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COMMUNITY STRUCTURE OF SHALLOW-WATER OPHIUROIDEA.

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\ • McGill Un.wersi ty

COMMUNITY STRIJC'ruP.E OF SHALLOW-WATER OPHIUROIDEA

1 OF BARaADOS, WEST Il-.'DIES.

~by \

Richard D. Bray

, -'

~ , , • :,,' \ A thesis sub~itted to the faculty of Graduate Studies and ~. Research in partial fulfillment of the requirements """S " for the degree ~of Master of Science in the Marine Sciences Centre

J Montreal, Quebec

March, f975 ,", - '.. ,i . ", . ® Richard D. Bray 1975 :"t' •

ABSTRACT , ,

This study investigated the ~unity structure of cryptic,

coral reef d~ell1n9 oph1uroids in terrns vf habitat, species com-

po~ition, abundance, and species diversity patterns. Three s~

~ ling sites were examined and compared~ f~ging reef, shallow "

rubble zone, and outer reef bank. A total of 27 species from 10

families was collected from the three sites. Eleven of these spe­

cies were additions to the reported ophiurdid fauna of Bariados ,,1 and the other islands of the Windward group.

On the fringing reef four habitat types were distinguished:

1) sand or limèstone platform/ 2) reef area with greater than 50\

living coral coverage, 3) reet area with less than 50\ living coral . . ~overage, and 4) rubble. There was an increase in species d1versity

and a decrease in mean ophiuroid density with decreasing spatial

heterogeneity. It was observed that the dominant reef ophiuroids

vere suspension feeders, rather than bottOM, detritus f~eders. Most

brittle-star species were generalfstsjn their choice of substrate.

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, '" { RESUME

Cette étude porte sur la structure oes communautés d'ophiures

~ryptiques habitant les récifs de coraux: niches écologiques, com­ position des.. espèces, de~sité, diversité. On étudia et compara 3 stations types: r~cif fr~eant, zone de débris pe~ profonde, ba~c .. '" corallien 'extérieur. 27 e~eces regroupees en 10 familles furent .. recueilles à ces 3 stations. Onze de ces especes sont ~velles

A mentions à la faune déjà connue de la Barbade et des autres iles .

"sous' le vent".

On distingua 4 habitats dans le récif frangeant: (1) un banc . de sable où de calcaine (2) une région recouverte de plus de 50\ de . coraux vivants (3) une autre recouverte-da-moins de 50\ de co~aux . , . v~nts, ~~ (4) une zone de débris.

p~~ent a une diminution de l'hétérogenéité spaciale on

note une augmentation de la diversité et uqe diminut10n de la dens-

ité moyenn~ de$·oph1ures. Les ophiuridés qui dominent, dans le récif

sont plutôt suspensivores, alors que dans le fond, il~ sont detritivores.

La plupart des espèces d'ophiures ne sont pas sélectives quand au choix

de substrat.

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CONTENTS

Page t " LIST OF TABLES ••••••••• ....1 • •• • :1 ••••••••••••• .vi

LIST' OF ILLuSTRATIONS •••••• .viii

1 f, INTRODUCTION

Purpose...... 1 Regional Setting.r •••••••• ...... · .. 1 Literature Survey ••••••.•••• . .5 Historical Accounts of Ophiuroids of Barbados .•• .10 Ackn-owledgements. Il ...... • •• 11

METHODS AND MATE RIALS

Study Area and Sampling Proceedure ••••• .13 Iden ti fi ca tion •••••••••••• • .17, Mathe~atfca1 Ana1ysis ••••••••••. .17 StmiXarity between samples •.• .17 Dominance. ..~ •••• , .. • •• 18 Aggregation ••• .19 Specializa tion ••••••.•••••••• .20 Oiversi ty ...... • •• 21 The species count ••• • •• 22 The cumulative p'er cent rnethod. .22 'Simpson's index of diversity •••• • .23 Information theory index .•••••.•••••••• • .24 / Statistics and Format •••••••••••••••• • • • • • • . • • • • • • • • • • • 25

RESULTS AND OBSERVATIONS

General •.•.••...•.• ·...... 26 The Fringinq Reef ••••••••• ·...... 26 Comp1eteness of sam~1ing. · ...... 31

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Similarity between samples •••• • ••• 34 I>œlinance •••••••••• • •.. . 35 Aggregation •••••••• ·...... • ••• 40 Specialization •• • ...... J. •• i • • • • • • • •• • 42 Size ...... • . • ...... •.• . 42 . i' Diversity ...... ~ . . _.. : ...... •.....••.. . 46 The species count. • •• 46 The cumulative per cent method. • •• 48 Simpson's index of diversity ••• • ••• • 48 Information the ory index ••••••• · .... . 50 General obse.rvations ...... 54 Coral coverage and ophiuroid abundance ••••••••••.•. 54 Feeding ~ ...... •...... 54 Commensalism •••••• .57 The Shallow RubbIe •.•••• .58 Similarity between samples •• .60 D<>min~.ce •••••••••••• · ... . 60 Aggregation •••••.•••• •••• 63 Size ...... ,...... • •. 63' Diversity. • •• 66 General observations. • ••• 67 The First Ridge ••••••••• .70

DISCUSSION AND CONCLUSIONS

The Fringing Reef .•.•••••.•••••••••••••• ...... 76 The Shailow Rubble ••••••••.• • ••••••••~ ••, 1[...... 79 The First Ridge ••.•••••••••• ...... 81

SUMl-lARY ...... · ...... - ...... •...... 84 C)

LITERATURli: CITED ••••••••••••••••••••••••••••••••••••••••••••••••• 85 ,. ". '4 ~ ~ . _~.:It •• ~, "-

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v LIST OF TABLES"

Table ,Page

1. The shallow-water Ophiuroidea of Barbados, West·

lndies ...... It ...... 27

2A •. List of species, their abundances, mean densities, and standard deviations for Type II .environrnents •.•.•••••• 28 2B. List of species, ~eir abundans~~~.~an densities, and standard deviations for Type I~I eny\ronments ••.•..••. 29 ) -;! ~ \ 2C. List of species, their abundances, mean densities, and standard deviations for Type IV environrnents ..•.•••••• 30

3. The values of CÀ for the cornparisons of sam?les II, III, and IV ...... I... I. ,...~ ...... 35 :' " (~ , 4A. List of fringing reef species dominants: type Il enviroIlI1\ents ...... '...... 36

4B. List of fringing reef species dominants: Type III environrnen:s ...... ) ...... 37

"J ' 4C. List of fringing reef species dominants: Type IV envirollT'lcnts, ...... --...... " ...... 38 S. Lists of ratios of observed Biological Index Values to maximum Biologicàl Index Values •.••••••.•...... ••.•••. 39

6. Population parameters for the fringing reef: Mean density, mean crowd1ng, and patchiness ..••••....••.••••••. 4l

7. List of Levin~' index of niche breadth for the fring- ing reef ...... 43

8. List of mean Biolog1cal Index Value and Levins' index of niche breddth for fringing ~ef species ••.•....••.••••• 44

9. ~:;~~. ~~ • ~~~ • ~~:~~~~~:. ~~~~~~{~ • ~~~ • ~~~ • ~~~~:~~:.' ••••••• 47

vi " 1 ~

( 1 Table Page

10. List of species, their abundances, mean densities and standard deviati~ns for the, shallow rubble zone •.••••• S9 . , 11. The val~es of CÀ for th~ comparisons of environ­ o mental Types tI, III, and rv with the shallow ~ub- • ble zone ...... •...... " ...... "...... 60

12. List of shallow rubble species dominants •••l', ••••••••••••••• 6 1

13~ Lists of the ratios of the obsefVed Biological Index p Value and the maximum Biological Ind~x Values ••••••••••••• 62 '" • 1 14. Population parameters for the two rubble collections •••••• 63

15. Summary of the diversity measures for the two rubble collections ...... ~ ...... •...... 67

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vii LIST OF ILLUSTRATIONS

Figure Page

1. Index map of Barbados ...... 2

2. Representative bottom profile of ~e west coast of Barbados .... " ...... , ... " ...... " •.. 3

3. Schemat1c representation of the fringing reef s~udy site ...... ~ ...... " ...... ~ ...... " ... . 14

4. Species-area curves .•••••••.••.••••••••••••••••••••••••••• 32

5. Htt-arca curves ...... 33

6. Cumulative size-frequency curves •.•...•.•••••••••••••••••• 45

7. Oiversity: Cumulative per cent method ••••••• ~ •••••••••••• 49

8. 01versity: Shannon-Weaver function5 •••.•••••• ~ ••••••••••• 52

... 9. Revised Simpson indices (ON) and evenness measures (J) .••• 53

10. Number of.-indiv1duals and percentage living coral coverage .. " ...... " .... " .... ! •...... 55

Il. Cumulative size-fre~uency curves ••••.•••••.••••••••••, : •••• 64 12. Graphs of arm length versus disc diameter for two collect10ns of Ophiocoma echinata •.••••••••••••••••••••••• 65

13. Number of individuals, number of species, and.meter number along transect •••.••••.••••••••••••.•••••.••••.••.• 68 1, 14. Mean number of individuals and mean habitable surface area versus per cent of distance along transect ••••••••••• 69

15. Graphs of arm length versus d1SC diameter for two collect1ons of Oph1othr1X (A.) suenson1 ..••••••••••••••••• 72 / 16. Ophiuroid abundance plotted against dry weight of Agelas Spa sponge ••••....•.•••.•.•••••.•...• " ••••••••.•••• 73

viii ;

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INTRODUCTION

Purpose

Many studies of tropical ophiuroid communities have been restricted

to qualitative descript1on. This is the first quantitative investigation

of a West Indian brittle-star assemblage associated with a fringing coral

reef and is an att~t to provide an understanding of the structure of a tropical b~ittle-s'ar community.

This study, ~hrough elucidating the patterns of discre~e ophiüroid

populations, attempts to further' the understanding of the importance of

the Ophiuroidea in shallow-wate~ tropical ecosystems. \ . Regional Setting

Barbados (Lat. 130 l0'Ni Long. 59030'~J) is a small, coral-capped

island in the ~tlantic Ocean; it is located 100 miles east of the Les-

ser Antilles, and 200 miles northeast of the island of Trinidad (Fig. 1). , Discontinuous, living coral fringing reefs are present mainly on the lee- ward or west coast of the island. These fringing reefs include the fol-

~ lowing zones (Lewis, 1960): Reef Flat, Diploria-Palythoa, Reef Crest, and

Seaward Slope (Fig. 2).

The Reef 'Flat Zone is situated between the shore and the zones of

actively,growing coral; this reef-rock surface varies in width From 10

1 to,70 meters. Depending upon the tidal!phase, this area has a water depth

1 • \

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St Lucia (J BARBADOS St Vincent ~ \) 1 ~ The Grcnadmes(" 4 , 1 .' Grenada O'----If---12°

1 , 1 Venezuela Ih 0

Area of study

BARBADOS . " \ \ 1 . 1 \ o 5 miles

( 1 Fig_ 1. Index map of Barbados. '.~

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1 I-()RIZON'tAl. SCALE 100m \'. "

VERTI CAL EXAGGERATI O~ THREE TIMES HORI ZONTAl D-At DIPLORIA-PALYTHOA , S S: SEAWARO SLOPE

D-P. SHORE ,ZONE SEA LEVEL :BAq< REEF REEF,~ CREST RUBBLE

TRENCH

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) \, .." . Fig_ 2. Rep~esentative Qottôm profile of the west coast of Barbados.

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averaging one meter or less. The bot tom mainly consists of a fIat rock

platform or reef debris composed of fIat boulders and/or loose1y cemen~-

ed calcareous fragments. The rock platform is frequently covered vith a

thick a19al turf or may be encrusted with cora11ine a1gae. The on1y com-

mon cora1s 1n this zone of the reef are encrusting colon1es of Siderastrea

radians and, rare1y, sma11 flattened colonies of Porites parites.

The Diploraa-Pa1ythoa Zone is between 15 and 20 meters widei at its

~ .. .,. , outer 1imit it is general1y covered by two feet of wa~er at, mean low tide. The dominant coral. is Diploria, c1ivosa with growths of Porites porites,

1 -

1 ~. astreoides, Montastre~.annularis, Favia fragum , and Agaricia agarici-

tes. The colonial zooanthid Palythoa mammillosa is lçcally abundant. At 1 , locations devoid of coral or other coelenterat7 encr?sters, the reef rock i5 covered with a 'layer of coralline algae. " The Reef Crest ~one is the next zonei it varies in width from 20 t~

100 meters. This is the'region of prolific coral growth characterized by " r . c.: <_~ a loosely organized spur and groove system. The average depth of the spur

tops is 1 to 2 meters. The vertical faces of the spurs are dorninated by

Montastrea annularis or, alternately, the massive Siderastrea sidereai

o the horizontal surfaces are dominated by Pori tes porites and ~. astreoides.

In the seaward portion of this zone, ~. porltes and t. astreoides ofteri

account for more than 75\ of the cover of the spurs. Poorly developed

spurs are characterized by the dominants being replaced by other corals

inc1uding Favia fragum , Agaricia agaricite~, the hydrocoral Millepora,

and large dead areas covered by encrusting coralline algae or a'coating

of detritus and non-calcareous algae.

'.The Seaward Slope Zone is characterized by the gratlual downward slope -\ ( t 1 G '1 Il j C . ,

5

of the ree!, and the dominance of Montastrea annularis. In addition;

Siderastrea s1derea may'be locally important on the spur sides. The

• outer limit of the slope, with a depth of 5 to 6 meters, i5 co-dominated

by Pori tes pori tes and Madracis mirabilis.

At the forward edge of the Seaward Siope, the low spurs disappear

) and are replaced by

In addition to the fringing reef along the west coast the island,

two\submerged barrier reefs parallel the coast at mean depths

230 feet. These are respectively referred to as the First an Second

Ridges (Macintyre, 1967).

Generally, the top of the First Ridge is domed and less than 100 . feet wide. Most of the corals consist of heads of Montastr a cavelnosa,

M. annularis, Colpophyll1a sp., Siderastrea siderea, ~~~~ astreoides,

and Isophyllastrea rigida. These corals seldom grow mor

above the substrate. The sub'strate is mammillary coral- base which

consists of very coarse coral debris. This base is commo covered with

coarse to medium carbonate sand (1 to O.25rnm), but is occas

ed to,show a pitted and corroded surface. Sponges, antipa~aria

, alcyonarians are abundant on the crest of the ridge.

