Seasonal Variation of Fish Assemblages in the Loano Artificial Reef (Ligurian Sea Northwestern-Mediterranean)

BULLETIN OF MARINE SCIENCE, 55(2-3); 401-417, 1994

SEASONAL VARIATION OF FISH ASSEMBLAGES IN THE LOANO ARTIFICIAL REEF (LIGURIAN SEA NORTHWESTERN-MEDITERRANEAN)

Marco Relini, Giovanni Torchia and Giulio Relini

ABSTRACT Thirty months after the construction of the Loano artificial reef a study of fish abundance was started. The method used both direct censuses at monthly intervals and limited fishing activity with longlines and trammels, The monthly census was carried out by two divers in the central part of the artificial reef made up of pyramids, each consisting of five concrete cubic blocks with 2-m sides, The census was carried out in two main phases: first the observer counted the fish moving around him for 15 min and then he explored the holes and the internal corridors. The second phase consisted of a 25-m crosswise movement between two pyramids, Observations were carried out over a period of 2 years, from February 1989 to February ]991, and 66 species of fish and invertebrates of fishing importance were caught and/or observed in the Loano artificial reef; 41 species (of which three were Crustaceans and two Cephalopods) were censused during the above-mentioned dives. The most numerous families were Sparidae and Labridae, followed by Serranidae, The predominance of the first two families seems to be one of the general characteristics of rocky sea-bed fish communities in the northwest Mediterranean, Seasonal changes in the qualitative and quantitative assemblages of fish are described. An important contribution to these changes was the appearance of juveniles, mainly in the latter half of the summer and in the autumn, It was in this period that the maximum fish density occurred, while the minimum was registered in June. The number of fishes increased with the age of the artificial reef and the evolution of macroben- thos settlement. In particular the development of algae improved the reef's attractiveness to the Labridae species.

Over the last two decades various artificial reefs have been built in the Medi- terranean (a list can be found in Bombace's study, 1989), but only for some of these are data available on the assessment of the fauna which is important for fishery. Only on a small number of these reefs has a census been carried out using the techniques of underwater observation. To the northwest of Marseilles, Bregliano and Ody (1985) used monthly observations over a full year's cycle to study fish in two zones with artificial reefs at 15- and 23-m depths and in a rocky natural environment. The authors did not find substantial differences between the zones with regard to the communities of fish; these were dominated by Labridae (J 2 species) and by Sparidae. They were, however, able to confirm a notable increase in the density of fish after the construction of the artificial reefs. In Israel, close to Haifa, Spanier et al. (1985) studied the colonization by fish of a reef constructed with old car tires, which showed what was initially a very large presence of fish with a density that levelled off slowly. Unfortunately, the study was limited to only 7 months from the immersion of the structures (from May to December). Close to Haifa, Diamant et al. (J 986) studied fish in a natural zone around a wreck using both the technique of underwater observation and rothenon to poison the fish. On the basis of the data gathered between 1975 and 1983 the authors were able to point to a greater specific richness on the wreck- 42 species, compared to the 25 and 26 of the two natural zones, rocky patch reef and vermetid platform walls. Some species of great commercial interest, such as

