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P[S[Z[N[] Marine Ecology\ 19 "0#] 38Ð51 "0888# Þ 0888 Blackwell Wissenschafts!Verlag\ Berlin Accepted] December 11\ 0887 ISSN 9062!8454 Habitat Selection and Ecology of Two Speleophilic Gobiid Fishes (Pisces: Gobiidae) from the Western Mediterranean Sea Ju rgen Herler 0 \ Robert A[ Patzner 1 \ Harald Ahnelt 0 + Helge Hilgers 0 0 Institute of Zoology\ University of Vienna\ Althanstr[ 03\ A!0989 Vienna\ Austria[ 1 Institute of Zoology\ University of Salzburg\ Hellbrunnerstr[ 23\ A!4919 Salzburg\ Austria[ With 5 _gures and 1 tables Key words] Submarine caves\ Corcyro`obius liechtensteini\ Dido`obius splechtnai\ cryptobenthic _sh\ Balearic Islands[ Abstract[ The life habits and microhabitat selection of speleophilic gobiid _shes were investigated on the Balearic Island of Ibiza "western Mediterranean Sea#[ Corcyro`obius liechtensteini "Kolombatovic \ 0780# was the most frequent species within submarine crevices\ cavities and caves[ Dido`obius splechtnai Ahnelt + Patzner\ 0884 co!occurred with C[ liechtensteini in several cases but showed a clear spatial separation based on a di}erent microhabitat preference[ The microhabitat selection of both species was con_rmed by habitat!choice experiments in an aquarium[ Corcyro`obius liechtensteini was frequent in depths between 4 m and 14 m and attained abundances of 03[1 individuals = m -1 [ This species inhabited the ceilings and upper parts of the walls within the caves[ D[ splechtnai was mainly found between 6 m and 00 m and showed abundances of approximately 1 indivi! duals = m -1 [ This species occupied the _ne sediment bottoms in the innermost parts of crevices and caves[ The growth and the maximum age of both species were determined by lengthÐfrequency distributions[ The overall sex ratio from catches of three di}erent years are given for C[ liechtensteini[ Problem Small!sized teleosts that are able to exploit spatially restricted habitats for food and shelter are designated as cryptobenthic _sh "Miller\ 0868\ 0885#[ Such species also occur within the Gobiidae in the Mediterranean Sea[ Most Mediterranean gobies live on soft bottoms or between pebbles on rocky substrates[ Some species show a close a.nity to cavities "Miller\ 0875^ Zander\ 0889^ Ahnelt + Kovac ³ic \ 0886#[ One of the evolutionary trends of this primarily epibenthic group is towards U[ S[ Copyright Clearance Center Code Statement] 9062!8454:88:1990!9938,03[99:9

Habitat Selection and Ecology of Two Speleophilic Gobiid Fishes(Pisces: Gobiidae) from the Western Mediterranean Sea

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P[S[Z[N[] Marine Ecology\ 19 "0#] 38Ð51 "0888#Þ 0888 Blackwell Wissenschafts!Verlag\ Berlin Accepted] December 11\ 0887ISSN 9062!8454

Habitat Selection and Ecologyof Two Speleophilic Gobiid Fishes(Pisces: Gobiidae) from theWestern Mediterranean Sea

Ju�rgen Herler0\ Robert A[ Patzner1\ Harald Ahnelt0 + Helge Hilgers0

0Institute of Zoology\ University of Vienna\ Althanstr[ 03\ A!0989 Vienna\ Austria[1Institute of Zoology\ University of Salzburg\ Hellbrunnerstr[ 23\ A!4919 Salzburg\Austria[

With 5 _gures and 1 tables

Key words] Submarine caves\ Corcyro`obius liechtensteini\ Dido`obiussplechtnai\ cryptobenthic _sh\ Balearic Islands[

Abstract[ The life habits and microhabitat selection of speleophilic gobiid _sheswere investigated on the Balearic Island of Ibiza "western Mediterranean Sea#[Corcyro`obius liechtensteini "Kolombatovic�\ 0780# was the most frequent specieswithin submarine crevices\ cavities and caves[ Dido`obius splechtnai Ahnelt +Patzner\ 0884 co!occurred with C[ liechtensteini in several cases but showed a clearspatial separation based on a di}erent microhabitat preference[ The microhabitatselection of both species was con_rmed by habitat!choice experiments in anaquarium[ Corcyro`obius liechtensteini was frequent in depths between 4m and14m and attained abundances of 03[1 individuals =m−1[ This species inhabited theceilings and upper parts of the walls within the caves[ D[ splechtnai was mainlyfound between 6m and 00m and showed abundances of approximately 1 indivi!duals =m−1[ This species occupied the _ne sediment bottoms in the innermost partsof crevices and caves[ The growth and the maximum age of both species weredetermined by lengthÐfrequency distributions[ The overall sex ratio from catchesof three di}erent years are given for C[ liechtensteini[

