Camptostemon philippinensis, a new record of endangered mangrove species in the Balikpapan Bay, East Kalimantan, Indonesia

Introduction

Camptostemon philippinensis (Vidal) Becc. is an endangered species comprising mangrove forests listed in the endangered category on the IUCN Red List (Duke et al., 2010). This species is one of Indonesia’s two protected mangrove species (MEF Regulation Number 106/2018), so it is a high priority for conservation. C. philippinensis is a rare mangrove species globally distributed in Indonesia and the Philippines, with an estimated number of mature individuals of around 200 (Duke et al., 2010; Primavera et al., 2004). In Indonesia, this species is only found on the islands of Kalimantan and Sulawesi (Duke et al., 2010) and mainly in isolated mangrove forests (Djamaluddin, 2018). That is a lesser-known species, and so far, there are no records of its use by the community. However, the bark and leaves of C. philippinensis have the potential to contain anti-melanogenic and antibacterial chemicals (Gadores et al., 2021).

Camptostemon philippinensis is one of three species in the genus Camptostemon (Malvaceae) (Beccari, 1886). This species was first published as Cumingia philippinensis S. Vidal in 1885, with type specimens originating from the island of Luzon. Beccarii (1886) suggested the move to the Camptostemon genus after observing the flower and fruit organs of the early species and discovering that the features in these two organs in Cumingia were comparable to those in Camptostemon. Van De Brink (1924) reduced the species C. aruensis to a synonym for C. schultzii based on his observations on the organs of flowers and fruits. That makes C. philippinensis and C. schultzii very easy to distinguish based on the morphological character of the leaf shape, where the first species has oblong leaf blades and the last species has elliptical leaf shapes. However, molecular studies have not been carried out specifically to support this opinion.

The population distribution of C. philippinensis on the island of Borneo is very limited. Previously, records of the distribution of this species in Borneo were only documented on the coast of Berau (Mukhlisi & Sidiyasa, 2014). In Balikpapan Bay, several mangrove floristic studies have been conducted and recorded the richness of mangrove species, ranging from 12 species (Kristiningrum et al., 2019) to 20 species (Warsidi & Endayani, 2017). Although various biodiversity studies have been carried out in the area, the presence of C. philippinensis has never been recorded (Kristiningrum et al., 2019; Sayektiningsih et al., 2012, 2020; Toulec et al., 2022; Willard et al., 2022).

Balikpapan Bay is a mangrove ecosystem in East Kalimantan with an area of around 168 km² (Toulec et al., 2022), which is an essential habitat for various species of endangered wildlife, especially Borneo’s endemic primate, the proboscis monkey (Nasalis larvatus). However, the threat of mangrove forest conversion is still present (Anwar et al., 2021b; Toulec et al., 2022). The study results show that this area has one of the densest proboscis monkey population distributions, with as many as 60 groups (Toulec et al., 2022). On the other hand, mangrove vegetation has a strong interaction with the presence of proboscis monkeys because the monkeys like young leaves, seeds, and mangrove fruit as food sources (Boonratana, 1993). Atmoko (2022) has reported as many as 41 plant species as food sources for proboscis monkeys from several habitats in East Kalimantan. In addition, proboscis monkeys often choose large mangrove trees on the banks of rivers or seas as sleeping trees to avoid predators. However, until now, information on the ecological role of C. philippinensis in the proboscis monkey’s natural habitats has been limited.

Documentation of the C. philippinensis population is important in supporting comprehensive conservation efforts, such as propagation efforts, and understanding its ecological role for the animals around it. More importantly, because some of the Balikpapan Bay areas will be developed as a site for the new Indonesian capital city (Ibu Kota Nusantara/IKN), this study can be used as a resource for stakeholders interested in the usage of the area.

