TERRITORIOS DEL PEZ STEGASTES PLANIFRONS EN FORMACIONES CORALINAS DEL PARQUE NACIONAL NATURAL TAYRONA, CARIBE COLOMBIANO: UN PANORAMA GENERA

The pomacentrid Stegastes planifrons is one of the most conspicuous inhabitants of the coral reefs and constitutes an important agent of natural coral mortality. These fishes kill coral directly by removing coral polyps for opening up a space for its algal turfs, which are their main food. The population density, territory and algal turfs areas of Stegastes planifrons were assessed at Chengue and Gayraca bays in Tayrona Natural Park, as a contribution to understand natural processes involved in the coral reef deterioration. During August to November 1999, belt transects (20 x 2 m) were evaluated at four reef habitat types: multispecific coral assemblages dominated by (1) Colpophyllia natans (COLP) or (2) Montastraea spp. (MONT); and monospecific coral stands of (3) Acropora palmata (APAL) or (4) A. cervicornis (ACER). In total 457 fishes were censused: 21% juveniles (2.6±0.6 cm), 3% subadults or intermediates (6.6±0.5 cm) and 76% adults (12.6±0.2 cm). The highest density of S. planifrons was observed in the ACER (1.52 terr*m-2) despite this habitat is very degraded. Lower densities were found in the others habitats (-0.5 terr*m-2), but this indicates that the fish is using also alternative habitats. The algal turf size was around 0.1 m2 and significatively lowest at APAL (0.07 m2), due to the high regeneration and growth rates of A. palmata, which balance the frequent fish biting. The high densities and algal turf size of S. planifrons suggest an important role of this fish in the natural mortality and dynamics of Tayrona coral communities.

Differences in composition of territories in relation to behaviour, stage, and depth of the three-spot damselfish, Stegastes planifrons, in Caribbean coral reefs

Coral reef diversity is correlated with the depth at which the reefs are found, the energy available for biological processes, and the species’ roles and presence throughout the food chain. Can a specific species activity alter the whole ecosystem? Can a small-scale, short-term activity such as fish behaviour have a long-term effect on a larger scale, that of the reef? Can the life stage of a species mediate substrate competition? The three-spot damselfish (Stegastes planifrons) is hypothesized to regulate competition between substrate coverage by actively farming – protecting from herbivores and weeding – in order to regulate the algal species composition and percent coverage of the reef. This behaviour is observed in both juvenile and adult fish. Deeper patches are predicted to have less coral diversity and higher algal diversity; juvenile fish are predicted to have less diversity in their patches than adults. Coral and algal diversity are hypothesized to be negatively correlated. In this study, behaviour of the S. planifrons was classified into one of four categories (active patrolling, passing patrolling, farming, and hiding) and palatable algae surface area coverage was digitized from photographs; life stage was either juvenile or adult. Coral and algal genus diversity were measured along a depth gradient of 0-16 m where the diversity of the reef was thought to be the highest. A three-way ANCOVA was performed to test whether fish behaviour (a small-scale, short-term process), depth, or fish development stage (juvenile or adult) had a significant effect on coral or algal diversity (a large-scale, long-term process). Results showed a significant effect of fish behaviour category on algal genera diversity, and a significant effect of depth on both algal and coral genera diversity. Farming yielded significantly more algal coverage than hiding. This study shows that small-scale, short-term behaviours by S. planifrons can have an effect on algal genera diversity on coral reefs in Utila, Honduras. Keywords: Stegastes planifrons (three-spotted damselfish); behaviours (short-term, small-scale); stage of development (juvenile, adult); depth; coral reef and algal diversity (long-term, large-scale); damselfish territories

CENTRE-EDGE DIFFERENCES IN BEHAVIOUR, TERRITORY SIZE AND FITNESS IN CLUSTERS OF TERRITORIAL DAMSELFISH: PATTERNS, CAUSES, AND CONSEQUENCES

Variation in behaviour and fitness with spatial position in a group (centre vs edge), as well as the causes and consequences, was studied in the permanently territorial threespot damselfish, Stegastes planifrons. These fish have individual territories, clusters of which occur on coral patch reefs. Fitness correlates varied with group position. Although, survival and age did not differ between fish resident in the centre or edge, central fish were larger and grew faster than edge fish. Central males also received more clutches, eggs/clutch, and cumulative number of eggs to defend than did edge males. The higher fitness in centre positions was then correlated with differences in behaviour by group position. Territories defended were smaller in the centre of groups. Aggressive interactions with conspecifics were more frequent for central fish, but interactions with heterospecifics, and overall interactions, occurred at much lower rates for fish in central positions. Centre fish lost less of the algal food in their territories to intruders. Feeding and courtship rates, and forays from the territory, did not differ by position. These behavioural observations suggest that the positional differences in fitness measures and territory size are due to lower energy costs of territory defence for central fish, permitting the greater investment in growth and reproduction. Centre-edge differences in behaviour and territory size could be due to a selfish-herdlike group position effect (i.e. position relative to neighbours determines rates of behaviour), the microhabitat variation that was found between these positions, or a combination of both factors. To test among these alternatives, fish peripheral to a central treatment individual were removed experimentally, thus altering that individual's relative position from the centre to the edge of a group, without changing the microhabitat features of its territory. Territory size and behaviour measures of position-altered fish changed in ways consistent with the interpretation that group position has a much greater effect on behaviour and territoriality than does microhabitat. Group position may thus influence the fitness measures that differ by spatial position. These results suggest that habitat geometry and/or fragmentation may affect individual territory size, and hence maximum population density, as well as per capita reproductive output, by altering the relative number of edge individuals in groups. Does S. planifrons recognize and compete for residence in the better central positions? If there is competition, then there should be (1) slower reoccupation, (2) lower rates of intraspecific aggression, and (3) fish resident in the centre should not compete for open edge space in newly opened edge territories, relative to newly cleared centre territories. Also, (4) colonization to completely cleared areas should preferentially be to the centre positions. The first three predictions were supported by a paired removal experiment, while the fourth prediction was partially supported in another experiment. Competition thus appears to be an important factor determining the local distribution of threespot damselfish on patch reefs.