Problem

Small!sized teleosts that are able to exploit spatially restricted habitats for foodand shelter are designated as cryptobenthic _sh "Miller\ 0868\ 0885#[ Such speciesalso occur within the Gobiidae in the Mediterranean Sea[ Most Mediterraneangobies live on soft bottoms or between pebbles on rocky substrates[ Some speciesshow a close a.nity to cavities "Miller\ 0875^ Zander\ 0889^ Ahnelt + Kovac³ic�\0886#[ One of the evolutionary trends of this primarily epibenthic group is towards

U[ S[ Copyright Clearance Center Code Statement] 9062!8454:88:1990!9938,03[99:9

Herler\ Patzner\ Ahnelt + Hilgers49

small body size and cryptic life habits "Miller\ 0868\ 0885#[ Data on the ecology ofsmall and more cryptic species\ which exclusively occur in crevices or caves ofbedrock\ are rare "Miller\ 0875^ Ahnelt et al[\ 0883^ Ahnelt + Patzner\ 0884\ 0885^Kovac³ic�\ 0886^ Patzner\ 0887a#[ Such species are di.cult to detect and oftenoverlooked[ The use of SCUBA techniques and direct observations reveal newinformation about the cryptobenthic _sh of sea caves[ Recent investigations on theBalearic Island of Ibiza showed not only previously known species that live incaves or closely related habitats "Ahnelt et al[\ 0883^ Ahnelt + Patzner\ 0885^Patzner\ 0887a# but also a new species "Ahnelt + Patzner\ 0884#[ The biology ofthese cave!dwelling gobies still remains largely unknown and justi_es investigationsof their ecology and habitat selection[ The observations in the western Mediter!ranean Sea showed that the gobiid species Corcyro`obius liechtensteini "Kolom!batovic�\ 0780#\ Dido`obius splechtnai Ahnelt + Patzner\ 0884\ and Gammo`obiussteinitzi Bath\ 0860\ occur in submerged crevices\ cavities or caves[ These threespecies are the only Mediterranean gobies\ which to date have been exclusivelyreported from such habitats[ The aim of this study was to give detailed descriptionsof the habitat selection and the space partitioning between C[ liechtensteini and D[splechtnai\ which showed co!occurrence in several cases\ and to provide informationon the ecology of both species and the occurrence of sympatric _sh[

Material and Methods

1. Material

In the years 0880Ð86\ 024 C[ liechtensteini and 17 D[ splechtnai were collected[ All specimens were fromthe north coast of Ibiza\ near Portinatx\ 28>91? N\ 90>94? E\ Balearic Islands\ Spain^ collected by R[ A[Patzner and J[ Herler[ The body size of the _shes is given in standard length "SL# ¦ caudal _n length"d � damaged#[

Corcyrogobius liechtensteini (Kolombatovic, 1891)

Twenty males\ 03[7 ¦ 3[0 to 12[3 ¦ 5[4 mm^ 44 females\ 02[8 ¦ 2[4 to 19[5 ¦ d mm^ 14 juveniles\5[4 ¦ 0[7 to 03[8 ¦ 3[2 mm and one specimen of unde_ned sex\ 05[9 ¦ 3[1 mm[ Collected in September0884\ May 0886 and September 0886[ Earlier material "0880Ð83# is published in Ahnelt + Patzner"0885#[

Didogobius splechtnai Ahnelt & Patzner, 1995

Seven males\ 05[8 ¦ 3[5 to 15[1 ¦ 5[7 mm^ eight females\ 07[8 ¦ 4[9 to 29[2 ¦ 6[4 mm^ _ve juveniles\09[1 ¦ 2[0 to 03[9 ¦ d mm and one specimen of unde_ned sex\ 12[0 ¦ 5[6 mm[ Collected in September0883\ August 0884\ May 0886 and September 0886[ Earlier material "0880Ð82# is published in Ahnelt+ Patzner "0884#[

