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INTRODUCTION
Sponges (phylum Porifera) makeup one of the most diverse and abundant groups of sessile animals on the seabed and are found in ecosystems as important and diverse as mangroves, seagrasses, coral reefs and the deep sea (Díaz, 2012; Cruz-Barraza et al., 2012; Carballo et al., 2014). For the coral reefs of the Caribbean Sea, more than 325 species of sponges have been registered, and it is considered that the diversity and biomass of these organisms in reef ecosystems may exceed that of scleractinian corals (order Scleractinia) and that of octocorals (subclass Octocorallia) (Cedro et al., 2007; Cortés et al., 2009; Díaz, 2012). In countries of the Caribbean region, such as Belize, Colombia, Cuba and Panama, exhaustive taxonomic studies have been carried out on reefs where more than 90 species have been registered (Rützler et al., 2000; Alcolado, 2002; Díaz, 2005; Valderrama and Zea, 2013).
In turn, poriferans play fundamental roles within reef ecosystems. These provide refuge for larvae, juveniles, and adults of many other organisms; they filter large volumes of water, which is why they are considered decontaminators; they constitute food for some fish, turtles (Eretmochelys imbricata) and invertebrates; they serve as a substrate; contribute to the incorporation of particulate material into the bottom, and they establish varied and important symbiotic relationships with other organisms. Given that they fulfill such diverse functions within reefs and other ecosystems, the study of their communities is vitally important (Díaz and Rützler, 2001; Rützler, 2004; Wulff, 2006, 2012; Bell, 2008).
However, research on sea sponges in Costa Rica has been very scarce and, specifically for the Costa Rican Caribbean, there are only six works on shoreline sponges (Risk et al., 1980; Loaiza, 1989, 1991; Cortés, 1996; Van der Hal, 2006; Cortés et al., 2009). Also, there are no known studies that address ecological aspects or the use of these organisms in coral reefs. Among the works that have contributed the most to the knowledge of this group in the country's Caribbean are those carried out by Loaiza (1989, 1991), which describe 17 species of the Demospogiae class for Uvita island and Puerto Vargas in the Costa Rican Caribbean. Cortés (1996) recorded 38 species of sea sponges for this region of the country from bibliographic reviews, identification of specimens preserved in the Zoology Museum of the University of Costa Rica, consultations with experts, and work in progress during that time. For his part, Van der Hal (2006) has been the only one to carry out an ecological study on sea sponges for his thesis, specifically in seagrasses and shallow reefs (1-4 m) in the Caribbean area. Subsequently, Cortés et al. (2009) recorded 65 species for the Costa Rican Caribbean included in one class, two subclasses, 10 orders, 29 families, and 45 genera. In these studies, the authors concluded on the need for more research, mainly related to the species present, their distribution, conservation status, and ecology.
The little ecological information generated for the Porifera ridge in Costa Rica has resulted in ignorance of the ecological value for the development of management plans for this group, and the little use of these organisms as a possible source of economic income for coastal communities. The sponges, being sessile, filtering beings, of wide distribution, persistent in time, of fast growth and with rates of change in their bottom coverage, reflect the average conditions of the environment. For these reasons, variations in their community structure may indicate changes in the environmental conditions of the ecosystems where they inhabit (Alcolado, 2007). Considering the above, the need arises to develop a baseline study evaluating the community structure of sea sponges in the reef patches of the Costa Rican South Caribbean and determining if it can be explained by the influence of abiotic factors such as sedimentation, substrate, and depth. The results of this study will form an important input for the development of guidelines for the conservation and use of sea sponges in the country.