40] 402 BULLETINOFMARINESCIENCE,VOL.55, NO,2-3, 1994

Epinephelus aeneus, E. alessandrinus, Dicentrarchus labrax, Sciaena umbra, proved to be present only on the wreck. Using three techniques, Duval and Duc1erc (1986) studied the fauna of two reefs, at Gruissan and Saint Ciprien, situated on the Languedoc-Roussilon coast in the south of France. Unfortunately, the authors are only able to provide a list of the fish surveyed during dives (41% of the total population), captured with trawls (73% of the species) and with gill nets (65%). Charbonnel (1990) studied the fish communities of several artificial reefs in France using the Harmelin- Vivien et al. (1985) census technique. He reported that the fish populations to be found in artificial habitats are very similar to those on rocky bottoms. On the basis of the data furnished by a few catches and occasional observations by scuba divers, lists of the fish present on the reefs in the Marconi Gulf, eastern Liguria (Relini et aI., 1986) and near Varazze, western Liguria (Relini, 1982) have been provided. Using only the technique of catching fish, in Italy, some artificial reefs in the Adriatic (Bombace et aI., 1990; Bussani, 1981) and in Sicily (Arculeo et al., 1990) have been studied. Direct censuses of fish in natural environments in the Mediterranean are reported in a paper by Harmelin (1987). In particular, the observations carried out in the Posidonia meadow (Harmelin- Vivien, 1982, 1983) in a reserve to the south- east of Banyuls and in the marine park of Port-Cros are of great interest, also because they provide us with terms of comparison with censuses in protected zones containing artificial reefs. To assess the fish population on the Loano artificial reef (LAR) the visual technique developed by Harmelin- Vivien and Harmelin (1975) Harmelin- Vivien et al. (1985) was used. The aim of the LAR is to protect the Posidonia meadows because of their importance in maintaining biological diversity, safeguarding the coast from erosion and promoting small-scale fisheries. The second series of ob- jectives is to protect the area off Loano from illegal trawling, to provide hard substrata suitable for the settlement of benthos organisms and to offer shelter and protection to eggs, juveniles and moulting animals (Relini and Moretti, 1986).

STUDY SITE

The study site is located in the central part of the LAR (Fig. IB) in an area of about 350 ha between 5 and 45 meters depth in the western Ligurian Riviera, northwest Mediterranean. The LAR is composed of two parts (Relini and Orsi-Relini, 1989, 1990): a central main group of 30 pyramids (Fig. IC), in a 100 X 200 m area (16 to 23 m depth) and a grid of single cubic blocks (200 of 1.2 m side and 250 of 2 m side) distributed around the central portion of a 3 X 1.5 km rectangle (Fig, 18). The census site consists of two pyramids, 25 m apart, at 18 m depth, Each pyramid is made up of four cubic blocks (perforated concrete blocks of 2 m side) at the base and one at the top (Fig. ID). The distance between the basal blocks is about 80-]00 cm and the holes have diameters of 20 and 30 cm. The basal cavities are 30 cm in width and depth.

METHODS

To estimate the fish population of the artificial reef, we used the above-mentioned Harmelin techniques of visual censusing (Harmelin-Vivien and Harmelin, 1975; Harmelin-Vivien et aI., 1985) from February 1989 up to September 1991, on at least a monthly basis. Though direct censuses cannot cover the entire fish population, as some species will always remain concealed to SCUBAdivers, underwater observation can be an effective method in the process of understanding the dynamics of population formation and seasonal variation on an artificial reef. Considering the limited time available for safe diving activity and on the basis of a preliminary analysis-which showed that there were no great differences between two and three pyramids in terms of the number of species detected-we decided on our sampling zone. This covered a total area of 312 m2 including two pyramids at 18 m depth (80 m) of artificial reef) and the distance that separates them, in a volume of water of 1,026 m), RELlNl ET AL.: SEASONAL VARIATION OF FISH AT LOANO 403

500 m I...... f !...... ! 1...... 1

ow B

-1-~-~-?-9T9-C?-I~I I I I I I I I I -0- -0- -0- -0- I I I I ; -0- -0- -0- -0- I I I I ; -0- -0- . -0- -0-

-~=~~?=~~~=~=9=9~j~I -- C D

Figure 1. Location of Loano in the northwestern part of Italy (A). General view of Loano artificial reef (B) with main reef in the central part. The structure of the main reef (C) composed of thirty pyramids. Each pyramid consists of (D) five large blocks.

First, two SCUBA divers placed themselves at the apex of the pyramids. From this position, they counted the fish present in the mass of water around the structure (phase A). This operation, which lasted 8 min, enabled them to carry out a count up to two m around the complete perimeter of the pyramid (5 m mean visibility) in a volume of water of 323 m'. Once this first phase was complete, the two divers moved slowly around the perimeter of the pyramid, and through one of the internal passageways. The aim here was to record the presence of the more sedentary and concealed crcatures, which are often underestimated in a visual census (Harmelin-Vivien et aI., 1985). The second phase lasted approx. 10 min (phase B). The third phase consisted in swimming through another corridor, which this time was rectilinear, 25 m long and approx. 6 m wide. In this way the divers reached the second pyramid, where phases A and B were repeated. Further information about the species present on the LAR was obtained using trammel nets and longlines (Relini et al. 1990). To show variability, the frequencies of the various species were calculated and expressed as a percentage of presence in all the surveys. Four levels of frequency of occurrence-those already employed by Harmelin (l987)-were used: first level> 75%, second level = 50-74.9%, third level = 25-49.9%, fourth level < 25%. 404 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994

The Kulczynski index (Kulczynski, 1927) for the qualitative measure of similarity was used to compare seasonal fish assemblages; "UPGMA" (Sneath and Sokal, 1973) was employed to carry out cluster analysis. Data on weather and sea conditions were recorded for all censuses. For fish nomenclature Fischer et al. (1987) was used.

