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 species (3 seem to community composition zona- studied Stolonifera, 4 Alcyonacea, 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, Anthozoa) 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 Downloaded from Brill.com10/11/2021 08:17:00AM via free access 2 S. WEINBERG - AUTECOLOGY OF SHALLOW-WATER OCTOCORALLIA 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 animals, 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 polyp, 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 Eunicella 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 •» Alcyonium 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 ). Downloaded from Brill.com10/11/2021 08:17:00AM via free access BIJDRAGEN TOT DE DIERKUNDE, 49 (1) - 1979 3 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