Physiology, environmental physiology, & functional morphology
  Aspects of physiology of sea urchins relating to temperature & thermal tolerance, gas exchange metabolism & Q10, salinity, pH & ocean acidification, and water currents are presented in subsections below.
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Temperature & thermal tolerance

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Research study 1

photograph of purple sea-urchins Strongylocentrotus purpuratus in protective hollowsA study on thermal tolerance and acclimation to temperature in purple sea-urchins Strongylocentrotus purpuratus at Hopkins Marine Station, Pacific Grove, California shows that they tolerate temperatures from 5-23oC.  If sea urchins are acclimated to low temperatures for periods of up to 35d, their respiratory rates gradually increase, and their behaviour, such as righting ability, becomes nearly normal.  In contrast, exposure to high temperature, such as at 20oC for 10d does not lead to acclimation, and exposure of individuals to 25oC is invariably lethal.  The authors provide evidence that S. purpuratus is acclimated to temperature conditions in different parts of its geographical range.  The means by which acclimation occurs is not known, but is likely related to quantitative and qualitative changes in metabolic enzymes.  Farmanfarmaian & Giese 1963 Physiol Zool 36: 237.

NOTE  in this area annual temperature records (10yr period) show a range of 9-17oC






Large aggregation of purple sea-urchins Strongylocentrotus
in protective hollows in sandstone. For individuals
exposed to air, harmful temperature and humidity fluctuations
in such habitats are additionally ameliorated by overhanging seaweeds
and by coverings of shells and stones. A single red urchins S.
has tried to fit itself into one of the too-small hollows

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Research study 2

map of collecting sites for purple urchins Strongylocentrotus purpuratusWhat is the thermal tolerance of sea-urchin embryos and larvae?  This is tested by researchers at the University of California, Santa Barbara by collecting adult purple urchins Strongylocentrotus purpuratus from 4 locations along the west coast (see map), rearing eggs to 4-arm pluteus stage, then measuring survival and levels of the stress-induced gene (hsp70) in gastrulae and larvae following 1h exposure to a range of temperatures (10-32oC). Results show no significant difference between the developmental stages at all sites in survival or levels of hsp70 expression.  Surprisingly, maximum hsp70 expression is exhibited at 25oC at all sites, but a somewhat purple urchins Strongylocentrotus purpuratus in tidepoolnarrower range in southern populations suggests that they are closer to their upper temperature limit than are northern populations.  The lack of a clear latitudinal trend suggests that the developmental stages of S. purpuratus have similar temperature tolerances throughout the portion of their distributional range studied.  Hammond & Hofmann 2010 Mar Biol 157: 2677.

NOTE  a family of genes that codes for heat-shock proteins.  These are molecular chaperones that aid in refolding or translocation of proteins damaged by temperature or other stresses, thus allowing the cell to maintain proper functions.  Heat-shock proteins are considered for adults of many marine invertebrates throughout the ODYSSEY, but this is the only report thus far for developmental stages

NOTE  with regard to this, one wonders why the authors did not extend their collections over the full range of the species’ distribution, i.e., from Baja California to Alaska?


Purple urchins Strongylocentrotus purpuratus in
protenctive hollows in a tidepool 0.25X

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Gas exchange, metabolism, and Q10


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Research study 1


Gas exchange in sea urchins occurs by diffusion through the thin-walled epithelia of the tube feet and, to a lesser extent, through the peristomial gills on the oral surface.  There is no circulatory system, and gases move to and from the organs via the coelomic fluid in the main body cavity.  During reproduction this cavity becomes largely filled with gonads, and the question arises as to whether oxygen consumption will rise correlative oxygen consumption of purple sea-urchins Strongylocentrotus purpuratus in relation to gonad indexwith the extra mass of gonads, or fall because of reduced diffusion.  This issue is addressed in a study at Hopkins Marine Station, Pacific Grove, California on purple urchins  Strongylocentrotus purpuratus.  Results show that oxygen consumption actually decreases with the extent of reproductive maturation (see graph). Measurements of oxygen consumption of different bodily components show that the body wall accounts for about 72% of the respiration in non-gravid sea urchins, with gonads accounting for only about 2%.  In gravid animals, however, gonads should theoretically increase respiratory needs by about 30-50% for females and males, respectively.  That these increased respiratory needs are not reflected in overall oxygen-consumption values in gravid animals is thought by the authors to owe to reduced diffusion of gases.  Giese et al. 1966 Biol Bull 130: 192.

