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North Pacific Marine Science Organization

An unusual gelatinous plankton event in the NE Pacific:
The Great Pyrosome Bloom of 2017
by Richard Brodeur, Ian Perry, Jennifer Boldt, Linnea Flostrand, Moira Galbraith, Jacquelynne King,
James Murphy, Keith Sakuma and Andrew Thompson
In the winter of 2016, and continuing into summer 2017,
people exploring the open ocean beaches of northwestern
North America were surprised and puzzled to find strange
gelatinous creatures littering the shoreline. These creatures
turned out to be colonies of the pelagic tunicate Pyrosoma
atlanticum (Fig. 1). This species is common in warm open
ocean waters throughout the tropics, but along the west
coast of North America it has been common only as far

Fig. 1

north as southern California, and is rarely seen north of the
state. However, in the past year these tropical tunicates
were highly abundant in the waters from Oregon to British
Columbia, and occurred in scientific samples as far north as
the Gulf of Alaska. In this report, we examine the
magnitude and extent of this anomalous event in the NE
Pacific, suggest possible causes, and describe some
potential ecosystem implications of this bloom.

A) Close-up of pyrosomes caught in the Gulf of Alaska; B) a large catch of pyrosomes from a pelagic survey off Oregon, C) pyrosomes on a
beach off Oregon in November 2017, and D) medusafish (Icichthys lockingtoni,) found in the body cavity of a pyrosome caught in pelagic surveys
off California.

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Routine plankton surveys along the continental shelf of
Vancouver Island began to collect pyrosome individuals
(less than 5 mm in length) and small colonies (greater than
4 cm in length) in spring and summer 2016. By February
2017, plankton surveys were catching pyrosome colonies
up to 15 cm in length from the continental shelf along the
west coast from Oregon to Vancouver Island. By late
spring and summer 2017, the pyrosome event was in full
bloom, with very high abundances and large colonies
occurring from California to Alaska and into the central NE
Pacific, including over open ocean seamounts.

What are pyrosomes?
Pyrosomes (Greek for “fire bodies” because of their
bioluminescence) are a small group of pelagic tunicates, of
which eight species in three genera have been described
worldwide. They are colonial, with each colony comprising
thousands of individual clones encased in a rigid gelatinous
‘tunic’ that is open at one end (Hirose et al., 2001).
Individuals draw water from the outside surface and release
water into the hollow core of the colony. This provides the
colony with a type of hydrostatic ‘skeleton’ and the means
for jet propulsion. Although individual pyrosomes are
small (mm in size), their colonies can reach lengths of
several meters; the species of this NE Pacific event is
known to reach over 80 cm in length. Colonies undertake
diel vertical migrations, sometimes over 700 m depth
(Anderson and Sardou, 1994), and have among the highest
phytoplankton clearance rates of any zooplankton grazer
(Perissinotto et al., 2007). It has been suggested that
internal lipid accumulation by pyrosomes is limited, with
colonies instead using their food intake to drive high
biomass turnover (Perissinotto et al., 2007).

Potential implications of this pyrosome event
The causes of this extraordinary event are unknown.
Individuals may have been advected into the NE Pacific
during the marine heat wave of 2014–2015 and the strong
El Niño in early 2016. They may have found an
environment in transition between these very warm
conditions and a return to normal conditions in 2017, which
provided sufficiently warm temperatures and ample food for
their growth and reproduction to accelerate. The causes of
this event remain under investigation but recent (November
2017) observations of small pyrosomes washing up on west
coast beaches similar to those seen in the winter of
2016/2017 suggest that conditions may be favorable for
another bloom in the summer of 2018 (Fig. 1).

