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2016 The interactions of a marine bivalve, zebra, with its epibionts Melissa Marieta Olguin

Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] 1

THE FLORIDA STATE UNIVERSITY

COLLEGE OF ARTS AND SCIENCES

THE INTERACTION OF A MARINE BIVALVE, , WITH ITS EPIBIONTS

By

Melissa M. Olguin

A Thesis submitted to the Department of Biological Sciences in partial fulfillment of the requirements for graduation with Honors in the Major

Degree Awarded: Spring, 2016 2

Dr. Sandra Brooke 3

Abstract

The Arca zebra is a marine bivalve that is able to accrue a copious amount of epibionts

(Vance 1978). Since Scandland (1979) the epibiont community on these shells for the Big Bend

Region has not been looked out. I set out to perform an epibiont community analysis on the Arca zebra off the coast of Dog Island. I found 106 different of organisms from 14 different

Phyla. The most frequent organisms were barnacles (Amphibalanus sp.), a colonial red tunicate

(unidentified, Class Ascidiacea), a stringy red alga (Gracilaria sp), a hydroid ( carneum), and two encrusting (Peyssonnelia sp. and unidentified, Family Corallinaceae).

Through a percent cover analysis I found that out of the most dominant encrusting groups, the encrusting coralline algae and the encrusting tunicates covered the most surface area. These results and their differences from Scandland (1979) have many implications and avenues for future study.

Introduction

This paper is focused on a population of a marine bivalve, the Arca zebra (Order

Arcoida, Family Arcidae; Swainson 1833), commonly referred to as the Turkey Wing Clam.

These bivalves tend to live in clumps of varying densities from depths of 0m- 140 m (460 ft) in hard-bottom habitats. They can be found as far north on the North American Atlantic coast as

New Jersey (Field Museum 2015), and Bermuda (Sarkis 1992, Tunnell et al 2014), down through the Gulf of Mexico (Felder and Camp 2009), throughout the Caribbean (Miloslavich et al 2010), and off the coasts of Mexico, Panama, Columbia, Venezuela, and Brazil (Tunnell et al 4

2014) (Figure 1). They are economically important for Cuba and Venezuala, both which have established fisheries for them (Sarkis 1992). The population specific to this study is found in the

Apalachee Bay in the northeastern Gulf of Mexico North Florida at a depth of about 12m.

Figure 1. Geographic distribution of Arca zebra. Source:

http://www.gbif.org/species/2286214

Arca zebra is a sessile organism anchored through the use of its which is connected to the foot (Sarkis 1992). This can be retracted or intentionally torn off and regenerated, enabling the bivalve to move to other locations. These bivalves usually group together, both attaching to the sea floor and to other A. zebra. These mats provide a hard substrate used for settlement of other sessile organisms (Figure 2). The survival of many marine benthic plants and depends on the dispersal and settling ability of propagules (Abelson 5 and Denny 2012). There are a number of living organisms that provide the necessary substrate for the settlement of sessile animals (Wohl and Mark 1999). These animals may be referred to as

‘basibionts’. Many times marine megafauna such as sea turtles (Scaravelli 2003) and cetaceans

(Whitehead 2014) can be seen covered with other organisms such as barnacles and .

Figure 2. Corals and other epibionts covering Arca zebra. Photo by Sandra Brooke.

Epibionts growing on bivalves creates the opportunity to study the communities of microhabitats over small spatial scales (Scandland 1979). In Venezuala, the Atlantic Pearl

Oyster, Pinctada imbricata, and the Turkey Wing Clam, A. zebra, provide necessary habitat for epibiont communities, in addition to Thalassia seagrass beds, corals, and rocks (Avila et al.

2013). Denser beds of bivalves allow for more complex macrofaunal communities, while 6 different species of bivalves can harbor different communities of epibionts; for example, some decapod communities vary among bivalve species (Avila et al. 2012).

The most recent work on the community composition of A. zebra epibionts in the Big

Bend Region region was done by Thomas Scandland in 1979 off the coast of Dog Island, North

Florida. He sampled 140 shells which included both A. zebra and A. imbricata, and found 153 different taxa. Scandland’s study on the community composition of epibionts also suggested that the substrate surrounding the Arca beds was unsuitable for most fauna due to coarse shifting sands. This makes the Arca zebra one of the few options for epibiont settlement and survival in this area.

