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  Life in the intertidal zone
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Sea-star wasting disease

 

The topic of life in the intertidal zone includes a section on seastar wasting disease considered here, and sections on TEMPERATURE & DESICCATION, WAVES & CURRENTS, SALINITY & OSMOTIC REGULATION, SEASTAR WASTING DISEASE, OCEAN ACIDIFICATION, OTHER PHYSIOLOGICAL STRESSES, COLOUR MORPHS OF PISASTER, and SYMBIONTS presented elsewhere.

 
Research study 1
 

photograph of ochre star Pisaster ochraceus showing lesionRecent mass mortalities of sunflower stars Pycnopodia helianthoides and other species along the west coast, including British Columbia have been attributed to a variety of causes, most popular of which is a condition known as “wasting disease”.  Symptoms include lesions on the skin, bodily disintegration, and autotomy of arms (see photograph for a view of early onset of disease).  Whether this is the same or similar affliction to that described in the present account for ochre stars Pisaster ochraceus by researchers at the Bamfield Marine Sciences Centre, British Columbia is not known.  Results from laboratory and field-caging experiments in this study implicate warm temperature as being an exacerbating influence in the severity of the condition. Observable differences in prevalence exist in localities separated by no more than a few km.  No sex or size differences are evident.  The authors note that theirs is the most northerly report of wasting disease in west-coast sea stars.   Although the authors refer to “disease prevalence”, “infection intensity”, and “pathogen growth”, no causative agent such as bacterium, fungus, or virus has yet been identified.  The authors note the late-summer prevalence of the condition in Grappler Inlet and other areas of Barkley Sound, and comment photograph of Dr. Drew Harvell, Cornell University examining diseased ochre stars Pisaster ochraceuson possible involvement of low-salinity conditions, restricted tidal flushing, and sewage inputs. Bates et al. 2009 Dis Aquat Org 86: 245.

NOTE  autumn 2013 in British Columbia, but similar outbreaks have been reported from other west-coast areas as far south as the Gulf of California

NOTE  this is soon to change, as Prof. Drew Harvell at Cornell University announced in November 2014 that she and her colleagues have successfully isolated and identified the causative agent in wasting disease. It appears to be a virus. The paper is now published and a summary of it is in Research Study 4 below. Photograph of Dr. Harvell and diseased ochre stars courtesy Laura James and Proc Nat Acad Sci 111 (19): 6855


Dr. Drew Harvell examines diseased
ochre stars Pisaster ochraceus

 
Research study 2
 

photograph of sunflower stars crawling rapidly downwards to avoid downwelling of dilute surface watersBut what if some manifestations of the condition are not disease-related but, rather, acute responses to exposure to warm, dilute surface waters being downwelled during autumnal “turnover” periods?  For example, an  area in which mass mortality of sunflower stars was witnessed in late summer/autumn 2013, namely Lighthouse Park in Burrard Inlet, British Columbia, is characterised by seasonal layering of surface waters into a 5-10m deep thermocline/halocline that remains fairly stable during summer.  In autumn the surface layer is turned over by onshore winds in predictable downwelling episodes.  Sunflower stars frequent shallow areas and loathe contact with low-salinity surface layers.  In fact, contact with localised downwelling of such layers is known to cause immediate and fast crawling of Pycnopodia to deeper waters.  In one such incident in late summer in Barkley Sound, British Columbia, a mass exodus of sunflower stars from shallow to deeper waters occurred as surface waters were downwelling, evidenced by swirling turbulence, cloudiness in the water, and typical visual refractiveness of freshwater mixing with high-salinity deeper seawater (for a later incident in Burrard Inlet, B.C. see photograph upper Right and associated video below). In another photograph of sick/diseased sunflower star Pycnopodia helianthoidesincident that occurred in North Pender Island, B.C. in late summer, a large specimen was carried by a SCUBA-diver from the sea bottom through roughly 6m of halocline to the surface, at which time it promptly dropped all of its arms in sequence.  A typical response to stress in sea stars and other echinoderms is a liquefaction of the connective tissues holding the skeletal elements together (described in another section of the ODYSSEY: “CATCH” CONNECTIVE TISSUES).  Within moments arms are lost in sea stars and the bodies of sea cucumbers “puddle”.  Could this be a possible explanation for at least some of the  "wasting disease- type mortalities described for late summer/autumn in British Columbia during the downwelling season?  Photograph above courtesy Donna Gibbs & Vancouver Aquarium.