Literature Survey

The Ophiuroldea are commonly known as brlttle-stars from the tend-

ency of the arms to break off easily, or as serpent stars from the snake-

like appearance of the arms. The nam~ derives fram the Greek ophis,

snake, and ~, tail, in reference to the resemhlance to the tail of a

snake. Ophiuroids, although less conspicuous than other marine inverte- brates, are one of the Most characteristic taxa of the marine environ- • ment; they are represented by approximatley 1900 species p1aced in 220 genera and three extant orders. Brittle-stars are, and perhaps--- have been since Ordovician times, the Most successfui of the echino-

de~ ,due to their smali size and agi lity (Hyrnan, 1955). , Since morphologically sirni1ar organisms are often placed in the

same taxon, the resu1tant classification of ophiuroids is essentially

ecologic rather than phylogenetic. Although some characters show evo­

f lutionary progression, these are usually at higher leve1s of class1fica-

tion (Fe1t , 1962). RegardIêss, the taxonomy of the britt1e-5tars i5 in-,"

completely known because of their cryptic habit and 1ack of interest in ~

the class . • Recent work on Many of the enigmatic families has greatly facili-

tated identificat10n and strengthened the taxonomie posit~n of Many of

the ophiuroids. The works of Ziesenhenne (1955) on the Ophiodermatidae,

Thomas (1962a, 1962b, 1965, 1966, 1973) on the Ophiodermatidae, the Ophi-

onereididae, and the Amphiuridae, A.M. Clark (1967, 1968) on the Ophiotrich- ç idae and the Ophiodermatidae, and Devaney (1970, 1974) on the Ophiocomidae

are imPOr~tudies.

The biology and ecèlogy of the ophiuroids have been extensive1y re-

viewed by Hyman (1955) and FeIl (1966); an excellent brief account i5

qiven by Nichols (1969). Britt1e-stars are found in a11 seas, at al1 latitudes, asso~ated

~ith a wide variey of substrates, and, over a wide bathymetric range

from the littoral environment to a record depth greater than 8000 meters

(Belyaev and Litvinova, 1972). They are mainly st~nohaline, but sorne 7

may t01erate estuarine conditions (Binyon, 1966; Stancyk, 1970).

ophiofragmus fi10g~aneus has been recorded from water with a salinity

of 7.7 0100, a record 10w for any ech1noderm (Thomas, 1961). \ . '

Numerically their importance 1n benthic enviro~ents has been re-

cognized for rnany yearsi ophiuro1ds are often used in designating dis-

crete community types (Thorson, 1957).' As most echinoderms; ophiuro1ds

are gregariousi th1S habit of livinq flosely together in large numbers

goes back to early geological times (Lad~, 1957). Denslty of Ophiothrix

fragilis has be~n recorded as h1gh as 370 ind1viduals per square meter

near Plymouth, England (Vevers, 1952). The coast of Brazil has yie1déd densities of,- Hemipho1is elongata as high as 1069 individùa1s per square meter ('l'onunasi, 1971). On the coral reefs of the Sudanese Red Sea,

Ormond and Campbell (1971) reported densities of ophiocomids to he ap-

proximate1y 45 individuals per square meter.

A review of the reproductive phys1010gv (Boolootian, 1966) 1isted

the reproduct1ve cycles of 17 ophiuroid species; only'two are from the

western tropical At1ant1c reg1on. Recently Glynn (1973) reported a sea-

sona1 pattern in oph1uroid recru1tment into enclosures suspended over a

Puerto Rican Porites patch reef iPnununity. Ophiuro1ds und~rwent heavy \. settlement between August and September exhibit1ng a settlement of 40 individuals per square mater. Schoener (1968) obtaincd. indirect evi-

dence for reproduct1ve periodicity in deep-sea oph1uroids by findingJab~n-

dant juven11es at certain t1mes of the year. Stancyk (1970), after exam-

ination of gonadal products, has determ1ncJ the reproduct1ve per1ods, of

six subtropical estua1'1ne brittle-stéirs. 'l'he only study of oph1uroid .

game~ogenesis was by Patent (1969) who worked with the basket star Gorg~- 8

nocephalus caryi.

Reproduction in ophiuroids may be sexual or asexual. The former is

usually oviparous although Fell (1966) reported that up to 50\ of the \ - fauna of southern'oceans may be viviparous. Development may include

larval stages or may be direct. Pearse (1969) indicated that direct

development may be an adaptation to adverse conditions. In a subtropical

estuarine envirbnment, modifications in development may give sorne s&lec-

1 tive advantage, much ,as they do in the more rigorous conditions of colûer

waters (Stancyk, 1973). D1rect developers are longer lived and more able

to survive estuarine conditions (Stancyk, personal communication). Some

species may reproduce by asexual division of the disc through the middlei

the resulting "halves" regenerate the remainder of the missing disc and

the lacking arms th~s yielding two complete individuals (FeIl, 1966). ~

Ophiuroids have neither intestine nor anus (Hyman, 1955) and, there-

fore, are incapable of the gross mud-gulping exhibited by sorne of the

asteroids, echinoids, and holothurians. They must be somewhat selective

in the cho1ce of material they 1ngest (FeIl, 1~6). The group's feed1ng

strategies are as diverse as the group 'ltself. A brittle-star may be

carnivorous, pianktotrophic, a detritus feeder, herbivorous (Yonge, 1954;

Fell,1966; Reese, 1966), or may possibly abforb dissolved organic mole-

cules through ~he ectoderm (Fontaine and Chia,.. 1968; Johannes, Coward, and. Webb, 1969). Species demonstrating all five feeding methods have been

, recorded (Fontaine, 1965), and the feeding strategy may change with ontog-

eny (Mortensen, 1927).

Feeding behavior rnay be the mechanism for the separation of congener-

ic ~phiuroid spec1cs (Buchanan, 1964). This generalization may not be 9

ubiquitous since deposi t feeders appear to specialize to habi tat type'"

(patch) rather than food resource or partic1e size of food (Kohn, 1971) •.

This has been demonstrated for 4 congeneric Pacifict species of Ophio-

corna (Chartock, persona1 communication)

The prirlcipal predators of ophiuroids are fishes and,asteroids.

Buchanan (1964) reported thAt luminescent specips were preyed upon by

bottom-feeding fisb norma1ly associated with day feeding. Economical-

ly important, bottom-dwelling fish, haddock and plaice, feed upon brit­

ile-stars in boreal seas. Randa11 (1967) ex~ined the stomach contents

of West Indian reef fishes and found 33 fish with'ophiurold fragments :

in their stomachs. The stomach contents of 10 fish con~isted of mor~

than 10\ brittle-star remains. The sole diet of the downy blenny (Lab­ " risomus kalsiherae) appeared to be brittle-stars. t Fenche1 (1965) described an ~eroid in the Baltic Sea, Luidia

sarsi, which feeds exclusively on ophiuroids, especially amphlurids. A

congener of !!. sarsi found in the Gulf of Mexico, !!. clathrata, sometlmes

takes ophluroids. ' '!'wo other subtropical ophluroids, Ophiothri x (2..)

angulata and Ophiolepis e1egans, are preyeù upon by the starfish~chin-

aster spinulosls (Stancyk, 1970).

The syrnbionts of ophiuroids inc1ude members of most invertebrate '\ phyla as weIl as algae. Hyman (1955) and FeIl (1966) have adeq~ately \ surveyed the associations of brlttle-stars with other organisms. Brit-

tIe-stars may be the host for uni cellular symbionts which include proto-

zoan ciliates, encrusting foraminifera, and green algae. Parasites or

cOl!1Inensals associated Wl th the Ophiuroidea may be sponges, nematodes,

trem~todes, and ann,elids. A po1ynoid annelid-ophiuroid relationship 10 may have a bivalve participant. Other symbionts of brittle-stars are gastropods, . barnaclJs, and arnphipods. Perhaps the most frequently ob- served symbionts are the copepods, many of wh1ch are parasitic and may exhibit highly modified morphologies associated with a parasitic habit.

In addition to being hosts for a variety of orgatiisms, ophiuroids may_exhibit epizoic, endozoic, or ectocoMmcnsal habits. Ophiuroids are • often observed cling1ng to or w1thin sponges and corals. Brittle-star..:: have aise been reported associated with benthic algae (Boffi, 1972).

Many brittle-stars are commensal wi th other echinodenns. Ophiuroids

", have been found associated with cornrnatulid crinoids and sand dollars.

The phenomenon of bio~uminescence as displayed by the Ophiuroidea \ is weIl surnmarized and documented for sevén species (Hyman, 1955; Mil- lot, 1966): Amphipholis squamata, Amphiur~ f111formis, Amphiura kanda1, , Acrocnida brachiata, 0Ehiocantha b1dentata, Ophiopsila annulosa, and

0Ehiopsila aranea. There are addi tional unverifi,éd or doubtful instances of luminescence by ophiuroids. The light emi5s10n i5 a "cold-light,"

{l • oxygen-dependent chemiluminescence caused by the br1ttle-stars themselves and not syrnbionts; i t requires an external stirnulu~.

Historical Accçmnts of Ophiuroids of Barbados

Thé Reverend Griffith Hughes, in 1750, pub11shed his account of the natural history of Barbados. In the portiorl concerned with "Exsangous

AnimaIs" and under the heading "'l'he Sea Scorpion" he wrote: "What we hcre call the Scorpion is by Petl.ver cal1ed Stella marina Scolopendrol.des.

Its five rays might perhaps properly cause it to be called the Stella .. ---~-=~~.~-~-~.~.~------..... ,

11

marina ...

This is the on1y reference to the ophiuroids by Hughes. It is most

like1y the same brittle-star species mentioned by Nutting, in the course , of his 1918 studies, "which occurred a1most litera11y \mder every stone

and scutt1ed away with amazing è'o1erity when disturbed." These are un-

doubtedly reports of the extreme1y common Ophiocomalechinata.

Bes ides -the s e ca. ual re f e rences ."- ~here have be~ re la t ive 1y f ew ". ''''--' " studies of the Barbadiar. bri ttle-star fauna; most of the reports merely

being species 1ists. The monographlc treatment of the West Indian ophiu- ....., roids by Koehler (1914) 1argely dea1t with those from 8arbados. A most

" extensive study of the island' s ophl.uroids was conducted by -the Iowa uni-

versity "8arbados-Antig\lP. Expedition of 1918" i the fauna was specifical-

1y dealt with by A.H. Clark (1921). In 1939, H.L. Clark described two

new species collected by A.H. Clark. The most recent mention of Barbadian

brittle-stars has been by Lewis (1960, 1965). The earlier work mentioned , a few brittle-stars which are found on the fringing reef; the latter

study of the deep water communities mentioned the importance of the'ophiu-

roids, and other echinoderms, between 100 and 300 meters.

Acknowledgements

l am especially indebted to my thesis advisor, Dr. John B. r.ewis,

for his financial support, advice', and encouragement during research.

His cri tical, review of the manuscript and patience du ring final prepara- tion is also acknowledged. Special thanks go to Bruce Ott who provided

stimulating discussion and whose knowlcdge of localities and diving as- e- sistance provided an integ'ral portion of the fieldl work. Gratitude is 12

~ a1so extended to Dr. Finn Sander, Director of the Bellairs Research

Illstitute of McGill University of Barbados, and to Kirk MacGeachy for their aid during field work. Sincere appreciation goes to my wife,

", Sharon, without whom this project would not have been completed.

The project was supported by a National Resl7arch Council of Canada grant to Dr. J.B. Lewis and a grant-in-aid of research from the Society of the Sigma X-i (

..

-~ --~---

L.. ,: ..,

.'

r METHODS AND MATERIALS

. Study Area and Sampling proeeedures The field work reported herein was condueted between May and Sep-

tember 1973 at the Bellairs Research Institute of McGill University of

Barbados.

The study are a designated for the detailed investigation was a

fringing reef similar to that described by Lewis (1960) and already mentioned. The location is directly offshore the Bellairs Research ,. /II< Insti tute (F igure 3). Selection of the site was based upon accessibil- ity of the reef and ease of equipment transfer to the reef. Detailed investigation of the shallow area (less than 50 feet) was essential sinee it was,determined that up to three hours of underwater work per square meter were required.

AlI speclmens were colleeted using Sclf-Contained Underwater Breath- ing Apparatus (SCUBA) or mask and snorkel. Ait recording was on an un- derwater, plexiglass slate. Observations werè conducted on the norther- ly portion of t~e reef by a ser1es of 50 randornly placed, square mecer quadrats in a study area of 120xSO meters. 'rhe short axis was paraI leI

l to the shore and three rneters from tt:he rnean low tide level. Randorn quadrats,..... were essential in this area to effeet efficient and thorough sampling of a heterogeneous environment.

Initially the square rneter quadrats were characterized according

13 '\ 14 \

\

~-.

•

Bellalrs Research X

'. .. 100ft 30m

-, ---- - N (E--- 1

Fig. 3. Schematic representation of fringing reef study site. A: 150x20 meter sampling areai B: 15 squar~ meter contîguous quadr ats • ",- .' ) j • 15

to depth -and substrate type. Four substrate types were defined: '- 1) Type -1- Sand or limestone platform. 1 2) Typè 11- Spur or buttress with greater than 50\ living coral coverage; designated "living reef." 1 , !JI' 3) Type III-Spur or buttress with less than 50% living coral coverage; designated "dead rcef." • 4) Type IV- Rubble or reef der1ved debris usually located in a ~ groovc or channel between buttrûsses.

After the depths of quadrats over sand were measured, the sediments were removed, transferred to shore, and sieved·through a f1ne screen. 'il In the buttress quadrats, aIl the living ophiuroids in a one meter

square were removed by dissembly of the buttress under water with ham-

mer and chisel. The percent living coral coverage, coral~spec~es, and

depth were recorded. The excised portions of the reef were placed in

buckets to be transferred to shore for f~rther dissemhly and eXru~1na-

tion. During the dissembly process, any ophiuroids in the square meter

being samp~ed were collected, placed in polyethylene bags, and trans-

ported ta shore. On shore the prev~ously collected portions of'the

buttress were further dissGnbled, aIl ophiuroids were collectcd and , ,

placed in ~eawater for eventual ident1fication and counting.

