J. Zool., Lond. (1975) 175, 179-199

The ethology of Abudefduf luridus and chvomis (Pisces : ) from the Azores*

GILLIANM. MAPSTONE Brooklands Technical College, Weybridge, Surrey

AND ELIZABETHM. WOOD Department of Biology, Goldsmiths’ College, London

(Accepted 11 June 1974)

(With 1 plate and 7 figures)

The behaviour of the two species of damsel fishes found in the Azores, Abudefduf luridus (Cuvier) and Chromis chromis (L.)** was studied using underwater techniques. A. luridus is a substrate species, whereas C. chromis alternates between a rock dwelling and a mid-water existence depending on its sexual condition. The male in both species sets up a breeding territory and, after spawning, cares for and protects the eggs. No pair bonds are formed. Social organization and reproductive behaviour in these two species is discussed in relation to other pomacentrids, for which comparable behaviour patterns have been reported.

Contents Page Introduction...... 180 Methods ...... 180 Results ...... 181 Abudefduf luridus ...... 181 Description of the species ...... 181 Habitat and feeding ...... 182 Social organization and territorial behaviour ...... 183 Population density ...... 183 Agonistic behaviour ...... 183 Behaviour of non-nesting individuals ...... 185 Breeding behaviour ...... 186 Behaviour of the juveniles ...... 187 Chromis chromis ...... 187 Description of the species ...... 187 Habitat and feeding ...... 189 Social organization and territorial behaviour ...... 189 Population density ...... 189 Agonistic behaviour ...... 189 Behaviour of non-nesting individuals ...... 191

*All correspondence concerning this paper should be sent to E.M.W. **The taxonomic status of the species is under study. 179 180 G. M. MAPSTONE AND E. M. WOOD Breeding behaviour ...... 192 Behaviour of the juvenile ...... 194 Discussion ...... 194 Summary ...... 197 References ...... 198

Introduction Pomacentrids are small brightly coloured fish which engage the attention of ethologists because of the wide variety of social behaviour patterns they display. The family is best represented in tropical waters, and there are descriptions of the behaviour of Chromis and Abudefduf species from the central Pacific (Helfrich, 1959; Hiatt & Strasburg, 1960; Swerdloff, 1970; Sale, 1971), eastern Pacific (Turner & Ebert, 1962; Limbaugh, 1964), Gt Barrier Reef (Keenleyside, 1972), western Atlantic (Longley & Hildebrand, 1941 ; Myrberg, Brahy & Emery, 1967; Albrecht, 1969; Cummings, 1969), the Indian Ocean (Eibl-Eibesfeldt, 1964) and the Red Sea (Fishelson, 1964, 1970). The only studies made on these two genera in more temperate regions have been by Abel(l961) in the Mediterranean and Russell (1971) in northern New Zealand. The Azores are also in the temperate zone, and Abudefduf luridus and Chromis chromis are the two species of pomacentrid found there. A. luridus is restricted to the eastern Atlantic but C. chromis is more widespread, occurring as far south as the , as well as in the Mediterranean.

Methods Our studies were carried out on Slo Miguel, the largest island in the Azores archipelago. Preliminary observations were made during 1972 from I to 22 August, and more detailed studies in 1973 from 2 to 26 August. Study areas were established both in 1972 and in 1973, but only the 1973 sites are described here. We selected two sites at the south western end of the island, one at a depth ranging from 10 to 18 m (Ponta das Caetanos, Populo), and the other on flatter ground, at a depth of 20 m (Ilheu da Vila Franca) (Fig. 1). The study area was in each case a 20 by 20 m square marked out by ropes and further sub- divided by ropes into 10 by 10 m squares. Both sites were predominantly rocky and at Vila Franca especially there were large boulders (approximately 5 m in diameter). At the beginning of the study we mapped the two sites and recorded the position and home range of all pomacentrids within the areas. The apparent centre of each home range was marked underwater with a labelled tag attached to a rock. On subsequent dives each fish was located where possible, its home range checked, and its behavioural patterns observed and often timed. The fish themselves were not tagged but they could often be recognized by size, colouration, or individual blemishes or markings. Futhermore, confusion of one fish with another was minimized because, for A. luridus especially, population density was low and nesting and non-nesting individuals were widely spaced. Observations were recorded in pencil on non-reflective grey “formica” boards. These boards were marked with a predetermined list of the predominant activities of each species, a time scale and a map of the area. During timed observations the activity being performed at the end of consecutive 30 sec periods was recorded in the relevant column. Any notable events (agonistic behaviour, reproductive behaviour) occurring within rather than at the end of a 30 sec period were also recorded. Timed observations on individual fish lasted for up to 45 min. Dives were made during the day and at night, but timed recordings were not possible at night because torchlight disorientated the fish and altered behaviour patterns. We were, however, ETHOLOGY OF POMACENTRIDS 181 able to check the presence and position of some of the fishes within the study areas. The majority of our work was carried out at the two mapped sites but additional observations were made at other sites around the island, notably Ponta da Galera. At the end of our study period we collected individual damsel fishes from the two study sites, with the aid of nets, short baited lines, or spear guns. Additionally, derris was used to capture rock dwelling C. chromis which lived in large numbers amongst a series of submarine arch structures at Ponta da Galera. The sex and sexual maturity of all these fish was determined, and their gut contents examined.

