Ethnobotany is the study of traditional knowledge on plant use. Seaweeds have had long and strong associations with humans. Indigenous people have inherited rich traditional knowledge, which contains a valuable history of culture and practices (Balick and Cox 1997). Human gathering of seaweeds has been practiced by many coastal communities worldwide. Testaments reflect on the broad-spectrum role of seaweeds on key human histories (Khalilieh and Boulos 2006, Erlandson et al. 2007, Dillehay et al. 2008, Pérez-Lloréns et al. 2020, Mouritsen et al. 2021). Concern, however, has repeatedly been expressed about the rapid loss of seaweed traditional knowledge due to neglect or lack of transmission (Turner 2016, Thurstan et al. 2018). Ethnobotanical studies, therefore, serve to record folk seaweed knowledge before its oblivion from the local communities and the scientific purview.

Sorsogon is the southeasternmost province on Luzon Island in the Philippines (Fig. 1). As the province is surrounded by marine waters, locals in Sorsogon largely depend on the sea for their source of food and income. A wide range of marine resources are abundant in the province (Trono 1992, Guanio 1993, Olaño et al. 2009, Nieves et al. 2013, Amano and Mojados 2018). Seaweeds, collectively referred to locally as ‘gulaman’, are one of the highly sought-after autochthonous marine resources in eastern Sorsogon (Llana 1992, 1994, Nyan 1993, Kraft et al. 1999). While this area is long recognized as home to rich seaweed diversities (Trono 1975, 1976, Kraft et al. 1999, Dumilag et al. 2020), seaweed ethnobotanical knowledge among the locals of eastern Sorsogon has received disproportionate attention. Despite the economic shift in Sorsogon from gleaning to farming seaweeds beginning in the early 1990s (Salayao et al. 1991) until the present (Andriesse and Lee 2021), seaweeds are still gathered today for a variety of purposes such as food and medicinal resources. No study has yet to compile information on seaweeds that have been exploited, and the diversity of applications to which the locals in eastern Sorsogon have put them. Here, we examine the selection and use of seaweeds, and the status of knowledge transmission among the local communities in eastern Sorsogon.

Knowledge was amassed concerning the seaweed selection and use among local inhabitants collectively referred to as the Bulusanon and Busaiganon from Bulusan (12°45′08″ N, 124°08′08″ E) and Sta. Magdalena (12°38′56″ N, 124°06′30″ E), respectively (see map in Fig. 1). Six sites were surveyed in Bulusan namely Dancalan, Dap-Dap, Mabuhay, Sabang, San Antonio and San Vicente (Buhang) while five sites for Sta. Magdalena, including Brgy 1 (San Francisco), Brgy 2 (Mother of Perpetual), Brgy 3 (Del Rosario), San Eugenio (Alig-igan), and San Rafael (Bil-og). Permits to conduct the study were given by various personnel from the local government units of Bulusan and Sta. Magdalena. A separate consent was given by each participant conveying their acceptance verbally after an interviewer clearly explained the goal of the study. Responses were obtained from participants using a combination of questionnaire survey (Supplementary Fig. S1) and semi-structured interviews. The survey form was originally written in English and later translated in Sorsoganon language comprising questions that collect information about demographic profile (age, sex, years of residency, educational attainment, and current or most recent occupation), local names of seaweeds, mode of food or therapeutic preparation, and history of knowledge transfer. Seaweed species cited during interviews were collected and verified by the interviewees. Voucher specimens were prepared and deposited at the Herbarium Sorsogonense (HS). The overall methodology including seaweed collection and species identification have been explained in Dumilag and Javier (2022). Ethnobotanical indices were measured. The frequency of citation per species was expressed as the sum of informants that cite the use for the species while proportion weight value of each species relative to all other taxa represented by the relative frequency citation or the RFC (Phillips et al. 1994). Calculation of use value (UV) and fidelity level (FL) followed that of Dumilag and Javier (2022). Each response was initially written in printed forms and later transcribed via Google Form. Responses were populated in Microsoft Excel ver. 10.60 and were analysed using Wizard Pro data analysis version 1.9.49 (Evan Miller, Chicago, IL, USA) for descriptive statistics in the form of frequencies and percentages. Knowledge transmissions (KT) were inferred based on the origin and to whom the knowledge was passed onto. To see the association of the number of seaweed selection and age, Pearson Correlation Coefficient analysis was computed. The flow of KT was presented in Sankey plots using SankeyMATIC (http://sankeymatic.com/build/) and were expressed in terms of weighted connections of knowledge transfer among the origin of knowledge, the respondents, and to whom the respondents passed the knowledge onto.

