# Concrete Reefs (DD-632)

> Concrete is one of the most widely used artificial-reef materials, both as purpose-built reef modules and as recycled rubble such as old culverts, pipes and bridge pieces. In the U.S., the National Fishing Enhancement Act of 1984 led to a National Artificial Reef Plan, first adopted in 1985 and revised in 2007. It judges reef materials on function, compatibility with the environment, durability and stability. Concrete scores well on durability, but fisheries guidelines say it should be clean and well cured, because fresh concrete is strongly alkaline at first. Hollow cinder blocks, like those dumped from a barge in the footage, are generally considered a poor choice on their own. They are light and break easily, and storms can scatter or bury them. Once sunk, hard surfaces are colonized by algae, sponges, barnacles and, in warm waters, sometimes corals, and fish gather around them. A 2020 meta-analysis of 39 studies found that artificial reefs can support fish communities comparable to natural reefs, but results depend heavily on location and design. Scientists still debate how much artificial reefs produce new fish and how much they simply attract fish from elsewhere, which can make them easier to catch.

- Department: Nature (also Tech)
- First published: 2025-08-06
- Last updated: 2025-08-06
- Permalink: https://detailenjoyer.com/case/concrete-reefs/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## On the timeline

- **1984**: The U.S. National Fishing Enhancement Act calls for a national artificial reef plan
- **1985**: The first National Artificial Reef Plan is adopted
- **2007**: The National Artificial Reef Plan is revised

Full timeline: https://detailenjoyer.com/timeline/?case=concrete-reefs

## Quick facts

- **DD-632-F01**: U.S. reef plans judge materials on function, compatibility, durability and stability. _(Write-up · Exhibit A (Rules for materials))_
- **DD-632-F02**: Artificial reefs' benefits depend heavily on location and design. _(Write-up · Exhibit D (Results vary))_

## Write-up

Reefs, made of concrete. Sunken concrete gives sea life something to grow on.

1. **Rules for materials**: The U.S. National Artificial Reef Plan judges materials on function, compatibility, durability and stability.
2. **Clean and cured**: Concrete is an accepted reef material if it's clean and well cured. Fresh concrete is strongly alkaline.
3. **Not cinder blocks**: Light hollow blocks can break, scatter or be buried in storms, so they're a poor choice on their own.
4. **Results vary**: A 2020 meta-analysis of 39 studies found artificial reefs can match natural reefs for fish, depending on place and design.
5. **Attract or produce?**: Scientists still debate whether artificial reefs produce new fish or mainly gather existing ones.

## Related case files

- [Battling Barnacles (DD-705)](https://detailenjoyer.com/case/battling-barnacles/): Another case about marine life growing on hard surfaces
- [Offshore Oil (DD-033)](https://detailenjoyer.com/case/offshore-oil/): More big structures on the seafloor
- [Visit This Tropical Paradise (DD-200)](https://detailenjoyer.com/case/visit-this-tropical-paradise/): I linked more about reefs
- [Let's Mix It Up (DD-240)](https://detailenjoyer.com/case/lets-mix-it-up/): I linked concrete put to work underwater
- [Amazing Underwater Forests (DD-291)](https://detailenjoyer.com/case/amazing-underwater-forests/): I paired it with another underwater habitat
- [Food Recycling (DD-569)](https://detailenjoyer.com/case/food-recycling/): Another case about giving waste a second use
- [Sandy Scaridae (DD-591)](https://detailenjoyer.com/case/sandy-scaridae/): I paired it with reefs people build on purpose

## Reel vs. record

- **Note**: 'Chemically inert': well-cured concrete is fairly stable in seawater, but fresh concrete is strongly alkaline, so guidelines call for clean, cured material.
- **Note**: 'Concrete blocks' in the footage are hollow cinder blocks. Reef guidelines generally treat these as a poor material on their own, because they're light, break easily and can scatter or be buried in storms.
- **Note**: 'Mimics the complexity of natural reefs': that depends on design. Loose blocks and purpose-built reef modules can perform very differently.
- **Note**: 'Restore damaged ecosystems': artificial reefs add hard habitat, but they don't replace lost natural reefs, and results vary by location and design.
- **Note**: 'Support fisheries': whether artificial reefs produce new fish or mainly attract existing ones is still debated. Gathering fish together can also make them easier to overfish.

