Proliminaqy Re2oi-t on itariiie Dtolog Study of Onot,or

Proliminaqy Re2oi-t on itariiie D t o l o g Study of Onot,or: Atoll, G i l b e r t Iu!.alds

P a r t I

by John

EE.

h d d l

Issuacl by

TI23 PACIFIC SCIENCE BGAW

National Acadenii o f Scioncos--National Research Council Eiashirigton, D. C.

December

15,

1352

PRTXfMINARY REPORT ON Mh?INZ EIOLO!X STUDY OF OI4OTOA ATOLL, GTLEFZT I%iU?DS

SC1'34 TIE'IC INVFS'I'IGATIOPJS I N D!XCPOiVESTA P a c i f i c Science Board

N~tionaL Research Council

D r .

.

^{H. Banner}

Uiiiversity of Hawaii Honolt~lu

,

Hawaii February 20, 1952 P a r t I T ~ d r . John E. Randall

University of H a t ~ a i i Honolulu

,

^Hawaii

March L+, 1952

This f i e l d xorlc was c a r r i e d on i n coni1eci;ion with t h e Coral A t o l l P r o j e c t of t h e P a c i f i c Science Board of t h e National Research Council and m s sxppor-Led by fut~?s granted t o t h e XatLon::l A c a d w of Sciences from the Office of Maw.?. Resenl,ch.

Generom cooperation was received fram the PIilitarj- A i r Transport Seyvlce and t h e United S t a t e s Coast Guard

Ln

anssisting with transportation, t i i n University of Hawaii i? supplying much needed equipnent, t h e admlnis- t r a t i v e o f f i c i a l s of tha G i l b ~ r t and E l l i c e I s l a n d s Colony. The author i s p z r t i c u l a r l y grateful. f o r t h e a s s i s t a n c e estended by Xiliss EMlestine Akers mcl Kz. Earold $. Coolidge of t h e P a c i f i c Sciecce Board.

. . . .

T h ~ k s a.re a l s o due t o D r , Preston E. Cloud, Jr., t h e l e a d e r of t h e

~ x p e d i t i o n , f o r t h e use of t h e map he made of t h e i s l m d , and t o R.

Tacker Abbo-bt of t h e U. S. National PIusevm f o r t h e i d e n t i f i c a t i o n of Bone of

the

molluscs.

The m r i ? e bio:lLogical r'rork on Uno'toa j.s d t v i s i b l e i n t o f i v e portions:

1. Tile investigatioil of shallow water ecological associations, re- por'ted !lerein:

A, The ecology of t h e rrindr,;ard r e e f ,

B. The ecology of t h e lagoon r e e f s and shores.

2. The i n v e s t i g a t i o n of t h c deeper water ecological asscciaticns, t o be reported by Dr. Pres-Lon E. CLond, Jr,

3.

The i n v e s t i g a t i o n of the rnnr'ine algae, t o be re??orted by D r . Edwin I40ul,

L.

The 5nvestigation of t h e ichthyofauna, reported by

Er.

John Randall and appended t o th6s report.

5.

The n a t i v e use of tlzz rfiarine liizvertobr-ates f o r food, reported herein.

iiy portion of t h e s t u c i ~ , t h e inarino i n ~ e ~ t e b r a t e s , rras severely l i m i t e d by an a t t a c k of blood poisoning and a subsequent a t t a c k oi' influenza t h a t r e s u l t e d from attemp-bing t o do f i e l d work :?hen not f u l l g recovered from t h e first i l l n e s s ; a s a r e s u l t of the-e two i l l n e s s e s , over ffive of the t e n %reeks spent on Onotoz rrere l o s t and the investigat-ions made were n e i t h e r a s thorough nor a s extensive as planned.

The followiing r e p m t s ore r e i , and should be taken t o show merely t h e extent of t h e work 60ne. Tho i d e n f i f i c a t i o n s a r e fiilld i d m t i f i c a t i o n s and must be confirmed by expatt.;, v i t h t h e except.ion of soiiie of tine mollum%

r,rliich have already been iden-Lified by R. Tucker kloiwt-t of tho TJ. S. ?rational 14usem; and no coccli~.sinns arc! ir1co::poratcd i n the reports. hJnen tliese reports a r e published t h e d e f i c i e n c i e s v i l l . be corrected.

The

-

ind?.rard r e e f on Gnotoa i s found along t h e northern, e a s t e r n and southern shores of t h e a t o l l , presen-Ling an a l n o s t unbroken barricade a g a i n s t t h e f o r c e of t h e p r e v a i l i n g wares, It v a r i e s i n vbd-l;h froi;~ t h r e e or four hundred f e e t t o o v a a q - ~ a r t e r of a 31i1e a?d i s nore extensfvely devsloped around the southern i s l a n d t h m arounr! t h e r o r t h e r n , As it i s of q u i t e uniform height, s t r u c t v e and b i o t i c zones, a sirlgle transec-t across i t s s u r f a c e rias

. .

deemed t o be i n d i c a t i v e of t h e general ecology of t h e r e c f . Condi.tims of Gk;?. Reef

---

The inshore border o? t h e Feel' i s coiqmsed eit,her of consolictated and eroded c o r a l rock o r :;nodeinzte1y Fine s a d ~ L t h t h e w p e r edge e x t e n d b g t o t h e m e x i n ~ u k ~ heigllt o f t h e sto:.i~ :taws 2nd tho 13rier- edge v x y i n g but u & ~ a l l y about

t h e 2.0 t o 2.5 f o o t ti& Level, Be:rond t h i s s k q ? shorerrard a r e a tine r?ef ilat e.,te.

..

^LK?S t o a m.iform s r e a of s l i g h t slope, vrii,h ,'re:pei?-t sr:.a;l. t o l a r g e s ~ ~ a l l o w p o o ~ s of ~ ~ a t e r lei.: ~~5 l o v $ids. Y:?s r x f f l ~ t i n t h e t r a n s s c t

s t x d i e d t a s 650 f e e t bi'c~ti, Cear~arcl of t h e ITS.? ;!.at i s a depres-;io?, the heck-ridgz trough, be"c.rb-.n 50 .w.d.1C0 fee: vld2

zie

r a g i n g i n de$h from

. .

about t h e 0,2 t o t h e

- ^{2 . 5}

f o o t t i d a l l e v e l . The f i n a l edge of t h e r e e f i s tile c o r a l l i n e ridge ( o r Lithotharmion r i d g e by previous ~ r o r k e r s ) , a

r~mpnr.t betveen l.0 and 2,O f e e t above the zero t i d e and 50

-

100 f e z t broad.