NOTE  diffusion rates will be impeded both by the bulk of the gonads and by relatively less coelomic fluid being present

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Research study 2
  graph showing the rate of decline in oxygen tension within the coelomic fluid of a purple sea-urchin held in air for several hoursAnother problem with living in a calcium-carbonate box is that gas exchange by diffusion is limited.  This is no problem when the sea urchin is immersed because the many tube feet can be extended to provide a large surface area for diffusion of oxygen and carbon dioxide.  In air, however, it is a different story.  Studies at Friday Harbor Laboratories, Washington show that if a purple urchin Strongylocentrotus purpuratus is exposed to air the oxygen tension in its coelomic fluid decreases steadily to a level about 25% of the level when immersed and stays at this level for up to 15h.  The volume of coelomic fluid in sea urchins therefore represents a store of oxygen that can be drawn on in times of need. The gas-exchange capability in air is effective for the duration of normal tidal exposure.  Johansen & Vadas 1967 Biol Bull 132: 16.

NOTE  although 2 other species are included in the study (S. franciscanus and S. droebachiensis), because they are not common intertidally and because they behave in a similar pattern to the one shown for S. purpuratus, their data are not included here.  Water temperature in the study is about 10oC and air temperature, about 15oC
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Research study 3

graph comparing oxygen-consumption rates in 3 species of sea urchins Strongylocentrotus purpuratus, S. franciscanus, and S. fragilisThree species of sea urchins occur in shallow waters off the coast of Oregon.  One of these, Strongylocentrotus purpuratus, occurs intertidally as well as subtidally; a second species, S. franciscanus, occupies a vertical range extending from the low intertidal area to subtidal regions; and a third species, S. fragilis1, lives only subtidally.  The intertidal species would, of course, be exposed to greater thermal variation than the subtidal species.  Predictions with respect to acclimatisation of metabolic rate to temperature would then be greater temperature indepence in the intertidal species and greater conformity in the subtidal ones.  This is tested at the Marine Science Center, Newport, Oregon, with results as shown in the graph2.  Although the experimenters do not analyse their data statistically for differences in slope, they do provide a “running” estimate of Q10 values for each species for 3oC temperature increments.  For S. purpuratus Q10’s start at about 2.6 and end at about 1.8 suggesting a degree of temperature compensation.  If the 9oC "outlier" datum point is omitted as likely being aberrant3 for S. franciscanus, the comparable values are 2.8 and 1.5, again suggesting temperature compensation.  Finally, for S. fragilis, the Q10 values are 1.1 photograph of deep-water sea-urchin Strongylocentrotus fragilis, courtesy NOAA, Goverment of U.S.and 2.2, indicating little or no temperature compensation over the range tested.  Ulbricht & Pritchard 1972 Biol Bull 142: 178. Photograph courtesy NOAA, Federal Government, USA.

NOTE1  formerly in the genus Allocentrus; now Strongylocentrotus

NOTE2   sample sizes are 12 for S. purpuratus and S. franciscanus, and 6 for A. fragilis.  The authors, however, use some individuals multiple times, adding a component of pseudoreplication to their data

NOTE3  however, if the 9oC value is accepted as being valid, as the authors rightly do, then S. franciscanus at least for the time being can be considered as temperature-dependent


Aggregation of sea-urchins Strongylocentrotus fragilis



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Research study 4

Researchers at California State and Stanford Universities confirm that oxygen consumption in purple urchins Strongylocentrotus purpuratus does not change significantly over the annual reproductive cycle. However, the data are characterised by high variability for which the authors have no explanation. They do note, however, that there is at least some anaerobic metabolism occurring within the gonad, but the extent of this is not known. One omission that may be important is the authors’ failure to include sex as a factor influencing oxygen uptake. There is no question that sex of each experimental animal was known, as each was dissected to determine its gonadal index, but it is puzzling that the photograph of sea-urchin gonads on the "half-shell", ready to eatresearchers assumed ovary and testes to have similar metabolic demands. Had sex been factored into the analysis, perhaps some of the variability would have been accounted for. Webster & Giese 1975 Biol Bull 148: 165. Provenance of photograph not known.