The 2017 Pyrosome event in the NE Pacific
Over the past three decades, P. atlanticum had occurred
regularly in offshore midwater trawl surveys off southern
California, but in 2012 there was a notable increase in their
numbers coincident with large abundances of salps (another
pelagic tunicate) (Wells et al., 2017). While their numbers
in 2013 were much reduced, pyrosome abundance
dramatically increased in 2014 and 2015 resulting in them
being the dominant organism collected off the shelf break of
California (Sakuma et al., 2016). Starting in June 2014,
they occurred in pelagic trawl surveys in offshore waters of
southern Oregon, moving progressively northward in the
summer of 2015 and 2016, but still in waters off the shelf
break. Collections were made using near-surface or
midwater trawls from research surveys conducted by the
National Marine Fisheries Service (NMFS), NOAA and
Fisheries and Oceans Canada (DFO) from May through
September of 2017 from southern California to the northern
Gulf of Alaska (Fig. 2). Pyrosoma atlanticum was found at
most sampled stations in these surveys, including high
catches on the continental shelf and close to shore.
Densities in some trawls were extraordinary, exceeding
60,000 kg/km3 at locations off Oregon, over 200,000
kg/km3 off Vancouver Island, and over 150 kg/km3 off SE
Alaska (Fig. 2). Catches were often so high that research
nets were ripped open due to the high biomass, and some
stations easily sampled in previous years had to be aborted
in 2017. The varying catch rates demonstrate that the
distributions of pyrosomes were not continuous along the
continental shelf, but that they tended to occur in clusters,
possibly associated with specific oceanographic conditions
(currently under investigation).

Pyrosome colonies were visible at the surface, and coated
oceanographic sampling gear and clogged fishing nets and
hooks throughout this region. Substantial negative impacts
have been reported on many different commercial and sport
fishing operations from Oregon to SE Alaska, including
salmon troll, shrimp and fish bottom trawl gear (Fig. 3A).
Estimates of the economic impact of this bloom on lost or
spoiled fisheries are not available but anecdotal reports
suggest that they may have a substantial negative impact to
coastal fisheries of the NE Pacific.
The impacts of this event to the marine ecosystems of the
NE Pacific are also being studied. Such a high biomass of
easily captured prey has obvious potential for marine
predators and integration into the food webs of high trophic
levels. However, the low accumulation of lipid stores in
pyrosomes (Perissinotto et al., 2007) suggests that they
may be a sub-optimal prey item. Studies of pyrosomes in
their normal tropical habitats show that numerous fishes,
seabirds, and marine mammals can consume pyrosomes
(Harbison, 1998). Fishers along the west coast of North
America during the peak of this event reported finding
pyrosomes in the stomachs of Pacific halibut, rockfishes,
sablefish, and other demersal fish species, and in juvenile
and adult Pacific salmon and other pelagic forage fishes
(Brodeur et al., in press). A beached fin whale in
Washington State had numerous pyrosomes in its stomach
(Fig. 3C). Pyrosomes have also been observed in the NE

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Fig. 2

North Pacific Marine Science Organization

Distribution and density (kg km–3) of pyrosomes
from A) NMFS Gulf of Alaska surveys during
summer of 2017 (July 4–August 16, 2017). B)
DFO integrated pelagic ecosystem survey (July
19–August 2, 2017), C) NMFS coastal pelagic
fish survey (June 25–August 9), and D) NMFS
coastwide Pacific hake survey (June 26–
September 6, 2017; data courtesy of NWFSC
FEAT group). Inset shows relative locations of
the panels in the Northeast Pacific Ocean. White
dots depict samples without pyrosomes and
yellow circles are scaled by pyrosome density
(note that the scale differs in each plot). In panel
A, solid circles are from surface trawls and open
circles from midwater trawls.

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B

A
Fig. 3

C

A) Pyrosomes caught on salmon fishing gear off British Columbia, B) pyrosomes being consumed by sea urchins (photo taken by ROV Hercules
in Quinault Canyon, off Washington State, courtesy of Ocean Exploration Trust), and C) pyrosomes taken from stomach of fin whale (courtesy
Jessie Huggins, Cascadia Research, Olympia, WA).

