Community structure at the Abrolhos Archipelago, Brazil

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1 Proceedings 9 th International Coral Reef Symposium, Bali, Indonesia October 2000 Community structure at the Abrolhos Archipelago, Brazil B. Segal 1 and C. B. Castro 1 ABSTRACT The Abrolhos Reef Complex, Brazil, comprises the most developed reef assemblages in the South Atlantic. Patterns of coral and benthic community structure were analyzed in the Abrolhos National Marine Park, at three and at depths (stations) between 1.9 and 4.0 m. Point intercept transects (n=5 per station) were sampled. Colony sizes (n=36-60) and distances (n=17-30) of the most frequent or abundant coral species were measured. Shannon-Wiener diversity indices were low ( ). Eleven coral species were recorded (total coral coverage = %). Dominant reef building organisms were the endemic coral Mussismilia braziliensis ( % cover) and coralline algae ( % cover). Significant differences among localities were detected in colony sizes, and in point-to-colony and colony-to-colony distances for some species, and among benthic communities. Some of the differences found are probably best explained by physical factors, mainly wind direction and intensity. Keywords Community structure, Coral reef, Abrolhos, Brazil Introduction Patterns of distribution of reef corals are an impor-tant component of the community structure of coral reefs. The several scales of distribution (regional, local or microhabitat) may be influenced by biotic (e. g. settlement, recruitment, mortality, competition, pre-dation) and abiotic factors (e. g. substrate, light, hy-drodynamics) (Birkeland 1997). Community structure is thus a result of specific responses to all these processes acting upon the organisms. While spatial patterns of distribution and diversity of reef organisms are relatively well known in shallow reef areas of the Pacific and northern Atlantic ocean (Porter 1972, Done 1982, Jaap et al. 1988, Harriott et al. 1994, Adjeroud 1997), these patterns are still poorly understood in Brazilian reefs. Also, the environmental factors related to community structure need to be investigated in Brazilian reefs. The unique geological and biological features found in these reefs could be the result of a particular relationship between biological and physical processes, and these processes may be different from those found in Caribbean reefs, for example. Therefore, the relationship between environmental features and patterns of distribution observed in Brazilian coral communities remains almost completely unknown. The Abrolhos Reef Complex form the most developed and diverse reef assemblages in the South Atlantic Ocean (Leão and Ginsburg 1997) and are unique, due to their low coral diversity and high degree of endemism. Despite its importance as a Marine Pro-tected Area in the Brazilian coast, there are few quan-titative ecological studies on the Abrolhos coral com-munities (but see Pitombo et al. 1988, Villaça and Pitombo 1997). However, a better understanding of community structure patterns in the Abrolhos area may provide essential background information for moni-toring and management programs. The aim of the present study is to characterize and compare coral communities from the Abrolhos Archipelago under distinct wind and wave conditions. Also, the relationships of the observed community patterns with respect to these physical settings are discussed. Materials and Methods The Abrolhos Archipelago (17º58 S, 038º42 W) lies among reefs, some 55 km offshore (Fig. 1). Its five islands are surrounded by shallow embryonic fring-ing reefs (Pitombo et al. 1988) in depths that rarely exceed 7.0 m. These embryonic fringing reefs are com-posed by coral communities growing on rocky subs-trates around the islands. Three localities were sam-pled: northern and southern shores of Santa Bárbara Island (NB and SB, respectively), and the northern shore of Siriba Island (SIR). These localities are under the influence of different wind systems (Fig. 2). Prevailing winds in the area are from the NE from September to February, and from the E in March and between July to August, the wind force being usually 4 to 15 knots. The southern wind prevails in April and May, but the highest wind force occurs from March to December, usually during southern wind storms (up to more than 45 knots). NB is strongly influenced by the constant and moderate NE and E winds, SB is affected by strong storms caused by S winds, and SIR can be affected with intermediate intensity by both wind regimes. Patterns of coral community structure were ana-lyzed in depths between 1.9 and 4.0 m. Data were collected during three field trips in 1997 (March, May, and October). One station/depth was sampled at NB, three at SB, and two at SIR. Five replicates of a point intercept transect were performed, using a 20 m weighted rope previously marked with 500 random points at each station (see Segal and Castro, in press). Each organism (species or functional group) positioned below the points was recorded. 1 Museu Nacional, Departamento de Invertebrados, Quinta da Boa Vista s/n o, São Cristóvão, Rio de Janeiro RJ, Brasil. bsegal@pobox.com

Fig. 2 Wind intensity and regime at the Abrolhos Archipelago (compiled from the Brazilian National Oceanographic Database, Brazilian Navy, 1998). Results Fig.

