Bijdragen tot de Dierkunde, 49 (1): 1-15 1979

Autecology of shallow-water Octocorallia from

Mediterranean rocky substrata, I. The Banyuls area

by

Steven Weinberg

Institute of Taxonomie Zoology, University of Amsterdam, The Netherlands

In factors Abstract 1977). other cases specific environmental dictate and The autecology of eleven mediterranean octocoral (3 seem to community composition zona-

studied Stolonifera, 4 , 4 was near Gorgonacea) tion, such as water movement (Wedler, 1975;

Banyuls-sur-Mer (southern France). Field observations were Geister, 1977; Wiedenmayer, 1977), sedimenta- carried out by means of SCUBA-diving in forty underwater of deter- tion 1970; or stations. The ecological amplitude each species was (Chardy, Weinberg, 1978a) light

mined for number of abiotic viz. a factors, water temperature, (Roos, 1967; Harmelin, 1969; Chardy, 1970; submarine irradiance, water movement, slope of substratum True, 1970; Zander & 1970, 1977; Du- and sediment. In this the niche for the different Heymer, way ecological claux & Laf & Vasseur, 1973, species was defined. The niches of several species partly argue, 1972; Jaubert

the survival of these defined overlap: “strategy” species was 1974; Kinzie, 1973; Schuhmacher, 1973; Boutler as “competitivity”. Other species display “specialization”, a et al., 1974; Gamulin-Brida, 1974; Grigg, 1974; strategy by which they avoid competitive situations. A third survival mechanism is “opportunism”, encountered in species Wedler, 1975; Weinberg, 1975a, 1978a; Dana, which to their environ- are extremely tolerant with respect 1976; Zander & Jelinek, 1976). ment. Although experimental work is needed to determine how As most are not selection and physical parameters indepen- niche occurs, larval juvenile stages are con- it is often to state which sidered to be critical in this respect. dent, problematic para-

meters really determine community composition Résumé zonation. or Moreover, quantified measurements

Onze espèces d’Octocoralliaires méditerranéens (3 Stoloni- are often lacking, leading to rather subjective quali- fères, 4 Alcyonaires, 4 Gorgonaires) ont fait l’objet d’une fications of the physical environment. A final diffi- étude autécologique dans la région de Banyuls-sur-Mer. Dans in with is the fact that but furent effectuées culty dealing a community ce des observations à l’aide du scaphan- dre autonome dans quarante stations sous-marines. Les ampli- it is virtually impossible to study biotic interrela- tudes écologiques vis-à-vis des facteurs abiotiques suivants tions in nature. furent déterminées: température de l’eau, irradiance sous-

In an to tackle of these marine, mouvement de l’eau, pente du substrat et présence attempt part problems,

définir de sédiment. C’est ainsi qu’on a pu la niche écologique populations of mediterranean Octocorallia (Coe- de chacune des espèces. Les niches de plusieurs espèces se lenterata, ) were studied. Whereas in recouvrent partiellement: la stratégie de survie de ces espèces Octocorallian la caractérisées fact communities as a whole were est “compétitivité”. D’autres espèces sont par each la “spécialisation”, une stratégie qui leur permet d’éviter la observed (Weinberg, 1978a), populations of

Un troisième mode de survie est “l’opportunis- compétition. treated in the species are separately present paper, me”, qui exige des espèces en question d’être extrêmement that the of other does tolérant vis-à-vis de leur environnement. Bien qu’un travail assuming presence species expérimental soit nécessaire afin de déterminer comment not interfere with them. This was done for two s’effectue le choix d’une il est probable les stades niche, que if it is reasons. Firstly even reasonable to suppose larvaires rôle très à et juvéniles jouent un important ce propos. that species interaction actually occurs, through

spatial competition or biochemical repulsion for I. INTRODUCTION there is without instance, no means, experimenta-

Submarine communities to determine in that the main are very complex systems. tion, way. Secondly

In of this is which most cases a depth-dependent zonation has been purpose study to assess abiotic

environmental determine the demonstrated (Roos, 1964; Loya, 1972; Schmidt, parameters presence

Van den and 1972; Castric-Fey et al., 1973; Bak, 1975; or absence of a species, on a more detailed

Hoek et al., 1975; Wedler, 1975; Burla et al., level, which are the ecological amplitudes (toleran-

1976; Benayahu & Loya, 1977; Wiedenmayer, ces) of each species for those parameters.