STUDY AREA
The Costa Rican South Caribbean is characterized by having sandy beaches with some rocky protrusions of fossil coral reefs, two islands near the coast with coral formations, in addition to calcareous, sandy substrates and terrigenous offshore sediments (Cortés and Wehrtmann, 2009). The climate is humid (70-100 %) and hot, with maximum temperatures of 32 °C; it presents two rainy seasons (November to March and June to August) with an average of 2500 mm per year in the southern part (Cortés and Wehrtmann, 2009; Cortés et al., 2010). The tides are of mixed type, with predominant diurnal ones, which vary between 30 and 50 cm in width (Fonseca, 2003; Cortés and Wehrtmann, 2009; Cortés et al., 2010). Also, the current near the coast is strong, as well as the waves it generates; and it moves from northwest to southeast (Fonseca, 2003; Cortés et al., 2010).
The reefs of this region can be divided into two sections: the reef patches and carbonate banks of the Cahuita National Park, and the fringe reefs, patches, algal crests and carbonate banks between Puerto Viejo and Punta Mona. A total of 41 species of scleractinian corals and 26 octocorals have been registered within these reefs (Cortés and Jiménez, 2003; Cortés and Wehrtmann, 2009).
Within the described area, four reef patches with the presence of sea sponges were identified and georeferenced (Table 1, Figure 1) through presampling (February-April 2015) and consultations with local tour operators, divers, and fishermen with extensive knowledge of the marine area. These sites, also, were characterized by being important for the economy of the area due to fishing and tourist activity. Two of the sites (Pequeño and 0.36) were located outside of protected areas, where there is no control over the activities carried out (Figure 1).
MATERIALS AND METHODS
Sampling methodology and sample analysis
The sampling was carried out with autonomous diving (SCUBA) in October 2015 and May 2016, when the oceanic and atmospheric conditions of the South Caribbean were optimal (i.e. low precipitation, low or no waves, and high visibility). Five 10 m long by 1 m wide band photo-transects were recorded at each of the sampling sites with a Nikon COOLPIX AW130 underwater camera. The transects were established utilizing a systematic random design based on the CARICOMP (2001) monitoring methodology. A 1 m2 frame was used as the sampling unit, made with PVC tubes and elbows, and with holes every 10 cm to facilitate its submergence in the water. The frame was subdivided into a total of 100 0.01 m2 grids using a thin rope, which intersected between the holes in the form of a network (modified from Weinberg, 1981).
The photographs of the 1 m2 frames were subsequently analyzed to quantify the number of individuals and estimate the percentage of total coverage by sponge species or by type of substrate available, using the 0.01 m2 grids as a reference with an accuracy of up to 0.001 m2. The percentage of available substrate coverage was classified into the bare calcareous pavement, calcareous pavement with sediments, calcareous pavement with coarse sand, and bottom with sediments.
Sponge species were visually identified to the lowest possible taxon using the guideline proposed by Collin et al. (2005) and the website www.spongeguide.org (Zea et al., 2014). Likewise, specimens that could not be identified in situ were collected in previously labeled plastic bags and the following characteristics were noted: shape, live color, consistency, and type of surface; according to the criteria of Loaiza (1991). Subsequently, the sponge samples were preserved in 90 % alcohol and taken to the Laboratory of Natural Resources and Wildlife (LARNAVISI), National University of Costa Rica, for identification based on external morphology of the sponges and morphometry of the spicules, as proposed by Boury-Esnault and Rüztler (1997), Hooper and Van Soest (2002) and Díaz (2005). For the preparation of the spicules, at least three fragments of approximately 2 cm2 were taken, corresponding to different parts of the sponge, which were digested in 3 % sodium hypochlorite for commercial use for a minimum of 30 minutes. Next, the preparations were observed under a light microscope on slides to identify and measure the spicules corresponding to each sample. Sponges that could not be taxonomically identified were separated and grouped according to their external morphological characteristics and their spicules, and they were assigned a name consisting of the word "species" and a consecutive integer.
Determination of sedimentation rates
To determine if there was any relationship between sedimentation and sponge abundance, sedimentation rates per site were determined through a modification to the methodology proposed by Garzón-Ferreira et al. (2002). It consisted of the use of two sediment traps per site, placed at the average depth where the sponges were found (Table 1). It was ensured that all the sediment traps were collected after the same number of days, with a duration of at least one month, when oceanographic conditions allowed it; or failing that, in a maximum of four months.