Its shore~mrd edge p r e s e n k an almost co.ltir~uous f r c l t of redclish c o r d l i n e algae, but on i t s s e z ~ a r d s i d e soon develop.e.eer, f i s s w e s o r surge channels a t rj.gi3-t w.gles t o . t h e shore t h a t reach s i x o r nor* f e e t below t h e s u r f a c e of t h e reef a i d t h a t are of varying rridthl, ~rridening a s they reach seariard.

T'ne seaward edge of tine c o r d l i n e r i d g e thus s e p a r a t e s i n t o a s e r i e s of

separa.te and depressed f i n g e r s t h a t f i n a l l g slope r a p i d l y d o m t o t h e growing r e e f surlacc beloti. The outermost r e e f o r t h e r e e f shelf i s r e l a t i v e l y

narrori, about t h r e e hundred f e e t i i d e , and slopes r a t h e r r a p i d l y from about ten f e e t deep on the shoremrd s i d e t o over t h i r t y o r t h i r t y f i v e f e e t deep

- . , .

on t h e seaward side; i t c o n s i s t s of l i v i n g c o r a l g r o ~ ~ i n c i n i r r e g u l a r ~nouncls r 7 i t h areas betmen t h e heads s t r e w x i t h dead c o r a l fragments. Beyond t h i s

. . . .

r e e f s h e l f t h e bottom drops suddenly a~ray, a t a s l o p e of perhaps norc than

L,S0

and soon disappears i n the t ~ r b i d ' a t e r s ; t h i s l a s t zone was n o t e q l o r e d a t a l l ,

The viniimrd reef f a c i n g t h e trade :rinds s c s t a i n s t h e almost continuous beatin? of t h e waves. :?t l o u t i d e t h e waves a r e broken e g a i n s t the c o r a l l i n e r i d g e and only s l i z h t m v e s a r e f e l t i n t h e backridge trough: I-Ior~ever~ when tile t i d e i s high, only a 7,ortion o f .the strong riaves is cxpmdcd a g a i n s t t h e c o r a l l i n e ~ i d g e and the a s j a c e n t t-ough and moderste s i z e d r.iz.ves srieep 'across t h e r e e f f l a t , carr~ying enough energy t o n o w coral. rocks a f o o t or two i n

The r c e f f l 2 . t froikx t h e c o r a l l i n e r i d g e back i s t h e evident r e s u l t of t h e consolidation of a l i ~ i n g c o r a l r e e f , c h i e f l y o r Heliopora, by c o r a l l i n e

--

algae; i n d x o s t a l l areas t h e o l d !!eliopora i s co.aploiely dead a ~ d covored rrith the algae t o make an a l d o s t table-like top.

his

top, hotrever, i s p i t t e d v i t h small t o l a r g e depressions, and i n many a r e a s p e r f o r a t c d ' b y

. .

burrotrs leading doym mong t h e o l d c o r a l fronds,

Animals l i v i n g upon t h e i l a t a r e subjected t o many b i o l o g i c a l v i c i s s i t u d e s in addition t o t h c action of .laves. In the ins!lore a r e a e s n e c i o l l y t h e r e e i

. .

f l a t i s exposed t o t h e a i r f o r s e v e r a i ho~urs a t a time a t t h e l o m r low waters, and those a i r t a l s t!iat cannot c i g r a t e t o t h e shallorr pools must be oble t o

~ r i t h s t m c l t h i s period of dessication. Those animals i n t h e p o d s , a s v e l l a s those exyosed t o t h e a i r must a l s o be able t o withstand g r e a t changes i n

s a l i n i t y of t h e i r environment, f o r t h e high t i d e has t h e normal ocean s a l i n i t y ,

~ i ' n i l e t h e loir t i d e mag expose thex to t o r r e n t i d r a i n s which riou3.d l o v e r t h e s a l i n i t y of t h e topmost l a y e r s a t l e a s t t o a l x o s t zero. Hotrever, because of t h e d i f f e r e n c e i n s p e c i f i c g r a v i t y and t h e a.bsence of a g i t a t i o n i n t k z s e small bodies of wntw it i s l i k e l y t h e t t h e bottoms of t h e pools and t h e b u r r o w i~

t h e rock es;3ecially ' L . t h e i r normal s a l t n i t y .

?robab:Iy the r,iost pl-onounced physical changa t h e m i n a l s a r e stlbjected t o i s t h e change i n t e m p r a t v r e for %be c?ark r e e f surface on low t i d e s i s exl,osed f o r long periods t o t h e t r o p i c a l sun. A t t h e s e times t h e r ~ a t e r i n t h e inshore pools become hot t o t h e touch (strtdies oil t e m p r a t w e m ? a by Strasburg w i l l be re!?orted by cloud): y e t y i t h tile flooding t i d e t h e temperature w i l l drop perhaps

lsO

i n a few milutes.

Previous s t u d i e s hayre sho-m t h a t t h e oxygen c m t e n t of Yne water over t h e r e e f a t high t i d e and i n the pools a t lor. ,tide i s a l m y s near i f n o t above i t s s a t ~ r a t i o n value. Gut as t h e t m p e r a t u r e r i s e s tLis s a l r r a t i o n value, in grams of ox:ygen per l i t e r of sea ?rater, decrease; rapidly, so t h e reef i n h a b i t a n t s must be able t o aclju-st t o l e s s than nonncl oxygen,

Tvo b i o l o g i c a l conditions o: t h e r e e f ?lit s h o ~ l d be r81entioned 2.s i.n- flucnclnr; i t s ecology. I n -:he f i i - s t place t h z r e e f s u ~ f a c e .lot i n t h e small t i d e pools i s covered i n most areas by a dense alga& mat t h a t a f f o r d s botA food and protection f o r t h e inhs?.>it,?nts; t h i s .ins ?ar-ticdarl:i t r u e i n tile middle and o u t e r portions of t h e r e e f ? l a & Secondly, r.hila fs; l x g c r : m x i a t o ~ s and

scavevengers l i k e la:-ger f i s h , l o b s t e r m d c r & s were f0ur.d rrhile the s m e y was conducted a t l:xi t i d e , they moved onto t h e r e e f ?.t high t i d e .

