University of Groningen Butterflyfishes of the Southern Red Sea Zekeria, Zekeria Abdulkerim IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2003 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Zekeria, Z. A. (2003). Butterflyfishes of the Southern Red Sea: Ecology and population dynamics. s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 26-09-2021 Butterflyfishes of the Southern Red Sea 31 Chapter 4 Resource Partitioning among Four Butterflyfish Species Z. A. Zekeria, Y. Dawit, S. Ghebremedhin, M. Naser and J. J. Videler Published in Marine and Freshwater Research. 2002,vol. 53, pp.1-6. 32 Chapter 4. Resource Partitioning Abstract Feeding habits and territorial behaviour of four sympatric Red Sea butterflyfishes were investigated in the Eritrean coastal waters. Feeding habits were studied by focal animal sampling. Individual bite rates and types of food consumed were recorded. Stomach contents of 125 specimens were analysed in the laboratory. The food items in the stomach were sorted and their volume estimated. The four species showed marked variation in their food preferences and feeding habits. The most abundant butterflyfish Chaetodon larvatus, an obligate corallivore, forms monogamous pairs. Each pair defends a relatively small territory against conspecifics and C. semilarvatus. The latter species also feeds on scleractinian corals but lives solitary or in small aggregations. The third species, Heniochus intermedius, feeds on non-coralline benthic invertebrates (mainly polychaetes); it usually lives in pairs or in aggregations of up to 24 individuals. Both C. semilarvatus and H. intermedius occupy undefended and overlapping home ranges. The least abundant species, C. mesoleucos, forms monogamous pairs, defends a territory and feeds mainly on non-coralline benthic invertebrates (mainly nematodes and polychaetes). The study reveals that the four species co-exist in the same habitat where they partition the food resources. Both C. larvatus and C. semilarvatus feed on scleractinian corals, but partition this food source by feeding at different times. While C. larvatus was observed to feed only during daytime C. semilarvatus feeds by day and night. Butterflyfishes of the Southern Red Sea 33 INTRODUCTION Fourteen species of butterflyfish are recorded from the Red Sea (Randall 1983). The distribution shows marked variations from north to south (Roberts et al 1992), as well as locally (Bouchon-Navaro & Bouchon, 1989 and Roberts & Ormond, 1987). Only twelve chaetodontid species are found in the southern Red Sea (Kemp 1998), of which four are common on the reefs around Massawa and the islands of the Dahlak archipelago (See chapter 3). The butterflyfish assemblage in the southern Red Sea differs from that in the north (Righton et al 1996). Chaetodon austriacus and C. paucifasciatus dominate the northern reefs and are absent in the south. C. larvatus, the most dominant chaetodontid in the south, has a very low density in the north (Roberts et al 1992). Butterflyfishes are one of the best-studied fish families on coral reefs (Motta 1989). Their feeding habits have been investigated in the Pacific (Reese 1975, 1981), Japan (Sano 1989), the Red Sea (Ormond 1972, Harmelin-Vivien & Bouchon-Navaro 1982) and in French Polynesia (Harmelin-Vivien & Bouchon-Navaro 1983). Distribution patterns of chaetodontids are documented for the Great Barrier Reef (Fowler 1990a), French Polynesia (Bell et al 1986’ Bouchon-Navaro 1986), the West Indies (Alevizon et al 1985), and the Red Sea (Bouchon-Navaro & Bouchon 1989, Roberts et al 1992). These studies have shown that a number of chaetodontids co-exist in the same habitat. Many butterflyfish species are known to feed on corals. However, there is little information on how these closely related species co-exist in the same habitat while most of them use similar food resources. Bouchon-Navaro (1986) and Pitts (1991) examined resource partitioning among butterflyfishes in the northern Red Sea and western Atlantic respectively. Results from those studies show partitioning of either food or space resources among co-existing species. In the present work, trophic and spatial partitioning among four chaetodontid fish species in the southern Red Sea was investigated. MATERIALS AND METHODS Study area The study was conducted in the southern Red Sea near Massawa (Fig. 