Distribution of the parasitic snail, Cyphoma gibbosum, and its effects on the health of its soft

coral hosts in Utila, Honduras

by

Muriel Magnaye

A report submitted to the Department of Environment and Geography,

University of Manitoba,

in partial fulfillment of the requirements for course

ENVR 4500 (Honours Thesis Project)

April, 2015

i

Abstract

Cyphoma gibbosum is a generalized predator of octocorals in Caribbean reefs. Its

contribution to the rapidly declining health of coral reefs, particularly disease and algal

overgrowth, is examined here. Benthic surveys were conducted at five sites surrounding Utila,

Honduras and one site was monitored regularly over 42 days to examine host preference and the

health state of the hosts. Adult C. gibbosum were found most frequently on Eunicea flexuosa,

Gorgonia ventalina, and Antillogorgia americana; juvenile C. gibbosum were found consistently

on A. americana. C. gibbosum does not select its host in proportion to the host abundance on the

reef. Adult snails were more abundant in shallow reefs (5m) than deep reefs (15m). Contrary to

previous research, C. gibbosum was not found to prefer diseased over healthy hosts. No

significant relationships were identified between snail occupation and disease and overgrowth.

Other environmental factors or anthropogenic effects may be the cause and should be considered

when investigating the declining health of coral reefs.

ii

Acknowledgements

First and foremost, I would like to thank my research supervisor Vanessa Lovenburg.

Without her assistance and support from the beginning and through every step of the way, this

project would not have been possible. She raised many important discussion points which I had

not considered beforehand, and I hope I’ve addressed them here. Thank you very much for your

patience and understanding through this past year and a half. I could not have asked for a better

supervisor, both in the field and afterwards.

I would also like to express my gratitude to Rick Baydack, Norman Kenkel, and David

Walker. Rick Baydack was my co-ordinator and mentor throughout the past three years and has

always pointed me in the right direction; I would not have come across the opportunity to work

on this project without your guidance. Norman Kenkel and David Walker assisted me with the

statistical analyses and offered important feedback and suggestions.

In June 2014, I went to Utila, Honduras through Operation Wallacea in order to collect

the data for this project. My time there provided me with important experience and the field

season would not have been successful without my fellow dissertation students and research

assistants. Finally, thank you Dan Exton for your guidance and consultation, both in the field and

off.

iii

Table of Contents

Abstract ............................................................................................................................................ i

Acknowledgements ......................................................................................................................... ii

Table of Contents ........................................................................................................................... iii

List of Tables .................................................................................................................................. iv

List of Figures ................................................................................................................................. v

Introduction ..................................................................................................................................... 1

Methods........................................................................................................................................... 6

Study Site .................................................................................................................................... 6

Benthic Surveys .......................................................................................................................... 8

Monitoring: ................................................................................................................................. 8

Statistical Analysis .....................................................................................................................11

Results ........................................................................................................................................... 15

Species distribution and preference .......................................................................................... 15

Host health ................................................................................................................................ 25

Discussion ..................................................................................................................................... 28

Bibliography ................................................................................................................................. 33

iv

List of Tables

Table 1: Octocoral densities and Ivlev's electivity index values (E) (Ivlev 1961) for adult and

juvenile Cyphoma gibbosum at 5m and 15m. Absence of electivity values indicate the absence of

host species at the respective depth. ............................................................................................. 16

Table 2: Distribution of Cyphoma gibbosum across shallow and deep reefs .............................. 20

Table 3: Residence time of Cyphoma gibbosum on hosts in Coral View Reef ............................ 24

v

List of Figures

Figure 1: Study Sites around Utila, Honduras ............................................................................... 7

Figure 2: Male Cyphoma gibbosum ............................................................................................. 10

Figure 3: Female Cyphoma gibbosum genital pore (gp) within the tissue of the foot ................ 10

Figure 4 C. gibbosum host distribution around the 5 sites: Coral View, Little Bight, Stingray

Point, Spotted Bay, and The Maze. ............................................................................................... 19

Figure 5: Host preference of C. gibbosum at 5m around the five sites: Coral View, Little Bight,

Stingray Point, Spotted Bay, and The Maze ................................................................................. 21

Figure 6: Host preference of C. gibbosum at 15m around the five sites: Coral View, Little Bight,

Stingray Point, Spotted Bay, and The Maze ................................................................................. 21

Figure 7: Cyphoma gibbosum host occupancy and movement around Coral View Reef............ 23

Figure 8: Frequency of adult and juvenile Cyphoma gibbosum by health class of hosts (0 –

healthy; 1 – light predation; 2 - heavy predation; 3 – light disease; 4 – heavy disease) around

Utila............................................................................................................................................... 26

Figure 9: Relation between Snail Occupation (SnO), a size corrected measure of frequency, and

Host Health, with regard to Predation, Disease, and Algal Overgrowth ...................................... 27

