FACTORS DETERMINING THE PATCHY DISTRIBUTION OF THE PACIFIC

SAND DOLLAR, EXCENTICUS, IN A SUBTIDAL

SAND-BOTTOM HABITAT

A Thesis Presented to the Faculty of California State University, Stanislaus through Moss Landing Marine Laboratories

In Partial Fulfillment Of the Requirements for the Degree Master of Science in Marine Science

By Tamara Lea Voss December 2002 DEDICATION

To my family for their constant love and unending support. Thank you.

iii ACKNOWLEDGMENTS

As with all accomplishments, they are never completed alone. I wish to thank the

Moss Landing Marine Laboratories community, fellow classmates who enthusiastically offered their help in the field, and their time with in the lab, and the MLML professors who generously shared their wisdom and experience.

I would like to thank my thesis committee: Drs. Stacy Kim, Kenneth Coale,

Pamela Roe, and Gary Greene for their help and support during my long tenure at

MLML. I especially wish to thank Stacy for her woulderful guidance and patient compasswn.

The Mary Stewart Rogers Fellowship from California State University,

Stanislaus, provided partial funding for this work.

iv TABLE OF CONTENTS

PAGE

Dedication...... m

Acknowledgements...... IV

List of Tables...... VI

List of Figures...... vn

Abstract...... vm

Introduction...... I

Materials and Methods...... 9

Results...... 17

Discussion...... 22

Literature Cited...... 30

Tables...... 36

Figures...... 46

Appendix...... 53

v LIST OF TABLES

TABLE PAGE

I Sampling schedule including site, date, location, sample type, . . ... 36 and number of replicates.

2 Statistical results for Del Monte Beach core samples...... 37

3 Mean and standard deviation of groupings per core...... 38

4 Statistical results for Coast Guard Jetty core samples...... 39

5 Sediment characteristics inside and outside 40 beds.

6 Statistical results for mean grain size, inside versus outside the sand 41 dollar beds.

7 Statistical results for settlement experiments...... 42

8 The mean and standard deviation of Dendraster excentricus...... 43 larvae that metamorphosed, remained as plutei, or were lost from the experiment.

9 Category groupings that resulted from post-hoc comparisons...... 44 of the settlement experiments

vi LIST OF FIGURES

FIGURE PAGE

1 Oral and Aboral views of Dendraster excentricus test...... 46

2 Dendraster excentricus beds comparing shoreward ...... 4 7 and seaward edges.

3 Perpendicular and parallel alignment of sand dollars within...... 48 a bed.

4 Competent Echinopluteus of Dendraster excentricus, ...... 49 showing adult rudiment within larval gut area.

5 Aboral view of a newly metamorphosed juvenile ...... 50 Dendraster excentricus.

6 Map of Monterey Bay, California showing the location of...... 51 the two study sites.

7 Seasonal adult Dendraster excentricus density at the Del Monte... 52 Beach site.

vii ABSTRACT

The Pacific , Dendraster excentricus, can form dense assemblages in the

shallow sandy subtidal. The distribution of beds of D. excentricus is patchy along the

Pacific coast, and factors controlling the distribution of sand dollars are not well

understood. The distribution of sand dollar beds at two sites within Monterey Bay was

evaluated for infaunal community structure. Infaunal organisms were determined to

belong to one offour groups (burrowers, predators, tube-builders, or Mollusca). These groups were examined for their effects on one another and on sediment stability, both

inside and outside of the adult sand dollar bed. Additionally, sand dollar plutei that were

competent to metamorphose were offered several substrata to determine what type of

settlement cue is necessary for successful settlement and metamorphosis to take place.

Larviphagy, the cannibalism oflarvae of D. excentricus by its adults, was evaluated as

another factor important in determining initial distribution of sand dollar beds. The results of the study indicate that the distribution of sand dollar beds are initially

established and maintained by settlement processes.

vi:ii. INTRODUCTION

Range and Distribution

The Pacific sand dollar, Dendraster excentricus, (Figure 1) is an irregular echinoid belonging to the Order Clypeasteroida. Patchy beds of D. excentricus exist from Alaska to Baja California, covering the sand bottoms of both sheltered bays and open coast areas (Chia, 1969; Merrill & Hobson, 1970; Birkeland & Chia, 1971; Timko,

1975, 1976; Niesen, 1977; Cameron & Rumrill, 1982; Highsmith, 1982). D. excentricus is found intertidally along its northern distribution and in shallow subtidal waters along its southern distribution (Chia, 1969; Birkeland & Chia, 1971; Timko, 1975; Niesen,

1977; Cameron & Rumrill, 1982). Subtidal sand dollars live in an inclined position with their anterior edge partially buried in the sand (Chia, 1969, Timko, 1975, 1976; Smith,

1981; Morin et al., 1985). D. excentricus can form dense aggregations of up to several hundred individuals per square meter (Chia, 1969; Birkeland & Chia, 1971; Smith, 1981;

Highsmith, 1982; Morin et al., 1985). These beds may exist for decades at the same location, much longer than the life span of the individuals, which is approximately eight years (Jensen, 1969; Birkeland & Chia, 1971; Highsmith, 1982).

The shoreward edge of a sand dollar bed seems to remain in the same location on the bottom throughout the year. Although periods of high surf can temporarily displace large numbers of sand dollars, the bed margin is reestablished within a few days after the storm (Morin et al., 1985). The shoreward edge is located where major sand movement stops, just outside the breaker line. The seaward edge is more distinct than the shoreward edge (Figure 2). It moves out during the winter until the bed reaches irs peak width in

1 January, when it starts migrating back shoreward (Morin et al., 1985). and P. giganteus, seastars that prey on D. excentricus in this environment, are found along the seaward edge of the sand dollar bed, and may influence its location

(Birkeland & Chia, 1971; Morin et al., 1985).

Habitat

Merrill and Hobson (1970) defmed four habitats that D. excentricus occupies: (1) bay, (2) tidal channel, (3) protected outer coast, and (4) exposed outer coast. Individuals of the "bay" type assume a horizontal position, lying flat on the sand or burrowing just below the surface of the sand. The substratum consists of fme, poorly sorted sand, usually with an overlying layer of detritus. Most individuals occur in water 0.6 to 1.2 meters deep. During unfavorable conditions, such as exposure during falling tides or when heavy rains decrease salinity, individuals of D. excentricus will burrow deeper into the sands rather than move to deeper water.

The "tidal channel" habitat includes strong tidal currents, and clean, well-sorted sand, with most individuals living in the inclined position. Populations of D. excentricus · within tidal channels can be found with either their lateral axis perpendicular to the surge current (Figure 3a), or parallel to the surge current (Figure 3b). When the sand dollar's lateral axis is perpendicular to the surge current its oral surface faces upstream, and when it's lateral axis is parallel to the surge current, its oral surface faces either right or left across the current.

Sand dollars of the "protected outer coast" maintain an inclined position with their anterior edge buried in the sand, and align their lateral axis parallel to the strong

2 onshore-offshore sweep of the current surge, which is perpendicular to the weaker long-. shore transport (Merrill & Hobson, 1970) (Figure 3b ). These beds tend to have sharp seaward margins, which exhibit the maximum density in 6 to 12 meters of water; the bed extends shoreward to approximately just outside the breaker line.

Sand dollars of the "exposed outer-coast" are not found close to the shore and are completely buried (Merrill & Hobson, 1970). According to Merrill and Hobson (1970) this situation extends north from Point Conception into Oregon and Washington, and less is known about the individuals found in these locations than those in the other three habitat types.

Natural History

Dendraster excentricus uses three different methods to feed, depending upon the type of food being handled. Food items include particles <50J.l1Il, non-motile material, and motile prey (Timko, 1976). Transportation of particles <50J.l1Il in size toward the mouth is by ciliary currents. Tube feet are used to grasp and push non-motile material,

>50J.l1Il in size, toward the food grooves. Small active prey are trapped by the spines, which enclose them, and create a cone-like trap. The large bidentate pedicellariae are then used to crush the prey before it is placed into the food grooves.

Dendraster excentricus spawning occurs from mid-April through August, during which time eggs and sperm are shed into the water column where fertilization takes place

(Strathmann, 1987). The larval form is a planktotrophic echinopluteus. Development takes 3-8 weeks and larvae are competent to metamorphose when the adult rudiment has

3 visible tube feet and spines and fills the larval body (Chia & Burke, 1977; Strathmann,

1987) (Figure 4). It takes 1-2 hours to complete metamorphosis from a bilaterally symmetric echinopluteus to a radially symmetric juvenile sand dollar (Figure 5)

(Strathmann, 1987).