Rubble quadrats were sampled in mu ch the same manner as the reef

samples. AlI the ru~ble in one squa~e meter was carefully cOlle~;1d in buckets for transfcr, te shore. During the ,rubble collection ~o-

cess, ~~ndering brittle-stars wcre placed in polyethylene baqs. The .., substrate beneath the rubble was al 50 examined for any ophiuroids.

Before being disscmbled or d~scarded, the boulders were measured alon9 16 the two principal axes.

series series of fifteen, meter square, contiguous'quadrats. The site

"",, selected was also directly offshore the Bellairs Research Institute, but associated w1th the southern portion of t?e fr~ging reef, specif- ically the Back Reef Zone (Figure 3). In a manner sirnilar to that al-' ready mentioned, the rubble was collected in buckets and the brittle- stars placed in polyethylene bags. The bediments under the rubble were ~ sifted to collect any ophiuroids.

On shore the brittle-stars from ail collections "ere identified, counted, and measured. In instances where positive ident1fication was not,possible in the'field, the individùals,were taken to the laboratory for critical examination. Any specimens not ultimately identifiable were preserved in 70\ ethanol and labelled. After identification, counting, and measurernent, individuals not retained for further study were returned,to the sea, to a location not associated with the sampling area. .J Quadrat sampling 1n deep water was limited by diving time restri~-

tions." This problem was c.ircumve~ted by the collect1on 'of "prepackaged"

samples of sponge with endo~oic brittie-stars. Ten colonies of Agelas sp. sponge were randomly collected from the 100 feet contour along the " First Ridge. The colonies were pri~d from their attachment, placed in polyethylene bags, and returned to the laboratory. T9tal underwater collection t1me was usually less than 5 minutes. In the -laboratory,

the sponges were carefully dissected pnd .all symbiont? removed. The ophiuroids were separated and counted. The sponge was,washed in fresh 1

" 17

v.ter, dried, and veighed. AlI brittle-st~s were preserved in 70\ " ethanol and labelled. , Identification

"No truly comprehensive key exists for the i)aentification of We~t 1 ~, Indian ophiuroids. various sources were consulted for ~roper identi- , fication and nec~ssary taxonomie revisions. The key of H.L. Clark (1933)

vas of central import~ce. FelI (1960) provides an extensive'key to

q the genera of the Ophiuroidea. Additional keys and discussions of l,

of families and genera are presented by Thomas-(Î962a, 1962b, 1965t 1966, /

- 0' 1973) for the Ophiodepmatidae, the Amphïuridae, and the genus aphionereis;

Parslow and Clark'(1963) for the genus Ophiocomella; A.M. Clark (1968) , for the Ophiotrichidae ; H.L. Clark (1933) for a<·discussion of two Bar-

be~ian additions to the genus Ophiothr~x, and Devaney (1970, 1974) for

QP9iocoma and Ophiolepis.

, Certain enigmatic specimens were positively'identifi~d by Dr. Lowell

P. Thomas of the University of Miami~ ..

Mathematical Analysis

S~ilarity between Samples

Morisita (1959) __ developed a method for calculating the degree of

simil~ity betweem samples and communities which is uninfluenced by sam- , pIe size., 1 The Morisita ~dex, C~, is calculated as follows: - ..

c~ '"' (1)

~------18 o wher"n1i and n2i "are the number of individuals of species i found

in s~ples land 2 respec,tivelYi 1. 1 and 1. 2 are the values of the Simpson (1949) index of divcrsity (See equation 10).

The Mor1sita index is interpreted as the probabi1ity that two

individuals drawn rahdom1y from populations NI and N2 will belong to (? the same species, relative to the P!obabi~ity of randomly drawing

two individuals of the same species fr~ NI or N2 alone. The values of the similarity index, CÀ' will be about 1 when the two samp1es

belong to the same s~le ~r community, or ar~ drawn from the same

population, and will be about 0 when there are no species in common

between them.

Dominance

Dominance was analyzed by a method outlin7d by McCloskey (1970).

~ each of the quadrats of the fringing reef samples, there were domi-

nant species, considered in respect to both abundance and frequency.

A Bio1ogica1 Index Value (BIV) may be ca1culated by ranking s~ecies

and assigning 20 points for each first place ranking, 19 for each sec-

ond, and 50 forth. For example, if a spec1es ranked first in each of D ten quadrats, it would be ass1gned a BIV of 200 with a frequency of

10. The index, therefore, is a reflection cf the frequency with which

the species occur in a series of collections, and gives the same weigh~

to each quadrat rogardless of the samp1e size. It is nat entirely rell-

able to conslder dominance solely as a function of abundance, for if only" one squa~e... mater of ten contributes aIl of the individua1s of species x, a numLer greater than sorne species y which is more equa11y then -e distJ:linutea'é)vcr- the sampling area / species x, in terms of abundance,------19

r~s higher than species y. This is an unrea1istic position since

x dominates only one square meter, and is not indicative of the total

sample.

Aggregation

The concept that ~imals exhibit crowding is a subjective infer-

ence, diff1cult tQ define~ and even harder to quantify. A contagious

discrete distribution is defined as having the property that the vari-

ance ex~eeds the mean. This sugg~sts the use of the variance:mean '1 ratio as a measure of aggregation. Pielou (1969) points out that this

ratio should nct be regarded as a test criterion, but merely as a sam-

pIe statistic descr1ptive of The variance:mean

ratio is only an estimation tion pararneter.

Lloyd (1967) proposed<:n "index of mean crowding" defl.ned as the

mean number per individual o~ other individuals in the same quadrat • • These other individuals may be thought of as co-occupants of the sarnpling

space with the first individual. "Mean crowding," ~, ist:n average over. individuals instead of over '\ sampling units. It is calculated by counting for each individual in the

"l _ population, N, the number of co-occupants, Xi' that share the ~ing ~ with iti (i = l, 2, ••• N). ~ ~--- Then, mêan.. ~:.owding is 0/

#t '-,;-'j. ~ -'_ (2 ) N ~ In terms of mean (m) and variance (0-2,~ the :~'s:

: = ID + (o2/m - 1) ( (3 ) Lloyd (1967) has also prov1ded an "index of patc\ines~" which is

dèfined- as the ratio of mêan clowding te ïnean- Qefisîty: ------20

m/m* \ (4 ) This is a property of.. spatial.. pattern considered by itself without re­ gard to density. Two populations may exhibit different degrees of

patchiness although the densit~es are the same.

In an ecological study based on random quadrats, the sampling area

forms only a small part of the area of study. The true mean density,

m, is unknown, but may be estirnated by the sample mean, Xi if the sam-

pIe variance, s2, is computed, and the nümber of quadrats censused, q,

is known, then the estimate of mean crowding prov1ded by Lloyd (1967)

is \ . (5)

and a measure of patch~ness is

xIx* - (6) ~ With the apove estimation by moments, the appropriate standard errors , are, for mean crowding:

S~E. [x]* ::: ~IV l/q (xix)* - (5'2 lx) (x* + 2s 2 lx) (7)

and for patchiness

S.E. [xix)* ::: (8)

where x>O.

specialization

Species are generalized or spec~aIized with respect to resource .

utilizationi resource specializa~ion (i.e. substrate, food) essentially

delimits the niche. Levins (1968) has developed a measure of ge~eral-

ization or niche breadth, B:

(9) -e wher~ Ni is the number ~ individuals of species i in the samplei -~ih .. 21 i5 the number of these using resource unit h. B may vary fro~ 1 to h, the total number of resource units available to the animaIs. This measure is biased in that it assumes aIl resources to be equa11y avai1- able. The reciproca1 is a convenient index of specialization for the.. i resource under consideration. .... Djversity )

Diversity is one of the most important indices used in the descrip- tion of a cornmunity. Severa1 theor1es re1ating diversity to other phe- nomena as predation, cornpeti~ion, and stabi1ity have been proposed

(Pianka, 1966). A statement of the specie~ divers1ty of a specif1ed ecosystem may refer ta the number of, species or it may be a more sophis- icated index wh1ch takes into consideration the aoundance of the 1ndivid- uals.

Essent1ally there are three mathematical approaéh~ to the species ,Af/IiI < diversity concept. ',The most elementaryare the indices determined by ,r the number of'. Sp~C1~S. The more species in any given samp1e of sorne 00- vironment.,. the greater the diversity (G1eason, 1922; Nargalef, 1957;

Hessler and Sanders, 1967; Sanders, 1968).

Another 0rouP of indices approaches d1versity as the re1ationship between number of ind1viduals and nunber of spec1es. In these measures( the 1ess equally distr1buted are the 1nd1v1dua1s are amoung the species the less'the diversity (preston, 1948; Sunpson, 1949i HacArthur, 1957;

Whittaker, 1961; Patten, 1962; Sanders, 1963)'.

The third group of d1vers1ty measures is derived from a branch of mathematical statistics and probabi1ity cal1eè information theory which dea1s W1 th the relàt1ve frequen~of nomin.é!.! __classE~,s _by __treatrncnt of the , 22 average uncertainty. The information theory indices are those of

Shannon and Weaver (1948) and Bril10uin (1956).

, For the present ana1ysis, four indices were se1ected and cam- pared in arder ta avoid 1095 of information, as frequent1y is-the case when only one index of dtversity is analyzed (Loya, 1972). The four indices emp10yed in this study werc 1) the spec1es count, 2) Sanders' cumulative per cent (1963), 3) Simpson's (1949) index of diversity, and 4) Shannon and \'leaver's' (1948) infonnation theory index.

r The Species Count , -, < The sirnplest and most straightforward approach to species diver- sity is the nurnber of species found in the samp1e. This rnethod has two principal disadvantages: 1) it fai1s to consider species abundance and 2) it is dependent upon the sample size (MacArthur and MacArthur,

1961; Preston,., 1962). Regardleas, after a nurnber of, collections, a nearly complete species 1ist rnay he ~ornpiled, and the cornpleteness of sampling rnay he tested.

The eurnu1ative Per Cent ~tethod

A cumulative per cent rnethod has b~en deve10ped for determining the species diversity of a sarnple. This rnethod involves plotting, the cumulative per cent of the indiv~dua19 on the ordinate and the curnu-

1ative per cent of the species on the abcissa (Sanders, 1963). If aIl species in the ~arnple ar~ represented by an equal number of indi- viduals, the resultant graph is a straight line. This diagonal re­ l' presents the Max~urn possible .diversity. The further the deviation fram the diagonal the less the d1versity.

The area under the cu~~ rn~ __ b~ _c?I!'put:~~ for a numerical estirnate ., 23 / (

of the diversity. Similarly, if the maximum possible diversity is

compared t0'the observed diver~ity, this per cent of the maximum , . possible area may b~ used fo'r comparative purposes.

Simpsonls Index of Diversity

Simpson (1949) developed an "index of concentration," >., that ( is interperted as "the probability that two ind1viduals~hosen at

randorn and 1ndependently from' the population will be foun~to belong

to the sarne group."

If the sample, N, is sufficiently large the following equation

may he used:

(lb)

where ni is the nurnber of indiv1duals of species 1 in the sample, N.

À attains its rnin1rnurn value of unity when the sample consists of one

species. In a rnanner Oppos1te to the SirnpsoQ_rneasure of diversity,

~,., the Shannon and tveaver index of diversity, H" (Sec following discus-

sion), has a value of zero when there is only one species in the sarn-

/ pIe. If aIl individuals are equally distributed in the sample, À = liS

and H" is at its rnax1mum value, logeS (where S is equal to the number

of. species).

In order to compare the two indices, the Simpson index may be alter-

ed as follows (Loya, 1972):

DN = l - 2}f (11) where Pi is the proportion of species i in the sample. DN = 0 when

there is only one species in the sample. This is also the case with

the Shannon and Weaver index. It is advantageous to use the revised

index because of its sensitiv1ty to the distr1bution of ind1v1duals

------

./ 24

amoung the species (Loya, 1972). Thus this revised version of the

Simpson index of divérsity is very similar to Pielou's "Evenness,"

J.

Information Theory Index

ç 1 Pielo (1966b) states that diversity is equivalent to the un-

certainty which ~xists regarding the species of an individual ran-

domly selected from a population. The greater the number of species,

the more equally the individuals are distributed amoung the species,

the greater the uncerta1nty, and thus the greater the d1versity.

., Information theory trcats the uncertainty of the outcome of a series of random observations on a random variable. Since information

content is a ~easure of uncertainty, it is a r~sonable estimate of -,

diversity. The info~a.ièn measure applied here is that of Shannon

and Weaver (1948) although others, as discussed in Pielou (1969), are

available. The average uncertainty,• H", measured in bits per individual, of a collection is the mean of the individuâl uncertainties:

H" . = Ïi' = -Diln Pi (12)

where the probability, ~i,is the likelihood of an individual being in-

cluded in species i. This measure varies continuously·with the chànges

in probab1litles, and reaches a maximum value when aIl events or ta~a

are equally probable and attains its minimum value when there is, only

one taxon (species) contained in the sample.

~ince the number of species in a population is unknown, H" is the

"maximum likelihood estimator of the unknown populatiop diversity, H' " - -- - [ (Pieleu-, 1966a) .-- Howeyer, -by- applyi~- the-methed of Pielou (1966bh --- -

\ 25

the plotting of the cumulative value of H" versus the number of col-

lections, it may be demonstrated that H" is a reasonable estimate

of HI.

Two additional components of diversity are also presented by

Pielou (l966a): H--max and J. The former, the maximum possible diver- sity that a cornrnunity may exhibit is defined:

"max ~ logeS (13) '- where S is the number of species. This value is reached when the occur-

rence of aIl species is equiprobable (Pielou, 1966b). The evenness

component, J, is the ratio of the observed diversity to the maximum

possible diversity:

J = H"/~x (14)

This measure lS a reflection of the evenness with which the individua1s

are distributed amoung the speçies.

• Statistics and Format o Essential sources for the statistical treatrnent of the data were

Siegel (1956) and Sokal and Rohlf (1969). The mathematical handbo~k

of the Chemical Rubber Company (Selby, 1973) was also very useful dur-

ing computation.