NOTE the main purpose of the study was to use a different analytical technique (oxygen electrode versus manometry) to confirm earlier findings that oxygen uptake in purple urchins is not correlated with reproductive cycle (see Research Study 1 above). Since the organic content of the body almost doubles during the cycle, such a finding is quite unexpected

Gonads on the "half-shell". These testes have been repacked for
sale. Note their large volume relative to that of the test

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Research study 5

photograph of purple urchins Strongylocentrotus purpuratus at low spring tide at Botanical Beach, British ColumbiaAlong the lines of “new and surprising”, a group of researchers at the Oregon Institute of Marine Biology in Charleston report that an air-exposed purple urchin Strongylocentrotus purpuratus creates an air space in its intestine that may act as a facultative “lung”. The air is associated with release of fluid from the esophagus. The space created is large, occupying about one-third of the intra-test volume, and is thought by the authors to act as a diffusion bubble to move oxygen and carbon dioxide between it and the fluid-filled perivisceral coelom. The authors note that the increased PO2 in the coelomic fluid during air-exposure leads to respiratory acidosis that, unlike in an air-exposed crustacean that has osmoregulatory capability, is uncompensated for in an osmo-conforming sea urchin. How does air enter the gut? The most likely explanation is via the anus: as fluid drains from the mouth below, its volume is compensated for by air entering the anus above. The presence of such a “lung” may be especially beneficial during seasonal gonadal maturation when gas exchange within the deep gonadal tissues is potentially most reduced. The authors do not discuss whether one “gut-full” of air is sufficient to last through a normal tidal cycle of air-exposure. If not, could the air be refreshed through further loss of fluid from the mouth? Finally, on re-immersion does the air bubble out from the anus? Burnett et al 2002 Biol Bull 203: 42.

NOTE most crustaceans are good osmoregulators, and this ability to regulate ionic titre correlates with a capacity to compensate for acid-base disruption. During normal immersion in water in a sea urchin, CO2 is eliminated via diffusion from the extensive surface area offered by the extended tube feet; in air, the tube feet are withdrawn and/or collapsed and PCO2 levels increase

Note in the air-exposed individuals above the low-tide
water level, gas exchange by diffusion would likely be
greatly impeded by collapsed spines and withdrawn tube feet

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Research study 1

Most species of echinoderms are intolerant of low salinities and west-coast sea urchins are no exception.  A study on purple urchins Strongylocentrotus purpuratus collected from Moss Beach, California and nearby areas shows that exposure to 70% seawater for as little as 3h can cause deleterious effects, both on adults and on developmental stages.  Giese & Farmanfarmaian 1963 Biol Bull 124: 182. 

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pH & ocean acidification

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Research study 1

histogram showing pH effects on developiing sea-urchin larvaeThere is growing interest in effects of increased ocean acidification accompanying climate change, but what is not generally known is that predicted century-end pH values are presently manifested in certain west-coast upwelling systems.  For example, even in Santa Barbara Channel, an area not known for intense upwelling, researchers from University of California, Santa Barbara have measured day-to-day pH fluctuations of up to -0.7 units.  The extent of effects of low pH on development of purple urchins Strongylocentrotus purpuratus is examined by rearing 4-arm pluteus larvae at 3 pH levels down to pH 7.7 and measuring body at Days 3 and 6 of development.  Results show no disruption of normal developmental pattern, but larvae in the lowest pH treatment are significantly smaller than ones raised under control conditions (see sample graph).  The size reduction is small, only 7-13% but, as noted by the authors, may have implications for swimming and feeding.  Yu et al. 2011 J Exper Mar Biol Ecol 400: 288.

NOTE  the differing pHs are obtained by equilibrating seawater with C02 of 370, 1000, and 1450ppm.  The first is a control, and the others give pHs of 7.7 and 7.5, respectively  