The material is deposited at the Natural History Museum Vienna\ at the Institute of Zoology\University of Vienna and at the Institute of Zoology\ University of Salzburg\ Austria[

Ecology of two speleophilic gobiid _shes 40

Fig[ 0[ The northern coast of the Balearic Island of Ibiza\ indicating study sites 0\ 1 and 2 of Corcyro!`obius liechtensteini "t# and Dido`obius splechtnai "T#[ Scale bar � 0 km[

2. Study area

The _eld studies were carried out near Portinatx on the north coast of the Balearic Island of Ibiza[ Thecoast morphology of this part of the island consists of bays with sandy beaches\ the so!called Calas\which alternate with rocky spits\ called Puntas[ The water temperature at the surface was 06 >C in Mayand 14 >C in September 0886[ Three sites were selected for investigation "Fig[ 0#] site 0 was situated onthe inshore side of Punta Galera\ where the rocky slope gives way to soft substrates at a depth of 19 mwith patches of the sea grass Posidonia oceanica "Linnaeus# Delile^ site 1 was located on the moreexposed Punta Mares\ where the rocky slope extends to 34 m^ and site 2 was situated on the mostexposed Punta Charraca\ where the hard bottom extends to about 31 m[ Sites 1 and 2 showed largeareas that were overgrown with the red alga Lophocladia lallemandii "Montagne# Schmitz\ an immigrantfrom the Red Sea "Patzner\ 0887b#\ and P[ oceanica[

3. Methods

The in situ observations were carried out in May and September 0886\ using SCUBA techniques[ Themicrohabitat choice as well as the shelters of C[ liechtensteini and D[ splechtnai were recorded for eachhabitat[ The de_nitions of caves\ cavities\ hollows and crevices follow Riedl "0855# and Patzner "0887a#]

Caves] Systems with height of entrance ³ length of cave[ The sizes ranged from 9[4 to 2 m entrancediameter and 0Ð7 m length[

Cavities] Height − length[ The entrance diameters and the lengths of small cavities varied from 9[4to 0 m[ Big cavities showed a width up to 6 m and a length of about 3 m[

Hollows] Hollowings out of big rocks[ Height ¦ length[ The heights did not exceed 9[4 m[ Lengthsup to 1 m[ They usually showed one main entrance and additional small ones[

Crevices] Small cave!like systems with height ¦ length[ Entrance diameters ³9[2 m[ Lengths ³0 m[The measurements of caves are given in width × height × length to the nearest 09 cm[ For habitat

description a longitudinal transect and the aufwuchs of each cave was recorded[ The identi_cation ofthe cave organisms follows Riedl "0872#[ Sympatric _sh species\ especially possible predators or com!petitors for the two gobiid species\ were noted[

The _sh were caught with a mixture of quinaldine and ethanol "0 ] 04#\ which narcotized small _sh

Herler\ Patzner\ Ahnelt + Hilgers41

after being spread over an area and enabled easy collecting with a hand!net\ yet allowed rapid subsequentrecovery[

The collections for the years 0880Ð84 and observations in 0885 by one of us "R[A[P[# are included togive a description of the abundance and depth distribution[ To obtain data about the abundance of C[liechtensteini within the submerged caves\ all specimens within a particular cave "designation] 0:86# in8 m water depth at Punta Mares\ measuring 0 m × 9[5 m × 0[2 m\ were recorded[ They were collectedafter quinaldine had been spread over the whole inner surface of this cave in September 0884 and inMay and September 0886 but only counted in September 0880 and 0885[ Two caves measuring5 m × 1 m × 5 m and 1 m × 2 m × 7 m\ in which most specimens of D[ splechtnai were observed\ werechosen to describe its frequency[ Because of the short ~ight distance\ visual estimation of the abundanceof this species was possible[ The depth distribution of both species was determined on the basis of theexploration of several caves at between 9[4 and 34 m water depth[

The time of reproduction could be recognized by typical features of male C[ liechtensteini within thebreeding season and by the occurrence of juvenile _sh[ Life period and growth of both species wereevaluated by lengthÐfrequency distributions "Gibson + Ezzi\ 0870#\ which included all C[ liechtensteinicollected in September 0880\ 0884 and 0886 and all D[ splechtnai collected in September 0880\ 0882\0883\ 0884 and 0886[ All _sh were measured after _xation in 3) formaldehyde and preservation in69) ethanol[ The sex ratio for C[ liechtensteini is based on the catches of September 0880\ 0884 and0886 and of May 0886[