Sunflower star Pycnopodia helianthoides
showing symptoms of arm dissociation

CLICK HERE to view a video made by researcher Donna Gibbs of the Vancouver Aquarium showing sunflower stars Pycnopodia helianthoides crawling rapidly downwards in apparent escape from downwelling low-salinity waters in Burrard Inlet, British Columbia in August 2009. A description of the event by Aquarium Researcher Jeff Marliave is below Right:

 

Below are photographs of the 2013 event courtesy Jon Martin, Simon Fraser University, B.C. (top photos) and Donna Gibbs, Vancouver Aquarium (bottom photos, taken from a video):

text describing behaviour of sunflower stars Pycnopodia helianthoides when contacted by downwelling dilute surface waters
photograph of rotting sunflower star Pycnopodia helianthoides photograph of rotting sunflower star Pycnopodia helianthoides
Photos of 2 massively degraded sunflower stars Pycnopodia helianthoides at Whytecliffe Park, West Vancouver, B.C. in autumn 2013
photograph of a healthy population of sunflower stars Pycnopodia helianthoides at Hutt Island, Howe Sound, British Columbia photograph of the same area at Hutt Island, Howe Sound, British Columbia a few months later
"Before" and "after" shots of P. helianthoides in the same subtidal region of Hutt Island, Howe Sound, B.C. taken in late summer 2013 and then a few months later
 
Research study 3
 

An undergraduate researcher and colleagues at Friday Harbor Marine Laboratories, Washington provide a description of the progression of wasting disease in a sunflower star Pycnopodia helianthoides.  First comes arm-curling, then a general “deflation” of the body, followed by white lesions that commence at the junctions of the arms with the central disc.  Arms may crawl away from the disc during early disintegration.  The disease culminates with general dissolution of all body parts (see photo series below). The author does not mention the time required for the disease to progress, but 6wk might be a reasonable guess.  Ni et al. 2014 Undergraduate Report Friday Harbor Marine Laboratories, Washington, 17pp.

 
photograph of healthy sunflower star Pycnopodia helianthoides before wasting disease photograph of sunflower star Pycnopodia helianthoides showing symptoms of wasting disease photograph of sunflower star Pycnopodia helianthoides with arm separation and lesions from wasting disease photograph of sunflower star Pycnopodia helianthoides dead and dissolved fromß wasting disease
Healthy Pycnopodia helianthoides Onset of wasting disease: curling/twisting Lesions & disintegration at arm junctions Disintegration & dissolution
 
Research study 4
 

map showing outbreak history for seastar wasting disease on the west coast of North Americaphotographs of seastars Pycnopodia helianthoides and Pisaster ochraceus in various stages of seastar-wasting diseaseThe first definitive report on the pathogen associated with seastar-wasting disease comes from a consortium of 25 researchers, with the senior author based in Cornell University, New York.  The experimental approach involves injecting 0.5ml aliquots of fresh and heat-killed extracts1 of diseased tissues from one set of diseased sea stars, for example, Pycnopodia helianthoides, into non-diseased, apparently healthy individuals of the same species.  In all cases the former inoculum causes symptoms of wasting disease to appear in the otherwise healthy recipients, while seastars receiving the latter injection remain asymptomatic.  The time-scale to wholesale infection is about 2wk.  Injections of extracts of increasing concentration leads to infection of correspondingly increasing magnitude.  Metagenomic2 analysis of extracts from  diseased west-coast species Evasterias troschelii, Pisaster ochraceus, and Pycnopodia helianthoides reveals closest match to a densovirus group known as Parvoviridae.  In field surveys, the virus is consistently more abundant in symptomatic than non-symptomatic seastars, and viral load becomes the main predictor of disease or impending disease.  It is also detectable in plankton, sediments, and other echinoderms (sea urchins, sand dollars, and ophiuroids) and, as a testament to the potential power of metagenomics, has been detected in 72yr-old museum specimens of west-coast seastars Evasterias troschelii and Pisaster ochraceus collected, respectively, at Cape Arago and histogram comparing densovirus load in several species of west-coast asteroidsCoos Bay, Oregon in 1942.  In a survey of 10 west-coast seastar species that are sympatric with the 3 species used in the above transmission experiments, all but Dermasterias imbricata carry a significance load of the virus (see histogram3). The disease is an old one, and the next research questions to ask should relate to the possibility of past, undetected outbreaks and, of course, proximal causes for the present one. Hewson et al. 2014 Proc Nat Acad Sci 111 (48): 17278.