During aIl phases of manuscript preparation the Council of Bio-

logical Editors Style Manual proved to be an invaluable guidehook and

reference.

__ J ---~------

-, -- 5

. ' •

RESULTS M~D OBSERVATIONS

General

The shallow-water ophiuroid fauna of Barbados proved to be rich

(See Table 1). Twenty-eight species, distr1buted amoung ten families,

were recbrded from the frinqing reef and the outer reef bank (First' , Ridge). Referring to. a previoùsly compiled species list for the area

(Parslow and Clark, 1963), this study provides Il additions to the

ophiuroid fauna of Barbados and the other islands of the Windward Group:

Amphiura fibulata A. stiMpsoni 2phiactis qU1nquerad1a 2,. savignyi Ophiothrix (Ophiothr1x) lineata OphiocoMPlla oph1actoides Ophiopsila riisei 9phionere1s o11va~ea Ophioderrna phoen1UIn o. guttatum Sigsbeia murrhina

Only 4 species, 3 being amphiurids, previously recorded by Parslow and

Clark (1963) were not found:

Amphiodia planispina ~. pulchella . Oph10cnida scabruscula Ophiolep1s elegùn6

• " The Fringing Reef

Systematic sampling of a 120xSO meter portion of the frinqinq reef

yielded 7 families and 22 species of brittle-stars. Sampling was conduct-

26 , . 27

Table 1. The shallow-water OphiurQ~dea of Barbados, • West Indies. GORGONOCEPHALIDAE Astrophyton muricatum (Lamarck)

BEMlEURY ALIDAE Sigsbeia murrhina Lyman

OPHIOMYXl DAE Ophiomyxa flaccida (Say) ,

AMPHIURIDAE Amphiura fibulata Koehler ~phiura stimpsoni Lütken

OPHIACTIDAE Ophiactis quinqueradia Ljungman • Qphiactis sav1Qnyi (Müller & Troschel)

OPHIOTRICHIDAE Ophiothrix (Acanthophiothrix) suensoni Lütken Ophiothrix (Ophiothrix) angulata (Say) Ophiothrix (Oph1othrix) brachyactis H.L. Clark Ophiothrix (Oph1othr1x) lineata Lyman Ophiothrix (OphLothrix) oerstedi Lütken ( OPHIOCOMIDAE Ophiocoma echinata {Lamarck) Ophiocoma pumila Lütken Ophiocoma wendti Haller & Troschel Ophiocamella ophiactoides (H.L. Clark) Ophiopsila haroneyer1 Koehler Ophiopsila r11se1 Lütken

OPHIONEREIDIDAE Ophionereis olivacea Il.L. Clark Ophionere1s reticulata (Sav)

OPHIODERMATIDAE Ophioderrna appressum (Say) . Ophioderrna brev1caudum Lütken OphiodeIl1la cinereum HülleI & Troschel Ophioderma guttatum Lütken Ophioderma phoenium H.L. Clark Ophioderma rubicundum Lütken

OPHIURIDAE Ophiolepis impressa Lütken Ophlôlepis paucispina (Say) 28

Table 2A. List of species, their abundances, means, and standard deviations (in parentheses) for Type II habitats • . Total Number of Mean Number of Species Individuals lndividuals per (11 collections) Quadrat (5.0.)

, Ophiothrix (O. ) oerstedi 817 72.27(72.67)

Ophiocoma echinata 129 11.73 (16.60)

0Ehiocoma Eumila 101 9.18(12.04) ... 0Ehioderma aPEressum 60 5.45(7.94)

0Ehiocoma wendti 45 4.09(5.59)

0Ehiomyxa f1accida 37 3.36 (5.12)

°Ehiothrix (O. ) angulata 10 0.91(1.22)

°Ehioderma Ehoenium 9 0.82(1.06)

°Ehiothrix (O. ) bracfWactis 7 0.64(0.92)

Ophiothrix (1\. ) suensoni 5 0.45(1.21)

°Ehiole.cis imEressa .. 3 0.27(0.65) 4i °Ehioleris EaucisEina 3 0.27(0.65) . Amphiura stimEsoni 3 0.27(0.65)

°Ehioderma rubl.cundum 2 0.18(0.40)

°Ehioderma brevicaudum 1 1 0.09(0.30)

Ophioderma guttatum 1 0.09(0.30)

°Ehiocomella °Ehiactoides 1 0.09(0.30)

TOT1\L 1234 112.18(89.33) ,(

29 .' Table 2B. List c:lf species, thei.r abundances, means.. and standard deviations (in parentheses) for Type III habitats.

Total Number of Mean Nurnber of '. Species Individuals Individuals per

c c (12 collections) Quadrat (S.O. ) .

°12hiothrix (O. ) oe:r:stedi 220 18.33(20.25) " °12hiocana pumila 93 7.75(9.27)

°12hiocoua echinata ,. 57 4.75{7.29)

°12hiocoma wendti 13 1.08(1.68)

°12hioderrna aE,Eressum 10 0.83(1.03) -='" °12hiothrix (O. ) angulata 8 0.67(2.31)

0,Ehiothrix (O. ) brachyactis 7 0.58(1.16)

O,EhioleEis im,Eressa 7 0.58(1.44) -,- 1 0,Ehiactis' qu5ngueradia 6 0.50 (1. 73)

0,Ehiomyxa flaccida 4 0.33(1.15) . 0,Ehioderrna rubicundum 3 0.25(0.45) ,\ 0.17(0.39) Ophiocom€lla ophiactoiaes 2 , 0,Ehio,Esila hartmà,yeri 1 0.83(0.29) 1 0,Eh iode rrna brevicàudum 1 0.83(0.29) . \ O,EhioleEis ,Eaucis,Eina l 0.83,(0.29) p " TOTAL 433 36.08(31.49)

L c 30

'~le 2C. List of species, their abundances, means, and 'standard deviations (in pareptheses) for T~ IV habitats.

Total Number of Mean Number of Species Individua1s 'Irldivid~als per (18 collections) • Quadrat (S.D. ) " " • ophiocoma 'echinata 135 7.50(6.69) " O,EhiothriX (O. ) oerstedi 92 5.11(7.85)

" r ÜI?hioderma appressum 59 3.22(5."95) \

O,EhioleEis Eaucis,Eina 45 2.50(3.54) 6 0,Ehiole,Eis lln,Eressa 23 1. 28 (1. 36) .' 0 Ophiocoma ,Eumila 13 0.72 (1. 53} . \, 0,Ehiocoma wendti Il 0.61(0.85)

0,Ehionereis reticulata 9 0.50(0.92) . 0,Ehiothrix (O. ) anSIuJ,ata 3 0117(0.51) .' 0,Ehiomyxa flaccida 3 . 0.17(0.51) l O,Ellioderma Ehoenium 3 . 0.17(0.51) . AmEhiura fibulata 1 0.06(0.24) " - 0 O,Ehioderma brevicaudum . 1 0.06(0.24)

1 \..'\. 0.06(0:24) 0,Ehioderma cinereum ,

TOTAL 398 22.11(18.09)

"

" ' 3.

31

ed and collections quantitatively analyzed by methods already outlined.

Tab~es 2A. 2B, and 2C rank, according to abundance, the 22 species and

2065 individuals recorded from the 50 square meters of the random sam-

ple. The results are arrapged according to the habitat type. No brit-

tle-st~s were found in Type l habltats, sand and limestone platform

quac;irats.

Completeness' of Sampling

To test completeness and adequacy 0: the sampling technique, two

t~sts were appl~ed to th~.data: 1) a cumulative species-cumulative

area curve and 2) a cumulative 'pecies divers~ty-cumulative area curve.

In other words, these methods determined how many square meters of

the respective habitat types had to be examined before there was no • . significant increase ,in the number of sI(ecies addcd wi th each new

square meter. Th~s point deflned the sample size where species started

accumulating at a decreaslng logarithmlc rate. Sampling beyond thlS

point "would have been superfluous.

Figure 4 plots the cumulatlve number of species as a functiQ~ of

the\l1umber of square meters sampled. AlI curves rise gradually and

level off lndicating a completeness of sampling. Figure 5 is the graph

of the cumulative values of the specles diversi ty, H" (See Equation 12) ,

versus the area sampled. Again aIl curves level off indicatlng no sig-

nificant increase in specics dlv~rsity or informat10n after collections

vere made from a min1mum of 7 square meters in aIl habltat types. 80th 6

graphs indi~~te sampling proceedures employed on the fringing reef pro-

vidèd representative. and approprlate sampfe Slzes for the purpose of this

s~ud~.

, , '1 -~ -~ - <' '.~ e , l /~o - ... 1 ,. l\.. 1

'~ r- <;

.-

l l' () 2] "- 10 Type IV

0 en Q) Ou 20 . , ( Type III'" • ...,w OJ .i.I~J'~~ --- .p ca ,tl "3 \ '1. E ·'V ::J .. u 20 1 .; ~~~ . Type Il ()

1°1 .f 0 5 10 15 20 Cumulative area sampled (m2)

Fig. 4. cumulati~~ ,pecies-cumulative area curves for ~ three environmental types of

the fringing reef. i~ . : " ° Il ' • • ~ .\ f '. • \e • e

~,

1 "

.: " \, w w Rubb1e

"

20 - Reef living 8 12 14 16 18 ~ "Number of collect'Ions

Fig. 5. Cumulative values of species diversity, H", plotted against the number of collections. A. Data for reef.buttresses with less than 50\ living coral cover. H"-2.2289, mean HM after last 5 collections, 2.l847~ 95% confidence limits for population diversity are 2,.1056

34 .. S~ilarity between Samples

The concept of siMilarity or difference between samples was ap­

proached in three ways. These were related to 1) substrate character,

2) ophiuroid density, and 3) species abundances and proportions as

measured by the Morisita index of similarity (1959).

The substrates which provided ~iving space for the brittle-stars

were easily discernable as reef areas and rubble a~eas. The reef areas

vere arbitrarily defined as "l1v1ng" or "dead" reef depending upon the

approximate per cent of, living coral coverage. The former category

vith greater than 50\, and the latter with less than 50\ living coral

coverage per square meter.

The me an density of the ophiuroids provided another method of clas­

sification. The mean densities for the three substrate types are 112,

36, and 22 individuals per square meter for substrate Types -II,~!II, and

IV respect1vely. The mean dens1ty of the living reef (Type II) is s~­

nificantly,~reater th an the dead reef ,Type III, at the 0.025 leve1

(Mann-\-llntney u-test; S1egel, 1956). Thé density of the living reef,

Type II, 1S also signlf1cantly greater than the mean density of the rub­

hIe collection, Type IV (Mann-vfuitnety u-test: p

There is no significant difference'between the rnean dens1ty of Type III

and Type IV environments.

The Moris1ta (1959) index of similarity between samples (Equation 1) ,

CÀ' has been calculated for the assemblages of the three environmentàl

types (Table 3). The h1gh value for the relationship between samples

II and III indicates a great deal of faunal similarity. In fact, the

two may be drawn fram similar populatlons with different denslties. 35 '~

Table 3. The values of CÀ for 'the comparisons of frinqing reef samples Il, III, and IV. .. (:J Samples Compared CÀ

II-III 0.947

II-IV 0.660

~ III-IV 0.600

When the rubble sample is compared wlth the reef samples, moderate .. values for CÀ are found (Table 3). These values indicate the rubble

is characteri~ed by a dl.fferent sui te of specimens, and may be con-

sidered indcpendently of the reef areas.

The above analyses ind,icate the subjective division of the fring-

ing reef according to substrate character is corro~obrated by density

pattern and/or faunal similarity as measured by the Morisita index of

\ simllarity.

Dominance

Dominance was analyzed by a method outlined by ~cCloskey (1970).

Tables 4A, 4B, and 4C list the specles of the fringing reef habitats

ranked accordl.ng to their Bl.ological Index Value (BIV).

The species dominating the reef areas (Types II and III) are re-

markably S1milar. The"five top-ranked species are identical: Ophio-

thrix (Q.) oerstedi, Ophiocoma pumila, Ophiocoma echinata, Ophioderrna

appressum, and Ophiocoma wendti. Although there are slight differ~nces

in the ranking of the species,~. (Q.) oerstedi is, by far, the domi-

nant species of the reef buttress areas. - by The rubble (Type IV) collection ls characterized;another suite , m 36

Table 4A. List of Type II species dominants, ranked accord­ ing to their Siological Index Val~e (SIV).

Speciès Abundance Frequency BIV* (U ocoU' ns) (11 coll' ns) ,

1) Ophiothrix (O. ) oerstedi 817 Il 218

2) Ophiocoma putnila 101 " ' la 177 3) Ophiocoma echinata 129 9 161

4) Ophioderma appressum 60 9 141

5) Ophiocoma wendti 45 8 138

6) Ophiomyxa flaccida 37 7 121

7) Ophioderma phoenium 9 6 92

8) Ot:>hiothrix (O. ) brachyactis 7 5 81

Ophiothrix (O. ) anSIu1ata 10 • 5 77 9) . 10) Ophiolepis impressa 3 2 32

10) Ophio1epis patk~spina 3 2 32

11) Ophiothrix (A. ) suensoni 5 2 30

11) Amphiura stl.mpsoni 3 2 30

12) 0,Ehioderma rub~cundum 2 . 2 28 \ l 13) Ophioderma brev1caudum 1 1 , 16 14) Ophioderma guttattnn 1 1 15

15) Ophiocomella ophiactoides 1 1 14 - '\If *based on 20-0 scalei maximum BIV = 220. 37

Table 4B. List of ,Type III species dominants, ranked accord­ ".ing to their Biological Index Value (B'tV}.

Species . Abundance Frequen<;:y BIV* (12 collins) (12 collins)

1) Ophiothrix (o. ) oerstedi 220 12 234

2) Ophiocoma pumila' 93 10 190

3) Ophioderrna appressum 10 6 101

4) Ophiocoma echinata S', 5 94

5) Ophiocoma wendti 13 , 4 68

6) Ophiothrix (2,. ) brachyactis 7 3 55 7) Ophiolepis impressa 7 , 3 53 a) Ophiodermël rubicundum J 3 48

9) Ophiocomella ophiactoides 2 2 35 • 10) Ophiomyxa flaccida ,.. 4 1 19

Il) °Ehiothrix (O. ) an2ulata. a 1 18 , y 12) °EhioleEis EaucisEina 1 1 17 • 12) Ophiactis quinquerad~a 6 1 17

13) Ophioderma brevicaudum 1 1 16 13) °EhioEsila hartmexeri 1 1 .... 16 .