iietk~ods ar,d LirnItztions of t h e Study:

- -

The o b j e c t s of t h e ir,vectigation .;rere t o f i x 6 the t r a n s i t i o n of dominant forms over tl.e r e e f surface, and, i f possible, t o clesignate sharply delimited

zones on t h e r e e f through a q u a n t i t a t i v e study,

On t h e main reof f l a t t h e study was conducted ?sy -3aytng out a s e r i e s of continuous s t a t i o n s , twenty f e e t v i d e aid f i f t y f e e t long, and within than areas ex'ten5ing t h e l e n g t h of the s t a t i o n on? o r two f e e t ?:ide. %thin t h e smaller a r e a all_ a n b n d s were c o l l e c t e d and counted; t h e l a r g e r a r e a

was

^then

inspected foy l a r g z r b u t i e s s coimon animals Like t h e l a r g e r s n a i l s o s e i cucmbers, etc. Then areas i n t h e sane tick1 zone adjacent t o t h e s t u d i e d

. . . .

zrea %rere s u p e r f i c i a l l y e x x l i n e i t o s e e i f t h e zone s e l e c t e d rras t y p i c a l ; it i:as found so i n a l l cases,

I n t h e inshore beach area, in t h e b a c ~ ~ i d g e trough9 and over t h a ol'fshore sheLf P O q u a n t i t a t i v e stuciy xas a t t e x p t e d because of d i f f i c u l t y i n obtaining e i t h e r enouo;h animals i n a t ~ ~ i c a l a r e a o r becavse of t h e &f..&ulty i n laying o c t :ti a r e a f o r study and c o l l e c t i n g i t (as i n twenty t o t h i r t y f e e t of ?rater),

~.

Gecause of poor t i d e s and poor rieathor c o n d i t i o ~ s ?,hen i.t was 9ossYsle f o r me

$0 do f i e l d rrork, alrnost no study rsas made bn t h e c o r d l i n ' e *idge a t a l l .

. ,

The l i m i t a t i o n s of t h e study a e :

1. The study i s l i n i t e d t o macroscopic i n v e r t e b r a t e s ; no microscopic i'orins of l i f e nor any f i s h a r e considered. i.k, Randall d i d a paralle: study

on f i s h and ? r i l l r e p o r t it seper:atcly. ^{. .}

2, Concerned a s it i s rrith t h e dominant animals, t h i s study omits t h e more r a r e mimals.

3 . ^{A l l} i d e n t i f i c c t i o n s of animals a r e b u t f i e l d i d e n t i f i c a t i o n s , and r r i l l be corrected upon t h e i d e n t i T i c a t i o n by experts, ^{. .}

.

The s tudy i s l i n t t e d by n e c e s s i t y t o t h e xore s u p e r f i c i a l l y ' o c c ~ r r r i n g

. .

animals; i t w,-s impossible t o explore' t h e t u b e s reaching d o m from t h e con- s o l i d a t e d surface of t h c reef.

5.

No s t a t i s t i c a l checks have been applied t o t h e q u a n t i t a t i v e r e s u l t s , and they should be accepted merely as rough i n d i c a t i o n s r a t h z r then accurate :;tcrbis,tj.cs; i n other :.rords, a sjlili1.a section two hundred f e e t ar?ay rilight give d i f f e r e n t f i g u r e s , but vo1G.d show tile sane trend*

Transect

--

Area A-0; Shorexard beach.

'Eqe 7rel.l-denarked bezch extends from about 2.5 f e e t t o about 8-10 f e e t above tile zero t i d e zone. It i s d i v i s i b l e i n t o t-ro d i f f e r e n t h a b i t a t s , t h e sancl beach coni~osed of loose a;id shifting sand, and t h e rocis beach consisting of c o n s ~ l i ~ a t e d c o r d and beach rock, eroded a?ld GZ.th soine snial.1 t i d a l pools.

The sand beach i s t h e h a b i t a t only f o r Ocypode ceratophthalma, the

-.--

"ghost crab" t h a t l i v e s i n deep burrows by day; a l s o a t n i $ h t t e r r e s t r i a l hermit crabs migrate dorm t o t h e upper zones of tine beach.

The rock 'beach is' iahalxited by Grapsus grapsus _{-.-.- -.-.--} in f a i r nmilbers, some

i d e n t i f i e d hermit crabs, and l a r g e nunbers of -:iI\?erita p l i c a t a (species marked -:i

-.-

---

i n d i c a t e s t h e i d e n t i f i c a t i o n has been confilmed . 1~ . . . R. Tucker Abbott.) Areas

! . - I

t o

A - ~ L .

These s t a t i o n s covered t h e r e e f - f l a t a113 presefit roughly t h e same type of sdostrate. The surface i s r e l a t i v e l y smootli, being b n i l t up by %he con- s o l i d a t i o n of t h e individual heads a i ~ d fronds of c o r a l .... by c o r a l l i n e algae, Its surfzce i s p i t t e d !rith ssinal!. shallorr depressions i n uhich

rater

stands a t low t i d e ; these a r e .usually l e s s than a square f o o t in axea a i d not over a,bout t h r e e .inches deep. The exposed surface of t h e c o r a l a.nd i n some areas t h e t i d a l pools, usua!.ly covered ?!it11 a more o r l e s s dense grorrth of algae

( t o be reported by Dr. iioul). The erceytions t o these [;eneralizations a r e i n t h e back-ridge trough (areas

A-13

and A-14.) rrhere t h e s u r l a c e i s below the l e v e l of t h e l o v e s t t i d e s . Areas A-7 and'il-8 and .A-9 ::ere at l e a s t in p a r t covered by a. s i n g l e extensive t i d e pooi; in these w e a s a fer: l i v i n g pieces of 2Heliol-iora were s t i l l - - graving uncovered by c o r a l l i n e algae.

- 5 -

. . .

..

