Dio Patra Ornat Beds

8/14/2019 Dio Patra Ornat Beds

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David Rivera

Peter Kirchner

Fish Assemblages in Diopatra ornata Beds

Introduction

The kelp forest ecosystem has an incredible amount of bio-diversity due to the

multitude of desirable habitats. One distinct habitat that occurs primarily at the sand and

rocky reef interface is created by a tube-dwelling polychaete Diopatra ornata. D. ornata

secretes mucus which is combined with sand algae and pieces of shells to construct

tubes up to !cm tall sticking out of the sand. D. ornata feeds primarily on drift algae and

detritus that accumulate in the D. ornata congregations "Kim #$$%&. These tube worms

form large dense colonies which provide habitat for a large diversity of infuana. D.ornata congregations or 'beds( are ideal habitats for many small cryptic organisms) they

provide these organisms with both food and shelter. *ommon to these beds are many

small crabs shrimp gastropods and fish.

D. ornata habitats are uni+ue in that they form isolated communities with well

defined borders that can vary greatly in si,e. These characteristics make D. ornata beds

ideal for testing the species area relationship "R& model which predicts that larger

habitats will have higher species richness. /arger areas will provide more desirable

habitat more resources more settlement and a lower e0tinction rate. 1y studying fish

assemblages in D. ornata beds the R model can be tested.

lthough it is +uite obvious that larger beds will have an overall higher

abundance of fish it is unclear as to how fish density relates to the si,e of these beds.

Knowing the relationship of fish density to si,e of bed will show how the resources of the

beds are being utili,ed. 2f fish density decreases with si,e of bed not all the resources of

the larger bed are being utili,ed and there is a possible preference for smaller beds.

D. ornata beds vary in overall height of the tubes that make up the beds. Taller

beds are older and tend to have more algae and detritus flowing through them. The

height of the beds may have an influence on abundance and overall density of the fish.

Taller beds may provide more shelter and food for fish then smaller beds.



The purposes of our study were3 "#& determine if larger D. ornata beds have more

species of fish "%& determine if there is a relationship between the si,e of bed and density

of fish present "4& and to determine if beds with taller D. ornata tubes have a higher

density of fish.

Methods

The study site for this pro5ect was 6opkins 7arine tation a 7arine Protected

rea located in Pacific 8rove * "49: 49;< #%#: =>;?&. 6opkins is home to a

Macrocystis kelp forest located on substrates consisting of high relief granite and sand

patches. 2n order to determine the fish assemblages for the eight species sampled #=

underwater surveys were conducted on *@1 by one dive team in various D. ornata

beds in the 6opkins reef.

The selection of the D. ornata beds sampled was based on two specific factors.

The si,e of the bed was important to note because it was necessary to only select beds

that were manageable for the dive team to finish on one dive. 1eds that were clearly

isolated without any ambiguity of confusing them with other beds were another factor

which was taken into account when selecting the beds.

s soon as the beds were chosen for sampling fish transects were then performed

by dividing each bed with meter tapes into smaller more manageable plots for fish

counting. The dive team then fingered through the D. ornata in each plot side-by-side

counting fish until the entire bed was sampled. Aight different species of fish were

observed consisting of3 Orthonopias triacis, Artedius corallinus, Oxylebius pictus,

Scorpaenichthys marmoratus, Rhinogobiops nicholsii, Gibbonsia spp., Sebastes carnatus

"5uvenile& and Apodichthys fucorum.

Once the fish transects were completed for each bed the dive team then measured

the longest diameters in each bed using meter tapes in order to calculate the area of each

bed. Binally after the diameters of the beds were recorded the dive team measured the

height of the D. ornata per bed and also recorded the algae and grass present in each bed.

Results

total of #= beds were sampled that ranged from #.> m% to #%.= m% with the

e0ception of one large bed that was %=.4 m%. Two to five species of fish were observed in

each bed but overall the beds were dominated by O. triacis "Bigure #&.



264

40 44

82 1 1 4

0

50

100

150

200

250

300

O . t r i a c

i s

A . c o

r a l l i n

u s

G i b b o n

s i a s p .