I

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METHODS These II. MATERIAL AND calculated for each station. parameters are:

average summer temperature (in °C), submarine Forty underwater stations were sampled near 2 daylight (average yearly irradiance in cal cm Banyuls-sur-Mer (France). For a detailed descrip- 1 ), water movement (in four classes), tion and comparison of the stations see Weinberg year average absence slope (in five classes), or of ( 1978a). Sampling consisted of counting the Octo- presence and For detailed within sediment, depth (in m). a ex- corallia a quadrat surrounded by a square planation of methods and results, see Weinberg PVC frame of 50 X 50 cm for communities of (1976b, 1978a) and Weinberg & Cortel-Breeman large, sometimes sparsely distributed , and

These results are summarized in 4. PVC frame of 20 20 for "minia- (1978). fig. a square X cm

Although the forty underwater stations were turized" communities of smaller, more crowded originally characterized by five classes animals (surf zone, caves). Number of animals slope

individ- (Weinberg, 1978a: table 3), these were partly (colonies) was counted and expressed as

2 united in the to form the uals m . In the case of intermingled, encrusting present paper following

three classes: (1) horizontal or ver- colonies (some Stolonifera and Alcyonacea) distinc- sloping, (2) tical cracks and holes. tion or overhanging, and (3) between individuals was made by pinching the Each station was further classified according to one , and counting all the subsequently con-

or absence of sediment, whereas the tracting polyps as belonging to the same colony. presence classified of all stations water movement was into one Ten counts were made at while staying average the following four categories: weak well within the borders of each community, to- (1) (0-100 h -1 h 1 m ), (2) moderate (100-200 m ), (3) gether forming the sample of that station. Its size, h 1 and turbulent 2 strong (200-350 m ) (4) (>350 4000 cm for "miniaturized" communities and

1 m h 2 for ). 25000 cm open communities, corresponds

with the most conservative estimates on the minimal III. SPECIES-PARAMETER RELATIONSHIPS area in these habitats (Weinberg, 1978b). that As an example of the type of relationship The following species were studied (the abbre-

used in and exist between the success (measured as viations are the figures tables through- may pop- of and its ulation density) a species abiotic environ- out this article) : ment, I take the gorgonian singularis.

Stolonifera: Since this is the most common octocoral in the

CC = Cornularia cornucopiae (Pallas, 1766) I area prospected, possess more data concerning CO — Clavularia ochracea Von Koch, 1878

of this than of the other ones. RR = the Roland ia rosea (Philippi, 1842) ecology species

Fig. 1 shows population density as a function of Alcyonacea: for the stations average summer temperatures forty PC = Parerythropodium coralloides (Pallas, 1766) considered. For each interval there are AA •» acaule Marion, 1878 temperature

ME = Maasella edwardsii (De Lacaze-Duthiers, 1888) stations with greater or smaller population den-

PS = 1822) Paralcyonium spinulosum (Delle Chiaje, with sities. However, if one considers the stations

maximum for a interval, Gorgonacea: population density given

= Eunicella 1794) which in ES singularis (Esper, are joined by a line the figure, one LC = Lophogorgia ceratophyta (Linnaeus, 1758) obtains a curve roughly representing a probabilistic PMC — Paramuricea clavata (Risso, 1826) Whereas at summer tem- CR = Corallium rubrum (Linnaeus, 1758) relationship. average

peratures higher than 20.1 °C the species apparently

The habitus of colonies of each is does species quite not occur (higher average temperatures were

in but distinctive in shape as well as colour, so that not found, the decline of population density confusion in the field is unlikely to occur. The between 19°C and 20°C strongly suggests that at taxonomie references used were those of Weinberg higher temperatures the species does not encounter

(1976a, 1977, 1978c). its optimum conditions), at the lower end of the

with number fair Together the faunistic inventory a scale (13.8°C) the species can still occur at

2 of environmental parameters was recorded and/or population densities (about 20 individuals m ).

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Number of colonies of Eunicella function of T Fig. 1 (top). singularis per m² (N) as a average summer temperature at

different indicate = weak, = moderate, = and = turbulent. Line forty stations. Symbols water movement: w m s strong t

joins stations with maximum population densities, the dotted line is a tentative extrapolation for lower temperature intervals.

of Fig. 2 (bottom). Number of colonies of Eunicella singularis per m² (N) as a function average yearly irradiance (I),

1. For explanation of symbols see fig.

the these conditions The dotted line is a tentative extrapolation of stations, although temperature are

curve obtained. These data suggest that although optimal, other conditions are not, thus restricting

able live at all local Eunicella If this is the the line in to temperatures, population density. case,

singularis flourishes between 16°C and 19°C. On fig. 1 joins those stations where the parameters

the other hand, even within this optimum tem- other than temperature reach (near) optimum

low densities and values. perature range population occur, Average summer temperature being depth-

at two stations the species does not occur at all. dependent (Weinberg, 1978a), water movements

This fact can be explained by assuming that at may also be expected to increase from left to right