TRURSECT, WD?lMPPRD REEF

FLAT

. ^:

S t a t i o n s A-1 t o

.4-14

In the t a b x l a t i o n s below those animals not q u a n t i t a t i v e l y estimated and those a ~ i m r . 1 ~ t h a t a r e r a r e , s c a t t e r e d o r very i r r e g u l a r in t h e i r o c c u r r d c e ( a s would be those found only i n t h e occasional loose c o r a l boulders) a r e in- dicated by

-

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Paribaccus sp- ¹

- -

^{, I}

- ..

^{- 1 . 1}

-

^{- , , .-. .}

-

^{I -}

I . . .

1 1 I 1

~ermi.4 crabs 800 ¹ 87 689 1500'3400 39CO 1720 1 . 1 1 1 60

-

^{1 -.-- . - -}

- -

^{I .}

-

I I 1 1 1

I k c n i a sp.

-

^!

- -

^{1 p}

-

^{- 1 .}

-

^{. . -}

^-

^{I , '} . . . ^{. . I -}

Drupa r i c i n a

-

_{' 1}

-

:

. . . ! . . . . . .

-:~onus ^' hebraeus 1 . ' t I I;.

-

_& ^{. .}

C. spon- I : I ^{1 I S} 1 ' '

d&s- ^{- . I , - ,}

-,.. 22 ¹ 81 100 500' l l l C

60

60 ^{1 1 2 0}

-

^{2 1 1}

-

' 1 . ' 1 1 I . . I ^{" "}

-

^{200' 20 280}

-

^:-

Cythara sp.

-

^I

^'-

. .

- -

^{I :- . - I}

-

4--

, :

^{I : I :.: , , :} . . ^{1 :} .... ^{' : . 1}

. . . . . ! : . 1 I . I " I'

V o l s s l l a ^{I I ' I I I}

-- --.--

a ~ r t i c u l a t a

-

^I

- -

⁴⁰¹

^{- -}

^{- I}

^{- -}

^{- I}

^{- -}

^{- I}

-

skIsognomon

-

I t I I I

perna 3 1 2

3

¹ 20

40

^{- 1}

-

^{20 6 0 1}

- ..

^{- I}

-

-

_{1 1 1 I I}

i(Ga£rarium ^{t I I I I}

p e c t i n a t a ^{- 1 -} 2 - 1

- -

^{- I}

- ^-

^{- I}

^{- -}

^{- 1}

^-

I 1 I 1 1

ECHINODElWATA ^{I I I t I}

I 1 I _I I

Tripneustes I I I I

----

^I

g r a t i l l a - I

- -

^{- I}

- -

^{- I}

- -

^{- 1 1}

^-

--

^{- 1}

-

I I

-

I I 1

1 I 1 I I

Echinometra ^I I I I I

--.-

mat!iael - 1 -

-

^{_ I}

.. -

^{- 1}

- -

^{- 1 1}

-

^{- 1}

-

I 1 I I I

Diadema I I 1 I t

---

paucispinus

-

¹

- -

^{- I}

- -

^{- I P}

-

^{- I}

- ^-

^{- 1}

-

1 I I I I

Distichopis sp.- ¹

- -

^{- I}

- -

^{- I}

- ^-

^{- 1}

^- -

-. -

_{I I I} ^{- 1}₁ ^P

-

^{.-- 1}

I I I I I

Ophiocoma I t I I I

-

or evapes

.

^{- I}

- -

^{- I}

^{- -}

^{- I}

^{- -}

^{- 1 1}

^-

^{- 1 p}

I 1 1 I I

Other b r i t t l e I I I I I

s t a r s 1.25~ 1 2 8 ^{- 1} l p

-

^{2P 1}

- - -

^t

-

^{120P P I}

-

HolO:&&ia ^. . I I 1 I I

--- _--

a t r a ^{- I} p ^{1 1 1}

^- -

^{I 1}

-

^{1 1 1}

^-

^{- 1}

-

I ^{" '} I 1 1 I

Other Ho3.0- ^{t I I t I}

tliurians - 1

- - ^-

^I

^{.. -}

^{- I}

^- -

^{2 0 1}

- -

- 1

-

. .

. . .

. . .C o r l l l i n e . ridge,.. . .

Yne topographical f e a t m e s of this r i d g e a r e described above.. Unfor-

, . t i m a t e l a t i d e s and -raves .... did n o t permit an exmination, w i t h e r q u a n t i t a t i v e

. . ^{. . . .}

. . .

: nor q u a l i t a t i v e , of t h e favna of this zone. The r n l a t i v c l y smooth s u r f a c e of

"'

th6 c o r a l l i n e Q a e d i d n o t o?fep any protectj.on f o r a n i n a l Life; t h e s h i f t i n g

. . . . .

rocks a% t h e bottom of t h e surga ch&nels offered l e s s , :Ior.f~ve-, rea:hLrg i n t o

'' t h d . ~ n e s s of tine c b r a l l k e elg-.e :rere n m e r o u s openings, u l d xitinin the: heads i1ei.e chu:ib%rs i n . :rhich many mj.msl.s li-ved. In t h i s h a b i t a t ?$ere found such

: . .. ^, ..

a n b a l s a s Echinometr; mz'Ynei

-- ----

⁹

---.-

A&erocentrosus sp., and s e v e r a l spaciss of

. . . . . . . . . . . . .

This area, l*ng beyond t h e outer edge of t h e corall'.ne ridge, tias es%Lnnated t o be about 3CWfee', 4 d e , f r o a 8-10 f e e t ?cep a t the c o r a l l i n e ridge t o 2bou.t 20 f e e t deep where t h e 'sottoin begins t o cirop away abruptly.

. -. I n t h i s a r e a no invertebmtas other than c o r a l s :rere olssei-ved, and no

. : . .facil?*ti*s' -rere a v a i l a b l e t o t r 2 n s p o r t heads of ccra2. t o shore f o r :?urther _{. . . .} exarnin~.tlc;i; hoirever, nw.krous ho!.es were' note6 i n t h e c o r a l f l o o r irhere

. .

crustacean's, irorins and. other f o m s could have 1.i-red.

,' .

The c o r a l on t h s h e l f rras r o ~ g h l y zoned, ~ i t h t h e domin,mt species in

. . . . . . . . .

the s h a l i d ~ ~ e r ir>.ter near t h e ' c o r a l l i n e ' r i d ~ e being Pociilopora nenndrina.