In order to investigate habitat choice\ an aquarium with a bottom area of 19 cm × 39 cm was _lledwith approximately 04 l of seawater[ The water temperature was maintained at 14>C[ The aquariumwas exposed to natural light[ One half of the aquarium was covered with black paper to protect it fromlight while the other half remained bright[ Most of the water surface was covered by a plate of XPS"extruded polystyrol\ 29 mm thick# which was pinned with several colonies of the bryozoan Myriaporatruncata "Pallas\ 0655#[ These arrangements simulated cave!like conditions\ which enabled the investi!gations of the preferences for light conditions and microhabitats[ The water was aerated during thenight[ The _sh were fed with nauplia larvae of Artemia salina[ Three specimens of each species wereobserved and the maximum number of specimens of both species kept together in the aquarium at thesame time was _ve[ The observation periods were] for C[ liechtensteini\ 5 days for two specimensmeasuring 03[8 mm and 06[2 mm SL and 2 days for one specimen measuring 11[9 mm SL^ for D[splechtnai\ 5 days for one specimen with 11[9 mm SL\ 3 days for one with 11[9 mm SL and 1 days forone with 09[1 mm SL[ The di}erences in size and colouration provided individual identi_cation[ Sixsites within the aquarium were distinguished[ 0] bottom:bright "b:b#^ 1] bottom:dark "b:d#^ 2] wall:bright"w:b#^ 3] wall:dark "w:d#^ 4] ceiling:bright "c:b#^ 5] ceiling:dark "c:d#[ The choice of the _sh for one ofthese sites was recorded six times each day between 9899 and 0899 h\ with intervals between 89 and079 min[ The preference of each specimen was shown by relating the frequency of appearance on oneof these sites to the total number of records[ The habitat choice of each species was given by the meanvalue of the three specimens[

Results

1. Microhabitats

Microhabitat I: Overgrown ceilings and walls

The ceilings and upper walls of the entrance areas of caves\ cavities\ hollows andcrevices "Figs 1A\ 1B and 2# were covered with sponges such as Spirastrella cuncta!trix "Schmidt\ 0757# and Anchinoe tenacior Topsent\ 0825\ scleractinians like Lepto!psammia pruvoti Lacaze!Duthiers\ 0786\ or Caryophyllia sp[ The bryozoan Myria!pora truncata "Pallas\ 0655#\ which was very abundant\ and the red alga Peysson!nelia squamaria "Gmelin# Decaisne built up a dense epigrowth on the ceilings andwalls of cavities and hollows as well as on the front areas of caves and crevices[The middle areas of caves and crevices were dominated by M[ truncata\ sponges

Ecology of two speleophilic gobiid _shes 42

Fig[ 1[ Schematic longitudinal sections of one cavity "A# and one cave "B#[ The approximate centres ofthe microhabitats I\ II and III are indicated[ Scale bar � 49 cm[

like Clathrina sp[ and the ascidian Halocynthia papillosa "Linnaeus\ 0656#[ Thepolychaete Protula tubularia "Montagu\ 0792# occurred frequently[ Large areasof the walls were covered with the green alga Palmophyllum crassum "Naccari#Rabenhorst and calcarous red algae belonging to the group of Corallinaceae[ Thelower parts often showed sponges of encrusting shape[ Secondary holes and boreholes of Lithopha`a lithopha`a "Linnaeus\ 0647# were very abundant on the ceilingsand the upper parts of the walls[

Microhabitat II: Bare ceilings and walls

Largely bare areas "Fig[ 1B#\ following microhabitat I backwards\ occurred in theinnermost regions of caves and crevices with height¦ length or in deeper waterregions\ where light intensity and water movement were minimal[ Only a few sessileanimals such as P[ tubularia and colonies of Sertella beaniana "King\ 0735# as wellas some stunted or encrusting sponges were found on the ceilings and walls[Secondary holes occurred on the ceilings and basal parts of the walls[ With increas!ing water depth\ the size of this microhabitat extended towards the entrance\ andthe innermost regions showed an {empty section| "Riedl\ 0855# which lacked anysessile organisms[