The sediments were transported to LARNAVISI where they were sieved with a 1 mm mesh eye strainer. Subsequently, the sediments were subjected to two washing sessions by precipitation in freshwater for two days to eliminate their salt content. Subsequently, the water was removed with the help of a rubber hose, they were placed in pre-weighted 100 ml beakers and dried in an oven at 90 °C for three days. Finally, using a Setra BL-410S analytical balance, the dry weight in grams was determined. The sedimentation rate was calculated from the following corrected equation by Garzón-Ferreira et al. (2002):
Where,
TFS: sedimentation rate per fraction (mg/cm2/day)
W: weight (g)
AB: trap mouth area
ND: number of days the trap was under the sea
Sedimentation rates were calculated considering the number of days during which the trap was submerged. This allowed comparisons to be made between the different traps even though they were removed after different times, between one and four months.
Data processing
For each of the sponge species per site, the relative percentage abundance (AR %) was calculated and the relative coverage percentage (CR %) was estimated; as well as the total densities (individuals/m2) of sponges per site. Also, the following indices were calculated: species richness (S), Shannon heterogeneity (H’) (Shannon, 1948), Pielou fairness (J’) (Pielou, 1969), and Simpson (D) dominance (Simpson, 1949), to determine sponge diversity by the site. These indices were selected to quantify, interpret, and compare the diversity of the sponge communities in this study with that recorded by other authors in Caribbean reefs. Likewise, the values of these indices will allow comparisons to be made on this same area in future investigations, and to detect if changes occur over time. Additionally, the criteria proposed by Alcolado (1999; 2007) were applied to determine the degree of severity and environmental predictability of the sites. This method consists of an inference diagram obtained from a scatter plot of pairs of H’ and J’ values, which is subdivided into 11 zones or classes of inference that reflect how severe and constant the conditions are for marine sponges on the site (Alcolado, 2007).
From these analyzes, except for the S index, sponges of the Siphonodictyon genus were excluded, because due to their perforating habit and the development of a large part of their tissues within the substrate they inhabit, it was not possible to determine exactly the number of individuals, nor estimate their coverage (Hofman and Kielman, 1992). Therefore, it was decided to modify the methodology and only record its occurrence frequency (%) using the following equation:
Where,
FA %: Occurrence frequency percentage
NCE: Number of 1m2 frames with the presence of the perforating sponge
TC: Total frames of 1m2 per sampling site
The determination of the degree of similarity between sites considered the relative abundances of all sponge species at each site. The Bray-Curtis similarity index was used as a measure of the affinity between sites and the average linkage as the fusion method of the samples pairs; as well as the Simprof test with a significance level of 5 % to determine if the grouping between sites was significant. To compare the similarity of the depth variables, percentage of the available substrate, and sedimentation rate versus the relative abundances of sponges between sites, a principal coordinate analysis (PCO) was performed (Anderson et al., 2008). This method reveals the relative sizes and directions of effects in complex experimental designs without plotting the samples. The analysis was performed with the PRIMER v7 vs PERMANOVA add-on programs (PRIMER-E Ltd, Plymouth, UK).
RESULTS
Registered species
In a total of 200 sampling units, 3048 individuals were quantified and 43 species corresponding to two classes, 11 orders, 22 families, and 28 genera were identified, according to the classification proposed by Morrow and Cárdenas (2015) (Annex 1). Of the 43 species, 28 had already been reported for the Costa Rican Caribbean, 13 were new records (Table 2), two were identified only up to genus, and eight species could not be taxonomically identified.
Coverage and relative abundances
The total coverage of the substrate by the sponges did not exceed 6.1 % in any of the sites, with Perezoso and Pequeño (3.0 %) being the sites with the highest and lowest coverage, respectively (Table 2). The species with the highest relative abundance in Perezoso were Niphates erecta (59.3 %), Iotrochota birotulata (14.0 %), and Scopalina ruetzleri (5.2 %). I. birotulata (1.1 %) and N. erecta (1.8 %) also presented the highest relative coverage at this site along with C. caribbaea (2.0 %) (Table 2).
