BULLETIN OF MARINE SCIENCE, 47(3): 721-724, 1990 PAPER

CO-DEFENSE OF TERRITORY SPACE BY TWO OF CORAL REEF FISHES

M. Draud, D. E. Itzkowitz and M. Itzkowitz

ABSTRACT In Jamaica, the saddle blenny (Malacoctenus triangulatus) and the beaugregory damselfish ( leucostictus) defend territories in small rubble and sand habitats. When defending separate territories, both species were highly aggressive to conspecifics and both attacked the egg-eating bluehead ( bifasciatum). When defending the same territorial space, both species remained highly aggressive to conspecifics. However, in this association, the beaugregory was the primary defender against the bluehead wrasse.

Animals are expected to be territorial when the seemingly large costs needed to maintain the territory are outweighed by the benefits gained from the territory (Brown, 1964). At present considerable attention has been given to mod- ulating their costs of defense by changing the size of the territory in response to both intruder pressure and territory quality (McNair, 1987; Schoener, 1987). It is also possible that territorial costs can be reduced by sharing the defense with a different species. Non-territorial co-defense (e.g., mobbing behavior or mixed species colonial defense) against predators (Kruuk, 1964; Hoogland and Sherman, 1976; Gladfelter et al., 1980) as well as overlapping territories (Robertson, 1984) have been re- ported. However, there are few accounts of two territorial species sharing their defense of an area against a common third species. This probably reflects a unique circumstance in which both have similar spatial requirements but are not in competition for resources. Here we present a preliminary study on two species of coral reef fish, the saddle blenny (Malacoctenus triangulatus) and the beaugregory damselfish (), defending the same area against a third species. We further suggest that, at least, the saddle blenny benefits from the association.

METHODS

The study took place from June to August 1988 in the shallow (1-3 m depth) back reefat Discovery Bay, Jamaica. Beaugregory damselfish males were prominent as they defended 1- to 2-m diameter territories in the rubble and sand habitat. Many individuals defended artificial breeding structures placed in the area on 5 June 1988. These structures consisted offour PVC tubes (15 cm long, 10 cm diameter) bolted in a cross pattern to a flat piece of plexiglass (Itzkowitz and Makie, 1986; Itzkowitz, in press). Beaugregory males prefer these artificial structures over their natural sites (Itzkowitz and Makie, 1986; Itzkowitz, in press). Saddle blennies also defend small territories in this environment and are often found, naturally, in association with beaugregory males. Similar to beaugregory males, saddle blenny males court passing conspecific females. Receptive females follow males to a crevice where they deposit their eggs. Females of both species appear to have home ranges, rather than territories, and do not participate in the protection or care of the eggs. Previous observations confirm that both species are highly susceptible to egg predation by the bluehead wrasse (Thalassoma bifas- ciatum). This study utilized two components in determining if the saddle blenny and/or beaugregory dam- selfish modify their behavior when co-defending a territory. In the first component, twenty five different male saddle blennies, co-defending the same areas as a beaugregory damselfish, were observed for 10 min each. Territorial adult male saddle blennies were easily distinguished from females by their coloration and highly aggressive territorial behavior. Adult beaugregory males differed from females in both size and coloration. They also defended the territory more aggressively than females. The observer floated within 3 m of the study while recording all aggressive and non-aggressive interactions on a PVC slate. Aggressive behaviors included lateral displays, chasing and biting. A non-

721 722 BULLETIN OF MARINE SCIENCE, VOL. 47, NO.3, 1990

Table I. Frequency of bites (bites/5 min) by a resident blenny or a resident male beaugregory damselfish directed at a flask containing either an intruding bluehead wrasse or an intruding saddle blenny. Blenny Alone = solitary saddle blenny; Beau Alone = solitary male beaugregory damselfish; Blenny with Beau = the behavior of either the saddle blenny or the beaugregory damselfish when sharing the same territory. The letters in parentheses denote the results of the eight residents in the six tests. Insignificant differences (N.M.e.; P > 0.05) between residents are indicated by continuous underline. Significant differences (P < 0.0 I) are indicated by separations of underline