*based on 20-0 scale; maximum BIV = 240 .

• -, 38 Table 4C. List of Type IV species dominants, ranked accord­ ing to their Biological Index Value (BIV).

Species Abundance Frequency BrV* (18 coll 'ns) (l8 coll'ns)

1) Ophiocoma echinata 135 17 334

- 2) °Ehiothrix (2..) oerstedi 92 13 243 -- 3) Ophio1epis impressa 23 Il 196

4) Ophioderma appressum 58 10 187

5) Ophiolepis paucispina 45 10 180

6) Ophiocoma wendti 11 7 119

7) Ophiocoma pumBa 13 6 103

8) Ophionereis reticu1ata 9 5 89

9~ Ophiothrix (o. ) angulata 3 2. 35

9) Ophiomyxa flaccida , 3 2 35 ~ 9) Ophioderma phoenium 3 2 \ 35 10) Ophioderma brevicaudum 1 l 17

10) Ophioderma cinereum 1 1 17

10) Am,Ehiura fibu1ata 1 1 17 1

*based on 20-0 scale; maximum BIV ... 360. 39

Table 5. Lists of the ratios of the observed Biological Index Value to the maximum Biological Index Value (BIV b IBIV x 100). o s max

, Environmenta1 Type Species II III IV

1) Ophiothrix (~. ) oerstedi 99.09 97.50 67.50

2) OphiocOOIa ech;inata 73.18 39.17 92.78

3) Ophiocona pumila 80.45 79.17 28.61

4) OphiodeI1lla appresnun .54.09 42.08 51.94

5) OphiocCll\a wendti 62.73 28.33 33.06 , 6) Ophiomyxa flaccida 55.00 7.92 9.72

n Ophioderma phoenium 41.82 - 9.72 8) Ophiothrix (O. ) brachyactis 36.82 22.92 -

9) Ophiothrix (2.. ) angulata 35.00 7.50 " 9.72

10) Ophiolepis impressa 14'.55 22.08 54.44

Il) Ophiolepis paucispina 14.55 7.08 50.00 12) Amphiura stimpsoni 13.64 - - 13) 92hiothrix (A. ) suensoni 13.64 - - 14) Ophioderma rubicundum ./ 12.73 20.00 - 15) Ophioderma brevicaudum 7.27 6.67 4.72

16) Ophioderma guttatum 6.82 - - 17) Ophiocanella ophiactoides 6.36 14.58 - 18) 92hiactis guinqueradia - 7.08 - 19) Ophiopsila hartmeyeri - 6.67 - 20) Ophionereis retlculata -- 24.72 ;r - 21) Amphiura flbulata 1- - j 4.72 ~ " . ,} 22) Ophiodermë). cinereum - - "';-;" , - 4.72 - " - --- ...

40 of ophiuroids: Ophiocoma echinata daninates the sample followed by

Ophiothrix (O.) oerstedi, Ophiolepis impressa, Ophioderma appress\.UII, and

Ophioleois paucispina. The inclusion of the op1liurids,~. irnpressa and

O. paucispina, is a significant departure from the dominants of the reef areas. ,In the living reef (:rype II) areas both species ~hare the

10th rank; in the dead reef areas (Type III habitats), O. il'l'lpressa ranks 7th and ~. paucispina ranks lOth.

Table 5 lists the ratl.OS of the obs.:.rved Biological Index Value and the maximum Biological Index Value (BIV obs/BIVmax) for the three substrate types. Conspicuous are 1) Ophiothrix

Type II areas, 6) Ophiomyxa flaccida is characteristic of the living reef areas, and 1) Ophiolepis paucl.spina and 2: i.mpressa are most irn- portant in the rubble areas.

Aggregation

Referring again to Figure 4, it has already been noted that aIl species-area curves rise slowly. Gleason (1922) noted that as an area of a sample is increased, the number of species approaches a certain ,

1imit asymptotical1y. He observed that if the area sarnpled is uniform, the curve nses rapidly and nears the asymptote quickly: if the curve rises slowly, i t indicates a patchy distribution.

Lloyd (196 7) provide~ 1neasures of population pararneters, but when deal~ng with multl.specific assemblages, the examination becomes more dif- 41 , Table 6. Population parameters for the three environmental . types of the fringing reef: Mean density, mean crowding, and patchiness (within parentheses are standard errors of est~ate or standard deviations) • . Parameter Environmenta1 Type II III IV

Mean denSl. ty , X 112.18 36~--- 1---zT.îl (89.32) (31. 48) (l8.09)

Mean crowding, x* 186.35 64.24 36.43 (±59.41) (±22.04) (±9.46)

Patchiness, x/x* - 1.66 1. 78 1.65 (±0.35) (tO.41) (±0.29)

ficult, and the interp~etation of the indices obscured. These values vere ca1culated on the total number of ind1viduals per quadrat. There- fore these indic~s indicate how the an~als, as a taxon, are d~stributed within the sample, and how one 1ndividual reacts with the other individ- uals.

Using the appropriate measures of Lloyd (1967), the values for the mean crowding and patchiness were calculated. Table 6 g1ves these values and the me an dens 1 t~es .

Mean crowding increases in the following manr.er: IV

42 Specialization

Species may be generalists or specialists with respect to sub-

strate u~ilization. Levins (196?) provides a measure of generaliza-

tion/specialization or niche breadth, B (See Equation 9). In this

ree are utilized by the brittle-stars. The.most specialized species occupy

one or mainly one substrate type; the generalized species are more

or less evenly distributed and exhibit values of B which are greater

tban one-half the maximum possible value (B>1.50).

Table 7 ranks the values of niche breadth, B, for the 22 species

of the fringing reef samples. Most of the species are generalists

(i.e. B>1.50). Substrate specialists (i.e. B<1.50) account for only

5.8\ of the total number of individuals.

Table 8 giv~s the value~ of the mean Biological Index Value \ and Levins' Index of Niche Breadth. Most of the dominant species

tend to be generalists (3)1.50). The Spearnan Rank Correlation Coef- \ .' ficient (Siegal, 1956) for this relationship, rs ~ 0.65, is signif-

icant at the 0.0001 level.

There are two notable exceptions to this relationship between

dominance and niche breadth: Ophiomyxa flaccida and aphiolepis pauci-

spina. Both of these species have distinct habitat preferences. The

former is found living in the living reef arcas (TynE II); the latter

is characteristically collected from the rubble areas (Type IV) usually

in the sediments beneath the rubble.

Size

Occurrence in the 'rubble of more numerous ~nd larger individuals •

43

Table 7. List of L,vins' index of niche breadth or specializa­ tion for aIl speciet of the fringin9 reef. . Number of Indivldua1s • Species .! II III IV B

Ophioderma brevicalalurn 1 1 l 3.00

Ophiocorna echinata 129 57 135 2.70 / . - - oPhlothrix '(O •. ) angu1ata . 10 8 3 2.56 Ophioderma aEEressum. 60 10 58 2.32 101 93 13 2.25 0Ehiocorna Eumi1a. Ophiocoma wendti 45 . 13 11 2.06 . Ophiothrix (O. ) brachyactis 7 7 - 2.00 Ophioderma rubicundum 2 3 - 1.92 Ophio1eEis imEressa 3 7. 23 1.86 ophiocome11a ophiactoides 1 2 - 1.80 °Ehiothrix (2.. ) oerstedi 817 220 92 1.76 Ophioderma Eho'enium 9 -- 3 1.60

O~hiomyxa flacc1da 37 4 3 1.39 . OphioleEis Eaucispina 3 1 45 1.18

Ophionereis reticulata J -- 9 1.00 Ophiactis quinqueradia - 6 - 1.00

°Ehiothrix (~. ) suensoni 5 - - 1.00 Amphiura stimEsoni 3 - . - 1.0~ °Ehiopsila hartmeyeri - 1 - 1.00 °Ehioderma cinereurn . - - 1 1.00 Ophioderma guttatum 1 - - 1.00 AmEhiura fibulata - - - 1 1.00 ~ '- <- . " .' v , ~ . . , , il " 44 - . ," • Table 8. List of the mean Biological IndeX' Value (BN) e and Levins' index of Niche Breadth (B) for aU' species ... , . . and all collections "of the fringing l:'eef. ~

Specie,:; " m B , Q Ophiothrix (O. ) oerstedi '-'!" 88.03 1.76, . . . Qphiocoma echinata 68.38 . 2.'10, . . . Ophiocana p~i1.a 62.74 . 2.25

Ophiodermi\ appressum .. cr 2: 70 2'.3,2 • - . " C.phiocana wendti 41.37 2.06 - Ophiolepis impressa 30.36 1 •. 86 1 , Ophiomyxa flaccida 24.21 1.39 . i , , ! 0,ehio1epis EaucisEina 23.88 1.18 ---' - Ophiothrix (O. ) brachyactis 19.91 2.00 . .

1 1 • .. \ 0Ehi,othr ix (O. ) angu1ata 17.41 2.55 , . O,ehioderma phoenium c 17.18 1.60

Ophioderma rubucundum 10.91 1.92

°Ehionereis ret1culata 8.24 1.00 - , , , J O,ehi 0 come 11 a °Elriaftoides 6.98 1.80

~ Ophioderma brevicaudum 6.22 3.00 . Amf:!hiura stimesoni 4.55 1.00 . , , (' . . . °Ehiothrix (A. ) suensoni 4.55 1.00 - . . 0Ehiactis 9uinqueradia 2.36 1.00 - " , 2.27 1.00 1 Ophioderma guttatum ~ , . _ k . . , Ophiopsila hartmeyeri . 2.22 . . ~ ; Amphiura fibulata 1.57 ., 1.00 . ,

Ophioderma rinereum 0 h57 1.00

c

L:. '. e " e

~ 100

1) 80 ... . '~ Rubble

... , ' ;60 ~ u o... Q.

G > b ",. -la :l40 . ' "" E ::) u ~ . " o

20

" " o ~'

•• ,1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1a 19 20 21 22 23 24 2.5 26 Z1 28 Oise diameter ., ..... mm

Fig. 6. '-'cùJnulati ve size-frequency curves for the rubble ('l-.Jpë IV) and the ç, " combined reef ~arnples .~Types II and III). '0

,,," t'

• 46

contribute to the displacement of the cumulative size-frequency dis-

tributions (Figure 6). The data from the reef areas (Types II and

III) have been ~ombined since there is no significant.difference be-

tween these samples. The ophiuroids of the rubble are significant1y , larger (p

nov one-tailed two-sample test: Siegel, 1956).

Divers1ty

One of the best descript1ve techniques whi~ prov1des an under-

standing of the structure of the community is an analys1s of its

diversity. A statement of the species diversity may be merely the . , number of species or it may be a more complex measure which takes

into consideration the abundance ot,thr- individual.. In this study,

to avoid any loss of 1nformat10n, the concept of species diversity was approached four ways: 1) the species count, 2) the cumulative

pe~ cent method (Sanders, 1963), 3) Simpson's (1949) index of diver-

S1ty, and 4) the Shannon and Weaver (1948) index derived from in for- mati on theory.

The Species Count

Figure 4 is the graph of the cumulat1ve number .of species versus

the area sampled (number of collections). AlI graphs rise slowly

and level off aftet a very few collect10ns indicating completeness of

sampling and patchy distributions. The living reef suite of collec-

\ tions (Type II) _has the. highest number of species (Table 9),17: fol- lowed by Type III with 15 species, and the rubble collect10ns, Type IV,

with 14 species. According to these results the diversity sequence

is IV,

,t 47

'.

Table 9. summary of the div~rsity measures for the ophiuroids of the fringing réef.

spp. - Substrate Count Cum. \* ON R" J

II 17 0.1791 0.5397 1.8582 0.4546 (895.7)

III 15 0.2519 0.6775 2.2289 0.5705 , (1259.5)

IV 14 0.3447 - 0.7936 2.6749 0.7026 n723.5) ~

*Given is area expressed as fraction of maximum possible .~­ . area. In the parentheses is the actual area under curve. Maximum possible arêa is 5000.

1

1

..... z a 48 versei the rubble, Type IV, is the least diverse.

The Cumulative Per Cent Method

Species diversity may be determined by a method that ~nvolves plotting the cumulative per cent of the individuals on the ordinate and the cumulative per cent of the species on the abcissa (Sanders,

1963). The further the deviation from the diagonal, the graph of , the maximum possible diversity, the less the divers1ty.

Figure 7 is the graph of the cumulat1ve per cent of the indi- viduals versus the cumulat1ve per cent of the species for the three fringing reef assemblages. It demonstrates that the lowest species div,ersity is encountered in the living reef sample (Type II); the greatest diversity is manifest by the rubble (Type IV) collcct10n, and the dead reef areas (Type IV) are intermediate in d1versity.

A numerical est1mate of the area under the curve was made

(Table 9) uS1ng Simpson's Parabo11c Rule (Selby, 1973). The diver- si~y sequence is II

Simpson's Index of Diversity

Simpson (1949) developed a measure of comput1ng species diver- sity, À. To ma~e.this measure directly comparable to the other , method used, the S1mpson index was modified (Loya, 1972). Thus, the , - '- .., revised index,~easures the probab11ity that two species picked at ran- 'f

~ , dom from the sample belong to different spec1es. W1th th1s revised version, the fol10w1ng probabilit1es (Table 9) were obta1ned for the

~ habita~ypes: II ~ 0.5393; III = 0.6758; IV ~ 0.7917. The diversity tre~ is II

.. 49

100 ....------...... ----:11

Rubbia Reet, liVing Reef dead

4' ., ëQ ::J "D"> :ti ..E '" .... 0 .;,. .. C ..(.) ... 40 ..a. ..> ;: III "5 E ::J CJ 20

20 40 60 80 100 Cumulative per cent of specles

Fig. 7. Cumulative pcr cent curves for ~he fringing reef collections. The diagonal represents the max1mum possible div€rsity •

.. 50

ed vith the cumulative per cent method.