Azores ;i.1000- km .i- -

t

Populo lheu do Vila Franca Ponto da Galera

SaO MIGUEL 10 km

FIG.1. SPo Miguel, Azores, to show the position of the study sites.

Results Abudefduf luridus Description of the species The majority of specimens we saw were adult, ranging in standard length from 11.7 to 12.8 cm. Non-breeding males and females are monomorphic, but there is a perceptible colour dimorphism in breeding fishes. The body and fins of non-breeding individuals and breeding females are predominantly black or very dark brown, becoming a little paler 182 G. M. MAPSTONE AND E. M. WOOD on the belly. There is a brilliant blue spot at the base of the pectoral fin, a blue streak on the first spine of the pelvic fin and a few scattered blue spots above and behind the eye (Fig. 2). Fowler (1936) reports black not blue markings, presumably after examining pre- served rather than living specimens.

. FIG.2. Abudefduf luridus (a) adult, (b) juvenile.

Breeding males have the same blue markings, but the body is dark brown rather than black. There may also be paler areas on the dorsal part of the head and on the belly. Juveniles have a dark brown body and fins and, in addition to the blue markings of the adult, a blue edging to both dorsal and anal fins, a blue line longitudinally behind the eye and a blue spot on the dorsal surface of the caudal peduncle (Fig. 2).

Habitat and feeding A. luridus was typically associated with rocky outcrops or boulder strewn areas. In- dividuals were seldom seen close to vertical cliff faces, above large areas of flat horizontal ETHOLOGY OF POMACENTRIDS 183 rock, or over sand, and we assume that such places did not provide sufficient shelter or suitable breeding sites. A. luridus was seen at all depths from 3 to 35 my although it was particularly abundant in the 5 to 20 m zone. It was not found in the surf zone. Examination of gut contents of male and female A. luridus revealed a predominance of filamentous , together with organisms associated with or attached to either algae or rock surface. The intestine was long and coiled, characteristic of an with a vege- tarian or partly vegetarian diet.

Social organization and territorial behaviour A. luridus is a non-shoaling, non-aggregating species, living dispersed amongst rocks. Adults belonged to one of two behavioural types; near ranging (moving within an area of about 4 m2) or far ranging (moving within an area of about 50 m2). Near ranging fish were nesting males and far ranging ones non-nesting individuals. The latter were mainly females, but also included males that were not actively breeding. Nesting males normally confined their movements to part of a vertical rock face or under the shelter of a boulder. They showed agonistic behaviour to almost all fish that passed within about 0.5m of the home range boundary, and this boundary can thus be considered a territorial boundary. The position of the boundary was the critical distance from the nest site at which exclusion of most species operated. The nest was the focal point of the territory and here the male spent most of its time. Territorial boundaries were not contiguous with those of other nesting or non-nesting individuals and, except during courtship activities, no confrontations between nesting and other individuals were seen. Non-nesting A. luridus ranged over rocky terrain, usually skirting round the lower edges of rocks and boulders, occasionally swimming into holes or crevices, and sometimes moving upwards to the tops of rocks. Each fish kept to one area of substrate and normally showed agonistic behaviour to intruding conspecifics, indicating that they maintained this area as a territory. In some cases territorial boundaries were contiguous or over- lapped, and this presumably encouraged agonistic behaviour.

Population density Nesting A. luridus were well spaced and their territories never overlapped those of other individuals. There were three nesting males at the 400m2 site at the Ilheu, and two at Populo (Fig. 3). There were also few signs of competition for space amongst non-nesting A. luridus. Territorial boundaries were often contiguous, but appeared to be respected, and conflicts occurred infrequently. There were nine non-nesting individuals in the 400 m2 site at the Ilheu, and three at Populo (Fig. 3).

Agonistic behaviour Agonistic behaviour at its lowest level consisted of a frontal display, and was the common attitude taken by nesting males to most fish which approached within about 2 m of the territorial boundary. The was raised and the pectoral fins spread outwards until almost at right angles to the body. Additionally, it was not uncommon to see the fish hold its mouth wide open for one or two seconds, apparently as an aggressive display. The aggressor remained stationary in a horizontal position, facing the intruder, until the latter swam away. 184 G. M. MAPSTONE AND E. M. WOOD

FIG.3. Location of nesting and non-nesting Abudefduf luridus at the study sites. ETHOLOGY OF POMACENTRIDS 185 A mutual frontal display sometimes occurred between two non-nesting individuals, usually on the territorial boundary. The fins were spread as described above but the fish were orientated differently, facing each other with head down and body tilted at an angle of about 20" to the horizontal. Both then made short head-on lunges at each other, finally turning away into their own territory with no sign of a real conflict. - I I