O . p i c t u s

S . m a r m

o r a t u s

S . c a r n a t u s

A . f u c o r u m

R . n i c h

o l s i i

A b u n d a n c e ( # o f f i s h )

Figure 1. Total abundance of fish sampled in all #= D. ornata beds.

Bish species richness significantly "p C .%$ r % C .>%& increased as area

of bed sampled increased "Bigure %&.

0

1

2

3

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0 5 10 15 20 25 30

Area (m2)

#

o f f i s h s

p e c i e s

Figure 2. Regression of number of fish species sampled versus si,e of bedsampled in each of the #= D. ornata beds.





Discussion

The relationship of species richness versus the area of D. ornata beds is

important because it supplies a better understanding of the habitat that D. ornata provides

for fish species. The fact that these larger beds do support a higher number of species

means that these beds are assisting in the maintenance of the populations of these less

common species that are not necessarily found in the smaller D. ornata beds.

This relationship also conveys the fact that this marine community will in fact

reach an inflection point) thus only a limited number of species of fish are able to survive

in the D. ornata beds. This is a basic representation of the pecies-rea Relationship

model. The R model is typically applied to terrestrial organisms and must beconsidered in creating terrestrial reserves. The dynamics and lack of defined borders in

the marine environment make it hard to apply the R model. 1ecause D. ornata forms

these defined beds it is one of the few e0amples of the R model being tested in a

marine environment. The fact that this can be applied to the marine community could

create an improved method for creating 7arine Protected reas "7Ps& and preserving

the rarer species. Burthermore being able to apply this model to the fish assemblages

study in D. ornata may allow other scientists to use the same basic model for future

studies.

maller beds are e+ually important to Macrocystis kelp forests due to there

distinctive characteristics. Results indicate that smaller beds do in fact have higher fish

density than larger beds. There are however several possibilities as to why this may be.

higher perimeter to area ratio is one possibility for this relationship. Eisual

observations made by the dive team suggest that the ma5ority of fish reside on the

surrounding perimeter of the D. ornata beds. 2nterestingly enough these smaller beds also

seemed to be better surrounded by rocky reef than the larger beds which were typically

seen in the large sand flats. Though no data was taken the hypothesis that the fish

preferred to reside on the perimeter and the observations that the rocky reef were closer

to the smaller beds could advocate the fact that fish were also coming from the rocky

granite reefs to the D. ornata beds in addition to the fish that were already present in the



beds. nother possibility as to why the smaller beds had a higher fish density is due to

resource availability for the fish. maller beds have more resources available than larger

ones) thus there is less competition between fish for these resources which could feasibly

result in higher fish densities. nother hypothesis which should not be ruled out for the

increase in fish density in smaller beds is due to the methodology of sampling. 2n the

smaller beds the fish would more likely be scared to the perimeter of the bed during

surveys which could lead to mistakes in counting the same fish more than once. This was

not as likely to happen in large beds because the ma5ority of the fish counted may not

necessarily have retreated to the perimeter during surveys) however this must not be

ruled out. This reasoning could also relate to the observations made by the dive team that

the ma5ority of the fish reside on the perimeter of the D. ornata beds.

The last hypothesis which is directly related to the second hypothesis states that

fish density is related to the height of the D. ornata beds. The data suggests that there is

indeed a correlation between the two which would result in higher fish abundance in

taller D. ornata beds. The prediction here is that fish have a better chance of survival in

these taller beds because these beds provide more shelter and protection from predators

than in shorter beds. Eisual observations made by the dive team suggest that the edges of

the D. ornata beds were taller than the middle which would also back up this data. 2f the

edges contain more fish and the edges are taller than there may be a relationship between

the two. 2n addition the detritus recorded by the divers was typically seen along the

perimeter more than in the middle. ince height of D. ornata is directly related to the

amount of food "detritus& "Kim #$$%& it is possible that the perimeter is most abundant in

resources which make for the prime areas for fish to reside.

References

Kim /.The Role of Drift Kelp in the Population Acology of a Diopatra ornata 7oore

"Polychaeta Onuphidae& Acotone. Fournal of A0perimental 7arine 1iology and Acology

#=9 "%&3%=4-%G%. #$$%

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