---,

and i n t h e dcenor v a t e r of ..the middle and ou.tor s h e l f , species of Acronora, _-.- I n t h e middle and outer portions of t h e s h e l f rnassive heads of P o r i t e s l o b a t a were conspicnous. Among the ot'ner c o r a l s found i n t h i s a r e a v e r e a l l of those re:?orted froiii t h e back-ridge trough and so;ile small specimens of

. . .

S t y l a s t e r gror~ing on t h e undersides of c o r a l heails in t m r i t y f e e t o r m o r e of .rater. L;rge areas of the bo-Lt,om rrere covered v i t h dead, loose fronds of . .

ABT.S lTOT IN LAGOO3.

I.

Lcevard Island Reef.

This a r e a l i e s t o . th e l e e of t h e ends o f t h e islands, r ~ e s t and northwest of Tabaurorae and h t s ncrthern reef. The regions f a m i s t i c a l l y approach t h e riind~rarcl re e f but on t h m t h e r e i s n o t a well-developed 'eef f l a t and no bsclcr.idge trough . . or c o r a l l i n e ridge v l ~ a t s o e m r , b x t i n s t e a d changes a t places

. .

q u i t e a b m p t l y i n t o conditions similar t o t k e r e e f s h e l f off the windward r e e f , ?n mtcr of noderate depths

--

' k o t o f i v e f e e t

--

t h e a a J w elanents of tLe fauna a r e t h ~ sane as t h e b a c h i d ~ e tro3e;h on t h s r r i n d ~ a r d reef.

The rnajor exception t o thesc gene:rali.tizs Lies in t h e region nor%h?rard of:

. .

the Yeliopcra f l a t s off: Lqteuna; here, . t h e . c o ~ d i t i o n s a r s s i m i l a r t o t h e a r e a r ? i t b . i n . t h e reef t3 t h e :!est of Lbenecnec I s l a n d ( t o be described b y

. . . .

Dr.. . ClouZ)

.

_{. .}

IT.. Heliopora F!.ats. . . .

Thc x e a s desihmated as F@liopora Fl?.ts a r e f o ~ m d i n a i r o t e c t e d region

' . ^, .

be&< th: rrindrrard ;-eel" a t t h e south 2nd of thz north isi;!ncl and n o r t h ~ r e s t of

. .

the t i p of t h e n o r t h is,land, . .

Tie sol%her;.l I&?-iopora f l a t consists of sin extensive t i d e ~jool about 800

. .

Zest i n d i a . e t c r , protecte:! o?: t h e ocemside by a coa-csc ccrnlli.ne boulder ridg?, and by elzvated sand and boiL?.ei- covered r e e f s on t h e other sides.

. .

Tila bottom of the pool i s estiniated t o be a l ~ o u t t h e 0,O tid.al l e v e l , and t h e

. . . . . .

wateir s t m d s a1:iort t ~ r e l v e .to eightecn inches dezp. The bottom i s s a d . The dominant a ? h i j l i s H&Lopora, 75th one ilea<. ahout

----

square :ard; P o r l t e s

---

: .SJ. i s p ~ r h a p s a t,enth.as f l e n t i f u l . giber corals, a l l infrequent, include

Q T b i c ~ U s P o c i l l o p ~ r a ~ Leptoria, Gn t h e exposed sand bottom no animals ex-

- - , ,

)

--

cept Holothuria a t r a a r e conspicuous.

---- -

Other i n v e r t e b r a t e s a r e found i n tvo habitats.

A. Under c o r a l heads. Here a r e found stomatopods (Pseudosquilla c i l i a t a ) ,

..--

Tethys, two species of t u n i c a t e s , four species of holothuroids, -%Thais

-. -

hippocastanurn,

.-

and s e v e r a l species of brachyuran crabs.

B e

In c o r a l heads. Here t h e dominant forms a r e crangonid shrimps and small xanthid crabs. Encrusting sponges of various types a r e common; black c o l o n i a l t u n i c a t e s a r e p l e n t i f u l ; one head only shoved numerous small sea anemones. Annelid. tronns, both Z r r a n t i a and Sedentaria, a r e moderately common.

Several species of clams, iqcluding ?~Isognomon

-

sp. and -:*Barbatia t e n e l l a , are found between t h e i n n e r brarches of t h e c o r a l ,

The northern Helionora f l a t i s f a u n i s t i c a l l y s i m i l a r t o t h e southern, with t h e same population. H o : J ~ v ~ ~ , it shows t h e t r a n s i t i o n , on i t s inner

side, between a t y p i c a l Feliopora f l a t a s described above with infrequent heads of Helio-oora reaching from t h e sand bottom, through a condition where the

---

ileliopora i s grorring t h i c k l y and t h e top ends were being consolidated by c o r a l l i n e algae, t o a consolidated condition l i k e t h a t described i n section A-8 of t h e windward reef. I n t h e l a b p i n t h i a n passages below t h e s u r f a c e con-

s o l i d a t i o n a r e numerous smll f i s h . Cn t h e outer edge t h e s e f l a t s gradually change in a moderately deep water c o r a l association with passages between t h e c o r a l six o r more f e e t deep;

. . . . ^, . . .

i. . . ^,

111. Shingle F l a t s .

. . . . . .

These areas of s h i n g l e

--

f l a t t e n i d a n d waveworn c d r a l r&ks l i e i n

.. . . . .

regions where t h e ?raves and t h e c u r r e n t s a r e strong enough t o sireep away t h e s&d, These conditions a r e found in t h e passes between t h e islands, a s in t h e t h r e e passes bebieen ITorth I s l a n d and South Island, and t h e two passes west of South Island. The s i a e of t h e rocks v a r i e s with l o c a t i o n , being l a r g e

xihere t h e r e i s an mbroken s l e e p of t h e .rater, 3s betveen t h e vindrrard s i d e o f t h e Abenemec passes, and grndually chmging i n t o fins g;~.vel on t h e inore protected extensions of t h e current, as t o t h e v e s t end of the southern t i p of ?.?orth island, !.~hich i n t u n i s replaced by t h e f i n e sand c!xiracteristli?

of t h e lagoon. h l l shingle i r e i s 5nspecti:d rrer? shove tile 0.0 t i d a l zone, and i n piaces extender: i ~ p -to t h e ed2;e of t h e t e r r e s t r i a l f l o r a . I n s s i e portions

of t h e passes t h e r e rierc developed broad shallo:: t i d a l ~ o o l s , u i t h a bottom of f i n e r rocks o r sand.