1

Introduction

Coral reefs are being lost worldwide at dramatic rates and their loss is most critically

observed in the Caribbean. The primary cause of reduced coral cover is attributed to disease

outbreaks (Aronson et al. 2003), and a phase shift from coral dominated to marcroalgae

dominated reefs (Wahle 1985). The past few decades have shown increased prevalence of

disease in Caribbean reefs and greatly reduced coral populations (Muller and Woesik 2012;

Harvell et al. 1999). The most widespread disease in the Caribbean, Aspergillosis, transported

via large Aeolian dust fluxes from Africa (Shinn et al. 2000), is hypothesized to secondarily

spread via the soft coral predatory snail, Cyphoma gibbosum (Rypien and Baker 2009). Coral

reefs are valued at just under 800 billion USD worldwide, for their contributions to fisheries,

coastal protection, tourism and recreation, and overall biodiversity value (Cesar et al. 2003). It is

important to understand the causes of degradation in order to implement informed and effective

management plans.

Octocorals are a group of cnidarians often called soft corals because they do not produce

a consolidated calcium carbonate skeleton; these are the dominant coral in the Caribbean reefs

(Bruno et al. 2011). Most octocorals are not considered reef-building (Jeng et al. 2011) because

they typically do not leave behind a calcium carbonate skeleton after death like scleractinian

(hard) corals. However, it has been suggested that Sinularia species in the Red Sea are also

capable of contributing material to create reef structures by the cementing of skeletal elements

called sclerites (Schuhmacher 1997; Jeng et al. 2011). Sclerites are spiny skeletal structures,

often used for identification (Bayer 1961; Aharonovich and Benayahu 2011). Soft corals provide

a three-dimensional structure to the reefs that fish and invertebrates utilize for habitat and

protection against predators (Sanchez et al. 2003). Like hard corals, they also rely on an

2

endosymbiotic relationship with zooxanthellae as an energy source in addition to nutrients from

planktonic organisms in the water column taken in through filter feeding (Patterson 1984;

McFadden 1986).

Coral disease is one of the main factors leading to the rapid decline of corals (Goreau et

al. 1998; Hernandez et al. 2009). At least nine coral diseases affecting Caribbean reefs have been

identified (Goreau et al. 1998). Bacterial and fungal growth is accelerated with higher

temperatures (Lesser et al. 2007); this, in conjunction with impaired host immunity with warmer

temperature, increases the susceptibility of corals to disease (Bruno et al. 2007).

Disease in corals is characterized by lesions or distinct bands of tissue loss and may be

caused by bacteria, viruses, or fungi (Harvell et al. 2007). It can alter or reduce the reproductive

success of a coral population, impacting the ecosystem dynamics, which can lead to an overall

change in the species composition and structure (Harborne et al. 2011). Aspergillosis is a disease

transmitted by the fungal pathogen, Aspergillus sydowii, and was first isolated in diseased sea

fans in 1996 (Smith et al. 1996); in Caribbean reefs, it has been observed in Gorgonia ventalina

and G. flabellum (Nagelkerken et al. 1997; Ward et al. 2006). The pathogenicity of A. sydowii in

sea fans is highly dependent on the genetic composition and health of the host (Alker et al.

2001), as aspergilli are known to be opportunistic and affect immune-compromised hosts (Kim et

al. 2000).

Symptoms of infected individuals include dark purple lesions, irregular patterns of tissue

and nodules. Lesions caused by Aspergillosis are areas of tissue necrosis and holes on the surface

of sea fans which are distinctly dissimilar to those formed from hurricane and storm damage and

predation (Nagelkerken et al. 1997) because the edges are often purple (Mullen et al. 2006). The

purple pigmentation of the sea fan blade is due to an increase in the proportion of sclerites

3

containing purple carotenoids. Smith et al. (1998) suggest that the recruitment of pigmented

sclerites serves as a defense mechanism to prevent the spread of disease in the colony. This

“purpling” has been associated with the production of a melanin layer which is thought to act as

a barrier against pathogens (Ellner et al. 2007). This results in thickened areas of tissue and the

protein gorgonin, called nodules (Bruno et al. 2011). The area of the sea fan blade exhibiting

these symptoms can be implemented as a measure of relative disease severity.

Octocorals have various secondary antifungal secretions that act as a defense against

fungal pathogens and predation (Kim et al. 2000); however, this is compromised at higher

temperatures or increased host stress (Ross et al. 1996). This is a growing concern with trends of

warmer sea temperatures because most microbial pathogens have a higher temperature tolerance

range than their hosts, favouring the success of the pathogen in current conditions (Alker et al.

2001). Octocorals also release chemicals that deter fish predation (Van Alstyne and Paul 1992);

these chemicals however, do not entirely negate predation by Cyphoma gibbosum.