RESULTS Using underwater observations, catches with trammel nets and data provided by fishermen, we were able to draw up a list of 66 taxa present on the LAR. A total of 4] species was observed in over 50 dives from February ]989 to Sep- tember 199]; 35 species were caught using trammel nets during the four sets we conducted; 44 species were caught by professional fishermen using trammel nets and longlines (Table I). A total of 41 species were observed during dives, but two of these (Pagellus sp., Scyllarus arctus) were only seen during nocturnal dives when a regular survey was not being carried out, and five (Seriola dumerilii, Serranus hepatus, Umbrina cirrosa, Labrus merula, Blennius sp.) only during dives whose sole purpose was photographic or on other pyramids not included in the census. Moreover, during the surveys the headings Spicara, Scorpaena and Symphodus were not divided into their relative species and appear as genera. Therefore the systematic groups which directly affect the survey are 28 (Table 1). Some species were found in all surveys, others only periodically, depending on the different seasons, others again were registered only sporadically and without any precise regularity. With regard to the levels of frequency of occurrence (Table 2) the following groups were found: level one (>75%) comprises eight taxa, three of which Serranus cabrilla, Chromis chromis and Diplodus vulgaris were present in all of the surveys (100% frequency of occurrence). The second level (50-74.9%) comprises two species: Blennius rouxi, which shows clear seasonal variations, and Gobius cruentatus whose presence was registered from the eighth survey (12-7-89) onwards in nearly all the remaining surveys. This species, together with the other eight taxa of the first level, can thus be considered as forming part of the base population of the artificial reef. These nine taxa can be considered as residents. Eight species belong to the third level (25-49.9%): in the case of two of these-Conger conger and Octopus vulgaris-the low frequency of occurrence can be attributed, respectively, to cryptic behavior and mimetic fea- tures. Moreover, these are species which, even when they are present, are represented by only a limited number of individuals, and the probability of en- countering and detecting them is low. These two species can probably also be included in the group of residents. In the remaining six cases one can mention them as periodic visitors to the reef. The fourth level groups together the remaining ]0 taxa «25%): here we find, in addition to the two Decapod Crus- taceans, Cephalopod Sepia officinalis and Serranidae Mycteroperca rubra, four wide-ranging swimming fish which occasionally frequent the pyramids and the Sciaenidae Sciaena umbra, a creature which has become rare on the Ligurian coast and is primarily active at night. This category also includes the Labrus bimaculatus, whose low percentage of occurrence is probably due to the fact that this wrasse has only recently started to colonize the reef. The number of individuals varies greatly during the course of the year. To understand these variations better we thought it would be useful to show in dia- gram form (Fig. 2) the state of the population with and without the Spicara genus. The individuals of this taxa appear at the study site at irregular intervals, in the RELINI ET AL.: SEASONAL VARIATION OF FISH AT LOANO 405

Table J. Species recorded by scuba divers, trammel catches and information from fishermen

