Burying Behavior in an Lndo-Pacific Sea Cucumber, Bohadschia

Home , Bohadschia, Bohadschia marmorata, Holothuria, Holothuria leucospilota

Micronesica

per m per er 19) eot 2 seis n vrg dniis f - pr m per 3-4 of densities average in species 26 reports (1994) Kerr (Federated States of Micronesia). of States (Federated heavily defended (Bakus 1968), what determines their habitat selection, and what and selection, habitat their determines 1968), what (Bakus defended heavily triggers spawning. This lack of research is perhaps due to the apparent lack of sea of lack apparent the to due is perhaps research of lack This spawning. triggers known. is poorly behavior theirbut region, inlndo-Pacific the fauna shallow-water bu hltuin eairl clg rmi uasee, uh swy hy are they why as such unanswered, remain ecology behavioral holothurian about unique color patterns make what activities they do undertake easy to study. to easy do undertake they activities what make patternscolor unique

f ad vr fv otn iue (ohm ed 93. tl,bsc questions basic Still, 1963). Held & (Bonham minutes ten to five every sand of

Kalk 1962, Yamanouchi 1956). Yamanouchi (1956) provided a general description a general 1962, 1956). provided (1956) YamanouchiYamanouchi Kalk "cryptic" (Francour 1997) behavior. Covering has been reported for sea cucumbersfor 1997) reported Coveringhasbeen behavior. (Francour "cryptic" uubr ciiy sne hi acsiiiy audne ad fe individually often and abundance, accessibility, their since activity, cucumber n h genera the in

marmorata

Abstract-Rhythmic

both populations, individuals came to the surface of the sand in mid-af in sand the of surface the to came individuals populations, both ternoon, were most likely to be fully exposed around midnight, and re and midnight, around exposed fully be to likely most were ternoon, marmorata buried before dawn. Individuals in the grassflats population were more were population grassflats the in Individuals dawn. before buried tat. Burying was not the result of water depth but rather time of day of time rather but depth water of result the not was Burying tat. n t eetv datg ivsiae.Toppltos of Two investigated. populations advantage selective its and

B likely to be completely buried during the day, and they emerged from the from day, emerged the they and during buried completely belikely to

the existence of this behavior were investigated: that they bury to avoid to bury they that investigated: were behavior this of existence the (1) exposure at low tide, (2) ultraviolet light (UVB), and/or (3) stingray (3) and/or (UVB), light ultraviolet (2) tide, low at exposure (1) edn gop. h tmn o te uyn ryh ad h lc o a of lack the and rhythm burying the of timing The groups. feeding adltri h a hntemnrv ouain Trehptee for hypotheses Three population. mangrove theday than in the later sand togcreain ewe ie n uyn spot h yohss that hypothesis the support burying and tide between correlation strong

Sea cucumbers (Echinodermata: Holothuroidea) are major components of the of components are major Holothuroidea) (Echinodermata: Sea cucumbers

n tp o sa uubr eair ht a be suid s oeig or covering, is studied been has that behavior cucumber sea of type One

Burying behavior in an lndo-Pacific sea cucumber, sea lndo-Pacifican in behavior Burying

urn address Current

(Bakus 1976, Galstoff 1933), with each sea cucumber processing one gram one processing cucumbersea each 1933), with 1976, Galstoff (Bakus

marmorata

02:4-5, 1997 30(2):245-257,

Jaeger (Holothuroidea): a circadian, not circatidal, rhythm circatidal, not circadian, a (Holothuroidea): Jaeger

cioyi, oasha Holothuria Bohadschia, Actinopygia,

were studied: in a mangrove channel and in a grassflats habi grassflatsa in and channel a mangrovein studied: were

bury to avoid UVB exposure. avoid UVB to bury

310

Ponape Agriculture and Trade School,

99th. Street 99th.

burying behavior in a sea cucumber was described was cucumber seaa in behavior burying

