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A COMPARISON OF THE BEHAVIOUR AND TERRITORY SIZE OF THE BEHNS DAMSELFISH WITHIN AND OUTSIDE THE NO FISHING ZONE

Introduction

The damselfish belong to the family Pomacentridae, a large family of tropical and subtropical fishes with a worldwide distribution.  The Indo-Pacific Ocean is particularly rich in the species.  Perhaps the most typical of all families associated with coral reefs, Pomacentrids are mostly small, laterally compressed fish with a distinctive shape and many are brilliantly coloured.  As a group they are great opportunists, colonising and exploiting reefs, creek and lagoon habitats wherever these are marginally suitable.   

Damselfish present a rich field for studies involving inter-relationships of species, coloration, ecology and behaviour. Territorial behaviour is strongly developed and it seems that most species are resident fishes that tend towards individual or group territoriality.  Konrad Lorenz (1972) suggests that the more brilliantly coloured species, such as the Behns Damsel (Neoglyphidodon nigroris) tend to possess the strongest territorial instincts.  Aggressive behaviour of the Behns is often focused on species of similar feeding habits and the defended area is usually well defined.  It has been suggested that individuals select a territory and the intensity of aggressive behaviour increases form the periphery of the territory inwards.     

Damselfish will use coral heads or other similar structures of reef material as a home base, as each head provides sufficient space for a certain number (Barnes, 1998).  Damselfish are ‘grazers’, either selectively or non-selectively upon algae in their territory.  The Behns Damsel is planktivorus on the bottom and in the water column.  The territories are often associated with the reef flats and crests where algal productivity is high.  They will defend their ‘algal garden’ from other grazing fish, which may control algal species composition (Ogden and Lobel, 1978). These gardens may occupy up to 60% of the reef flats; hence they are important contributors to community structure.  Therefore, territorial behaviour may be an indication of resource limitation. 

 

Aims

  1. To examine the abundance and density of Behns Damselfish at a number of sites to enable a comparison to be made.
  2. To understand the effect of habitat availability in a protected No Fishing Zone on the number of territories and their size of individual Behns Damselfish.
  3. To examine the behaviour, intra and interspecific interactions between Behns.
  4. To examine changes in density with depth along a reef wall.

 

Objectives

  1. To count the number of Behns Damselfish along 3 replicate 50m transects, each separated by a 5m space.  3 replicates to be taken to calculate average density.
  2. To map the territory size by observing one individual over a 15 minute period.  Perimeters of the territory to be marked with pink ribbon to allow the size to be measured using a tape measure.  3 replicates on separate occasions on individual species at each site.
  3. To observe the behaviour and interactions (given below) of individuals within those territories.  Recordings taken in 1-minute blocks for 15 minutes.  Same 3 individuals, 3 replicates.
  4. To count the no. of Behns Damselfish along 5m transect every meter from a depth of 15m to the reef crest.  

 

Hypothesis

Within the NFZ the abundance of species will be high, therefore, intraspecific competition between Behns Damselfish will also be high.  This will result in smaller territories and more aggressive behaviour.

 

Methodology

The Wakatobi Marine National Park was set up in 1996 including a Stakeholder (managed) Zone between the islands of Hoga and Kaledupa.  A voluntary No Fishing Zone was set up by the Bajo villagers along the home reef of Hoga, within the Stakeholder Zone.

Seven sites were selected within the stakeholder zone, both inside and outside the No Fishing Zone:

 

Behns Damselfish populations were assessed by visual census over transects, using SCUBA.  Sale (1991) states that reefs are easy to study using this method due to the clarity of the water and the limited reaction of the fish to SCUBA divers.   

The Line Intercept Transect method (LIT) was used to estimate the percentage cover of coral along transects at different sites, by calculating the fraction of the length of the line is intercepted by the object (Gates, 1979).  Transect lines were set up along the reef crest, each line being 50m in length, with a 5m gap, at a depth of approximately 5m. For each of these sites the transect line was replicated three times.   

These replicates were surveyed three times, giving a total of three benthic surveys and nine Behns Damselfish abundance surveys for each site.  When each transect line was laid they were left for approximately 10 minutes before the survey commenced to minimize the effects of diver positive and diver negative influences. 

Behns density and distribution with depth was measured using a 5m transect.  The number of Behns in each 1m segment was recorded every metre from 15m to the reef crest.  Coral cover (in lifeform categories) was also recorded at depths of 15m, 10m, and 5m.  For each site the transect were repeated three times, 25m apart.  The replicates were also surveyed a total of three times. 

The territory size and behaviour of three Behns Damselfish were recorded at sites within the No Fishing Zone and outside (Buoy 4).  Territories were chosen randomly, approximately 10m apart 3m below the reef crest.  Perimeters of each territory were marked using pins and pink ribbon to allow accurate measurements to be taken using a tape measure.  Behaviour of each damsel was measured in 1minute blocks for a period of 15 minutes.

 These replicates were repeated a total of three times.

 

Preliminary results

As yet, no analysis has been carried out on the data that has been collected over the last eight weeks; however, some interesting observations have been made.  The territory sizes within the No Fishing Zone appear to be smaller overall compared to those outside the No Fishing Zone (Buoy 4).  There is also a greater incidence of aggressive behaviour between Behns Damselfish in the territories studied within the No Fishing Zone.  At both sites aggressive behaviour of individual Behns was generally towards other damselfish, but particularly towards the Indo-Pacific sergeant (Abudefduf vaigiensis) and Bicolor Damselfish (Stegastes partitus). 

The data may be analysed using ANOVA to examine the relationship between habitat or coral cover and Behns abundance and density, to enable comparisons to be made between the sites.

 

Dissemination of results

Dissertations entitled  A comparison of the behaviour and territory size of the Behns damselfish within and outside the No Fishing zone will be produced by Amy Cadby, University of Sussex and Joanna Rowe, University of Birmingham by February 2003

Reference List

Barnes, R.S.K.and Hughes, R.N.  (1998) Introduction to Marine Ecology.  Blackwell Science Publications. 

Gates, C.E.  (1979) Line transect and related issues in Sampling Biological Populations.  Inter. Co-op Publishing House, Maryland. 

Lalli, C.M. and Parsons, T.R.  (1997) Biological Oceanography an Introduction.  Butterworth-Heineman Ltd. 

Sale, P.F.  (1991).  The Ecology of Fishes on Coral Reefs.  Academic Press Ltd. London. 

Edinger, E.N. and Risk, M.J.  (2000) Reef classification by coral morphology predicts coral reef conservation value.  Biological Conservation, 92, 1-13. 

Reese, E.S.  (1981) Predation on corals by fishes of the Chaetodonidae family, implications for the conservation and management of coral reef ecosystems.  Bulletin of Marine Science, 31, 594-694. 

Roberts, C.M. and Ormond, R.G.F.  (1987) Habitat complexity and coral reef fish diversity and abundance on Red Sea fringing reefs.  Mar. Ecol. Prog. Ser. 41, 1-8. 

Wilkinson, C. (Ed.).  (1994) Survey Manual for Tropical Marine Resources.  ASEAN