Distribution, abundance and substrate versatility relationships in Chaetodontidae and Pommacanthidae.

Transcription

1 1 Luke Hately-Broad BIO-162. Quarter. Marine Ecology Field Distribution, abundance and substrate versatility relationships in tidae and Pommacanthidae. Hately-Broad L School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, England.

2 2 Abstract: The distribution, abundance and feeding preferences of eight species of tidae and two species of Pomacanthidae were examined within a reef complex on the island of Moorea, French Polynesia. The reef complex was divided into four areas; fringe, fringe patch, crest patch and crest. In each area a ten minute abundance survey and five fifty meter habitat availability transects were conducted. The feeding preference of every individual seen in three hours was also recorded for each area. Species richness was found to increase from the fringe to the crest reef. Two species Centropyge flavissimus and citrinellus were found to have a generalist diet and were the most abundant species at all sites. Five species were found to feed mainly on live corals and so were more abundant in coral rich areas, these species were; lunula, lunulatus, ornatissimus, reticulates and unimaculatus. ephippium and vagabondis were found to feed mainly on and so were most abundant in areas with a high availability of. The Final species Centropyge bispinosus was only observed in crevices in Porites rus in the fringing reef. Key words: Abundance, Coral reef fish, Distribution, Habitat specialisation, Versatility. Introduction: Ecological versatility is defined by McNally (1995) as the degree to which organisms can fully exploit the available resources in their local environment. Within coral reef fish assemblage s species vary in terms of their resource versatility (Futuyma & Moreno 1988). The effect of this resource versatility on the distribution and abundance of organisms has received much theoretical attention (e.g. McNaughton &Wolf 197, Morris 1996). From this research it is suggested that generalists potentially will have a greater local abundance and distribution as they have access to more of the local resources. Where as specialists may be able to out compete generalists in the use of certain resources (Bean et al. 2). In terms of habitats used this means that generalist species should occur in a broad range of habitats, while specialist species will only be found in a few habitats (Bean et al. 2). Both of these extremes in resource versatility have associated costs and benefits, in terms of competition and resource availability. The theoretical relationships between the level of resource versatility and the distribution and

3 3 abundance of organisms, has only recently been tested in terrestrial ecosystems (Hughes ). Research on the effects of resource versatility in coral reef fish assemblages is very limited (Jones et al. 2). Coral reef fish communities are highly diverse and have representatives of the full spectrum of habitat versatility, from specialist species associated with only a few coral species to generalists which are found on most substrate types present on the reef (Munday & Jones 1998, Syms & Jones ). Many species of fish show habitat selection at settlement (Ormond et al. 1996) however the habitat usage of an individual may vary during its life cycle and this may be important in evaluating the processes affecting the distribution and abundance of adults. The habitat usage of adults has mainly been studied in speciose families such as gobies (Munday et al. 1997) and damselfishes (Meekan et al. 1997). Although studies that relate habitat versatility to distribution and abundance have been conducted for some families (Bean et al. 2), little research has been conducted to compare these relationships between different families, geographical areas or to relate the findings to the evolutionary age of the species concerned. The tidae are a very speciose family and it has been suggested that the reason for this may be the differentiations in diet found among the species. Allen et al 1998 placed all tidae species into five groups depending on their feeding types. These groups are those that feed on; hard corals, soft corals, small benthic invertebrates, zooplankton and omnivores. In this study I examine the potential relationships between substrate association, in terms of food preferences, and the distribution and abundance of coral reef fish species from two families found around the island of Moorea, French Polynesia. Ten species from the two families were examined tidae vagabondis (Linnaeus 1758), unimaculatus (Bloch 1787), lunula (Lacépède 13), citrinellus (Cuvier 1831), reticulatus (Cuvier 1831), lunulatus (Quoy & Gaimard 1824), ornatissimus (Cuvier 1831) and ephippium (Cuvier 1831). Pomacanthidae Centropyge flavissimus (Cuvier 1831) and Centropyge bispinosus (Günther 18). Naming follows that used in Allen et al (1998). I tested the following hypotheses: -Given equal habitat availability, species that feed on a wide variety of substrates will have a greater local abundance and distribution than species restricted to a few substrate types. -For generalist species food preferences will be related to food availability, and so will change between areas. -There will be significant differences in food preferences between species