Patchiness

The distribution of sand dollar beds is patchy along the Pacific coast. There are many locations in the shallow, sandy, subtidal environment, some adjacent to standing beds, that are uninhabited by Dendraster excentricus (Smith, 1981; Highsmith, 1982;

Morin et al., 1985). Patchiness or spatial heterogeneity of D. excentricus beds provides a unique opportunity to examine if particular shifts in the abundance patterns of infaunal organisms occur across sand dollar bed boundaries. Sand dollar beds can be created and maintained by many different mechanisms. Both biological and physical factors have been used to explain the patchy distribution of sand dollars (Birkeland & Chia, 1971;

Timko, 1975; 1976; Niesen, 1977; Cameron & Rumrill, 1982; Brenchley, 1982; Morin et al., 1985). From a physical perspective, near-bottom hydrodynamic flow across the bed is altered, relative to non-settled regions of the seafloor, by the high densities of sand dollars, and may facilitate filter feeding (Timko, 1975). From a biological perspective, mass spawning in close proximity may enhance reproductive success, by increasing the likelihood that eggs and sperm will meet quickly in the water above the beds. Other biotic causes of patchiness can include differential larval settlement, differential larval survival, or spatial separation of competitors or between predators and prey (Wilson,

1968; Newell, 1970; Muus, 1973; Meadows & Campbell, 1972; Gray, 1974; Pickett &

4 Cadenasso, 1995). Adults are thought to provide a biochemical cue for settling larvae, that signals good habitat (Highsmith, 1982). Recruitment success is improved when

larvae settle and metamorphose in a location suitable for adult survival (Caldwell, 1972;

Burke, 1984). The dense numbers of sand dollars in beds may also provide protection from strong currents by dissipating the energy of the wave surge, or by providing refuge for the newly metamorphosed juveniles from predation due to adult and predator

interactions (Timko, 1975, 1976; Woodin, 1976, 1978; Highsmith, 1982). Sand dollar bed formation can also be episodic and therefore temporally variable. The understanding of where and why beds form is crucial to autecological understanding and predictive capacity.

Infaunal Community

Biological factors such as competition, predation, adult-larval interactions, and the re-working of the sediment are well known for the structuring of soft sediment

communities (Woodin, 1974, 1976, 1978; Wiltse, 1980; Smith, 1981; Brenchley, 1982;

Ambrose, 1991; Zajac & Witlatch, 1991). Infaunal organisms found inside the sand

dollar beds may affect Dendraster excentricus by preying on the settling larvae or newly

metamorphosed juveniles. Alternatively, the reworking of the sediment by the infauna

during locomotion and deposit feeding may cause young sand dollars to be buried or

incidentally ingested. On the other hand, dense aggregations of D. excentricus along the

central California coast may play an important role in the stabilization of the soft

sediment communities in that locality. Sand dollar beds may alter the infaunal

community by reducing near bottom current speeds and stabilizing sediments, providing

5 a different habitat than the nearby shifting sand. Whether sand dollar beds in soft sediment provide habitat that hosts unique communities can be determined by firSt ascertaining any differences in the infaunal communities found inside and outside the bed area, and then developing testable hypotheses that explain why these differences occur.

Larval Settlement Cues

Marine invertebrate larvae initiate settlement, and metamorphosis to the juvenile stage, in response to a variety of cues. Cues may be physical (e.g. substratum rugosity;

Gray, 1974; Crisp, 1974), or biological (e.g. microbial films; Celmer, 1975), and cues may act as attractants or repellents (Doyle, 1975; Burke, 1984; Woodin, 1991 ). Cues often act in combination, and interact with other factors such as larval supply and hydrodynamic flow to defme settlement success (Butman, 1987; Eckman, 1983). For

Dendraster excentricus·there is a small temporal window of opportunity for settlement and metamorphosis; larvae must first reach a stage in their development in which they are competent to metamorphose before they will respond to settlement cues. Larvae that have been competent for too long may settle even in the absence of appropriate cues, because the larvae do not have enough energy reserves to delay metamorphosis any longer (Birkeland et al., 1971; Highsmith & Emlet, 1986).

Highsmith (1982) has demonstrated that intertidal adults of Dendraster excentricus play a beneficial role and signal good habitat for larval settlement and metamorphosis. Cues released by the adults in the subtidal populations may be waterborne or sand-bound, or sandy subtidal substratum may be a sufficient textural cue for settlement and metamorphosis. Differential survival of settlers affects recruitment

6 success, or survival to reproductive age, but the initial distributional pattern is established by larval settlement.

Larviphagy

Larviphagy, the cannibalism of!arvae by adults, was reported by Timko (1975,

1979) as a density dependent filter of settlement success. Woodin (1976) developed a hypothesis that predicts that settlement of essentially all larvae, including larvae of their own species, would be prevented by a high density of suspension feeding adults. If

Iarviphagy occurs given that adults are filter feeders that can ingest settling larvae, adults of Dendraster excentricus may have a negative role in larval settlement success. Timko

(1975) suggested larviphagy as a mechanism to explain the erratic settlement cycles of

Dendraster excentricus, as described in the literature, by predicting, "only very low levels of settlement (are) to be expected where adults are abundant and dense." On the other hand, a successful settlement event would be predicted only when the adult density has decreased; and space has opened up within the bed. As a result, beds of D. excentricus should demonstrate age distributions with dominant year classes. Timko

(1975, 1979) carried out Iarviphagy experiments by placing individuals of D. excentricus with their oral surface up and injecting larvae onto the oral surface of the test using a syringe with a catheter tube connected to its end. Highsmith (1982), on the other hand, found that Iarviphagy did not occur during his experiments. He placed larvae in a bowl with an adult D. excentricus lying with its oral surface down. If the larvae were competent to metamorphose, they did so. If the larvae contacted the adult they were eventually rejected by the tube feet lining the food grooves. The major differences

7 between these two works were the position of the adult, either oral side up (not natural) or oral side down (natural), and the placement of the larvae. Timko placed the larvae on the oral surface of the adult, whereas, Highsmith added larvae to the adult's bowl and allowed the larvae to come into contact with the adults on their own. More work using adults in a normal feeding position is required to answer the question of whether or not larviphagy occurs, and what effects it might have with respect to larval recruitment in D. excentricus.

Hypotheses

An initial factor that controls sand dollar bed distribution is settlement success.

Settlement success is an interplay of (1) larval supply, (2) substratum selection and metamorphosis, and (3) larval or early juvenile mortality, which results in specific patterns of settlement. The factors influencing larval settlement patterns must first be better documented and understood so that sand dollar bed patchiness can be explained: I will examine factors affecting settlement success with a combination of field observations and laboratory experiments.

The objectives of this study are to:

I. Provide a description of the infaunal community found within a protected

outer coast sand dollar bed, and assess the potential influence of in faunal

species (e.g. by predation, tube-building or burrowing activities) on sand

dollar recruitment.

2. Test for differential larval settlement and metamorphosis in response to

various cues from a subtidal sand dollar bed.

3. Determine if larviphagy occurs in subtidal sand dollars.

8 MATERIALS AND METHODS

Study sites

The fieldwork for this study was conducted along the southern end of Monterey

Bay, California (Figure 6). Two protected outer coast sand dollar beds were investigated

for density of Dendraster excentricus, description of infaunal organisms, and grain size

analysis. The first site was along the Del Monte Beach next to the commercial wharf in

Monterey. The second was located near the Coast Guard Jetty in Monterey. Laboratory

experiments, investigating larval settlement cues, were carried out at the Moss Landing

Marine Laboratories facilities using adults collected from the Del Monte Beach

population.

Del Monte Beach

The sand dollar bed at the Del Monte site is in deep, clean sand located at 36°

36.07' N, 121 o 53.29' W (Figure 6; site 1). No rock outcrops, no attached algae or kelp,

and no drift algae or kelp were observed in over 15 SCUBA dives and several other free

dives. Centimeter size ripple marks were typically present at Del Monte Beach. When

individuals of Dendraster excentricus were buried, they were invisible under the rippled

surface. A film covered the sand by late summer. The bed was protected from

prevailing wind and swell. Its shoreward margin extended to just outside the breaker line

in water depth of 4.5 meters, and was not as distinct as its seaward edge, which ended

abruptly in waters of seven meters depth. Individuals of D. excentricus were inclined on

9 their anterior edge, perpendicular to the beach, and parallel to the surge current (Figure

5b ). After storms or rough surge, sand dollars were redistributed, outside their usually defined beds, or completely buried, but would rapidly reform the bed and return to an

inclined position within a few days.

Coast Guard Jetty

The beach at the Coast Guard Jetty also has a protected outer coast sand dollar bed. This beach is located at 36° 36.57' N, 121 o 53.62' W (Figure 6; site 2). There are

boulders nearby with attached algae and kelp to the west, and a deep sand channel,

running generally north-south, to the east. There were thick stands of the red alga

Gracilaria sp. within the adult sand dollar bed. Individuals of Dendraster excentricus

were very dense underneath the Gracilaria. The bed was in 5-10 meters of water

(shoreward and seaward edges, respectively). This site was visited twice in August 2001;

individuals of D. excentricus were observed to be inclined and parallel to the surge

current.