Table 2 Abundance, coverage, and density of sponge species by sampling site.
AR: relative abundance; CR: relative coverage; *: new registration.
In the case of Pequeño, Ircinia felix (15.9 %), Species 4 (13.3 %) and S. ruetzleri (12.3 %), had higher relative abundances. However, of these sponges, only I. felix (1.0 %) and Specie 4 (0.8 %) showed the highest relative coverage, followed by Haliclona caerulea (0.2 %) (Table 2).
In Coral Garden, N. erecta (28.4 %), I. birotulata (13.7 %) and S. ruetzleri (12.2 %) presented the highest relative abundances, similar to that of Perezoso. The Svenzea zeai species was only registered at this site, where it presented the highest relative coverage (1.3 %) along with other sponges such as I. birotulata (0.9 %) and N. erecta (0.6 %) (Table 2).
In 0.36, the highest relative abundances were represented by N. erecta (26.9 %), Mycale laevis (15.2 %), and Clathria curacaoensis (7.8 %). The I. felix sponge had the highest relative coverage (0.9 %), followed by N. erecta (0.8 %) and Ircinia campana (0.7 %). The highest number of individuals was also observed at this site and (982) among the four sampled sites and, therefore, had the highest density of sponges (19.6 individuals/m2) (Table 2).
The occurrence frequency percentage of boring sponges of the genus Siphonodictyon remained below 45 % at all sites. In Coral Garden S. brevitubulatum was the most frequent boring species (38 %); furthermore, this was the only site where S. coralliphagum was registered (2 %). The S. xamaycaense species turned out to be a new registry for the country and it was only presented in Perezoso, where it had a higher occurrence frequency percentage (24 %) than S. brevitubulatum (16 %). In Pequeño reef patch, no species of this genus were recorded during the sampling (Figure 2).
Diversity indices
Coral Garden registered the largest number of sponge species with a total of 34. Despite this, it showed values of heterogeneity, evenness, and dominance of species very similar to those of Pequeño and 0.36. Therefore, when applying the diagram of the severity degree and environmental predictability, it was found that the sponges of these three reef patches live under somewhat severe to favorable conditions and from almost constant to constant. This contrasts with what was found for Perezoso, which, due to its lower values of heterogeneity and evenness, was classified as a severe and unpredictable environment. In addition to the above, Perezoso presented the only dominance value higher than 0.1 (Table 3).
Abiotic factors and similarity between sites
Sedimentation rates were accentuated during the transition from the dry to the rainy season (October-December) and decreased with the passage from the rainy to the dry season (August-September, and September-October); except in 0.36 where the rates remained relatively constant and did not exceed 32.4 ± 6.0 mg/cm2/day (Figure 3). The highest sedimentation rates and variations by periods were obtained in Perezoso and Pequeño. However, it does not appear that the above affect the similarity between the sites with respect to the relative abundance of the sponge species present (Figure 4).
Figure 4 Similarity between the sampling sites with respect to the relative abundance of sponges and the average sedimentation rates (mg/cm2/day). 1) Perezoso, 2) Pequeño, 3) Coral Garden, 4) 0.36.
Substrate availability was equal to or greater than 67.0 % at all sites. This minimum value corresponded to Coral Garden, where the only bare calcareous pavement was found. The largest amount of available substrate was presented by Perezoso (74.0 %) and Pequeño (69.1 %). In both sites, three of the four types of substrate found in this study were recorded. However, in Perezoso, the bare calcareous pavement predominated (48.7 %) while the calcareous pavement with sediments (35.1 %) predominated in Pequeño. On the other hand, in 0.36 the calcareous pavement with coarse sand (66.2 %) predominated and it was the only place where this type of substrate was found (Table 4, Figure 5).