4 4 To test these predictions the abundance and feeding preferences of each species was recorded in each of the four areas at the sample site, habitat availability was also recorded for each site. Materials and Methods: This Study was conducted in four areas at the public beach site (17º S. 149º 5 91 W) on the island of Moorea, French Polynesia during November and December 2. The areas were the fringe, fringe patch, crest patch and crest reefs (Figure 1). Figure 1: A, Map of Moorea (French Polynesia) showing the location of the sampling site; B, Schematic cross section of the study site showing the location of the four sampling areas. The fringe reef is dominated by Porites rus which occurs in large patches, in this area both macro and turf algae is common with some Porites lobata also present. The average depth is about 1 meter. The fringe patch reef contains all the substrate types listed bellow but is dominated by with P. lobata being the most common coral and an average depth of about 1.8 meters. In the crest patch is still the most common substrate with P. lobata being the dominant coral however the diversity of corals present here is higher than in the two previous areas this is the deepest site with an average depth of about 2.3

5 5 meters. The crest is the most coral rich of the four areas, P. lobata is still dominant but to a lesser extent and coverage is much reduced the average depth is about 1.5 meters (Figure2). The channel was not sampled as Bouchon-Navaro (1981) found no chaetodontidae present in this area during his survey and suggested that this was due to the strong currents and barren bottom found in this area. All observations were made by snorkling. In each of the four areas the habitat availability was recorded using five randomly positioned 5 meter transects, along which the substrate was recorded every 2.5 meters as:, dead coral,, macro algae, turf algae, Porites rus, Porites lobata, Pocillopora verrucosa and faveolata. The abundance of the species within each area was recorded as the number of individuals seen in ten minutes of swimming. For this the swimming speed was kept constant for each survey and only fish within two meters of the observer were recorded to eliminate bias from changes in visibility. Lastly feeding preferences were recorded for as many individuals of each species as could be found in three hours of searching. This involved recording the substrate the individual was first seen to feed on or pecked at, (from the substrate list for the transects). The data was analysed using Pearson Chi-squared tests and graphical techniques using SYSTAT 9 and Microsoft Excel for Windows. Results: 7 Percentage cover Figure 2: Bar graph showing the habitat availability in the four areas of the study site (Public Beach, Moorea, French Polynesia).

6 6 The diversity of the species studied is highest in the crest patch with 8 species and a total of 67 individuals being recorded here during the abundance surveys. The diversity of the crest and fringe patch reefs is similar even though this is not reflected in the number of species or total individuals found in these areas (Table 1). Table 1also shows that the fringe reef is the least diverse of the four zones even though the same number of species are found here as in the fringe patch with more individuals being present. Table 1: Showing the, total number of species and individuals and the diversity (calculated using the Shannon-Weaver index H = -_Pi logpi) for the study site (Public Beach, Moorea, French Polynesia). Total Number Total Number of Individuals of Species Diversity Fringe Fringepatch Crestpatch Crest Figure 3 shows the number of individuals of each species found in the four areas. C. flavissima is the domminant species in all four areas, C. citrinellus is the next most abundant on all four areas. C. bispinosus was not found in any areas during the abundance surveys but was found during the food preference surveys. C. lunula was not common in any of the areas but was most abundant in the crest patch and was also found in small numbers in the crest and fringe reefs but was absent from the fringe patch. C. lunulatus was also absent from the fringe patch, this species was quite abundant in all other areas with the most individuals being recorded from the crest patch. C. ornatissimus was only observed in the crest patch and crest reefs being most abundant in the later. C. reticulatus was also only found in the crest patch and crest reefs but was most abundant in the crest patch. C. ephippium was only found in the fringe patch and crest reefs. It was not common in either of these areas but more individuals were seen in fringe patch. C. unimaculatus was not found in the fringe reef area and was only represented by a few individuals in both the fringe patch and crest reefs, however in the crest patch this species is the third most abundant. C. vagabondis was found in small numbers in all areas with a peak in abundance in the fringe patch. In table 2 the results of the Pearson Chi-square tests, which tested for significant between habitat availability and feeding preferences, are presented. A significant value shows that the species in question, is in that area, actively seeking out a particular food type or types. This means that the species is not randomly feeding on any