Herler\ Patzner\ Ahnelt + Hilgers43

Microhabitat III: Fine sediment bottom

Bottoms covered with _ne sediment "Figs 1B and 3# occurred in the same habitatsas described for microhabitat II[ The innermost regions were characterized by dimlight and high sedimentation\ resulting in a persistent layer of _ne sediment[ Withinthis microhabitat\ algae and sessile animals were absent and the walls were bareexcept for a few colonies of S[ beaniana "microhabitat II#[

2. Microhabitat selection

Corcyro`obius liechtensteini was the most abundant gobiid _sh within the sub!merged caves\ cavities\ hollows and crevices along the northern coast of Ibiza[ Thisspecies exclusively occurred in microhabitat I "Figs 1 and 2#[ The individuals movedupside!down in the thicket of P[ squamaria and M[ truncata[ The _sh hid insecondary holes and L[ lithopha`a bore holes on the ceilings and upper walls[ Thecollections in September showed no di}erence in the habitat selection of juvenileand adult specimens of either sex[

Dido`obius splechtnai occurred in the innermost parts of caves and crevices"Figs 1B and 3#[ All specimens were found on bottoms covered with _ne sediments"microhabitat III#[ The individuals stayed close to the bare rocky walls\ where theyused small holes as hiding places[ This species showed a preference for the darkestparts of caves[ The observations and collections revealed no di}erences in habitatselection by juvenile and adult individuals of either sex[

Table 0 shows the epibenthic\ cryptobenthic and hyperbenthic _sh species thatwere observed regularly in caves inhabited by C[ liechtensteini and D[ splechtnai[The most common _shes were a tripterygiid\ Triptery`ion melanurus Guichenot\0734\ represented by the subspecies T[ m[ melanurus\ and a blenniid\ Lipophrysni`riceps "Vincinguerra\ 0772#\ belonging to the subspecies L[ n[ portmahonisCastanos\ 0822[ While the former occurred not only on the ceilings but also on thewalls and on the bottoms\ the latter exclusively stayed on the ceilings and on thewalls\ where it used secondary holes and bore holes of L[ lithopha`a as hiding

Table 0[ Fish species which were frequently observed in the habitats of Corcyro`obius liechtensteini andDido`obius splechtnai[

habitat family species

cryptobenthic Gobiidae Gammo`obius steinitziBlenniidae Lipophrys ni`riceps portmahonisTripterygiidae Triptery`ion m[ melanurus

epibenthic Scorpaenidae Scorpaena notataScorpaena porcus

hyperbenthic Apogonidae Apo`on imberbisSerranidae Serranus cabrilla

Serranus scriba

Ecology of two speleophilic gobiid _shes 44

Fig[ 2[ Corcyro`obius liechtensteini in its typical microhabitat on the ceiling in the middle of a cave[ The_sh moves upside down between sponges and colonies of the bryozoans Sertella beaniana and Myriaporatruncata and hides in secondary holes\ which can be seen in the background[

Fig[ 3[ Dido`obius splechtnai inhabits caves with a soft bottom[ It is found on the bottom of theinnermost areas\ staying close to the rocky walls\ where it hides in secondary holes[ This microhabitatis almost free of sessile organisms[

Herler\ Patzner\ Ahnelt + Hilgers45

places[ Furthermore\ the gobiid G[ steinitzi was common but showed a preferencefor microhabitat II[

The epibenthic scorpaenids Scorpaena notata Ra_nesque\ 0709\ and Scorpaenaporcus Linnaeus\ 0647\ were frequent in all microhabitats[ While S[ notata usuallyoccurred on the bottoms\ S[ porcus also occupied the ceilings and walls[ Amongthe hyperbenthic _shes\ Apo`on imberbis "Linnaeus\ 0647# was frequent in caves\where it occupied the innermost regions[ The serranids Serranus cabrilla "Linnaeus\0647# and Serranus scriba "Linnaeus\ 0647# visited cavities and the front areas ofcaves[

3. Habitat choice under aquarium conditions

Both species clearly preferred dimly lit habitats within the aquarium "Fig[ 4#[ Theindividuals of C[ liechtensteini exclusively stayed on the ceiling "c:b and c:d#\

Fig[ 4[ Habitat choice of Corcyro`obius liechtensteini and Dido`obius splechtnai in an aquarium[b:b � bottom:bright^ b:d � bottom:dark^ w:b � wall:bright^ w:d � wall:dark^ c:b � ceiling:bright^c:d � ceiling:dark[

swimming around upside!down[ One D[ splechtnai individual spent half of its timenear the ceiling "c:d#\ where it rested on branches of M[ truncata\ but was neverseen swimming upside!down like C[ liechtensteini[ The other D[ splechtnai speci!mens spent most of the time on the bottom "b:b and b:d#[ On several occasionsthey swam up to the middle of the walls "w:d#[

4. Abundance and depth distribution

Table 1 shows the quantity of C[ liechtensteini observed or collected in the di}erentyears within cave 0:86^ the number varied from eight to 06 specimens[ The cal!

