This literature review examines the deep-sea red tree coral, Primnoa pacifica. It discusses P. pacifica's role as a habitat-forming octocoral and focuses on its sexual reproduction, which includes both broadcast spawning and asexual budding. The review finds that P. pacifica populations in both deep-sea and shallow-water fjord habitats exhibit similar reproductive strategies and cycles, despite environmental differences. It also notes that P. pacifica is slow-growing and recruitment occurs decadally, making it vulnerable to fishing impacts. Further research is needed to better understand threats to P. pacifica from human activities.

1. Caitlin Grant
11/29/15
IndependentStudy
Literature Review on the Red Tree Coral, Primnoa pacifica
The deep-sea is home to a diverse community of unique organisms that hold
many elusive answers to our questions about the evolution of the wide expanse of
marine biodiversity present in a habitat that proves difficult to explore and study.
Described as an environment with limited light, nutrient availability and unique
topography, inhabiting species have had to adapt and specialize to reproduce and
survive in these ecosystems(Watling et al., 2011).
Among the marine taxa present, octocorals have been highlighted in recent years
as a species of interest, (Waller et al., 2014; Roberts et al., 2006) in part to its particular
vulnerability to fishing disturbances, and more prevalent as of late, the impact of
warming temperatures and changes in seawater chemistry may have on these corals
(Roberts et al., 2006). Much of the wealth of knowledge already explored in octocorals
is scattered, with gaps in many areas of octocoral reproduction, ecology and
distribution.
In the 1800s, cold-water corals were discovered and found to be incredibly
abundant, found in all ocean basins around the world at considerable depths (Watling et
al., 2011). There are two major subclasses of cold-water corals: Hexacorallia, the hard
corals, and Octocorallia, the soft corals. This review focuses on the subclass
Octocorallia, which represents the most diverse group of corals, with 75% of the 3000
species known found in waters deeper than 50 m (Cairns, 2007a).
Octocorals are characterized by the subdivision of polyps by eight mesenteries
consisting of tentacles containing lateral pinnules and tissues embedded with hardened
sclerites (Watling et al., 2011). Within this subclass, 4 orders divide into Helioporacea,
Alcyonacea, Gorgonacea, and Pennatulacea.
In the interest of this review, I have focused on species contained within the
order Alyconacea. Order Alyconacea is further broken down into 6 suborders, one of
which is the suborder Calcaxonia that embodies 5 families, 98 genera, all mostly
distributed in deep waters, comprised of species with a solid axial skeleton, containing
large amounts of non-scleritic calcareous material (Watling et al., 2011). Out of the 3
largest families within the suborder: Primnoidae, Chrysogorgiidae, and Isididae,
Primnoidae has been identified as particularly abundant and diverse in deep waters,
and are present in shallow water habitats as well (McFadden et al., 2006). Cairns &
Bayer (2009) found cladistic evidence supporting the origination of Primnoidae in the
Antarctic, where they are most abundant but found also in the North Pacific, North
Atlantic and subantarctic South Pacific regions (Waller et al., 2014).
Called the “quintessential deep-water octocoral family” (Cairns & Bayer, 2009),
Primnoidae is most common at bathyal-slope depths, with a vertical distribution of 8-
5850 m (Watling et al., 2011). There are 233 valid species within the Primnoidae family,

2. making it the 4th largest octocorallian family, recognizable by the armor of scale-like
sclerites covering their polyps (Watling et al., 2011).
Primnoidae’s ability to form large, branching thickets provide a suitable habitat for
other invertebrate species, including polychaete worms, copepods, amphipods, and
brittle stars (Coleman & Bernard, 1991). One such invertebrate, the polynoid worm
Gorgoniapolynoe caeciliae has been observed to settle on colonies of the primnoid,
Candidella imbricata. When the worm becomes 25 segments long, it creates “arbor-like”
tunnels along the basal polyp sclerites, inducing changes in the corals morphology to
support its growth (Ecklebarger et al., 2005). Due to these commensals utilizing these
octocorals, any damage inflicted on these corals from fishing gear would also be
causing habitat destruction to the invertebrates living within them.
In regards to food habits of deep-water and shallow-water corals, there are
differences and crossovers in their preferences. Shallow-water gorgonians consume
items such as phytoplankton, picoplankton, autotrophic nanoplankton, invertebrate eggs
and detrital particulate organic matter (POM) (Orejas et al., 2003) and is likely that along
with diatoms and dinoflagellates, deep-water species such as Primnoisis antarctica and
the primnoid, Primnoella feed on these materials as well (Sherwood et al., 2008).
The red tree coral, Primnoa pacifica, has become a focal species in reproductive
studies, due in part to its important role as a habitat forming octocoral and its distribution
along shelf and upper slope areas, making it particularly vulnerable to fishing gear
(Waller et al., 2014). In an effort to understand the extent of P. pacifica’s ability to
recover from damage, it would be useful to conduct further studies on reproductive
strategies, biogeographic patterns, and population connectivity (Watling et al., 2011).
Primnoa pacfica is a long-lived, slow growing octocoral, and these disturbances have
been seen to cause detrimental effects to their reproductive fitness, via planulae
expulsion and resource allocation, reducing fecundity and possibly wiping out
populations that would take years to return (Waller et al., 2014).
Preserving colonies of P. pacifica in the Gulf of Alaska, where a shallow-water
population was recently discovered, is of particular interest to fishery managers due to
the keystone refuge habitats P. pacifica provides for 12 species of rockfish (Sebastes
sp.) (Waller et al., 2014). This shallow-water occurrence of normally deep-water P.
pacifica is explained by Waller et al. (2014) as deep-water environments are being
mimicked in shallow-water, high altitude fjords, a phenomenon termed “deep-water
emergence.” Other coral species have been seen to adapt to different environments as
well. Species of shallow-water Stylasteridae corals have been found to originate in the
deep-sea. Although not well studied, Lindner et al. (2008) hypothesizes that in contrast
to the stable deep-sea abyss, there are opportunities for the evolution and
diversification of these corals to migrate into shallow, highly dynamic upper bathyal
environments. Key deep-water characteristics provide evidence that supports deep-
water corals in shallow-water fjord areas by both supporting nutrient-rich upwelling, low
temperatures like bathyal depths, strong currents and low light levels (Waller et al.,
2014).
Both the deep-water populations in the North Pacific and the shallow-water Tracy
Arm habitats reside on shelf and upper slope areas, where limited energetic inputs and
potential masked temporal and seasonal signals restrict energy available to octocorals
to invest in reproduction (Watling et al., 2011). This restriction also affects external cues

