Biodiversity of Sessile Fauna on Rocky Shores of Coastal Islands in Santa Catarina, Southern Brazil

The epilithic sessile fauna of coastal islands off Santa Catarina, southern Brazil, was analyzed along two 30 m long sublitoral transects. A total o f 111 taxa were identified of which 55 are new records fo r the South Atlantic epilithic assemblages. Exotic sponges, bryozoans and ascidians (Paraleucilla magna, Sch izoporella errata, Bugula dentata, Styela plicata respectively) were found at Marine Protected Areas. This paper gives further knowledge on the marine sessile fauna of the coastal islands of southern Brazil for environmental monitoring programs. A more complete list of epilithic species will certainly provide a baseline to detect future environmental changes and local anthropogenic impacts on the biodiversity of southern Brazilian ecosystems.


Introduction
The rocky shores off Santa Catarina, southern Brazil, extends for 562 Km bordering the coastline of the mainland and 130 islands scattered from the Babitonga Bay until the southernmost limits of the main Santa Catarina Island [1]. The epilithic co mmun ity of the sublitoral zones is rich and diverse, mostly dominated by sessile groups [2]. The Marine Biological Reserve of Arvoredo (REBIOMA R), the only Brazilian full marine protected area (MPA) in southern Brazil, occupies a polygon of 17,600 ha to protect sublitoral rocky environ ments of some islands and few submerged reefs, all fringed with a broad band of subtidal hard bottom communit ies. This MPA was set up in 1990 to ensure recruit ment and reco lonization ofadjacent areas which are permanently threaten by all kinds of anthropogenic impacts associated with the economic development along Santa Catarina coastal zone [3]. Ho wever, the pro ximity of the islands with the mainland threatens the biodiversity of their rocky habitats subject to the contamination of urban and industrial development in the last decades.
Due to the co-occurrence of a wide variety of organis ms and their trophic interactions, including symbiosis, the sessile benthic co mmun ities formed a specific rocky ecosystem with great heterogeneity of micro-habitats and, therefore, high bio logical richness [4,5].
An important factor to consider is presence and abundance of species considered invasive due to the fact that these organisms interfere in the survivability of other community species [26], plus the ability to generate economic and environ mental damage, and in some cases to human health. Invasive organisms can cause marked changes in commun ities by altering the evolutionary pathway of native species by competitive exclusion site, niche displacement, hybridizat ion, introgression, predation, and possibly extinction [27,28]. Together the introduction of exotic species, degradation and / or transformation of habitat, overexploitation of organis ms for consumption or ornaments, are the b iggest threats to marine and coastal biodiversity.
Worldwide, the rate of degradation of natural coastal habitats has been faster than conservation initiatives. In Brazil the actual legal framework that supports conservation policies along the coast is poorly supported by ecological data [3]. Th is study aims to contribute for a better knowledge of the marine biodiversity in the State of Santa Catarina, with emphasis on cnidarians and bryozoans, in order to provide technical support for marine conservation in southern Brazil.

Study Area
The region is in a transitional belt of latitudes between tropical and temperate regions, on the western boundary of the South Atlantic basin. Oceanographic conditions off southern Brazilian coast are strongly affected by the seasonal north-south displacement of the Subtropical Convergence. Onshore bottom intrusions of the oceanic South Atlantic Central Water (ACAS) along the Santa Catarina continental shelf in summer are due to north winds-induced Ekman transport of surface waters offshore, decreasing water temperatures at the bottom. In winter, winds are predominantly fro m south. They transport subantarctic waters of lower salinities, strongly affected by the outflow of the La Plata River. The hydrographic environment is therefore very dynamic during the annual cycle [29,30]. This affects the composition and the seasonal dynamics of regional epilithic assemblages [31,3].
The hard bottom of the islands is relatively shallow but physically heterogeneous, consisting of rounded rocks arranged in a delicate slope toward the sandy bottom. Large rocks form caves and walls up to about 15 m deep. The sublitoral cliffs at REBIOMA R, may extend beyond 30 m depth. The taxonomic co mposition and quantitative data on the epilithic co mmun ity were analy zed fro m manual collections of individual and pieces of colonial groups, with additional non-destructive photographic records were taken with digital camera Sony DSC-W90. Seven dives were exclusively dedicated to the inventory of hydrozoans, bryozoans and ascidians. The collected animals were anesthetized with menthol and fixed in formalin 4%, except sponges that were fixed in 70% ethanol, for later identification in the laboratory.

Results
We have recorded 111 taxa belonging to the phyla Porifera, Cnidaria, Bryozoa, Entoprocta and Chordata (subphylum Tunicata, class Ascidiacea), distributed in 54 families, of wh ich 27 taxa could not be identified at the specific level. The most representative groups were the Cnidaria with 38 hydrozoans and 11 anthozoans, followed by ascidians with 32 taxa, 18 sponges, 11 Bryozoa species and Entoprocta with only one not identified species ( Table  2). Representatives of dominant sessile groups indentified during the sampling surveys can be seen in the photographic panels of Figures 2a (sponges), 2b (cnidarians) and 2c (ascidians and bryozoans). Fifty five taxa are new records for Santa Catarina, wh ich account for 50% of all specimens recorded. New records of species occurred for all phyla, but mainly in the Class Hydrozoa and the Phylum Bryozoa with 31 and 10 species, respectively. Five new Porifera, 4 Anthozoa and 5 ascidians were identified. The hydrozoans Lafoeina tenuis [32], Antennella secondaria [33], Sertularella rugosa [34] and Hincksella cylindrica [35], and the sea squirt Didemnum cf. calliginosum [36] have their geographic distribution e xpanded for the South Atlantic (Table 3).   Arvoredo I. was the second in richness (42 species), with 24% of new records. This records percentage low is due probably to the previous samplings in Arvoredo I. The hydrozoan Lafoeina tenuis, previously described for southern Florida and the Bahamas [37], was identified in the Arvoredo and Deserta islands. These are their first records for the southwestern Atlantic.
Fifty-four percent of the species identified in the Graças Archipelago were new records, 75% of which are hydrozoans. On the Campeche island 48% are also new records ( Figure 3) and all bryozoans recorded here in Santa Catarina coast represent also new records for the southern Brazilian coast. Seven taxa of Cheilostomata and four Ctenostomata were found among all.