NOTE1
  filtered to include only particles <0.2um in size

NOTE2  also known as environmental genomics, metagenomics is a broad field involving the study of genetic material collected from field samples from every imaginable source, including diseased tissues, polluted rivers and oceans, and so on.  In effect, it provides a reference library to a wide range of microbial genetic sequences, in this case about 50 million of them

NOTE3  the authors include 2 other species in their survey Orthasterias sp., and Astropecten polyacanthus, neither of which were symptomatic, but as each is only represented by a single individual, they are omitted from the graph shown here (i.e., the "asymptomatic" state of a single individual has little significance)

 

 
Research study 4.1
 

A novel approach to the study of sea-star wasting disease in sunflower stars Pycnopodia helianthoides is taken by researchers
at Cornell University, New York. These authors compare body-wall tissues extracted from symptomatic and asymptomatic sea stars obtained during the onset of wasting disease in Puget Sound, Washington (October 2013). The gene-transcription profiles1 of each set of samples are then compared for evidence of differences in tissue stability, metabolic activity, immune responses, and other disease-related features. Not surprisingly, individuals with wasting disease show differential expression of genes2 involved in body-wall tissue maintenance and degradation processes, and metabolic activity in the 2 experimental groups. For example, higher levels of the protein disintegrin, involved in lesion formation and general tissue degradation, are detected in diseased individuals. Puzzling, however, is the finding that expression of immunity-related genes is not enhanced in either group. The biggest differences between the 2 groups are related to gene profiles of associate microorganisms such as Pseudomonas and Vibrio, and relatives. Neither bacterial3 type is implicated in the actual disease itself but, rather, likely in secondary infections arising from tissue degradation in the symptomatic group. The authors’ most significant finding in the study is that wasting disease seems actually to stimulate autocatalytic cell-death processes in the body-wall tissues (apoptosis). Gudenkauf & Hewson 2015 PLoS ONE 10 (5): e0128150.doi:10.1371/journal.pone.0128150.

NOTE1 the term metatranscriptome is used for the combined gene-transcription profiles of host tissues plus any associate microorganisms

NOTE2 the authors actually identify changed levels of expression in several hundred genes, but most of unknown function

NOTE3 wasting disease is caused by a virus, the most promising suspect being a densovirus SSaDV

 
Research study 4.2
 

chart plotting X-fold increases in 12 genes in the transcriptome of sunflower stars Pycnopodia helianthoides in response to presence of wasting disease pathogens being injectedA similar approach is used by a 14-member consortium of U.S. scientists to study transcriptional immunological1 responses to wasting disease in sunflower stars Pycnopodia helianthoides. However, instead of comparing field-collected symptomatic with asymptomatic individuals as in the foregoing Research Study 4.1, these researchers inject virus-bearing extracts from diseased individuals into apparently healthy ones (specimens obtained from sites in Puget Sound, Washington in 2014). Nine days later when disease symptoms appear in the experimental group, coelomocytes are extracted for RNA-sequence analysis. Results show that a number of immune genes2, as well as genes involved in nervous-system processes and tissue remodeling, are differentially expressed in the 2 groups. Of 2,103 genes expressed at higher levels in treated individuals than in controls, the authors identify 17 related to immune response, cytokine production, and cell adhesion, with 13 of these being associated with the first category, immune response (see chart for X-fold increase in 12 of these). The authors note that the transcriptome3 generated here for P. helianthoides is the first of its kind for Class Asteroidea. The information it provides is invaluable for understanding how sea stars respond defensively to wasting disease. Fuess et al. 2015 PLoS ONE 10 (7): e0133053. doi: 10.1371/journal.pone.0133053.