4.1). The fishes used for analysis of stomach contents were collected from the reef east of Sheikh Said Island. Observations on the feeding and ranging behaviour of the fish species were made on Resimedri reef near Massawa, and surveys of the distribution and abundance of the butterflyfishes took place on seventeen reefs around Massawa and in the Dahlak archipelago. Most of the reefs in the study area are of the fringing type and reach a depth of 10 m. The dominant coral genera found in the study area are Porites, Echinopora, Montipora and Stylophora. The coral cover of eastern Sheikh Said and Resimedri reefs is 34 Chapter 4. Resource Partitioning 45% and 57% respectively. These values are relatively high compared with the mean coral cover of 23% found for the seventeen reefs studied (See chapter 3). Distribution and abundance of fishes A belt-transect method was used to estimate the abundance of the butterflyfishes (Crosby & Reese 1996) at seventeen sites in the study area (see chapter 3). At each site, three lines, each 100-m long, were laid parallel to the shoreline. Visual census of fishes was conducted by slowly swimming or diving along the line and counting all the butterflyfishes observed within 2.5 m distance on either side of the line. Crosby & Reese (1996) recommended a transect width of 10 m. However, owing to poor visibility and because of the narrowness of many surveyed reefs we reduced the width to 5 m. The fishes were identified to species level and their abundance was recorded on a PVC slate. Data collection took place between 0900 and 1300 hours in March, April and August 2000. Figure 4.1. Study site. Asterisks indicate locations of surveyed reefs. RM = Resimedri; SS = Sheik Said Island; TW = Twalot Island. The two arrows indicate the observation and the fish collection sites. Butterflyfishes of the Southern Red Sea 35 Collection of fishes 125 fishes belonging to four chaetodontid species were caught in a barrier net while diving and snorkelling. Immediately after capture, fishes were preserved in ice and transferred to a laboratory where lengths and weights were measured. The sampled fish were stored in a deep freezer until dissection. Collection took place at different times of the day from November 1999 to April 2000. On 14 April 2001, forty-five additional specimens of C. larvatus, C. semilarvatus and H. intermedius were collected to investigate the fullness index of their stomach. Five individuals from each species were captured in the morning (0600–0700 hours), after noon (1200–1300 hours) and in the evening (1800–1900 hours). Dissection and stomach content analysis Total length, standard length and body depth were measured to the nearest mm; body mass was measured to the nearest g. After dissection mass of the stomach and length of the intestine were measured. Stomachs were opened under a dissecting microscope, and their contents were spread out in a Petri dish and examined under a microscope. The bottom of the Petri dish was divided into 0.25 mm2 squares. Prey items were classified as turf algae, scleractinian corals (coral polyp, zooxanthellae, nematocyst and coral mucus), nematodes, sedentary polychaetes, errant polychaetes, hydrozoans, crustaceans, ascidiaceans and larvaceans. The volumetric percentage of a given food item was estimated by determining the number of grid squares covered by each food type as a fraction of total number of squares covered by the stomach content (Mol 1995). For the fish collected on 14 April 2001, the gutted mass and the mass of the stomach content were determined. Field observations Field observations were carried out while snorkelling or diving on the reef slope at depths varying from 2 to 5 m. Each fish was followed for 15 min, and the number of bites and the type of coral consumed were recorded on a PVC slate. Feeding observations were made for at least three days for each species from January to April 1999. During each day at least three replicate feeding observations were made three times: morning (0600–0800 hours), noon (1130–1300 hours) and evening (1700–1930 hours). Ranging habits were investigated by following the movement of fishes for 3 h per day and for five days for each fish species. Five individuals from each species were marked by applying subcutaneous injections of Alcian Blue (De Jonge & Videler 1989). The movements