Infaunal Description

Samples were taken from inside and outside the adult Dendraster excentricus

beds at both the Del Monte Beach and the Coast Guard jetty sand dollar beds to provide

descriptions of the infaunal community (Appendix A). All biological cores were

collected by myself using SCUBA, which allowed for observation of the D. excentricus

bed and careful sample acquisition. The biological samples were collected using 13 oz

10 coffee cans with both ends removed. The bottom of the can was replaced with tightly sealed 500Jlm mesh screen and the top had a watertight plastic lid. The samplers had a

2 diameter of 10 em and length of 15 em (0.008m ). The average depth of a collected core was 10 em. The samplers were carefully pushed into the sediment. A watertight snap-on plastic lid was shoved down along side the can until it could be fitted over the opening.

The core was then dug out and the lid checked to make sure it was well sealed. Bed cores were not taken in areas unoccupied by D. excentricus; in areas of sparse occupation, cores were taken where there were visible aggregations of D. excentricus. Cores were also collected from an area outside the adult D. excentricus bed, this was located 5-6 meters seaward of the sand dollar bed. Six cores were taken from each site at each time.

This number of replicates was sufficient for infaunal community evaluation based on data from other quantitative studies (Hodgson & Nybakken, 1973). Once on shore the samples were immediately screened with a 500Jlm sieve and all screened organisms were fixed with 5% buffered formalin in seawater. After 24 hours the formalin was poured off, the sample was rinsed in fresh water, and stored in 70% alcohol. The were later sorted, identified and counted under a dissecting microscope. Polychaete and crustacean species were assigned to one of three functional groups: tube-builders, active burrowers, or predators (Fauchald & Jumars, 1979; Slattery, 1980). Nematodes and cope pods were considered to be representative of meiofauna and were not quantified.

The density of D. excentricus individuals larger than 1em was determined by use of a 0.25 m2 quadrat. The quadrat was dropped pseudo-randomly in the bed and all individuals of D. excentricus within it were counted. This resulted in a pattern of haphazard, though presumably unbiased, sampling rather than a strictly random one.

11 This was done for practical considerations due to the difficulty in relocating a sand anchor that would have served as a point of origin, from which a random sampling pattern could have been set-up. After November 2000, the technique was changed

slightly, and the sediment and animals were scooped out of the quadrat area and screened

underwater through a 1mm sieve. All specimens of D. excentricus were placed into a

sack and brought to the surface, to be counted. This change ensured that the very small

"yearlings" of D. excentricus were not under-counted. Counted sand dollars were

returned to the bed. The density of D. excentricus specimens smaller than 1em was

obtained from the infaunal core samples.

Sediment was analyzed to ascertain any difference between inside and outside the

adult sand dollar beds. A sediment core (diameter 3 em, length 15 em) and its duplicate

were taken at each study site within and outside the bed for analysis. The samples were

first dried and then sieved through a series of seven sieves (2.0mm, 1.0mm, 0.355mm,

0.250mm, 0.180mm, 0.125mm, and 0.090mm), which were placed on a mechanical

shaker for 15 minutes. The fraction retained by each sieve was weighed. Mean grain

size, sorting coefficient, percent silt and clay, and percent and type of debris were

determined (Folk, 1968). Twenty-five sampling events were made from April2000 to

August 2001 (Table 1).

Larval Settlement Selectivity

Larvae of Dendraster excentricus that were competent to metamorphose were

used to evaluate several different substratum cues that might be needed for

metamorphosis to occur. Cues tested included the presence or absence of sand, adults,

12 and an unidentified chemical cue in the sand or water from an adult sand dollar bed.

Larvae for these experiments were spawned in the laboratory from adults collected from the subtidal bed at the Del Monte Beach site. Eggs and sperm were collected by injecting sand dollars with 1 mL of 0.5 M KCl periorally. They were then placed aboral surface down in a small glass dish. Eggs and sperm are easily distinguished. Eggs of D. excentricus are pale orange, 110-125 fliil in diameter, and are covered by a thick jelly coat (Strathmann, 1987). This jelly coat contains small peripheral red granules, which are cells (Strathmann, 1987). One to two drops of sperm were added to the dish containing the eggs and fertilization was allowed to occur. After approximately 2-3 hours, the fertilized eggs were placed in a large bowl with -1.5 liters of filtered seawater and the bowl was placed on a wet table in the aquarium room at Moss Landing Marine

Laboratories. After the early pluteus, 2-armed stage was reached, the larvae were divided into small dishes and fed with Duna/iella every other day. Larval cultures were neither stirred nor bubbled with air as this causes damage to the developing larvae. Cultures were maintained on a running seawater table at -15-16°C. The range of time from spawning to competence was 3-5 weeks. Larval competence to metamorphose was determined by the presence of the adult rudiment, tube feet, or spines in the larval gut area (Birkland & Chia, 1971; Highsmith, 1982; Caldwell, 1972). Settlement experiments involved introducing competent larvae into beakers that contained the various substrata to be evaluated and scoring their response as '.'metamorphosed," "remained as larvae," or were "lost from the experiment."

Four different settlement selectivity experiments were run. The experiments evaluated seven substratum types: (A) filtered seawater, (B) bed seawater, (C) "baked"

13 sand, (D) sand from an adult bed, (E) an adult specimen of D. excentricus only, without sand of any type, (F) an adult of D. excentricus plus "baked" sand, and (G) an adult of D. excentricus plus sand from the adult bed. Sand for the settlement experiments was collected from densely populated areas of the Del Monte Beach bed on the morning the experiment was to start. Sand from a bed that was to be used for the baked sand substratum type was collected earlier and baked for 24 hours at 150°C in an oven to deactivate any chemical cue which might be present. Water for the treatment type that used bed seawater was taken from an aquarium used as a holding tank for sand dollars that had contained animals for several weeks prior to the water being used in the substratum experiments.

For the first experiment, 10 competent larvae were placed in each of 1-liter beakers containing one of the seven different substratum types being tested. Three replicates of each substratum were used, for a total of 21 beakers. When the experiments were terminated, each replicate was fixed with 5% buffered formalin and rose bengal in seawater. After 24 hours the replicates were rinsed with fresh water, screened with a

250Jlill sieve, and stored in 70% alcohol. With the aid of a dissecting microscope, replicates were later scored as metamorphosed individuals, larvae still present, or individuals lost from the experiment. The first experiment testing all seven substrata ran for 48 hours. The second experiment, also testing all seven substrata, ran for 18 hours and used five replicates, each with nine competent larvae. The decrease in time between the first and second experiment was made to ensure that the larvae were not undergoing metamorphosis simply because they were ready and had reached a "now or never" period. The time period necessary for metamorphosis was tested by placing two

14 competent larvae in a small dish with an adult. Complete metamorphosis was observed to take place in approximately three hours; thus, if metamorphosis of competent larvae is initiated on contact with a suitable cue, an 18-hour time frame should be sufficient for complete metamorphosis. The third experiment that tested two substrata types using three replicates with eight larvae each was run for 18 hours. The treatments, selected to refme the results of the two initial experiments, were (C) baked sand and, (F) D. excentricus plus baked sand. The fourth experiment compared the treatments (D) bed sand, (E) D. excentricus only, and (G) D. excentricus plus bed sand, using three replicates with nine larvae each, and was run for 18 hours.

Larviphagy Experiments

The concept of larviphagy was investigated because of the apparent contradiction between the larvae returning to an adult bed due to the "signaling" of good habitat by the adults, and the fact that adults of Dendraster excentricus are filter feeders and have been reported to consume the returning larvae (Timko, 1975, 1979). Adults of D. excentricus that had been collected within the week were offered plutei at the 4-arm, 6-arm, or 8-arm stage. Behavior of the adult and plutei were watched for an hour. After the initial hour of observation the dishes containing the adult and plutei were placed on the seawater table and checked again the next day. Adults of D. excentricus were also offered newly hatched Artemia nauplii that are of similar size as the D. excentricus larvae (500-750~IDJ).

Additional observations were made using D. excentricus adults that had been held in aquaria for several weeks and were presumably in a starved condition.

15 Statistical Analysis

Infaunal samples from the Del Monte Beach bed were evaluated for differences over time and differences between inside and outside the adult Dendraster excentricus bed. The Coast Guard Jetty study site was evaluated for differences between inside and outside the adult sand dollar bed. They were evaluated using both ANOVA and t-tests for differences between three types of functional groups, tube-builders, active burrowers, and predators as well as differences in the density of Mollusca, the total number of species, the total number of individuals, and the density ofjuvenile sand dollars.

Statistical calculations employed the use of SYSTAT I 0.0 (SPSS Inc, 2000). When necessary, data were ftrst transformed using In ( x+ 1) to correct for homogeneity. If variances were not homogenous even after data were transformed, a Kruskal-Wallis test was used.