Species DIVE TRAM. INFORM. Apogon imberbis (Linnaeus, 1758) * * Blennius (=Parablennius) rouxi Cocco, 1833 * Blennius sp. * Boops boops (Linnaeus, ] 758) * * * Chromis chromis (Linnaeus, 1758) * * Conger conger (Linnaeus, ]758) * * Coris julis (Linnaeus, 1758) * * Dentex dentex (Linnaeus, 1758) * * Dicentrarchus labrax (Linnaeus, 1758) * * Diplodus annularis (Linnaeus, 1758) * * * Diplodus puntauo (Cetti, 1777) * Diplodus sargus (Linnaeus, 1758) * * * Diplodus vulgaris (E. Geoffroy S1. Hilaire, ] 817) * * * Cobius cruentatus Gmelin, 1789 * Homarus gammarus (Linnaeus, 1758) * Labrus bimaculatus Linnaeus, 1758 * Labrus merula Linnaeus, 1758 * * MugU sp. * * Mul/us surmuletus Linnaeus, 1758 * * * Mycteroperca rubra (Bloch, 1793) * Oblada melanura (Linnaeus, ]758) * Octopus vulgaris Cuvier, 1797 * * * Pagel/us erythrinus (Linnaeus, 1758) * * * Palinurus elephas (Fabricius, 1787) * Sciaena umbra Linnaeus, 1758 * Scorpaena notata Rafinesque, 1810 * * * Scorpaena porcus Linnaeus, 1758 * * * Scorpaena serofa Linnaeus, ] 758 * * Scyl/arus arctus (Linnaeus, ] 758) * * Sepia officinalis Linnaeus, 1758 * * * Seriola dumerilii (Risso, 1810) * * * Serranus cabrilla (Linnaeus, 1758) * * * Serranus hepatus (Linnaeus, 1766) * Spicara maena (Linnaeus, ] 758) * * * Spicara flexuosa Rafinesque, 1810 * * * Spicara smar;s (Linnaeus, (758) * * * Spondyliosoma cantharus (Linnaeus, 1758) * Symphodus cinereus (Bonnaterra, 1788) * * Symphodus mediterranus (Linnaeus, 1758) * * Symphodus tinea (Linnaeus, 1758) * * * Umbrina cirrosa (Linnaeus, 1758) * * Arnoglossus laterna (Walbaum, 1792) * * Bothus podas (Delaroche, 1809) * Engraulis encrasicolus (Linnaeus, ]758) * lllex coindetii (Verany, ] 839) * Lepidotrigla cavil/one (Lacepede, 180]) * * Lithognathus mormyrus (Linnaeus, 1758) * Loligo vulgaris Lamarck, 1798 * * Merluccius merluccius (Linnaeus, 1758) * * Monochirus hispidus Rafinesque, 1814 * Mul/us barbatus Linnaeus, ] 758 * * Murena helena Linnaeus, 1758 * Pagrus pagrus (Linnaeus, ] 758) * Pagel/us acarne (Risso, (826) * Sarda sarda (B]och, ] 793) * Sardinel/a aurita Valenciennes, ] 847 * Scomber japonicus Houttuyn, 1780 * * Scophthalmus rhombus (Linnaeus, 1758) * Serranus scriba (Linnaeus, 1758) * * 406 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994

Table 1. Continued

Species DIVE TRAM. INFORM. Solea vulgaris Quensel, 1806 * Sparus aurata Linnaeus, 1758 * Squilla mantis (Linnaeus, 1758) * * Trachinus sp. * Trachurus sp. * Uranoscopus scaber Linnaeus. 1758 * * Zeus faber Linnaeus, 1758 * winter and spring months, without any precise regularity and in sometimes very numerous groups (between 50 and 200 individuals). The resulting peaks thus alter the seasonal variations connected to the rest of the population. The number of individuals recorded in the 1,026 m3 volume of water being studied fluctuate between 81 on 14 June 1989 and 484 counted on 19 September 1991. Overall the population shows an obvious summer low (Fig. 2) in the period between June and July for all 3 years (1989-1990-1991), followed by a high between August and November. To understand the causes of this, we examined the seasonal quantitative variations of four of the species which form the largest part of the total number and which show broad temporal fluctuations (Fig. 3).

Table 2. Percentages of presence for the species surveyed between February 1989 and January 1991 and their relative levels of frequency