2 Fig. 2 Wind intensity and regime at the Abrolhos Archipelago (compiled from the Brazilian National Oceanographic Database, Brazilian Navy, 1998). Results Fig. 1 Map of the Abrolhos area, off eastern Brazil, showing studied localities. At each locality five species were sampled (Agaricia agaricites, Favia gravida, Mussismilia braziliensis, Porites branneri, and Siderastrea stellata) in distances from random points to nearest colonies, distances from these colonies to their nearest neighbors, and colony sizes. Sampling points were randomized using a 50 m weighted rope previously marked with 30 random points. Ropes were placed at the bottom, parallel to shore, and at an isobath of circa 3 m in each of the three study localities. Size of colonies consisted of the longest linear distance between opposite margins of the colony, taken with a tape measure. Stations were compared by doing a multi-dimensional scaling (MDS) and a multivariate analysis of similarities (ANOSIM), using the Bray-Curtis similarity coefficient (Clarke and Warwick 1994), with the aid of a computer software (PRIMER, Plymouth Marine Laboratory). Shannon-Wiener (H ) and Simpson s (λ) diversity indexes (Magurran 1988) were calculated in a spreadsheet (Excel 97, Microsoft). Non-parametric statistics (Kruskal-Wallis and Kolmogorov-Smirnov tests) (Siegel 1975) were used to compare diversity indexes, distance measures, and colony sizes between localities, with the aid of a computer software (STATISTICA release 4.3, Statsoft). Eleven coral species (including one hydrocoral) were recorded in the transects for the whole studied area (Table 1). Besides coral coverage, zoanthid and algae coverage were also counted. Zoanthids were divided in two groups: Zoanthus spp. and Palythoa spp. Zoanthus spp. includes mainly Z. sociatus. Palythoa spp. includes mainly P. caribaeorum. The algae were divided in three groups: coralline, foliose, and turf. The coralline group is composed of several species, but mainly species of Lithothamnion, Lithophyllum, Sporolithon, and Porolithon. The latter being the most abundant at depths between 0.5 and 5.0 m (M. Figueiredo, pers. comm. 1998). The most abundant foliose algae at these localities are Dictyota mertensii, D. cervicornis, Dictyopteris plagiograma, D. justii, Stypopodium zonale, Lobophora variegata, Padina sanctaecrucis, and Sargassum sp. (M. Figueiredo and J. Creed, pers. com. 1998). The main turf algae found at these localities are Ceramium spp., Sphacelaria spp., Polysiphonia spp. and cyanophytes (M Figueiredo and J Creed pers. com. 1998). Other organisms, like sponges, anemones, and echinoderms were grouped into a single entity called others. Fig. 3 shows the perpendicular profiles at each locality, with depth of each sampled station. The study revealed that dominant reef building organisms at these localities were the endemic coral Mussismilia braziliensis (1.9 to 24.5%) and coralline algae (13.8 to 19.5%) (Table 1), with Siderastrea stellata sharing the dominance among corals with M. braziliensis in SB (Fig. 4). Total coral coverage is low at the Archipelago, ranging from 6.6 to 31.7%. The highest total coral cover (31.7 ± 6.3%) is observed at NB (Table 1), but this locality presents the lowest diversity (Table 2; Kruskal-Wallis, H (2, n=30) =9.37, p=0.09; Kolmogorov-Smirnov SIR-SB n. s., SIR-NB p<0.05, SB-NB p<0.01). Diversity indexes including only coral species are given in Table 2.