Ecology of two speleophilic gobiid _shes 46

Table 1[ Populations of Corcyro`obius liechtensteini in di}erent years in cave 0:86[ � � observationonly^ SL\ standard length

8:80� 8:84 8:85� 4:86 8:86

sex n SL in mm n n SL in mm n SL in mm n

juvenile 6[4Ð 8[4 1 01[3Ð03[1 3 6[6Ð02[9 5female 02[8Ð19[5 01 03[5Ð08[8 5 04[1Ð04[6 1male 03[7Ð19[3 2 Ð 9 05[2Ð10[9 3total 7 06 01 09 01

culated area of the ceiling and the upper walls of this cave is 0[1m1\ yielding anabundance of 5[6 to 03[1 individuals =m−1[

In caves of high abundances\ D[ splechtnai specimens kept distances of about9[4m from each other within the narrow region between the sand bottom andlower walls[ The abundance in this region was up to 1 individuals =m−1[

Corcyro`obius liechtensteini was frequent in depths between 4m and 14m\ butone of us "R[A[P[# also found this species in crevices at 9[4m and at 39[4m duringthe investigations in the years 0880Ð85[

In 0886\ D[ splechtnai populations were found in two big caves at 6m and 00mdepth[ The shallowest site was situated in 3[4m depth[ One of us "R[A[P[# alsoobserved single specimens in caves at 39m depth[

5. Reproduction, growth and longevity

The observations in May 0886 showed some specimens of C[ liechtensteini withtypical features for the breeding season[ Two males "08[8 and 12[3mm SL# hadelongated D0 rays\ with D0I reaching 16[3 to 17[3) of SL\ a well!developedurogenital papilla and a conspicuous coloration with a very dark head and enlargedblack spots on the branchiostegal membrane[ This species attains maturity at a SLof approximately 04mm[

Juvenile C[ liechtensteini were observed in September\ but not in May[ Fig!ure 5"A# shows _sh size in the _rst and the following years of life[ A rather longreproduction period is indicated by very small "6mm SL# juveniles in Septemberand the lack of distinct accumulations of specimens within certain size ranges[ InSeptember\ the o}spring of this year attained 6 to 01mm SL "9¦#[ One year later"0¦#\ most of the specimens measured between 02 and 07mm[ A small numbercan reach a second breeding season and attain a SL of 13mm[ Maturity is thereforereached when they are 0¦and the longevity for this species is about 1[4 years[Thus\ the value for the relation between the average adult lifespan and the age atmaturity is about one[

The overall sex ratio "females ]males#\ taking the catches of C[ liechtensteini from0880\ 0884 and 0886 as a whole\ is 1[47 ] 0[

Dido`obius splechtnai attains maturity at a SL of about 06mm[ Juvenilesoccurred in September\ but there were none in May[ In September of the _rst year

Herler\ Patzner\ Ahnelt + Hilgers47

Fig[ 5[ LengthÐfrequency distributions[ A] Corcyro`obius liechtensteini "n � 095# and B] Dido`obiussplechtnai "n � 11#[

"9¦#\ they reached 09Ð03mm SL "Fig[ 5B#[ In the autumn of the following year"0¦#\ they had grown to between 06 and 12mm[ Therefore\ they reproduce as 0¦_sh[ The third peak in the lengthÐfrequency distributions was built up by 06[8)of the collected specimens\ which survived a second breeding season and measuredbetween 15mm and 29mm[

Discussion

The investigations of marine caves in the Mediterrranean Sea by Abel "0848#and Riedl "0855# showed the blenniid L[ ni`riceps "as Blennius ni`riceps# and thetripterygiid T[ melanurus "as T[ minor Kolombatovic�\ 0780# as cave!dwelling specieswithin the benthic _sh fauna[ These species were designated as {speleophilic| byRiedl "0855# because of their permanent occupation of caves[ These authors didnot mention any gobiid species\ which exclusively occurred in caves[ Such crypto!benthic _sh are capable of dwelling in such ecotopes because of their small bodysize\ which permits exploitation of spatially restricted habitats "Miller\ 0868\ 0885#[According to Zander "0889#\ such cave!dwelling _sh belong to the mesolithion[

