Mark Spalding and colleagues have recently released a study assessing the state of the world's marine protected areas.  Although uptake has increased over the last decade, and we might actually be on track for reaching 10% ocean protection by 2020 (the goal was originally by 2012... we missed that by a long way), the authors note all is not quite what it seems.  Paper highlights (taken from this paper review, plus an addition from me) are as follows:

A small number of large MPAs are responsible for much of the global growth. The 20 largest MPAs account for 60% of the entire global MPA coverage, with an increasing trend to cover remote and off shore areas.  By contrast, in terms of numbers, the majority of MPAs are small and are found in coastal and near-shore waters. Even with these there is a focus on sparsely populated areas. The average MPA is small and most are not effectively managed.

MPA coverage is highly variable — while 28 countries have now exceeded 10% coverage of their waters, some 111 are still at less than 1%.

MPA coverage does not equal protection. MPAs can be ineffective due to failures in management or design. A simple numbers-based approach ignores the challenges of effectively designing MPAs to provide the most benefit for marine biodiversity and for people.

Designing MPAs for people — is crucial to get right. For the past decade or more, the conservation community has touted MPAs as tools to help reduce poverty and improve human well-being for local communities. While some are doing that quite effectively, they are rare. This study was the first to plot MPAs alongside coastal density, finding that most MPAs are in areas far away from people, in remote ecosystems that typically have high levels of biodiversity and few conflicting demands for ocean space.

MPA success at reaching biodiversity targets and rebuilding of associated ecosystem serves is heavily dependent on how we use the surrounding waters.  MPAs are not islands isolated from the rest of the ocean.

The original paper is open access - meaning free for all to read.