7 7 45 Number of Individuals Centropyge bispinosus Centropyge flavissima lunula lunulatus ornatissimus reticulatus ephippium citrinellus unimaculatus vagabondis Figure 3: Bar graph showing the number of individuals of each species found in the four different areas at the sample site (Public Beach, Moorea, French Polynesia). substrate it comes across. Values that are not significant, are generally explained by the absence of that species from that particular area. There are three values that are not significant and the species does occur in that area. These are C. vagabondis in the crest patch and C. reticulates and C. ephippium in the crest reef. The reason for these values not being significant is an insufficient sample size. The bar graphs of feeding preferences are shown as figures 4-13 in the appendix, they show the percentage of the total feeding actions that each species used on the different substrates in the different areas. Figure 4 shows that C. bispinosus was only observed in the fringe patch reef and here it fed primarily on macro algae and some dead coral. Figures 5 & 11 show the feeding preferences for C. flavissima and C. citrinellus. Both of these species are generalists wit C. citrinellus feeding on all substrates in the fringe, fringe patch and crest patch. C. flavissima feeds on dead coral, macro algae P. lobata and P. rus in these areas. In the crest reef both species feed on M. faveolata. Five species feed mainly on live corals, these are C. lunula, C. lunulatus, C. ornatissimus, C. reticulatus, and C. unimaculatus, the graphs for these species are shown in figures 6, 7, 8, 9 & 12. C. lunula only feeds on P. lobata in the crest patch reef, whilst C. lunulatus feeds mainly on Porites sp in all areas and M. faveolata where it is available. C. ornatissimus feeds

8 8 Table 2: Showing the results from Pearson Chi-square tests between habitat availability and feeding preferences. + shows a significant value (P<.5), - shows a non-significant value (P>.5). Degrees of freedom were never more than 9 and were usually less. Species Fringe Fringe Patch Crest Patch Crest Centropyge bispinosus Centropyge flavissima lunula lunulatus ornatissimus reticulatus ephippium citrinellus unimaculatus vagabondis on P. rus in the fringe reef with P. lobata being favoured in the other areas, C. reticulates also feeds on P. rus but in the fringe patch rather than in the fringe, M. faveolata is the preferred food types in the crest patch and crest reefs. C. unimaculatus was only observed in the fringe patch, crest patch and crest reefs where it mainly feeds on M. faveolata, in the fringe patch and crest patch this is the sole food type whilst in the crest small amounts of other substrates are eaten. C. ephippium and C. vagabondis both feed mainly on dead coral, and rubble (Figures 1 & 13). C. ephippium favours dead coral in the fringe patch and crest patch reefs, however this is not fed on in the crest. In this area rubble is the dominant food type. Sand is the preffered food type of C. vagabondis in all areas, but in the fringe and fringe patch it displays a more generalist diet. Table 3: Showing the results from Pearson Chi-square tests between for feeding preferences between species. + shows a significant value (P<.5), - shows a non-significant value (P>.5) shows a test that was not run due to replication. Degrees of freedom were never more than 9 and were usually less.

