PW and heat-shock exposure elicited both the heat-shock response (73 kDa protein) as well as expression of the 253 kDa glycoprotein. These data demonstrate the use of expression of endogenous macromolecular markers to distinguish exposures of embryos to different perturbations. Arsenic (as sodium arsenite), a metal constituent of PW, also induced the 253 kDa glycoprotein in early gastrula-stage embryos. We suggest that this glycoprotein may be a marker for PW (and a metal constituent) exposure in sea urchin embryos, and may be related to morphological abnormalities.     

Fische als Feinde tropischer Seeigel

The techniques used by 9 species of fish (representing 3 families) to capture Diadema sea urchins were observed under water in the Red Sea at Eilat, Israel. Different species displayed different techniques. Fish belonging to the Lethrinidae and Labridae families devoured the entire urchin after capture; Labridae alone were also capable of breaking up large sea urchins by banging them on rocks. The fish did this by shaking its head while holding the urchin in its mouth. Under experimental conditions, fish can distinguish between large and small urchins, and show a preference for the small urchin. The fish also shun contact with some other species of urchins. The trigger fish Balistes fuscus exposed to a dummy sea urchin responds to optical stimuli (body shape and spines); when exposed to a living sea urchin it responds to both optical and behavioural stimuli (movements of the spines). Morphological and ethological preadaptation of the fish to alter its preference for other food is essential before it can develop differentiated capture techniques. The ecological significance of the behaviour of fish in the coral reef ecosystem and the alternating influences in the predator-prey-relationship are discussed.     

8种常见农药对海胆胚胎各发育期的急性毒性

为初步探讨农药对海胆胚胎的急性毒性效应,以虾夷马粪海胆(Strongylocentyotus internedius)为实验材料,研究了8种常见农药--草甘膦(Glyphosate)、百草枯(Paraquat)、异菌脲(Iprodione)、代森锰锌(Mancozeb)、三唑醇(Triadimenol)、霜霉威(Propamocarb)、百菌清(Chlorothalonil)和速克灵(Procymidone)对海胆胚胎各发育期(二细胞期、四细胞期、上浮囊胚期、原肠期、棱柱幼体期、四腕幼虫期)的半数效应浓度(EC50),并分析了正辛醇/水分配系数(LogP)与EC50的关系.结果显示:1)8种农药对海胆胚胎各发育期均具有一定的急性毒性,以四腕幼虫期为例,8种农药的EC50值分别为草甘膦(3.99mg·L-1)>百草枯(10.38mg·L-1)>代森锰锌(20.77mg·L-1)>速克灵(55.42mg·L-1)>霜霉威(56.09mg·L-1)>异菌脲(86.29mg·L-1)>三唑醇(273.20mg·L-1)>百菌清(647.38mg·L-1).2)LogP与EC50呈现一定的正相关性,即随着LogP的增加,各农药对海胆胚胎的抑制率逐渐降低.     

Incidence,occurrence and distribution of the nematode Echinomermella matsi in its echinoid host,Strongylocentrotus droebachiensis,in northern Norway

The incidence, occurrence and distribution of the nematode Echinomermella matsi (Jones and Hagen) in its host, the echinoid Strongylocentrotus droebachiensis Müller, were examined in Norwegian waters from Nordmre (63° N) to the Russian border (70° N) in a range of habitats (e.g. kelp cover and community type) from 1982 to 1992. The results are used to examine the likely influence of the parasite on fitness (individual growth and gonad production) and its potential in regulating the population size of its echinoid host. The nematode infections are restricted to areas between Vikna (Vega) and middle Troms, with the highest prevalence (40 to 88% infected) in the Bodø area, the focus of the distribution. The prevalence rates are similar on kelp beds and barren grounds. No difference in growth rates between infected and noninfected sea urchins was found. Nematode-infected sea urchins in kelp bed populations had gonads weighing about one-sixth of those of equivalent uninfected individuals. This indicates that nematodes are really parasites causing reduced reproductive capacity. Areas with high prevalence (>40% infected) of nematodes had low sea urchin densities. High nematode intensities were found in the areas with high prevalence. The mean abundance in high prevalence areas was highest (eight nematodes) in the 4-to 7-yr-old age group and decreased to zero among the oldest age groups. The ratio of variance/mean abundance was also highest among 5-to 8-yr-old sea urchins. At highly and slightly infected locations, the relationships between the log of the variance and the log of the mean abundance of parasites were 1.35 and 1.69, respectively. Measurements of the frequency distribution of nematodes in sea urchins and the corresponding estimates of the negative binomial distribution showed significantly higher counts in estimated than observed subpopulations exceeding 20 nematodes per sea urchin. These results may explain nematode-induced sea urchin mortality. The low density of the host in the Bodø area, which had high prevalence, may be a result of increased host mortality caused by nematodes, by lower recruitment because of reduced gonad production, or by other factors. Low prevalence among older sea urchins may be caused by nematodeinduced host mortality or by cycles in infection. However, studies on the life cycle of the nematode and long term investigations of host density and nematode intensity/prevalence will be needed before any true conclusions can can be drawn.     