Ecology of two speleophilic gobiid _shes 48

Prior to the recent investigations along the northern coast of the Balearic Islandof Ibiza "Ahnelt et al[\ 0883^ Ahnelt + Patzner\ 0884\ 0885^ Patzner\ 0887a#\ amongthe Gobiidae only G[ steinitzi was known to inhabit submarine caves "Bath\ 0860#[In addition to this species also C[ liechtensteini and D[ splechtnai were found increvices and caves of bedrock in the North of Ibiza[ These three gobies were foundregularly within the suitable habitats[ Therefore\ the apparent rarity of such cave!dwelling gobies seems to be more an e}ect of inadequate sampling methods thanof natural causes[ A careful search by spreading quinaldine over large areas in anumber of di}erent habitats outside of caves in the years 0880Ð86 revealed no C[liechtensteini\ D[ splechtnai or G[ steinitzi "Patzner\ 0887a#[

A cryptic life habit among the Mediterranean gobies is especially known fromsmall benthic species of the genera Chromo`obius\ Milleri`obius\ Thoro`obius andZebrus "Miller\ 0875^ Ahnelt + Patzner\ 0885^ Ahnelt + Kovac³ic�\ 0886^ Patzner\0887a#[ Corcyro`obius liechtensteini\ the smallest _sh in the Mediterranean Sea\ D[splechtnai "³2[0 cm SL# and G[ steinitzi with an maximum SL of 2[5 cm representhighly specialized species among the small gobies because of their distinct crypticbehaviour[ During the recent investigations no adult or juvenile individuals ofthese three species were found outside of caves[ Although nothing is known abouttheir larval stages\ the positive phototactic behaviour of gobiid larvae\ as mentionedby Kinzer "0859# for several species\ could support the possibility that the larvaeleave the caves for a short planktonic stage[ Furthermore\ no C[ liechtensteinijuveniles smaller than 6mm and no D[ splechtnai smaller than 09mm were foundwithin the caves[ Juveniles of this size and larger can be found in the typical habitatof the adult specimens[

The microhabitat described for C[ liechtensteini corresponds with the typicalmicrohabitats of L[ ni`riceps and T[ melanurus "Abel\ 0848^ Riedl\ 0855^ Zander\0889#\ both also observed at Ibiza[ These microhabitats belong to the di}used lightzone "Riedl\ 0855^ Zander\ 0889#\ which receive less than 0) of the surface light[The positions of the microhabitats change within the four described habitats withincreasing water depth[ In deeper water regions they are found closer to theentrance because of the decrease of light and water movement within the cave\which limits the existence of algae and _lter!feeding organisms in the inner regions"Riedl\ 0855#[ In a similar manner to L[ ni`riceps\ C[ liechtensteini occupies smallholes such as bore holes of L[ lithopha`a within the caves\ which were describedby Abel "0848# using the term {cave in a cave|[ Corcyro`obius liechtensteini is foundnot only in small crevices but also in big caves\ where it occurs on the upper partsof the walls and on the ceilings in the upside!down position\ as is also known forblenniid\ gobiesocid and tripterygiid species dwelling in similar habitats "Abel\0851^ Riedl\ 0855#[ Upside!down positions were exhibited by G[ steinitzi too\ butthis species also occurs on the bottom\ especially of small caves[ Other gobiidsshow upside!down positions only during spawning "Kinzer\ 0859^ Ota et al[\ 0885#[The strong link of benthic _shes to the substrate leads to upside!down positionswhen occupying overhanging habitats "Abel\ 0851#[ Thus\ the upside!down posi!tions of C[ liechtensteini and G[ steinitzi can be seen as an adaptation to life on theceilings of cavities and caves[ Dido`obius splechtnai prefers darker microhabitatsand occurs in the innermost parts of the caves^ when pursued\ it also ~ed into smallholes[ This species never exhibited upside!down positions[

The restriction of C[ liechtensteini\ D[ splechtnai and G[ steinitzi to crevices and

Herler\ Patzner\ Ahnelt + Hilgers59

caves leads to an aggregated distribution[ For example\ C[ liechtensteini can attaindensities of 03[1 individuals =m−1[ This makes it di.cult to compare their abun!dances with those of gobies from more wide!ranging habitats\ which show a muchlower abundance per m1 "Gibson + Ezzi\ 0870^ Nash\ 0871^ Ahnelt + Kovac²ic�\0886#[