9 9 Table 3 shows the results for Pearson Chi-square tests between for feeding preferences between species, this was done to see if there is significant differences in what different Centropyge bispinosus Centropyge flavissima lunula lunulatus ornatissimus reticulatus ephippium citrinellus unimaculatus vagabondis Centropyge bispinosus Centropyge flavissima lunula lunulatus ornatissimus reticulatus ephippium citrinellus unimaculatu s vagabondis species eat. Most species show significantly different diets from each other. The major exceptions are C. lunula which is not significantly different from C. flavissima, C. lunulatus, C. ornatissimus or C. reticulates. Also C. lunulatus is not significantly different from C. ornatissimus. Discussion: The finding that species richness increases from the fringe to the crest agrees with Bouchon-Navaro s (1981) findings that species richness of chaetodontidae increases across the same gradient and can probably be explained by increasing coral richness. The high abundances of chaetodontidae in the crest and crest patch also agree with his findings. The general increase in diversity from the fringe to the crest reefs, the decrease at the crest can be explained by the dominance of C. flavissima. Supports the idea that chaetodontidae communities are dependent on coral diversity and cover to maintain their diversity (Bouchon-Navaro 1981). The reason for this may be niche separation, this is that each species feeds on a specific range of food types and these are significantly different to those found for all other species, this would allow many species to exist with out competition but will only work if all the required food types are present. The results

10 1 in table 3 may support this idea as they show that most species have significantly different food preferences. The lack of significant differences between C. lunula and most other species is probably due to the low numbers of observations for the feeding preferences of this species as explained above. However Bell et al (1985) found that there was no relationship between coral cover and number of individuals. The results from the Pearson Chi-square tests for feeding preferences between species, shown in Table 3, show that there are significant differences in food preferences between the pommacanthidae and the chaetodontidae. However due to very few pommacanthidae species being recorded this question can not be fully addressed. Centropyge bispinosus This species was only observed in small numbers in the fringe reef, it was always seen in cracks in P. rus that were surrounded by turbinaria. It was only seen feeding on dead coral and macro algae around these cracks. This agrees with Allen et al s (1998) description of this species as being shy and never straying far from reef crevices, and may explain the low number of observations through individuals being missed during surveys. Centropyge flavissima This is the most abundant species in all the areas, and has the highest abundance at the crest reef followed by the crest patch then fringe, the lowest abundance was found in the fringe patch. This species was seen to be a generalist feeder, which fed on every substrate type in at least one of the areas. The results of the statistical analysis of food choice against habitat availability show that this species actively sought out specific food types and did not just eat the most abundant types. The fact that it fed on all substrates could be because it feeds on filamentous algae (Allen et al 1998), which may have been growing on the substrates. lunula Only a small number of observations were made for this species at the fringe, crest patch and crest sites during the abundance surveys but was only observed feeding on P. lobata four times in the crest patch reef. This was because even though it was found in the other areas during the food preference surveys, it was followed for thirty minutes and was not seen to feed. This can be explained by the fact that this species is supposed to forage mainly at night (Allen et al 1998). The low abundances agree with findings from other studies, as does its occurrence in all the areas (Bouchon-Navaro 1981). lunnulatus The fringe, crest patch and crest were the only areas where this species was recorded during the abundance surveys, however during the food preference surveys it was observed in all areas. This species fed mainly on live corals. In the fringe the preferred species was P. rus but this was probably due to it being the dominant coral species. In all four areas