P.O. Box 39, Pohnpei, FM 96941

Introduction

oohra atra Holothuria

808

CLOUSE

e ok Y I York, New0025 NY

can reach densities of over 30 over of densities reach can

and

Stichopus

Bohadschia

rm Kosrae from

Mca & (Macnae

In .

individ

is also the

marmorata)

I investigate

has been sug

move from the

Bohadschia bivit

(now

Actinopygia lecanora)

Holothuria atra,

B. marmorata,

move from open sand to under

Yamanouchi discoveredtwo as

Jaeger from the Micronesian is

(now

Bohadschia marmorata

Stichopus chloronotus

individuals exposed tideatlow (Bon

(since synonomized withB.

variegatus

Holothuria bivittata

individuals that are above the surface of the

B. marmorata,

Micronesica 30(2), 1997

range from the Indian Ocean through Westernthe Pa

Holothuria lecanora

Bohadschia marmorata

is possible that sand and other coverings are needed to pro-

B. marmorata

Holothuria leucospilota

Held 1963).

The purposeThe ofthis studywas to investigate variety a ofbasic questions about

In addition to describing the burying behavior of & Bohadschia marmorata

Midday tropical sunshine has the potential to damage sea cucumbers. Hav

tata), H. scabra, an.dBohadschia vitiensis of coveringbehavior from Palau: (1) 246 sand surface to under corals, and (4) from moving on grasses to underneath, (3) bury in the substrate, (2) grasses. About burying behavior in and entrainedby light: cucumberssea keep rhythmtheir in dark aquaria for several days, their rhythm can be reversed by reversing light schedules, and they bury continue feeding while on the surface. the Second, burying rhythm is endogenous but cease feeding while under the sand; later, they ingest sand as they emerge and pects notthat areimmediately obvious. First, burying individuals theyfeed bury as

when exposed to 30 minutes of light at night. land Pohnpei of (7°00'N, 158°10'E). What is the general form ofthis rhythm, and how much does it vary? Does this rhythm have a circatidal component? How does the ecology ofburying in this rhythm compare between different populations ofthe same species? What are cific Doty& (Rowe Adults from 1977). the populations used here reach 500g (live the major factors that might select for this rhythm? sticky tubes released through the anus) and separate sexes. Spawning occurs dur

weight) and are usually a light grey or tan with sharply-defined, dark brown, indi ing day or night in the still water at the peak of extremely high tides (pers. obs.). vidually-unique, map-like spots. This species has Cuverian tubules (defensive,

rhythms, sunlight, and predators. Changes in water depth overthe tidal cycle may could impair a variety of physiological mechanisms that require an influx of ing little or no habitat protection from biologically harmful UVB radiation three factors that may contribute to the evolution of burying behavior: tidal uals are found placesin where they can be exposed at low tide, and such exposure (280-320 nm), burying in the substrate may be the only escape. Other observa sandflats and which does not bury under the substrate, only completely black species;perhaps such heavy pigment blocks more just than be important for sea cucumbers in shallow water. water-respiration, locomotion, and excretion. sand during daylight hours remain covered with a thin layer of sand as they feed; First, the speciesonly cucumberof around whichPohnpei livescompletelyon bare

tions also suggest the importance of sunlight for shallow-water sea cucumbers against radiation in visible light. Second, gested that sand coverings reflect light and that sand and mucous coverings guard

this finesand covering is immediately dropped when the sun sets. ham

common sea cucumber in the shallow grass:flats, with with grass:flats, shallow the in cucumber sea common

Stichopus horrens horrens Stichopus appearing appearing

low tide have small corals mixed with grass. grass. with mixed corals small have tide low

Bohadschia marmorata marmorata Bohadschia is the most most the is

habitat has a substrate of coral rubble and sand, and deeper areas not exposed at at exposed not areas deeper and sand, and rubble coral of substrate a has habitat

deep channel on the North; this is the location of the "grass:flats population." This This population." "grass:flats the of location the is this North; the on channel deep

between the ruins of Nan Madol on the South, the barrier reef to the East, and a a and East, the to reef barrier the South, the on Madol Nan of ruins the between