Prey defense,predator preference,and nonrandom diet: The interactions between Pycnopodia helianthoides and two species of sea urchins

Interactions between the predatory sea star Pycnopodia helianthoides (Brandt, 1835) and two of its natural prey, the sea urchins Strongylocentrotus purpuratus (Stimpson, 1857) and S. franciscanus (Agassiz, 1863), are examined with regard to predator preference, predator diet, and prey defenses. The sea star is able to detect both species of sea urchin upstream in a Y-trough, but does not consistently choose one over the other (i.e., no preference). However, when the sea star is presented with equal numbers of similar-sized specimens of the two species of sea urchin, its diet is markedly nonrandom, since S. purpuratus is eaten almost 98% of the time. The defensive responses of the two species of sea urchin differ in form and effectiveness. S. franciscanus employs its long spines as defensive weapons, pinching the rays of an attacking sea star. This defensive response is more effective than the pedicellarial response used by S. purpuratus. The nonrandom diet of the predator seems to result primarily from prey defensive responses that differ in effectiveness, rather than from an intrinsic, behavioral preference of the predator at an earlier stage in the predator/prey interaction.     

Host preference,site fidelity,and homing behavior of the symbiotically luminous cardinalfish,Siphamia tubifer (Perciformes: Apogonidae)

The sea urchin cardinalfish, Siphamia tubifer (Perciformes: Apogonidae), is unusual among coral reef fishes for its use of bioluminescence, produced by symbiotic bacteria, while foraging at night. As a foundation for understanding the relationship between the symbiosis and the ecology of the fish, this study examined the diel behavior, host urchin preference, site fidelity, and homing of S. tubifer in June and July of 2012 and 2013 at reefs near Sesoko Island, Okinawa, Japan (26°38′N, 127°52′E). After foraging, S. tubifer aggregated in groups among the spines of the longspine sea urchin, Diadema setosum, and the banded sea urchin, Echinothrix calamaris. A preference for D. setosum was evident (P < 0.001), especially by larger individuals (>25 mm standard length, P < 0.01), and choice experiments demonstrated the ability of S. tubifer to recognize and orient to a host urchin and to conspecifics. Tagging studies revealed that S. tubifer exhibits daily fidelity to a host urchin; 43–50 and 26–37 % of tagged individuals were associated with the same urchin after 3 and 7 days. Tagged fish also returned to their site of origin after displacement; by day two, 23–43 and 27–33 % of tagged individuals returned from displacement distances of 1 and 2 km. These results suggest that S. tubifer uses various environmental cues for homing and site fidelity; similar behaviors and cues might be used by larvae for recruitment to settlement sites and for the acquisition of luminous symbiotic bacteria.     

Effects of predators on sea urchin density and habitat use in a southern California kelp forest

Grazing sea urchins can reduce kelp abundance and therefore strongly affect kelp forest community structure. Despite the ecological importance of sea urchins, direct field studies on the role that urchin predators play in shaping urchin populations are rare for southern California. We conducted surveys and manipulative experiments within kelp forests near San Diego, CA, (32–51′28″N, 117–16′00″W) from 2006 to 2009 to determine whether predators such as sheephead (Semicossyphus pulcher) and spiny lobsters (Panulirus interruptus) may be linked to purple urchin (Strongylocentrotus purpuratus) and red urchin (Strongylocentrotus franciscanus) distribution and habitat use, as well as purple urchin density-dependent mortality. Purple urchins were less dense and more cryptic inside a local marine protected area (MPA) that contained high predator abundance than in nearby heavily fished areas, whereas red urchins rarely were found outside the MPA. Urchin proportional mortality was inversely density dependent during the day when sheephead were active, despite fish aggregations in plots of high urchin density, but was density independent during the night when lobsters were active. Urchin mortality was reduced under understory algal cover during the day, but not during the night. Examining whether urchin mortality from predation is density dependent and how habitat complexity influences this relationship is imperative because behavioral changes and increases in urchin populations can have vast ecological and economic consequences in kelp forest communities.     

