First Survey of Heterobranch Sea Slugs (Mollusca, Gastropoda) from the Island Sangihe, North Sulawesi, Indonesia

Abstract

Indonesia is famous for its underwater biodiversity, which attracts many tourists, especially divers. This is also true for Sangihe Islands Regency, an area composed of several islands in the northern part of North Sulawesi. However, Sangihe Islands Regency is much less known than, e.g., Bunaken National Park (BNP, North Sulawesi). The main island, Sangihe, has recently experienced an increase in tourism and mining activities with potentially high impact on the environment. Recently, monitoring projects began around BNP using marine Heterobranchia as indicators for coral reef health. No information about this taxon exists from the remote islands in North Sulawesi. The present study represents the first monitoring study ever and focuses on marine Heterobranchia around Sangihe. In total, 250 specimens were collected, which could be assigned to Sacoglossa (3), Anthobranchia (19), and Cladobranchia (1). Despite the low number (23 versus 172 in BNP), at least eight species (35%) are not recorded from BNP, probably indicating differences in habitat, but also influence of a strong El Niño year in 2016. Here we also report for the first time a Chromodoris annae specimen mimicking C. elisabethina, and the discovery of a new Phyllidia species.

First Study on Marine Heterobranchia (Gastropoda, Mollusca) in Bangka Archipelago, North Sulawesi, Indonesia

“…Families and species are listed in the same order as in the text below. The table also provides information about the presence of the particular species in BNP, Sangihe, and Lembeh Strait according to the recently published surveys [16][17][18] to highlight those species that are only recorded from our study area. All species listed in Table 2 are also depicted by at least one specimen, together with the specimen identifier, if the animal was collected, and are available for further investigations.…”

“…All species listed in Table 2 are also depicted by at least one specimen, together with the specimen identifier, if the animal was collected, and are available for further investigations. In the following sections, species and specimens are discussed and compared to other studies from North Sulawesi [1, [16][17][18].…”

“…List of species, specimen identifiers, and further metadata of the material; (*) indicate species that were identified only by photo-documentation. The last three columns indicate the number of specimens or occurrence of the respective species in other study areas nearby (information is taken from Eisenbarth et al (2018) [16], Undap et al (2019) [18], and Ompi et al (2019) [17]: BNP, Lembeh Strait, and Sangihe Island).…”

“…Burghardt et al [15] recorded molluscan diversity for the first time in North Sulawesi (Bunaken National Park, BNP), including heterobranch taxa. More recently, several publications on heterobranch diversity have been published from North Sulawesi, including Bunaken National Park, Lembeh Strait and Sangihe Island [1, [16][17][18], which renders this area as one of the best investigated places in Indonesia with regards to this taxon. Our study in Bangka Archipelago increases our knowledge on the biodiversity of heterobranchs in North Sulawesi in an area that has never been documented before.…”

“…Bangka Archipelago comprises small islands located in the northeast of North Sulawesi, thus lying in between the recently well-studied area of Bunaken National Park, and the famous Lembeh Strait, whereas Sangihe Island lies approximately 200 km to the north. All studies have shown that these areas differ in heterobranch composition due to the differing habitat compositions [16][17][18]. Bangka Island exhibits biogenic reefs, volcanic rocks, and a few areas with mangroves and sea grass meadows.…”