3 Table 1: Bottom coverage (average percentage and standard deviation) for each group or species in each station sampled at Abrolhos Archipelago. NB = northern shore of Santa Bárbara Island; SB = southern shore of Santa Bárbara Island; SIR = Siriba Island; T1-T3 = groups of transects at increasing depths (see Fig. 3). NB SB SB SB SIR SIR Species T1 T1 T2 T3 T1 T2 Agaricia agaricites 1.2 ± ± ± ± ± ± 0.6 Favia gravida 0.7 ± ± ± ± ± ± 0.3 Favia leptophylla ± Millepora alcicornis 1.1 ± ± ± Montastrea cavernosa 1.0 ± ± ± ± 0.2 Mussismilia braziliensis 24.5 ± ± ± ± ± ± 1.4 Mussismilia harttii 0.4 ± ± ± ± 0.2 Mussismilia hispida ± ± ± ± 0.2 Palythoa spp. 1.3 ± ± ± ± ± ± 2.1 Porites astreoides 0.0 ± ± 0.3 Porites branneri 0.5 ± ± ± ± ± ± 0.3 Siderastrea stellata 2.3 ± ± ± ± ± ± 0.9 Zoanthus spp. 1.5 ± ± ± ± ± ± 0.8 Coralline algae 17.7 ± ± ± ± ± ± 3.8 Foliose algae 0.1 ± ± ± ± ± ± 2.4 Turf algae 45.8 ± ± ± ± ± ± 3.4 Others 1.8 ± ± ± ± ± ± 1.2 Corals 31.7 ± ± ± ± ± ± 1.7 Table 2. Coral species richness (S), Shannon-Wiener (H ), and Simpson s (λ) diversity indexes for each station sampled at Abrolhos Archipelago (N=5 for each station). NB = northern shore of Santa Bárbara Island; SB = southern shore of Santa Bárbara Island; SIR = Siriba Island; T1-T3 = groups of transects at increasing depths (see Fig. 3). Station S H' λ NB T ± ± 0.10 SB T ± ± 0.11 SB T ± ± 0.06 SB T ± ± 0.11 SB Total ± ± 0.10 SIR T ± ± 0.08 SIR T ± ± 0.10 SIR Total ± ± 0.09 The number of size measures (n) varied among species and localities (average n = 50.1 ± 8.4; range = 36-60; Table 3), because many times there were not colonies of certain species nearby the random point or from the first colony found. Significantly different colony sizes were found only in Mussismilia braziliensis and Porites branneri (Table 3-4). Larger colonies of M. braziliensis were found at NB (Kolmogorov-Smirnov p<0.05 in both comparisons), while P. branneri colonies were smaller at SIR (Kolmogorov-Smirnov p<0.05 in both comparisons). Number of point-to-colony (average = 25.7 ± 3.9; range = 19-30) and colony-to-colony (average = 24.5 ± 4.9; range = 17-30) distance measures also vary for the same reason pointed out for size measurements. Table 3: Colony sizes (cm) and distances (cm) from random point to nearest colony (Point-Colony) and from nearest colony to its nearest neighbor (Colony-Colony) (notation = average ± standard deviation) for Agaricia agaricites, Favia gravida, Mussismilia braziliensis, Porites branneri, and Siderastrea stellata from three localities in the Abrolhos Archipelago: NB = northern shore of Santa Bárbara Island; SB = southern shore of Santa Bárbara Island; SIR = Siriba Island. Species Locality Colony Size n Point-Colony n Colony-Colony n A. agaricites NB 3.21 ± ± ± SB 3.44 ± ± ± SIR 3.20 ± ± ± F. gravida NB 3.90 ± ± ± SB 3.73 ± ± ± SIR 3.40 ± ± ± M. braziliensis NB ± ± ± SB ± ± ± SIR ± ± ± P. branneri NB 6.58 ± ± ± SB 5.47 ± ± ± SIR 3.90 ± ± ± S. stellata NB 6.30 ± ± ± SB 5.97 ± ± ± SIR 5.25 ± ± ±