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Research study 2

photographs of larvae of mussel Mytilus trossulus and sea urchin Strongylocentrotus franciscanusA similar investigation but with broader goals is undertaken by researchers at the Bamfield Marine Sciences Centre, British Columbia who attempt to quantify the potential for  evolutionary response to ocean acidification in sea urchins1 Strongylocentrotus franciscanus and mussels Mytilus trossulus.  The measures chosen to assess this are levels of phenotypic and genetic variation in larval2 size (arm and shell lengths, respectively) for predicted future atmospheric carbon-dioxide levels.  Estimates of maternal and paternal sources of variation provide indices of potential heritability, and are used in simulations of multi-generational selection to the year 2100 to assess the potential of each species for adaptive evolution.  This is a tall order, and the authors should be commended for their ambitious research aims. Larvae of each species are cultured from hatching to start of feeding (65h for M. trossulus and 5d for S. franciscanus) at pH levels of 8.3 (ambient) and 7.9 (predicted for year 2100).  Initial growth results are presented here only for sea urchins S. franciscanus, but levels of phenotypic and genetic variationin this species are found to be much greater than in mussels M. trossulus.  Note in the graph that effects of increased acidity on growth are about -2%, and hereditary effects come mostly from maternal contributions. Estimates of heritability over 45 overlapping generations (to year 2100) are up to 140 times greater for sea urchins than mussels. The presumptions3 and analyses in the study are complex, and readers are invited to assess for themselves the level of success achieved.  In using this approach, the authors have attempted to sidestep the criticisms leveled at other similar studies that simply assess acute responses to pH without incorporating an estimated time-scale for adaptation.  Sunday et al. 2011 PLoS ONE 6 (8): e22881.

NOTE1  the selection of such disparate species appears to be based on their mutual economic importance to the west-coast mariculture industry

NOTE2  larvae are cultured in a large factorial-design cross with 9 females and 10 males for S. strongylocentrotus and 10 males and 4 females for M. trossulus.  Culture temperature is 12oC

NOTE3  for example, larval fitness is estimated from literature reports on survival in relation to larval duration in the plankton (mortality from predation, advection, starvation, and disease).  On these bases, longer developmental time is equated with decreased fitness

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Research study 2.1

histogram comparing fertilisation success in red sea-urchins Strongylocentrotus franciscanus under different carbon-dioxide conditionsA study done at the Bamfield Marine Sciences Centre, British Columbia relating to ocean acidification involves the effects of pH on fertilisation success in red sea-urchins Strongylocentrotus franciscanus.  The researchers avoid the pitfalls of similar previous studies by employing biologically realistic egg-sperm contact times over a wide range of sperm concentrations.  The researchers allow a 30sec window for fertilisation to occur for each treatment, then wait for 3h before assessing percentage success.  Results show that elevated pC02 decreases the range of sperm concentrations over which high fertilisation success occurs.  The authors conclude that elevated future CO2  concentrations may exacerbate present-day limitations on fertilisation success stemming from water turbulence and low population density. Reuter et al. 2011 Global Change Biol 17: 163.

NOTE  3 pH treatments (8.0, 7.8, and 7.6) are created by bubbling C02 into seawater at 400, 800, and 1800ppm concentration, respectively, representing present and predicted future (yr 2100 and yr 2300) conditions

NOTE  the authors cite many studies worldwide on C02 effects on sperm motility and fertilisation success in shallow-water invertebrates, and note the high variability in the results possibly relating to inappropriate and/or inconsistent methodologies.  The authors actually provide a correction for their own published data on fertilisation efficiencies at Reuter et al. 2011 Global Change Biol 17: 2512

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Research study 3

graph showing effect of 6d exposure to different pHs on growth of larvae of purple sea-urchins Strongylocentrotus purpuratusgraphs showing effect of pH on lipid utilisation during early development of purple urchins Strongylocentrotus purpuratusWhat may not be commonly known with respect to ocean acidification and global warming is that in regions of the California coast natural upwelling events regularly bathe inshore areas with water of pHs1 equivalent to, or higher than, those predicted by Climate-Change experts to occur 100yr in the future.  A question raised by scientists from the University of California, Santa Barbara and University of Aukland with respect to this relates to the extent of plasticity of development in sea urchins Strongylocentrotus purpuratus, given their past evolutionary contact with lower pH waters.  The researchers rear larvae for 6d to the 4-arm pluteus stage in culture pHs2 of 8.1 (control), 7.7, and 7.5, and monitor rates of growth and lipid/protein/phospholipid utilisation at intervals over that period.  The larvae are not fed in culture in order to force them to use their endogenous lipid stores.  Results show a significant reduction in growth at elevated pCO2 levels (see sample graph for a single female on Left) but with no associated change in lipid/protein utilization rates (sample graphs on Right for the same female).  Initial phospholipid contents of the eggs are later observed to affect larval size, but only at control pCO2 levels, not elevated ones.  The authors suggest that in upwelling regions with relatively high natural levels of pCO2, purple urchins may have an inherent physiological plasticity to resist exposure to moderately low pHs (at least during early development).  The study provides a useful introduction to the growing subject of ways in which impending ocean acidification may affect the physiology3 of marine invertebrates.  Matson et al. 2012 Biol Bull 223: 312.