Species Occurrence Frequency Apogon imberbis 36.7 3 Blennius rouxi 66.7 2 Boops boops 3.3 4 Chromis chromis 100.0 I Conger conger 30.0 3 Coris julis 40.0 3 Dentex dentex 6.7 4 Dicentrarchus labrax 3.3 4 Diplodus annularis 93.3 I Diplodus puntazzo 26.7 3 Diplodus sargus 96.7 I Diplodus vulgaris 100.0 I Gobius cruentatus 70.0 2 Homarus gammarus 3.3 4 Labrus bimaculatus 6.7 4 MugU sp. 6.7 4 Mullus surmuletus 43.3 3 Mycteroperca rubra 3.3 4 Oblada melanura 43.3 3 Octopus vulgaris 36.7 3 Palinurus elephas 3.3 4 Sciaena umbra 6.7 4 Scorpaena spp. 86.7 1 Sepia officinalis 6.7 4 Serranus cabrilla 100.0 I Spicara spp. 46.7 3 Spondyliosoma cantharus 93.3 1 Symphodus spp, 96.7 I RELINI ET AL.: SEASONAL VARIATION OF FISH AT LOANO 407

number of Individuals' 1000 m3 500

400

300

200

100

o F M A MJnJl A SON D J F M A MJnJl A SON D J F M A MJnJl A S

11989 11990 months 11991

~ without Splcara -t- with Splcara

Figure 2. Total fish counts in the study area from February t 989 to September 1991, with and without the Spicara genus.

number of Individuals' 1000 m3 250

200

150

100

o F M A MJnJl A SON D J F M A MJnJl A SON D J F M A MJnJl A S /1989 11990 months 11991

Blennlus roud Chromls chromls S. cantharus Corls Julls

Figure 3. Counts of four of the species which fonn the largest part of the total number and which show broadly fluctuating temporal tendencies. 408 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994

Spring 1989 A c

Q.sargus 6.8% O,sargus 9.4% .imberbIS 1.4% corp'sene SOD. 0,8 O.annuleris 2.0'£ others 2.9'£ ~ Y mphodus 1.7% MSurmuletu8 0.9% S.cabrilla 2.7% a.boeps 1.6% D.annularls 3.7% S.centriefuS 2.0% SymphOdUS spp. 1.7% M.3urmuletus 2.7%

Spicars spp. 24.9%

Spring 1990 Summ.r 19QO B o

O.melanura 2.3% others 3.9%

Scorpaena app. 2.1%

SymphQdUS spp. 8.9%

Figure 4. Population composition: main species as percentages in spring 89 (A), spring 1990 (B), summer 1989 (C), summer 1990 (D).

Between June and July 1989, between May and July 1990 and between May and June 1991 the populations of Coris julis, Blennius rouxi, Chromis chromis and Spondyliosoma cantharus reach their lows at the same time, Starting from August, both in 1989 and 1990, there was a simultaneous rise in the numbers of Blennius rouxi, Coris julis and Chromis chromis. When the representatives of these three start their decline in October, the individuals of Spondyliosoma cantharus reach their maximum. In 1991 the situation was a little different, for there was a delay in the appearance of juveniles of the Coris julis species. These were counted only from September onwards, (instead of August, as in the previous 2 years) and there was an almost total disappearance of Spondyliosoma cantharus individuals, only a reduced number of which were counted starting from the second half of Septem- ber. The fish fauna of the LAR thus show different (qualitative and quantitative) compositions in different seasons. The diagrams (Figs. 4 and 5) show the 12 species which are the most numerous in each season. In spring (Fig. 4A, B) in both 1989 and 1990 the fish community is dominated by Spicara, Chromis chromis, Diplodus vulgaris. Also present in spring is Dblada melanura. In summer the situation appears to be very different (Fig. 4C, D), Chromis chromis becomes the dominant species, Spicara disappears completely, and the second most numerous species is Blennius rouxi, with 22% of the total amount in summer 1989 and 20% in summer 1990. The third most abundant species was RELINI ET AL.: SEASONAL VARIATION OF FISH AT LOANO 409

Aurumn 1989 Winter 1990 A c

Olhars 1.8% D.sargus 6.3% \ Msurrrulelus 2.1% Olhara 3.5% Splcara sPP 5,0'1. Q.annularls 4.4% G.cru6Qlatus 19% £g~~nl~2~s 0.9% S.cabrilla 3.9% O.metanura 2.3%

Autumn 1990 Winter 1991 B o

C.chromls 41.8%

a.vulgariS 24.7'l. Q.vulgarls 10.0'£

a.sargus 5,2% others 1.9% ymphodus spp. 9.1% ScorpoBna SOP. 2.1% &~~2~?2I~Ss~~% 1..5%

S.canlharus 12.2% C.julls 6.3%

Figure 5. Population composition: main species as percentages in autumn 1989 (A), autumn 1990 (8), winter ]990 (C), winter ]991 (D).

