Second survey of heterobranch sea slugs (Mollusca, Gastropoda, Heterobranchia) from Bunaken National Park, North Sulawesi, Indonesia - how much do we know after 12 years?

Abstract

Background: Bunaken National Park (BNP) is one of the most famous marine national parks in Indonesia with an extraordinary diversity in marine life forms. However, this diversity is threatened by an increasing population on the islands, ongoing destructive fishing techniques and lately by an increase in tourism. Protecting and managing the future use of BNP resources will require the assessment of both, local marine biodiversity through monitoring efforts and the identification and subsequent reduction of any threats or changes in the park. A high diversity in marine Heterobranchia indicates a high diversity of metazoan life forms and a diverse habitat structure. Surveying the complete biological diversity across taxonomic groups found in BNP would be an extensive undertaking, so focus on heterobranch diversity as an indicator of coral reef health was initiated and a model group on which future monitoring and conservation efforts can be based is provided. This study follows up the first investigation of marine Heterobranchia in BNP, conducted 12 years ago, while assessing molluscan diversity, and intends to present a base line for future monitoring programs. Results: The diversity of marine heterobranchs around BNP was surveyed with an emphasis on Bunaken Island by diving and snorkeling at nearly 20 sites. Species are listed with photographic documentation (81 species) and results compared with the former study on molluscan species diversity in BNP. Taking these two studies into account 135 species are now recorded from BNP. The low overlap of described species (21) between the two BNP studies illustrates the gap of knowledge about overall species diversity in this particular area. A comparison with other studies from the region and Indo-Pacific also provides evidence for undersampling, but show similar taxa composition except of a somewhat higher cladobranch number in relation to Anthobranchia. Conclusions: BNP is still under-sampled with regard to sea slug diversity. Thus conclusions as to whether or not a shift in species has occurred during the 12 years since the first study cannot be drawn. More and extensive studies are necessary to completely document the species richness in this area.

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

“…In order to monitor potential damage to the environment around Sangihe, irrespective of its original cause, we have started with a first survey in 2016, focusing on marine Heterobranchia. Here we present the first results from this collecting period and compare our results with former studies in Bunaken National Park [13,14] and other areas in and around Indonesia.…”

“…This spectrum covers nearly all sessile organisms (algae, poriferans, cnidarians, ascidians, bryozoans, tunicates). Thus, this group was already used for monitoring coral reef diversity in North Sulawesi [12][13][14][15]. Because marine Heterobranchs are also very attractive to tourists, additional data are and will be available through citizen science due to documentation in websites or personal information and provision of images on personal bases.…”

Assessing cryptic marine fauna diversity as underwater macrophotography (UMP) objects in Sempu Strait, Indonesia

“…The identification process is carried out by comparing the morphological details of each specimen from the photograph with material source like books and journals, and also got its taxon verified by the World Register of Marine Species' website [18]. The fishes identifications are mainly compared to identification books [19][20][21], while the sea slugs are compared to various sources like book [22], scientific publications [23][24][25][26][27], and additionally the Bill Rudman's Sea Slug Forum [28]. The polyclad flatworms identified by comparing to journals [29][30][31][32], while the arthropods (crustacean) identifed by comparing to book [33].…”

Description of a new Moridilla species from North Sulawesi, Indonesia (Mollusca: Nudibranchia: Aeolidioidea)—based on MicroCT, histological and molecular analyses

“…During various species diversity studies in Bunaken National Park, North Sulawesi, Indonesia Kaligis et al 2018), four undescribed species of Noumeaella Risbec, 1937 were recorded. Edmunds (1970) postulated a close relationship between Noumeaella, Palisa Edmunds, 1964 andMoridilla Bergh, 1888, based on similarities of rhinophores, foot tentacles, cerata shape and radula morphology.…”

“…A barcoding approach of the Bunaken material from the studies of Eisenbarth et al (2018) and Kaligis et al (2018) revealed that two of the therein mentioned Noumeaella species actually group with the genus Moridilla. This corroborates the difficulty in assigning specimens correctly to the genera mentioned.…”