The flamingo tongue snail, C. gibbosum, is a marine snail which acts as the primary

consumer of octocorals in the Caribbean reefs, as it feeds on them exclusively (Gerhart 1986;

Lasker et al. 1988). Octocorals serve as a food source, protection, and provide a site for mating

and laying eggs (Lasker et al. 1988; Nowlis 1993). The many chemical defenses octocorals

produce appear to be largely ineffective against predation from C. gibbosum (Harvell and

Fennical 1989), who will actually sequester these toxic allelochemicals and use them as defense

against its own predators, such as hogfish (Gerhart 1986). The mantle of flamingo tongue snails

is brightly coloured when they reach adulthood, which serves an aposematic function, or warning

signal (Rosenberg 1989). Cyphoma gibbosum has been observed in clumped distributions when

found on prey (Gerhart 1986; Lasker and Coffroth 1988); Hazlett and Bach (1982) conclude that

4

this distribution was not attributed to the size of colonies or the distance between the nearest

neighbouring host colony. It is hypothesized that snails aggregate to decrease risk of predation

(Gerhart 1986) and to find mates (Nowlis 1993).

Octocorals that are subject to predation exhibit little physical damage (Harvell and

Suchanek 1987) and the colonies suffer only partial mortality (Chiappone et al. 2003). However,

an extreme case at Mona Island, Puerto Rico resulted in mass mortalities of gorgonian corals due

to an outbreak of C. gibbosum (Schärer and Nemeth 2010). An average density of 34.4 snails per

colony and a maximum density of 190 snails per colony were reported, resulting in over 90%

total loss of shallow-water octocorals in the area. Such cases are rare and extreme but highlight

the detrimental effects of a prey/host imbalance in an ecosystem.

Cyphoma gibbosum occupation and foraging may have other secondary effects that

attribute to soft coral degradation. Cyphoma gibbosum predation exposes the skeleton and allows

macroalgae to colonize, which inhibits regeneration of octocoral polyps (Harvell and Suchanek

1987). A fragmented host may result in reduced fecundity of the coral polyps (Burkepile and

Hay 2007).

The flamingo tongue snail has been found to prefer diseased over healthy tissue to inhabit

(Nagelkerken et al. 1997) and has thus been suggested to act as a vector of disease (Slattery

1999; Rypien and Baker 2009). Aspergillus can be spread by grafting infected tissue onto

healthy tissue and by inoculating healthy colonies with cultures of Aspergillosis (Smith et al.

1996). Rypien and Baker (2009) suggest that C. gibbosum attributes to the spread by ingesting

the diseased tissue and as it migrates to healthy colonies, viable fungal spores are passed through

its digestive system and left in its waste. Furthermore, damaged tissue makes gorgonians more

susceptible to pathogens. Predation by this snail may go as deep as the coral’s skeleton, allowing

5

algae to settle and grow over the exposed area.

We will test the following hypotheses:

1. Cyphoma gibbosum show a preference for diseased hosts

2. Life stages and behaviour predict host preference

This study aims to determine the host preference of C. gibbosum and the health of its

octocoral host. We will also examine the relation between predation and the overall health of the

host coral. The health parameters addressed in this study are the two primary causes of reduced

coral cover: disease and algal overgrowth (Wahle 1985; Aronson et al. 2003).

6

Methods

Study Site

This study took place on Utila, the second largest Bay Island of Honduras. It is

approximately 29 kilometers from the Honduras mainland and is surrounded by the Caribbean

Sea. The island is 13 kilometers long and four kilometers wide with a population of

approximately 7000 people, most of which live around the Eastern Harbour (Saunders et al.

2009). The Bay Islands are the eastern-most extent of the Mesoamerican Barrier Reef Complex,

which is the second largest reef in the world, after the Great Barrier Reef in Australia. The

average water temperature during the field season was 28°C.

Three sites were surveyed from the south side of the island: Little Bight, Coral View, and

Stingray Point; and two from the north side: The Maze and Spotted Bay (Figure 1).

7

Figure 1: Study Sites around Utila, Honduras

8

Benthic Surveys

Benthic surveys of Cyphoma gibbosum were carried out on SCUBA at five sites around

the island of Utila, Honduras during June-August 2014. Data of octocoral abundance and

richness at the same sites were collected in 2013 and used in this study as a measure of host

availability. Divers placed a total of 30 50×1m belt transects at two depths at each site: 5m at the

crest and 15m at the slope and each depth had three replicates. The presence of C. gibbosum

within the belt was recorded, as well as the species of coral on which it was found, the height of

the coral, and the size of the snail. The health of the coral was scored on a relative scale of 0 – 4:

0 = no visible symptoms of disease or predation

1 = low levels of predation

2 = high levels of predation

3 = low levels of disease and predation

4 = high levels of disease and predation

The life stage of C. gibbosum was determined based on shell length; those equal to or

greater than 2cm were considered adult, and those less were considered juvenile.

Monitoring:

In the beginning of the field season, coral colonies at Coral View Reef within an area of

50x50m over a depth of 2m-12m, which had at least one C. gibbosum present were tagged to

examine the progression of predation, disease, and algal overgrowth. A total of 34 snails were

tagged and followed through the season; 23 snails were considered in the analyses due to lack of

confidence in tracking some individuals. A rank system was used to quantify the health of the

hosts. Predation (P), disease (D), and overgrowth (OG) were examined separately with the

9

following rank system:

0 = no visible symptoms

1 = low levels of P, D, or OG

2 = Intermediate levels of P, D, or OG

3 = High levels of P, D, or OG

These colonies were revisited at least four times a week over 42 days for changes in

health. The snails and their colonies were photographed for record. The individual snails were

also tagged to track their movement within and between colonies, and determine residence time.