Caris juLis in 1989 and SpondyLiosoma cantharus in 1990. At all events Coris juLis was the fourth most numerous species in summer 1990, which confirms precisely the same composition of the summer population, in a pattern that is repeated over 2 years. In the autumn seasons (Fig. 5A, B) Chromis chromis remains the most abundant species, in particular in the autumn of 1990, when it accounted for more than 40% of the population. Other main species are DipLodus vuLgaris and SpondyLio- soma cantharus, in addition to those species which are more typical of the summer population (Blennius rouxi and Coris juLis); these are still present, although not in the same numbers as in the previous season. During the winter of both 1990 and 1991 (Fig. 5C, D) a quarter of the population was made up of seabream DipLodus vuLgaris. A further large proportion was made up of Chromis chromis, the second most numerous species in 1990 and, with over 36% of individuals, dominant in 1991. Making a comparison between the different seasonal compositions using the Kulczynski similarity index (Table 3, Fig. 6) we find confirmation that the same seasonal patterns are repeated with relative similarity. For the two summers (Kul- czynski index = 0.82) the fish assemblages are almost identical. Cluster analysis shows that high affinity exists between summer and,autumn, and between winter and spring. However, the differences between the summer and winter and between the summer and spring populations are often very marked. If we observe the temporal variations of the number of individuals at the level 410 BULLETIN OF MARINE SCIENCE. VOL. 55. NO. 2-3. 1994

Table 3. Kulczynski index calculated for each pair of seasonal compositions

Spring 89 Summer 89 Autumn 89 Winter 90 Summer 90 Autumn 90 Winter 91 Spring 89 0.50 0.62 0.66 0.47 0.48 0.74 Spring 90 0.69 0.42 0.52 0.54 0.48 0.50 0.61

Spring 89 Summer 89 Autumn 89 \VinleT 90 Spring 90 Autumn 90 Winter 91 Summer 89 0.50 0.76 0.54 0.42 0.71 0.59 Summer 90 0.47 0.82 0.78 0.60 0.48 0.75 0.53

Spring 89 Summer 89 Autumn 89 Winter 90 Spring 90 Summer 90 Winter 91 Autumn 89 0.62 0.76 0.73 0.52 0.78 0.68 Autumn 90 0.48 0.71 0.71 0.59 0.50 0.75 0.65

Spring 89 Summer 89 Autumn 89 Winter 90 Spring 90 Summer 90 Autumn 90 Winter 90 0.66 0.54 0.73 0.54 0.60 0.59 Winter 91 0.74 0.59 0.68 0.73 0.61 0.53 0.65

of single species, we find that the peaks are often determined by the arrival of young. The Chromis chromis species (Fig. 7) shows three fairly clear periods of low abundance between June and July 1989, April and May ]990 and June and July 1991. In these months Chromis is present with only approximately 20 individ- ua]s, all adults, over the entire area under study, as against values which ap- proach and even exceed a hundred, recorded from Ju]y to October in all 3 years. The abrupt summer increase is due to the arrival of masses of young which appear punctually in each of the 3 years at the end of July. They reach their maximum of density in August and September and then in the first 2 years disappear gradually in the winter months. The adults reach their highest values

o Similarity Index

Figure 6. Dendrogram of similarity (Kulczynski index) resulting from normal qualitative cluster analysis (UPGMA) for high seasonal composition. RELINI ET AL.: SEASONAL VARIATION OF FISH AT LOANO 41 I

number 0' Individuals I 1000 m3 250

200

150

100

o F M A M In JI A SON 0 J F M A M In JI A SON 0 J F M A M In JI A S months 11989 * 11990 * 11991 * _ Juvenile _adult