!Tithaat exception %ese 2.ctud pass areas r c r e found t o be d e m i d of 1 w g e r a h c 1 . s ; even t h c t i d a l pools a y p e z e d l . i i e l e s s , Howa-er, vhere thew, rcas s l i g h t protection e i t h e r from is?.ancls or from bars, t h e r e uas a feeble i'a11na developed, : i t h soiile %anthi& crabs, a fevr spollges a n d h e a d s 31"

---

P o r i t e s i n t h e t i d a l pools. In the f i n e gravel zoiles, t r ~ a s i t i o n d . betvieen the shingle and tile lrgoon sand, sonic 15fe xis f o u 4 i n t h e ?.eveis :Tea7 t h e zero t i d e zone.

Durro~~Lng i n t o t h e dead coral. me;' unS.er these areas iisre f.o~md sipunculids and ennellds; i n tile small. shallow t i d d pools vere found. occasional brit-Lle s t a r s , s o l i t a r y zooanthids andsma'2.1 crabs 'u&r t n e sen-Ltcred l o o s e boulders,

Lil.GCGN kR:.LG

IV.

S m d Foreshore.

... . .. . .

<

/\long .the l ~ g o o n s i d e o f ";he i s l a n d t'ne foreshore, from about the trio f o o t t i d a l l e v e l up aii;ernn.i;cs betrieen f.'.ne sand and consoliclatec! beach rock i:ith more a m a s of beachrpck of: t h e northeiv i s l a n d and more s a i d off t h e

. . . . ..,.. .. ...

sou2LheTn. Only r.ear .the tip of the i s l a n d s and a r o u n d s : n a l l e F i s l a n d s l i k e Antema and Abenccnec ? r e tilo,?e tvo c??aractori,stic beach formations replaced

. .

by c o r a l shingle. The sand ;oreshore i s devoid of l i f e except f o r occasional ghost crabs Ocypode c e r a t o p h t i ~ a h a

--

t h e same species t h a t i s found much nore

p ~ . e n t i ? u l l y on t'ne riindmrd sand beach,

., .. . .

V. Beach-rock Foreshore.

Alte~"nct;_ng n i t h t h e sand foreshore a r e areas :?@ere t h e elevated beach-

. .

rock of t h e i s l a n d f s base i s exposed by :rave action. This s l a b i s eroded on t h e top s u r f a c e i n t o t h e t y p i c a l cupped pattern, and oft2n i s undercut along t h e lorrer ed.ge by cave action and possibly s o l u t i o n by f r e s h y a t e r from t h e

. . . .

islanc: lcns, A t places, e s b e c i a l l y i n t h e lo!~er t i d a l zones, t h e y d e r c u t t i n g _{. .} has proceeded f a r eno&h so tilri; s l a b s up t o & e v a r a l f e r t o r m o p l ~ n g _. have

. ..

broken 0% trom t h e base roclc a d l i e f r e e on t h e s u b s t r a t e of e i t h e r beach- roclc o r of sand,

Animal communities 5.n t h i s habita-t rrhen t h e t i d e i s out a r e subjectecl t o _{. . ~ . .}

. . .

dessication a i d heat, t o ra$n and especj.ally t o t h e i l o r i n g . . f r e s h . .ratesg common a l i along the shore; vhen tile ti& i s i n , t o inod~ra-te ;?am action (excegt,

~ ~ o s s i ' v l y il.uring periods of s t o m s from t h e iiest.:~hen t h e rrave a c t i o n rrould be vigorous).

. .

. .

The rocks can be r?~.b2iv$.ded. i n t o four x%soci.?.tFons:

. .

A. The l i i ~ h e r bsach-rock areac This is above about t h e 2.5 f o o t t i d a l

n e i t h e r as cormlon a s on the s i m i l a ~ rocks on t h e .rin&ard s i d e of t h e island.

. .

B. Lo~r-;.r beach-rock area, rocks 1y;i.g on s o l i d s u b s t r a t e o r undercvt

.'

^:

s o l i d roclc; T h e s rocks .. l i e l;et::een . . . t h e 0.0 and 2,s t i d d zones. I n them . .

aye ie%dbur?o.ring s i p u n c u l i ~ :rams; _.. near t h e edzes of the roclcs a r e numerous

. . .

Holothuria a t r a a n d l e s s numerous Xolothuria monocs?xia, sone colonies of

-

, ^{. .} _{. ..} ^. . c o l o n i a l t u n i c a t e s a d some sponges; under them a r e n m e r o u i ' crabs of a t l e h s t four species, four o r more s;?ecies of crangonid shrixps,'very few

~ . . . h e m i t crabs, and no :rorxls.

C. Lorrer beach-rock, rocks l y i r i g on 'sand. These w e i n t h e scnle zone a s 9 abo-ie, but l i e ;?it11 the base inbedded i> t'ne sand, Ahoul, thk- e 6 g ~ s i s t h e coiimor, ;;olothuria ahra a n d c l u s b e r s - of _--.-..

--

w o a n t l i i ; i n burroirs under .them i n t h e sand a r e nunierous large r r m s of t h e gsnus EuryLhoe and t h r e e species ~ o f . _-.-- crm-gonii, s h r i i p s .

D. Lo7rer beach-rock, s u s p n 6 e d rocks, These, l ~ y i n g :iith one end on o t h e r rocks, leave a l a r ~ e surface underneath open t o :re:, c i r c d . a t i o h . ' o f water o r a i r , and protection ?rox t h e sun and r a i n . Gn t h i s s c f a c e , hanging dorm, a r e h.ydroid colonies i n p r o f s s i m , and some c o l o ~ i - a 1 t v n i c a t e s , a ferr spongcs.

V I iiud Eats.

In a s:lort narrow area a1or.g the micXle of t h e :Tor%h Island, belo-i t h e foreshore and behind the i n c i p i e n t beach-rock (BIL) t h e r e i s a mud f l a t , The h e i g h t of t h e mud f1a.t i a sli.:<l~tl;r a.bov t h e zero t i d e l e v e l . The mud i s s o f t , s o t h a t a person r a l k i n g over f i t rrciuld sink bet~re-n ankle and hoe-deep;

s l i c p e r y 75th l i t - t l e a.w115.r,~xe of sand9 and i n orgarkc matter rrh.ose decompxi-tion gives i t t h e c h a r a c t e r i s t i c odor of hydrogen s u l f i d e .