St at ion a r y u) 80- !? t ? Slow swimming L n0 Fast swimming m c 60- - 3 u) P

0E fl tc n o 40-

c5 1c 8

20 -

NESTING NON-NESTING FIG.4. Histogram to show swimming activities and associated behaviour in nesting and non-nesting Abudefduf luridus. The figures are derived from the activity being performed at 30 sec intervals and is based on 123 min observation of eight nesting individuals, and 56.5 min observation of five non-nesting individuals. High intensity agonistic behaviour consisted of a head-on approach, with fins spread, at which the intruder invariably took flight and was chased away. Fish which were attacked as they entered the territory of a nesting male took immediate flight, and were normally followed at least until clear of the territory, sometimes for several metres. When the conflict was between two non-nesting fishes a circular chase often ensued before the intruder swam away. Behaviour of non-nesting individuals Non-nesting A. luridus did not necessarily adhere to exactly the same territory from day to day, but certainly remained in the same vicinity. Individuals had no apparent focal point in their territory although they tended to have several specific rocks within the terri- tory beneath which they rested. The majority of their time was spent swimming slowly round within the territory, and they frequently cropped at algae and other encrusting material from the rocks. A histogram comparing swimming activities of nesting and non- nesting individuals is shown in Fig. 4. 186 G. M. MAPSTONE AND E. M. WOOD Non-nesting A. luridus ignored other species (e.g., Thalassoma pavo (L.), Coris julis (L.), Chromis chromis, Sphaeroides spengleri (Bloch)) which swam within the territory, and on occasions passed 0.5 to 1.0m from a conspecific without conflict. Usually, however, when one A. luridus strayed into the territory of another a conflict occurred. If the confrontation was close to the territory boundary then both fish usually took up an aggressive attitude and a mutual frontal display took place. lf it was within a territory then the resident fish showed high intensity agonistic behaviour and chased the intruder away. At the time we carried out our studies the majority of non-nesting individuals were females, and some were seen to spawn with nesting males.

Breeding behaviour Breeding occurred during August and probably extended into September, but we do not know when it commenced. Courtship activities were seen throughout the day. The nest site was always on a sheltered rock, usually on a vertical or overhanging rock face, the surface of which had only a thin covering of algae and sponges. The resident male often removed pieces of algae from the nest site and carried them in the mouth before dropping them in open water 0.5 to 1.0 m away. Spawning took place within the territory, but preliminary courtship activities occurred outside. The male left its territory and swam rapidly and directly towards the territory of a neighbouring female. There it began to make circling darts in a nearly horizontal plane, often swimming partly beneath a boulder. It usually swam in loops around the female, always with a fast flickering of the tail, and attempted to lead the female back to its territory. This display lasted only two or three minutes and if unsuccessful, the male swam rapidly back to its own territory. If successful, however, both fish returned to the male’s territory where the male restarted the circling movements, and began to rub its belly repeatedly against the prepared rock surface. If the female swam away at this point the male continued his actions; if not, spawning activities commenced. The two fish circled close together, sometimes head to tail, often almost touching, and rubbed alternately on the nest site, moving forward with a quivering motion. Eggs and sperm were not seen, but it is likely that they were discharged at this stage. Finally the female was driven away and the male remained to protect and care for the eggs. Although the male normally led the female to its territory, females sometimes entered a male’s territory uninvited, and some of the motions described above then occurred. It is possible that the female was attempting to initiate spawning, or else that it persisted in returning after spawning had finished. On one occasion the male appeared to accept the female on her first three visits and the two fish circled closely together, the male rubbing at intervals against a particular spot on the rocks. On the next two visits, however, which occurred within two minutes of each other, the female was chased fiercely away. It did not return, but the male continued for a further five minutes to rub intermittently against the rocks and to patrol the area. Our observations revealed that nesting males prevented all but two species from entering their territory. The first of these, a regular visitor, was the scorpion fish (Scor- paena maderensis Valenciennes), the second the small grouper (Serranus atricauda Gunther). Other fishes (Table I) were excluded by being warned (by aggressive display) or chased when they approached the territory boundary. The male’s aggressive activities ETHOLOGY OF POMACENTRIDS 187 in this area beyond the boundary varied from a high to a low level and were sometimes completely lacking. Such variation occurred over a short period e.g., one particular male observed over seven minutes ignored three fish (two female, one male Thalassoma pavo), displayed to two (Chromis chromis, male T. pavo) and chased six (two female, four male T. pavo). These fish were all close to the apparent territory boundary and there was no obvious reason for the disparity in aggressive behaviour. There were also variations be- tween individuals e.g. the average number of fish chased per ten minutes (based on 126.5 min observation of 11 nesting males) was three; the highest number being eight, and the lowest none. Fish most commonly chased were the small wrasses (Table I).