Pacific being eaten by benthic animals such as sea
anenomes, crabs, sea urchins and sea stars (Archer et al., in
Press), even at bottom depths of several hundred meters
(Fig. 3B). The impacts of these very high biomasses of
pyrosomes that die and sink to the bottom, drawing down
oxygen concentrations as they decompose, is unknown, but
the die-off of these blooms has the potential to provide a
substantial input of carbon to the benthic food web (Lebrato
and Jones, 2009). An additional positive effect has been the
observation that some pelagic fishes (medusafish and
juvenile rockfish) have been seen living inside the tubes of
pyrosomes and potentially consuming part of the pyrosomes
in coastal waters (Fig. 1D), thus providing a possible pelagic
refugium from predation and source of food for these fishes
(Janssen and Harbison, 1981).

unknown, but warrant further investigation.
Conclusions
In the past few years, anomalous ocean conditions in the
NE Pacific, including the marine heat wave (Bond et al.,
2015; Di Lorenzo and Mantua, 2016), have been
accompanied by unusual occurrences of species (Perry et
al., 2017). Some of these occurrences were isolated events
(e.g., first ever record of a Pacific angel shark in British
Columbia waters in 2016; Perry et al., 2017); whereas,
others are broad both spatially and temporally, such as the
extended toxic algae blooms and consequent marine
mammal deaths in 2015 (McCabe et al., 2016). The 20162017 bloom of pyrosomes was also a large-scale event and
is expected to last into 2018. Both positive and negative
impacts of the pyrosomes are expected to occur, however,
the cumulative impacts of this event are not known but are
presently being investigated in different laboratories along
the west coast of North America. There is more to learn
about how ocean conditions are linked to these events and
the implications of these blooms on the trophodynamics of
the Northeast Pacific marine ecosystems. Projected climate
change in the coming decades may lead to anomalous
events such as the pyrosome bloom becoming more
common in the future, requiring continuing monitoring to
assess its impacts.

Previous work on the feeding of P. atlanticum in tropical
waters has found a preference for phytoplankton cells
greater than 10 µm in diameter (Perissinotto et al., 2007).
The diet composition of this species in the more productive
coastal waters of the NE Pacific is unknown but several
studies are underway to examine this. The very high
filtration rates may also reduce phytoplankton biomass
locally when abundances of pyrosomes are very high (Drits
et al., 1992), although how extensive this grazing pressure
may have been in 2017, and its implications for coastal
productivity during the NE Pacific event, are presently
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Lebrato, M., Jones, D.O.B. (2009) Mass deposition event of
Pyrosoma atlanticum carcasses off Ivory Coast (West
Africa). Limnol. Oceanogr. 45: 1197–1209.
McCabe, R.M., Hickey, B.M., Kudela, R.M., Lefebvre, K.A.,
Adams, N.G., Bill, B.D. Gulland, F.M.D., Thomson, R.E.,
Cochlan, W.P., Trainer, V.L. (2016) An unprecedented
coastwide toxic algal bloom linked to anomalous ocean
conditions, Geophys. Res. Let. 43: 10,366–10,376,
doi:10.1002/2016GL070023.
Perissinotto, R., Mayzaud, P., Nichols, P.D., Labat, J.P. (2007)
Grazing by Pyrosoma atlanticum (Tunicata Thaliacea) in
the south Indian Ocean. Mar. Ecol. Progr. Ser. 330: 1–11.
Perry, R.I., King, S., Boldt, J., Chandler, P. (2017) Unusual
events in Canada’s Pacific marine waters in 2016. In
Chandler, P., King, S., and Boldt, J. (Eds.) State of the
physical, biological and selected fishery resources of
Pacific Canadian marine ecosystems in 2016. Can. Tech.
Rep. Fish. Aquat. Sci. 3225: 243 + vi pp.
Sakuma, K.M., Field, J.C., Mantua, N.J., Ralston, S.,
Marinovic, B.B., Carrion, C.N. (2016) Anomalous
epipelagic micronekton assemblage patterns in the neritic
waters of the California Current in Spring 2015 during a
period of extreme ocean conditions. Calif. Coop. Ocean.
Fish. Invest. Rep. 57: 163–183.
Wells, B.K., Schroeder, I.D., Bograd, S.J., Hazen, E.L., Jacox,
M.G., Leising, A., Mantua, N., Santora, J.A., Fisher, J.,
Peterson, B., Bjorkstedt, E., Robertson, R.R., Chavez, F.P.,
Goericke, R., Kudela, R., Anderson, C., Lavaniegos, B.E.,
Gomez-Valdes, J., Brodeur, R.D., Daly, E.A., Morgan,
C.A., Auth, T.D., Field, J., Sakuma, K., Mcclatchie, S.,
Thompson, A.R., Weber, E.D., Watson, W., Suryan, R.M.,
Parrish, J., Dolliver, J., Loredo, S., Porquez, J.M., Zamon,
J.E., Schneider, S.R., Golightly, R.T., Warzybok, P.,
Bradley, R., Jahncke, J., Sydeman, W., Melin, S.R.,
Hildebrand, J., Debich, A.J., Thayre, B. (2017) State Of
The California Current 2016–17: Still anything but
“normal” in the North. CALCOFI Rep, 58: 1–55.