I n t!iis mud f l ~ t proper i s only one s p x i e s v i s i b l s , -the b r i l l i a n t l y colored P d d l e r crab, l i v i n g i n blu^ro~,is. . I n a m a s trans!.tiona!. betireen t h e niud f l a t and t h e sand. z r e found some hu.rro:rs of s t o m a t o ~ o d s , % w e :!ere no

t r a c e s of annelid.burro:rs o r of other macrosco;xi.c l i f e , V I I I n c i p i e n t Bsach-rock

h m a l l ,-re? off mi&!le of t h e n6rthern island, bounded inshore by t h e . ~'

rnudflats (VI) and off shore 'and a t t h e ends by sax! I^lats o r t u r t l e grass . . :

(VIII and

a).,

Fs co:n:>osed of b e a c h ~ r o c k i n t h e process of formation, according t o D r . Clovd, T!% rock is as f i r m , ' o r allilost, ?.s f i m as t h e t y p i c a l elevated beach rock (v) h u t i t s surfacc, necr t h e zero t i d e zone, r;as rouzhly eroded Like the xore exposed rock (IV-A).

In ,pro.tected areas i n thg ~.oc!;, a s i n d.eeper cusps, ' i ~ . f i s s u r e s and m d e r . tile. occas;.onal loose r o c k s a r e t h e following s n a i l s 2 ?'Th.ais hippocas-

-.

,."anurn; "tra v i r g a t a and

%.

litterata.?'%ynathiutn chlorostomum and ':'Conus ^:

P

---- -

⁹

^{- -}

^{,- . . . .}

-

hebraeus.

-

Unde' t h e rocks a r e nmerous h e r ~ n i t crabs. Burcowing i n t o t h e rock were sipunculoid rrorms and s e a anemones were found

in

p r o t e c t e d loca-

t i o r ~ s j h e r e they were l i v i n g i n shallow p i t s t h a t p r e c i s e l y f i t t e d t h e b a s a l -portions .of t h e i r colwms. In shallow b u t r a t h e r long burrows t h a t t h e y have e i t h . e r excavated o r ta::en a r e t h e l a r g e red-eyed crabs'and; f i d d l e r crabs;

a t t h e entrance o f - t h e s e burrows were v a s t numbers of CollemboZz*. . . :

. .,.

V I I I Sand F l a t s . .,. . . .

The :nos% extensive h a b i t a t i n t h e lagoon i s t h e s a n d f l a t ; . These f l a t s run f r o n -the inshorc beach along t h e t h r e e major i s l a n d s extending a s a broad, a1;nost l e v e l , f l a t from the inshore beach outwards f o r s e v e r a l hundred f e e t vide t o a half mile o r more. Cn the outrrard edge -they e i t h e r continue as the sand bottom of t h e lagoon or a r e cove~ed. by t u r t l e grass

(IX),

o r a r e de- mar!:cd by a decadent coral. reef ( X ) . Thc portions of t h i s area described belaw run Prom about hro f e s t above t o s e v e r a l f e e t belorr t h e zero t i d a l zone.

??he.'sand v a r i e s fror~i l e s s th!m an i n c h t:xicl:, coveriizi: o l d c o r a l r e e f , t o a t

l e a s t s e v e r a l f e e t thick. . .

The f a m a of t h i s zone var5.e~ rrith t h e depth i n t h e t i d a l zone, t h e fine- ness of sand p a r t i c l e s , t h e amount of wave actlcn, and !rith t h e depth .of t h e saml. The d i f f e r e n c e s b? t l ~ e fauna a r e iiot'rrel? demwked a n d ~ l o s t o:ften a r e quantita-Live r a t h e r t h w q ~ ~ a l i t a t i v e

--

t h e same species present in most areas,

.

but varyirig i n r e l a t i v e abundance, O f course, ~ 6 t h t h e d i f f e r ~ n c e i n depth t h e fauna changed ::xarkedly; :for example, i n t h e highest portioni h e r e conskdered

(soae t i d a l pools i n t h e m i d d l ~ t i d a l zone off h t e w n a ) , t h e only elements of

-

¹⁹

-

t h e fauna l e f t were t h e Enteropnnustan,

---

Ptychodera, and on t h e other hand, be- l o ~ t h e -1,O t i d e l e v e l s o l i t a r y heads of c o r a l wou3.d reach rip above t h e sur- rounding sand.

'Thesc s o l i t a r y heads of c o r a l in t h i s area, l i k e those i n the T u r t l e grass area, collstitni;ed microenv~ronmaits n:a;.kedly diifeirent from t h e surrowding sand, For t h a t rea.son they a r e coiisidered a s a s e p a r a t e subdivision below.

A. Sand a r e a proper, f a m a :

Forifera: Purple sponge, black sponge (trro kinds), oranze sponge, Coelenterata: Zooantliids ( c o r a l s considered below).

Anne!.ida: Tubeworms 7:1ith l e a t h e r y tubes an6 e i t h sand tubas; ttro . .~ . .

species o; Ema1tA.a; m a l l and g i a n t sipunculids,

.. ^~

Crustacea:

--

Lysiosquilla --

--

^maculata;

-

Callianassids, Calappa spo iIollusca: (Note : remarkably few t r a c e s of l i v i n g mollusca were

folliid, al.thoue;h dead shel3.s ?rere seen in some areas; t h i s may

,. ..

be a t t r i b u t e d t o t h e f;ct .that ~ ! ; o s t o_^ th e sand f i a t molluscs

. . . . . . . . .

a r e esteened a s . . food by t h e ~ i l b e r t e s e . ) C l z n s , various

, . :,. .:

. .

?. A,

species including "Cai'rar!! pectinata, "Tellina crassi$ica%a,

.. ..

,c >,

" T e l l i n a

--

sp., '3la.utica sp., various species of W t r a ,

--

^Terebra,

. .. . ^{. .}

. .

Cchinodermata:

Holothmia a t r a (extrei,ieS;; cornon in some arcas, counted a% _.