One More Time Wreck

Figure 3. Location of Arca zebra sampling site for this study; the One More Time wreck near Dog Island in the Apalachee Bay, North Florida

Different kinds of interactions arise between epibionts and the organisms that provide hard substrate. In some cases, the basibionts are negatively affected. Increased density of epibionts on periwinkle snails can actually reduce both the speed and reproductive output of the 7 gastropod, thereby only benefiting the epibionts (Buscham and Reise 1999). The interaction between bivalves and epibionts can be mutualistic, such as with the jewel box clam, Chama pellucida (Vance 1978), where both groups benefit from reduced mortality via . The epibionts make predation on the bivalves cumbersome for starfish while the bivalves provide substrate habitat outside of the range of foraging sea urchins which would prey on the epibionts.

Some studies suggest that the shells of some bivalves have evolved so that they can procure more epibionts, as seen with the spines of the Thorny Oyster, americanus (Feifarek 1987) and the Noah’s Ark Shell, (Marin and Belluga 2005). Additional studies have shown that the chemical composition of some epibionts provides an even greater deterrent from predation than their physical presence (Laudien and Wahl 2004).

The objective of this study was to determine the epibiont community on an Arca zebra population at the One More Time Wreck located near Dog Island in the Apalachicola Bay

(Figure 3). My study placed some focus on the differences between the communities of epibionts from the natural site near Dog Island studied by Scandland and the artificial site created by the One More Time Wreck. This led me to question the competitive processes occurring on individual shells and also to examine the use of the Arca zebra by several species of corals in the Gulf of Mexico. Understanding more about the interactions between epibionts and

Arca zebra could lead to better management decisions, particularly regarding organisms such as corals. If A. zebra is a significant habitat for corals, then one step would be preventing a fishery from forming for these bivalves, as has been the cases on other countries.

8

Methods

Sixty seven Arca zebra shells were collected from the “One More Time” Wreck in the

Apalachee Bay (29o42’21”N; 84o37’25”W). The site was at a depth of approximately 12 meters.

After collection, the shells were housed at the Gulf Specimen Marine Lab and Aquarium. Upon examination, three of the shells were determined to be Chama sp. which left the sample size at

64.

Shells were placed in a grid formation and covered with a tarp covering the tank to prevent algal growth. For initial processing, each shell was removed from the tank using a small

Tupperware container. Photographs were taken of each side and the top of the shell along with a floating label documenting the shell number and collection date. The shells are flattened on the dorsal side, adjacent to the hinge so they present a different aspect from the sides of the shells.

Next, a description of all visible epibionts was written down. Finally, a razor was used to cut off samples of any soft tissue organisms such as , tunicates, and algae. These samples were preserved in labeled vials of ethanol and recorded on a separate sheet. Calcareous and hard surfaced epibionts were identified and counted.

The vials were taken to a lab and the samples were examined under a dissecting microscope at 2x and 4x magnification. Additional epibionts such as mobile macrofauna and a couple of meiofauna were discovered and recorded.

For the identification of the polychaetes, the taxonomic information on the Natural

History Museum’s website was used. Corals were identified with the help of the Brooke Lab at

FSU. Sponges were identified using their spicules with the aid of the Wulff Lab at FSU. 9

Bryozoans were identified with the help of Dr. Burgess at FSU. The rest of the groups were identified using other online papers and databases as well as Felder and Camp (2009).

Species accumulation curves were created for comparing species richness of epibionts observed via the naked eye with the diversity of epibionts when aided by technology. Using each shell as a sample and a Bray-Curtis similarity matrix, both a cluster analysis and SIMPROF were run to see if any groupings of shells were created by the communities living on them. Using this, a Non-metric Multi Dimensional Scaling (NMDS) plot was created to display those groupings.

Then, using five size classes (6-6.99 cm, 7-7.99 cm… etc) as factors, an Analysis of Similarity

(ANOSIM) was run on a Bray Curtis matrix to determine whether there were differences between epibiont communities based on the size of the shell they were on.