Effects of sea urchin disease on coastal marine ecosystems

Outbreaks of disease in herbivorous sea urchins have led to ecosystem phase shifts from urchin barrens to kelp beds (forests) on temperate rocky reefs, and from coral to macroalgal-dominated reefs in the tropics. We analyzed temporal patterns in epizootics that cause mass mortality of sea urchins, and consequent phase shifts, based on published records over a 42-year period (1970–2012). We found no evidence for a general increase in disease outbreaks among seven species of ecologically important and intensively studied sea urchins. Periodic waves of recurrent amoebic disease of Strongylocentrotus droebachiensis in Nova Scotia coincide with periods when the system was in a barrens state and appear to have increased in frequency. In contrast, following a major epizootic that decimated Diadema antillarum throughout the Caribbean in 1983, subsequent outbreaks of disease were highly localized and none have been reported since 1991. Epizootics of Strongylocentrotus in the NW Atlantic and NE Pacific, and Paracentrotus and Diadema in the eastern Atlantic, have been linked to climate change and overfishing of sea urchin predators. The spatial extent of recurrent disease outbreaks in these species, and the frequency of phase shifts associated with these epizootics, has decreased over time due to the expansion of the macroalgal state and its stabilization through positive feedback mechanisms. Longitudinal studies to monitor disease outbreaks in sea urchin populations and improved techniques to identify causative agents are needed to assess changes in the frequency and extent of epizootics, which can profoundly affect the structure and functioning of coastal marine ecosystems.     

Experimental evaluation of aggregation behavior in the sea urchin Strongylocentrotus droebachiensis

Defensive aggregation by Strongylocentrotus droebachiensis has been invoked as the fulcrum for the transformation of macroalgal beds into coralline barrens in the northwest Atlantic. We critically examined some of the mechanisms contributing to aggregation behavior by experimentally manipulating sea urchins, purported predators and food during autumn 1983 and spring 1984 both in the laboratory and field. We utilized several approaches to examine a range of sea urchin responses to the presence of food, tethered predators, caged predators, crushed con-specifics in the field and predators in laboratory tanks. Some of the field cages had the property of allowing free passage to sea urchins while retaining lobsters; this allowed distinctions to be made between artifacts caused by cage walls or topographic barriers and unrestricted behavioral responses of sea urchins. The results falsified the hypothesis that aggregations of S. droebachiensis are elicited by predators. Except in the presence of algae, sea urchins always avoided decapod predators (but not sea stars) and fled from the vicinity of injured conspecifics. However, avoidance behavior was subordinate to feeding responses, demonstrated by mass migrations of sea urchins into cages (with lobsters) to feed on algae. We reaffirmed by observation and manipulation previous studies which showed that sea urchins aggregate only in the presence of food. Two types of sea urchin groupings were delineated: (1) surficial two dimensional associations, often caused by topographic or other features which inhibited dispersal and (2) cohesive three-dimensional aggregations induced by food.     

Evaluating growth of larval walleye pollock, Theragra chalcogramma, using cell cycle analysis

Cell cycle analysis of muscle cell division rates offers a new and efficient technique to analyze growth of larval fish. Using this approach, growth of larval walleye pollock was estimated by determining cell proliferation rates, reasoning that growth during early life stages is probably attributed to increases in cell number rather than to increases in cell size. Characteristic patterns of brain and muscle cell division rates were produced in larval walleye pollock by manipulating their diet in the laboratory. The fraction of dividing muscle cells and, to a lesser extent, the fraction of dividing brain cells were direct indicators of fast and slow growth. A model was produced to estimate average growth rate from the fraction of dividing muscle cells. We developed a simple method for preparing and storing the muscle tissue that ensures nucleic acid stability for subsequent analyses and permits sampling in the field. We envision that the cell cycle methodology will have on-site applications, presenting an opportunity to attain real-time estimates of larval fish growth at sea. Determining the proportion of first-feeding larvae with a high fraction of dividing muscle cells may yield a means for predicting the proportion of fast-growing fish, i.e., the potential survivors.     