An ANOVA or t-test was used for larval substratum selectivity experiments. If the null hypothesis of no difference was rejected, a post-hoc test (Tukey's or

Bonferroni's) was used to make multiple comparisons to determine which of the means were significantly different from one another. The assumptions of independent data were addressed by careful experimental design. Homogeneity of variances were evaluated using the Cochran's test (Winer, 1971) and were calculated by hand. The Kolmogorov­

Smirnov test was used to test for normality of data.

16 RESULTS

Infaunal Cores

Del Monte Beach

When statistical tests were used to test for differences between tube builder, active burrowers, predators, Mollusca, juvenile sand dollars, total number of species, and total number of individuals with respect to date and location inside or outside sand dollar beds (Table 2). There was a significant difference in both time and location for juvenile sand dollars and for Mollusca, with more juveniles occurring inside the adult bed and during August 2001 (Table 3). There was a significant difference over time, but not location, for active burrowers and the number of species present, with more individuals occuring in the summer (Table 2). There was a significant interaction between time and location effect for number of species and for the number of individuals, but not for any of the other groups, indicating that, for total number of species and individuals, the factors of season and location cannot be separated.

Coast Guard Jetty

When infaunal cores were analyzed for differences between inside and outside the adult sand dollar bed, using the same groups as in the Del Monte data (Table 4), there were significantly more active burrowers, juveniles, number of species, and number of individuals inside than outside the bed (Table 3, 4). There were also significantly more

Mollusca outside the bed (p = 0.026) (Table 4).

17 Grain Size Analysis

There was no significant difference in grain size, sorting value, percent silt and clay, and percent and type of debris, between inside and outside the adult sand dollar

beds at either of the study sites (Table 5, 6). The sorting value, which is a measure of

standard deviation, for both sites was< 0.35

Adult Density

Mean densities of Dendraster excentricus were significantly higher at the Coast

Guard Jetty site than at Del Monte Beach for adults larger than I em, measured in 0.25m2

2 quadrats (224 ± 120 and 7 ± 5 animals per 0.25m , respectively,p = 0.001). Adults ranged from 26 to 405 animals per 0.25m2 at the Coast Guard Jetty study site, and from 1

to 13 animals per 0.25m2 at Del Monte Beach. The density of adult D. excentricus

changed seasonally at the Del Monte site (Figure 7). Seasonal density decreases in the

winter and increases in the summer at the Del Monte site were statistically significant (F

= 2.870,p = 0.015, n = 43). The decrease in density during the winter when surge was

heavier reflects changes in the areal distribution of the bed rather than fluctuations in the

number of D. excentricus (Morin eta!., 1985).

18 ~.,,,,,,:·

Larval Substrate Selectivity Experiments

When patchiness of the adult Dendraster excentricus bed was tested to determine

if it was the result of differential settlement of larvae, the initial assumptions of

homogeneity of variances and normality of data were supported by results of Cochran's

and Kolmogorov-Smirnov tests, respectively (Table 7).

Experiment 1

In the first experiment, in which seven substrate types were used (Table 8), and

the experiment ran for 48 hours, the ANOVA analysis produced a finding of significance

between the different treatment means (F-ratio = 68.154,p = <0.0005, n = 21). The

treatment results grouped into three different categories: treatments not associated with

adults, treatments associated with adults, and the adult with baked sand treatment, which

grouped by itself (Table 9). The mean of each treatment in a group differs significantly

from every other treatment mean in the other two groups, but does not differ significantly

from the other treatment means within the group.

Experiment 2

In experiment two, which included all seven substrata types and ran for I 8 hours,

the one-way ANOVA analysis of the treatment means showed a significant difference (F-

ratio= 34.268, p = 0.000, n = 35). Again the means of each treatment in a group differed

significantly from every other treatment mean in the other group, but did not differ

significantly from the other treatment means within the group (Table 9). The resulting

19 groups were similar but not exactly the same as in the first experiment. The treatment type adult with baked sand grouped with the filtered seawater, bed seawater, and baked sand treatments. The second group, those treatments associated with adult sand dollars, remained the same.

Experiment 3

The two-sample t-test was not significant (t = 3.0, p = 0.058, n = 6) in experiment three, in which only two substrata, baked sand, with and without an adult, were compared

(Table 8). The power of this analysis was 0.764. There are two complications to interpreting the results of this experiment. The first is that one replicate of the adult with baked sand treatment type was lost due to the death of the adult during the experiment.

The second observation is that there were more metamorphosed larvae for these two treatments than in either of the previously run experiments. These larvae were the oldest

(35 days from spawn to date used in an experiment) used, and may have reached their metamorphosis threshold.

Experiment 4

In the fmal experiment, which compared three substrata, the treatments associated with adult sand dollars; adult only, bed sand, and adult with bed sand (Table 8) there was significant difference (F-ratio = 7 .0, p = 0.027, n = 9) shown by the ANOVA. A

Bonferroni post-hoc test determined a significant difference between the adult and adult

20 with bed sand treatments. The other two comparisons were not significantly different

(bed sand, and adult only; bed sand, and adult with bed sand).

Larviphagy

Larvae that added to containers with adults swam around and contacted the spines and tube feet of the adults, but no adult behavior, such as using the spines to trap the larvae or extending the pedicellariae to crush larvae, were seen. During two of the trials involving 8-arm, competent larvae, three individuals were observed to undergo metamorphosis.

Larvae of early developmental stages ( 4-arm, 6-arm, and 8-arm pre-competent) were observed to continue development, comparable to the larvae in the culture dish from which they had been taken. Fully competent, 8-arm, larvae were found the next day to either be swimming around or were seen to have completed metamorphosis over night and the newly metamorphosed juveniles were crawling around on the bottom of the dish.

When larvae of Artemia, (brine shrimp) were added to the dish the adult immediately reacted by initiating a trapping response with its spines. The tube feet and pedicellaria also grabbed the brine shrimp larvae, which were rapidly captured, crushed, and put into food grooves, where they were transported to the oral surface and into the mouth.

Adults in trials using sand dollar larvae with adults that had been held unfed in seawater aquaria for several weeks, and were presumed to be starved, displayed spine­ trapping and used their tube feet and pedicellaria to capture and place the larvae into their food grooves.

21 DISCUSSION

The soft-bottom environment of the shallow subtidal is a variable habitat with strong wave surge and constantly shifting sand. In shallow water, soft sediment stability is altered by physical disturbances that re-suspend sediment via high-energy wave surge

(Gray, 1974; Ortb, 1977; Eckman, 1983). There are also biological factors that can act to either stabilize or destabilize the sediment. Sediment stability can be increased by the tube building activity of small crustaceans and polychaetes (Rhoads & Young, 1971 ).

Sea grasses and other objects can stabilize sediment by buffering currents and damping wave action (Ortb, 1977). The stability of the sediment can be decreased by burrowing and deposit feeding activities of the infauna, which rework the sediment (Rhoads &

Young, 1970; Rhoads, 1974).

This soft-bottom shallow water habitat has been recognized as having distinct community assemblages (Fager, 1968; Merrill & Hobson, 1970; Davis & VanBlaricom,

1978; Oliver et al., 1980; Kastendiek, 1982; VanBlaricom, 1982; Morin et al., 1985), characterized by low species diversity and density (Dexter, 1969; Day et al., 1971). The different infaunal communities can alter the physical character of their environment and thus influence their surrounding community structure by interaction via predation, competition, and sediment reworking (Woodin, 1974, 1978; Ortb, 1977; Brenchley, 1978,

1981, 1982; Smith, 1981; Highsmith, 1982; Ambrose, 1991). Woodin (1976) described competitive and trophic interactions of three functional assemblage groups that were burrowing deposit feeders, suspension feeders, and tube-builders, and explained that the observed sharp boundaries between assemblage groups were due to interactions among the established infauna and settling larvae. Burrowers and tube-builders compete for

22 space, with tube-builders binding the sediment and restricting the activity of burrowers.

Burrowers rework the sediments, preventing survival of tube-builders, and increasing the

re-suspension of sediments which 'clogs' the filters of suspension feeders, and ingest the

settling larvae of both groups. Suspension feeders filter all the groups' larvae from the

water column, inhibiting successful settlement. Thus the autecology and abundance of

benthic organisms interact with and influence the community and habitat structure.

Brenchley (1981) experimentally demonstrated a significant reduction in tube-builder

density after the addition of active burrowers ( Upogebia pugettensis, Abarenicola pacifica, and Dendraster excentricus).

In the intertidal, Dendraster excentricus destabilizes sediments by burrowing into

the sediment at low tide to prevent desiccation, and inclining at high tide to filter feed.

The sediment destabilization due to intertidal sand dollars leads to significantly more

tube-builders outside sand dollar beds, and significantly more active burrowers inside the

beds (Smith, 1981; Brenchley, 1978, 1981). In addition, Smith (1981) found lower

species diversity inside intertidal sand dollar beds, indicating that fewer species were able

to coexist with intertidal D. excentricus.