Methods

Results

The population of C. philippinensis was found on Pantai Lango Village and Kowangan Island in Penajam Paser Utara District, East Kalimantan ( Figure 1) (Mukhlisi, 2023; Sitepu et al., 2023). It was found in a narrow area, although the Balikpapan Bay mangrove forest is relatively large. The C. philippinensis habitat is on the west shore, in the middle of Balikpapan Bay. Only one individual (height = 2 m, diameter = 15 cm) was found on a small island (Kowangan Island), whereas most others inhabited the mainland’s western shore in Pantai Lango. The distance between these two locations is around 500 m.

Figure 1. Habitat and distribution of Camptostemon philippinensis in Balikpapan Bay, East Kalimantan Indonesia.

Based on our observations in Pantai Lango, there were around 527 individuals of C. philippinensis that were dominated by seedlings (452 individuals), followed by trees (49 individuals), and saplings (26 individuals) ( Figure 2). This demonstrates that even though C. philippinensis has a relatively limited range; its natural regeneration potential is functional. However, the number of saplings found was less than the tree stage, and this may be due to competition for space in a limited habitat. Generally, in mangrove forests, the number of seedlings is more abundant than the saplings, and the sapling stage is more numerous than the trees (Islam et al., 2015; Winata et al., 2017).

Figure 2. The percentage of the number of individuals of Camptostemon philippinensis in Pantai Lango based on the growth stage.

(Total n=527 individuals).

The saplings and trees of C. philippinensis have an average tree diameter ( Figure 3) similar to the flora in the area. The tree was observed in the early of fruiting season in March 2023, we found flowers and unripe fruits ( Figure 4).

Figure 3. Profile of diameter at breast height (dbh) for trees and saplings of Camptostemon philippinensis in Pantai Lango.

Figure 4. Fruiting specimens of Camptostemon philippinensis (A), from Balikpapan Bay the flower (B), the fruit (C), and a herbarium specimen deposited in Herbarium Bogoriensis (D).

The license mentioned in the Methods section included permission to collect specimens.

A population of C. philippinensis was found in the middle area of Balikpapan Bay. Our investigation found that the soil texture around the habitat of C. philippinensis is predominantly sandy, with moderate to low-intensity sea tides in the area with Balikpapan Bay. A study reported that this area experiences daily semi-diurnal tides, with a tidal range of almost 2.5 m during spring tides and 1 m during neap tides (Anwar et al., 2021a). At our study site, C. philippinensis inhabits the second layer of the mangrove zone, where the inundation occurs only during high tide, while the first layer zone is always inundated.

Discussion

J. van Borssum Walkes identified C. philippinensis in Indonesia in 1962 based on herbarium specimens collected by CNJ Welmaar in 1919 from Pulau Laut, South Kalimantan (Bakhuizen van den Brink, 1924; Troll, 1933). In the following period, it was never recorded in various publications or scientific collections, so it was stated that it was no longer present in Kalimantan and grew only limitedly in the Papua region (Macnae, 1968). However, Noor et al. (2012) continued to list this species along with C. schultzii as a type of mangrove plant in Kalimantan until publication by Mukhlisi and Sidiyasa (2014) based on botanical records in Tanjung Batu, Berau. While in Sulawesi, it was reported in Bunaken National Park (Djamaluddin, 2018; Djamaluddin & Djabar, 2022) and Donggala (Wahyuningsih et al., 2012). In the Philippines, however, this species has reported to be widely spread but less abundant in each population (Primavera et al., 2004).

In a limited habitat, populations of C. philippinensis tend to form stands in groups. The population is quite dominant at a certain point in a habitat, but not like Rhizophora spp. (Mukhlisi & Sidiyasa, 2014). When compared with populations of other mangrove species in a wider sampling area, the population of C. philippinensis is classified as the lowest (Djamaluddin, 2018; Pototan et al., 2021; Wahyuningsih et al., 2012). Several previous studies have also found a similar phenomenon where the population of C. philippinensis is known to be exclusive and limited to a narrow range of habitats (Djamaluddin, 2018; Djamaluddin & Djabar, 2022; Mukhlisi & Sidiyasa, 2014). Although all mangrove propagules have buoyant abilities, which allows seeds to float away by seawater (hydrocory) (Van der Stocken et al., 2019), C. philippinensis requires specific ecological compatibility to colonize new habitats.