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in fig. 1. This indeed seems to be the case. The Fig. 3 shows three histograms. The left one

therefore also be the stations curve obtained might a tur- depicts average population density at

with and bulence-dependent one. weak, moderate, strong turbulent water

E. thrives in Fig. 2, showing population density as a function conditions, respectively. singularis the of follows middle in smaller yearly submarine irradiance, a pro- two classes, occurs quantities babilistic well. Eunicella when is weak pattern as singularis occurs average water movement (but as we

cal 1 with this is between 20 and 25000 a have seen be due to irradiance) and cm^year , may maximum for values between 300 and 2500 cal lacking at stations where turbulent water conditions

1 cm^year . Irradiance, however, is not solely depth- are encountered. Here also the general shape of the dependent, as more or less shaded stations are histogram suggests a probabilistic relationship, or included in the Water with the wherever survey (Weinberg, 1978a). a binary one, species occurring movement, as indicated by the symbols in the water conditions are not turbulent.

is with irra- central in graph, not correlated average yearly The histogram fig. 3 shows the av- diance. It therefore becomes apparent now that erage population density as a function of slope at all the stations with turbulent water movements, the stations concerned. Five slope-classes were

devoid E. used: irrelevant of light conditions, are of horizontal (0-30°), sloping (30-60°), ver-

absent from tical singularis. The species appears to be (60-90°), overhanging (>90°), cracks and turbulent On the weak obtained waters. other hand, water holes. The histogram suggests a rather

below movements occurring certain depths are linear relationship: as substratum becomes more correlated with weak irradiance. The fact that the horizontal, population density increases. population density is rather low at stations with An explanation for this relationship is given by weak water movements probably depends on the the right histogram. At stations retaining sediment

these their low irradiance values at stations. on substratum (predominantly horizontal and

sloping ones) average population density (28.1

2 is than times individuals m ) more fifteen that at

2 stations devoid of sediment (1.84 individuals m ).

There seems to be a nearly binary relationship with

In sediment. a true binary relationship no Eunicella

at all would have been found in the class "without

sediment". It must be stressed, on the other hand,

that sediment is always present in minute quantity.

In this way, the existence of three types of relation-

ships is demonstrated: a probabilistic one with

temperature and irradiance (and possibly water

with movement), a gradual (linear?) one slope,

and a binary one with sediment (and probably

with water movement as well).

In the following section population density of

each species is given as a function of these different

For and parameters. temperature irradiance a

simultaneous graphical representation is given.

of Therefore, the underwater are re- Fig. 3. Histogram showing average population densities forty stations Eunicella singularis as a function of different in parameters. presented a graph (fig. 4) where in addition Numbers indicate number of stations into each falling para- to their in the defined place plane as by average meter class. The first histogram shows water movement with

classes: = summer the W M = S = irradiance and following weak, moderate, strong, yearly average temperature,

T = turbulent. The second histogram shows of sub- slope each station has been characterized by its water

= with the classes: h = = stratum, horizontal, s sloping, v its movement, slope and the or absence = and = presence vertical, o overhanging c cracks and holes. The of sediment. At number of stations third histogram shows sediment: + = present, — = absent. a light and

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defined Fig. 4. Representation of the forty stations in the plane by yearly irradiance (I) and summer temperature (T). Each

and absence sediment indicated of Water symbol represents one station. Slope classes presence or of are by means symbols.

= = = = turbulent. movement is indicated by lettering: w weak, m moderate, s strong, t The sigmoid curve joins open

of sediment. Other stations receive less light than the horizontal or gently sloping stations, most them retaining possible lack maximum at each corresponding depth. Most of these stations are not horizontal and sediment.

both with IV. ECOLOGY OF THE SPECIES temperature are interdependent, as vary

depth. This is the case for most horizontal and 1. Temperature and irradiance slightly sloping bottoms. The graphic representa- As can be seen in 5, each has its own tion of the fig. species values displays a one-sided boundary the factors water tem- in which demon- requirements regarding the shape of a sigmoid curve perature and submarine daylight. Cornularia cornu- strates the existing relationship between the copiae and Clavularia ochracea are obviously sur- logarithm of irradiance (which decreases almost face animals living above the thermocline, but with linearly with depth) and summer temperature irradiance conditions. Rolandia of the a large tolerance to (which is S-shaped because thermo- coralloides This is also valid for rosea and Parerythropodium are cline). relationship open very and under all tolerant, occur virtually circum- water. The other stations have exposition co-

the former is not found in efficients smaller than 1, and are therefore stances, although very

with situated the left of the with shallow stations an average summer tem- at curve, corresponding be for dark the above 19°C. The same can said stations as compared to surrounding open perature which in stations with water. In the next section dealing with the ecology Alcyonium acaule, occurs

is medium does of the species, the same graphical representation irradiance values, as Maasella ed-

but the stations the wardsii. in used, are characterized only by Paralcyonium spinulosum occurs deeper,

absence of darker is presence (and population density) or places. Eunicella singularis quite tolerant,

each species. but thrives on (sub)horizontal stations which are

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5. absence Fig. Presence (closed symbols) or (open symbols)

of the eleven species in the forty stations studied, in a

graphical representation analogous with fig. 4. Numbers indicate population densities of each species (in colonies m²)

at those stations where they occur.

