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Concrete Reefs

Short answer: 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.

VideoWrite-up5 sources
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What should you know about Concrete Reefs?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. U.S. reef plans judge materials on function, compatibility, durability and stability.

    DD-632-F01 · Write-up · Exhibit A (Rules for materials)

  2. Artificial reefs' benefits depend heavily on location and design.

    DD-632-F02 · Write-up · Exhibit D (Results vary)

Video transcript: Concrete Reefs: Reefs, Made of Concrete

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!

Burned-in captions, read frame by frame (see transcript.md) · 28.2s Reel ·

Video coming soonConcrete Reefs · Instagram Reel
Concrete Reefs: Reefs, Made of Concrete Instagram Reel · · 28.2s

The write-up

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

  1. Exhibit A

    Rules for materials

    The U.S. National Artificial Reef Plan judges materials on function, compatibility, durability and stability.

  2. Exhibit B

    Clean and cured

    Concrete is an accepted reef material if it's clean and well cured. Fresh concrete is strongly alkaline.

  3. Exhibit C

    Not cinder blocks

    Light hollow blocks can break, scatter or be buried in storms, so they're a poor choice on their own.

  4. Exhibit D

    Results vary

    A 2020 meta-analysis of 39 studies found artificial reefs can match natural reefs for fish, depending on place and design.

  5. Exhibit E

    Attract or produce?

    Scientists still debate whether artificial reefs produce new fish or mainly gather existing ones.

Questions people ask about Concrete Reefs

Which U.S. law led to the National Artificial Reef Plan?

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)

Why should reef concrete be well cured?

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

Why are hollow cinder blocks a poor reef material on their own?

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)

How many studies did the 2020 meta-analysis include?

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

What is the long-running debate about artificial reefs?

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

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. Which U.S. law led to the National Artificial Reef Plan?

    1. The National Fishing Enhancement Act
    2. The Clean Air Act
    3. The Endangered Species Act
    4. The Rivers and Harbors Act
    Show the answer

    Answer: A. The National Fishing Enhancement Act 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)

  2. Why should reef concrete be well cured?

    1. Fresh concrete is strongly alkaline
    2. Fresh concrete floats
    3. Cured concrete is softer
    4. It changes color
    Show the answer

    Answer: A. Fresh concrete is strongly alkaline 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

  3. Why are hollow cinder blocks a poor reef material on their own?

    1. They're light and break or scatter
    2. They dissolve in seawater
    3. They're poisonous
    4. They float
    Show the answer

    Answer: A. They're light and break or scatter 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)

  4. How many studies did the 2020 meta-analysis include?

    1. 39
    2. 3
    3. 390
    4. 3,900
    Show the answer

    Answer: A. 39 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

  5. What is the long-running debate about artificial reefs?

    1. Attraction versus production of fish
    2. Whether fish can see them
    3. Whether they're legal
    4. Whether they glow
    Show the answer

    Answer: A. Attraction versus production of fish 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

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/

Permalink: https://detailenjoyer.com/case/concrete-reefs/ · Last updated

Markdown version

Cite a single fact by its ID, for example DD-632-F01 → https://detailenjoyer.com/case/concrete-reefs/#DD-632-F01