4 Fig. 3 Depth profiles of studied localities in the Abrolhos Archipelago. NB = northern shore of Santa Bárbara Island; SB = southern shore of Santa Bárbara Island; SIR = Siriba Island; T1-T3 = stations. (NB and SIR adapted from Pitombo et al. 1988). Average distances are shown in Table 3. For point-tocolony distances significant differences are found among localities for M. braziliensis, F. gravida, and S. stellata (Table 4). S. stellata presents significantly smaller distances at NB (Kolmogorov-Smirnov, p<0.01 in both comparisons). M. braziliensis also presents smaller distances from point-to-colony at NB (Kolmogorov-Smirnov, p<0.05 in both comparisons). F. gravida shows a significant difference only between SB and NB (Kolmogorov-Smirnov, p<0.01). In Kruskal-Wallis tests, there are no significant differences among the three localities in relation to colony-to-colony distances, although for M. braziliensis the p value (p=0.059) is considered low (Table 4). The two-sample test performed for this species shows difference between SIR and NB (Kolmogorov- Smirnov, p<0.01), with smaller distances at NB (Table 3). Table 4. Kruskal-Wallis test results for comparisons between the three localities (Siriba Island, northern and southern shores of Santa Bárbara Island) at Abrolhos Archipelago in relation to colony size, colony-to-colony distances (col-col), and random point-to-colony distances (point-col). Species Size col-col point-col Agaricia agaricites p=0.858 p=0.091 p=0.472 Favia gravida p=0.104 p=0.269 p=0.001 Mussismilia p=0.018 p=0.059 p=0.048 braziliensis Porites branneri p= p=0.275 p=0.070 Siderastrea stellata p=0.333 p=0.779 p=0.000 The MDS (multidimensional scaling) comparing benthic cover among all stations strongly evidences only one group, including NB replicates (Fig. 5). The other stations are grouped all together, with only partial exclusive distributions, as in the case of transects at maximum studied depths (SB-T3, NB, and SIR-T2)1. However, the ANOSIM among all stations resulted in significant differences among almost all localities (R = 0.642, global significance level = 0.0%), as shown in Table 5. The only exceptions are comparisons among different depths at SB. Discussion A similar dominance of Mussismilia braziliensis and coralline algae was found by Pitombo et al. (1988) and Villaça and Pitombo (1997) in the same area. Pitombo et al. (1988) did not have replicates, but the coral cover of their transects lies within the range of individual lines in our replicates. The three groups of replicates compared above (NB, SIR-T1, and SIR-T2) were sampled next to marking pins fixed by Pitombo et al. in Shannon- Wiener diversity indexes are low (ranging from 0.28 to 0.53) when compared to some Caribbean (H =3.2) (Porter 1972) and Indian Ocean reefs (H =3.36) (Bouchon 1981). Brazilian coral fauna is characterized by a very low richness. At the studied area, it was only 11 of 18 coral (Scleractinia and Milleporidae) species reported to Brazil (Laborel 1969, Castro 1994). Furthermore, some species have a high dominance in the area, lowering even more the diversity indexes. The main biotic differences between the three localities are related to total coral cover and diversity parameters. It is suggested that some of these factors may be affected by physical differences among the three localities, mainly wind direction and intensity. Stations at SB experience the highest wave impact due to the strong