Changes in sea urchin populations after the destruction of kelp beds

In St. Margaret's Bay, Nova Scotia, Canada, there are large areas in which sea urchins (Strongylocentrotus droebachiensis) have eliminated beds of kelp (Laminaria spp.). Sites were identified where destruction of kelp beds had taken place 1, 2, 3, 3.5 and 4 years ago. With increase of time since kelp disappearance, the sea urchins showed decreased growth rate, reduced gonad size, but an increase in numbers resulting from high recruitment rates in the first two years after kelp bed destruction. These sea urchin populations, by their browsing, effectively prevent the regeneration of kelp. There is, as yet, no evidence of the sea urchin populations being starved out to allow the kelp to return.     

Comparative feeding preference of Strongylocentrotus droebachiensis (Echinoidea) for the invasive seaweed Codium fragile ssp. tomentosoides (Chlorophyceae) and four other seaweeds

Laboratory experiments conducted during 1987 on Appledore Island, Maine, USA, tested whether feeding preference or the absence of an attractant was the cause for the occurrence of beds of Codium fragile ssp. tomentosoides (herein referred to as Codium fragile) within rocky barrens grazed clear of kelp by the sea urchin Strongylocentrotus droebachiensis. Consumption of C. fragile in single-diet experiments (1 seaweed/sea urchin) was highly variable and was not significantly different from that for several other seaweeds (Agarum cribrosum, Ascophyllum nodosum, Chondrus crispus, and Laminana saccharina) important in the field diet of the green sea urchin. In multiple-diet experiments (5 seaweeds/sea urchin) significantly less Codium fragile was eaten than Chondrus crispus, but significantly more Codium fragile was eaten than A. cribrosum. Chemosensory experiments suggest that C. fragile does not attract the sea urchin. Sea urchins are unable to detect C. fragile but will eat it when they come in contact with it.     

Succession in sea urchin and seaweed abundance in Nova Scotia,Canada

From 1980 through 1983 sea urchin mass mortalities were at least 245 000 t. The habitat released to seaweed is expected to support a standing crop of 1.8 million tons and an annual production of 7 million tons. An extensive survey of 2 900 km of Nova Scotia shoreline revealed that 511 km² of habitat (rock bottom less than 15 m deep) was available to seaweeds. Areas most exposed to ocean swells bordered 26% of the shoreline length but included 82% of the seaweed habitat. Before mass mortalities, seaweed refuges from sea urchin grazing included very sheltered habitats, very exposed habitats, and boulders set among shifting sand; however, these were less than 10% of the total habitat. In the 1 to 2 years following mass mortalities seaweed cover and occurrence increased significantly for all of five categories of wave exposure and for six of seven algal taxa respectively. In at least three locations the sea urchin population began to recover as a result of larval recruitment but in 1983 was again reduced by disease. Sea urchins appear to lack natural resistance to disease, at least at warm temperatures. In the laboratory all sea urchins collected from the Bay of Fundy, southern Nova Scotia, eastern Newfoundland, and an area recovering from mass mortalities died following exposure to diseased animals. Also, field mortalities included a wide variety of habitats. Interviews of Nova Scotia lobster fishermen revealed that sea urchin mass mortalities have probably occurred before in this century, but infrequently.     

Diel foraging patterns of the sea urchin Centrostephanus coronatus as a predator avoidance strategy

During the day, the diadematid sea urchin Centrostephanus coronatus occupies holes and crevices in shallow subtidal rocky substrata. Individuals emerge from these after sunset and forage on organisms attached to the surrounding rock surface. Each urchin travels <1 m from its shelter and returns to the same one before sunrise. The sheephead wrasse Pimelometopon pulchrum does not remove urchins from their shelters, but will attack and consume urchins placed in normal feeding locations during the daytime. The active periods of the sheephead and the urchin do not overlap; urchins begin foraging about 20 min after the diurnal sheephead retire in the evening and return to their shelters 1 to 2 h before sheephead resume feeding in the morning. We infer that the urchin's daytime crevice-dwelling and nocturnal foraging habits have evolved as a response to sheephead predation. Moreover, because shelters are limited in supply, shelter fidelity may have evolved to insure refuge from sheephead.