Divers collected snails in individually labelled Whirlpak bags and transported them to the field

station’s wet lab for tagging and sex determination.

The sex of the snails was determined by submerging them in a solution of 5% methanol

in saltwater for approximately 3-5 minutes, until the foot of the snail appeared relaxed, according

to methods described by Nowlis (1993). If the foot was still retracted after 10 minutes in the

solution, the snail was removed, placed under running saltwater, and submerged in saltwater for

10 minutes before returning to the methanol solution for a second attempt.

Once the foot of the snail was relaxed, the right side of the foot was gently stroked, as if

to pull the foot away from the mantle and shell. If male, a penis was found (Figure 2); if female,

a genital pore (Figure 3), which appeared to be a small pore or tube within the tissue of the foot.

After the sex was determined, the snails were run under saltwater to rinse the solution off, and

then submerged in saltwater. The snails were then returned to the colonies on which they were

found within three hours after collection.

10

Figure 2: Male Cyphoma gibbosum

Figure 3: Female Cyphoma gibbosum genital pore (gp) within the tissue of the foot

11

Three methods of tagging were employed, with varying success. In all cases the snails were

placed in a petri dish of seawater, with their shell partially submerged, and the mantle was

separated on the back of the shell in order to tag the area.

1. Nail polish: Once the top of the shell was dried, small roman numerals were painted on

with nail polish, and a red dot was painted on if female, blue if male. The mantle was

held apart as the nail polish dried. This was unsuccessful because the nail polish wore off

in the water almost immediately in several cases.

2. Nail File: A nail file was used to make unique markings on the shell, making sure to hold

the mantle apart so as not to damage the snail tissue. This was the method of tagging used

by Lasker et al (1988), however, we decided the amount of distress this caused the snails

made this an unacceptable tactic.

3. Waterproof paper and glue: Once the shell was dry, a small piece of numbered waterproof

paper, affixed with waterproof glue was placed on the shell, keeping the mantle down

until the glue dried. This method proved the most effective, remaining attached for 2 – 5

weeks.

Statistical Analysis

All statistical tests were performed using R (R Development Core Team 2014) using the

packages Rcmdr (Fox 2005), stats (R Development Core Team 2014), Hmisc (Harrell et al.

2014), and vegan (Oksanen 2013); graphs were made using Micrsoft Excel.

Species distribution and preference

A diversity index was calculated for the octocoral composition at 5m and at 15m using

12

the Simpson-Gini Index value (Eq. 1) to get a measure of host availability for the sites using

extensive octocoral species data collected in 2013 (Lovenburg, unpublished). This measure is

less sensitive to rare species than the Shannon Index (Hill, 1973), which is important given the

number of rare species found around Utila. The inverse of the Simpson index is used.

Eq. 1

D = 1

∑ 𝑝𝑖2𝑠

𝑖=1

Ivlev’s (1961) Electivity Index was used to examine prey selection (Eq 2). This value

ranges from -1 to +1; a value of -1 indicates that C. gibbosum does not utilize the host at all, 0

indicates that C. gibbosum utilizes the host in proportion to its abundance, and a value of +1

indicates C. gibbosum prefers a host and does not utilize any others. Spearman rank correlation

tests coefficients were used to assess the relationship between octocoral availability and

occupancy (Chiappone et al. 2003)

Eq. 2

𝐸 = (ri − pi)

(ri + pi)

ri = proportion of host species occupied

pi= proportion of host species available

The distribution of C. gibbosum across shallow (5m) and deep (15m) reefs surrounding

Utila was examined using a proportion test, with the null hypothesis that they are distributed

evenly across different depths.

Goodness of fit was tested for the data collected from the five sites using chi-square

analyses to determine if C. gibbosum is distributed evenly among different host species. The

distribution of adult and juvenile snails on octocoral hosts was evaluated against the expected

distribution based on the null model that snail frequency is independent of host type/identity.

13

The distribution of C. gibbosum around Coral View Reef was analyzed based on patterns

outlined by Lasker et al. (1988):

i. Occupancy: the number of times C. gibbosum was observed on a host species throughout

the monitoring period.

ii. Movement: when a snail changed host species or a previously unrecorded snail appeared

on a host within the monitoring area.

iii. Residence time: the number of days an individual spent on a single host.

Occupancy and Movement was analyzed using chi-square analyses, with the null

hypothesis that the distribution of C. gibbosum is random. Residence time was analyzed using

ANOVA to examine the difference in variance of residence time between different host species.

Host health

Chi-square analysis was done to examine distribution of C. gibbosum based on the health

state of its hosts. The observed frequency of snails was compared to the expected distribution by

health class (0 – healthy; 1 – light predation; 2 – heavy predation; 3 – light disease; 4 – heavy

disease), assuming the null model that C. gibbosum distribution is independent of health of the

host.

