Use of Seaweed for Teaching Taxonomy with Everyday Language in High School Biology
2026 年 18 巻 p. 2-9
詳細
2026 年 18 巻 p. 2-9
This paper proposes a teaching strategy to provide high school students with an engaging biology exercise (seaweed taxonomy) in the field using simple and inexpensive tools to revive field-based education, shift teaching methods to active learning, and overcome the limitations of a typical Philippine public high school laboratory. In the course of our reconnaissance, we were able to identify a coastal area with high seaweed diversity just fifteen minutes away from our school. In our proposed exercises, high school students will be able to identify actual seaweeds in the field using freely downloadable pictorial guides. They will also be able to perform other basic, taxonomic tasks such as taking field photographs and notes, creating a character matrix, and constructing a dichotomous key. Finally, we gave suggestions on how to link field biology teaching with other disciplines such as chemistry and physics for a more integrated science learning.
The biodiversity and ecological crises that we are currently facing can be partly attributed to a decline in human interactions with nature (Soga and Gaston, 2022). Similarly, in education, field-based activities have declined through the decades (Soga and Gaston, 2024). Recently, the Philippine Science High School System (PSHSS), widely acknowledged as the premier high school of the country, has been pushing for a radical change in instruction. Specifically, teachers have been instructed to move away from traditional, lecture-heavy instruction, and hypothetical-, paper-based exercises, and move towards active learning, project-based learning (PBL), and authentic assessments. Until recently, the biology specialization track in our campus had fewer enrollees compared to chemistry and physics because of how the subject was taught, which was mostly the memorization of a collection of facts. Taxonomy and associated skills such as identification and the construction of taxonomic keys were taught through lectures using either textbook examples or, to make the lesson slightly more engaging, fictional organisms such as extra-terrestrial aliens (M. Uy, pers. obs.). While these skills are pre-requisites for higher science education and student research, they are also critical to broader societal goals, including biodiversity conservation, agricultural transformation, and shift towards a bioeconomy (Hackel et al., 2025).
As is the case of field experience, taxonomic education and expertise in the Philippines are fading in secondary schools and universities. Philippine public schools such as ours face limitations in laboratory equipment and facilities—challenges that have been exacerbated in recent years by funding cuts. In our campus, taxonomy and natural history are not only unpopular in Biology, but also unpopular research fields. Most student research projects focus on the applied sciences, particularly natural product chemistry and material science. To address these issues, selected teachers from the Biology Unit of our campus have been actively working over the past few years in implementing authentic student-centered learning, diversifying teaching strategies and research topics through the exploration of nearby ecosystems and utilizing them as natural laboratories.
For Philippine rural schools close to the seashore, we propose field-based teaching and the use of abundant, diverse intertidal organisms such as seaweeds as teaching materials for taxonomy instead of the more readily available land plants since students are more engaged if the learning experience is fun and not ordinary, such as a fieldtrip to the sea (Boxall, 2016). Further, terrestrial plant taxonomy is heavy in unavoidable technical terminology, which increases the burden on students' memory and comprehension and makes learning more complicated. However, unlike terrestrial plants, most seaweeds are undifferentiated in morphology in that their thalli are not divided into discrete subparts. Hence, the use of simple, everyday English instead of technical terms to describe seaweeds will suffice for this field taxonomy exercise. The use of plain English has been proven to be effective in teaching more complex biology lessons such as photosynthesis (Brown and Ryoo, 2008) and microbial physiology (Schoerning, 2013).
Argao is a first-class municipality in Cebu province with an area of 191.50 km2 and about 78,000 residents (Philippine Statistics Authority, 2020). It is one of Cebu’s oldest towns and is known for its rich natural resources and key biodiversity areas such as the Mt. Lantoy Key Biodiversity Area and the Casay Marine Sanctuary (Mecha et al., 2022, Rios, 2022). The shoreline of Tulic in Argao is adjacent to a national highway, the Natalio Bacalso Avenue, lined by sparse residential and business establishments. Our observations indicate that activities of the coastal community include small-scale fishing and gathering mollusks for home consumption. To determine the suitability of the Tulic shoreline for teaching taxonomy, we surveyed intertidal seaweeds over a three-year period from 2023 to 2025 in the form of opportunistic walks. The surveys were carried out at low tide in January of the aforementioned years, when most of the seaweeds were either exposed to air or submerged in shallow water less than one meter deep. Photographs of some seaweeds commonly found in the site are shown in Figure 1.