On the East side of Temwen are several hectares of grass:flats which stretch stretch which grass:flats of hectares several are Temwen of side East the On

tersection during their life. life. their during tersection

several months, it became clear that they are very unlikely to move out of this in this of out move to unlikely very are they that clear became it months, several

isolated by deep channels and reef: by following the fates of ten individuals over over individuals ten of fates the following by reef: and channels deep by isolated

tween tidal extremes and the substrate firm. This "mangrove population" is is population" "mangrove This firm. substrate the and extremes tidal tween

morata morata are located at one end of this intersection where the current is strong be strong is current the where intersection this of end one at located are

strate is mostly sandy with small patches of of patches small with sandy mostly is strate

Halimeda Halimeda algae. Almost all all Almost algae. . mar B.

channels that forms a shallow shallow a forms that channels area area bu 1mi imtr h nescin sub intersection The diameter. in 15m about

morata morata is located on the West side of Temwen at an intersection of mangrove mangrove of intersection an at Temwen of side West the on located is

between Temwen and the main island (Figure 2). One population of of population One 2). (Figure island main the and Temwen between

. mar B.

surround Temwen, and natural channels cut through this• forest where it grows grows it where forest this• through cut channels natural and Temwen, surround

is connected to Pohnpei proper by a short coral road (Figure 1 ). Mangrove forests forests Mangrove ). 1 (Figure road coral short a by proper Pohnpei to connected is

The populations in this study live around the small island ofTemwen, which which ofTemwen, island small the around live study this in populations The

Methods Methods

after a low tide. tide. low a after

ways form when the tide is rising, sea cucumbers may be most likely to bury just just bury to likely most be may cucumbers sea rising, is tide the when form ways

nte esnt uy stetd bs Scn,snesiga edn gop al groups feeding stingray since Second, ebbs. tide the as bury to reason another

is even slightly reduced by seawater, then increased UVB exposure at low tide is is tide low at exposure UVB increased then seawater, by reduced slightly even is

cially true of the tide, which may presage or exacerbate other factors. First, ifUVB ifUVB First, factors. other exacerbate or presage may which tide, the of true cially

not mean that that part of the environment is what is being avoided. This is espe is This avoided. being is what is environment the of part that that mean not

Finding that a burying rhythm follows a certain environmental variable does does variable environmental certain a follows rhythm burying a that Finding

regularly. regularly.

stingray feeding groups have the potential to kill a large number of sea cucumbers cucumbers sea of number large a kill to potential the have groups feeding stingray

common potentially catastrophic events in the lives of grass:flats inhabitants, inhabitants, grass:flats of lives the in events catastrophic potentially common

(Forsskal) engages in group foraging as the tide rises, and being one of the most most the of one being and rises, tide the as foraging group in engages (Forsskal)

stingray group foraging. In the grass:flats, the stingray stingray the grass:flats, the In foraging. group stingray

Himantura Himantura prob. prob. uarnak uarnak

tions of whether predation selects for burying are restricted to investigating investigating to restricted are burying for selects predation whether of tions

to those that ingest them whole (e.g., seastars and fishes). In this study, investiga study, this In fishes). and seastars (e.g., whole them ingest that those to

cour 1997) include those that eat sea cucumbers piecemeal ( ( piecemeal cucumbers sea eat that those include 1997) cour

e.g. e.g. small crustaceans) crustaceans) small

it o rdtr. ito nw ad upce saccme peaos (Fran predators cucumber sea suspected and known of list A predators. of riety

as skin toxins and Cuverian tubules, imply an evolutionary "arms race" with a va a with race" "arms evolutionary an imply tubules, Cuverian and toxins skin as

predation (Francour 1997). Indeed, the numerous defenses of sea cucumbers, such such cucumbers, sea of defenses numerous the Indeed, 1997). (Francour predation