the represented by points situated on (or near) boundary values, differs significantly from the

the of of sigmoid curve forming right-hand border ones outside (e.g. is the population density

Maasella edwa dsii the cloud of points. The same is even more true r between yearly irradiance values

Paramuricea lavata and cal 1 dif- for Lophogorgia ceratophyta. c of 330 10000 cm significantly

band of conditions ferent from the ones below 330 and over 10000cal tolerates a very narrow light

Corallium 1 only, but is quite tolerant to temperature. cm^year ?). The aim of the first analysis is to

darker show whether rubrum is found exclusively in cooler, threshold values exist, below or over

of stations. which a species occurs most the time, whereas

will be what It now examined the ecological the second analysis may yield an optimum range the factors for defined and lower threshold optima are for each species regarding a species, by upper

For carried and water temperature and submarine daylight. this values. Analyses were out by computer,

variance have been carried all values combinations thereof in purpose, analyses out, boundary (or the main principles of which are briefly outlined the second analysis) were scanned automatically

used. One chosen here. Two types of analyses were was over the following ( arbitrarily ) values.

For a one-boundary variance analysis, investigating average summer temperature: 13, 14, 15, whether the population density of a species on one 16, 17, 18, 19, 20 and 21°C.

value differs For irradiance: side of a given boundary significantly average yearly 0, 10, 330, 1000,

the and from the population density on other side 3300, 10000, 33000 100000 cal cm 2year i.

is the Each (e.g.: population density of Clavularia choice of a boundary (or two boundaries)

stations with the data in which ochracea at an average summer tem- divides two (or three) intervals,

different from the the be perature

in with number 1 one stations an average summer tem- of observations ) within each interval perature> 16°C?). The other was a two-boundaries variance whether the analysis, investigating pop- J) Each observation is the of population density a given ulation densities of a species between two given species in a given station.

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depends on the boundaries chosen, and is not ne- probability of 99% to find the species over

the Two can now be the entire cessarily same. hypotheses temperature range.

formulated: Alcyonium acaule:

— the means of the observations are the same j<19 (P< 1%) (F = 8.01 ) within each interval for < 18 = highest probability y (F 10.41)

— the means of the observations in the various Maasella edwardsii: intervals differ from each other. 14 < < 18 and 18 y y < (P<1%)

< 19 < The first can be tested J (P 5%) hypothesis (H 0 ) through

the magnitude: Paralcyonium spinulosum:

k 16<;/<17 (P< 1%)

S 2 (xk x) •*/(* 1) <18 j (P < 5%) 1 F= Eunicella singularis : k nk

2 16 < < 19 = S S j (P<1%) (F 6.01) (xi» x fc) /(« —*)

1 ;= 1 >-<20 (P < 5%)

where: = number of = number of for 17 < < 18 intervals [(k-1) highest probability j boundaries] (F = 11.67) n = number of cases (stations)

n = number of cases interval k k belonging to Lophogorgia ceratophyta:

x = value for station ; and interval k ilt < 14 = y (P<1%) (F 10.08)

= for k Xft mean interval 7 <19 (P< 5%) x = total mean for all the intervals

F Paramuricea clavata: has (n-k) and of freedom. H can be (£-1) degrees 0 rejected

in the case of the test = 40, k= for F one-boundary (« 2) no conclusion possible with a probability of (38.1): 95% or better, which means that there is a if F > 4.06 (error probability P < 5%) find probability of 99% to the species over if F > 7.36 (error probability P < 1%) the entire temperature interval. and in the case of the two-boundaries test (» =40, £= 3)

for F (37.2): Corallium rubrum:

if P 15 < <16 F > 3.25 (error probability < 5%) y (P< 1%) (F= 29.27) if F > 5.24 (error probability P < 1%) y <17 (P<5%)

These calculations yielded the following results

These results are in 6. in relation to the represented fig. average summer temperature (in

where stands for the interval °C), y temperature

within which each species is mostly found, and P

the corresponding error probability according to

the F-values calculated.

Cornularia cornucopiae:

18 < and 18 <19 < ƒ <7 (P 5%J

Clavularia ochracea:

< = 20 y (P< 1%) (F 14.71)

17 < y (P

Rolandia rosea:

17

for < < highest probability 17 y 19

(F = 4.59) for Fig. 6. Probability intervals the occurrence of each species

(for code see as a function of Parerythropodium coralloides : species text) temperature

(linear scale) and depth. Thin lines show 95% probability no conclusion possible with a probability of interval, thick lines 99% probability interval as calculated by 95% or better, which means that there is a means of variance analysis.