Though intertidal sand dollars destabilize the sands through their burrowing

activities, subtidal sand dollars may stabilize shifting sand and allow infaunal organisms'

access to this high-energy area. Because subtidal sand dollars do not bury and incline

with each tidal cycle like intertidal sand dollars do, there is a less dramatic reworking of

the sediments by the subtidal sand dollars. This resulted in less disturbance, and even

enhances habitat stability. Sediment stabilization by a single species can play a major

role in structuring the community (Kim, I 989). My results of no significant difference in

23 abundance of tube-builders or active burrowers inside or outside the Del Monte sand

dollar bed support my prediction of little or no sediment-reworking disturbance within the bed. Evidence for increased stability in subtidal D. excentricus beds is demonstrated

by the significantly higher number of species and individuals observed inside the bed than outside the sand dollar bed at the Coast Guard Jetty. Mollusks, mostly sedentary, were significantly higher outside the bed at both study sites. This was an expected pattern due to the competitive interactions between sedentary suspension feeders and

active burrowers, as described by Woodin (1976).

Smith ( 1981) listed the infaunal species found inside and outside intertidal sand

dollar beds and indicated just one species that occurred in only one location. The tube­

building amphipod Ampe/isca agassizi occurred solely outside sand dollar beds. All other organisms had varied abundances but were found inside and outside sand dollar beds in at least one of the 10 sites studied. The subtidal sand dollar beds investigated by

Merrill and Hobson ( 1970) also shows no animals endemic to sand dollar beds, but many

organisms were recurrent and were regarded as characteristic. Merrill and Hobson

(1970) hypothesized that subtidal sand dollars not only stabilize the substratum by

curtailing the erosion of sand in this high-energy environment but also provide refuge

from predation. I also found no species endemic to the subtidal sand dollar beds studied

(Appendix A). The species lists of organisms found inside and outside the bed were

similar and differed only in the abundances of the organisms.

24 Substratum Selectivity

Settlement, the influx of the youngest age class, is an important mechanism shaping the structure of a population (Cameron & Schroeter, 1980). The understanding of Dendraster excentricus bed patchiness is improved with the increased knowledge of sand dollar larval settlement. Larval settlement in response to a specific cue has been determined for several marine invertebrates (Crisp, 1974; Cameron & Hinegardner, 1974:

Gray, 1974), and recruitment success is improved when larvae settle and metamorphose in a location suitable for adult survival (Caldwell, 1972; Highsmith, 1982; Burke, 1983).

Settlement cues can include far field signals like waterborne chemicals, temperature or light, and near field signals that may be tactile such as substrate rugosity or grain size, or chemical contact signals from conspecifics, prey, or biofilms (Crisp, 1974; Celmer, 1975;

Chia & Burke, 1977; Burke, 1983; Highsmith, 1982; Butman, 1987; Woodin, 1991).

Larvae of intertidal Dendraster excentricus are known to settle and metamorphose in the presence of adults of the species (Caldwell, 1972; Highsmith, 1982). It is believed that a chemical cue is released by adults of D. excentricus and is sequestered in the sand of the bed. The results of the current subtidal study were similar. Greater larval metamorphosis occurred in treatments associated with adults. Highsmith's (1982) results with intertidal sand dollars determined that the greatest metamorphosis occurred in response to the adult only treatment. The subtidal work showed the greatest metamorphosis occurring in the bed sand treatment (experiment 1) and adult with bed sand treatment (experiment 2). The

25 adult only treatment was second, for both experiments. Although the presence of the adult is important in providing the chemical cue and thereby conditioning the sand, what appears to be more important for triggering metamorphosis in larvae is the presence of conditioned sand. The different results for the adult with baked sand treatment between the first two experiments leads to the further question of how long it takes for an adult to condition the sand. Although the length of time the experiments were allowed to run was shortened to 18 hours after the first experiment of 48 hours as a precaution for larvae reaching the "now or never" stage, this did not end up being a concern, but led to the discovery of a potential time factor in which the sand must be exposed to the adults for the concentration to reach a level sufficient for the larvae to detect, settle, and metamorphose. The shorter time in the second experiment (18 hours vs. 48 hours) was evidently insufficient for the adult to introduce the settling cue into the sand. This indicates that the chemical cue released by the adult is held in the sand, a more localized cue for a settlement response than if it were released into the water column.

Additionally, the sand itself may provide a physical substratum that the metamorphosing larval can "hold on to" as metamorphosis occurs. Cameron and Hinegardner (1974) showed that larvae of Arbacia punctulata are induced to metamorphose by a combination of a soluble chemical cue and tactile stimulation of the primary podia of the adult rudiment.

Extrapolation of these results suggests that there should be more settlement and metamorphosis of larvae inside an existing adult D. excentricus bed than outside of the bed. For both study sites, Del Monte Beach and Coast Guard Jetty, there were significantly more newly metamorphosed juveniles inside the bed than outside the bed as

26 determined by the infaunal core data. These results were independent of the different mean densities of adults within the beds; Coast Guard Jetty had a higher density of sand dollars than the bed at Del Monte Beach. Larval substratum selection is an initial controlling factor for the establishment of the stabilizing species, Dendraster excentricus, in this community. This is an important first order process in understanding the patchiness of adult sand dollar beds.

Larviphagy

The third objective of this study was to determine iflarviphagy occurs in subtidal sand dollars. Results from this study indicate that larviphagy does not occur under normal conditions. If the adults are in a starved condition then larviphagy may occur. This differs from Timko's (1975) research indicating that larviphagy acted as a density regulator within the beds. Because sand dollar larvae metamorphose is in response to conditioned sand within the sand dollar beds, and is not dependent on contact with the adults, larval mortality due to larviphagy even during conditions that are poor for the adults, may be low.

Although this work did not address the question of exclusion of infaunal or epifaunal predators from the sand dollar bed, this would be an area of further study, and some preliminary predictions based on this and earlier work can be made. Though differences were not significant, there were more predators inside the bed at both study sites; most of these were active burrowers. Infaunal predators, if they were active burrowers, would probably not be excluded from the bed, but if they were sedentary or tube-builders (such as Leptochelia dubia; Highsmith, 1982), there would probably be

27 negative adult D. excentricus-predator interactions. Epifaunal predators, such as

Pisaster brevispinus, would have difficulty maintaining traction on top of the dense sand dollar bed in high surge because of the inclined position of the sand dollars. P. brevispinus would have to make forays into the bed to feed, and retreat when surge increased.

Within this study there were no unique physical characteristics that explained the presence or absence of D. excentricus. It has been determined that the adult-conditioned sand is important in triggering oflarval metamorphosis. In addition, sand grains probably provide a physical substratum for the larvae to hold on to during metamorphosis. If so, it is reasonable to assume that there would be a minimum and maximum grain size in which the larvae's ability to effectively anchor themselves is lost.

To understand the patchy distribution of Dendraster excentricus beds along the

Pacific coast it is necessary to first understand recruitment processes and factors influencing settlement. A population's recruitment will be determined by larval supply, substratum selection and metamorphosis (settlement), and early juvenile mortality. From this settlement study, it was determined that, observed sand dollar bed patchiness is maintained by larval response to both the presence of adults and adult-conditioned sand as suitable settlement cues. There were no significant differences in predator abundance within the beds and outside the beds, and no occurrence oflarviphagy. This indicates that at these two subtidal sites, the early juvenile mortality pressures were the same inside and outside the bed. The numbers of newly metamorphosed juvenile sand dollars found inside versus outside the sand dollar beds were significantly higher at both sites. The

28 results of this study indicate that patchiness of D. excentricus beds are maintained by settlement processes.

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34 TABLES Table I. Sampling schedule including site, date, location, sample type, and number ofreplicates, collected for each type of analysis. Location refers to either inside the sand dollar bed or outside of it. Live Dendraster or Bed Sand refers to when adults or sand from the adult bed were collected to be used in the larval settlement exe.eriments. Live Dendraster Stud~ Site Collection Date Location lnfaunal Core Quadrat or Bed Sand Grain Size

Del Monte Beach 4/21/00 Inside n = 3

Del Monte Beach 5/6/00 Inside n =4

Del Monte Beach 7/19/00 Inside n =3

Del Monte Beach 8115/00 lnside n =6 core Del Monte Beach 8/30/00 Inside samples lost n =5 core Del Monte Beach 10117/00 Inside samples lost n =9

Del Monte Beach I 1/6/00 Inside IJ = 4*

Del Monte Beach 2/6/01 Inside IJ = 4*

Del Monte Beach 4/24/01 Inside IJ = 4*

Del Monte Beach 6113/01 Inside n =2

Del Monte Beach 6/20/01 Inside n =4 n =4* n > 40 indiv. Del Monte Beach 7/7/01 Inside & bed sand

Del Monte Beach 8/9/01 Inside n =6 n = 6*

Del Monte Beach 8/23/01 Inside n > 20 indiv.