Snail Occupation, a size-corrected measure of frequency (separate from previously

mentioned Occupancy), was calculated for each colony at the end of the monitoring period

(Eq.3). Pictures taken at the end of the monitoring period were analyzed using ImageJ to

estimate the cover of predation, disease, and overgrowth on the hosts. Snail Occupation values

were log-transformed to correct for skewed distribution resulting from a small sample size.

Incidence time for sea fans (Gorgonia ventalina), Eunicea spp., and A. americana was calculated

14

and analyzed using ANOVA to examine the relationship between occupancy and host health,

with the null hypothesis that mean snail occupancy is equal for low, medium, and high levels of

predation, disease, and overgrowth.

Eq. 3

SnO =Obs

ap,d,or o frequency/cm2

SnO = Snail Occupation

Obs = number of observations of C. gibbosum

ap, d, or o = relative area cover of predation, disease, or overgrowth, respectively, at the end of the

monitoring period (cm2)

15

Results

Species distribution and preference

Octocoral host densities for Utila, Honduras are given in Table 1. Shallow reefs

(D=10.06) were much more diverse than deep reefs (D=4.64). This indicates that shallow reefs

were more even octocoral distribution. Antillogorgia elisabethae abundance increases with

depth, making up approximately 19% of the reef at five meters and 44% of deep reefs.

Conversely Gorgonia ventalina density decreases dramatically at deeper reefs, making up 20%

of the reef at five meters and only 4% at fifteen meters. Briarium asbestinium and Eunicea

flexuosa decrease moderately in density with depth.

Adult Cyphoma gibbosum show a high preference for Pseudoplexaura porosa at 5m

(e=0.0.931) and 15m (e=0.937); Antillogorgia americana at 5m (e=.711) and 15m (e=0.875); and

E. flexuosa at 5m (e=0.513) and 15m (e=0.674), given their respective host densities. Juvenile

snails show a high preference for for A. americana that almost completely excludes all other

hosts (e=0.929, e=0.935 respectively) (Table 1). Spearman rank correlation coefficient tests

resulted in a significant correlation between adult C. gibbosum density and octocoral density (r =

0.46; p<0.01). There was no significant correlation between juvenile C. gibbosum densities and

host densities (r = 0.19; p>0.05).

16

Table 1: Octocoral densities and Ivlev's electivity index values (E) (Ivlev 1961) for adult and

juvenile Cyphoma gibbosum at 5m and 15m. Absence of electivity values indicate the absence of

host species at the respective depth.

Octocoral Density Electivity Index (E)