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irradiance 2 When regarding yearly (in cal cm

1 the results where year ) following were obtained, z stands for the irradiance interval within which each species is mostly found, and P is again the corresponding probability.

Cornularia cornucopiae:

2 < 330 (P< 5%)

Clavularia ochracea:

no conclusion possible with a probability of

which that there is 95% or better, means a Fig. 7. Probability intervals for the occurrence of each species

(for species code see text) as a function of irradiance. Thin probability of 99% to find the species over lines show 95% probability interval, thick lines 99% prob- the entire irradiance interval. ability interval as calculated by means of variance analysis.

Rolandia rosea:

2. sediment and movement 330 3300 (P< 5%) Slope, water

As was shown in section 11, the following Parerythropodium coralloides: para- meter classes were distinguished. For slope: (1 ) no conclusion possible with a probability of

horizontal vertical or is or sloping, (2) overhanging, 95% or better, which means that there a and (3) cracks and holes. For sediment: (1) probability of 99% to find the species over

and absence. For water movement: the entire irradiance interval. presence (2) (1) weak, (2) moderate, (3) strong and (4) Alcyonium acaule: turbulent. and z < 1000 10 < z < 1000 (P<1%) For each of the above parameter classes the

Maasella edwardsii: is percentage of stations where a given species

330

2 calculated. species m at those stations was Paralcyonium spinulosum: per number These data combined yielded the average 2<330 (P

330 < z < 3300 and 1000 < z < 3300 from which the optimum intervals of the different

(P< 1%) each species for parameter can be deduced. 330 (P < 5%)

V. RESULTS highest probability for 330 < z < 3300

(F = 8.03) The ecological amplitudes of the different species

are given in this section, partly based on the results Lophogorgia ceratophyta : the of preceding paragraph, partly on what is no conclusion possible with a probability of known about the communities (Weinberg, 1978a), 95% or better, which means that there is and partly on incidental observations. the a probability of 99% to find species over

the entire irradiance interval. 1. Cornularia cornucopiae

Paramuricea clavata: This species was found between 0 m depth (Grotte

and z < 330 (P< 1%) de Béar, Grotte du Troc) 22 m depth (Cap

surfaces and the 10 < z < 330 (P< 5%) l'Abeille), on rocky on tunicate

It Microcosmus spp. is encountered above the ther- Corallium rubrum : mocline, the minimum summer temperature ob- z <10 (P<1%) (F = 55.26!) served being 17°C and it is found in strongly z < 330 (P< 5%) moving or turbulent waters, mostly in dark places

1 These results are represented in fig. 7. (<330 cal cm-äyear ), although it is found in

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species slope sediment water movement

h + s v + o c + h - + W M S T

CC 0.03 2.07 0.00 1.48 0.03 0.00 0.81 1.20 1.06

CO 6.18 30.59 0.00 23.93 4.89 0.00 9.64 8.90 41.42

RR 3.72 1.92 1.34 1.93 3.74 0.65 3.02 4.65 1 .87

PC 6.06 14.53 28.33 16.13 6.22 13.45 7.29 6.45 18.70

AA 5.72 2.76 1.67 1.97 6.96 5.36 6.68 3.55 0.00

ME 6.62 1.92 0.00 1.25 7.95 4.48 5.87 6.20 0.00

PS 1.08 2.24 10.00 3.02 1.28 6.88 2.14 0.19 0.00

ES 21.65 4.61 0.67 1.94 26.70 3.93 20.96 20.10 0.00

LC 3.85 0.04 0.00 0.03 4.41 1.82 2.68 3.30 0.00

PMC 0.11 11.21 0.00 7.89 0.13 0.28 9.12 2.64 0.00

CR 0.00 19.86 136.00 33.63 0.00 58.48 18.34 0.00 0.00

TABLE I

of the different colonies stations various classes. For Average population density species (in m²) at belonging to parameter

= = slope: h + s = horizontal or sloping, v + o vertical or overhanging, c + h cracks and holes. For sediment: + pres-

= = = = = — absence. W M T turbulent. code ence, For water movement: weak, moderate, S strong, For species see text.

with cal 2 places irradiances of up to 10000 cm 3. Rolandia rosea

1 . As a result, it encounters optimum living year Found from 7.5 m (Jetée Port Vendres) to 38 m conditions the vertical walls of on or overhanging it tolerates wide of depth (Cap l'Abeille), a range near-surface where it is found with caves, together irradiance temperature (14-19°C) and (60-2500 Clavularia ochracea and coral- Parerythropodium cal 1 is cm ) conditions, although it most often It with loides. occurs rather sparsely, population found in places not too dark and just below the 2 densities never exceeding 10 colonies m . thermocline, thereby avoiding turbulent surface