TABLEI Agonistic encounters in nesting male A. luridus. Based on 1265 min observations of I1 individuals

Number of individuals Species attacked by A. luridus

Thalassomu pavo (male and female) 20 Coris julis (female) 11 Blennius sp. 2 Abudefduf luridus 1 Chromis chromis 1 Sphoeroides spengleri 1 Chelon Iabrosus 1

In addition to maintaining a territory, and thereby guarding the nest site, the male also moved slowly over the eggs at intervals, fanning them with slow synchronous beats of the pectoral fins. At other times the male “nipped” at the eggs, possibly to remove settled material and/or dead eggs.

Behaviour of the juveniles Juvenile A. luridus were rarely seen, and presumably spend their first year(s) elsewhere. Those seen were aggressive to adult conspecifics and oder species, and were apparently trying to set up a small territory amongst the rocks.

Chromis chromis Description of the species Existing descriptions of C. chromis are based on examination of specimens from the eastern Atlantic (Fowler, 1936) and Mediterranean (Bini, 1967). There are, however, noticeable differences in Chromis from these two areas, including differences in colouration.* Adults seen in the Azores varied in standard length from 8-5 to 11-1cm. Colour di- morphism is especially apparent in breeding fish but also occurs between aggressive and non-aggressive individuals (almost certainly males) (Plate I). Body colour of females is predominantly golden brown, and the paired fins are orange. The caudal fin bears a white streak on its posterior margin, and this is edged in black on the anterior side; the remainder is orange. Non-nesting and non-aggressive males are of similar colour. During breeding, nesting or agonistic activities, however, the body often becomes vivid mauve with mauve tinges on the dorsal, anal and caudal fins. In some particularly aggressive individuals this *The taxonomic status of this species is under study. 188 G. M. MAPSTONE AND E. M. WOOD mauve becomes very pale, almost white. The period of time over which this colouration exists varies from a few seconds to several days. Juveniles varied in standard length from 4.5 to 6.1 cm and were of the female coloura- tion. None possessed the brilliant blue markings described by Abel (1961) and Bertram (1965), but they may have passed through this stage earlier in the year.

PLATEI. Chroniis chromis to show colour dimorphism, (a) aggregating individual, (b) nesting male. (half natural size) ETHOLOGY OF POMACENTRIDS 189 Habitat and feeding C. chromis, like A. luridus, was confined to rocky areas and was seen from 3 to 35 m, being particularly abundant in the 5 to 20m zone. Individuals occupied two different habitats; some remained close to the rocks while others swam, alone or more usually in aggregations, 2 m or more above the rocks. An examination of stomach contents revealed that C. chrornis feeds both on planktonic and benthic organisms. Eight out of 11 individuals contained predominantly planktonic, and three predominantly benthic organisms. A large number of developing fish eggs, almost certainly those of C. chromis, were found in one individual, and small numbers in four others. The intestine was short in comparison to that of A. luridus, typical of a carni- vorous animal.

Social organization and territorial behaviour Certain individuals seen amongst the rocks were semi-permanent dwellers, remaining there for weeks or possibly months ; others were temporary visitors from aggregations and remained for minutes or perhaps hours. The semi-permanent group was composed of juveniles and nesting males. Juveniles usually occurred in groups and were non-aggressive. Nesting males moved within a defined area of about 2-5m2. They showed agonistic behaviour to intruding conspecifics and this suggested they were defending a territory. Temporary visitors were non-nesting individuals and an inspection of 21 collected from amongst rocks at Ponta da Galera revealed that 90 % were males. During their stay each remained in a particular area (from 1.0 to 36.0 m2) and sometimes showed aggression to nearby conspecifics. Aggregations, containing up to 40 individuals, were composed of females and non- nesting males. As far as we know females only descended to the rocks to mate. However, during the summer at least, some or all males visited the rocks intermittently (temporary visitors: see above) whilst others remained for a longer period during breeding (semi- permanent dwellers : see above).

Population density Figure 5 shows the population density and distribution of nesting males and temporary visitors (probably mostly males) on the bottom at the two study sites during the period of our observations. There were four nesting males in the 400 m2site at the Ilheu, and five at Populo. Aggregations were often present above the rocks but these are not shown in the figure. In most cases territory boundaries did not overlap, and thus conflicts between adjacent territory holders were rarely seen. At Ponta da Galera, however, where the pop- ulation density was much higher, conflicts were common.

Agonistic hehaviour Agonistic behaviour was witnessed most often in nesting males, but the intensity of this behaviour and the number of encounters which occurred were not necessarily consistent in any one individual. Generally, however, the defending fish displayed as the intruder approached within 6 to 2m of the territory boundary, raising its dorsal fin, and sometimes changing to a bright mauve colour. This low intensity behaviour was often followed by a rapid chase (high intensity behaviour) in which the defender swam rapidly towards the intruder with fast flickering movements of the caudal fin. These movements 190 G. M. MAPSTONE AND E. M. WOOD

\'

;-\ Territorial nesting 6'

0 Ternporory visitor (probably non- nesting 0') (arrows not to scale, but indicate directional movements)

at the study sites. ETHOLOGY OF POMACENTRIDS 191 accentuated the white fin margin and probably gave an additional warning signal. All defensive encounters observed were successful and the intruder fled rapidly. The species chased most frequently were conspecifics and bottom dwelling wrasses (Table 11).