Species 5m 15m Adult 5m

Adult

15m

Juvenile

5m

Juvenile

15m

Antillogorgia acerosa 0.020 0.010 -1.000 -1.000 -1.000 -1.000

A. albatrossae 0.002 0.000 -1.000

-1.000

A. americana 0.030 0.029 0.711 0.875 0.929 0.935

A. elisabethae 0.191 0.442 -0.846 -0.694 -1.000 -1.000

A. hummelincki 0.009 0.006 -1.000 -1.000 -1.000 -1.000

A. kallos 0.009 0.004 -1.000 -1.000 0.507 -1.000

A. rigida 0.002 0.006 -1.000 -1.000 -1.000 -1.000

Antillogorgia sp. 0.005 0.008 0.555 -1.000 -1.000 -1.000

Briareum asbestinum 0.066 0.010 0.182 -1.000 -1.000 -1.000

Eunicea calyculata 0.016 0.029 -1.000 -1.000 -1.000 -1.000

E. clavigera 0.016 0.049 -0.001 0.243 -1.000 -1.000

E. flexuosa 0.041 0.008 0.513 0.674 -1.000 -1.000

E. fusca 0.041 0.057 -1.000 0.360 -1.000 -1.000

E. knighti 0.005 0.000 -1.000

-1.000

E. laciniata 0.007 0.014 -1.000 -1.000 -1.000 -1.000

E. laxispica 0.007 0.006 -1.000 -1.000 -1.000 -1.000

E. mammosa 0.034 0.037 -1.000 -1.000 -1.000 -1.000

E. pinta 0.000 0.014

-1.000

-1.000

E. succinea 0.061 0.070 -0.251 0.745 -1.000 -1.000

E. tourneforti 0.080 0.012 0.399 -1.000 -1.000 -1.000

Eunicea sp. 0.007 0.002 -1.000 -0.274 -1.000 -1.000

Gorgonia mariae 0.068 0.035 -1.000 -1.000 -1.000 -1.000

G. ventalina 0.202 0.043 0.143 -1.000 -0.759 -1.000

Icilligorgia sp. 0.000 0.006

-1.000

-1.000

Muricea atlantica 0.000 0.000 1.000

-1.000

M. laxa 0.005 0.002 -1.000 -1.000 -1.000 -1.000

Muriceopsis flavida 0.011 0.035 0.473 -1.000 0.760 0.583

Muriceopsis sp. 0.000 0.004

-1.000 1.000 -1.000

Plexaura homomalla 0.014 0.004 -1.000 -1.000 -1.000 -1.000

Plexaura sp. 0.005 0.000 -1.000

-1.000

Plexaurella dichotoma 0.016 0.025 0.599 0.519 -1.000 -1.000

P. fusifera 0.000 0.004

-1.000

-1.000

P. grisea 0.002 0.000 0.750

-1.000

P. nutans 0.002 0.006 -1.000 -1.000 -1.000 -1.000

Plexaurella sp. 0.005 0.000 -1.000

-1.000

Pseudoplexaura crucis 0.002 0.000 -1.000

-1.000

P. flagellosa 0.005 0.006 -1.000 -1.000 -1.000 -1.000

P. porosa 0.002 0.002 0.931 0.907 -1.000 -1.000

P. wagenaari 0.011 0.002

-1.000

-1.000

Pseudoplexaura sp. 0.000 0.002 0.166 -1.000 -1.000 -1.000

Pterogorgia anceps 0.002 0.000 0.750

-1.000

P. citrina 0.000 0.014

-1.000

-1.000

18

Chi-square tests indicated that there was significance in the frequency that snails were

found across the five sites. Adult C. gibbosum was found most frequently on Eunicea spp.

(28%), Antillogorgia spp. (22%), and Gorgonia ventalina (21%); juvenile snails were found

primarily on Antillogorgia spp. (86%) (χ2 = 74.76; df = 8; p «0.001) (Figure 4).

Proportion tests indicated that more adult snails occurred in shallow reefs (71%)

compared to deep reefs (χ2 = 12.96; df = 1; p «0.001). Juvenile snail distribution reflected adult

distribution; 65% of juveniles occurred in shallow reefs (χ2 = 4.98; df = 1; p< 0.05) (Table 2).

The proportion of juveniles and adults does not change with depth; there are approximately 60%

adults and 40% juveniles in the reefs, regardless of depth (Error! Not a valid bookmark self-

reference.).

The host preference of C. gibbosum at 5m reflects the overall preference given in Figure

4. Juvenile snails were found primarily on Antillogorgia spp. (95%); adult snails occurred largely

on Gorgonia ventalina (28%), Antillogorgia spp. (22%), and Eunicea spp. (17%) (χ2 = 49.64; df

= 7; p«0.001) (Figure 5). Host preference of C. gibbosum at 15m however, differs from its

preference at 5m. Juvenile snails were found predominantly on Antillogorgia spp. (68%) at 15m;

however, a larger proportion was found on Muricea/Muriceopsis spp (32%) than at 5m. Adult

snails were frequently found on Antillogorgia spp. (48%) and Eunicea spp. (41%), though none

were found on G. ventalina (Figure 6) at this depth. Cyphoma gibbosum was found on a wider

variety of hosts at 5m than at 15m, reflecting the diversity of host availability.

19

Figure 4 C. gibbosum host distribution around the 5 sites: Coral View, Little Bight, Stingray Point,

Spotted Bay, and The Maze.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pro

po

rtio

n o

f C

. g

ibb

osu

m

Host

Juvenile

Adult

20

Table 2: Distribution of Cyphoma gibbosum across shallow and deep reefs

Depth 5m 15m

Proportion of Juvenile snails (n=65) 0.65 0.35

Proportion of Adult snails (n=79) 0.71 0.29

Life Stage Juvenile Adult

Proportion at 5m (n=98) 0.40 0.60

Proportion at 15m (n=46) 0.41 0.59

21

Figure 5: Host preference of C. gibbosum at 5m around the five sites: Coral View, Little Bight, Stingray

Point, Spotted Bay, and The Maze

Figure 6: Host preference of C. gibbosum at 15m around the five sites: Coral View, Little Bight, Stingray

Point, Spotted Bay, and The Maze

00.10.20.30.40.50.60.70.80.9

1P

rop

ort

ion

of

C.

gib

bo

sum

Host

Juvenile

Adult

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Pro

po

rtio

n o

f C

. g

ibb

osu

m

Host

Juvenile

Adult

22

Distribution around Coral View Reef

The distribution of C. gibbosum based on Occupancy and Movement throughout the

monitoring period in Coral View Reef is given in Figure 7. This distribution differs significantly

from a random expectation. Snails showed preference in occupancy for Eunicea flexuosa (36%),

and Gorgonia ventalina (33%) (χ2 = 130.87, df = 6, p«0.001). Similar patterns are observed in

the movement data: G. ventalina (38%) and E. flexuosa (28%) were preferred based on snail

migration patterns (χ2 = 147.03, df = 6, p«0.001). The average residence time of C. gibbosum

was longest on Plexaurella spp. (20 days) and on Antillogorgia spp. (19.5 days), and shortest on

algae or rock (1 day). However, an ANOVA test failed to reject the null hypothesis that residence

time is independent of host species (F = 1.45, df = 6, p > 0.20) (

23

Table 3).