Figure 5 Similarity between sampling sites to the relative abundance of sponges and the percentage of available substrate 1) Perezoso, 2) Pequeño, 3) Coral Garden, 4) 0.36.
The depth range varied between 5.0 ± 0.9 and 18 ± 3.4 m, with Pequeño being the shallowest site and Coral Garden the deepest (Figure 6). The most similar sites to each other based on the relative abundance of sponges were Perezoso and Coral Garden (1 and 3), with an important differentiation to Pequeño and 0.36 (Figure 4, Figure 5, and Figure 6).
DISCUSSION
Registered species
The record of 13 sponge species not previously reported for the Costa Rican Caribbean demonstrates the insufficient research carried out in the country on this group. This was pointed out by Cortés et al. (2009), who with a specimen collection campaign in this region of the country increased the number of new records in 28 species. The development of studies related to this group in other reef patches and ecosystems (mangroves, seagrasses, among others) in the area is likely to lead to new records, as well as the discovery of new species, which could help to better understand the distribution patterns of sea sponges, as well as the dynamics and processes that occur in the ecosystems where they are found.
Relative coverage and abundance
Regarding sponge coverage, none of the four studied sites showed to be particularly favorable for the horizontal growth of the poriferans. This is evident if we make a comparison with other reefs in the Caribbean such as those of Santa Marta (Zea, 1994) and Gulf of Urabá (Valderrama and Zea, 2003) in Colombia where sponges cover over 5.0 % of the substrate and it can reach up to 33.3 % of the total coverage. The coverage percentages found in this study (CR < 6.1 %) are in a similar range to those documented in the eastern coast of Cochinos bay, Cuba, by Caballero et al. (2009). These authors considered sponge cover percentages below 8 % as low and possibly associated with reefs in the natural state with a predominance of corals.
Only two of the registered species had coverage higher than 1.5 %, C. caribbaea (2.0 %), and N. erecta (1.8 %), specifically in Perezoso. These sponges made up more than half of the coverage of these organisms at the site. The N. erecta species also turned out to be the most abundant (26.9-59.3 %) in three of the four sampling sites (Perezoso, Coral Garden, and 0.36) and represented more than half of the individuals in Perezoso. This was reflected in the dominance index obtained (D = 0.4) for this site.
Niphates erecta is considered to be a heterotrophic species, does not have photosynthetic endosymbionts, and is strictly dependent on filtration as a food source (Romero et al., 2013). For this reason, it is common to find high abundances of this sponge in sites with environmental conditions similar to those of Perezoso, where turbulence, currents, sediment discharges, and turbidity are high. Documented examples of the above include the rocky-sandy bottoms of Nelson island in Trinidad and Tobago (Hubbard, 1990), the coral areas of the Gulf of Urabá in Colombia (Valderrama and Zea, 2003), Mero beach and Punta Brava in Venezuela (Romero et al., 2013). Also, N. erecta is frequent in mangroves and is among the five most abundant species in the shallow reefs of Bocas del Toro (Caribbean of Panama), where there is low urban and tourist development, but the treatment of its wastewater is almost null (Díaz, 2005; Gotchfield et al., 2007).
Diversity and abiotic factors
Sponge species richness seemed to increase with the average depth of the sampled sites. This pattern has been documented in other reefs in the Caribbean region by Valderrama and Zea (2003) in the Gulf of Urabá in Colombia and by De la Nuez et al. (2011) in those of Bajo de Sancho Pardo in Cuba. However, the other diversity indices calculated for this study did not appear to be linked to any of the abiotic factors considered. Only Perezoso showed exceptions to this trend with contrasting values in their indices (H' = 1.6; J' = 0.5; D = 0.4), in addition to being the only site classified as severe and unpredictable when applying the severity and predictability diagram.