Del Monte Beach 9118/01 Inside bed sand

Del Monte Bench I 0/8/01 Inside bed sand

Del Monte Beach 10/24/01 Inside bed sand

Del Monte Beach 8113/00 Outside 1l = 6

Del Monte Beach 6/20/01 Outside n =5

Del Monte Beach 6/13/01 Outside 1l = 2

Del Monte Beach 8/9/01 Outside n =3

Coast Guard Jetty 8/7/01 Inside n =6 1l = 2

Coast Guard Jetty 8/14/01 Inside 1J = 4*

Coast Guard Jetty 8/24/0 I Inside 1l = 4*

Coast Guard Jetty 8/24/01 Outside n =6 n =2

36 Table 2. Statistical results for Del Monte Beach core samples. A two way ANOVA was pe1jormed on each grouping. Collection dates a/August 13 and 15, 2000 were analyzed as the same date. Significance at the p ~ 0. 05 level is indicated by *. In Cochran's test, critical values greater than observed values indicates variances are homogeneous. In Kolmogorov-Smimov's test p > 0.05 indicates data are normal. For Mollusca and Number ofIndividuals, data were transformed using In (x +I) prior to analyses to correct for homogeneity. Kruskai-Wallis test was used for active burrowers because variances were heterogeneous even after transformation.

Cochran's Test Kolmogorov- Groupings Time effect Location effect Interaction effect observed critical Smirnov's Test

Tube-builders p ~ 0.060 p ~ 0.061 p ~0.190 0.3914 0.4447 p ~ 0.061

'"'o,-J Active burrowers p ~o.ou* p ~0.175 N/A N/A N/A N/A

Predators p ~0.634 p ~ 0.079 p ~ 0.095 0.4307 0.4447 p ~0.811

Mollusca p ~ 0.000* p~0.021* p ~ 0.545 0.3484 0.4447 p ~0.181 Juveniles of Dendraster excentricus p ~ 0.007* p ~ 0.000* p ~ 0.183 0.3456 0.4447 p ~0.905

No. of Species p ~ 0.000* p ~ 0.698 p ~ 0.038* 0.4212 0.4447 p ~0.831

No. oflndividuals p ~ 0.056 p ~ 0.936 p ~ 0.036* 0.3778 0.4447 p ~0.652 . ''[~•. -"~-,

Table 3. Mean and standard deviation ofindivuiduals per grouping per core (0. 008m2).

Study Collection Tube Active No. of No. of Site Location Date Builders Burrowers Predators Mollusca Juveniles SEE· indiv. 0.33 ± 0.58 87.33 ± 84.48 6!.67± 76.16 2.67 ± 2.52 2.33 ± 2.52 10.67 ± 4.51 148.00 ± 16!.93 Del Monte Beach Inside 4/21/00 n = 3 n =3 n = 3 n = 3 n =3 n =3 n =3 0.50 ± 0.84 5.83 ± 1!.86 35.83 ± 19.94 0.00 4.50± 4.09 4.17 ± 2.14 38.17 ± 20.88 Del Monte Beach Inside 8115/00 n = 6 n = 6 n =6 n = 6 n =6 ll = 6 n =6 1.25 ± 0.50 9.25 ± 10.63 16.75 ± 14.29 0.00 7.25 ±4.65 3.50 ± !.29 16.75 ± 14.29 Del Monte Beach Inside 6/20101 n =4 n =4 n =4 n = 4 n = 4 n =4 n = 4 0.83 ± 1.33 8.17 ± 4.54 42.17 ± 26.11 !.67 ± !.21 13.00±4.86 1!.50 ± 3.27 60.33 ± 3!.37 Del Monte Beach Inside 819101 n =6 n =6 n =6 n = 6 n = 6 n = 6 n =6 w 00 0.50 ± !.22 2.67 ± 2.73 20.67± 12.16 0.33 ± 0.82 0.50± 0.84 4.33 ± 2.07 22.17±12.51 Del Monte Beach Outside 8113100 n =6 n = 6 n =6 n =6 n =6 n = 6 n = 6 2.00 ± 2.35 6.60 ±4.04 25.4 ± 1!.89 0.80 ± 0.45 0.80 ± 1.30 6.80 ± 1.10 34.80 ± 10.06 Del Monte Beach Outside 6120101 n = 5 n =5 n =5 n = 5 n =5 n =5 n =5 3.33 ± 2.08 20.33 ± 8.33 13.00 ± 5.29 2.67 ± 2.08 3.00± 2.00 9.00 ± !.73 40.7± 15.31 Del Monte Beach Outside 819/01 n =3 n =3 n =3 n = 3 n =3 n = 3 n = 3 1.17±1.17 10.00 ± 4.15 9.83 ± 7.36 l.OO ± 0.89 14.33 ± 6.59 9.17 ± 3.66 2!.50 ± 7.23 Coast Guard Jetty Inside 817101 n = 6 n =6 n =6 n =6 n =6 n =6 n =6 2.30 ± !.86 1.17 ± 0.98 4.17 ± 3.60 3.50± 2.17 l.OO ± 0.89 4.50 ± 1.5 2 10 .. 67 ± 3.67 Coast Guard Jetty Outside 8/24101 n =6 n =6 n =6 n =6 n = 6 n =6 n =6 r! Table 4. Statistical results for Coast Guard .Jetty core samples. A t-test was performed on each grouping. Significance at the p ~ 0. 05 level is indicated by *. In Cochran's test, critical greater than observed indicates variances are homogeneous. In Kolmogorov- Smirnov's test p > 0.05 indicates data are normal. For Active burrowers and Juveniles, data were transformed using In ( x + !) prior to analyses to correct for homogeneity.

Cochran's Test Kolmogorov- Groupings p value observed critical Smirnov's Test

Tube-builders 0.223 0. 7172 0.8772 p ~0.818

Active burrowers 0.000* 0.5106 0.8772 p ~ 0.423

Predators 0.121 0.8068 0.8772 p ~ 0.582

Mollusca 0.026* 0.8545 0.8772 p ~ 0.737 Juveniles of Dendraster excentricus 0.000* 0.5312 0.8772 p ~0.796

No. of Species 0.016* 0.8532 0.8772 p ~0.638

No. oflndivuals 0.008* 0.7952 0.8772 p =0.945

39 ···~·~·~··~~··~·~~.•... lf•i!l,,

Table 5. Sediment characteristics inside and outside beds of Dendraster excentricus, at both study sites (Del!vfante and Coast Guard Jetty).

Study Site mean grain size (phi) sorting value (phi) %silt & clay % debris (broken shells) m out m out m out in out Del Monte 2.025 ± 0.007 2.015 ± 0.007 0.235 ± 0.007 0.250 ± 0.000 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00 Coast Guard Jetty 1.940 ± 0.014 1.920 ± 0.014 0.340 ± 0.000 0.345 ± 0.007 1.28 ± 0.09 1.15 ± 0.07 1.22 ± 0.06 1.05 ± 0.07

,_ 0 ...,,,fij;, ••vw···

Table 6. Statistical results for mean grain si:::e, in versus out. A t-test was pe1jormedjor each study site. In Cochran's test, critical greater than observed indicates variances are homogeneous. In Kolmogorov-Smirnov's test p > 0. 05 indicates data are normal.

Cochran's Test Kolmogorov- Study site p value t -Statistic n observed critical Smimov's Test

Del Monte Beach 0.293 1.414 2 0 0.9985 p =0.999

Coast Guard Jetty 0.293 1.414 2 0 0.9985 p = 0.999 ..,. ,_. 3',

Table 7. Statistical results for settlement expeiments. Significance at the p = 0.05 level is indicated by*. In Cochran's test, critical greater than observed indicates variances are homogeneous. In Kolmogorov­ Smirnov~s test p > 0.05 indicates data are normal.

Cochran's Test Experiment p value Statistic 11 observed critical Kolmogorov-Smimov's Test

Experiment I 0.000* F =68.154 3 0.5386 0.5612 p = 0.251

Experiment 2 0.000* F = 34.268 5 0.3546 0.4307 p =0.353

Experiment 3 0.058 t = 3.000 3 0.6667 0.975 p =0.999

~ Experiment 4 0.027* F =7.000 3 0.7779 0.8709 p ·= 0.266 Table 8. The mean and standard deviation oflan,ae of Dendraster excentricus that metamorphosed, remained as plutei, or were lost fi'om the experiment.