TABLEI1 Agonistic encounters in nesting male C. chromis. Based on 105 min observation of five individuals

Number of individuals Species attacked by C. chromis

Chromis chromis (male and female) 46 Thalassoma pavo (male and female) 12 Coris julis (female) 6 Sphoeroides spengleri 1 Diplodus sargus 1

Behaviour of non-nesting individuals Non-nesting C. chromis spent the majority of their time in aggregations of up to 40 individuals. They usually swam slowly about 0-5 to 3.0m apart and about 4m above the rocks, but occasionally, either as groups or individuals, descended closer to the rocky sea bed. The time spent on the rocks varied, but frequently the fish swam back to their original position after one to two minutes. Disruption of the aggregation often occurred while it was near the rocks, but it always reformed before returning to the mid-water position. The distance covered by aggregations varied considerably. They were often almost stationary, but one moved 15 m in 30 minutes. Such movements may be associated with the availability of food. On two occasions an aggregation closed up into a tight group (18 individuals in 0.6 m2) and swam randomly within this area for five minutes, before opening out again. The significance of this action was unclear. Fish in aggregations spent approximately 94% of their time swimming slowly, sculling with the pectoral fins, and the remainder swimming fast (Fig. 6). This latter activity was often associated with ,aggression. Aggressive behaviour was apparently initiated when one fish strayed too close to another. It followed the normal pattern, except that the chase was abbreviated and served only to place the intruder back in its original position. Aggression was not seen to be accompanied by a colour change, and the sex of the aggressive individuals could not be determined. Although females appeared to spend almost all their time in aggregations and only descended to the rocks to spawn, and occasionally to feed, the males left for a period to set up a breeding territory, and returned only after the eggs had hatched. An example of this was fish 3 from Populo. After caring for a batch of eggs this fish rejoined an aggrega- tion which was often present above its territory. Several days later, however, it was seen to swim down from the aggregation to its old nest site and remain there for six to ten minutes. During this time it showed high level agonistic behaviour towards a con- specific 6 m away amongst a shoal of trumpet fish (Macrorhamphosus scolopax (L.)), and towards a second three minutes later. Non-nesting males roamed an area on the bottom which varied in size from 1 to 36m2, much larger than the original breeding territory. They swam slowly or at a medium pace from rock to rock, occasionally feeding 192 G. M. MAPSTONE AND E. M. WOOD but never frequenting one particular rock surface. Interchange between aggregations and the home range was often witnessed. A histogram comparing swimming activities of rock dwelling and aggregating individuals is shown in Fig. 6.

Breeding behaviour Breeding probably occurs throughout the summer and individuals were observed preparing the site, spawning, and caring for the nest throughout our observation period (August). Males descended from the aggregation to the rocks where they set up a small breeding territory (about 2.5 m2). This usually incorporated a depression or crack in the rocks, destined to be the nest site (called here the lair) where the male spent the majority

c0, 2% ”r 80 - L- S to t tonary YI 2Ym 2 mw c c Slow swimming -? ---c 0 ee Fast swtmming -c m a2 E‘ 60- E 3 v) 6 e 0)c 40- 0) 5i c L 0 8 20 -

I ROCK DWELLING AGGREGATING FIG.6. Histogram to show swimming activities and associated behaviour in rock dwelling and aggregating Chromis chromis. The figures are derived from the activity being performed at 30 sec intervals and is based on 35 min observation of six rock dwelling individuals, and 73 min observation of eight groups of aggregating individuals. of its time. Some fish were observed cleaning the nest site by removing algae with the mouth and depositing it a few metres away. Courtship followed and involved a cycle of activities by the male in an attempt to attract a female from the aggregation. It swam up- wards 1 to 3 m from the lair, rapidly flicking the caudal fin, which accentuated the white fin margin and caused the whole body to vibrate. It then returned to its lair and performed rubbing movements over the potential nest site. This involved pressing the belly against the rock, and with fast movements of the caudal fin bringing about lateral flexures of the body while moving forward a few centimetres. It then turned and rubbed again on the nest site several times, sometimes interspersing these movements by patrolling close to the ETHOLOGY OF POMACENTRIDS 193 lair. This was then usually followed by the tail flicking jump and the whole cycle was repeated, as shown graphically in Fig. 7.