The images taken of each side of the shells were used to conduct a percent cover analysis of the dominant epibiont groups. Photos taken of the Top, Left, and Right side of each shell were opened in the program, ImageJ and calibrated using a ruler that had been placed underneath the

Arca zebra shell in the photo. The photo depicting the ventral side of the shells was not used for this analysis since the thick periostracum, (an organic coating) prevents a majority of epibionts from settling on that part of the bivalve (Scandland 1979). The most frequently occurring encrusting organisms such as algae, sponges, tunicates, and barnacles were used for this part of the study. These were determined from abundance counts. The percent values from ImageJ were used to determine the most dominant epibiont to colonize A. zebra.

Results

A total of 106 different species were identified representing 14 different plant and phyla (Figure 4, Table 1).The mean species richness per shell was 14.8 (SD 4.43). The species 10 accumulation curves (Figure 5) showed the initial species richness of the samples observed on the shell compared with after the samples were examined under a microscope. Additional species were found during this process, the curve shows that the overall species richness of the data increased after processing of samples. The species accumulation curve using all epibionts does not reach an asymptote, indicating insufficient sampling. The cluster analysis (Figure 6) revealed eleven different community groups based on a similarity matrix. This was used to create an NMDS plot (Figure 7) which spatially arrayed the shells based on their community composition. Additionally, new groups were created using the size of each shell as a factor. Five size classes were created were created from the range of sizes measured; these were used as the factor in a cluster analysis and another NMDS plot was created (Figure 8). An analysis of similarity (ANOSIM) revealed that there was no significant difference (R=0.008, p= 0.42) in shell community based on the size of the shell.

Abundance

1% 1% Demospongia 2% 0% 2% 2% 6% 4% Calcerea

7% Anthozoa 5% 0% 4% 2% Malocostraca 0% Maxillopoda Ostracoda 11% Rabtitophora 3% 39% 9% 3% Polychaeta 0% 0% Echinoidea

Figure 4. Pie chart based on the abundance counts for each order of epibiont. 11

Table 1. All of the organisms found on the A. zebra specimens of this study. This is organized by Phylum, Class, Order, Family, and epithet. Organisms that were unable to be identified were left “unidentified”. Phylum Class Order Family Genus species Porifera Demospongia Poecilosclerida Microcionidae Clathria (Clathria) prolifera Clathira (Microciona) affinis Clathria sp. Tedaniidae Tedania ignis Dictyoceratida Dysideidae Dysidea fragillis Dysidea etheria Irciniidae Ircinia felix Ircinia sp. Haplosclerida Chalinidae Haliclona (Rhizoniera) curacaoensis Suberitida Halichondriidae Halichondria sp.1 Halichondria sp.2 Dendroceratida Dictyodendrillidae Igernella notabilis Calcerea Leucosolenida Grantiidae cf. Leucandra sp. Clathrinida Clathrinidae Arthuria canariensis Clathrina coriacea Unidentified Unidentified unidentified 1 species Anthozoa Actinaria unidentified 3 species Actiniidae Bunodosoma cavernata Scleractinia Scleractinia incertae Cladocora arbuscula sedis Caryophylliidae Phyllangia americana Hydrozoa Eudindridae Eudendrium carneum Tubulariidae Ectopleura crocea Unidentified 1 species Leptothecata Dynamena Dynamena disticha 12

Sertulariidae Pasya quadridentata Nematoda unidentified Arthropoda Malocostraca Alpheidae Alpheus angulosus Panopeidae Dyspanopeus sayi Epialtidae Libinia dubia Mithracidae Mithraculus forceps Porcellanidae Petrolisthes armatus Isopoda unidentified unidentified Amphipoda unidentified Several species Maxillapoda Sessilia Balanidae Amphibalanus sp. Harpacticoida unidentified unidentified Ostracoda Unidentified unidentified unidentified Platyhelminthes Rabtitophora Polycladida Stylochoplanidae Cf. Digynopora americana Gymnolaemata Bugulidae Bugula neritina Claudibugula sp. Schizoporellidae unicornis Watersiporidae Watersipora subtorquata Membraniporidae tenuis Gastropoda Nudibranchia Aeolidiidae Berghia stephanieae depressa Crepidula fornicata Bostrycapulus aculeatus decussata Naticidae Polonices sp. Nassariidae Nassarius vibex Triplofusus giganteus Terebridae Terebra protexta Terebra sp. 13