Experiment I Treatment type Metamorphosed Plutei Lost Time (hrs)

Filtered seawater 0.00 ± 0.00 10.00 ± 0.00 0.00 ± 0.00 48 Bed seawater 0.67 ± 0.58 9.33 ± 0.58 0.00 ± 0.00 48 Baked sand 0.33 ± 0.33 9.33 ± 0.58 0.33 ± 0.58 48 Bed sand 8.00 ± 0.00 1.67 ± 0.58 0.33 ± 0.58 48 Adult only 7.67 ± 0.58 2.33 ± 0.58 0.00 ± 0.00 48 Adult & baked sand 3.00 ± 1.00 6.33 ± 0.58 0.67 ± 0.58 48 Adult & bed sand 7.67 ± 1.53 1.67 ± !.53 0.67 ± 0.58 48

Experiment 2 Treatment type Metamorphosed Plutei Lost Time (hrs)

Filtered seawater 0.40 ± 0.54 8.60 ± 0.55 0.00± 0.00 18 Bed seawater 0.60 ± 0.55 8.40 ± 0.55 0.00 ± 0.00 18 Baked sand 0.00 ± 0.00 8.40 ± 0.55 0.60 ± 0.55 18 Bed sand 5.60 ± 1.14 3.00 ± 1.41 0.40 ± 0.55 18 Adult only 3.00±0.71 5.80 ± 0.84 0.20 ± 0.45 18 Adult & baked sand 0.00 ± 0.00 7.80 ± 1.10 0.40 ± 0.55 18 Adult & bed sand 6.20 ± 1.92 2.40 ± 1.52 0.40 ± 0.55 18

Experiment 3 Treatment type Metamorphosed Plutei Lost Time (hrs)

Baked sand 5.00 ± 1.00 3.00 ± 1.00 0.00 ± 0.00 18 Adult & baked sand 6.00 ± 2.65 1.33 ± 1.53 0.67 ± 1.15 18

Experiment 4 Treatment type Metamorphosed Plutei Lost Time (hrs) Bed sand 5.33 ± 0.58 3.33 ± 0.58 0.33 ± 0.58 18 Adult only 4.33 ± 1.53 4.67 ± 1.53 0.00 ± 0.00 18 Adult & bed sand 7.33 ± 0.58 1.00 ± 0.00 0.67 ± 0.58 18 43 Table 9. Category groupings that resulredji·om post-hoc comparisons ofthe settlement experiments.

Experiment I Group A GroupB Groupe Filtered seawater Adult & baked sand Bed sand Bed seawater Adult only Baked sand Adult & bed sand

Experiment 2 Group A Group C Filtered seawater Bed sand Bed seawater Adult only Baked sand Adult & bed sand Adult & baked sand

44 FIGURES Mouth

Oral surface

Ocular plate Petaloid ambulacra

plate

~Ambulacrum

./

'- /

Genital pore ...... _ / ,Z.....Jnterambulacrum '- .

Madreporite

Aboral surface

Figure I. Oral aud aboral views of the test of Dendraster excentricus. Figure modified from Nybakken, West Coast Invertebrate Laboratory Manual, West Coast edition, with permission from the artist, Lyun McMasters.

46 ~-"~"~~-"" ""-,~-~- ""'-' ,__ ,----"" ""'"" ""_,__ ""-" ~"-----"-''"""--"~ --~~~---' _,_, ____ """"-~-~~--"~~" --""-~'-"-----" "~------~1

Shoreward Edge Seaward Edge

1 \

Open Bay

Shore

Figure 2_ Beds of Dendraster excentricus comparing shoreward and seaward edges. The shoreward edge (left) is less distinct, compared to the "piled-on" effect at the seaward edge (right).

47 A) Perpendicular alignment

Seaward edge

Shore

B) Parallel alignment

Seaward edge

Shore

Figure 3. Alignment of Dendraster excentricus within an inclined bed. Straight edge denotes oral surface and convext edge denotes aboral surface. A) Perpendicular alignment of sand dollars to the surge current, with oral surface facing upstream. B) Parallel alignment of sand dollars to the surge current, with oral surface facing right or left with respect to long-shore transport.

48 Adult rudiment

Adult spines

500um

Figure 4. Competent echinopluteus of Dendraster excentricus, showing adult rudiment within the larval gut area. Total length oflarvae- 750um.

49 500um

Figure 5. Aboral view of newly metamorphosed juvenile of Dendraster excentricus.

50 . . Santa Cruz t

I 10 Kilometers I Pacific Ocean

0 400 BOO Meters

Site 1 •

Monterey

Figure 6. Map of Monterey Bay, California, showing the location of the two study sites. Site I is Del Monte Beach. Site 2 is Coast Guard Jetty Beach.

51 Seasonal adult density 40

35 -

30 - N E 1£) f"! 25 - ~ I.. Cl.l Ln c. 20 - '" -;;"' ·;:"1:1= 15 - ·-"1:1 ·-= 10

5

0-r-----~------,------,------,------,------,------,------,-----~ 5/6/00 7/19/00 8/30/00 10/17/00 11/6/00 2/6/01 4/24/01 6/20/01 8/9/01 Sample date

Figure 7. Seasonal density of adults of Dendraster excentricus at the Del Monte Beach site. APPENDIX Appendix A: A list of the number of organisms per taxon per core (.008m2). DM =Del Monte beach, CG =Coast Guard Jetty, IN = inside sand dollar bed, and OUT = outside the sand dollar bed. Life Stratagies were determined to fit into one of four types; b = burrowers, p = predators, t = tube builders, or und = undetermined Life Strat Organism Study Site Location Date Core I Core 2 Core 3 Core 4 Core 5 Core 6

Crustacea b Euphilomedes longiseta DM IN 4/21100 55 18 29 b,p Mandibuloplzoxus gi/esi DM IN 4/21/00 118 4 23 b,p Rlzepoxynius lucubrans DM IN 4/21100 6 0 2 p Synchelidium shoemakeri DM IN 4/21100 24 0 8

Polychaeta b Armandia brevis DM IN 4/21100 I 0 0 p Hessionella complex DM IN 4/21/00 3 7 3 b Mage/ana sacculata DM IN 4/21100 2 1 1 t Apoprionospio pygmaea DM IN 4/21/00 1 0 0 b Scolop/os sp. DM IN 4/21/00 0 0 p Typosyllis sp. DM IN 4/21100 12 I 2

Other Worm Groups p Nemertea (Cerebratu/us) DM IN 4/21100 I I 0 b Oligochaeta DM IN 4/21100 I 0 0

Mollusca und Tel/ina bodegensis DM IN 4/21/00 und Rochefortia sp. OM IN 4/21/00 3 2 und 0/ivel/a bip/icata DM IN 4/21/00 Echinodermata und Dendraster excentricus DM IN 4/21/00 12 I 9

Crustacea b Euphilomedes longise/a DM OUT 8113/00 0 I 0 5 I 0 b,p Mandibulophoxus gilesi DM OUT 8/13/00 0 0 I 3 I 0 b,p Rhepoxynius lucubrans DM OUT 8/13/00 0 2 0 0 0 I p Synche/idium shoemakeri DM OUT 8/13/00 0 3 0 I I 0

Polychaeta t Capitellidae DM OUT 8/13/00 0 0 0 I 0 0 p Hessionel/a complex DM OUT 8/13/00 0 0 23 12 14 4 b,p Nephtys californiensis DM OUT 8/13/00 I 0 0 0 0 0 p Phyl/odoce sp. DM OUT 8/13/00 0 0 0 0 0 I Apoprionospio pygmaea DM OUT 8/13/00 0 0 0 2 0 0 p Typosyllis sp. DM OUT 8/13/00 I II 6 6 18 11

Mollusca und 0/ive//a bip/ica/a DM OUT 8/13/00 0 0 0 2 0 0

Echinodermata und Dendraster excentricus DM OUT 8/13/00 3 I 0 3 0

Crustacea b Euphilomedes /ongiseta DM IN 8/15/00 0 0 0 0 8 0 und Juvenile Mysid DM IN 8/15/00 0 0 0 0 2 0 b,p Mandibulophoxus gi/esi DM IN 8/15/00 0 0 0 0 19 0 p Synchelidium shoemakeri DM IN 8/15/00 0 0 0 0 4 I Polychaeta t Dispio uncinata DM IN 8115/00 I 0 0 0 0 0 p Hessionel/a complex DM IN 8/15/00 4 26 30 68 15 24 b,p Nephtys californiensis DM IN 8/15/00 0 I 0 0 I ( Apoprionospio pygmaea DM IN 8/15/00 0 0 0 0 2 0 p Typosyl/is sp. DM IN 8/15/00 5 5 0 0 0 5

Other Worm Groups p Nemertea (Cerebratulus) DM IN 8/15/00 0 0 0 2 I I b Oligochaeta DM IN 8/15/00 0 I I I 0 0

Mollusca NONE DM IN 8/15/00

Echinodermata und Dendraster excentricus · DM IN 8/15/00 0 0 0 0 I 2

Crustacea und Anchico/orus occidenta/is DM IN 6/21/01 I 0 0 0 b, p Mandibu/ophoxus gilesi DM IN 6/21101 22 I 14 0 p Synchelidium shoemakeri DM IN 6/21/01 0 I 15 2 t, p Zeuxo normanii DM IN 6/21101 2 I I I Polychaeta p Hessionella complex DM IN 6/2I/OI 3 2 I 0