Diurnal burying and other cryptic behavior could be an adaptive response to to response adaptive an be could behavior cryptic other and burying Diurnal

base their burying rhythm on changes in light. light. in changes on rhythm burying their base

marmorata marmorata bury to avoid something rather than obtain a special food, and that they they that and food, special a obtain than rather something avoid to bury

water (Jerlov 1950, Kirk 1994). Third, Yamanouchi's (1956) results suggest thatB. thatB. suggest results (1956) Yamanouchi's Third, 1994). Kirk 1950, (Jerlov water

tect against UVB underwater also, since UVB can easily penetrate clear shallow shallow clear penetrate easily can UVB since also, underwater UVB against tect

Clouse: Burying behavior in an Indo-Pacific sea cucumber cucumber sea Indo-Pacific an in behavior Burying Clouse: 247 247 248 Micronesica 30(2), 1997

1sa0 1o·e ~ mangroves

ll!i!lilreef

7"00'N

Figure 1. Pohnpei island, showing location of main study area (box). PATS= Ponape Agriculture and Trade School.

occasionally. Adult grassflats individuals are about three times smaller than man grove individuals, although their spicules and coloration are identical.

TIME OF BURYING AND WATER DEPTH In the mangroves, I censused the entire population. In the grassflats, two fixed 2m by 2m plots were censused; one was in the typical grassflats habitat, and the other was in a disturbed, sandy area sometimes used for coral dredging. For both populations, each individual in the census area was described as having 100, 75, 50, 25, or 0 percent of its body above the surface of the sand. For those individuals that were completely buried, I counted them in each census by subtracting the number of individuals above the sand for that census from the maximum number ever seen above the sand in that population (79 for the mangrove population, 34

....__

et, n te orsodn tms ni te n o te edn eet several event, feeding the of end the until times corresponding the and ments, hours later. hours eidadt h ieofeig rusbten 1Nvme, 94 n 1 1994, 11 Januand November, between groups offeeding side the toand behind move stingray sizes, group of estimates record and area the of middle the in self

passing feeding group. To test for this, I compared the abundance of abundance the comparedgroup.To I for this,feeding test passing of stingrays was impossible. However, an obvious result of stingrays feeding on feeding stingraysof However,result obviousan impossible.stingrayswas of rnet m n imtr meitl bfr o fe cutn bhn a stingray a behind counting after or before Immediately diameter. in 4m transect marmorata

the group. the ary,

ru,Iue h aemto t on idvdas na ra 1 area of an in Om side individualsthe to count to method same the used I group,

ye y acltn 9% ofdne nevl fr ah ofiin; overlapping coefficient; each for intervals confidence 95% calculating by lyzed confidence intervals indicated no significant difference between coefficients. between difference significant no indicated intervals confidence ad ro, n "S" en ±tnad eito. uyn mdl wr ana were models Burying deviation. ±standard means "±SD" and error, dard

ih h ae dph ttetm o essn (al 1 was (Table exposure However, censusing). of time the at depth water the with avoid being exposed at low tide. Often they can be found deflated and stranded on stranded and deflated found be can they Often low attide. exposed avoid being

agoe n gaslt ppltos epsr ws o sgiiaty correlated significantly not was exposure populations, grassflats and mangrove

an exposed sand bar, only to continue normal activities after low tide. For both the For bothlow tide.after activities normal continue only to bar, sand exposedan

1995. A few seconds after a group passed over an area, I censused a circular a censused I area, an over passed group a after seconds few1995. A

Because of their size and local taboos, killing and dissecting a large number large a dissecting and killing taboos, local and size their of Because

o-aaerc ttsisaeue o o-oml aa ±E mas ±stan means data;"±SE" for non-normalare used statistics Non-parametric

It became clear by watching by clear became It

ol ea meit dpein fsaccmes ietybhn a behind directly cucumbers sea of depletion immediate an be would

agoe Population Mangrove

coefficient

al 1 Wtr et addph fms rcn tdl xrm ver extreme tidal recent most of depth and depth Water 1. Table R rsfas Population Grassflats

2.02 X 2.02

R coefficient

1.93 X 1.12 X

1.90 X

u ecn o oy bv h sn:mdl qain, R equations, model sand: the above body of percent sus

ecn epsr = exposure percent

depth+

ecn exposure= percent

and coefficient and

(1.90 X (1.90

0.01

0.28

lue uyn behavior Burying Clouse:

10 10

- -

(1.12

1 1

10-

WATER

)

95%

rvos ia etee depth extreme tidal previous

rsfas populations. grassflats

8.72

1.96

DEPTH B. marmorataB.

ofdne nevl frmnrv and mangrove for intervals confidence

)

rvos ia etee depth extreme tidal previous

Results

95%

6.69

95%

-6.51

84 X -8.47

1.54

(2.02

an Indo-Pacific sea cucumber sea Indo-Pacifican

N BURYING AND

ofdne interval confidence

(1.93

at night that they do not strongly not do they that night at -

X 1

)

urn wtr depth water current

2.26

1.57

4.88

1.04 X 10 1.04 X

)

urn water current

values,

(n.s

(n.s.)

)

marmorata

251

B. =

Time

BURYING

coefficient was significantly larger in the

are indicated byarrows

0.28). In the grassflats population, the model co

Micronesica 30(2), 1997

1iMING

were most likelyto be buried from dawn until mid-af

17 pairs;17 paired t-test).

The percentage of the body above the surface of the

13)and maximum (23:00) times, as determined from the

. ~------r------,

--l---H.-.--1----.-----.----.--r-4~=r-e>--1

06:30 09:50 13:10 16:30 19:50 23:10 02:30 05:50

0 sand versus time for the mangrove population. The minimum (09

model Figurein 5

0.93; n

100

Figure 3

0.01, grassflats R

0.90 %/min) was not different from sea cucumbers in shallow water (x

Bohadschia marmorata

slightly positively correlated with the most recent tidal extreme (mangrove popu

efficient for the tidal extreme variable (0.19) was significantly larger than in the 252 lation R ial rate, ial the percent the of body buried per minute for sea cucumbers in deep water (x

mangrove population model (0.11). In the test of the effect of water depth on bur 0.91 %/min; p

coefficients. The model for the disturbed, sandy grassflats plot was not signifi cantly different from the normal grassflats plot and will not be discussed further. ternoon (Figures 3, 4). Table 2 details the 95% confidence intervals for the model The normal grassflats plot and the mangrove population models were very similar;

mangrove population (2.31) than in the grassflats (1.62). The result was a general however the "t" coefficient was not different from zero for the mangrove popula lowering of exposure values in the grassflats population, especially during daytime tion, and the absolute value of the "t Clouse: Burying behavior in an lndo-Pacific sea cucumber 253

100 --r------,------, 80 ! y

20 0057 !I

06:30 09:50 13:10 16:30 19:50 23:10 02:30 05:50

Time

Figure 4. The percentage of the body above the surface of the sand versus time for the grassflats population. The mini mum (10:09) and maximum (00:57) times, as determined from the model in Figure 5, are indicated by arrows.

Table 2. Time (as number of minutes after 06:30) versus percent of body above the sand: model equations, R2 values, and coeffi cient 95% confidence intervals for mangrove and grassflats popu lations.

Mangrove Population Percent exposure= 7.01 - (1.13 X 10- 1) time+ (4.02 X 10- 4) time 2 - (2.31 X 10- 7) time 3

R2 = 0.27 coefficient 95% confidence interval -1.13 X 10- 1 -2.37 X 10 1 to 1.13 X 10- 1 (n.s.) 4.02 X 10-4 3.19 X 10- 4 to 4.85 X 10- 4 -2.31 X 10- 7 -2.92 X 10- 7 to -1.71 X 10- 7

Grassflats Population (Normal Survey Plot) Percent exposure= 7.46 - (1.21 X 10- 1) time+ (3.29 X 10- 4) time 2 - (1.62 X 10-7) time 3

R2 = 0.28 coefficient 95% confidence interval -1.21 X 10- 1 -1.28 X 10- 1 to -1.13 X 10- 1 3.29 X 10- 4 3.34 X 10- 4 to 3.24 X 10- 4 -1.62 X 10- 7 -1.66 X 10- 7 to -1.58 X 10- 7 254 Micronesica 30(2), 1997 and early evening hours (Figure 5). However, grassflats individuals were more likely to be exposed in the early morning hours. The time of maximum probability of :finding individuals above the surface of the sand was earlier (23:00 hours) in the mangrove population than in the grassflats population (00:57 hours).