Intruder Bluehead wrasse Saddle blenny

Resident Median Mean ± SE Median Mean ± SE Blenny Alone (a) 64 68.1 ± 9.4 (e) 72 65.0 ± 5.5 Beau Alone (b) 167 164.1 ± 3.4 (f) 0 1.1 ± 0.5 Blenny with Beau Blenny (c) 0 2.7 ± 1.8 (g) 51 55.7 ± 9.1 Beau (d) liS 106.0 ± 13.1 (h) 0 0.7 ± 0.5 N.M.e. Test: c f h ~ d b aggressive interaction occurred when two fish passed within 30 cm of each other without subsequent chasing or lateral displays. The second component consisted of introducing model intruding fish into blenny or damselfish territories, the "model-bottle" technique used successfully by Myrberg and Thresher (1974). Either an adult male saddle blenny or an adult bluehead wrasse was placed in a flask and introduced into the territory defended by a male saddle blenny alone, a male beaugregory damselfish alone, or males of both species. None of the male saddle blennies were defending eggs at the time ofthe flask presenta- tions. Five min counts were taken of the defender's number of bites at the flask, number of lateral displays (resident presents side view to flask with all unpaired fins extended), and the total time spent within 10 cm of the flask. Empty flasks were presented to a seperate set of fish in the study area as controls. They were ignored by both the saddle blenny and the beaugregory damselfish and were not included in this analysis. Model intruder presentations were done at a rate of 5-10 per day, and were all completed within a month. Adult beaugregory damselfish were not used in the presentations since saddle blennies were never observed to defend against them. Adult beaugregory males defending against conspecific males are treated elsewhere (Itzkowitz, in press). Data were compared by the Nonparametric Multiple Comparison Test (N.M.C.) (Zar, 1984).

RESULTS AND DISCUSSION During the lO-min observation periods, male beaugregory damsel fish passed within 30 cm of resident saddle blennies on 63 occasions in response to which aggression was never observed. The resident saddle blenny attacked bluehead wrasse 11 times. Previous studies in Jamaica (Itzkowitz, in press) and in other Islands (Ebersole, 1977) revealed that the bluehead wrasse was com- monly attacked by defending male beaugregory damselfish.

Table 2. Frequency of lateral displays (see legend Table I for further details)

Intruder

Bluehead wrasse Saddle blenny

Resident Median Mean ± SE Median Mean ± SE

Blenny Alone (a) S 9.6 ± 0.9 (e) 12 12.1 ± 0.6 Beau Alone (b) 9 8.1 ± 0.8 (f) 0 o Blenny with Beau Blenny (c) 0 1.1 ± 0.4 (g) 13 12.1 ± 1.3 Beau (d) 8 7.8 ± l.l (h) 0 0.3 ± 0.2 N.M.e. Test: c f h a b d ~ DRAUD ET AL.: CO-DEFENSE OF TERRITORY SPACE 723

Table 3. The total amount of time (sec) either the saddle blenny resident or the male beaugregory damselfish resident spent within 5 em of the flask (see legend Table I for further details)

Intruder

Bluehead wrasse Saddle blenny

Resident Median Mean ± SE Median Mean ± SE Blenny Alone (a) 275 261.7 ± 10.2 (e) 275 274.9 ± 18.8 Beau Alone (b) 280 279.0 ± 2.2 (f) 0 2.0 ± 0.9 Blenny with Beau Blenny (c) 4 19.3 ± 8.5 (g) 284 248.9 ± 24.9 Beau (d) 270 272.0 ± 6.2 (h) 0 1.7 ± 1.3 N.M.C. Test: h f c a b d f g