NOTE1 pHs as low as 7.6 have been recorded during such upwelling events

NOTE2   these are obtained by bubbling seawater with C02 at concentrations of 365uatm (pH 8.1), 1039uatm (pH 7.7, and 1444uatm (pH 7.5)

NOTE3  an interesting sidebar comment by the authors is that meta-analyses show that data on responses of a variety of marine species to ocean acidification vary from positive or negative but are, on average, negative

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Research study 3.1

A consortium of researchers from Washington, Norway, and Sweden culture purple sea urchins Strongylocentrotus purpuratus from 2-cell embryos to 7d pluteus larvae1 in three pCO2 conditions and monitor growth effects. The 3 CO2 levels are 350µatm (pH 8.1), equivalent to 1990 ocean conditions, 700µatm (pH 7.9) based upon predicted levels for year 2100, and 3,000µatm (pH 7.2) based upon year 2300 expectations. Results show variable levels of budding2 in all 3 treatments: non- significant levels at Days 2-3 in the control treatment group for offspring of one of 2 adult females, and significantly higher level for another adult female at Day 4 in the 700 and 3,000µatm treatments. At this time some 56% and 72% of the population, respectively, are budding. The buds mostly break free and do not survive, and their significance is not known3. Chan et al 2012 Mar Biol DOI 10.1007/s00227-012-2103-6. Photograph courtesy the authors.

NOTE1 for some reason the researchers term all post-fertilisation stages “larvae”, yet this stage is not reached until after gastrulation. At the culture temperature used here (14oC), a “prism” or early larval stage would likely not be reached until 3d post-fertilisation, so budding recorded earlier than this, for example, at 2-3d post-fertilisation, is likely occurring in blastula/gastrula stages, not the larval stage

NOTE2  “budding” in biology is used to describe asexual (clonal) production of a new individual by an organism. In this study, none of the “buds” is monitored over time to determine whether they are viable, or just a type of abnormal growth. For more on larval budding in echinoderms see SAND DOLLARS

NOTE3  the authors title their report “Ocean acidification induces budding in larval sea urchins” but, like most other investigations that purport to relate to climate change/acidification, this title is somewhat of an exaggeration. First, the protocol is questionable. Four female S. purpuratus only are collected in California, photograph of 7d pluteus larva showing bud formationtransported to Sweden, and spawned and cultured in Swedish seawater. A control culture using California seawater is not included. The test is acute, lasting 1wk only and incorporating no long-term time element, such as would occur naturally with global climate change. In each of 2 experiments, eggs from only 2 adults are used. Results are variable and only partially convincing. The authors may simply be witnessing acute effects arising from use of Swedish seawater. In answer to this criticism, they note that acute exposure to pH levels of the magnitude used here is known to occur naturally in the upwelling habitats occupied by purple urchins off the California coast (see RS3 above). But given that this is true, what is the value of this short-term experiment? Much more useful, if it were possible, would be a longer-term study maintaining adult populations into successive generations while exposing them to gradually increasing CO2 concentrations and then monitoring for effects

7d post-fertilisation pluteus larva at 3,000 µatm CO2 with developing bud. The adult rudiment is
visible within the larva, but at this stage of development (at 14oC) larval arms should be present. Why is
arm suppression or loss not mentioned by the authors as a possible effect of elevated CO2 treatment

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Research study 4

In a related study1 to Research Study 3 above, members of the same research group at University of California, Santa Barbara investigate the capacity of purple urchins Strongylocentrotus purpuratus to adapt to increased levels of ocean acidification expected from future climate change.  Larvae are bred from adults collected from 2 locations2 that differ markedly in their natural pH levels, and larval size is again used as an expression of fitness.  In this study, male and female urchins are cross-bred from the 2 sites.  Since males contribute only genetic material, this enables the genetic variation for size of larvae to be teased out and compared for males from low- and high-pH sites.  Thus, if there is local adaptation to pH, offspring of males from the low-pH site would be expected to produce larger larvae under low-pH experimental conditions than offspring from males from the high-pH site.  Larvae are reared for 5d (just to the end of the nonfeeding stage) under 2 pH levels: 8.0 for present ocean conditions and 7.6 for expected year 2050 conditions.   Results show that larvae, contrary to the researchers' prediction, are actually about 10% smaller under future conditions than under present-day conditions, but that genetic variability is higher, indicating greater scope for heritability of size (i.e., evolution).  Comparison of growth performance of larvae cultured from adults from the 2 locations also suggests a slightly greater scope for growth of larvae cultured from adults from lower pH natural conditions (pH~7.9) than from normal pH conditions (pH~8.1).  There thus appears then to be local adaptation to different pH conditions in the field.  The concept and design of the experiments are admirable, and the authors are to be complimented on their fine work3Kelly et al. 2013 Global Change Biol 19: 2536.

