The "barnacle strategy" involves leveraging the marketing efforts of a larger, well-established entity (the "whale") to grow your own business without incurring heavy marketing costs. Andrew Wilkinson explains that by attaching your business to a larger platform, like he did with Shopify, you can benefit from the traffic and growth of that platform, allowing you to generate revenue with minimal marketing expenditure. This strategy can be applied to various software ecosystems that aren't overly saturated, such as Discord or Adipar 1 2.