. . .

5-15

per square yard), Chordata:

Ptychodera

--

^{s ~ .}

B. I s o l a t e d c o r a l hezds, fauna:

P o r i i e r a : sa,ie a s akove,

C o c l c n t , e r ~ t a : P o r i t e s sp. ( d o w a n t ) ; Poci.Uopor3 damicornis;'..

. .

--

Acropora s e r v i c o r n i s ; Orbicella; &her c o r a l s ' $ n n ; : l e s s e r

-

. .

. ' "

numbers.

. . . . . . . _{... . .}

Pennaria. . . .

Amelida: Tube brorms i n l i n y tubes; sipunculids ' .

Cyustacea: Crmgonids, various species; brach3ruran 'crabs.

. . . . . . . . .

Hollusca: Cyprea eroya "?ionwtaria ::ione-b, 3 9 a r b j t i a _{-_I-J -.}

-- --

. . .

Chordata:. Colonial t m i c a t e s .,: . . . .

.

.

^. . . ^{,.:. .} . .

. . : . . . . , . . . . ^{. .}

lXc Turtle Grass ^{' '}

, .;.. . . . ^{:,,. "} . . . . . _, . . . < .

Large are& i n C'ne northern p a r t of t h e lagoon and portions of tine southern

. . . . . ..: . .

lagoon a r e d6m&&tkd by T u r t l e Grass ( ~ h a i l i s i a ' s p . ) rrhich extends over the

. ,. .

. . . . .

. . _. , , : : : . . ^{) . : .}. . . : . . .^I. ^.. . ^{, .}

stifid b o t t o ~ ~ f ~ b m !:~at&r 2b6Ut ^{2 . t} t:~&:<ero t i d e l i n e ' o r a l i - I t l e above t o six

. . .

. ^,

. . .

. . . . .

.:

^{: . . . .}. . ^{. .} . .

o r t e h ' f m ' c beiotr%he surfs&.

Tk;;

' i i t l e Grass, &.oh makes a dense stand

. . . . .

. , . . ^{. .} . . .

'Xilcc - t h e 'hoi-the& eel-grass ( i d s t o > a ) , .kldom grorrs over a f o o t or more high;

: . .

, . , . . . .

,its creep&; r h i i o n & make a dense i n t e n r o ~ e n mat i n t h e sand substrate.

In

. . . . ....

. :., . . . . .

the s6utneri1 poriion of t h e lagoon l e s s a r e a i s adaptable t o t h e gro-trth of

. . . . . . .

. . ,.

I t h e plmt,, 2n$

i n

. & & : i t i s i i m i t c d t o a r e l a t i v e l y narr.ow zone near t h e

.., . ^{., ,}

shore of 'die ~ i s l d n d ; , i n ' t h e roicldle 02 t h e lagoon, o f f t h e ?asses betmen

. . . . . . ., . .

North and South Island and t h e zdjucent areas, a n d ' o f f Tabuarorae and t h e southrrcsternmost .L20rtion of t h e lagoon tilere i s no T u r t l e Grass :rhatsoever,

. ^. . . . ^{. .}

. . . . . .

.

^.

The ~ ~ i r t 1 e ' G r i s s propcr i s rela'&vely devoid of i n v e r t e b r a t e l i r e . On t h e fronds of t!le grass a r e found black c o l o n i a l t u n i c a t e s and occasional sponges of scve?al t y p s ; a5out t h e baszs of t h e grass a r e nore sponges of t h e same t y y md, n o s t abundant i n iilmy areas, a ' p a p i l l o s e green-black holotlmrian. It vas impossible, once digging rTas started, t o dig out t h e

few b ~ r r o r i i n g znimals detected becauce of t h e clouds of fqne s i l t t h a t rendered .unr!.ec:atz v i s l o n il~;3ossible. The burrmiing animls, l;o:;svcr, a r e fer: i n n m b e r and appeared t o be i i ~ n i ~ c t t o a sinall s q u i l l i d ( ~ y s i o r q u i U z ) --.-.-

a d sorie b w r o ~ r i n g xorms, . ..

In t h e ciecper pwt,ions cf t h e Turtle Grass beds, especia!.ly in t h e area off t'ne nortllem island, there x p e a r s o l i t c r y an6 sepwated c o r d masses, l i k e is1,mds in a sea of grass. Thase i s o l a t e d masses nre r i c h in l i S e , both f i s h and invertebra%e, Tiley e r i d e n l y a r e made ^l1.p primarily of

--.

F o r i t e s , but they e r e covered i n a l a r g e extent by o t k y c o r a l s lii:c --L.- Acronora, --.- ?ocillopora,

-

r n c e l l a e t c o The i n v c r t a b r . ~ t e f a m a i s i n g m e r a l s i m i l a r t o t h e fauna i d

of c o r a l he& i n tile sanc! beach a r e a (iinl-E),

X.

Decadent Coral Reef,

Iil mmy orees tho sand :"lats prade eraddu!.?_3r f n t o a r e o o n of dead co:d r e e f s t h a t l i c bctrrcen

#

1 , O and

-

1.0 t f d a l level. These a r e a s a p p x r t o be .those -1here t h e riave action and c w r e n t action i s strong-r, s w e p i n g t'he veneer of sand, from tile flardnr s u b o t w t e , They aye founii t o t h e sou-bheast of m t e m ~ a ; off t h e sou.thern po'tisn of :he 2'orth I s l a n a xid t h e northern portion of 'the Sou-Lh 1slan-l ahd t h e passage:, bc.t-,rcen; and She;. a r e extensively de-

-rer?ebratzs: on t h e harc! c o r a l t h e r c a r e places of a'c*,acbmen-t, protected and unpro-kected, f o r seasl'.lc Tomis; i n n?tu?~lJ.;. occurr5lg spaces and i n bwrorrs i n t h e c o r d ti;er? a r e $aces .'oz t h e sme:Ll.er iilvertebrstes t o hide;

i n %he a r s a s be'tvem t h e heads 02 coral, tither broken off a s t h e r e e f rras p;ro~,ring or s ~ b s e r j u m t l y c:ot?z& rrcm the r e e f s u r f a c e a r e pockets of sand and gravel t o accommodate bur:'ouLng f o m s ; t h e s e pockets, some o f them many f e e t