In ~ition to revealing the pattern of diversity of the three

assemblages, the revised Simpson index, ~, is sens,itive to the dis-

tribution of the individuals amoung the species. Thèse values indi-

eate the greatest degree of dominance, or inequality, amoung the spe-

eies of the living reef collection (Type II); intermediate dominance

in the dead reef collection (Type III), and the least dominance i5

~ found in the rubble sample (Type IV).

Measure derived from.lnformation Theory

pielou (1966a) states that diversity is equated vith the amount

of uncertainty which exists reqarding the species of an individual

randomly selected from a populat10n. The greater the number of species

and the more equally the individuals are distributed arnoung the species,

the greater the uncertainty, and the greater the diversity. S1nce

"information,content" is a measure of uncertainty, it is a reasonable

estimate of the species diversity.

Since the Shannon and Weaver (1948) information theory 1ndex,

H", is merely "the maximum like11hood estimat~ of the unknown popula­

tion diversity, H' " (Pielou, 1966a), it must be~emonstrated that

this value, H", is a reasonable e~timate of H' (Pielou, 1966b). Fig-

_ ure 5 gives the graphs of H" versus the nurnber of collections. The eurves level off after ~ minimum of 7 collections, indicat1ng that with .. samples added thereafter, any reduction of the diversity due to the (\ addition of common species is balanced by addit}onal rare species which ) tend to increase the diversity. Table? gives the 95% confidence lim- ( 1 1 its for the values of H'~ the mean values of H", and the number of \ 51 1

quadrats poo1ed for the ca1cu1ations. The diversity sequence is iden-

tical with that obtained with the cumulative per cent method and the

Simpson index of diversity: II

The various parameters of the diversity index derived trom in for-

mati on theory (Figure 8) indicate these trends: Observed diversity in-

creases, II

fashion, IV

The final p.lrameter, J, indicates the eVenness with which the individ-

uals are distributed amoung the species: Type II environments have the

greatest degree of single-species dominance.

(.Evennèss is ~ssential~y the same measure -as the revised Simpson

index of diversity, DN (Laya, 1972). 80th indicate the pariey with

which the indiviùuais are d1stributed amoung the species (Figure 9).

There is a very high degree of correlation, r = 0.997, which is sig-

,nif1cant at p

SakaI and Rohlf, 1969).

The methods empIoyed to determine spec1es d1versity of the three

collections show that the diversity of the ophitlr01ds is the greatest

for the animaIs liv1ng in the rubbIe, Ieast for the animaIs of the Iiv-

ing reef (Type Il), and intermediate for the brittle-stars of the dead

reef (Type III). The species.count, with its inherent disadvantages,

is the only method' that-.did not concur wilh ttf' other diversity measures.

, 52

4. ...,r 1 0

- '"'"

• C"I r- J ; =co .. C"-I ~ 3 0- oc. r- 0.8 -- U) 'CIO= =en ("") . ("") • .. r-- ~ 0)( ~ ::r:E

2 5- <.0 1- 06 ""=r-- ~ = 0 0 en • ~ -, ::r: r- U) CI)- c-.... ~ CI) - -n Q) r-= C >- cr') ... C \ ., ~ CD 0'"> = ... co > Q) c--.. w > c--.. ~ c--.. 1- 61 5- ...... c.o 04 cc ~ -r> 1'-\2- ='""" , , - , -

o'5- -02 ,

Reet, Reet, Rubbia living dead

Fig. 8. Graphs of diversity (H"), maximum possible diversity (~ax)' and evenness (J). 53

"

.. .' .- 0.8i- r-I0.9 . .7- o , -0.8 " , " o. 6- ~O .7 . 1- -0 .60 z 4- rD 5 a , CI)- CI) 1 3- i ~ o. t r-O. 4 -§ c G) G) > ~ o. 2- ~. 3 a

o. 1- -O. 2

. Reet, Reet, Rubbia Il \II ng dead

Fig. 9. Pielou's "evenness" index and Simpson's diversity index for the three environmental types of th~ fringing reef. S4

General Observations

Coral Coverage and Ophiuroid Abundance

The reef buttresses characteristically displayed significantly

different ophiuroid densit~es. The living reef (Type II) had higher

o densities than the dead reef (Type III). The graph of the number

Qf ophiuroids versus the per cent living coral coverage (Figure 10)

indicates a positive relationship between the two. The Spearman Rank

Correlation Coefficient (Siegel, 1956) f~r the data, rs = 0.57, demon-

strates a moderate relationship between the number of brittle-stars

. and the per cent living coral coverage per square meter. This is sig-

nificant at the 0.01 level.

Feeding

Feeding by ophiuroids was observed in the field and in the labo-

ratory. During nighttime observations in the field sorne ophiuroids

were seen feeding. Ophiothrix (~.) oerstedi and Ophiocoma echinata,

, the Most numerous species, employed similar feeding methods. The

Pori tes porites banks and patches were packed with brittle-stars. The

ophiuroids were partially concealed amoung the, coral branches; aIl individuals were vigorously moving their arms through the water, obvious-

ly suspension feeding.

A cursory examination of the stomach contents of Ophiothrix (~.)

oerstedi, Ophiocoma ech~nata, and o. we~dti revealed mostly calcareous - ~ particles and sorne algal fragments bound in a mucus matrix. The stom-

ach contents of o. wendti were similar to tllose of Q. echinata, except

the particles in the stomach of the former were smaller, and the amount e. of b~nding mucus was/less. e -e

350 o ." l' ~ '" .~':I t

r'- ~ ~ •

250 • en ... ro V= -1.37 + 1.55X ::J *" (0.473~<,B'<2.3636) '0 , ;; .' )1 '0 C o VI VI '0 150 ... o 0 ~~~~~~~~ ~~ Q) G":;:' ...... 0 ,..~.,. .... _ .. - E ...... :::J O Z ...... 0 ,..-- ... -- o o ... "" ... .,.-- o ..... ' ...... -," 0 50 _-~~~~--~ .,...... -­ o ...... 0 o • ... __ ...... 0 o o o _~.".-~--o 0 .. , ... - o o 20 40 60 80 100 Percentage of living coral cover Fig. 10. Number of ophiuroids and percentage of living coral cover for 23 meter square quad­ rats; the equation is fittedDY Model II regression. 56

The ophiuroids examined fed only during certain hours. Collec-

tions and dissections performed during dayliqht hours,did not provide

significant or consistent amounts of gastric contents. Brittle-stars

were observ~d act1vely feeding a few hours after sunset, but they had

not accumulated any material in the gastric peuch. A few hours after

sunrise, their stomachs were usually ernpty. The greatest amount of

stornach contents was 10und shortly before sunrise. These observa-

tions indicate that feeding takes place ~etween sunset'and sunr1se

with cessation of feeding around sunrise and egesti~n of waste and un-

digested material.

During the course of systematic sampling, specimens of Ophiaderma ~ Appressurn with swollen, ,distended, or rnisshapen discs were noticed., Exarnination revealed that the stoMaeh contents consisted of various

echinoderm fragments: Arro seqrnents of Ophiocorna echinata or spines of

the eehinoid Diaderna antillarum. One specimen ~. appressum, with 1 a dise diarneter of 15rnrn, yielded, upon dissect10n, a 16mrn spine frag-

ment of D. antillarum.

The ophiodermatid, O. appressum, proved ta be a rapid egester

of stomach contents. Upen being disturbed, the jaws went agape, and

the stomach contents egested. This characteristic af rapid egestion

made the exarnination of stomach contents of aIl br1ttle-stars diffi-

cult. Species ta be examine~had to be plaeed in separate polyethylene

bags in order to collect gastric ~terial, and insure that the gastric

material of d1fferent spec1es cou Id not be combined upon egestion.

In the laboratory, sorne of the ophioderms were voraeious scaveng-

ers._ Oph1oderma cinereum was the most aggress1ve of the gro~. Addi-

u 57

tion of an algal fish food or tissue extracts of Oiadema antillarum

ellicited an immediate response from most tPhiuroidS. The most vig­

orous response was that of the oPhiodermat}dS. This response was

an increased aetivity of the arms. After thls initial respon~e,

the ophioderms moved ~rd the stimulus. ~ Fragments of Oiadema antillarum, espeeially.the spines, were

quickly ingested by the ophiodermatids. The distal portion of the

brittle-star' s arm grasped the ,spine, and, wi th an oral flexion of

the arm, the proximal, artieulato~ part of the sp~ne was thrust

, 4 '.... , between the jaws in a prehensile fashion. The spine fragment usually'

protruded from the mouth, and remained in that preearious position

until ~gestion. .. Commensalism

Ouring the course of this study, eommensals were observed asso-

eiated with brittle-stars. The polynoid worm, Harmothoë lunulata,

vas cammonly found on th~ arms or dise of the sand-dwelling Ophionereis

retieulata. This relationship has been previously reported and describ-

ed (Millott, 1953). . One group of commensal organisms commonly associated with ,ophiur-

oids is the Copepoda. Freque'ntly, a small «O.5mm) cope~ was observed

on the disc of Ophiothrix (Q.) oersted~ ~his ~identified eopepod was

.- neither attachéd nor speeialized fot attaèhment, but rather wandered

freely over the o~al and aboral surfaces of the di~c. The only dis tin-

guishing features of this translueent copepod were the brillant red

eyes.

Many times when eollecting from the rubble, the small Ophiolepis 58 " .. pau~spina was found loosely attached to an arm of Ophiocoma echinata.

Although this is a doubtfvl, perhaps fortuitous, association it was

observed a number of tim&s. 'ûne1possible explanation 1S thae as the

boulders were picked up, the underlying sediments wete disturbedi

perhaps the curre'nts created"'" carried the very small O. paucispina

into o. echinata.

The Shallow Pubble

The southerly lobe of the reef off Bellairs Research Institute

(Figure 3), in contrast to its northerly counterpart, has an extremely

shallow back reef rubble zone that is subJect to very high wave en-

ergies •.

This rubble zone, sim1lar to that descr1bed by LeW1S (1960), was

sampled with a"series of f1fteen cont1guous quadrats placed perpen-

dicular to the shore. The first of the quadrats was positioned 30 meters from the low tide mark at a point slightly beyond the sand belt • . The~ean depth of these èOhtiguous~uadrats was 55.80 centimeters

(5.0. = 5.53) although during an extremely low t1de, depths of 25 centi- meters were recorded along the transect. Th1S region slopes gently

seaward at 1.33 cm/m or approximately 1°. This un1form shallow depth \ contrasts w1th the deeper and more variable Tvpe IV rubble w1th a mean

1 depth of 364.55 cent1meters (5.0. = 146.94) fer the 18 random quadrats ~ sampled in the northerly lobe.

Systematic samp11ng of the l5 contiguous quadrats Y1elded 541 ophi- uroiàs distr~buted amoung 9 species and 5 families. Table 10 ranks the

'species according to abundance. 59

Table 10. List of spe~ies, their abundances, means, and stan­ dard deviations (in parentheses) for the Snal,low Rubble Zone.

• i"I~ota1 Number ol ,Mean Number of Species Indi vidua1s Individuals per (15 collccti'Ons) Quadrat (S.D.)

Ophiocana ~çhinata 462 30.80 (12.91) °Ehiocoma Eum ila 22. • 1.47 (2.72) .: °Ehiodenna aEEressum, 15 ! 1.00 (1. 89)

OphioleEis irnpressa 12 -:0 0.80 (0.94). i

Ophionereis olivacea Il 0.73 (1.10)

°Ehiodenna brevicaudum 10 0.67 (0.90) .. . . Ophiothrix (2.. ) oerstedi 5 0.33 (0.62) • ~ 0phionereis reticu1ata 3 0.20 (0.56)

°Ehiothrix (O. ) brachyactis 1 0.07 (0.26)

TOTAL 541 36.07 (21.08)

, 10 1 , .,..

•

.t l, 60

Table Il. The values of the Morisita index of • sLnilarity between samples, CÀ' S.R. Shal­ ':: .. Ir low rubble colle ction.

Samples Compared CÀ

II-S.R. 0.173

III-S.R. 0.249

IV-S.R. 0.660

Similarity betwee~ Samples

Table Il 1ists the values of the ~orisita (1959) index of simi-

larity between samples, CÀ' It ~s evident, as expected, that the shal-

low rubble collection ~s most similar to the Type IV rubble collection.

Combined the two samples contribute a total of 16 species. There are

only 7 speC1es ~n common between the two rubble collections. The mean

density of the br1ttle-stars of the shallow rubble, 36 1ndividualg per

square meter, 1S s~gn~ficantly greater, at the 0.05 level, than that

of the Type IV rubble, 22 individuals per square meter.

Dominance

The dominant species of the shal10w rubble (Table 12) are s1milar

to the dominant species of the Type IV ruhble (Table 13). In both as­

semblages, Oph10coma e~hinata 1S, by far, the dominant spec~es. Ophi-

olepis impressa is also lmportant to both collections.'

Notable ~~fferences between the two samples are 1) the slight con-

tr1hution of Ophiothr~x (~.) oersted1 to the shallow rubble sample, 2)

displacement of Ophlonere1s ret~culata 1n the shallow rubble zone by 1tS • congener, ~. olivacea, 3) extremely high ranking ~f Ophioderma brevicaudum

in the shallow rubble collection, and 4) the absence of Ophiolepis pauc1-

t, 61

\

Table 12. List of Sha110w Rubble species dominants,l ranked according to their Biologica1 Index Values (BIV) •

Species "\ Abundance Frequency BIV (15 co11n's) (15 coll'ns)

1) Ophiocoma echinata 462 15 150

2) Ophiolepis impressa 12 8 66 c J) °Ehioderma brevicaudurn 10 7 60

>- 4) 0Ehiocoma pumila 22 7 59

5) °Ehioderma aeeressum 15 ,- 6 52 ~- - -- 6) 0Ehionereis olivacea 11 6 50

7) °Ehiothrix (2,. ) oerstedi ,< 5 4 32 8) 0Ehionereis reticulata 3 2 16. 9) °Ehiothrix (O. ) brachyactl.s 1 1 7 . , .. *based on 10-0 scale~im~ BIV = 150 •

, "

.... > 62

Table 13. Lists of the ratios of the ob~erved Bio1ogica1 Index to the maximum Biological ~nde~ Value (BIV obs /BIV max x 100).