NOTE1  for whatever reason the authors do not cite the previous study in their paper

NOTE2  upwelling in some California locations brings colder, lower pH waters to the surface, in some cases with pHs as low as projected for the end of this century

NOTE3 in a later publication, members of this research group form a large consortium with several other scientists to explain the aims, intentions, and present research activities taking place in CCLME (California Current Large Marine Ecosystem). The Ecosystem encompasses the geographical region of upwelling used in the present Research Study north to central Oregon. It employs a sensor network at 6 intertidal sites that provides continuous data on ocean pH, pCO2, alkalinity, temperature, salinity, and currents that are matched with assessments of physiology, ecology, and genetics of resident marine invertebrates. CCLME represents a cohesive programme of investigation into acidification effects related to global warming. Hofmann et al. 2014 Biogeosciences 11: 1053.

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Research study 5

graphic illustration of pH effects on transcriptomic responses in purple sea-urchins Strongylocentrotus purpuratusWhat can transcriptomics1 tell us about the level of metabolic activity in an organism, such as a sea-urchin embryo, being challenged by exposure to lower pH seawater?  Will levels in offspring of parents from upwelling areas that are regularly exposed to fluctuating2 low-pH conditions differ significantly from ones from more steady higher pH conditions?  These questions and others are addressed by University of California Santa Barbara researchers using developmental stages of purple urchins Strongylocentrotus purpuratus cultured in 3 pCO2 levels to reflect present-day pH ("high"=8.0 and "mid"=7.8) and predicted future ocean conditions ("low"=pH 7.6).  Results show an ability of gastrulae (44h post-fertilisation) and early plutei (92h) to maintain calcification3 activity under "mid" pH conditions, but this ability falters in simulated future "low" pH conditions.  Thus, transcriptomic response is actually greater under present-day pH regimes than under simulated future conditions.  The authors identify 4 cellular processes in gastrulae most affected by elevated pCO2 level: calcium homeostasis, ion transport, cell signaling, and transcription.  Of 153 genes identified as being differentially expressed in gastrulae in the mid-pH culture (7.8), 48 are down-regulated and 105 up-regulated relative to the high pH culture of 8.0.  In comparison, only 10 genes are identified as being differentially expressed in the low-pH future-culture conditions (7.6), and all are down-regulated (see “heatmap” illustration).  Three of these 10 genes have previously been identified as transport proteins involved in pH regulation.  Given that present-day upwelling-induced reductions in pH are moderate and temporary, the gastrulae could recover, but on the basis of the transcriptomic evidence the authors doubt the ability of the gastrulae to cope with more drastic future CO2-driven decreases in pH.  In the plutei only a handful of genes  are differentially expressed across all pH levels, indicating a generally less robust transcriptomic response to decreased pH levels.  The researchers consider these results as only temporary, and are now on a quest to find purple-urchin habitats with even more variable pH regimes.  The present research makes an excellent contribution to the topic of ocean acidification and the researchers are to be congratulated.  Evans et al. 2013 Mol Ecol 22: 1609.

NOTE1  this is the measure of all RNA molecules being produced in a cell and is thus an indication of gene expression at any given time.  The processes of RNA extraction and labeling,  and quantification and statistical analyses of gene expression are complex and labour intensive

NOTE2  natural fluctuations in pH in the area of the Oregon coast from which the broodstock urchins are collected range from 8.4 to 7.5.  Some of the fluctuation owes to daily respiration/photosynthetic cycles, but extreme low pHs are mostly credited to upwelling

NOTE3  the larval skeleton begins building in the gastrula stage in the form of calcareous spicules, and culminates in the pluteus stage in the form of calcareous body framework and arm rods