The morphological diversity of some Tulic seaweeds. A. Padina sp. B. Beached Sargassum sp. C. Halicoryne sp., and D. various other seaweed taxa.
Our three-year data shown in Figures 2 and 3 present the abundance and diversity of seaweeds in Tulic. A total of ten genera can be found in the Tulic littoral zone: Rhodophyta: Amphiroa J.V. Lamouroux, Phaeophyta: Dictyota J.V. Lamouroux, Hormophysa Kützing, Hydroclathrus Bory de Saint-Vincent, Padina Adans., Sargassum C. Agardh, Chlorophyta: Bornetella Munier-Chalmas, Codium Stackhouse, Halicoryne Harvey, Halimeda J.V. Lamouroux. Beached remains of Sargassum were also commonly found in the area. Among the three major seaweed groups, the Phaeophyta was the most abundant during the survey period (Fig. 3).
Generic diversity and relative abundance of seaweeds in Tulic, Argao, Cebu. Each slice of the pie chart corresponds to the number of individuals observed for a given genus.
Representation of the three major seaweed groups in Tulic, Argao, Cebu. The area of each slice represents the number of genera observed for a given group.
For a collaborative exercise, the students can be divided into pairs or teams. They may use the freely downloadable pictorial identification guide of Hurtado-Ponce et al. (1992), which is available from the Southeast Asian Fisheries Development Center (SEAFDEC) website. Seaweeds can only be identified at the genus level in the field since the SEAFDEC guide is in black and white, making species identification difficult. In our case, we used hard copies of the second edition of the same title (Hurtado-Ponce et al., 2006) because that version is in color. Each copy costs only 5 U.S. dollars or less than 300 Philippine pesos; more affordable than most science references sold in the country. Alternatively, the black and white SEAFDEC reference can still be used effectively, but in conjunction with the freely downloadable, colored, photographic guides Seaweeds of Mu Ko Thalae Thai (SE Thailand) by Coppejans et al. (2010) and Seaweeds of Hawaii: A Photographic Identification Guide by Magruder and Hunt (1979). The seaweed genera in those two foreign references overlap with the genera in Hurtado-Ponce et al. (2006), and the use of either will result in identical taxonomic determinations. The students are asked to take seaweed photographs using either their smartphones or the school’s digital camera. They are also asked to note field data on the distinctive features of the seaweeds using simple, everyday English, e.g., “fan-shaped” for Padina spp., “net-like” for Hydroclathrus spp., “plant-like” for Sargassum spp., “cylindrical branches” for Amphiroa spp., “chains of plates” for Halimeda spp., “strap-shaped” for Dictyota spp., and “convoluted masses” for Codium spp. Upon returning to campus, based on their field notes and photographs, the students are asked to construct a table of characteristics (character matrix) which serves as a precursor to constructing a dichotomous key (see Appendix). The teaching of technical terms in phycology and other biological aspects of seaweeds can come after the completion of this exercise.
We found the Tulic intertidal zone to be ideal for experiential learning for the following reasons: First, the seaweeds in Tulic exhibit morphological and taxonomic diversity, making them suitable for a simple morphological and taxonomic exercise. Second, there is a high similarity of seaweed flora, at least at the genus level, between Tulic and the focal site of SEAFDEC’s pictorial guide, Panay, facilitating identification. A major hurdle in practicing land plant taxonomy in the Philippines is the lack of resources on national or even regional flora, making teaching even more difficult.