STINGRAY FEEDING GROUPS After several dozen attempts to see complete stingray group feeding events, only eight occurences were wittnessed in their entirety. All group feeding events oc curred as the tide was beginning to rise, and group feeding events were most likely to occur if the tide started to rise before noon ( average starting time 10:23AM;range 09:49-14:00; N = 8). Two species frequented the grassflats at this time, Himantura grantulata (MacLean) and H. prob. uarnak (Forsskal), but only the latter formed feeding groups. About ten stingrays would begin cruising the edge of the exposed grasses while the water was still flowing out, and as soon the current began to change, they started excavating the substrate. Rays would lie alone on the bottom feeding for :fiveto ten minutes before approaching the edge of the exposed grass and other rays. Walking in the water at this time attracted rays: they could be seen chang ing their course to approach, because their pectoral fin tips came out of the water. After about an hour, up to five groups of two to :five individuals would form. At times, these groups would merge and split, and a steady stream of stingrays would enter the grassflats. All individuals would stay in water at least 20 cm deep, but in large groups, some individuals would move out of the water across the backs of oth ers to reposition themselves in the group. Over the course of the next hour, large groups of 20-60 individuals would form, and these would move slowly through the

100

mangroves -- 80 grassflats --- "O Q) 1/) 0 C. 60 X Q) +-' C eQ) 40 Q) a. 20

0 06:30 13:10 19:50 02:30 Time

Figure 5. Burying models, including 95% confidence in tervals, for the mangrove and grassflats populations. Clouse: Burying behavior in an Indo-Pacific sea cucumber 255

shallow water to the Southeast edge of the grassfl.ats, where they would disband. In their wake could be found broken clam shells. Predicting when groups would form was difficult, for on some days of seemingly perfect conditions, no rays were seen. The number of B. marmorata found directly behind stingray groups (x = 2.27 ±SE 0.38) was larger than the number to the side (x = 1.68 ±SE 0.39) (p = 0.05; N = 11 pairs; Wilcoxon).