Mounting evidence has shown those seaweeds in eastern Sorsogon are abundant and diverse, yet those that are regarded as ethnotaxa are not documented. Currently, there are about 250 seaweed species recorded for the area (Trono 1975, 1976, Kraft et al. 1999, Dumilag et al. 2020). In this study, only 12 species were identified to have ethnobotanical values. Many seaweeds with various known uses (see Pereira 2016) are also found in eastern Sorsogon however not used by the locals there. Comparative counts indicated that seaweed ethnotaxa represented only about 5% as compared with that of the current estimate of the entire roster of seaweed species reported for the area. This finding indicated that only a few seaweed species are currently tapped by the locals from among the otherwise greater number of available species. The low seaweed ethnotaxa reported in this study cannot be ascertained, although factors on taste preference and degree of perceived usefulness among the locals cannot be ruled out. We found that local seaweed selection in eastern Sorsogon was limited to rhodophytes yielding either carrageenans (Betaphycus gelatinus, Kappaphycopsis cottonii) or agars (Acanthophora spicifera, Gelidiella acerosa, Gracilaria spp., Ohelopapa flexilis) and to edible siphonous algae (Caulerpa spp., Codium cf. edule). A clear congruity in traditional and scientific knowledge classification of seaweeds was generally not found. It is surprising that despite a long list of edible or medicinal seaweeds known in the Philippines (Pereira 2016, Dumilag and Javier 2022), no phaeophytes were utilized by the locals in eastern Sorsogon. The local term ‘Kulapu’ is a collective term for the Sorsoganon Fucales. These include several species of Sargassum, Turbinaria, and Hormophysa that are used as fodder. In one instance, ‘Kulapu’ were seen utilized as a cover protecting seaweed harvest during boat transport (Fig. 3A). Future studies on ethnobotany emphasizing the use of fucoids as fodder in eastern Sorsogon is desired. Knowledge on seaweed selection intersected among sites in eastern Sorsogon. C. chemnitzia (‘Lato’) and Gelidiella acerosa (‘Gulaman indudulsi’) appeared to be the most commonly used seaweeds in the area (with high RFC and UV). The popularity of C. chemnitzia and G. acerosa is driven by a number of factors including, but not limited to, a strong drive towards maintaining local food systems, and sourcing resources for a livelihood. Gelidiella acerosa has been historically a valuable seaweed export (Kraft et al. 1999) and its use in jellies (dulsi) is found today in Sorsoganon kitchens. The use of C. chemnitzia in restaurant settings outside the collecting area was also observed. It is said that if the origin of C. chemnitzia is from eastern Sorsogon, its taste quality is better as compared from those collected elsewhere in Sorsogon. This so called “regional image” creates unique identity of the seaweeds collected from eastern Sorsogon. Kraft et al. (1999) also alluded similar notion for eastern Sorsogon’s Betaphycus gelatinus (as Betaphycus philippinensis) as the only source of ‘highly prized’ beta-carrageenan in the Philippines.

Caulerpa racemosa was the least cited seaweed species among the locals. The local name of C. racemosa is ‘Bulagsong’, which means fake. This etymological cue points to seaweed preference to the morphologically similar-looking but “real edible” C. chemnitza. Many of our respondents knew that C. racemosa can be eaten but they prefer to collect and eat C. chemnitza. C. chemnitzia was said to be less briny and comes in bite-sized pieces, and so easier to chew. One of our respondents also claimed that C. racemosa can be poisonous (nakahudong). First isolated from a Philippine Caulerpa by Aguilar-Santos and Doty (1968), the toxin caulerpin has shown no acute significant toxicity in mice (Vidal et al. 1984). Only in rare cases C. racemosa may contain pathogenic bacteria that may cause foodborne disease (Kartika et al. 2021). However consumption of C. racemosa has proven safe and can provide multiple benefits to health (Nagappan and Vairappan 2014).

The use of one species, Codium cf. edule (‘Abalang’), was limited to San Vicente in Bulusan yet its use is reported from all sites in Sta. Magdalena. As San Vicente is the nearest town of Bulusan to Sta. Magdalena (see Fig. 1). It appeared that knowledge on the local use of Codium cf. edule was more widespread among Busaiganon than to those of Bulusanon. Codium edule is regarded as an edible seaweed in Japan, Hawaii, and the Philippines (Abbott 1978, 1984, Arasaki and Arasaki 1983, Agngarayngay et al. 2005). Besides being edible, the Philippine C. edule has anti-cancer properties (Bayro et al. 2019, Vasquez et al. 2019). Including C. edule, six other Codium species were reported from eastern Sorsogon (Dumilag et al. 2020). Codium materials from eastern Sorsogon may also be tested to diversify seaweed species selection for drug discoveries.

Only three species were identified as having perceived medical value. Chondria armata and Digenea simplex were used as vermifuge while C. chemnitzia as a treatment for goiter. These species consistently had folk claims from elsewhere (Tseng 1935, Tungpalan 1983, Phang 1987, Anggadiredja 2009, Dumilag and Javier 2022) and were also tested scientifically (Kreitmair 1925, Mori et al. 2018, Tapotubun et al. 2020). Chondria armata contains domoic acid while kainic acid can be found in D. simplex. These compounds are classified as neurotoxin responsible for their anti-helminthic property (Higa and Kuniyoshi 2000). Care should be considered when taking these substances as these are known to be lethal in certain dosages (Wright et al. 1989, Perl et al. 1990). Most of the respondents indicated that the decoction of the alga was still a choice drug, especially when caught short of finances or if commercial medicine is unavailable. Information dissemination would particularly benefit the public on the proper use of these seaweed resources to avoid uncalled-for incidents.

We initially hypothesized that age was a factor in knowledge accumulation, however we found that seaweed knowledge in eastern Sorsogon appeared to be homogenous across all ages. Female relatives (mothers and grandmothers) were the predominant providers of seaweed knowledge while children were favored as the largest beneficiaries. Our finding are consistent with previous studies (Voeks 2007, Teixidor-Toneu et al. 2021). Although seaweed knowledge was conserved and transmitted vertically through family dissemination within families, still, a significant portion of the population withheld what they knew. The adaptive function of culture is said to be dependent on strong knowledge transmission (Berkes et al. 2000). Dissolution of knowledge transmission therefore thwarts the capacity of the locals to entrench preservation of culture at large. What is now needed is a broader promotion of traditional knowledge, to study the information it offers, and to incorporate science-driven data to traditional knowledge. All these efforts aid in collectively crafting appropriate resource management recommendation.