The rare occurrence of C[ liechtensteini in depths of less than 0m possibly re~ectsinfrequent observation because this species was also found in shallow water in thenorthern Adriatic Sea "Kovac³ic�\ 0886#[ The depth range of about 39m for all threespecies depends on the presence of suitable habitats and is restricted by _nesediment bottoms at depths of about 39m along the northern coast of Ibiza[Sympatric occurrence of all three species was observed in several cases and wasalso reported by Ahnelt + Patzner "0884\ 0885#[ Nevertheless\ the co!occurrenceof C[ liechtensteini and G[ steinitzi is more typical because\ unlike D[ splechtnai\they are not restricted to caves with a sediment bottom\ which are less frequent inthe north of Ibiza[ Within the caves\ the three species show a characteristic spacepartitioning\ with C[ liechtensteini occupying the front parts and G[ steinitzi inhabit!ing the interior parts of the ceilings and walls[ Dido`obius splechtnai only occurson the bottom of the interior parts[ The habitat of C[ liechtensteini overlaps withthat of G[ steinitzi in a narrow region[ The habitat choice of C[ liechtensteini andD[ splechtnai within the aquarium con_rmed the _eld observations[

The age at sexual maturity and the longevity of C[ liechtensteini and D[ splechtnaiare more similar to those of small\ short!lived epibenthic gobies like Pomato!schistus!species "Miller\ 0864\ 0868\ 0875^ Gibson + Ezzi\ 0870# than to those ofbigger\ cryptobenthic species "Miller\ 0850\ 0868\ 0875#[ The value of about onefor the relation between the average adult lifespan and the age at maturity for C[liechtensteini and D[ splechtnai is less than those of larger cryptobenthic gobies"Miller\ 0885#[ Despite a similar longevity\ more D[ splechtnai "06[8)# seem toreach a second breeding season than C[ liechtensteini\ in which most individualsdie after the _rst breeding season[ Such a mode of reproduction strategy with along breeding season with several spawnings and with a short adult lifespan\ whichcovers one or two breeding seasons is characteristic for species that were termedabbreviate iteropares by Miller "0873#[

The female ]male sex ratio of C[ liechtensteini is much higher than that of othergobiid species\ where the numbers of males are usually similar or exceed thenumbers of females "Miller\ 0850^ Gibson + Ezzi\ 0867\ 0870^ Nash\ 0871#[ Thishigh percentage of females may be an e}ect of too low numbers of collectedindividuals and the sampling method\ which did not include all specimens fromeach habitat[ Furthermore\ it is possible that the guarding males show a morecryptic behaviour during the breeding season and are therefore less frequentlycollected[

Summary

The investigations on the northern coast of Ibiza "Balearic Islands# showed themicrohabitat selection of two speleophilic gobies\ Corcyro`obius liechtensteini andDido`obius splechtnai[ Corcyro`obius liechtensteini occupied the ceilings\ where itstayed upside!down\ whereas D[ splechtnai was found on _ne sediment bottoms in

Ecology of two speleophilic gobiid _shes 50

the innermost parts of crevices and caves[ The microhabitat preference of bothspecies was con_rmed by habitat!choice experiments in an aquarium[ Corcyro!`obius liechtensteini was frequent in depths between 4 and 14m and showed abun!dances from 5[6 to 03[1 individuals =m−1[ The breeding season started in earlysummer and lasted several months[ The maximum size of 12[4mm SL was attainedafter approximately 1[4 years of life\ as revealed by lengthÐfrequency distributions[The overall sex ratio "females ]males# from catches of three years was 1[47 ] 0 forC[ liechtensteini[ Most D[ splechtnai were observed in caves at 6 and 00m depth[This species attained abundances of 1 individuals =m−1 within the caves and a sizeof 29[2mm SL at its maximum age of 1[4 years\ with 06[8) of the specimensreaching a second breeding season[

Acknowledgements

This work was partly supported by a grant of the International O.ce\ Vienna and by the Institute ofZoology\ University of Vienna[ The authors wish to thank Pamela Zolda and Anne!Marie Patzner fortheir help during the SCUBA dives[ We are grateful for the comments and suggestions made by P[ J[Miller and a second\ anonymous reviewer[

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