Unidentified unidentified 2 species Bivalvia Arcidea Arca zebra Ostreidae Crassostrea virginica americanus unidentified 2 species Unidentified unidentified 1 species Annelida Polychaeta Phyllodocida Chaetopteridae Chaetopterus variopedatus Syllidae 3 species Polynoidae 1 species Nereididae sp. 1 species Hesionidae 1 species Terebelida Cirratulidae cf. Aphelochaeta sp. Terebellidae 1 species Sabellida Sabellidae Bispira melanostigma unidentified Eunicida Oenonidae 1 species Eunicidae 1 species Not assigned Scalibregmatidae 1 species Capitellidae 1 species Orbiniidae 1 species Echinodermata Echinoidea Arbacioida Arbaciidae Arbatia punctulata Ophiuroidea (Ophiothrix) angulata Holothuroidea Dendrochirotada Cucumariidae Pentacta pygmaea Chordata Ascidiacea Aplousobranchia Polyclinidae Apilidium stellatum Aplidium solidum Aplidium sp. Didemnidae Diplosoma sp. 14

Didemnum perlucidum Didemnum sp. Polycitoridae Eudistoma hepaticum Stolidobranchia Pyuridae Boltenia sp. Molgulidae Molgula occidentalis Phlebobranchia 1 species Unidentified unidentified 3 species Rhodophyta Florideophyceae Rhodymeniales Rhydymeniaceae Botryocladia sp. Peyssonniales Peyssonneliaceae 1 species Ceramiales Callithemniaceae Calithamnion corymbose Wrangeliaceae Plumaria plumosa Corallinales Corallinaceae unidentified Gracilariales Gracilariaceae Gracilaria sp. 1 Gracilaria sp. 2 Chlorophyta Ulvophyaceae Bryopsidales Caulerpaceae Caulerpa sertularioides Codiaceae Codium decorticatum Cladophorales Cladophoraceae Cladophora sp. Ulvales Ulvaceae Ulva flexuosa Ochrophyta Phaeophyceae Fucales Sargassaceae Sargassum hystrix Foraminifera Globothalamea Rotaliida Cibicididae Cibicides lobatulus 15

Species Accumulation Curve 120

100

80

60 Additional Initial

40 Combined Number of Species ofNumber

20

0 1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 Number of Samples

Figure 5. Species accumulation curves from the abundance data comparing species richness from the initial epibiont observations of the shells with the observations of additional epibionts under the microscope. These two combined make the third line, which indicates inadequate sampling of epibionts since an asymptote was not reached. 16

Cluster Analysis

Figure 6. Cluster plot using a Bray-Curtis similarity matrix reveals eleven groupings of shells within the

sample set of 64 shells. Based on the species richness and abundance of all specimens observed.

Figure 7. NMDS Plot created using the eleven groupings from the cluster analysis. Each group is

represented with a different symbol. Circles represent 35% similarity. 17

Figure 8. NMDS with shell size class as a factor. Circles represent 35% similarity. Analysis of Similarity revealed that there was not a significant difference in community based on the size of the shell (R =

0.008, p = 0.42).

During the processing of each shell, the dominant encrusting groups of organisms were determined to be tunicates (Class Ascidiacea), sponges (Phylum Porifera), calcareous encrusting algae (Family Corallinaceae), red encrusting algae (Family Peyssonneliaceae), encrusting bryozoans (Order Cheilostomatida), and barnacles (Genus Amphibalanus). The number of shells that these groups occurred on were counted and a percent frequency was calculated to show how common they were relative to each other (Figure 10). The percent cover data revealed that the

Ascidiacea and the Corallinaceae groups contained the dominant encrusting epibionts on A.zebra

(Figure 11) covering a total area of 2.75 and 2.73 m2. The next group covering the largest 18 surface area was Peyssonneliaceae, followed by Porifera, Amphibalanus, and finally

Cheilostomatida.