The student exercises we propose will be able to cover multiple skills, such as taking field notes and photographs, identifying and classifying seaweeds, evaluating references’ utility, creating a character matrix, and constructing identification keys. These exercises can enhance student cognitive levels, such as remembering, understanding, evaluating, and creating, through higher order thinking (Table 1).
| Cognitive Domain Level | Exercises / Skills | Tool/s used |
|---|---|---|
| Remember* | · Identifying seaweeds at the genus level based on their most striking morphological features. | Pictorial identification guide |
| Understand* | · Grouping seaweeds by similarity during the key construction process. | Field notes, field photographs |
| Apply*** | · Applying basic physics lessons, e.g., drag, elasticity, flexibility. | Onsite studies |
| Analyze** | · Inferring the adaptive advantage or predict the function of the morphological features in relation to wave action. | Onsite studies, field notes, field photographs |
| Evaluate* |
· Assessing the utility of the pictorial identification guide. · Testing the utility of student-made dichotomous keys. · Comparing the utility of a professionally-made identification guide and a student-made guide. |
Pictorial identification guide, student-made keys |
| Create*/**/**** |
· Preparing a character matrix using layman’s terms only. · Constructing a dichotomous key using layman’s terms only. · Formulating mini projects to determine the chemistry and biological activities of substances contained seaweeds, as informed by field observations (i.e., seaweeds are sessile, photosynthetic organisms that need chemical tools for defense and food manufacture) |
Field notes and photographs, or onsite studies, pictorial identification guide |
*Suggested activity for simple morphological and taxonomic work
**Suggested activity for evolution or ecology classes
***Suggested activity for physics classes
****Suggested activity for chemistry classes
Based on our observations, many students in our school fail to understand the connection between and among the scientific disciplines—that biology, chemistry, and physics exist independently, and that pursuing a particular track during their specialization years means abandoning the other two completely. To connect biology with physics, an onsite study of seaweed morphology in relation to their responses to wave action could be incorporated by physics teachers in their classes to tackle simple topics related to drag, elasticity, and flexibility. Using a small amount of seaweed tissue (0.1 – 2 grams) and common, inexpensive laboratory materials, students could link seaweed biology with chemistry through bench studies on photosynthetic pigments (Katayama et al., 2003) and secondary metabolites (Rupapara et al., 2015).
From a long-term standpoint, exposing high school students to fieldwork could also influence their college and career choices (Scott et al., 2012), contributing to the scientific manpower of the country.
We are grateful to the local government unit of barangay Tulic in Argao, Cebu for allowing us to conduct our class activities in their barangay and to the biology majors of PSHS-CVisC for their genuine enthusiasm in our classes.
Name_______________________________________ Date Performed ________________
EXERCISE NO. 1
Field Taxonomy and Dichotomous Keys
MATERIALS
Clear, white plastic folder as a modified slate board, for note-taking
Pencil, for note-taking
Smartphone, for field photography
Laminated taxonomic reference (Hurtado et al., 1992), for field identification
PROCEDURE
A. Field instructions
1) Familiarize yourselves with local seaweed diversity using the pictorial guide “Seaweeds of Panay” by Hurtado et al. (1992) the day before our fieldwork.
2) Using the abovementioned reference, spot-identify all the seaweeds that you will see during our seashore walk. Genus-level identification will suffice.
3) Take pictures of the seaweeds using your smartphone.
B. Lab instructions
Sample Character Matrix
| Seaweed | Overall Form | Color |
|---|---|---|
| Padina sp. | Ear-shaped | Brown |
| Dictyota sp. | Strap-shaped | Brown |
| Hypnea sp. | Bare branches | Red |
| Acetabularia sp. | Umbrella-like | Green |
Sample Dichotomous Key
1) Seaweed brown ………………………………………2
1) Seaweed color other than brown ………………………………………3
2) Seaweed parts ear-shaped ……………………………………… Padina sp.
2) Seaweed strap-shaped ……………………………………… Dictyota sp.
3) Seaweed looks like bare plant branches ……………………………………… Hypnea sp.
3) Seaweed umbrella-like ……………………………………… Acetabularia sp.