Rub on nest site & display nearby I

I L 0 50 I00 I50 200 250 300 350 Time (sec) FIG.7. Graphical representation of display behaviour patterns in three nesting male Chromis chromis. (a) No females within 10 m of this male. The significance of the signal jump is therefore obscure and may have been displacement behaviour (possibly initiated by the presence of the observer); (b), (c) females present. When a female was attracted down to the nest site by a displaying male, spawning usually followed. This was seen on several occasions, during daylight in each case, between 06.00 and 18.00 hrs. The two fish swam in a circle (about 0-3m in diameter) on the nest site, usually abreast, but sometimes head to tail. Both performed rubbing move- ments and, although gametes were not seen, it is probable that spawning was in progress. Other C. chromis individuals rarely came closer than 2 m from the nest site during mating, but if one did, the male left the female and chased it off, returning within seconds. The male often showed low intensity agonistic behaviour towards the female throughout spawning, without the latter being driven away. Eventually, however, it was driven 1 to 2 m from the nest site and the male returned to care for the eggs. Spawning was seen to continue for up to 15 min but may have lasted longer. 194 G. M. MAPSTONE AND E. M. WOOD As the eggs developed the male swam slowly over them at intervals, fanning them with the pectoral and caudal fins. It displayed agonistic behaviour to conspecifics and other species which approached within approximately 2 m of the nest site; only Scorpaena maderensis appeared to be tolerated. After the eggs had hatched the male became much less aggressive and roamed over a larger area, only visiting the nest site occasionally. Many males took on a mauve colouration at the onset of the breeding season, and re- tained it throughout courtship and nest care. Others became mauve sporadically and momentarily during courtship, spawning and territorial behaviour.

Behaviour of the juvenile It is not known exactly when the young move from a planktonic to a rock-dwelling existence. It is probable, however, that juveniles (standard length 4.5 to 6.1 cm) collected from amongst rocks were nearing the end of either their first or second year after hatching. Bertram (1965) reports that C. chromis in the Mediterranean are approximately 3.5 cm long after one year's growth. All juveniles roamed close to the rocks, feeding on particulate matter. Most formed into aggregations of up to 20 individuals, others swam alone or followed a non-nesting adult. They were usually tolerated by adults but were sometimes chased, presumably if they entered the territory of a male. Male juveniles began to set up territories when 6.0 to 8.5 cm in standard length (i.e probably at the beginning of the third year) and, in densely populated areas, were subjected to attack from nearby adults. For example, one young damsel fish at Ponta da Galera was able to defend a territory little larger than itself, and was presumably only able to enlarge it as it matured.