Percent Frequency 120

100

80

60 Percent

40

20

0

Ascidiacea Porifera Corallinaceae Peyssonneliaceae Cheilostomatida Amphibalanus

Figure 9. The most frequent encrusting epibionts shown as the percent of shells they appeared on. Shows

a relatively even distribution: Ascidiacea (82.5%), Porifera (77.2%), Corallinaceae (96.5%),

Peyssonneliaceae (78.9%), Cheilostromatida (57.9%), Amphibalanus (94.7%).

19

Percent Cover 60

50

40

30

20 Percent Cover (avg) Cover Percent

10

0 Ascidiacea Porifera Corallinaceae Peyssonneliaceae

Cheilostomatida Amphibalanus Bare Shell

Figure 10. Results from the percent cover analysis of the dominant encrusting epibionts with standard error. The average percents were: Ascidiacea 15.9% (SD=20.2), Porifera 6.84% (SD=12.5), Corallinaceae

15.8% (SD=17.8), Peyssoneliaceae 9.81% (SD=16.5), Cheilostomatida 1.39% (SD=5.71), Amphibalanus

2.96% (SD=3.94). The average percent bare shell space per side of shell was 52.7% (SD= 1.60).

Discussion

The shell samples were all taken from the same place at the same site, so it is not surprising that the grouping of the points in the first NMDS plot (Figure 7) suggests high similarity in community structure. Only two shells were statistically different from the others at the p= 0.05 level. The fact that there was not a significant difference in community structure caused by shell size in the second NMDS plot (Figure 8) could mean that community of A. zebra shells and their epibionts are mature, so the larger shells haven’t been around that much longer 20 than the smaller shells to accrue a different community than them. It could also mean that demand for space is so high that it does not matter what size an epibiont settles on. Species abundance curves (Figure 5) curves comparing observation by eye and microscope observation reveal the increased complexity of the community structure with increased resolution of examination. This calls for a more accurate system for determining community structure in these habitats. The fact that the “combined” curve does not reach an asymptote reveals that the species richness of epibionts is underrepresented in this data set. The total species richness and diversity of the epibiont community on the Arca zebra at this location is likely higher. However, since everything cannot be accurately observed and counted, it brings up an interesting issue of taxonomic resolution. One could look closer and closer at these communities until even bacteria and viruses are included. Understanding this issue is important in being able to compare studies regarding community structure, species richness, and abundance across spatial scales. Scandland

(1979) does not mention using a microscope for finding and documenting epibionts, so his taxonomic resolution was different. Such differences preclude statistical comparisons of these data sets; however some observations are possible.

Scandland (1979) found 9 different species in the epibiont community while this study found 14. Only one order of corals (Scleractinia) was represented by my data set and two orders (Octocorallia and Scleractinia) were represented in Scandland (1979). Scandland (1979) found no hydroids on their Arca zebra, while in this study they were found on 45.6% of the Arca zebra. However, in all but two of the shells, hydroids were only discovered after looking at samples under a microscope. On the reverse side, certain groups, such as zooanthids, were reported in Scandland (1979) but not in these results. Scandland (1979) observed roughly three times the species of bryozoans as I did. Due to our differences in experience and expertise, the 21 polychaetes described in our studies are very different. I know how to accurately describe down to family level, while Scandland (1979) was able to describe to species level. The remaining groups were not so different from what I found when it comes to species richness.

While Sclandland (1979) found that barnacles, bryozoans, Chama sp and Ostrea sp were the most frequent epibionts, the most frequent specific, individual epibionts found in this data set were barnacles (Amphibalanus sp.), a colonial red tunicate (unidentified, Class Ascidiacea), a branching red alga (Gracilaria sp), a hydroid (Eudendrium carneum), and two encrusting algae

(Peyssonnelia sp. and unidentified, Family Corallinaceae). A distinction must now be made between frequency and dominance. Although these individuals were found on nearly every shell, the most dominant groups used later for the percent analysis were those covering the most surface area. For the purpose of this study, the dominant groups were of varying taxonomic specificity (1 Phylum, 1 Order, 3 Families, and 1 Genus). One final noticeable difference in epibiont frequency from Scandland (1979) was with the Scleractinia, which were much more frequent in Scandland (1979).