conditions. It is encountered as inconspicuous warts

rocks and 2. Clavularia ochracea or stoloniferous growths on of

the but is able form Microcosmus, to respect- This species was also found between 0 m (Grotte membranaceous dead able encrustations on gor- de Béar, Grotte du Troc) and 22 m (Cap Rédéris),

axes of Eunicella see the substrata gonian (mainly singularis), on same as the preceding species and Plate III It the Weinberg & Weinberg (1979: C). may once on decapod crustacean Pisa nodipes Leach, the latter that this be for reason species seems to 1816 (fig. 8). It likewise lives above the thermo- occur mostly in places with sedimentation (see cline (>17°C), mostly occurring in turbulent sur- section V.8), but the also thrives in turbid face waters (>20°C). Although being rather in- species and slightly waters. This is demonstrated different to irradiance conditions (it is found in polluted by the fact that the population densities places with irradiance values of between 30 and greatest colonies 2 found outside the cal 1 it in (17-20 m ) are just 10000 cm^year ), never occurs per- harbour entrance of Port Vendres. manently sunlit places but is able to form extensive

of 2 patches over 100 colonies m on the vertical of 4. Parerythropodium coralloides and overhanging walls near-surface caves, where it is encountered together with Cornularia cornu- Encountered in depths from 0 m (Grotte de Béar)

40 It is copiae and Parerythropodium coralloides. to m (Cap Béar). extremely tolerant to a

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upright lobes reminiscent of Alcyonium, and as an

in encrusting epibiont on gorgonians, especially

deeper waters (cf. Weinberg & Weinberg, 1979:

Plate HIB, D). Differently coloured specimens

occur in the same area (Weinberg, 1975b, 1977).

Wine-red colonies are the most common ones and

found Pink colonies occur are at every depth.

deeper than c. 15 m, while white ones are en-

countered below c. 25 m only.

5. Alcyonium acaule

This species is quite tolerant, except for turbulent

surface conditions, and as a result it is found in

waters with summer temperatures of below 19°C

and yearly irradiance values of below 2000 cal

2 1 with for stations with values cnr year a preference

of below cal 1 It from 10 m 1000 cm -year . occurs

depth (Ile Grosse, incidental observation) to 40 m

with depth (Cap Béar) on all slope types a max-

imum on horizontal and sloping bottoms contain-

ing sediment. High population densities (20-30

colonies 2 encountered with nr ) were at places a

regular, moderate to strong, current (Cap Béar,

Cap Rédéris). ochracea Fig. 8. Small colony of Clavularia on the crab Pisa nodipes Leach, 1816. Polyps (p) and stolon (s) are visible.

the 6. Maasella edwardsii It is not sure whether the stoloniferan actually settled on decapod crustacean, as the latter is known to camouflage itself Encountered from 2 m depth (Grotte de Béar, with of small pieces sponge or sea-anemones by actively incidental to detaching them from their natural substratum and transferring observation) 32 m depth (Cap them its This found 13 onto carapax. specimen was at m l'Abeille), the species is seldom found in shallow depth at Cap du Troc, Banyuls-sur-Mer (Photograph: Louis water, and although occurring from 14.4° C to van der Laan). 19.8° C it mostly occurs in cool to medium tem-

conditions and medium ir- perature (14-18°C) wide range of temperature and irradiance (30- radiance values (100-2500 cal cm^year 1 ). Al-

1 2300 cal cm^year ) conditions, as well as to tur- though difficult to discern underwater, the small

and It in with bulence slope. is found on such different brown colonies occur populations densities substrata as tunicates Microcosmus to colonies One incidental observation 32 m2. rock, ( spp.), up shells ( Pteria hirundo (Meuschen, 1787)) and (see above) excepted, the species is not found in gorgonians (Eunicella singularis, Lophogorgia turbulent water conditions. It thrives on horizontal

where is ceratophyta. Paramuricea clavata). Although table or sloping sediment-covered bottoms, it

I cracks and this with suggests an optimum for holes, invariably found together the gorgonian Euni- impression results from the fact that number of cella singularis. colonies counted instead of was percent coverage. 7. Paralcyonium spinulosum The highest population density (85 colonies m 2)

encountered in small holes but This from was at Cap Rédéris, species occurs 15 m (Cap Rédéris)

colonies. known these were small, wartlike The species downwards, but is mostly from deeper finds its optimum conditions in turbulent surface waters. It lives below the thermocline (<18°C) caves, like the Grotte de Bear, where it is able to in rather dark places (60-400 cal cm-Syear 1 ) form large encrusting colonies sometimes forming although incidentally encountered in places with

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irradiance much cal 1 share Eunicella’s niche on hor- 1500 . values of as as cm^year orange gorgonians in Previously described as exclusively hypolithic (Lau- izontal and sloping sediment-covered bottoms,

this situated in It thrives bier, 1966), it was found on all slope types, case depths over 10 m.