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Research study 6

histogram showing sample data comparing skeletal-rod lengths in sea-urchin larvae Strongylocentrotus purpuratus grown in normal and high carbon-dioxide conditionsTo what extent is the genetic capacity for adaptation modified in purple urchins Strongylocentrotus purpuratus that have evolved in naturally fluctuating pH levels in west-coast upwelling areas?  This question is addressed by researchers at Bodega Marine Laboratory and other laboratories associated with the University of California by attempting to correlate low and fluctuating pH conditions experienced by populations of purple urchins along the California and Oregon coasts with the frequency of occurrence of certain “low pH”-adapted alleles in these same populations. Adult urchins from 7 populations spanning 1200km from central Oregon to southern California are spawned within each population and embryos cultured under 2 pCO2 conditions: 400µatm (present day) and 900 µatm (projected future).  For genomics analyses larvae are sampled at various intervals post-fertilisation from each treatment combination, and mRNA extracted and sequenced for allele frequencies.  In total, the authors examine genetic change1 at almost 20,000 loci in larvae from the 7 geographic populations.  Results show that high pCO2 has little apparent effect2 on development and growth of the larvae, at least not over  the first 17d in culture (see histograms showing whole body skeletal rod length).  In contrast, gene expression is active at this time, most notably in those genes that are involved in mineralisation3, metabolism, and pH regulation.  Thus, a general lack of overt symptoms of pH stress, such as stunted growth, belie an intensity of gene expression suggestive of a large capacity for rapid evolution in face of future ocean acidification.  The research demonstrates the amazing role that transcriptomics is already playing in studies of evolutionary processes in west-coast invertebrates.  Pespeni et al. 2013 Proc Nat Acad Sci 110 (17): 6937; see also review by Pespeni et al. 2013 Integr Comp Biol 53 (5): 857.

NOTE1  comparisons of this sort are made possible by the fact that the complete genome of this species has been known for almost a decade

NOTE2  the authors discuss the absence of this effect in light of contrary findings in other studies, and suggest that it may owe to lower, more natural, larval densities used in their cultures  

NOTE3  based on knowledge of protein components of the skeletal elements and regulatory genes that generate the rods , the authors know of 350 genes involved in sea-urchin skeletal formation

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Research study 7

photograph of purple urchins Strongylocentrotus purpuratus in sandstone hollows in a tidepoolSeawater acidification in combination with warming, both consequences of anthropogenic production of CO2, are investigated by a research group based at University of California, Santa Barbara for effects on skeletal growth, developmental rate, and respiration rate of larval purple sea-urchins Strongylocentrotus purpuratus.   Several significant genomic (transcriptomic) responses are also recorded.  The researchers expose fertilised eggs to combinations of 2 temperatures (13oC and 18oC) and 2 pCO2’s (400 and 1100µatm) and collect gastrulae (30-40h post-fertilisation) and pluteus larvae (55-67h) for analyses.  Results show that simultaneous exposure to high levels of both factors reduces larval metabolism and causes a widespread downregulation of genes that encode histone.  High pCO2, but not temperature, impairs skeletal growth and reduces expression of a number of genes, including one that expresses an important spicule-matrix protein (SM30-alpha protein).  No effects on developmental rates are seen.  The authors discuss their results in the context of impending climate change Padilla-Gamino et al. 2013 Proc Roy Soc B 280: 155.

NOTE  the elucidation of the complete genome of S. purpuratus in 2006  (28,036 putative genes) has created a powerful research tool for such studies

NOTE  with a few exceptions current researchers continue to treat their application of acute levels of pH and temperature as reflective of chronic future conditions.  Such chronic conditions would actually come gradually over many generations, and perhaps be accompanied by not insignificant levels of adaptation.  There is no remedy for the time aspect involved, but at least a mention of the limitations of the predictive ability of such studies would be helpful


Purple urchins Strongyloentrotus purpuratus and
a single red urchin Mesocentrotus franciscanus in
sandstone hollows at Botanical Beach, British Columbia

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Research study 8
  With respect to genomic research on purple urchins Strongylocentrotus purpuratus, a large consortium of mainly California scientists have published a review paper that in timely fashion addresses a number of key issues relating to genomics and ocean acidification, most notably questions surrounding local adaptation to seawater pH. The emphasis in the article is, of course, on purple urchins, but the guidelines for research are applicable to any other “calcified” marine invertebrate, whether its genome is known or not. The article should be considered as “must” reading for anyone interested in doing research in this field. Evans et al.l 2015 Comp Biochem Physiol A 185: 33.
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Water currents