During the intruder presentations, blue head wrasse evoked the most intense bite response from both solitary beaugregory males and those beaugregory males with saddle blennies (Table I). Beaugregory males rarely attacked saddle blenny intruders. The resident saddle blenny vigorously attacked intruding saddle blen- nies when defending alone or in residence with the beaugregory male. There was a significant reduction (N.M.C.; P < 0.01) in the saddle blennies' bite rate against the bluehead wrasse when in residence with a beaugregory male. Beaugregory males rarely displayed laterally to saddle blenny intruders (Table 2). Saddle blenny defenders intensely laterally displayed to saddle blenny intrud- ers, irrespective of the presence or absence of beaugregory males. Beaugregory males laterally displayed to bluehead wrasse intruders under all circumstances while saddle blenny defenders significantly reduced their lateral displays (N.M.C.; P < 0.01) when beaugregory males were present. Time near the intruder (Table 3) resembles both bite-rate and lateral-display data. Beaugregory males spent little time near flasks containing saddle blennies and significantly increased the time near the intruder when the flask contained a bluehead wrasse (N.M.C.; P < 0.01). Saddle blenny defenders spent considerable time near intruding saddle blennies and bluehead wrasse. However, when the saddle blennies resided with beaugregory males, there was a significant decline in time spent near the bluehead wrasse intruder (N.M.C.; P < 0.01). These data support the natural observations that little aggression occurs between saddle blennies and male beaugregory damselfish. The saddle blenny appears to benefit from this association because the larger male beaugregory damselfish plays a larger role in defending against the bluehead wrasse. As both the saddle blenny and the beaugregory damselfish eat small invertebrates within their territories, it is possible that both are attempting to exclude a third competitor (i.e., the bluehead wrasse) from the area. However, iffood was limited, the larger beaugergory dam- selfish should also attempt to exclude the resident or "flasked" saddle blenny from his territory. An alternate possibility is that beaugregory damselfish and the saddle blenny are attempting to exclude an egg predator common to both. Further work is required to determine ifmale saddle blennies, associated with male beau- gregory damselfish, have enhanced lifetime reproduction through superior nutri- tion and/or reduced egg loss.

ACKNOWLEDGMENTS

We thank R. Gates and R. Jaeger for critical readings of earlier drafts of this manuscript and H. D. Haese for positive species identification. This project was funded by NSF (OCE-85l5281) awarded to M. Itzkowitz. 724 BULLETINOFMARINESCIENCE,VOL.47, NO.3, 1990

LITERATURE CITED

Brown, J. L. 1964. The evolution of diversity in avian territorial systems. Wilson Bull. 76: 160- 169. Ebersole, J. P. 1977. The adaptive significance of interspecific territories in the reef fish, Eupoma- centrus leucostictus. Ecology 58: 914-920. Gladfelter, W. B., J. C. Ogden and E. H. Gladfelter. 1980. Similarity and diversity among coral reef fish communities: a comparison between tropical Western Atlantic () and tropical Central Pacific (Marshall Islands) patch reefs. Ecology 61: 1156-1168. Hoogland, J. L. and P. W. Sherman. 1976. Advantages and disadvantages of bank swallow (Riparia riparia) coloniality. Eco\. Monogr. 46: 33-56. Itzkowitz, M. In Press. Heterospecific intruders, territorial defense, and reproductive success in the beaugregory damselfish. J. Exper. Mar. BioI. Ecoi. ---and D. Makie. 1986. Habitat structure and reproductive success in the beaugregory damselfish. J. Exper. Mar. BioI. Ecoi. 97: 305-312. Kruuk, H. 1964. Predator and anti-predator behaviour of the black-headed gull (Larus ridibundus). Behaviour (Supp\.) II: 1-129. McNair, J. N. 1987. The effect of variability on the optimal size of a feeding territory. Amer. Zoo!. 27: 249-258. Myrberg, A. A. and R. E. Thresher. 1974. Interspecific aggression and its relevance to the concept of territoriality in reef fishes. Amer. Zoo!. 14(1): 81-96. Robertson, D. R. 1984. Cohabitation of competing territorial damselfishes on a Caribbean coral reef. Ecology 65: 1121-1135. Schoener, T. W. 1987. Time budgets and territory size: some simultaneous optimization models for energy maximizers. Amer. Zoo\. 27: 259-291. Zar, J. H. 1984. Biostatistical analysis, 2nd Ed. Prentice-Hall, Englewood Cliffs, New Jersey. 718 pp.

DATEACCEPTED: June 29, 1990.

ADDRESS: Department of Biology, Williams Hall 31, Lehigh University, Bethlehem, Pennsylvania 18015.