References
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(Tunicata, Thaliacea): diel migration and vertical
distribution as a function of colony size. J. Plankton Res.
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Archer, S.K., Kahn, A.S., Leys, S.P., Norgard, T., Girard, F.,
Du Preez, C., Dunham, A. (In press) Pyrosome
consumption by benthic organisms during blooms in the
NE Pacific and Gulf of Mexico. Ecology.
Bond, N.A., Cronin, M.F., Freeland, H., Mantua N. (2015)
Causes and impacts of the 2014 warm anomaly in the
NE Pacific, Geophys. Res. Lett. 42: 3414–3420,
doi:10.1002/2015GL063306.
Brodeur, R.D., Hunsicker, M.E., Hann, A., Miller, T.W. (In
press) Effects of warming ocean conditions on feeding
ecology of small pelagic fishes in a coastal upwelling
ecosystem: a shift to gelatinous food sources. Mar. Ecol.
Prog. Ser.
Di Lorenzo, E., Mantua, N. (2016) Multi-year persistence of
the 2014/15 North Pacific marine heatwave. Nature
Climate Change, published online: 11 July 2016
DOI:10.1038/nclimate3082.
Drits, A.V., Arashkevich, E.G., Semenova, T.N. (1992)
Pyrosoma atlanticum (Tunicata, Thaliacea): grazing
impact on phytoplankton standing stock and role in organic
carbon flux. J. Plankton Res. 14: 799–809.
Harbison, G.R. (1998) The parasites and predators of
Thaliacea. In: Bone Q. (Ed.) The biology of pelagic
tunicates. Oxford University Press, Oxford, pp. 187–214
Hirose, E., Ohshima, C., Nishikawa, J. (2001) Tunic cells in
pyrosomes (Thaliacea, Urochordata): cell morphology,
distribution, and motility. Invert. Biol. 120: 386–393.
Janssen, J., Harbison, G.R. (1981). Fish in salps: the
association of squaretails (Tetragonurus spp.) with pelagic
tunicates. J. Mar. Biol. Assoc. U.K. 61: 917–927.

Dr. Richard Brodeur (Rick.Brodeur@noaa.gov) is a Research Fisheries Oceanographer working in the Fish
Ecology Division of the Northwest Fisheries Science Center, NOAA Fisheries, based in Newport (Oregon,
U.S.A.). Ric began his career working on early life history and recruitment dynamics of walleye pollock in the
Gulf of Alaska and Bering Sea for the Alaska Fisheries Science Center and became interested in jellyfish
following their dramatic increase in that ecosystem. He has published on a variety of topics ranging from
satellite oceanography to fisheries acoustics, but has focused much of his research on feeding and food web
interactions in the pelagic ecosystem. Ric has been heavily involved in PICES, serving on several committees and
expert groups and organizing a number of topic sessions and workshops at past Annual Meetings.
Dr. Ian Perry (Ian.Perry@dfo-mpo.gc.ca) is a Research Scientist with Fisheries and Oceans Canada at the
Pacific Biological Station in Nanaimo and the Institute of Ocean Sciences in Sidney, BC. His research expertise
includes the effects of the environment on finfish and invertebrates; the structure and function of marine
ecosystems; ecosystem-based approaches to the management of marine resources; the human dimensions of
marine ecosystem changes; and scientific leadership of international and inter-governmental programs on
marine ecosystems and global change. Within PICES Ian is a member of the FUTURE Scientific Steering
Committee.