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Research study 1

graph showing effect of current speed on spine angle in red sea-urchins Strongylocentrotus franciscanusSCUBA-diving observations by researchers at Friday Harbor Laboratories, Washington reveal that red sea-urchins Strongylocentrotus franciscanus adopt more streamlined spine-angle shapes in faster current flows.  The streamlining changes the shape of an urchin from typical pincussion-shape to more of a limpet-shape. The authors use experimental flumes to quantify decrease in spine angle in flow speeds of 0-65cm . sec-1 (see graph and photo series below).  Measurements of drag and lift in photograph of red sea-urchin Strongylocentrotus franciscanus with green alga Ulvarealistic models show that streamlined models have less drag but more lift than “normal” models in current speeds between 10-40cm . sec-1, rates that are commonly encountered by sea urchins in the field.  The authors remark that the behaviour, although doubtless contributing to better attachment in high current flows, may lead to reduced capture of drift algae, especially in deeper water.  The algae, which ar trapped on upright spines and then eaten, pass by in quantities directly related to current speed.  In shallower water, the sea urchins tend to feed more directly on attached algae such as kelps.  Stewart & Britton-Simmons 2011 J Exp Biol 214: 2655. Photo series below courtesy the authors.

Red sea-urchin S. franciscanus with
entrapped green algae Ulva sp. 1X

Effect of current speed on spine angle
in red sea-urchins Strongylocentrotus franciscanus. Spine angles range from about 40o up to about 35o down at
the 2 extremes of current speed
photo series showing effect of current speed on streamlining of spines in red sea-urchins Stroongylocentrotus franciscanus    
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Research study 2

graph comparing spine lowering (streamlining) by sea urchins Mesocentrotus franciscanus, Stronglylocentrotus droebachiensis, and S. purpuratus in relation to current velocitygraph comparing effectiveness of sea urchins Mesocentrotus franciscanus, Strongylocentrotus droebachiensis, and S. purpuratus in capturing drift algae The question raised in the foregoing RS1 about possible negative effects of streamlining in high current speeds on food capture is addressed for sea urchins Mesocentrotus franciscanus, Strongylocentrotus purpuratus, and S. droebachiensis by researchers at Friday Harbor Laboratories, Washington. Flow-tank experiments show that all 3 species1 flatten their spines to some extent in fast currents (streamlining), with S. droebachiensis being the most reluctant to lower spines as velocities are experimentally increased, and M. franciscanus being the quickest to do so (see graph on Left). Of the 3 species, M. franciscanus has the largest drag profile, while S. droebachiensis has the least. When food particles2 are added to the flow tank, M. franciscanus is significantly more effective at capturing them than the other 2 species (see graph3 on Right). Note also that S. purpuratus is efficient in capturing particles in “spines up” mode, but this advantage is lost when it lowers its spines in higher velocities. Interestingly, capture of drift food in all 3 species is mainly a function of spines, not tube feet. Once captured, though, the tube feet anchor the bits and transfer them to the mouth. Another factor at play, noted by the authors, is that spine-flattening in higher current velocities actually reduces the thickness of the boundary layer surrounding the urchin, thus potentially bringing more food bits into reach of the tube feet. Finally, measurements of capture efficiency suggest that S. droebachiensis overall is least efficient, to the extent that drift-capture would not represent a viable feeding strategy for it. George & Carrington 2014 J Exp Mar Biol Ecol 461: 102.

NOTE1 the authors remark that neither S. purpuratus nor S. droebachiensis has been shown to exhibit streamlining behaviour in any previous studies

NOTE2 “particles” are 1sq cm or 9sq cm pieces of kelp Costaria costata, known to be eaten by all 3 species

NOTE3 data shown are for larger particles; however, a similar pattern is exhibited for smaller particles

photograph of red sea-urchin Mesocentrotus franciscanus catching drift algae on its spines photograph of purple sea-urchin Strongylocentrotus purpuratus catching debris on its spines photograph comparing relative spine lengths of sea urchins Strongylocentrotus droebachiensis and S. purpuratus
Mesocentrotus franciscanus slewers some drift algae, a juvenile bull kelp Nereocystis luetkeana, on its spines Purple sea-urchin Strongylocentrotus purpuratus also "captures" debris bits that provide protection Two species S. droebachiensis and S. purpuratus show relatively different spine lengths (former is longer)
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