My results show some great differences in the epibiont community structure between

Dog Island in 1979 and 2015. Unfortunately, due to the differences in structure and taxonomic resolution between the data sets of these studies, they cannot be compared by any statistical means. Many factors could be driving these differences. One factor could simply have been that the two sampling sites have different environmental parameters and could support different fauna. The One More Time Wreck is actually 4m higher than the natural site near Dog Island.

This elevation provides more currents which are very important for epibiont health. Currents bring food and oxygen to sessile filter feeders and also carry away waste products, so different currents could potentially create different epibiont communities. Another factor that could be 22 driving the differences is time. Increases in sea surface temperatures (SST) are reported through the years (NOAA 2015), and since 1979 more coastal development has lead to increased nutrient input in the Big Bend Region. This benefits and algae but can have some severe consequences on other organisms. Increased turbidity in the water would deprive corals of the light necessary for their zooxanthellae (Symbiodinium sp.) to survive. For organisms like hydroids, this wouldn’t be an issue. In fact, the increased nutrients could benefit hydroids since they mainly rely on filter feeding. This difference could explain why Scandland (1979) found much greater abundances of corals, but no hydroids, while my study found little coral, and seemingly ubiquitous hydroids.

Like Scandland (1979), the epibionts were often unable to settle along the dorsal hinge.

However, Scandland reported that 50% of the shell surface was unused and most of this was the top of the shell. My results differed in that the top was almost always settled and that an average of 52.7% (SD= 20.9) of shell surface was used, based solely on the measurements of the most dominant encrusting groups. The observation by Scandland that the dorsal side of the shell was unused was accredited to the hinge of the A. zebra’s valve being located dorsally. Although in my study I found that this did not prevent colonization of the top of the bivalve, in many cases it did create a small barrier for encrusting organisms to cross. On some shells there was one encrusting organism on the left and another encrusting organism on the right, with a fine, straight line in between them (Figure 11). I would propose that this barrier creates a condition whereupon natural selection can bring forth the best encrusting organism. Whichever organisms are able to cross over have quicker access to a greater surface area and dominate that specific shell. 23

Figure 11. Showing the two encrusting organisms on either side of the bivalve’s hinge.

Additionally, interactions between the epibionts could be looked at. With such a need for settlement space there is likely to be heavy competition for encrusting organisms. Many of the dominant epibionts are seen overgrowing each other. Some of the epibionts, such as the long lived coralline algae, can have growth rates close to 1mm a year (Dethier and Steneck 2001), while tunicates and other algae have much faster growth rates. Interestingly enough, the

Corallinaceae and Ascidiacea groups were dominant despite their differences in growth rate.

Examining how this dominance changes through time could reveal if growth rate as well as life history has a significant part to play in the competition between these two dominant groups. The

Peyssonneliaceae, coming in third place, had almost a meter less of surface coverage than the first two groups. However, one advantage of this group observed on the A. zebra was its flexibility in growth form. This alga often began growing up the stalks of branching algae and bryozoans. I wouldn’t expect to see this happen so much with the calcareous Corallinaceae, since movement from the branched epibionts might cause it to chip and break off. The group Porifera 24 contained many sponge taxa with different growth forms, many which appeared to be early on in development. It would be interesting to see if the growth of these sponges over time caused a shift in the dominance of encrusting epibiont groups, or if epibionts that eat the sponges (such as polychaetes) keep them at a manageable or constant size. Epibionts such as barnacles depend on spat settlement and once they settle they don’t move. They do not have a way of escaping from other organisms overgrowing them. In the percent analysis, although they were the second most frequent group (second to Corallinaceae), they were not often considered dominant since they were almost always overgrown by the other encrusting groups. The encrusting bryozoans in the group Cheilostomatida were frequent but covered a much smaller area compared to the other encrusting epibionts. However, one specific shell was almost entirely covered in an encrusting bryozoan. This leads me to hypothesize that it is possible that Cheilostomatida might be dominant only in the absence of other more dominant encrusting epibionts. This type of epibiont community would be driven by larval dispersal and post settlement conditions; therefore we would expect communities from regions with different environmental regimes to be different from each other. These shells create good replicate units for studying communities from different regions without complicating factors such as differences in habitat type.