Discussion Burying in Bohadschia marmorata is clearly a circadian, not circatidal, phe nomenon. Moreover, since buried individuals engage in almost no activity under the sand, it seems that they bury to avoid something during the day. Are they avoid ing a diurnal predator, the sun itself, or both? It seems unlikely that B. marmorata bury to avoid stingrays. Sea cucumbers do not strongly respond to water depths, a major predictor of stingray activity, and apparently stingrays abandon many (if not all) sea cucumbers removed from the substrate. The higher probability of sea cucumbers to be buried after a low tide, es pecially in the grassflats, is expected if burying is stingray avoidance. However, this effect is extremely slight: although water depth in the grassflats rarely exceeds 1.5 m, my model requires another 1 m of water at high tide to increase exposure by only 25%. Such a weak but statistically significant correlation may be explained by spawning, in which mature individuals emerge from the sand, at least anteriorly, even during the daytime if the tide is extremely high. On some censuses, then, I may have found an unusually large number of individuals exposed during the day time because they had just finished spawning after an especially high tide. Al though stingrays could be killing sea cucumbers, even if just by accident, it seems now that burying adds little to just Cuverian tubules. The burying rhythm strongly suggests that B. marmorata bury to avoid UVB. The timing of burial insures that they are under the sand during the times of most intense sunlight, especially on the grassfl.ats, where there are no trees to provide protective shade. Sea grasses provide some shade, but their leaves are too narrow to completely cover even the smallest sea cucumbers. In addition, the sun rises over the reef and shines directly on the grassflats as soon as it is above the horizon. In the mangroves, thick foliage and Temwen Island block direct sunlight until mid morning and after mid-afternoon. Having no pronounced circatidal rhythm, Bohadscia marmorata are unlike many marine organisms that live in or near the intertidal zone (see Decoursey 1976, Morgan 1991 for reviews). In many ways this is understandable, given that B. marmorata rely on a resource that does not change access with the tide (sand), and they apparently can withstand a certain amount of exposure. Some aspects of their behavior show a tidal component, such as spawning, but this was seen only three times during the study. It has only recently been widely documented that many organisms use bio chemicals or behavior to avoid UVB damage (Calkins & Thordardottir 1980, Car lini & Regan 1995, Masuda et al. 1993, Stocha et al. 1994). Moreover, the loss of 256 Micronesica 30(2), 1997 stratospheric ozone and subsequent increase in UVB doses has led to a surge of studies on the ecological effects of ozone loss (El-Sayed 1988, Holm-Hansen et al. 1993, Smith et al. 1992, Weiler & Penhale 1994 for a review). The use of photo taxis to avoid UVB has already been suggested for some protists (Calkins & Thor dardottir 1980), and this constitutes an important link between ethology and envi ronmental studies in light of concerns over human impact on ozone levels. When present in Holothurians, phototaxis has always been negative (Bakus 1976, Bon ham & Held 1963), and Holothuria captiva may show signs of stress-releasing Cuverian tubules-when exposed to strong sunlight (Bakus 1976). This study sug gests that some sea cucumbers use a circadian rhythm to achieve the same goal as negative phototaxis. For an animal that lives in a habitat that provides few substan tial shadows and is exposed to a fairly constant level of UVB throughout the year, reliance on burying controlled by an endogenous rhythm maybe the most efficient and reliable way to avoid UVB damage. Testing the UVB hypothesis directly is technically difficult, but it should be attempted. During this study, cages were built to house sea cucumbers above the sand during the day. Half of these cages were lined with a DVB-blocking plastic, and half with normal plastic. However, three problems emerged: (1) sea cucum bers were extremely adept at escaping, (2) silt settled on the plastic continually, and (3) the normal plastic became DVB-blocking after a few weeks in the water. However, from what data we did collect, it seemed that individuals exposed to UVB lost more weight, and they developed skin lesions. This failed attempt to test the effects of UVB directly should serve as lesson and encouragement to any fu ture investigators.

Acknowledgments Mike Brady and Boin Treacy helped collect grass:flats census data. Tom and Judy Schutt, May Okihiro, and Patty Ruze volunteered observations and trans portation. Doug Clouse, Aikiko Ikeguchi, Eric VanderWerf, Harbor Branch Oceanographic Institute, and the Dade County Public Library located literature. G. Kurt Fiedler, Joyce Friedenberg, Dan Corrou, and Eric Norton listened to and helped test ideas. Keith Tarvin provided graphics instruction. I owe special thanks to Archbold Biological Station for support during the writing phase of this project. This paper was greatly improved by anonymous reviewers.

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Yamanouchi, T. 1956. The daily activity rhythms of the Holothurians in the coral coral the in Holothurians the of rhythms activity daily The 1956. T. Yamanouchi,

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elr C S & .. ehl 19. lrvoe rdain nAtria Measure Antartica: in radiation Ultraviolet 1994. Penhale P.A. & S. C. Weiler,

ogn E 19.A apasl f ia atvt ryhs Crnbooy Interna Chronobiology rhythms. activity tidal of appraisal An 1991. E. Morgan,

Masuda, K., M. Goto, Goto, M. K., Masuda,

Rowe, Rowe,

Macnae, W. W. Macnae,

Smith, R. C., B. B. Prezelin, K. S. Baker, et al. 1992. Ozone depletion: Ultraviolet Ultraviolet depletion: Ozone 1992. al. et Baker, S. K. Prezelin, B. B. C., R. Smith,

Leger, D. W. W. D. Leger,

Kirk, J. T. 0. 1994. Optics ofUV-B radiation in natural waters. Archiv Archiv waters. natural in radiation ofUV-B Optics 1994. J. T. 0. Kirk,

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