C. philippinensis often inhabits a small area; its dominant habitat in Balikpapan Bay is restricted to 300 m along the mainland shore. Rhizophora apiculata, R. mucronata, Sonneratia alba, Avicennia alba, Lumnitzera littorea, Osbornia octodanta, Ceriops tagal, and Xylocarpus granatum are among the mangrove flora associated with this species. The mangrove forest formation in this location has C. philippinensis in the second layer, behind the R. apiculata, S. alba, and R. mucronata formations. Meanwhile, one individual of C. philippinensis found on Kowangan Island inhabits the shoreline. On Kowangan Island, mangrove vegetation is situated next to a mountainous terrestrial forest in a narrow configuration that is often sparse. Rhizophora apiculata, A. alba, Pongamia pinnata, Hibiscus tiliaceus, Lumnitzera littorea, and Osbornia octodonta are associated with mangrove species on Kowangan Island.

We did not specifically observe the endangered species, proboscis monkeys (Nasalis larvatus). However, based on information from the local people (Darman, personal communication, 20 March 2022), he has seen two groups of proboscis monkeys on Kowangan Island and one group in Pantai Lango. Our observations revealed primate bite scars on the leaves of C. philippinensis, although we do not have clear evidence of the identity of the species.

Proboscis monkeys are arboreal primates that rely heavily on the presence of the mangrove tree canopy. They often use large and tall trees as sleeping sites at the water’s edge.

The average diameter of C. philippinensis trees in Balikpapan Bay was similar to that in other locations (Primavera et al., 2004; Pototan et al., 2021). In Banaybanay, Philippines, Pototan et al. (2021) found that the average dbh (diameter of breast height) of C. philippinensis was 16.25 cm. It can naturally reach heights of 15 m and diameters of up to 50 cm (Primavera et al., 2004).

The threat of C. philippinensis populations in Balikpapan Bay is increasing, primarily due to anthropogenic activity. The population is localized in a narrow and extremely limited area; damaging its habitat increases the risk of local extinction ( Figure 5). Changes in the status of regions in the mangrove area of Balikpapan Bay and surrounding areas (e.g., the Indonesia’s New Capital City area (IKN)) would lead to alterations to the landscape and human population, which could pose a threat to its habitat. Current threats to C. philippinensis include the conversion of mangrove forests, environmental pollution, illegal logging, and the development of IKN.

Figure 5. Camptostemon philippinensis tree in the shoreline of Pantai Lango close to the community settlement.

Conserving C. philippinensis from extinction can be done with several efforts, such as prevention, species and habitat protection and preservation, habitat restoration, and ex-situ conservation. Prevention efforts can be carried out through education and outreach to various parties regarding the existence of C. philippinensis populations in the IKN area so that their habitat can be maintained. Protecting its natural habitat can be done by establishing a local protected area for the local community. Habitat restoration can be carried out by restoring degraded habitats and raising the number of individuals in their populations.

C. philippinensis in Indonesia has been listed as a protected plant under government law, and one of its natural habitats on Bunaken Islands has been designated as a conservation area and assigned as a national park. Unfortunately, no report on habitat restoration and ex-situ conservation efforts has been made until the present. Therefore, it is necessary to save genetic material from existing populations through seed storage and efforts to propagate both generatively and vegetatively, which can be used as a source of genetic material for habitat restoration or ex-situ conservation activities, as well as land rehabilitation. It is also necessary to study the genetic diversity of C. philippinensis in Indonesia, especially to determine conservation strategies, evaluate the success of restoration or reintroduction programs in other populations, and maintain genetic variation that will be important for the survival of this species.

Conclusions

This study recorded 527 individuals of C. philippinensis found in Pantai Lango Village. This population has a complete structure, including seedlings, saplings, and trees. The large number of seedlings shows that its natural regeneration potency is still significant. However, saplings face challenges in growing into the tree strata, possibly due to intense competition for growing space in the natural habitat, along with other environmental factors. This species is increasingly threatened, mostly due to human activity.