24

Figure 7: Cyphoma gibbosum host occupancy and movement around Coral View Reef

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Pro

po

rtio

n o

f o

bse

rv

ati

on

s

Host

Occupancy

Movement

25

Table 3: Residence time of Cyphoma gibbosum on hosts in Coral View Reef

Host Average residence time (days)

Plexaurella spp. 20.00

Antillogorgia spp. 19.50

Eunicea flexuosa 14.29

Muricea/Muriceopsis 9.20

Gorgonia ventalina 7.56

Other Eunicea spp. 5.00

Algae/rock 1.00

26

Host health

A significant difference in the distribution of snails around Utila was observed between

different levels of health of the hosts (χ2 = 32.13, df = 4, p «0.001). Approximately 70% of adult

snails recorded were found on hosts that showed signs of past predation, while only 18% were

found on hosts that showed any symptoms of disease. Over 50% of all juvenile snails were

found on healthy hosts that showed no signs of disease or predation; only one of the juvenile

snails was found on a host that showed any sign of disease (

Figure 8).

ANOVA tests failed to reject the null hypothesis that mean snail occupancy is

independent of level of disease (F = 0.39; df = 3; p>0.75) and overgrowth (F = 0.92; df = 3;

p>0.45). However, a test of variance on levels of predation rejected the null (F = 6.10; df = 3;

p<0.05); greater occupancy results in higher levels of predation. Increased occupation is

associated with higher levels of predation, but not disease or overgrowth (Figure 9).

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4

Pro

po

rtio

n o

f C

. g

ibb

osu

m

Health Class

Juvenile

Adult

27

Figure 8: Frequency of adult and juvenile Cyphoma gibbosum by health class of hosts (0 – healthy; 1 –

light predation; 2 - heavy predation; 3 – light disease; 4 – heavy disease) around Utila

0

0.1

0.2

0.3

0.4

0.5

0.6

0 1 2 3 4

Pro

po

rtio

n o

f C

. g

ibb

osu

m

Health Class

Juvenile

Adult

28

Figure 9: Relation between Snail Occupation (SnO), a size corrected measure of frequency, and Host

Health, with regard to Predation, Disease, and Algal Overgrowth

0

0.04

0.08

0.12

0.16

0.2

0 1 2 3

Sn

O (

freq

/cm

2)

Predation

0

0.04

0.08

0.12

0.16

0.2

0 1 2 3

Sn

O (

freq

/cm

2)

Overgrowth

0

0.04

0.08

0.12

0.16

0.2

0 1 2 3

Sn

O (

freq

/cm

2)

Health State

Disease

29

Discussion

Data collected from monitoring Coral View Reef show no significance in the relationship

between Cyphoma gibbosum occupation and host health, with respect to disease or overgrowth.

This trend is also reflected in the benthic surveys, which show that neither adult nor juvenile

snails prefer diseased octocoral hosts. This differs from previous conclusions that C. gibbosum

prefers diseased hosts (Nagelkerken et al. 1997) and that flamingo tongue snails act as a vector

of Aspergillosis in Caribbean reefs (Rypien and Baker 2009).

Wahle (1985) reported that heavy predation that exposes the octocoral axis leads to

marcoalgal overgrowth, though this is not the case in Utila. Since no significant correlation was

identified between snail occupation and algal overgrowth, the data cannot support or refute

Wahle’s conclusion (1985). Some cases of algal blooms were found on hosts, which had only

light predation or none at all. Perhaps the monitoring period was not long enough to observe

overgrowth, or the predation observed was not severe enough to lead to overgrowth.

Data shows that C.gibbosum does not select its host based on its abundance in the reef.

The factors that largely influence preference and distribution of the flamingo tongue snail are

host species and characteristics, predator life stage, previous snail occupancy, and reef depth.

Lasker et al. (1988) suggests that snails may move from colony to colony in a random

pattern, but certain traits of a colony determine occupation. Sclerite size and concentrations may

affect host selection (Lasker and Coffroth 1987); Harvell and Suchanek (1987) reported a

negative correlation between C. gibbosum foraging time and spicule size, which suggests that

sclerites provide corals with defense against predators. Eunicea flexuosa has a high percent

composition and one of the largest sclerite sizes of all Caribbean octocorals (Grajales et al.

2007). Despite this, E. flexuosa is one of the preferred hosts of adult C. gibbosum. Van Alstyne

30

and Paul (1992) concluded that sclerites act as a deterrent to predators, however, the high

occupation and sampling/grazing behaviour of C. gibbosum on E. flexuosa in the current study

suggests that while sclerites may reduce grazing, they do not eliminate predation entirely.