* no census

Figure 7. Counts of Chromis chromis (two different size classes) from February 1989 to September 1991. in the early months of 1989. Moreover, they seem plentiful in October and November, probably owing to the share of August young which have grown in the meantime. The Serranus cabrilla species proves to be present throughout the year and its numbers remain fairly constant over the course of time (Fig. 8). Intermediary individuals and adults are still present, whereas the young, in all 3 years, appear in the summer period. The Spondyliosoma eantharus species shows quite broad fluctuations in the course of the year (Fig. 9). In 1989-1990 we recorded a low between May and June, in '91 in July and later the species disappeared altogether. A clear high was recorded from October 1989 to February 1990, caused by an increase in all three age groups. Already in August and October 1990 the population of Spondyliosoma had reached high values. In the course of summer 1991, on the other hand, S. eantharus was almost absent, if one ignores the presence of a few large-sized specimens. Individuals belonging to the Symphodus genus are present in almost all the surveys. Their abundance varies from two to six individuals up to March 1990 (Fig. 10). From April of the same year onwards the individuals of this genus increased to 16 specimens in May; 19 specimens in August, mainly juveniles, and 38 in September, 43 in October. Symphodus spp. recruits, which were not present during the summer of 1989, did, however, appear in masses the following year. This is probably due to the abundant development of algae that took place in 1990, which allowed them to find shelter. Until May 1990 the most numerous species was Symphodus tinea. Starting from April 1990, new species appeared, 412 BULLETIN OF MARINE SCIENCE, VOL. 55, NO. 2-3, 1994

number of Individuals I 1000 m3 16

14 ......

..... 12 ...... -..... " .. ..

10 ... ·.·.M .._.....•• ·_...... -

8 ......

6 .... , ....

4 .. ..

2 I····· . o I F M A M In JI A SON 0 J F M A M In JI A SON 0 J F M A M In JI A S 11989 * 11990 months * 11991 *

LJ ( 9 em _ 9 - 18 em _ > 18 em

* no census

Figure 8. Counts of Serranus cabrilla (three different size classes) from February] 989 to September 1991. mostly in the form of juveniles (Symphodus mediterraneus, S, cinereus). In the summer of 1991 no young of this genus appeared. The individuals belonging to the Spicara genus show broad fluctuations from one census to another. It is, however, clear that these are species which do not frequent the pyramids in the summer months (Fig. 11). Spicara spp, are absent from July to September 1989, from June to December 1990 and from August 1991 onwards. The specimens surveyed were all adults.

DISCUSSION AND CONCLUSIONS Of the 66 species caught and/or observed in the LAR, 41 (of which three were Crustaceans and two Cephalopds) were censused during the dives carried out in the same zone at the central core of the reef; this number, which might be even greater if we were able to make specific identification of some genera (Mugil, Spicara), indicates a high specific richness. Visual transect techniques are good non-destructive methods, and are widely used to assess the abundance and diversity of fishes in many habitats and in particular on artificial reefs (Brock, 1954; Buckley and Hueckel, 1989; Jessee et aI., 1985), Comparisons have been made between visual transects and a number of other visual censusing methods (De Martini and Roberts, 1982; Greene and Alevizon, 1989). When one compares the Loano list with that of fish censused in the natural rocky area of Port-Cros (Marseilles, France), where 43 different species were censused (Harmelin, 1987), one notes that the two environments share some similar characteristics. A full 27 species are common to both biotopes. Chromis RELINI ET AL.: SEASONAL VARIATION OF FISH AT LOANO 413

number of Individuals I 1000 m3 60

o F M A M In JI A SON D J F M A M In JI A SON D J F M A M In JI A S 11989 * 1,990 months * 1,99, *

0, 8 em _ 8 - 16 em _) 16 em

* no census Figure 9. Counts of Spondyliosoma can/harus (three different size classes) from February 1989 to September 1991.

chromis is dominant in terms of numbers in both communities. At both Port-Cros and Loano the family represented by the most species is that of the Sparidae, followed by the Labridae and Serranidae. The predominance in numbers of species of these latter two families seems to be one of the general characteristics of rocky sea-beds in the northwest Mediterranean (Harmelin, 1984, ]987). When we make a comparison with other reefs, the fauna at Loano proves to be very similar to that censused or caught with various fishing gear at Saint Cyprien (Duval and Duclerc, ]986), in the Adriatic near Monte Conero (Bombace et aI., 1990) and in Sicily in the Castellamare Gulf (Arculeo et aI., 1990). Many of the species censused at Loano are the same as those caught in the Posidonia meadows during studies carried out on the French coast (Bell and Harmelin- Vivien, ]982; Harmelin- Vivien 1982, 1983). These authors also state that most of the species which frequent the Posidonia meadow are not exclusive to this biocoenosis. There are exchanges between the two environments-rocky bottoms and Posidonia meadow-and these are further evidence of the importance of artificial reefs, not only in the protection of the Posidonia from illegal trawling, but also in the possible communications and exchanges of fauna which can be established between the two environments. It was possible to distinguish within the population a group of 11 species (some at level of genus) which can be considered residents because they were present throughout the year and were permanent on the artificial reef. The rest of the community can be divided into three categories: those present on the pyramid according to season; those infrequently censused because of their rarity and/or 414 BULLETIN OF MARINE SCIENCE. VOL. 55. NO. 2-3. 1994