and although apparently being more common in cracks on mud-covered deep places, reaches high

with in No and holes weak or moderate water movement population densities cooler waters. cor-

and without sedimentation. Thebeautiful transpar- relation with submarine irradiance has been estab-

stations ent colonies are not often found in the Banyuls lished, but fig. 5 shows that it occurs in

densities with irradiance values of between 140 and 2600 area, but may occur in population reaching

2 1 30 colonies nr cal and from warm and turbulent (Cap Rédéris). cm^year , apart

wide of and waters, tolerates a range temperatures 8. Eunicella singularis water movements.

studied The most common species in the area

10. Paramuricea clavata (these white gorgonians occur at 27 out of 40

it densities surfaces stations) reaches very high population Typical for vertical and overhanging

2 and 26 (up to 84 colonies m ) over large areas (several between 13 m depth (Cap Béar) m depth

hectares the where the reaches den- at many places along coast), thereby (Cap Rédéris), population

2 often the of the under- sities of to 55 colonies m it is also found in determining general aspect up ,

1979: much smaller numbers horizontal and water scenery (see Weinberg & Weinberg, on sloping

with plate lA). It is virtually absent from places bottoms in deeper waters (32-38 m at Cap l'Abeille

turbulent surface conditions and As the (although one colony Cap Rédéris). a result, species appears

the Grotte de and the was observed at 2 m depth at Béar), to be indifferent to temperature conditions,

and reaches maximum population densities in stations whereat it occurs share only one condition:

1 places with medium summer temperature values a low level of irradiance (<330 cal cm^year ).

A the In 5 of 120-330 (16-19°C). phenomenon occurring during fig. an even more narrow range

cal 1 is In summer of 1973 has given another indication of its cm^year apparent. this respect E. sin-

tolerance. P. temperature During a long period with- gularis and clavata have opposite demands, as out wind, the water layer above the thermocline was confirmed by measurements at the boundary

heated above 24°C. All the of different The was up to temperatures two specifically populations. colonies of Eunicella died in this zone (observa- population of Eunicella received 3-3 times the tions at Jetée Port Vendres, Cap Béar, Ile Grosse amount of light than the population of Para- and Cap Rédéris), while colonies of Lophogorgia muricea, although the measurements were carried ceratophyta survived these extreme conditions out a 50 cm from each other (Weinberg, 1975a).

(Weinberg, 1975a). Although encountered at The purple colonies of Paramuricea are not found

with 2 in places irradiance values of 30-10000 cal cnr surface caves probably because of turbulent con-

1 the species thrives in places with irradiance ditions. year , conditions of 330-3300 cal 1 At two sta- cm^year . 11. Corallium rubrum tions where the population extended from deeper

certain limit water upto a (5 m at Ile Grosse and Absent from horizontal and sloping sediment-

irradiance conditions this is in 13 m at Cap Rédéris), the covered bottoms, species found deeper were quite similar in both (2359 and 2586 cal water, mostly below the thermocline. It thrives in

1 2 cm^year respectively). The species occurs mainly dark places with irradiance values <130 cal cnr

horizontal and 1 and is found in weak on slightly sloping sediment-covered year or moderate water bottoms. conditions exclusively. Unfortunately, Corallium is

the In- an endangered species in area studied. 9. Lophogorgia ceratophyta considerate divers do great damage to populations

Although not as common as the previous species of this species, as the colonies are favourite sou-

13 40 with maximum venirs. ( it occurs at out of stations, a Now, the populations mostly consist of

2 of 17 colonies nr these tall small 7-8 with population density ), (on average cm high) colonies, an

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estimated of 20-30 colonies to those of other in this age years. Large gorgonians study, probably

has vulnerable larval and estimated to be over a century old are not to be more young stages.

found The be saved the Whether the found for each environ- any more. species may by ranges

mental reflect the adult establishment of a protected area (Réserve Marine parameter tolerances of

de Banyuls) which is effectuated in January 1979- colonies, or whether they rather reflect the require-

ments of larval and juvenile stages cannot be determinedwithout experimentation. However, the VI. CONCLUSIONS AND DISCUSSION than youngphases being infinitely more vulnerable

underwater Field observations at a large number of the adult colonies (Weinberg & Weinberg, 1979),

stations led to the recognition of optimum intervals they probably determine where, and to what extent,

for a number of abiotic factors for each octocoral a species survives.

species studied. Species that tolerate extreme conditions (Cornu-

Correlations with laria and Clavularia in surface Corallium most physical parameters con- caves,

dark reach the cern average values of the latter. Extremes may in very places) highest population

play a far more important role, but these values densities observed, simply because there is little

difficult in with for either octocorals are to assess. However, places competition space, by or by

other is the high average values maxima are more likely to organisms. The opposite displayed by

than in with low and This is occur places average values, alcyonacean Parerythropodium. species not

in- vice versa. The correlations therefore clearly particular about its abiotic environment, which

dicate in what is sensitive for enables it lead life. Wherever way a species a given to an opportunistic

parameter. a suitable substratum becomes available (and the

the is restricted this Although each spines (with possible ex- species not very in respect either),

ception of Parerythropodium coralloides; see it is able to settle.