11 11 this species fed on with this being the dominant food type in the fringe patch and crest patch, in the crest M. faveolata was the favoured food type. This usage of mainly live coral agrees with the fact that this species is supposed to feed only on live corals (Allen et al 1998). ornatissimus This species was absent rom the fringe reef but was found in the other three sites and had the highest abundance on the crest reef, however this species is never common any where. This species as stated in Allen et al (1998) was only observed to feed on live corals, particularly Porites sp. It also feeds on M. faveolata in the crest patch and crest reefs. reticulatus During the abundance surveys this species was only recorded from the crest patch and crest reefs, however whilst conducting the feeding preference surveys it was also recorded from the fringe patch but it was never recorded from the fringe. This species fed exclusively on P. rus in the fringe patch and preferred this food source on the crest reef, in the crest patch it fed mainly on M. faveolata and only fed on this food source on the crest patch and crest reefs These findings agree with the description of this species as feeding mainly on coral polyps (Allen et al 1998). ephippium Observations of this species were limited to a few individuals in the fringe patch and crest reefs. During the feeding preference surveys it was also recorded in the crest patch where it fed exclusively on dead coral, in the other two areas it also fed on rubble and. When doing this the species was probably feeding on benthic invertebrates and algae s which are recorded food sources for this species (Allen et al 1998). citrinellus This is the second most abundant species in all four areas. This finding agrees with the findings of other studies on Moorea that this species is one of the most abundant chaetodontidae (Bouchon-Navaro 1981). In the fringe, fringe patch and crest patch reefs this species fed on almost all substrate types showing a preference for P. rus and in the fringe, P. lobata and in the fringe patch and dead coral, and M. faveolata in the crest patch. In the crest this species fed on dead coral and P. rus but mainly M. faveolata. These findings of food preference agree with Allen et al s (1998) placing of this species in the omnivore feeding group. unimaculatus C. unimaculatus was found in the fringe patch, crest patch and crest reefs, in the first of these two zones this species fed exclusively on M. faveolata. In the crest M. faveolata was still fed on but P. rus was the preferred food type but in this area it also fed on dead

12 12 coral and rubble. This suggests that in Moorea etleast this species may have a more restricted diet than the omnivore one suggested in Allen et al (1998). vagabondis This species was recorded in small numbers from all four areas and was most abundant in the fringe and fringe patch reefs. It feeds on a wide variety of substrate types but preferentially fed on in all four areas with dead coral and rubble being important food sources in the fringe patch, crest patch and crest. In the fringe P. rus was an important food source but this was probably due to P. rus dominating the substrate availability so much. When feeding in this species is probably feeding on polychaete worms as reported in Allen et al (1998). In further research the results of this study will be related to other studies describing the feeding preferences and distributions of pommacanthidae and chaetodontidae both for the area studied and other geographical areas to examine the biogeographical repeatability of these findings. The results will also be analysed in light of the evolutionary age of the species to see if any relationships exist between the findings and this factor. Acknowledgements: I wish to thank Drs G. Bernardi and P. Raimondi for there help at all stages of this study. I also would like to thank all the staff of the C.R.I.O.B.E. research station for enabling me to conduct this study. I extend my thanks to B. Perlman, M. Readdie and J. Engel for their help in data collection. Appendix: Figures 4-13 show the relationships between the number of times a species fed on a particular substrate and how this changes between areas at the sample site Public Beach,

13 13 Moorea, French Polynesia. Centropyge bispinosus Figure 4: The relationship between the number of times C. bispinosus fed on a particular substrate and the variation in these numbers between areas. Centropyge flavissima Figure 5: The relationship between the number of times C. flavissima fed on a particular substrate and the variation in these numbers between areas.

14 14 lunula 1 Number of times fed on 1 Figure 6: The relationship between the number of times C. lunula fed on a particular substrate and the variation in these numbers between areas. lunulatus 1 Number of times fed on Figure 7: The relationship between the number of times C. lunulatus fed on a particular substrate and the variation in these numbers between areas.

15 15 ornatissimus 1 Number of times fed on 1 Figure 8: The relationship between the number of times C. ornatissimus fed on a particular substrate and the variation in these numbers between areas. reticulatus 1 Number of times fed on 1 Figure 9: The relationship between the number of times C. reticulates fed on a particular substrate and the variation in these numbers between areas.

16 16 ephippium 1 Number of times fed on 1 Figure 1: The relationship between the number of times C. ephippium fed on a particular substrate and the variation in these numbers between areas. citrinellus Number of times fed on Figure 11: The relationship between the number of times C. citrinellus fed on a particular substrate and the variation in these numbers between areas.

17 17 unimaculatus 1 Number of times fed on 1 Figure 12: The relationship between the number of times C. unimaculatus fed on a particular substrate and the variation in these numbers between areas. vagabondis Number of times fed on Figure 13: The relationship between the number of times C. vagabondis fed on a particular substrate and the variation in these numbers between areas.

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