Alexandra Kler Lago
Field Support and Partnerships Manager, MERMAID
Reef monitoring just became more complete. Teams can now collect, manage, visualize, and analyze macroinvertebrate belt survey data across MERMAID’s connected tools: Collect, Explore, and the R package mermaidr.
Small animals, important insights
Macroinvertebrates—including sea cucumbers, sea urchins, giant clams, lobsters, crown-of-thorns starfish, and other conspicuous invertebrates—play essential roles in coral reef ecosystems. They contribute to grazing, nutrient cycling, sediment turnover, and other processes that influence reef condition and resilience. Many species are also culturally and economically important to coastal communities.
Changes in their abundance and distribution can provide valuable information about fishing pressure, management effectiveness, ecosystem function, and environmental change. By combining macroinvertebrate observations with fish and benthic data, monitoring programs can build a more complete picture of reef health and track changes over time.
How the macroinvertebrate belt method works
During a macroinvertebrate belt survey, an observer records individuals found within a defined belt along a transect. The transect length and total belt width define the surveyed area, allowing counts to be converted into comparable density estimates.
For each observation, surveyors record the taxon or group, number of individuals, and—when included in the monitoring protocol—estimated size. The type of size measurement may vary by organism; for example, total body length for a sea cucumber or shell length for a giant clam.
Programs can continue following their established field protocols, including their preferred transect dimensions, search approach, target taxa, size measurements, and number of replicates. MERMAID standardizes how the resulting observations and survey effort are recorded, validated, and analyzed.
From field observations to reef health metrics
Raw counts can be difficult to compare when survey areas differ. MERMAID uses transect length and total belt width to calculate the surveyed area and convert abundance into density per hectare.
As data are entered, MERMAID automatically calculates:
Total abundance for each transect
Total macroinvertebrate density in individuals per hectare
Density by groups of interest, such as sea cucumbers, sea urchins, giant clams, lobsters, crown-of-thorns starfish, and corallivorous snails
These summaries update in real time—even when working offline—providing immediate feedback that can support data validation and quality control.
Collect and manage data in MERMAID
In MERMAID Collect, users can collect macroinvertebrate data by adding a new macroinvertebrate belt sample units to their projects and record the survey location, date, management regime, transect dimensions, observers, environmental conditions, and field observations.
Macroinvertebrates can be recorded at species, genus, or family level, depending on the precision of the field identification. Users can also record observations using supported groups of interest.
MERMAID’s taxonomic reference is based on the World Register of Marine Species (WoRMS), helping teams use consistent and accepted taxonomic names. If a species is not yet available, users can propose it for review from within MERMAID Collect.
Sample units can be saved, checked using MERMAID’s validation workflow, and submitted when complete. Detailed instructions are available in the macroinvertebrate documentation.
Visualize density results in MERMAID Explore
Submitted macroinvertebrate data can be viewed in MERMAID Explore, MERMAID’s interactive platform for discovering and visualizing reef monitoring information.
Users can filter results by project, organization, country, date, macroinvertebrate belt method, and data-sharing policy. The interactive map, metrics, and charts respond to the selected filters, making it easier to explore patterns across sites and monitoring periods and to consider macroinvertebrate results alongside fish and benthic data.
Programs can open Explore directly from their project in MERMAID Collect. Publicly shared data can be discovered by anyone, while logged-in project members can access the detailed data available to them. Filtered datasets can also be exported for further use.
Visit the MERMAID Explore documentation to learn how to navigate, filter, visualize, share, and export data.
Access macroinvertebrate data in R
For reproducible analyses, custom visualizations, statistical models, and reporting workflows, submitted macroinvertebrate data can be accessed directly in R through the R package mermaidr.
The package provides macroinvertebrate data at three complementary levels:
Observations: Taxonomic records with class, order, family, genus, group of interest, size, count, and calculated density
Sample units: Transect-level total abundance and density, including density by group of interest
Sample events: Site-and-date summaries, including average total density, average density by group of interest, and associated standard deviations
Users can select method = "macroinvertebrate" when retrieving project data with mermaid_get_project_data(). This structure makes it possible to move from taxon-level analyses to comparisons among transects, sites, and monitoring periods in a reproducible R workflow.
Installation, authentication, and data-access examples are available in the mermaidr documentation.
Give historical data a new life
The new method is not only for future surveys. Many programs hold years—or even decades—of valuable macroinvertebrate observations in spreadsheets and other legacy formats.
Bringing these records into MERMAID can help:
Preserve long-term datasets in a centralized system
Standardize taxonomic names
Document survey effort and metadata consistently
Calculate comparable density metrics
Connect macroinvertebrate records with fish and benthic monitoring
Make data easier to visualize, analyze, share, and use in reporting
The MERMAID team can help programs review, prepare, and ingest historical macroinvertebrate datasets. We also offer training and guidance for teams beginning to use the method.
Help us spread the word
We encourage the MERMAID community to share this release with partners who currently collect—or have previously collected—macroinvertebrate belt survey data. Adding both historical and newly collected observations to MERMAID can strengthen collaboration, protect valuable monitoring records, and expand our shared understanding of coral reef ecosystems.
Ready to get started? Visit MERMAID Collect to add macroinvertebrate belt surveys to your projects.
For training, support with historical data, or more information, contact the MERMAID team at contact@datamermaid.org.