below) has its own ecological niche, it will tolerate

Three different survival strategies are thus revealed: other species well in the case that their niches

the co-existence the overlap. Examples: of Clavularia, competitivity: species are wel equipped for

Cornularia and Parerythropodium in surface caves; certain environmental conditions. In their

or the communities from deeper waters of Eunicella niches they are able to compete with the other

This is and Lophogorgia on horizontal bottoms, often species. the mechanism mostly dis-

associated with Maasella and/or Alcyonium (see played. Typical species: Alcyonium acaule,

also Weinberg, 1978a). This may be due to the Maasella edwardsii, Eunicella singularis Para-

fact that all the species studied are filter feeders, muricea clavata.

each them which — the well for of possessing polyps are equally specialization: species are equipped

well equipped for the capture of plankton and extreme environmentalconditions where others

this do not particulate organic matter; in way, they cannot live, and thus they monopolize or do-

with really compete each other. minate the corresponding niche. Typical exam-

The observed differences in maximum Corallium rubrum. pop- ple: ulation density between species are therefore not opportunism: the species are not particular in the result in their able of differences ecological amplitude, requirements. They are to settle and but rather reflect differences in recruitment and survive under most environmental conditions. vitality. Large gorgonian colonies, with thousands The fact that they hardly ever become dominant

is due of polyps, emit scores of planula larvae, thus in- to the competitivity of other species.

the number number creasing of potential settlers, a Typical example: Parerythropodium coral- impossible to meet for the smaller alcyonacean loides. and stoloniferan colonies. On the other hand, Lo- phogorgia which in spite of its large colonies (with Many species show combinations of these strate-

estimated 10000 for Clavularia ochracea for is an polyps an average colony) gies. instance, a specialist surface does not occur in population densities comparable in caves, but a competitor in deeper habitats.

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The mechanisms involved with the selection of GAMULIN-BRIDA, H., 1974. Biocoenoses benthiques de la Mer

Adriatique. Acta 15 1-102. The Adriat., (9): a niche are still not known. importance of The influence of GEISTER, J., 1977. wave exposure on the larval and in this respect has still to juvenile stages ecological zonation of Caribbean coral reefs. Proc., 3rd with octocorals be shown. Though experiments are internat. Coral Reef Symp., Miami: 23-29.

and the is the ideal GRIGG, R. W., 1974. Growth rings: annual periodicity in two not easy to carry out, sea not Gorgonian corals. Ecology, 55 (4): 876-881. place for experimental work, I have attempted to des HARMELIN, J.-G., 1969. Bryozoaires grottes sous-marines these will be the clarify some of They aspects. obscures de la région marseillaise. Faunistique et écologie. subject of future publications. Téthys, 1 (3): 793-806.

C. A. M. CORTE HOEK, VAN DEN, L-BREEMAN & J. B. W.

WANDERS, 1975. Algal zonation in the fringing reef of ACKNOWLEDGEMENTS Curaçao, Netherlands Antilles, in relation to zonation of

of corals and gorgonians. Aquatic Sincere thanks are extended to Dr. Jacques Soyer, Director Botany, 1: 269-308.

the Laboratoire Arago in Banyuls-sur-Mer, for his kind hos- JAUBERT, J. & P. VASSEUR, 1973. Essai d'interprétation de

facilities certains Grand Récif pitality and the use of his laboratory during my peuplements sciaphiles du de Tuléar

wife of the à des variations visits. My helped me with an important part (Madagascar) partir d'enregistrements

carried de l'éclairement. underwater work. Nearly all of the present study was C. R. Acad. Se. Paris, 276 (D): 2059-

with the faithful at 2062. out "CIAO", a ship generously put my

father. Strauss-Kahn duration and disposal by my Dr Dominique helped & , 1974. Light measurements: aspects distribution with the statistics. Prof. Dr. Jan H. Stock and Prof. Dr. C. the of benthic organisms in an Indian Ocean

for of coral reef 2nd Coral den Hartog are acknowledged their critical review the (Tuléar, Madagascar). Proc., int. manuscript. Mr. Hans Moll kindly polished the English text. Reef Symp., Brisbane: 127-142.

87-117 from KINZIE, A., This research was carried out under grant the R. 1973. The zonation of West Indian gorgonians.

Pure 23 Netherlands Organization for the Advancement of Bull. mar. Sei., (1): 93-155.

Research (Z.W.O.). LAUBIER, L., 1966. Le coralligène des Albères. Monographie

biocénotique. Ann. Inst, océanogr., Paris, 43 (2): 139-

316.

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