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Dr. Jennifer Boldt (jennifer.boldt@dfo-mpo.gc.ca) is Research Scientist with Fisheries and Oceans Canada at
the Pacific Biological Station in Nanaimo, British Columbia. Her research interests are pelagic forage fish
ecology, including responses to biological and environmental drivers, as well as ecosystem indicators and
reporting. In PICES, she chairs the MONITOR Committee and is a member of Working Group (WG 36) on
Common Ecosystem Reference Points across PICES Member Countries.

Linnea Flostrand (Linnea.Flostrand@dfo-mpo.gc.ca) is a biologist with Fisheries and Oceans Canada at the
Pacific Biological Station in Nanaimo, British Columbia. Her responsibilities and research interests support
efforts to monitor pelagic ecosystems and forage fish populations with an emphasis on herring, eulachon and
sardine.

Moira Galbraith (Moira.Galbraith@dfo-mpo.gc.ca) is an invertebrate taxonomist specializing in zooplankton,
on the west coast Canada, in particular. She works at the Institute of Ocean Sciences in Pat Bay, British
Columbia.

Dr. Jacquelynne (Jackie) King (Jackie.King@dfo-mpo.gc.ca) is the Program Head of Basin and Coastal-scale
Interactions program with Fisheries and Oceans Canada. Her research investigates linkages between coastalscale ecosystems and basin-scale processes and ecosystems include climate forcing, large-scale oceanographic
processes, connectivity in large marine ecosystems and the exchange of energy, between coastal areas and the
north Pacific. She collaborates in integrative pelagic field studies along the continental shelf, with her primary
focus on understanding the factors controlling the abundance, distribution, and production of salmon and
associated species in marine ecosystems. She is also the lead for the Canadian Pacific Shark Research
Program; responsible for all Canadian Pacific elasmobranch research and conservation. Within PICES she is
Vice-Chair of the Fishery Science Committee, Co-Chair of the Section on Climate Change Effects on Marine
Ecosystems, and a member of the FUTURE Scientific Steering Committee.
Jim Murphy (jim.murphy@noaa.gov) is a Fisheries Research Biologist at NOAA’s Alaska Fisheries Science
Center, and is currently a member of the Salmon Ocean Ecology and Bycatch Assessment team at the Auke Bay
Laboratories, in Juneau, Alaska. His research has focused on the marine ecology of Pacific salmon and other
pelagic fish species in the northern Bering Sea and Southeast Alaska. Current research includes the application
of juvenile abundance to salmon run forecasts models, and life-history classification and diversity in Yukon River
Chinook salmon. Jim is a member of the US/Canada Joint Technical Committee of the Yukon River Panel.

Keith Sakuma (keith.sakuma@noaa.gov) is a Research Fisheries Biologist at NOAA Fisheries’ Southwest
Fisheries Science Center, Fisheries Ecology Division, in Santa Cruz, California. He is the Chief Scientist on the
Groundfish Analysis Team’s annual Rockfish Recruitment and Ecosystem Assessment Survey, which conducts
midwater trawls and CTD casts along the entire coast of California during the spring upwelling season. His
research interests include early life history and taxonomy of marine fishes as well as examining the
oceanographic factors that affect recruitment strength.

Dr. Andrew Thompson (andrew.thompson@noaa.gov) is a Research Fisheries Biologist at NOAA’s Southwest
Fisheries Science Center in La Jolla, CA. At present, his research primarily focuses on using larval fish and
oceanographic data collected by the California Cooperative Oceanic Fisheries Investigations (CalCOFI)
program to elucidate causes of dynamics of fish distributions and population sizes in the California Current
Ecosystem. He also supervises 3 postdoctoral researchers who are using CalCOFI data to 1) develop Next
Generation Sequencing methods to rapidly identify fish species that are present in plankton samples; 2) assess
feeding condition of larval anchovy and sardine using bulk and compound-specific stable isotopes and 3)
understand if larval condition quantified through otolith characteristics impact rockfish recruitment success.
Previously he used field studies, mathematical modelling and genetics to better understand processes affecting
the ecology and evolution of mutualistic gobies and shrimps on coral reefs, stream fish in the Appalachian
Mountains and southern California, and lizards in the Coachella Valley, California.

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