Discussion Habitat preference for the two pomacentrids in the Azores, Chromis chromis and Abudefduf luridus, is basically similar, both species inhabiting rocky areas in water depths from 3 to 35 m, and possibly deeper. The two species differ, at least during the summer, in their social organization. A. luridus is a solitary substrate species, feeding on algae and benthic organisms from the rocks. Some C. chromis individuals occupy a similar position; others form aggregations above the rocks, and all feed primarily on plankton. They also take benthic organisms, including eggs which are almost certainly of their own species. Other observations on these two genera indicate similar habits. The majority of Chromis species typically form plankton feeding aggregations in mid-water (Gosline & Brock, 1960; Hobson, 1968), and only descend to the substrate at night, when threatened, or during the breeding season. There is evidence to suggest that in Abudefduf a bottom dwel- ling, often solitary existence is more usual, for example: Abudefduf taurus Mueller & Troschel (Columbia, South America) lives singly or in small groups on the rocks (Albrecht, 1969), Abudefduf Zeucozona (Bleeker) (Indian ocean) lives close to the coral (Eibl- Eibesfeldt, 1964) and Abudefduf zonatus (Cuvier & Valenciennes) (Great Barrier Reef) moderately dispersed on the reef flat (Keenleyside, 1972). Fishelson (1964) reports that Abudefduf leucogaster Bleeker and Abudefduf melas Cuvier & Valenciennes (Red Sea) live singly or in pairs and roam indiscriminately among the coral cliffs. Abudefduf saxatilis (L.) (Red Sea) is found in small groups during winter, but during summer the groups ETHOLOGY OF POMACENTRIDS 195 break up, nesting males remaining on the bottom and others forming feeding aggregations and schools above the coral (Cummings, 1969; Albrecht, 1969; Fishelson, 1970). In most pomacentrids territoriality is shown only by the breeding male (Helfrich, 1959; Reese, 1964; Albrecht, 1969; Fishelson, 1970; Swerdloff, 1970), but in some cases (e.g. Abudefduf zonatus, Keenleyside, 1972) both sexes are territorial. A. luridus falls into this category, for all fish apparently maintain a territory on the bottom. Agonistic behaviour in nesting males is intense and is directed primarily towards other species rather than conspecifics, possibly because of the low density of the latter (not exceeding 1 per 100 m2). Territorial activity in females and non-nesting males is much less evident, and agonistic behaviour infrequent and of low intensity. Only nesting males adhere strictly to their boundaries, whereas females and non-nesting males are less strict and sometimes range beyond territorial boundaries. The territory of the nesting male is small (4 m2) in comparison with that of the non-nesting male, and is presumably reduced in size prior to breeding to ensure that the eggs can be given adequate protection. Territoriality in nesting males presumably increases reproductive success, but in non-nesting males and females its function is less certain. Non-nesting males may maintain a territory to ensure a potential nesting area, but this could not apply to females. Possibly both sexes defend a territory for its ecological resources, e.g. food, although they do not show aggression to other species (e.g. labrids) that might compete. Only nesting males exclude such fish from their territories, and this is probably to protect eggs rather than a grazing area. Chromis chromis individuals follow the more usual pattern of the male alone defending a territory. Females are never involved in this activity, but live above the rocks in feeding aggregations of up to 40 individuals, many fewer than reported for other Chromis species (Myrberg et al., 1967; Russell, 1971 ; Sale, 1971). Non-nesting males apparently maintain a territory, but at a low level; they spend much time in feeding aggregations above the rocks and only visit the territory at intervals, sometimes showing agonistic behaviour to conspecifics and others. The territory of breeding males, as in Abudefduf luridus, is smaller and more vigorously defended. In contrast, however, the majority of agonistic encounters in C. chromis are with conspecifics. This could be due either to their relatively high density, or to the fact that they take eggs more readily than A. luridus, as suggested by the presence of eggs in the stomach of the former, but not the latter. It is curious that in the Mediterranean (Abel, 1961) nesting male C. chromis do not interfere with one an- other even though their density is much higher (163 individuals per 100 m2) than in the Azores (up to 20 per 100 m2). We found no evidence that nesting male C. chromis jointly defend a territory, as reported in the English summary of Abel's paper. This statement does not, however, appear in the German text, and can be assumed to be a mis- interpretation. Territory size in Azores C. chromis varies (1.0 to 4-5 m2), being com- parable with that of some other Chromis species (Chromis caeruleus (Cuvier & Valenciennes), Sale, 1971 ; Chromis multilineata (Guichenot), Myrberg et al., 1967), but larger than Abel's figure of 0.6 m2for Mediterranean C. chromis. Juveniles of both species live close to the rocks, A. luridus singly and C. chromis usually in groups of up to 20 individuals. Extremely few young A. luridus were seen, which suggests that several years are spent elsewhere, possibly in deeper water. In contrast, there were many young C. chromis (standard length 4.5 to 6.3 cm) which had presumably hatched in the summer of 1971 or 1972, and returned some time before summer, 1973. It appears 196 G. M. MAPSTONE AND E. M. WOOD that these latter individuals are tolerated when small, but subject to attack as they grow larger. Between 6.5 and 8.5 cm standard length females leave the group to join feeding aggregations and males begin to establish a territory. In all pomacentrids a basic sequence of events is followed during reproduction and particular patterns which have evolved for various species are reviewed by Reese (1964). In both A. luridus and C. chromis the male selects and prepares a nest site within the terri- tory, always on a protected surface. Female A. luridus sometimes visit the territory of a nesting but non-displaying male; a type of approach which has also been described for Abudefduf abdominalis (Quoy & Gaimard) (Helfrich, 1959), Chromis multilineata (Albrecht, 1969), C. dispilus Griffin (Russell, 1971) and Hypsypops rubicunda (Girard) (Limbaugh, 1964; Clarke, 1971). Female C. dispilus apparently initiate the spawning sequence, but there is no evidence for this in A. luridus. Female C. chromis did not approach nesting males and thus, as in A. luridus, it is the male which begins the courtship activities. Male A. luridus make horizontal excursions to attract a mate, arching and looping close to the rocks when a female is in the vicinity, and then leading it back to the nest. A similar pattern is reported for A. abdominalis (Helfrich, 1959) and A. zonatus (Keenley- side, 1972), except that in the latter no