NOTE1 the echinoderm immune system acts through a combination of cellular components (e.g., coelomocytes) and soluble entities (e.g., agglutinins). In function it parallels the immune system of vertebrates (macrophages/lymphocytes and antibodies) and the 2 systems are likely homologous

NOTE2 included are genes involved in Toll (over 200 of these have been identified in sea urchins) signaling pathways, complement cascade, melanisation response, and arachidonic-acid metabolism

NOTE3 the entire transcriptome consists of 29,476 sequences, which the researchers reckon is close to representing the entire gene complement of P. helianthoides

 
Research study 5
 

graph showing abundances of sunflower stars Pycnopodia helianthoides and green sea urchins Strongylocentrotus droebachiensis in areas of Washington and British Columbia before and during large mortality event in 2013map showing sites used for study of post-mortality events involving sunflower stars Pycnopodia helianthoidesA recent addition to the seastar wasting-disease literature from a consortium1 of British Columbia researchers describes post-2013 environmental events in Puget Sound, WA and Howe Sound, BC (see map). The events following the mortality event constitute a trophic cascade involving2, in order, an approximate 90% decrease in sunflower stars Pycnopodia helianthoides, a 400% increase in numbers of green sea urchins Strongylocentrotus droebachiensis, and a significant decline in kelp cover (mainly brown kelp Agarum fimbriatum). The urchins are both preyed upon by sunflower stars, and migrate away from close contact with them, so loss of sunflower stars from wasting disease would be predicted to lead to greater presence of sea urchins, with a resultant depletion of kelp (by 80%). In support of a behavioral explanation for increased post-event presence of sea urchins (rather than predation), the authors point to the synchrony of seastar depletion with the sea-urchin increase (see graph3). If decreased predation were to have been the main cause, numbers of sea urchins would have rebounded much more slowly. What about red sea-urchins S. franciscanus? The authors remind us that this species is much larger than the green species, has longer spines and is thus better defended, and does not show the same avoidance behaviour to sunflower stars. Now, while the events could still be coincidental, evidence for an underlying cause-and-effect relationship is compelling. Note in the graph the 3yr lead time of relative population stability for the two species before the synchronous changes occur. Schultz et al. 2016 PeerJ DOI 10.7717/peerj.1980. Photographs courtesy Donna Gibbs, Vancouver Aquarium Marine Science Centre.

NOTE1 Simon Fraser University, Vancouver Aquarium Marine Science Centre, and Stantec Consulting Ltd. Burnaby

NOTE2 other alterations in commity structure involving cup corals, shrimps, and crabs occurred, but the tri-trophic cascade described is the major one

NOTE3 the data are obtained from over 1500 REEF surveys conducted from Jan 2010 to Nov 2014 in Washington and British Columbia, with an extra 20 sites in Howe Sound, BC (see map). REEF is an organisation based in Key Largo, Florida that promotes interest in conservation of coral reefs and also many types of shallow-water ecosystems worldwide, through educational programmes, discussion foruums, and volunteer survey expeditions REEF

 
photograph of healthy sunflower star Pycnopodia helianthoides Donna Gibbs photograph of healthy sunflower star Pycnopodia helianthoides Donna Gibbs photograph of healthy sunflower star Pycnopodia helianthoides Donna Gibbs
Sunflower star Pycnopodia helianthoides, healthy specimen Virus-infected specimen shows loss of turgor pressure and ruptured body wall Final stages involve autotomisation of limbs and general tissue disintegration
 