The diversity indices and the classification given by the diagram for Perezoso were possibly influenced by the high average annual sedimentation rate (104.5 ± 52.9 mg/cm2/day) that occurs at the site. Perezoso retain sediments mainly of terrigenous origin, carried from rivers such as La Estrella, Suárez, and the Perezoso gorge. This sedimentation, rich in organic content, has already been documented with rates between 30 and 360 mg/cm2/day (Cortés and Risk, 1984); and it is considered that it generates very negative effects on the Cahuita reefs (Cortés and Jiménez, 2003). The main source of these sediments is believed to be banana plantations and deforestation in the Valle de la Estrella (Cortés, 1981, 1994; Cortés and Jiménez, 2003). This drag of material, generated by soil erosion and the infiltration of agrochemicals on the banks of the la Estrella river, is favored by the coastal current that travels from northwest to southeast in the Caribbean of Costa Rica (Cortés and Jiménez, 2013), as well as the PNC deck shape, which favors the retention of sediments in the northern part where the Perezoso barrier is located.
Sponge biomass at sites near sewage and agrochemical discharges has been shown to tend to increase in terms of abundance, coverage, or density. In turn, when the concentration of these organic pollutants increases, a decrease in the diversity of the sponges present and proliferation of specialists are common, which can be used to monitor these conditions in the environment (Rützler, 2004). This could be the case of C. venosa (AR = 2.7 %; CR = 0.2 %) since this species was only found in Perezoso with coverage and relative abundance similar to that of other common species such as I. felix and M. laevis. Clathria venosa has been used as a bioindicator species of organic contamination in Cuba (Busutil and Alcolado, 2012), therefore, its presence in Perezoso could be related to the contaminants that are dragged into the sediment by rivers near banana plantations such as La Estrella river.
The severity and predictability diagram should be used and interpreted with caution. For Perezoso, this diagram does seem to be sensitive to environmental disturbances through the values of heterogeneity and fairness obtained at the site. However, for Pequeño, it showed discrepancies that do not coincide with the results obtained. Pequeño presented an average annual sedimentation rate similar and even higher than Perezoso (107.6 ± 42.3 mg/cm2/day) and, even so, it was classified as a favorable and constant environment due to the values obtained in heterogeneity (2.6) and fairness (0.8).
The incidence of high sedimentation in Puerto Viejo has already been documented by Cortés and Jiménez (2003). However, the composition and dynamics of the sediments at the site appear to be different from that of Perezoso. While in Perezoso the processed sediments were very fine, black in color, they seemed to be mostly of terrigenous origin and contained a large amount of decomposing organic matter; in Pequeño, the sediments had a lighter coloration, coarser particles combined with sand and less amount of decomposing organic matter. Furthermore, the sediments in Perezoso accumulated and clogged very easily on the walls and bottom of the barrier, contrary to Pequeño where they were deposited in some cracks, slopes, and on the bottoms with sandy sediments.
This could indicate that the composition of the sediments, the topography of the bottom, and the dynamics of the currents allowed the displacement and deposition of the sediments outside and around the patch, preventing sedimentation from having such a pronounced effect on diversity of sponges in Pequeño. Likewise, there is the possibility that the high sedimentation rates at this site did not have as much effect on the composition, diversity, and abundance of the sponge species as they could have on its cover. This phenomenon could be limiting and reducing the growth rates of this group due to the obstruction of their aquifer systems (Bell et al., 2015).
Another possibility is that Pequeño was undergoing a process of repopulation and colonization since the sponges' present were mainly of small sizes (less than 10 cm), possibly young and that have not completed their critical phase of colonization. This could indicate a still incomplete environmental selection process (Zea, 1993; Alcolado, 1999), possibly linked to the earthquake that occurred in 1991, which raised the continental shelf in the Costa Rican Caribbean between 50 and 190 cm (Cortés et al., 1992). The phenomenon caused the exposure of the substrate and generated high mortality of invertebrates.