The composition of secondary chemical compounds may also affect the viability of a host

to a migrating snail. Octocorals are well known to be rich in allelochemicals that deter predation

(Epifanio et al. 2007; Harvell and Fenical 1989; Van Alstyne and Paul 1992). Cyphoma

gibbosum has evolved biochemical resistance mechanisms, such as glutathione S-transferase

(GST), a family of enzymes whose primary function is the detoxification of chemical defenses

released by their hosts (Whalen et al. 2010). Secondary compounds from gorgonians widely

vary, which may explain the vast range of hosts that snails occupy. Gorgonians, such as Plexaura

homomalla, have high concentrations of deterrent cyclopentenon prostaglandid, which act as

strong GST inhibitors to deter predation (Whalen et al. 2010). Epifiano et al. (2007) suggest that

the chemical defenses released by Antillogorgia americana originate from the symbiotic

zooxanthellae. Kim et al. (2000) demonstrated Gorgonia ventalina and G. flabellum possess

antifungal compounds. Antifungal assays revealed that both antifungal and antimicrobial

properties were found in crude extracts from sea fans, which suggests a generalized antimicrobial

reaction, irrespective of the colonizing microorganism.

Defense mechanisms such as sclerite composition and secondary chemical defenses were

not examined in this study, therefore could not be included in the analyses. The preference of C.

gibbosum for G. ventalina, Eunicea spp., and A. americana suggests there may be more benefit

to be gained from these hosts, or conversely, the defenses of these hosts are the least effective.

Harvell and Fennical (1989) reported a negative correlation between sclerite dry weight and

crude extract dry weight of Pseudopterogorgia rigida (Antillogorgia rigida), which suggests an

31

evolutionary trade-off between the two defense mechanisms. A species will likely concentrate on

one defense method over the other, depending on the stresses placed on it.

Prior occupation of conspecifics may also affect the distribution and occupation of C.

gibbosum. Chemical defenses may be induced by previous foraging (Harvell and Suchanek,

1987), which could make a preferred host species less inhabitable by future snails. Findings from

the current study differ from this observation; most adult snails were found on hosts that had

received previous predation. However, predation levels were generally low, which suggests that

gorgonians can tolerate a certain level of predation and increased chemical defenses are released

beyond a certain threshold. Data from the monitoring period shows that movement between

colonies is not random, like Lasker et al. (1988) suggested, instead choosing hosts in a pattern

that almost mirrors occupancy (Figure 7). These data bolster the hypothesis that snails follow the

mucous trails of other conspecifics (Gerhart 1986), which supports the evolutionary theory of

gregarious behaviour in the aposematically coloured C. gibbosum.

It is unclear whether juvenile snails also follow mucous trails of conspecifics. Juveniles

were consistently found on Antillogorgia americana that showed no signs of previous predation,

though this does not necessarily mean no previous occupation occurred. Many studies have

examined adult Cyphoma gibbosum host preference (Lasker and Coffroth 1988; Lasker et al.

1988; Chiappone et al. 2003), though none have shown juvenile preference, therefore this study

provides important baseline information going forward. Although A. americana was one of the

preferred hosts for adult flamingo tongue snails, there was often little to no sign of predation;

perhaps C. gibbosum utilizes hosts for different purposes. Lasker et al. (1988) reported that

Pseudopterogorgia americana (A. americana) received the least predation of the available hosts,

and was mainly used for egg deposition, taking advantage of the large size and structural

32

complexity for safety from predators. Although the larvae of marine gastropods are typically

pelagic veliger larvae (Jablonski & Lutz 1983), the chemical signal of C. gibbosum egg

deposition might be a cue that future larvae use to settle on the colony.

Reef depth largely influences Cyphoma gibbosum distribution, although it is not well

studied or understood. Adult distribution varied significantly between 5m and 15m reefs. Goulet

and Coffroth (2003) concluded that the symbiotic relationship between octocoral and

zooxanthellae remains stable over different depths however, morphological changes in the host

were observed. Depth and wave exposure are the main factors related to the variation in

octocoral composition and densities (Sanchez et al. 1998). The difference observed in C.

gibbosum preference at 5m and 15m may be due to the difference in reef composition. No snails

were found on Gorgonia ventalina at 15m, though there was a much lower abundance of sea fans

in the deeper reefs. The reduced variety of host occupation at 15m reflects the reduced diversity

of the reef.

Although more extensive monitoring and longer intervals are necessary to fully assess the

distribution and host-predator dynamics of Cyphoma gibbosum and its hosts, data suggests that

there is no relationship between snail predation and algal overgrowth or Aspergillosis, and

flamingo tongue snails do not prefer diseased over healthy gorgonians which contradicts

previous studies on the relationship between C. gibbosum and octocoral disease (Nagelkerken

1997). Kim et al. (2000) concluded that predation by C. gibbosum reduces the health of its host,

which allows pathogens such as Aspergillus to establish, however this is not observed in the data.

This may be because the measure of Snail Occupation (SnO) doesn’t differentiate between

different snail behaviours; it assumes that the snails are always feeding, but they may be

sampling, mating, or laying eggs. If C. gibbosum predation doesn’t influence disease or

33

overgrowth, other environmental factors or anthropogenic effects may be the cause and should

be considered. The factors identified to influence preference include: host species, life stage, and

reef depth. Future research should examine previous C. gibbosum occupation and host defenses

such as: sclerite size, shape, and concentration; and chemical defenses.

34

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