Research study 6
 

graph showing recruitment of ochre stars Pisaster ochraceus during the years 2001-2015 on the Oregon coasthistogram comparing seastar predation on sea mussels Mytilus californianus in Oregon before and during period of wasting diseaseA summary of seastar wasting disease is provided by researchers at Oregon State University, Corvallis for ochre stars Pisaster ochraceus at several sites along the length of the state. The disease outbreak commences April 2014 and spreads quickly, with 90% of all individuals being afflicted by September 2014. Infection rates decline through to spring of the following year when, unexpectedly, all areas experience large recruitment (see graph on Left). The authors describe several stages in expression of the disease: 1) arm twisting, 2) body deflation, 3) arm loss, 4) grip loss, and 5) disintegration (see photos below). The researchers consider the proximal cause to be the same or similar densovirus reported by other authors (see RS4 above), but the ultimate cause remains unclear. Warm temperature would have been one possibility, were it not for the fact that the outbreak increased through a general cooling period during spring/summer 2014. As only one example of cascading effects of the ochre-star loss, mussel populations along the coast are enjoying a reprieve from predation through absence of their chief predator (see graph on Right). Menge et al. 2016 PLOS ONE DOI; 10.1371/journal.pone.0157302. Photographs courtesy the authors.

NOTE wasting disease was first seen in summer 2013 in British Columbia and northern California, and quickly spread, eventually to affect some 20 seastar species from Baja California to Alaska

 
Stages in progression of wasting disease in ochre stars Pisaster ochraceus. Photos are 0.3-0.5 life size photograph of ochre star Pisaster ochraceus with early-stage wasting disease photograph of ochre star Pisaster ochraceus with early-stage wasting disease
  Early symptoms include arm-twisting. Compare with asymptomatic individual on Left Subsequent stages include "deflation", caused by loss of most or all coelomic fluid
photograph of ochre star Pisaster ochraceus with early-stage wasting disease photograph of ochre star Pisaster ochraceus with early-stage wasting disease photograph of ochre star Pisaster ochraceus with early-stage wasting disease
Lesion stage of disease progression. Some lesions have penetrated the body wall Later symptoms include progressive loss of "grip" on the substratum. Note stretched tube feet Final stage of disease, where the individual "melts" away caused, in part, by dissolution of connective-tissue
 
Research study 7
 

ochre stars Pisaster ochraceus in a more halcyon timegraph showing survival of ochre stars Pisaster ochraceus afflicted with wasting disease at 4 different experimental temperaturesA similarly recent study by a consortium of researchers on the disease etiology in ochre stars Pisaster ochraceus in Puget Sound and on the outer coast of Washington indicates a somewhat different pattern to that reported for ochre stars in Oregon in RS6 above. The timing is similar, from outbreak in late 2013 and maximum mortality in summer 2014, but warmer temperatures are implicated both correlatively and experimentally. Seasonal monitoring at 16 sites from Puget Sound to the outer coast of the Olympic Peninsula discloses an overall 60% mortality in summer 2014. Water temperatures at that time are 2-30oC warmer than past seasonal averages. Laboratory experiments at Friday Harbor Laboratories involving exposure of apparently asymptomatic1 individuals to 4 temperatures ranging from 12-19oC2 for periods of up to 19d additionally show significantly higher adult mortality at 19oC than at lower temperatures (see graph). Note that temperature effects on juvenile survival in the same treatments are not as severe. A second new finding in this study is a size effect. Larger-sized individuals are afflicted more slowly3 than juveniles, and disease progression occurs at a slower rate. The authors speculate on the widespread effects that loss of this important keystone predator will have on benthic community dynamics in the afflicted areas. Eisenlord et al. 2016 Phil Trans Roy Soc B 371: 20150212. Photographs courtesy the authors.

