Algae Species Richness and Percent Cover in Pa'ea Lagoon Fish Pond

Authors: Maya Rink, Taylor Byrd, Sarah-Rose Nicolson, and Jayden Kaptein
Survey Dates: July 31-August 1, 2024
Location: Pa’ea Lagoon, Tahiti Nui, French Polynesia

Algae Research of Pā’ea Fish Pond - French Polynesia Summer 2024

Authors: Maya Rink, Sarah Nicolson, Jadyn Kaptein, Taylor Byrd

Survey Dates: July 31 - August 1

Locations: Pa’ea Lagoon, Tahiti Nui, French Polynesia

INTRODUCTION

This survey studied the types of algae species inside of and on the rock walls of the Paea Lagoon Auai’a fish pond in Pā’ea, Tahiti, French Polynesia on August 1st, 2024. This type of fish pond was historically used by Polynesians to collect fish to eat within its walls (a rock barrier), however, the practice fell out after French colonization and large-scale fishing became more widespread.

The Paea Lagoon Auai’a fish pond is one of the original historical fish ponds, however it underwent restoration four years ago, and is now only used for scientific observation, not for harvesting fish.

The team has been hired by a private client to identify all of the types of algae observed in the fish pond and on all sides of the rock barrier. The barrier is a structure of large uneven rocks. Currently, the client knows there is some algae present in the fish pond, especially along the walls, but is uncertain of the species richness and percent cover of algae present.

This research is building upon previous Wildland Studies programs’ projects from August 2023 and May 2024 who also surveyed algae presence within the pond. This comparison will answer the given research question: how has the richness and percent cover of algae in the Paea Lagoon Auai’a fish pond changed over time since Summer 2023. The team will use the previously collected data to develop a trend analysis to address this question.

The research will differ from previous surveys as it will emphasize the development of a complete species list of algae present in the fish pond, where previous surveys have grouped their data by agal families.

Furthermore, the surveyors collaborated with another research team that is analyzing the substrate present in the same fish pond. Our teams will compare algae relationships with substrate cover.

METHODS

Fish Pond Survey
The team began by taking a preliminary survey of the area. Two swimmers measured the fish pond and scanned the area to gauge an understanding of the quantity and general types of algae that would be studied.

The 15.25m*15.25m fish pond was then divided into five transects. Three transects were used to study the fish pond’s rock barrier walls (Transect 1, 4, and 5). The other two were dedicated to the inner pond (Transect 2 and 3). Each cross-shore transect was spaced 5.1m apart. The transects were then split into five survey points which occurred every three meters. The quadrat method was utilized to conduct the survey. Starting at 0m, a 50*50cm quadrat was placed with its top right corner (when facing the ocean) on the survey point, with the first quadrat measuring the first 50cm of sand following the shore.

The same transect lines as the substrate research group type were used to obtain complementary data.

The method for the rock barrier and surrounding area was slightly altered to obtain more representative data of the algae cover. Two quadrats were used at each specified marker on the transect. One quadrat was used from the center of the rock barrier to the left side, and the other quadrat was used from the center of the rock barrier to the right side. The quadrat’s length was extended an extra 25 cm (making the total length 75 cm) to include the area surrounding the wall.

Start: 8/1/2024, 12:15pm, beaufort 2, 23°C, partly cloudy 30%, wind blowing from SE.
End: 8/1/2024 4:00pm, beaufort 4, 22°C, partly cloudy 40%, wind blowing from SE.

The four person team assigned two people to hold the transects and the other two to be swimmers, collecting the data using quadrats. The first observation of each species of algae was sampled and stored in a numbered plastic bag to be studied and identified after the survey. Ten bags of samples were collected, some of which were revealed to contain repeat species.

Beach Survey
From 2:50pm to 3:00pm, the team completed a terrestrial survey, sampling the 15.5m of beach adjacent to the fish pond to study the species richness of washed up algae. This survey was done opportunistically with all four team members collecting as many unique species of algae as possible.

Following the surveys, the team separated the samples to identify each species. A microscope was utilized to closely observe smaller species of algae. Identification was completed through the use of an algae identification book: Algae of French Polynesia (Payri et al., 2000).