Other Worm Groups p Nemertea (Cerebratulus) DM IN 6/21101 0 I 0 0

Mollusca NONE DM IN 6/2I/OI

Echinodermata und Dendraster excentricus DM IN 6/21/01 0 5 2 0

Crustacea und Anchicolorus occidentalis DM OUT 6/21/01 0 0 3 0 0 und Diastylopsis tenuis DM OUT 6/21/01 0 0 2 0 0 b Euphilomedes longiseta DM OUT 6/21101 3 12 3 3 2 b,p Mandibulophoxus gilesi DM OUT 6121/0I 0 0 1 0 0 b, p Rhepoxynius lucubrans DM OUT 6/21101 2 0 0 0 2 p Synchelidium shoemakeri DM OUT 6/21101 0 I I I 2

Polychaeta b Armandia brevis DM OUT 6/21/0I I 0 0 0 0 b Chaetozone sp. DM OUT 6/2I/OI 0 I 0 0 0 b Haploscoloplos sp. DM OUT 6/2110I 0 0 0 0 p Hessionella complex DM OUT 6/21/01 I2 I3 24 43 23 b Mage/ana sacculata DM OUT 6/2I/01 I 0 0 0 0 t Apoprionospio pygmaea DM OUT 6/2110I 0 6 2 1 I ·······~

Other Wonn Groups p Nemertea (Cerebratulus) DM OUT 6/21/01 I I 0 0 0 b Oligochaeta DM OUT 6/21/01 I 0 0 0 0

Mollusca und Tel/ina bodegensis OM OUT 6/21/01 0 I I I 0 und Nassarius perpinguis OM OUT 6/21/01 0 0 0 0 I

Echinodennata und Dendraster excentricus DM OUT 6/21/01 3 0 0 0 I

Crustacea und Anchicolorus occidentalis OM IN 8/9/01 0 0 0 I 0 0 t Callianassa sp DM IN 8/9/01 0 0 0 2 0 0 und Cyclaspis sp. OM IN 8/9/01 0 0 0 I 0 0 b Euphilomedes longiseta OM IN 8/9/01 0 7 0 I 3 2 b,p Rhepoxynius lucubrans OM IN 8/9/0 I 2 0 0 I 0 I p Synchelidium shoemakeri OM IN 8/9/01 4 I 4 4 5 4 und Megaluropus longimarus OM IN 8/9/01 0 0 0 0 0 I

Polychaeta t Dispio uncinata OM IN 8/9/01 2 0 0 I 0 0 b Armandia brevis OM IN 8/9/01 9 0 I 3 4 9 b,p Glycera sp. OM IN 8/9/01 0 0 0 0 0 I p Hessionella complex OM IN 8/9/01 19 86 17 41 20 32 b Magelona sacculata DM IN 8/9/01 0 0 0 0 0 I b,p Nephtys californiensis OM IN 8/9/01 0 3 0 0 0 0 und Opheliidae OM IN 8/9/01 0 0 0 2 2 9 ·······~

p Phyllodoce sp. OM IN 8/9/01 1 0 0 0 0 0 und Protodrilus!Saccocirrus OM IN 8/9/01 0 4 0 2 1 1 und Spionidae OM IN 8/9/01 0 0 I 0 0 0 p Thalenessa sp. OM IN 8/9/01 0 I 0 3 0

Other Worm Groups p Nemertea (Cerebratulus) OM IN 8/9/01 I 0 0 0 0 I

Mollusca und Tel/ina bodegensis OM IN 8/9/01 2 0 0 I 0 0 und 0/ivel/a bip/icata OM IN 8/9/01 0 0 0 0 1 0 und Naticidae OM IN 8/9/01 0 0 0 0 I 0 und Tresus -like OM IN 8/9/01 0 1 0 0 0 0 und Modiolus sp. OM IN 8/9/01 0 0 0 0 I 0 und Simomactra planulata OM IN 8/9/01 0 0 I 0 0 0 und Nassarius fossa/us OM IN 8/9/01 0 2 0 0 0 0

Echinodermata und Dendraster excentricus OM IN 8/9/0 I IS 6 II 10 19 17

Crustacea b Euphilomedes longiseta OM OUT 8/9/0 I 0 0 t Pinnb:a occidentalis OM OUT 8/9/01 0 0 1 b,p Rhepoxynius lucubrans OM OUT 8/9/01 0 I 0 p Synchelidium shoemakeri OM OUT 8/9/01 0 0 I und Megaluropus longimarus OM OUT 8/9/01 0 I 0

Polychaeta '''''""'~~

b,p Glycera sp. DM OUT 8/9/0 I 2 I 2 b Hap/oscoloplos sp. DM OUT 8/9/01 I 2 8 p Hessionel/a complex DM OUT 8/9/01 4 I2 IO b Magelona sacculata DM OUT 8/9/01 0 9 0 t Apoprionospio pygmaea DM OUT 8/9/0I I 5 3 b Opheliidae DM OUT 8/9/01 24 20 0

Other Worm Groups p Nemertea (Cerebratu/us) DM OUT 8/9/0I I 3 2

Mollusca und Tel/ina bodegensis DM OUT 8/9/0I I 3 0 und Olivella biplicata DM OUT 8/9/0I 0 I 0 und Simomactra planulata DM OUT 8/9/0I I I 0 und Macoma sp. DM OUT 8/9/0I 0 0

Echinodermata und Dendraster excentricus DM OUT 8/9/0I II3 I2 73

Crustacea und Cyc/aspis sp. CG IN 8/7/01 0 0 I 0 0 0 und Juvenile Mysid CG IN 8/7/0I 0 0 0 0 2 0 und Paraeurystheus sp. CG IN 8/7/01 0 0 0 I 0 0 b,p Rhepoxynius lucubrans CG IN 8/7/0I I 0 2 I I 0 p Synchelidium shoemakeri CG IN 8/7/0I 0 0 I 8 2 IO

Polychaeta b Armandia brevis CG IN 8/7/0I 5 14 7 2 I IO '~

b C/1aetozone sp. co IN 8/7/01 0 0 0 0 l 0 b Cirratulus/Tharyx sp. CG IN 8/7/0 l 2 0 0 0 0 0 b,p Glycera sp. CG IN 8/7/01 0 I 0 0 0 0 p Gyptis sp. CG IN 8/7/01 I 0 0 0 0 0 p Hessionel/a complex CG IN 8/7/01 0 0 0 0 I 0 b Magelona sacculata CG IN 8/7/01 I 0 2 0 0 0 t Mediomastus sp. CG IN 8/7/01 0 0 0 I 2 0 b,p Nephtys californiensis CG IN 8/7/01 0 0 2 0 0 0 t Nereidae CG IN 8/7/01 I 0 0 0 0 0 b Orbinia or Orbiniidae? CG IN 8/7/01 I I I 0 2 0 p Phyllodoce sp. CG IN 8/7/01 0 I 0 0 0 0 t Apoprionospio pygmaea CG IN 8/7/01 0 0 0 0 0 p Typosyllis sp. CG IN 8/7/01 20 0 2 0 0 p Pi/argis berkeleyi CG IN 8/7/01 I 0 0 0 0 0 und Unknown Poly CG IN 8/7/01 0 0 0 0 I 0

Other Warm Groups p Nemertea (Cerebratulus) co IN 8/7/01 0 0 0 I I I b Oligochaeta CG IN 8/7/01 0 0 0 0 I 0

Mollusca und Tel/ina bode gens is CG IN 8/7/01 0 I 0 0 0 0 und 0/ivel/a biplicata CG IN 8/7/01 I I 0 0 0 0 und Trachycardium sp. CG IN 8/7/01 0 0 I 0 0 0 und Naticidae CG IN 8/7/01 0 0 I 0 I 0

Echinodermata und Dendraster excentricus CG IN 8/7/01 18 9 6 12 17 24 .,JI

Crustacea und Lamprops sp. CG OUT 8/24/01 0 0 0 0 0 I p Synchelidium shoemakeri CG OUT 8/24/01 2 2 2 I I 9

Poly chaeta b Armandia brevis CG OUT 8/24/01 0 0 0 0 I I t Capitellidae CG OUT 8/24/01 4 0 0 I I 0 b,p Glycera americana CG OUT 8/24/01 0 3 I 0 0 0 b Mage/ana sacculata CG OUT 8/24/01 I 0 0 0 0 0 t Apoprionospio pygmaea CG OUT 8/24/01 I I 2 I 3 0 p Thalenessa sp. CG OUT 8/24/01 0 0 0 0 0 I p Typosyllis s p. CG OUT 8/24/01 I 0 0 0 I 0

Other Worm Groups p Nemertea (Cerebratulus) CG OUT 8/24/01 0 0 0 0 0 3

Mollusca und Tel/ina bodegensis CG OUT 8/24/01 0 I 0 0 0 0 und 0/ivel/a biplicata CG OUT 8/24/01 2 6 0 5 0 3 und Simomactra p/anulata CG OUT 8/24/01 0 0 0 0 2 0 und Saxidomus nuttal/i CG OUT 8/24/01 I 0 I 0 0 0

Echinodermata und Dendraster excentricus CG OUT 8/24/01 0 I I 2 0 2