NOTE1 the researchers think that these individuals were likely to have been exposed to the disease virus in their natural habitat, but not yet showing symptoms

NOTE2 these experimental temperatures represent the range recorded by temperature loggers at the time of peak disease prevalence at the intertidal-study sites

NOTE3 the authors actually state that “while larger ochre stars develop disease signs sooner than juveniles, diseased juveniles die more quickly than diseased adults” . The second part of the statement is fine, but the first is not supported by the graphed data (Fig. 4b in the published paper)

Stages in progression of wasting disease in ochre stars Pisaster ochraceus:

 
image of asymptomatic seastar Pisaster ochraceus image of ochre star Pisaster ochraceus in early stage of wasting disease image of ochre star Pisaster ochraceus in early stage of wasting disease image of ochre star Pisaster ochraceus in early stage of wasting disease
An apparently healthy ochre star Early lesion-stage of wasting disease Later arm-dropping phase Final tissue necrosis and death
 
Research study 8
 

A follow-up paper by a consortium of U.S. researchers that includes several of those involved in the previous RS7, investigates1 effects of wasting disease on subtidal populations of asteroids in 5 inland basins around Vancouver Island and within Puget Sound, and a 6th “basin” along the outer coast of Washington (see map). Data are obtained from 10yr of sighting observations2 by recreational SCUBA divers throughout all areas3, and from concentrated attention at 8 sites in the San Juan Islands using strip transect-survey methods (during spring/summer 2014-15). The first of these data sets focuses on 3 subtidal species, leather stars Dermasterias imbricata, pink sea stars Pisaster brevispinus, and sunflower stars Pycnopodia helianthoides, with observational entries of “Abundance Scores” (“single”, “few”, “many”, “abundant”). The second investigation provides similar abundance data for 11 subtidal species, and health data (defined as presence of lesions and/or arm loss) specically for 3 species: mottled stars Evasterias troschelii, blood stars Henricia spp., and P. helianthoides. Results show a broad spectrum of disease susceptibility both among species and, to some extent, geographically. Abundance of some species actually increases from pre-2013 to 2015 in some species (e.g., D. imbricata, 1.2-1.5-fold over predictions), then returns to known pre-disease levels. In contrast, densities of P. brevispinus decrease in several inshore basins by 65-97%, and in the Outer Coast basin by 100%. Most severely hit overall is P. helianthoides in Central Basin, Northern Straits, and Outer Coast, where abundances in 2015 are <4% of pre-2013 values (see graph on Right). The foregoing synopses represent just a small sampling of the rich summary of data provided. The authors are to be congratulated for these 2 recent and excellent contributions to our understanding of wasting disease in west-coast asteroids. Montecino-Latorre et al. 2016 PLoS ONE 11 (10): e0163190.doi:10.1371/journal.pone.0163190.

map showing study sites for an investigation into wasting disease on the west coast of North America
graph showing counts of sunflower stars Pycnnopodia helianthoides in various ocean basins on the west coast of North America during 2006-2015
 

NOTE1 the authors base their paper on an odd premise regarding wasting disease, that “little detail is known about its impacts to subtidal species”. This may be true for some species, but not strictly so for the subtidal sunflower star Pycnopodia helianthoides, as the authors are well aware that it was among the first west-coast asteroid species to manifest the disease…subtidally

NOTE2 most useful in this regard is information from more than 8000 REEF-sponsored surveys conducted in the study areas during 2006-2015. REEF (Reef Environmental Education Foundation) is an informal organisation of divers and marine enthusiasts committed to ocean conservation, based in Florida, which sponsors and encourages regular surveys the world over by cadres of volunteer “ocean stewards and citizen scientists” http://www.reef.org

NOTE3 the authors include some data for echinoids, for interest sake, as red sea urchins Metacentrotus franciscanus are harvested in tribal fisheries along areas of the Washington coast. Both red and green urchins Strongylocentrotus droebachiensis increased in numbers in most basins after 2013, presumably through loss of their own asteroid predators