Species Shall~ Type IV Rubble • Rubble

1) Ophiocoma echinata 100.00 92.78 \ 2) Ophio1epis impressa 44. pei 54.44

3) Ophiodenna brevicaudum 40.00 4.72 4). 0,Ehiocoma Eumila 39.33 28.61 5) 0,Ehiodenna appressum 34.67 . 51.94 6) 0,Ehionereis olivacea 33.33 -

7) Ophiothrix (O. ) oerstedi 21.33 67.50

8) Ophl.onereis retl.culata 10.67 24.72

9) O,Ehiothrix (O. ) brachyactis 4.67 - ." • ,Eaucis,El.na 50.00 la) 0,Ehl.ole,El.s - - . . 11) 0,Ehiocoma wendtl. - 33.06 - 12) 0,Ehiothnx (O. ) angulata - 9.72 13)-0,Ehiomyxa f1accida - 9.72 14) Ophioderma ,Ehoenium - 9.72 15) 0,Ehl.oderma cinereum - 4.72 .. • 16) AmEhiura fibulata - 4.72

,

\ 63

Table 14. Population parameters for the two types of rubble: mean density, mean crowding, and patchiness (wlthin parentheses 18 standard error of estmate or standard deviatlon).

Parame ter Environmental T~e IV Shallow Rubble

Mean density, x 22~11 36.07 (18.09) (21.08)

Mean crowding, x* 36.43 47.64 (±9.46) (f8. 86)

Patchiness, ~/x 1.65 1.32 , (±0.29) (fO.14) ( spina in the shallow rubble collection.

The aggregation of the brittle-stars of the shallow rubbLe differs from that of the Type IV rubble collection (Table 14). Not only are the animaIs more crowded in the shailow rubble, but the patchlness i5" slightly less.

Size • The animaIs from the shallow rubble suite of collections are larg- er than the Type IV ophiuroids. Larger indlviduals of essential1y the same species tend to displace the cumulative size-frequency distribu- tions (Figure Il) of the two samples (p

Figure 12 is a graph of the arm length plotted agalnst the dis~ diameter for the most numerous and dominant species of the two rubble collections, 0Ehioc~~a echinata. Each regression 1ine was determined by Type II regresslon: BartIett's Method (Sokai and Roh1f, 1969).

The lines indicate the dise diameter range of the two samples.

A sample of 25 indlvlduals was used for the Type IV rubble calcu- e e

100 (~ 4. "

80

Rubbia t • . '. ,-,." ,<'_ 60 \ - , c l, '-J ..~ QI Q.

el > .- ~ 10 '" :; 40 E ::l U

20 •

2 :3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 23 24 25 26 27 28 DIse diameter mm ~ Fig. 11. Cumulative size-frequency curves for the Type IV rubble and the shallow rubble. •

6S e· ,cl--

.....

120

100 OQbiQcoma echlnata ys:: 29.93 +3.09X (O.37<,d'< 6.92)

80

·E

E "- ,c'GO Y=--l.96+4.44X ... (3.96<,.6' < 5.30) cc:n~ Q) L, ~, ... E ". ~ 40

~ 20

2 4 6 8-' 10 1-2 14 16 18 20 22 24 26 28 Disc diameter, mm

Fiq. 12. Arm length and disc diameter for two collections of Qphiocoma cchinata~ the equations are fitted by Model II re~ression •

• 66 lation. For Ophiocoma echinata of Type IV rubble collections, the .. regression equation (95\ <:onfidence limi ts are wi thin the parentheses) is

y ~ 29.93 + 3.09X (0.37<13'<6.92)

The equation and confidence limits for the 53 Ophiocoma echinata collected from the shallow rubble are

y = -1.96 + 4.44X (3.96<13'<5.30)

The confidence limi ts for the former regression reflect the small sam- pIe size. A Kolmogorov-Smirnov one-tailed two-sample test (Siegal:,

1956) indicates the disc diameter of the shallow rubble o. echinata '1 i5 significantly larger than the same species collected from Type IV rubble (p

Oiversity

For aIl measures of diversity, the shallow rubble collection ex- hibited lower values than the Type IV rubb1e (Table 15) and, in most cases, lower than the diversities of the other environmental• types.

The extremely 10w Shannon and Weaver, Evenness, and Simpson indices indicate not only very low species diversi ty, but aiso a high degree of sing1e-species dominance. The dominant species of the shallow rub- ble zone is Ophiocoma echinata which accoùnts for .85\ of al! individ­ r • ua1s.

" 67

Table 15. summary of the diversity measures for the brittle­ stars of the shallow rubble and the Type IV rubble.

Spp. Sul:lstrate Count Cum. \* DN HfI J , Shailow 9 0.2202 0.3017 1.2009 0.3789 Rubble (1101.2)

Type IV 14~- ~3447 0.7936 2.6749 0.7026 Rubble ( 723.5)

*Given is area expressed as fraction of the maximum possible ," area. In the parentheses is, the actual area under curve Maximum possible area is 5000.

General Observations , The brittle-stars of the shallow rubble, being id a more wave agi-

tated environment, are larger and have shorter arms. Hany of the species

assume a "reclining" position: Ophiocoma echinata, Q. pumila, and Ophi-

oderma brevicaudum were often found covered with sand, and embedded in

the substrate

In this zone there are marked relationships between the environment

and the animal numbers. The Spcarman Rank Correlation Cc1efficl.ent

(Siegal, 1956) for the relationship between the number of species and

the distance from shore (Figure 13), rs = 0.69, l.ndicates a moderate

correlation which is significant at the 0.05 level. More highly corre-

lated is the number of individuals and the distance from shore: u r s =

0.81 which is also significant at the 0.05 leveI.

Assuming that an area of an ellipse (A = lrab; where a and b are

the principal axes) is a good approximation of the surface area of the

rubble of the back reef available to the brittle:stars. The sum of aIl habitable surfaces per square meter is the arnount.. of living spa ce avail­ , . \ . • ... -

\' 70., 1 J4 >J ...r r ~ ... 1 ...."0 Q--"'--Q 1 \ '\ ', \ 1 , ,/ \ H2 , " \ :'> Il , '1 \ \ : "cl \ 1 , \, ,1 \ 50 , \ 1 1 ~ \ 1 1 \ • .. 1 \ 9 ,1 ,, 1 1 , en . , b Cl) fi) , u co ,1 Q) :::l 8 a. q , fi) "0 ,. 1 \ : > 1 \ , 0 \ , - "'0 / \ ,, ... c Q) " / \ , CD - 1 \ 1 ..0 '" .... 30 l , , 0 6 E b_--.o ;:) '- f z Q,) . .~'" J:J E :::l .R, 1"'./ .~ z i 1\ 1-4

10 2 • ~ -.-'"

2 3 4 5 6 7 8 9 10 J J 12 13 14 15 Meter number along transect

Fig. 13.1 Number of individuals and species versus length along the transect. 69

!--.

10 2.9

-0 1 /0- 0 Li • o • ,.... _- 1 • 1 -- • , -.. _-...... "<1" •1 , - -0 1 .... • 1 2$.. 1 1 1 .. 1 ..'- 1 2.1 4; ... 50 - 1• CP 1 ...CI) ... 1 CP , E 1 E 1 CI) 1 CI) 1 ~ ... 1 cu cu 1 :J j l' 0- 1 en g 1 1 ~ ... 1 CI) CI) , Q. Q. ,, , ., , cu Cl) ~JO 25 ~ """JO co -0 o Cl) :> CJ , " cu "Cc ,l' ... ,l' -:J en 0 ,. " -... CI) CI) """, .rJ co ------~!---I---- .. ------.------_.___ ~ ___L ... E .rJ j cu c J::. c 10 23 c ra cu CI) 0 Cl) ~ ~

20 40 60 80 100 Per cent of distance from shore

Fig. 14. Mean nurnber of individuals and mean habitable surface area per quadrat versus the per cent of the distance from shore to the end of the transect.

\' . 10 able to the bri~tle-stars. The average number of ophiuroids plotted

against the average habitable surface area per quadrat (Fi~ure 14)

is positively correlated (rs = 1.00) at the 0.01 l~vel.

The First Ridge

Obsertations on the First Ridge were conducted from depths of

45 to 160 feet. These observations indicated an ophiur01d fauna

different from that of the fr1ng1ng reef. The most obvious feature

of the oute~ bank fauna was the great n~er of epizoic brittle-stars,

mostly ophiothrich1ds, which werè characteristically found on various

sponges. The most numerous of the epizoic species was Ophiothrix (A.)

suensoni.

This speciec was never concealed, but always exposed. Although

usually"found c11ng1ng to sponges, it was also observed in assoc1ation

with Porites por1tes and Hillepora alc1corn1s. On the outer bank, Oph1-

othrix CA.) suensoni was collected from the tOE of the b~nK! ~EP~~x_i_-_____

mately 50 feet, to the bottom of the hank, 150 feet. Although ab~dant

on the outs1de of the outer reef bank, Q. (~.) suènson1 was not seen on

the inside slope of the First Ridge. Th1S species was also collected

from the fr1nging reef; aIl lccations of the collections were on the

Seaward Slope.

Oph10thr]y.~~) suenson~ ma~~ests differen~ morpholog1es as a

, ' . , function of depth. Two small collections from 50 and 150 feet reveal-

• ed that the deeper specimens are a much darker shade of red and lack

definitl.on of the yellow 10ngitud1nal arm stripe. In addition, the ,e deep and the shallow collections possess different allometries. 71

Figure 15 i5 the grapn of the arm length plotted against the disc

diameter for both collections of Ophiothrix (~.) suensoni. The

regression equation and 95\ confidence limits for the shallow col-

lection are

A Y = -15.89 + 10.46X (5.78<8'<18.01)

While the regression statistics for the dcep watcr collection are

y = 1.62 + 6.32X (3.81

The brlttle-stars of the shallow water collection from the First Ridge

tend to have longer arms.

l.fany invertebrates inhabi t cavi ties excavated in scleractinians L by bivalves, sponges, and slpunculids, but wlthln coral lnfaunal ophi-

uroids werc found to be the least important group (Grass le , 1973h

~pecimens of llontac;trea annul arlS collecled from the Flrst Ridge con-

tained a diverse fauna including brittle-stars. The same specles col-

lected from the frlnglng raef dld not ']enerally possess th1.s op}nuroid

fauna (MacGcachy, personal cŒ~nunlcat1.0n).

The int.erlor of massive sponges is also capable of supporl.i.ng il

brittle-star fauna, usually residcnt. 1.n the incurrent passages of the

sponge. 1\.n A']clar; sp. sponge harbors a dlvcrsc-communlty of brlttle-

,) stars, decapods, bivalves, var1.OUS W01TlS, and otller invC'rtebralcs.

The ophiurolds arc nUl"i'lerOUS, but only two speciC's are \oJC']] reprcsentcd:

1 Figure 16 1.S a ']~aph of the number of endozoic brittle-stars plot-

ted as a [upcllon of the spon

~-.!

.1

140 QQhlothrix CA) su()ns~ni

• 110

,.. y= -15.89 10.46X 100 + _____----'-(~5.78<,B'

E 80 o E

150 feet

y = 1.62i-G.32l -' (3.&I

\ r \, ~

<., 1 1 J i 1 " 1 1 1 1 1 1 1 2 3- 4 5 6 8 9 ID il TL 13 • Dise dlamctcr, rn..r:lL- " Fig. 15. l\l-m length and dise di amcLer for blo collections of 2!~i OL-,~-j ~ (l\Cëll_~J:.<..?l?!l1othn x~ ~cnsoni; t.hC' equëlt ions élre fi t.lcù by,

Model II reCJrc~Slon. F>

• )

73 •

, .,

\ , .

200 "

• ., u c CI • "§ 100 • , • D CI • "- • :0"... :J 2: ,. ' Cl, 0

• .. ~'I 1 /0",/°. \ l, • •

.~

2 0 '4 a 600 1000 \\ [?,rv we(ght of sponge (grams).. • r::,. • 1 Fiq. 16 . . •Ophli uroU!'' J.abundance versus the dry vciqht of Ar!clas 8p. spongc ... (grams) • .• e .' 74

between abundance and sponge dry we1ght, rs = 0.81, lS sign1f1cant

at the 0.01 level.

On 12 July 1973 a character1stically deep water hemieuryalous

brittle-star (the type speclmen was collected from 175 fathoms) was

collectcd froM 70 feet. The spec1mens were cling1ng to the hydro-

coral Stylaster roseus. Upon being returll'd to the laboratory, an in-

diVidual or indlvlduals released Juven1les. Thus Slgsbe1a murrhina

is a vivlparous speCles.

ApproXlmatply 30-45 minutes after sunset ophiurolds became a

v1sible component of the outer bank fauna. The most ObViOUS and Im-

preSSlve speCles was the basket-star, l\strophyton muricatum. The adults

of the speCles, approxlmately one meter ln diameter, were conunonly ob-

scrved on Psc>udopterOqOrqla ~nler lcana. Thcse 1ndiv1duals, W1 th their

arms fully outstr€'tched, were in the feedHlg pObturf'. Juveniles, up

to la centiml'ters ln ùlaJ:\cter, werf' not founel on these qorgonlans, but , l , rather at the very tops of the sea fan, Gorgonla flabellum. Astrnphyton

muricat~1 was not characterlstic of the frinqlng rpef fauna. Only one

inthvldual wac; obscrvE>ù on the fringlnq reef, approXlmaLely 150 meters

from shore in the Senwatd ~lope Zone.

'l'Iw ahovC' mentloned speclc<; were the only completely exposed, noc-

turnal hntlle-stal'<" alonq wlth the eplzolc fOrIns. Many ophiurolds

Inhabl t In'1 holes i'h th!" coral'; l'l,ide by horlnq orrJanisme; wC'rp actlvt'ly

('('dUl'J; only thelr armn protrudf:'d from the CXCdViltpd cavltlCS. Wander-

1ng brtttlC'-sl"rs wl'n' usually pùrtlillly concf:'ilI('d hy topographlc and

('roc;lonal feùlurf':' of the cor"l C010111(,<;.

ralchC'c; ()f c,llCall'(H1S s;\nd contalnf'd many hiolumlIlCC;Cf'nt, Infa.unal 75

ophiuroids,~ith the arms ~xp?sed. This'species, Ophiopsila hart- .. ~eyeri~ was collected from the top of the outer bank to 100 feet , with the greatest densities between 70-90 feet. When the arms were

touched, they briefly glowed a blue-green color. • j

.'.