Abiotic factors and similarity between sites
The only factor that seemed to better explain the similarity between sites with respect to the composition of sponge species and their relative abundances are the percentage of the available substrate. In both Perezoso and Coral Garden, bare limestone pavement was the predominantly available substrate (48 < LP % < 67) and this could be favouring the colonization, growth, and permanence of N. erecta, I. birotulata, and S. ruetzleri. These three species were shared by both sites as the most abundant despite their average depths and contrasting sedimentation rates. This could be linked to the merely heterotrophic and generalist habit of these sponges, since they can survive and proliferate under the effect of different stressors such as fluctuations in salinity, turbidity, sedimentation, illumination, and nutrients; provided they have an appropriate substrate for their fixation (Nuñez et al., 2010; Romero et al., 2013).
On the other hand, Perezoso and Coral Garden also shared the highest occurrence frequencies of boring sponges of the genus Siphonodictyon (40 %) and were the only sites where the presence of the bio-eroding species C. caribbaea was recorded. The presence of sponges of the genus Cliona in the PNC had already been documented by Cortés and Guzmán (1985), who recorded coverage of up to 1 m2, similar to what was found in the present study. The C. caribbaea sponge was found in the Archipelagos of San Andrés and Rosario, Colombia, with a distribution that varied from 5 to 20 m deep and with a slight tendency to be more abundant in sites with greater availability of calcareous substrates as dead coral and pavement (López-Victoria and Zea, 2005). This coincides with the depth range and the type of substrate with the highest availability presented by Perezoso and Coral Garden.
In the Caribbean, there are reports that the coverage of boring sponges of the genus Cliona has increased considerably during the last three decades (López-Victoria and Zea, 2005). This is worrisome, since these species, together with those of the Siphonodictyion genus, tend to have very aggressive growths and considerable damage to the reefs when their abundance and coverage are high. For example, the excavation caused by these sponges can cause the breakage of large coral colonies as a consequence of erosion, accompanied by the production of muddy sediments. In turn, the growth of boring and bio-eroding sponges can be enhanced by increases in available organic matter and by high temperatures (Rützler, 2004), conditions that are also extremely stressful for corals and were observed within Perezoso.
CONCLUSIONS
The number of species of sea sponges in the Costa Rican Caribbean exceeds 80, with 13 new records in this study. The densities, abundance, and relative coverage of the sponges found are an important input in understanding the dynamics of the reef patches and their similarities, as well as the possible natural and anthropogenic pressures that contribute to shaping them. The use of ecological indices are tools that can help infer the level of disturbance to which sponge communities are exposed, provided they are interpreted cautiously and contrasted with physical and chemical factors in the environment. It is recommended to test and adjust the diagram to assess the degree of environmental severity and predictability according to the geographic area where you want to implement it.
The depth of the reef seemed to influence the species richness of sponges present, with increases in the number of species as depth increased. On the other hand, sedimentation rates did not show an effect on the similarity between sponge communities, but the origin and composition of these sediments could be influencing the coverage of poriferans, the abundance of specialists such as C. venosa and the dominance of sponges' resistant to sediment and turbidity such as N. erecta. Only the high percentages of bare calcareous pavement as the predominantly available substrate could explain the similarity between the Perezoso community structure and Coral Garden. This seemed to favour the abundance of heterotrophic and generalist sponges N. erecta, I. birotulata and S. ruetzleri, as well as the occurrence frequency of sponges of the genus Siphonodictyon and coverage of those of the genus Cliona. Furthermore, the evaluation of the occurrence frequency and the coverage of these two genera indicated that these sponges could be causing negative effects for the stony corals of Perezoso due to bioerosion. The use of this information will contribute to the selection of reefs where it is most urgent to take mitigation measures, and even those with the potential to develop restoration projects. Although this study broadens the understanding of the community structure of sea sponges in the Costa Rica Caribbean, it is recommended to carry out more research in this field and determine if there are other factors, both biotic (food availability, predation, competition) and abiotic (water movement, local currents, turbidity, roughness of the bottom), which could influence to a greater extent the community structure of the poriferans.