 

photographs of a rocky outcropping in the Strait of Georgia, British Columbia before and after decimation of sunflower stars Pycnopodia helianthoides by wasting diseaseViews of a rocky outcropping in the Strait of Georgia, British Columbia before and after decimation of sunflower stars Pycnopodia helianthoides by wasting disease (October 2013 vs. 3wk later). Photographs courtesy the authors and Neil McDaniel, a professional underwater photographer and videographer in British Columbia http://www.neilmcdaniel.com

 
Research study 9
 

An interesting development in the the epidemiology of wasting disease in west-coast sea stars is the identification of a certain allele (known as ins allele) in ochre stars Pisaster ochraceus that appears to be lethal when homozygous but not when heterozygous. In fact, the condition of heterozygosity may actually confer greater fitness, manifested in Pisaster as greater resistance to wasting disease. Researchers from the Universities of Georgia and California assay the occurrence of the allele in 81 symptomatic and 147 asymptomatic P. ochraceus from 9 sites ranging from British Columbia to California. In 69% of infected individuals the allele is homozygous, suggesting a greater susceptibility to the disease. However, these are “here and now” data. The difficulty in interpreting the significance of the mutation is in knowing the details of its evolution, and information on proportional deaths of homo- and heterozygous individuals from wasting disease during past years is lacking. From what limited time-based data are available in the study, the scientists do not see an increase in frequency of the favourable allelic insertion as would be expected. Also perplexing and unhelpful to the understanding of the situation in Pisaster is the fact that the allele has not been identified in other disease-afflicted asteroid species. The authors discuss the relevance of their findings to possible increasing tolerance to heat stress in face of global warming, and how this might relate to resistance to wasting-disease densovirus and other pathogens. Wares & Schiebelhut 2016 PeerJ 4:e1876; DOI 10.7717/peerj.1876.

NOTE an intonic insertion allele harboured in the elongation factor 1-alpha locus

 
Research study 10
 

photographs comparing densities of ochre stars Pisaster ochraceus on Tatoosh Island, Washington in 1986 and 2015Largely for historical interest, a short but interesting review written by researchers from the Universities of Chicago and Washington is included here. The paper is a naturalists account of wasting disease in ochre stars Pisaster ochraceus, with etiological details of appearance and distribution, and comments on ecological impact. Wasting disease has reduced populations of ochre stars at some locations by over 90%, from densities of about 7 individuals per sq m in the 70’s to a fraction of that now (see photographs of a study location on Tatoosh Island, Washington). The authors cite several examples of other echinoderms, including sea urchins and crown-of-thorns sea stars, that have also suffered mass mortalities through disease. Paramount in everyone’s minds is whether populations of ochre stars and 8 related sea-star species also afflicted can fully recover from the disease, and what the ecological implications will be for west-coast shores in the absence of the chief predator of sea mussels Mytilus californianus. The authors joke that at one time, in their efforts to remove all ochre stars to monitor effects on sea mussels and other community members, Robert Paine and his students also were a type of “pathogen”. But this was small scale stuff; present-day wasting disease will have large-scale geographic effects of a magnitude and complexity that can only be guessed at. Pfister, Paine, & Wootton 2016 Nat Hist Notes Front Ecol Envir 14 (5): 285; photographs courtesy the authors.

NOTE of the 3 authors listed the first and last are former doctoral students of Robert Paine, whose contribution to west-coast marine ecology has been inestimable (for more information on his work see LEARNABOUT/SEASTAR/keystone species). Paine died in 2016, so this note entitled, “The iconic keystone predator has a pathogen” is one of his final contributions to a subject that occupied his research attention for more than 6 decades and, as such, the article bears a certain poignancy and a sense of loss

 

 

Images of one of Paine's study sites on Tatoosh Island, Washington comparing densities
of ochre stars Pisaster ochraceus in Augus 1986 (top) and August 2015 (bottom). Sea
stars are plentiful in the top image, but absent in bottom. A clue to how recent
the sea stars have been missing from the site is in plain view...can you spot it?

answer to question posed in Research Study 10 in A SNAIL'S ODYSSEY about sea-star wasting disease

 
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