## Video: Concrete Reefs: Reefs, Made of Concrete

- Duration: 28.2 s · Published: 2025-08-06
- File: https://detailenjoyer.com/assets/videos/DNCAtJDSAmL.mp4

### Transcript

DID YOU KNOW? Concrete blocks are commonly used as artificial reefs because they provide a durable, stable, and chemically inert structure that mimics the complexity of natural reef habitats. When placed on the seafloor, these blocks offer shelter and attachment surfaces for marine life like corals, sponges, and algae, which in turn attract fish and other organisms seeking food and protection. Over time, these artificial reefs enhance local biodiversity, restore damaged ecosystems, and support fisheries by creating new underwater habitats. NOW YOU KNOW!

## Questions & answers

**Q: Which U.S. law led to the National Artificial Reef Plan?**  
A: Passed in 1984. _(Source: Write-up · Exhibit A (Rules for materials) · Federal Register (Mar 28, 2007): National Artificial Reef Plan (as Amended); ASMFC/GSMFC: Guidelines for Marine Artificial Reef Materials, Second Edition (2004))_

**Q: Why should reef concrete be well cured?**  
A: Guidelines call for clean, cured material. _(Source: Write-up · Exhibit B (Clean and cured) · ASMFC/GSMFC: Guidelines for Marine Artificial Reef Materials, Second Edition (2004); Australian Government (2023): National artificial reef guidelines, Version 1.0)_

**Q: Why are hollow cinder blocks a poor reef material on their own?**  
A: Storms can move or bury them. _(Source: Write-up · Exhibit C (Not cinder blocks) · ASMFC/GSMFC: Guidelines for Marine Artificial Reef Materials, Second Edition (2004))_

**Q: How many studies did the 2020 meta-analysis include?**  
A: 39 studies. _(Source: Write-up · Exhibit D (Results vary) · Paxton et al. (2020): Meta-analysis reveals artificial reefs can be effective tools for fish community enhancement but are not one-size-fits-all, Frontiers in Marine Science)_

**Q: What is the long-running debate about artificial reefs?**  
A: Do they make new fish or gather existing ones? _(Source: Write-up · Exhibit E (Attract or produce?) · Powers et al. (2003): Estimating enhancement of fish production by offshore artificial reefs, Marine Ecology Progress Series 264)_

## Sources

- [Federal Register (Mar 28, 2007): National Artificial Reef Plan (as Amended)](https://www.federalregister.gov/documents/2007/03/28/E7-5711/national-artificial-reef-plan-as-amended-guidelines-for-siting-construction-development-and)
- [ASMFC/GSMFC: Guidelines for Marine Artificial Reef Materials, Second Edition (2004)](https://www.gsmfc.org/pubs/SFRP/Guidelines_for_Marine_Artificial_Reef_Materials_January_2004.pdf)
- [Paxton et al. (2020): Meta-analysis reveals artificial reefs can be effective tools for fish community enhancement but are not one-size-fits-all, Frontiers in Marine Science](https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2020.00282/full)
- [Powers et al. (2003): Estimating enhancement of fish production by offshore artificial reefs, Marine Ecology Progress Series 264](https://doi.org/10.3354/meps264265)
- [Australian Government (2023): National artificial reef guidelines, Version 1.0](https://www.dcceew.gov.au/sites/default/files/documents/national-artificial-reef-guidelines-version-1-2023.pdf)

## Cite this case file

Easterling, Marcus. "Concrete Reefs." The Detail Department (DetailEnjoyer), case file DD-632, last updated Aug 6, 2025. https://detailenjoyer.com/case/concrete-reefs/