looping occurs. C. chromis makes vertical move- ments, termed signal jumps (signalsprung) by Abel (1961), and described for related species (Abudefduf saxatilis, A. taurus and Chromis cyanea (Poey), Albrecht, 1969; C. multilineata, Myrberg et al., 1967, Albrecht, 1969; C. caeruleus, Sale, 1971). Signal jumps in Azores C. chromis are interspersed at regular intervals by rubbing motions on the potential nest site, movements which correspond closely to fanning and spawning described for A. taurus, A. saxatilis, C. multilineata (Albrecht, 1969) and C. dispilus (Russell, 1971). The pre-spawning rubbing activities seen in Azores C. chromis seem, with the signal jumps, to function as display behaviour. Signal jumps and rubbing motions were, however, sometimes performed in the absence of females, much as reported for C. multilineata (Albrecht, 1969), presumably as displacement behaviour, and possibly due to the presence of the observer. Too close an approach may set up a conflict between fighting and fleeing, as described for Crenilabrus melanocerus (Risso) (Potts, 1968), and this can then result in displacement activities. Colour change and tail flicking by male C. chromis give additional visual signals to the female during display. Colour change is striking, can appear rapidly, and can either last a few seconds or be sustained throughout breeding. In contrast, colour dimorphism in A. luridus is barely perceptible. Intensification or change of colour has been reported for other pomacentrids (Helfrich, 1959; Turner & Ebert, 1962; Stevenson, 1963 ;Albrecht, 1969; Sale, 1971 ; Russell, 1971), including C. chromis from the Mediterranean (Bertram, 1965). Courting males are stated to be “jet black”, which is distinctly different from the light blue or white of courting males in the Azores. Rubbing continues in both A. luridus and C. chromis whilst male and female are close together on the nest site, presumably as the two fish spawn. Abel(l961) reports that Med- iterranean C. chromis rarely spawn at the same time, but that the male hovers close to the nest, tail flicking and chasing intruders, only spawning when the female has departed. We also saw evidence of this delayed spawning, for the maleof bothspecies oftencontinued rubbing activities after the female had been chased away. Alternatively the male could have been fanning the eggs, or exhibiting displacement activity. The male in both species cares for and protects the eggs, chasing almost all intruders ETHOLOGY OF POMACENTRIDS 197 from the territory. In neither species is there any evidence that any long term pair bonds are formed, and in A. luridus at least, the male is polygamous. Multiple synchronous spawning is common in both Abudefduf and Chromis species (Longley & Hildebrand, 1941 ; Turner & Ebert, 1962; Limbaugh, 1964; Myrberg et al., 1967; Albrecht, 1969; Swerdloff, 1970; Russell, 1971; Sale, 1971), but was not seen in either of the pomacentrids in the Azores. Abel (1961) reports from the Mediterranean that male C. chromis set up a territory and then, with the females in a shoal above them, display and spawn within a three day period. After this the females leave, and the males remain about another three days, until the eggs have hatched. He does not know how many times spawning occurs within this short time. Spawning in C. chromis in the Azores occurs more irregularly, and the males remain within the spawning area for longer, possibly because the eggs take longer to develop. There is also evidence that males spawn more than once during the breeding season. Our studies have revealed both behavioural and morphological differences between Mediterranean and Azorean Chromis chromis, and we conclude that such differences have probably arisen as the result of geographical isolation. Individuals from Maderia are morphologically of the Azores type, and we suggest that behaviour also would be similar. This, however, remains to be verified. Summary Both Abudefduf luridus and Chromis chromis frequent rocky areas, from a depth of 3 to 35 m or more. They are most abundant in the 5 to 20 m zone. A. luridus is closely associated with the substrate; a territory is maintained by both sexes, but is most clearly defined in nesting males. C. chromis nesting males also defend a well defined territory amongst the rocks, but females aggregate in open water above, and non-nesting males alternate between these two positions. Sexual dimorphism is barely perceptible in A. luridus but is striking in C. chromis, consisting of a colour change which is either a permanent feature throughout breeding, or else assumed and lost within minutes. Breeding behaviour follows the general pattern described for other pomacentrids. In both species courtship behaviour is initiated by the male which leaves the territory for brief periods and displays to a neighbouring female. C. chromis males perform vertical signal jumps in the water whereas A. luridus makes horizontal excursions and then looping movements close to the rocks. In either case the female is led back to the male’s territory and begins to deposit eggs, rubbing on the nest site alternately with the male. The latter presumably releases sperm, although this was not actually seen, and they may be deposited after the female has departed. There was no evidence of multiple synchronous spawning in either species. The eggs are attached to the substrate by a cord of fine adhesive threads and the male protects and cares for them, showing intense agonistic behaviour to intruding fish. The events between hatching and resettlement on the adult grounds are uncertain; C. chromis probably returns within a few months, but juvenile A. luridus appear to live else- where during their first year. It is suggested that geographical isolation is responsible for various morphological and behavioural differences between Mediterranean and Azorean populations of C. chromis. 198 G. M. MAPSTONE AND E. M. WOOD We are grateful to Dr G. W. Potts (Marine Biological Association, Plymouth) and Dr C. C. Hemmings (Marine Laboratory, Aberdeen) for help and advice during the formulation of the research programme, and for continued support from them and frcm Mr G. E. Barnes (Chelsea College). We are indebted to Mr A. C. Wheeler (British Museum (Natural History)) for arranging the loan and transport and collection equipment, and for invaluable help in identification of specimens. This work would not have been possible without the assistance of members of the University of London (ULSAC) and Exul (ExulSAC) Sub Aqua Clubs, and we would like to thank all those who participated in the two expeditions, in particular, Mr C. R. Wood, Dr N. B. Mapstone, Miss A. Cooper Willis and Mr W. H. L. Williams. We are indebted to the following for generous financial support: University of London Central Research Fund (to E.M.W.), Surrey County Council (to G.M.W.), Royal Geographical Society (to ULSAC & ExulSAC), World Expeditionary Association (to ExulSAC), and Gilchrist Educa- tional Trust (to ExulSAC).

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