RESULTS

see Figure 2. Species Index: https://docs.google.com/document/d/e/2PACX-1vT4dP08Q0ozwChf3HqfIb2_oDwA5l-xTakvLPqUiBLrflnHBzW9SEa3cL-wt3aEOrXBTR68FB-MOjuX/pub

see Data Set: https://docs.google.com/spreadsheets/d/1lgfq4BT0JQU3NYPJq31JUx_b4gDFCwIZgzQo0q153DM/edit?gid=0#gid=0

see Figure 4. Percent Coverage Comparison of Algal Species: https://docs.google.com/document/d/e/2PACX-1vT4dP08Q0ozwChf3HqfIb2_oDwA5l-xTakvLPqUiBLrflnHBzW9SEa3cL-wt3aEOrXBTR68FB-MOjuX/pub

INTERPRETATIONS

When examining the collected data from various transects, several key trends and observations emerged:

1. Species Distribution and Dominance:
   The accumulation of the data collected found 15 different species in total ranging between family rhodophyta, chlorophyta, and paethaedae. The survey found the dominant algal species in the fish pond to be Microdictyon umbilicatum, a type of microalgae or turf, representing 68.6% of all algal species.

When comparing algal presence across all transects, there is a clear increase in abundance along the walls as compared to the inner pond, represented by transect two and three. Here, the substrate consists of artificial rock. Turf algae, specifically Microdictyon umbilicatum, was the most prevalent species on these rocks. This suggests a positive correlation between the artificial rock substrate and the abundance of turf algae, indicating that substrate type significantly influences algae distribution.

When comparing algal presence on the inner and outer sides of the walls, percent cover is consistently higher on the inner sides of the wall. This could be alluded to several potential reasons including possible increased herbivory by adult fish on the outside of the pond or rougher condition on the outer walls preventing algae from growing. More research should be done to make a conclusion.

Algae coverage was compared with another research group focusing on substrate type using two of the same transects, 2 and 3. Both teams also collected data from the area surrounding the pond’s walls (transect 1, 4, and 5). The quadrats within the fish pond that exhibited the highest algae coverage primarily contained white fine sand and black fine sand.

Conversely, the data collected by the substrate group indicated that the primary substrate on the walls, where algae coverage was the most abundant, consisted of artificial rock, with some white and black fine sand present.

1. Comparison with Historical Data

In previous years, data was collected on the general algae coverage in the fish pond quadrats. During the Summer 2023 assessment, the algae coverage was found to be 28% with a standard deviation of 0.2614, with seven genuses observed. In Spring 2024, the average algae coverage dropped to 23.87% mean coverage with a standard deviation of 0.12572084, with five species observed. These previous studies examined quadrants both on the walls of the fish pond and within the pond itself. Our data from this year revealed a 27% algae coverage in the fish pond our standard deviation was 0.1144220727.

Our Summer 2024 findings identified a greater variety of algae types which originally totalled seven genuses. We identified 15 algae species, with 13 total genus, indicating potential yearly variations in algae diversity. However, more data should be collected over an extended period of time to make this conclusion.

DISCUSSION

Potential for Error
During the team's trials, several errors were encountered. Two transects broke, affecting the overall trial duration due to the additional time needed to replace them. Strong currents impacted the linearity of the transect lines.

Human error, including misidentification is also possible to have occurred. Additionally, issues with gear, such as leaking snorkels and masks, should be noted, potentially affecting species observation. It's important to highlight, also, that the identification book, Algae of French Polynesia, was published in 2000, meaning there could have been revisions to the taxonomy of the algae since its release.

In addition, some of the algae collected required a microscope for identification. It was not possible to use a microscope for every site in the field, so microalgae and germlings of macroalgae could have possibly been looked over.

For future studies, the team recommends using high-quality transects and gear capable of withstanding unexpected weather, given the cold and windy conditions encountered during the trials. Additionally, conducting more trials would make the data even more accurate.

Posted on August 3, 2024 10:06 PM by langzi