There are a few sources of error in the methods that would need to be corrected should this study be replicated. Abundance data for the macrofaunal groups was not accurate since many were found living within other epibionts such as tunicates, sponges, and algae. These epibionts were only sampled partially and dissected. For an accurate measure of diversity, those epibionts would have to be completely removed and dissected to discover and identify all organisms living within them. In addition to this, many of the barnacles were unable to be identified because they were overgrown with other epibionts. Another challenge faced was the 25 outdated or absence of accurate literature to help with identification. An example of this is seen within the flatworm group, where the previous taxonomic work was restricted to very shallow samples (4m) and this study was conducted at a depth of 12m.

Since all the shells were kept in the same tank, it is possible that motile epibionts such as decapods could have moved between shells and thrown off the abundance counts. Additionally, many of the smaller decapods were discovered hiding within the empty shells of dead barnacles.

Without being able to remove them it was very difficult to identify what species was present.

Initially this study was designed to include some form of replication so an accurate comparison could be made of the present epibiont communities on the Arca zebra in different reefs on the big bend region. Due to weather and time constraints this did not happen and so the only comparison is with Scandland (1979), describing a community from 37 years ago.

Finally, as the initial sampling process went on, it was easier and easier to find things living on the shell since more experience had been gained. This could have produced some error in species richness counts.

To better understand the interactions occurring between the epibionts and the Arca zebra, the next steps would be to conduct predation tests as well as monitor the aggregations of the

Arca zebra. Though literature has not revealed any observations or studies on local predation of the Arca zebra, there are many potential predators in the Apalachee Bay. Anderson et. al’s

(2008) study on the common octopus, Octopus vulgaris, in the Caribbean Island Bonaire showed that one of the bivalves that they fed on was the Arca zebra. Some generalist bivalve predators that are seen locally are starfish. The diet of Astropecten duplicatus, is composed primarily of bivalves, which makes it a potential predator as well (Espinosa 1982). The Florida Stone Crab, 26

Menippe mercenaria, is known to eat small oysters and southern oyster drills (Brown and

Haight, 1992) as well as other small mollusks. An investigation of these possible predators could determine whether or not having certain epibionts protects the Arca zebra.

If having epibionts shows an increased survival of the Arca zebra, then monitoring how these bivalves aggregate to form their mats would also need to be investigated. During this experiment, they were observed to move around quite a bit, dropping their byssi and growing new ones. They formed two clumps main clumps within the tank, which soon became littered with discarded byssi. They might move toward areas of greater flow where they are more likely to accumulate settling epibionts.

It is clear that many ecological aspects of this unique habitat need to be investigated. As more and more fisheries arise through time, it is imperative that this system is understood sooner rather than later. Fisheries for this organism already exist in other areas of the world, and with the recent crash of the oyster fisheries, it is possible that A. zebra could be considered next. In order to know how to protect these habitats, or even if they should be protected, studies must continue to investigate their importance as well as how much ecological redundancy exists for hard substrate in the Big Bend Region. Additionally, with organisms such as corals using the

Arcas as habitat, there should be more emphasis on exploring the ecological value of A. zebra beds.

27

Acknowledgments

This project could not have been done without the help and advice from my committee members: Dr. Sandra Brooke, Dr. Janie Wulff, and Dr. Amy Baco-Taylor. Thank you for making this such a valuable learning experience. I also want to thank Kathleen Kaiser for helping me ID sponges as well as Arvind Shantharam for teaching me how to ID polychaetes. Finally, thank you to my peers in the Marine Biology Honors Program for all of your help and support.

References

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Menippe adina (Williams et Felder). Journal of Experimental Marine Biology and

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Buschbaum, C., & Reise, K. (1999). Effects of barnacle epibionts on the periwinkle Littorina

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