\--' ,

------,---- -l------

•

'. .e f /

DISCUSSION AND CONCLUSIONS \

The Fring1ng Reef

The ophiur01ds of Barbados' are weIl represented on the fringing

--_____reef by 22 of a total of 27 spec1es. Th~ one conspicuously absent

family of brittle-stars is the amph1urids. The scarcity of this clas-

sically mud-dwelling group (Thomas, 1962a) may be attributed ta the

~ lack of sU1table substrate. Macintyre (1967) has demonstrated the

marked absence of silt and clay size mater1al along the west Coast of

Barbados.

Most early records of ophiuroids of Barbados were obtained from

the region of Pelican island. Recently the island has been reclaimed

and these 10cal1t1es are subsequently lost. In addition, l did not

make any collect10ns from the Bridgetown Harbor area. These could be

the reasons for not collecting the four species recorded by parslow

and Clark (1963).

Ophioderma brevispinum is a confusing congener of Q. appressum

and the separa~10n of the two i9 difficult. Careful examination of

all o. ~ppressum collectcd during the study fai1cd to detect any O. 1 •

brevispinum in the sarnples. Species lists (Parslow ana Clark, 1963)

indicate that Q. brevisplnum 1S restr1cted from the southeastern por-

tion of the ~aribbean Sen. This specics has been recoxded from Aruba

to t~c west add the St. Croix-St. John area to the north. Obviously

76 .. "\.'. 77

the spread of this species has been limited by sorne factor in the

Lesser Antilles. .:

In contrast to the outer bank, the sand patches assoc~ated with

the fringlng reef do not contain ~nfaunal ophlurolds. The ma~ntenance

of the reef grooves by uns table condlt~ons.has been establ~shed (Shinn,

1963). Since ~nstab~l~ty of scd~rnents rnay account for d~str~but~ons \. of trop~cal infaunal qrganisms (Newell et al., 1959; Purdy, 1964;

Jackson, ly72; Aller and Dodge, 1974), the5e shlfting sands may place

toc rnuch stress on burrowlng br~ttle-stats. ,Thus it is conc1uded

that, due to the phys~cal instab~l~ty of nearshore calcareous sands,

infaunal ophluroids are restrlcted ln their dl~~lbut~on to the more

stable sands of the offshore reef bank.

Diversity and denslty can be more re11ab1y estimated ln rubb1e

habitats (Type IV) rather than buttress or re€f environments (Types

Il and III). ThlS lS pcrhaps due to the relatively homogeneous nature

of the rubb1e and lack of topographie features with a pronounced ver-

tical cornponent (Kohn, 1971). Dens~tles recorded on the frlng~ng reef

indicate that 'lype' II habl tats are 5 timer; more df>nse ly populated than

Type IV environrncnts. The density of 'Type III habitats is lnternedlate

betweell the two. Conversely, the diverslt'l trends indicate that the

homogeneous rubb1c has a hlqhcr dlvennty tha~ the buttresscs.

Siml1ar trends have been recorded for the gastt"opod COIIUS from

beneh and reef habitats (Kohn, 1971): Low divPl~lly arf'as arc.' associ-

1· atE.d wi th high d~nsi ty. Th Hl re1atlnnship between an,ithal demd ty and

diversity i5 nol a1ways observpd. On the repfs of Jamalca, Kinzic (1974)

\ in his ~,tudy of the gorgomdc; reportf'd low dlverr;i ty ansoci 'lted wi th 78

low density. ..

It has been suggested that a spatlally heterogeneous environ-

ment can support a more dlverse biota than a homogeneou~ area, Slnce

more habltats are avallable (MacArthur, 1965; Valentine, 1969).

Diverslty of coral reef organlSffis is often related to spatlal or

" substrate heterogenel ty (Kahn, 1971; Grassle, 1973; l- Kinzie, 1974).

ThlS hypothes15 15 based upon the concept that an ecological niche

15 objectively deflneable a prlorl and mdy be circular reasonlng

(Pianka, 1966). '. , This study lndlcates that, for ophluroids assoclateG wlth an

increasing spatial heterogeneity gradient (i.e. rubble

ing reef) , there 15 a decreasln~ dlv~rslty trend. It is stressed

that, although sorne studie~ relatlng mlcro-spatial heterogenclty to

5pecles diverslty may be pleaslng and appllcable ta sorne habltats and

organisms, they secm unreallstlc ln relatlon to this frlnging rcef

brlttle-star fauna.

A high populatIon denslty with a correspOndlnQ small body SlZC

i5 characterlst.ic of buttress arcas (Types II and III). This sr,lall

.body 5ize may be a rcflectl0n of micro-habltat or micro-patch size, • for SlZC may be a rcsponse to the physlcal conflguration of the cnVlron-

ment. The coral bouldors of the rubble present larger cnvircnmental

...,spaccs that are available to the brittle-stars. Larger environmcnta1 !", e1ement& allow by larger lndlviduals.

No enviro ent i5 unchanging in time for local perturbatl0ns in-

sure that no ha al 15 predlctable. A mixcd gtrateqy i8 ortimum in

rcsPQn~c to an uncertaln environment and domInant specIcs tend to he

·/ ! \ 79

broad-niched (Levlns, 1968). It is concludcd, for the fringing reef

ophiuroids, that high populatlon denslty and substrate gencralization

are adaptatlons to relatively unpredictable environmental events.

The fringing rcef presents, a faunal mosaic superlmposcd upon a

phYSlcal rnosalC. The topographlc varlet y of the coral buttrcsses

and the sand or rumble fllied qrOQves is parallcled by a faunal omnl-

formlty. Assemblages of h1gh dens1tï and low divers1ty are found on

the spatially h~terogeneous buttresses i low density and l11gh d1versity

are assoclated w1~the fauna of the more unlform rubble.

The Shallow Rubble

The shallow rubble presents a fauna sublect to h1gh wavc energies.

This results ln adaptations WhlCh may be at the specles or the commun-

ity levcl. Although the fauna of the shallow rubble IS simllar to that

of the 'l'ypé IV rubb1e, 7 SpeCIC'3 of 14 (l.e. 50%) which occur in the TYpe

IV rubble arc absent from the shallow rubblc collectIon. Converscly, of

9 species occurrlng ln the shallow rubblc 7 are found in the Type IV col­ '~ leetion; this accounts for more than 75\ of the specics.

This data aqrccs with the predlctlon that InvaSIon of low predIct- 'u" ability arcas from high pr<.!dlctabiiity environment5 i5 less probahle than

the reverse process (Slobodkln and Sanders, 1969). Japzpn (1967) rcstatcs

that hypothesis: "The more predlClablf> the envlronment, the sMaller the change in that enVlronment needs_to be to serve as an lITlI'lediate or long

.j 1 term oarrlcr to dispersal." 'l'hus there is ea~ed r~strictlon of specles range or "fldcllty" of the Type IV as comparcd to the shal~ow rubbl(~ SlleClCS. 80

Slobodkin and Sanders (1969) define unpred~ctable enV1ronments as

those in Wh1Ch the var1ances of env1ronmental propcrties around the1r

mean values are relatively high and unpred1ctable both spat1ally and

temporally. 'l'hus the shallow rubble is a mire unpred~ctab1e enV1ron-

ment than the deeper Type IV rubble. The temperature, tides, and wave t-. ~ actl.on fluctuate wldely in the shallow area. Th1S shallow zone lS more

"physically <:ontrolled" than the Type IV rubble WhlCh is, perhaps, "bio-

logically accanodated" (Sanders, 1968).

In environments contal.n1ng a phys1cally controlled" commun1ty, the

() physical cond1tl.OnS flucuate w1dely and an1mals are exposed ta severe

physiolo~1cal stress. Assemblages of thlS type contain a pauclty of

spec1es (Sanc1ers, 1968).

A biologlcally controlled or accomodated commun l ty, such as the

Type IV oph1uroid collection, lS subJect to relatlvely constant and

unlform physl.cal conditl'ons. Blolog1cal stress 1S mcd1ated by blOlog-

ical interactlons (Sanders, 196B).

The shallow rubble zone is much less prcd1ctabjf:' than the nearby

frlnging rcef; environmental predictabillty determlnes the spectrum of

species~undance measured as Specl('s dlversity. The cxtrcmely low species d1vcr51ty.. values ('l'able 15) of tins unpredictable environmcnt are a result of the rcstr1ctlons which the environment places upon the

organ1srns.

It is concluded that the unpredlctable shallow ruhble zone and the

more predictable Type IV ruhble f1t weIl Slohodkin alld Sùnders' prcd1c-

tians concernlnq thp SpCC1CS d1verslty and relative migration to and

from such arCi"l.5.

# ",

/' 81

It is suggested that S1ze and reclinlnq hab1t of shallow rubble

spccies are adaptations to the severity of the env1ronmental cond1-

tions, especlally wave action. The selectIon of larger, more robust

indlv1duals lncrcascs the ophiuroJds' stal:'>ilty. Rohust skeleton<;

(Ballam, 196~) and specIal growth fOrIns (Vaughan and Wells, 1943) (

have becn assoclùtcd wlth strong water agitatIon. Th1S is also the

controlllng agent effect1ng the size of the br1ttle-stars of the shal-

low rubb1e zone.

Anothcr pOin,of Intercst 1S the relatlonship betwcen anImal

abundance and d1sta~o from shore. Rather than reflect1ng Increaslng

depth, the dIstance from shore is à crude measure of decreasing wave

energy. The hlgh correlation between the number of Indlvldua1s and

the distance from shore (wave energy) indic.:ates the acuteness wlth

which the anImaIs sense and respond to the physical faotors.

Thr F1rst RIdqe . .

The common eplzolc bn. ttle-star of the outer bank, Ophlothr 1~ (~.)

~u('n_soni, cxhilnt<; dlffçrent morphologies as a funct10n of depth. This

is analogous to the> allomctric dl ffercntI ation of the shùllow ruhblc

and Type IV rubble specles. O. (~.) s\lensor1Î from, the top of the bank

hùs ù larger d15c and longer arms than its counierpart from the bottom

of the bank. TIns 15 S1ml1ar to Q!.Ü1Iocom~ echinn.-!~'s re<;ponse lo pre-

d1ctable ancJ unprc.Jl G lahle envlronments. R,lthcr lhan envlronncntal

prOp(·rlICS. the [00'] r('~)ourccs of O. (~.) .sl1nn...?~.!:L ffilghl be the f luctu- .. a tl fig propP'l-t y. P..N]u]at1on of predator S17.(' by "the abundance of food

ha.:; }H:!f'1l hYl'othf'f.l;:Nl (;;<.,ltoC'll(.'r, 1ge,9). 1l1q}, food abundancp should favur ~

., 82 the selection of larger ~nd~v~duals.- Small individuals~hould be se- lected for by low food abundance • • The d~str~but~on of Ophiothr~~ (A.) suensoni and Astrophyton

muricaturn ~s restricted to the seaward port~on of the First Ridge and

the Seaward Slope Zone of the fr~nglng reef. ThlS is identical w~th

distribut~ona1 pattern of the unstalked crlno1ds of Bar~ados (Meyer,

personal commun1cation). The llv~ng habits, feeding behav10r, and

skeletal structure of the cor~atu11d. crino1ds are ullimately re1ated

to the reglme of watèr ~ovement, for the suspens~on feed~ng me~hanism

of the crinoids depends upon externally produced water movements (M~yer,

J 1973). It 18 concluded that the distr1butlon of 2.. (~.) suenso,nl and

A. mur1catum 15 'also 1ntimately relatcd to local water movemen(s. " Endozo1c hiittle-stars are also common ln sponges: The an~mals

1~vlng withln the varlOUS chambers and canals of the sponge. Small

spec~mer'ls of ;~l1e clrcumtroplcal Oph1act1s savlgny1 were found in dense

c1usters wlthin an Agelas sp. sponge. The me •an denslty was PlUch less

than the 1892 individuals per 100 grams of spongc reported by Boffi

(1972). The occurrence of these six-armed 1ndividuals ~as becn aLtribut-

ed to schizogeny, but this lS doubtful Slnce pentamerous ,spcclmens are

• rare (pars1ow and Clark, 1963). No pentamerous specimens of O. sav1gnyi

were c01leeted durlng th1S study.

In additIon ta Q. savignY1, 2QhIôctis quinqueradla ~s a codominant

brittle-star of the Aqclas communlty. Bath specics are found w~thin the

incurrent passages of the sponge. This implies that these optl1urol.ds are

depcndent upon Ule pwnpi ng act1011 of the sponge for their food supply.

The basket star, Astrophyton :nuricatum, 15 a nocturnal predator of 83 of the outer bank. This ophiuroid is dependent on pseudopterogorgia americana for its surface attachment and subsequent feeding posture.

As recent~.1 as August 1973 a pharmaceutica1 company was harvesting

this gorgonid for tissue extracts. If this proceedure reaches large proportions the effect on the population' is obvious. '1

~. 1, . •

i •

.. •

" . ..

/- •

-...."• SUMMARY 1. samples of,ophiuroids.. were obtained from random and contiguous quadrats on fringing and bank reefs at Barbados, West Indies.

2. The samples were analyzed for speci€t. similarity, dom1nance,

1 aggregation, specialization, d1vers1ty, and S1ze distr1bution.

3. High species divers1ty was associated with low br1ttle-star den-

sity and low speci~s diversity was associated with high density.

\ 4. Environmental heter~eneity did not account for the observed

specics d1versity.

5. High densities of ophiuroids populating the reef areas were as-

sociated with smal! body size.

( 6. The dominant ~ecies of the fringing• recf were"substrate genercilists. , 7. 50\ of the species collected from the deeper, fring~ng reef rubble zone were absent from the sha!low rubb!e collection.

8. Robust morphologies and a reclining habit w~re' characte~istic of

dominant spccies of the sha!!ow rubb!e areas subject ta wave acti6n

and other severe environmental conditions. " 9. On the outer recf hank many ophiuro1dslwere found w~thin cavities

of sponges, crevices, and holes in the reef framework made by bor-

ing organü;ms.

.. 84 •

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/

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