number ot Individuals I 1000 m3 50

o F M A M In JI A SON 0 J F M A M In JI A SON 0 J F M A M In JI A S

11989 * 11990 months * 1199 t * o Juvenile _ adult

* no census

Figure 10. Counts of Symphodus spp. (two different size classes) from February 1989 to September 1991. their nocturnal habits; fish which can swim in vast areas and which occasionally frequent the artificial reef. There is an obvious seasonal change in the community on the Loano reef, shown by the fact that some species are present only during certain periods of the year, and by the regular seasonal variations in the number of individuals of other species. These variations are often linked to the arrival of young, an event which for the majority of the species occurs in mid-summer and in autumn. On the whole, these changes in the composition of the community lead to a minimum number of individuals in June and a maximum in late summer and autumn. Confirmation of this particular trend comes from a study carried out on the artificial reef near Marseilles, in the western Mediterranean (Bregliano and Ody, 1985). Here too, the authors obtained low values of total abundance in May and June, and a maximum from September to December. Considering the 3 years of study there are some differences which confirm a progressive development of the fish community. In particular, in the second year of the study the individuals of certain species (Spondyliosoma cantharus, Sym- phodus spp., Gobius cruentatus, Diplodus annularis, Apogon imberbis) increased; in this context one can speak about the progressive colonization of artificial structures. The development of the fish community is closely linked to changes in the macrobenthic settlement on the blocks of the LAR. In 1990, the particular, there was a development of the algal substratum (Dictyota sp., Sargassum vulgare) covering the horizontal levels of the pyramids. In relation to this change the number of-especially young-Labridae which live on the reef increased con sid- RELINI ET AL.: SEASONAL VARIATION OF FISH AT LOA NO 415

number of Individuals I 1000 m3 200

150

100

o F M A M In JI A SON 0 J F M A M In JI A SON 0 J F M A M In JI A S 1,989 * 1,990 months * 1,99, *

_adult * no census

Figure II. Counts of Spicara spp. from February 1989 to September 1991. erably, thus reducing the gap between the number of species of Labridae on the LAR compared to the other areas of northwest Mediterranean studied by Bell (1983) and by Bregliano and Ody (1985). Benthonic evolution has also affected the hollow passageways through the blocks, where an ever denser knot of hy- droids, bryozoans, sponges and bivalves developed, making these hollows excel- lent shelters and possible grazing zones for both adult and young individuals of many species. In the second year there was a decrease in the numbers of some particular cryptic species (Conger conger, Octopus vulgaris), perhaps caused by the greater structural complexity of the reef. This made the act of censusing these individuals more difficult, although in this context the factor of illegal catches cannot be excluded. In 1991 there was a reduction in the algal cover. It is also true that the winter was particularly cold, with temperatures reaching 12°C, 2°C below the previous February. Perhaps because of one of these factors or a combination of the two the young of many species were missing.

ACKNOWLEDGMENTS

This research was financed partly by a contract between the Municipality of Loano and the Uni- versity of Genoa and partly by a grant from the Ministero Marina Mercantile. Many thanks go to the students M. Bellingeri and A. Maurizi who participated in the census activity. Special thanks go to Captain G. Mazzitelli, Mr. L. DeFrancesco, Mr. D. De Domenico and Mr. A. Enrico for their important help in the field and for allowing us the use of their boats.

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DATE ACCEPTED: April 30, 1993.

ADDRESS: Islilulo de Zoologia, Laboralari di Bialagia Marina ed Ecologia Animale, Via Balbi 5, 16126 Genova. Italy.