3. necessary for gametogenetic development and spawning synchrony in populations of
octocorals (Gage & Tyler, 1991; Young, 2003).
Most octocorals are gonochoristic, and both deep-sea corals and their shallow-
water counterparts share common strategies of sexual reproduction (Watling et al.,
2011). In P. pacifica, sexual reproduction occurs within the autozoids, as well as
asexual reproduction via extratentacular budding along the central axis (Waller et al.,
2014). There are two types of sexual reproduction that occur in octocorals: broadcast
spawing, where fertilization and development occur in the water column, and brooding;
where fertilization occurs within the maternal colony (Watling et al., 2011). Given the
limitations in deep-sea octocorals’ energy stores for reproduction, internal fertilization
and brooding would be predicted to be favored, however, deep-sea species of sea pens
have been found to be exclusively broadcast spawners (Ecklebarger et al., 1998).
Kahng et al. (2011) reported that internal brooding is a mode conserved among
Primnoidae octocorals, but Waller et al. (2014) discredited this and confirmed that P.
pacifica exhibits broadcast spawning instead. Alternately, soft corals in the Order
Alyconacea, sometimes within the same genus, will exhibit both forms of sexual
reproduction, showing a greater degree of reproductive flexibility (McFadden et al.,
2001).
In deep-sea corals, several stages of developing oocytes or spermatocysts are
commonly present in a single polyp, supporting a highly asynchronous method during
gametogenesis (Rice et al., 1992). This feature was also observed by Waller et al.
(2014) in P. pacifica, as well as a pattern among shallow-water species, suggesting a
possible common phylogenetic feature of continuous gametogenesis in octocorals
(Watling et al., 2011). Primnoa pacifica also shows seasonality trends in reproductive
processes, Waller et al., (2015) collected samples from Eastern Pacific P. pacifica
showing all four stages of spermatocytes present at one time.
Waller et al., (2014) found that the fecundity of vitellogenic oocytes seemed to be
on more than a yearly cycle, as well as sperm maturation appearing to take just over a
year to complete. These octocorals may extend the process of gametogenesis and
oogenesis in an effort to synthesize larger, yolkier eggs (Orejas et al., 2007; Waller et
al., 2014). This is also possibly to compensate for limited temporal cues, such as
photoperiod, temperature and productivity peaks that effect synchronizing spawning
activity (Watling et al., 2011). Waller et al. (2014) also noted that during
spermatogenesis, corals may only be able to produce germ cells on yearly cycles and
may only be able to mature oocytes sporadically when suitable conditions are present.
The availability of food and lipid synthesis both affect these reproductive cycles (Waller
et al. 2014) and need to be taken into consideration on top of possible anthropogenic
activities harmful to the species. Due to the pulses at which plankton become available
to these corals, this food availability cannot be relied on to fuel year round reproduction,
based on the vertically distributed habitat (Waller et al. 2014).
The deep-water and the shallow-water populations of the red tree coral, P.
pacifica, show many similarities in terms of reproduction, ecology, and environments.
Given that this species is slow growing, with recruitment events seen to be on a decadal
scale (Waller et al., 2014), this species is particularly vulnerable to fishing pressures,
especially the larger, more reproductive colonies. Primnoa pacifica is also known as an
ecosystem engineer that will change the local environment, providing a microhabitat for

4. colonization of associated species (Waller et al., 2014). Further research should be
conducted in an effort to continue finding relationships between the two different
habitats where P. pacifica flourishes to better understand how human interactions may
negatively affect this species.
Works Cited
Cairns, S. D. (2007a). Studies on western Atlantic Octocorallia (Coelenterata:
Anthozoa). Part 8: New records of Primnoidae from the New England and Corner
Rise sea- mounts. Proceedings of the Biological Society of Washington. 120, 243-
263.

5. Coleman, C. O. and Barnard, J. L. (1991). Amatiguakius forsberghi, a new genus and
species from Alaska (marine Amphipoda: Epimeriidae). Proceedings of the
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Eckelbarger, K. J., Tyler, P. A. and Langton, R. W. (1998). Gonadal morphology and
gametogenesis in the sea pen Pennatula aculeata (Anthozoa: Pennatulacea) from
the Gulf of Maine. Marine Biology. 132, 677-690.
Eckelbarger, K. J., Watling, L. and Fournier, H. (2005). Reproductive biology of the
deep-sea polychaete Gorgoniapolynoe caeciliae (Polynoidae), a commensal species
associated with octocorals. Journal of the Marine Biological Association of the
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Orejas, C., Gili, J. M. and Arntz, W. E. (2003). Role of small-plankton communities in
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Sherwood, O., Jamieson, R. E., Edinger, E. N. and Wareham, V. E. (2008). Stable C
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