5 southern wind storms. NB is influenced by more frequent wave action, although less strong, because of the prevailing northern winds. SIR seems to be intermediately exposed from both northern and southern winds. Following Sheppard (1982), the algal coverage tends to be very high in environments with strong wave action, with a comparatively smaller contribution of coral species. This is in accordance with our results, which show a smaller total coral coverage at SB. The highest coral cover is observed at NB, due to the dominance of large heads of M. braziliensis, which presented significantly larger colonies at this locality. The lowest diversity is also found at this locality, influenced by the dominance of this species. Furthermore, this locality presents smaller point-to-colony distances for the two coral species with highest cover in the area (M. braziliensis and Siderastrea stellata see Fig. 4), suggesting higher density for these species or their patches in the area. M. braziliensis has by far the largest colonies in the area (Table 3). Its colonies are high, with an almost spherical shape (Laborel 1969). Therefore, it is probably also the easiest to dislodge among the studied scleractinian species, especially in shallower stations. This could explain the co-dominance of S. stellata and M. braziliensis at locality SB (with strong waves), with a decrease in M. braziliensis cover, while there is an absolute dominance of a single species (M. braziliensis) at the other stations (Fig. 4). Fig. 4 Relative abundance (cover) of coral species in regard to total coral cover in the Abrohos Archipelago. NB = northern shore of Santa Bárbara Island; SB = southern shore of Santa Bárbara Island; SIR = Siriba Island. Intermediate disturbance levels can lead to an increase of local diversity (Connell 1978). Such idea could explain the highest diversity at SIR, where disturbances are not strongest in both wind regimes. Although studies in other reef areas, with a broader depth range, found light to be the main physical factor controlling community structure (Bak and Engel 1979, Gili et al. 1989, Adjeroud 1997), we believe hydrodynamics to be such factor at the Abrolhos Archipelago, a conclusion based on community studies and the depths of the local reefs. Furthermore, since the area presented low coral coverage, low frequency of coral species coexistence (Lins de Barros et al. in press), and lack of voracious predators, such as some starfishes or mollusks, we reject the possibility of biotic interactions, such as predation and competition, acting as a strong force structuring coral communities at the Abrolhos Archipelago. Acknowledgements The authors thank C. A. Echeverría, C. C. Ratto, and M. M. Lins de Barros for field assistance and the Brazilian Environmental Agency for license to conduct research in a Federal Conservation Unit. The Fundação O Boticário de Proteção à Natureza, Brazilian National Research Council (CNPq), Federal Foundation for Graduate Education (CAPES), and the Rio de Janeiro State Science Foundation (FAPERJ) provided grants and fellowships. References Adjeroud M (1997) Factors influencing spatial patterns on coral reefs around Moorea, French Polynesia. Mar Ecol Prog Ser 159: Bak RPM, Engel MS (1979) Distribution, abundance and survival of juvenile hermatypic corals (Scleractinia) and the importance of the life history strategies in the parent coral community. Mar Biol 54: Birkeland C (1997) Life and Death of Coral Reefs. Chapman and Hall, New York: 536 pp Bouchon C (1981) Quantitative study of the scleractinian coral communities of a fringing reef of Reunion Island (Indian Ocean). Mar Ecol Prog Ser 4: Castro CB (1994) Corals of Southern Bahia. In: Hetzel B and Castro CB (eds) Corals of Southern Bahia. Nova Fronteira, Rio de Janeiro: Clarke KR, Warwick RM (1994) Changes in marine communities: an approach to statistical analysis and interpretation. Plymouth Marine Laboratory, Plymouth: 144 pp Connell JH (1978) Diversity in tropical rain forests and coral reefs. Science 199: Done TJ (1982) Patterns in the distribution of coral communities across the central Great Barrier Reef. Coral Reefs 1: Gili JM, Murillo J, Ros J (1989) The distribution pattern of benthic cnidarians in the Western Mediterranean. Scient mar 53: Harriott VJ, Smith SDA, Harrison PL (1994) Patterns of coral community structure of subtropical reefs in the Solitary Islands Marine Reserve, Eastern Australia. Mar Ecol Prog Ser 109: 67-76

6 Jaap WC, Halas JC, Muller TG (1988) Community dynamics of stony corals (Milleporina and Scleractinia) at Key Largo National Marine Sanctuary, Florida, during Proc 6 th Int Coral Reef Symp 2: Laborel J (1969) Madréporaires et hydrocoralliaires récifaux des cotes brésiliennes. Systématique, écologie, répartition verticale et géographique. Ann Inst océan 47: Leão ZMAN, Ginsburg RN (1997) Living reefs surrounded by siliciclastics sediments: the Abrolhos coastal reefs, Bahia, Brazil. Proc 8 th Int Coral Reef Symp 2: Lins de Barros MM, Castro CB, Pires DO, Segal B (in press) Coexistence of reef organisms in the Abrolhos Archipelago, Brazil. Rev. Biol Trop. Magurran AE (1988) Ecological diversity and its measurement. Princeton University Press, Princeton: 179 pp. Pitombo FB, Ratto CC, Belém MJC (1988) Species diversity and zonation pattern of hermatypic coral at two fringing reefs of Abrolhos Archipelago, Brazil. Proc 6 th Int Coral Reef Symp 2: Porter JW (1972) Patterns of species diversity in Caribbean reef corals. Ecology 53: Segal B, Castro CB (in press) A proposed method for coral cover assessment: a case study in Abrolhos, Brazil. Bull Mar Sci. Sheppard CRC (1982) Coral populations on reef slopes and their major controls. Mar Ecol Prog Ser 7: Siegel S (1975) Estatística não-paramétrica (para ciências do comportamento). McGraw-Hill, Rio de Janeiro: 350 pp Villaça R, Pitombo FB (1997) Benthic communities of shallow-water reefs of Abrolhos, Brazil. Rev bras oceanogr 45:

Conservation status and spatial patterns of AGRRA vitality indices in Southwestern Atlantic Reefs

Conservation status and spatial patterns of AGRRA vitality indices in Southwestern Atlantic Reefs Ruy K.P. Kikuchi 1, Zelinda M.A.N. Leão 1 & Marília D.M. Oliveira 1 1. Universidade Federal da Bahia, CPGG/IGEO,