Discussion
Biodiversity inventory is the first step for understanding ecological processes at coastal or even at broader oceanic scales. The remarkab le nu mber of new records of benthic fauna in Santa Catarina islands reveals the lack of taxono mic studies to better access the state of the marine conservation in the southern Brazilian coast. So far we have been unable to identify endangered species, due to the scarcity of data that might indicate even natural fluctuations of sessile invertebrate populations threatened by many anthropogenic impacts such as sedimentation associated with habitat losses at the coast, pollution and overfishing [38,39]. In general, a reef environ ment exposed to excessive loads of pollutants, responds to changes and often simplify the structure of biological co mmunit ies [40]. Unfortunately, little is known on the effect of overfishing on the biodiversity in Brazilian subtidal reefs and rocky shores [41,42].
Among the new records for the South Atlantic the sea squirt Didemnum cf. calliginosum, orig inally described by [43] on the Caribbean island of Guadeloupe, had its distributional range extended to the State of Santa Catarina, more exactly on the Campeche I. The ascidian commun ity in Brazil is typically tropical with little overlap with the Argentina and Patagonia fauna [44]. The presence of these species in Santa Catarina state subtropical waters is probably due to the mu ltip le introductions of the species in the southern coasts [45,46] where major harbor facilit ies are located. The lack of historical records prevents us from defining the status of many species that remain cryptogenic, but we believe the develop ment of molecu lar studies of global scope will reveal invasion of exotic species in the western Atlantic, some of them already recorded in Brazilian waters. According to [47] there are forty species of exot ic zoobenthos along the Brazilian coast, twelve of wh ich are sessile animals. In the coastal islands off Santa Catarina four species of his list of exotic zoobenthos were identified. For instance, the invasive sea squirt Styela plicatawas first recorded to Brazil at Rio de Janeiro [47]. The type specimen was fro m Philadephia and some authors consider S. plicata as widely distributed species along the warmer coast of Atlantic, Pacific and Indian Ocean and also Mediterranean Sea [48]. Here it was found within the MPA of Arvoredo and Galés Is. Dense aggregates of this species are formed at the sublitoral of Santa Catarina Is. where each indiv idual takes an elongated shape with a stalk of attachment. In southern Brazil, it is rarely found in the natural environ ment, preferring strings of mariculture grounds and floating artificial substrates of harbour facilities [49]. Yet, it was first recorded in a natural rocky shore of Santa Catarina.
The calcareous sponge Paraleucilla magna [50]has an undefined status about native or exot ic specie status. P. magna has been found along the Brazilian coast and it was found in the Moleques do Sul and Aranhas archipelagos, in the northern coast of the Santa Catarina island (Bouzon, personal observation). She is a cryptogenic specie (Cavalcanti, personal co mmun ication), i.e., cause we cannot say whether it is native or exotic specie. It has a full life cycle in nature and evidence of population increase over time, but without apparent environmental or socioeconomic impact. The exotic bryo zoan Schizoporella errata (Figure 2c) wh ile Bugula dentata were common ly found in the islands. The first is an established species and B. dentata is present in the natural environ ment but without further increase in abundance and distribution [46]. However, since we found it in reasonable abundance in the islands of Santa Catarina as well as in the coast off Cabo Frio, Rio de Janeiro the status of this exotic species in Brazil should be reviewed because we considered it considered already established.
Distributional limits of the northern Brazilian tropical sessile fauna were extended southwards in our records. Subtropical provinces of the southeastern and southern Brazil have been regarded as a transitional zone for the temperate fauna of the western Atlantic [51]. However, the study area belongs to the Paulista Province [52] where ca 40% o f the records which are also found along other sections of the Brazilian coast were endemic to it. This province extends from the Espírito Santo to Rio Grande do Sul (~ fro m 22° to 32° S) and is characterized by high incidence of endemic species, and can expect a s mall difference in species composition across the province, with the predominance of tropical species to the north and temperate species to the south. Nevertheless, besides low temperatures in southern Brazil during winter time, the lacking of rocky shores further south fro m Santa Catarina represents an additional barrier for the dispersal of epilithic organis ms.
The taxono mic analyses of the sessile fauna here described for the southernmost islands off Flo rianópolis have demonstrated they are equally or even more diverse than the assemblages of the islands of the Arvoredo MPA in the northern coast of Santa Catarina. Hence it should also be protected. This study has improved substantially the knowledge on the marine biod iversity in the coastal zone of Santa Catarina state. We hope it will contribute for the development of a mo re technically oriented conservation policy for the coastal ecosystems of southern Bra zil.