MPA Perspective: Developing Design Guidance for Offshore MPAs

By Jennifer A. Brown and Lisa Wooninck

As human impacts on offshore ecosystems intensify, there is increasing interest in creating MPA networks for spatial protection of offshore resources. However, most of the scientific guidance for designing MPA networks – such as recommendations on size, number, and configuration of MPAs – has been developed for networks located nearshore, in shallow-water habitats like coral reefs and kelp forests. As managers consider network design for deeper, offshore habitats, it is important to consider whether recommendations developed for nearshore MPAs are appropriate for offshore sites.

To address this issue, the Monterey Bay National Marine Sanctuary (MBNMS) co-hosted a workshop in December 2006 of marine ecologists and fisheries biologists, in partnership with the National Marine Protected Areas Center. The workshop asked participants for preliminary guidance on designing zones in offshore habitats (deeper than 100 m) of the 13,783-km² MBNMS. These zones, which are theoretical thus far, would focus on enhancing habitat/biodiversity conservation and research opportunities in the multiple-use sanctuary. They could feature a range of regulations, from allowing some extractive activities to a full ban on extraction.

Although these guidelines were developed specifically for an MBNMS stakeholder group that is considering the utility of offshore MPAs, they may also be useful to stakeholders and scientists in other regions. The workshop conclusions are summarized below.

1. Habitats should be used as proxies for species, and areas with high habitat heterogeneity may indicate areas of high species diversity. According to workshop participants, the distribution and abundance of deepwater benthic habitats is relatively well-known, including large topographic features (e.g., submarine canyons) and smaller features such as sediment type, rock type, relief, and depth. Comparatively less is known about deepwater species – especially adult movements and larval dispersal patterns – although some information on general habitat-species associations is available, particularly on how species assemblages vary with substrate type and depth. Consequently, benthic habitats were recommended as proxies for the location of species assemblages. For example, if the goal of an offshore MPA is protection of species diversity, then targeting areas with high diversity of benthic habitats (i.e., “habitat mosaics”) may be a good way to achieve this goal.
2. Increased species diversity may be achieved by overlaying benthic mosaics with persistent pelagic features or processes. In addition to evaluating heterogeneity of benthic habitats for site selection, called a primary habitat consideration, participants discussed a variety of oceanographic processes and features that were termed secondary habitat considerations. Some oceanographic features, for example (upwelling shadows, retention zones, and frontal waters), are associated with increased diversity and abundance because they aggregate plankton and attract pelagic animals. In some cases, these pelagic habitats are persistent because they are associated with fixed topographic features.
3. Offshore MPAs may need to be larger compared to nearshore MPAs to capture adequate, suitable habitat and species abundances. On the U.S. west coast, hard-bottom habitats tend to be more abundant nearshore, becoming sparser as depth increases. Densities of macrofauna tend to be lower in the more homogeneous soft-bottom habitats that dominate offshore ecosystems. In addition, fishes in offshore waters tend to have larger ranges of movement, possibly due to the need to forage over homogeneous soft bottom habitat.
4. Compared to the many, smaller MPAs of nearshore networks, offshore networks should contain fewer, larger MPAs (see above) that are distributed widely. This type of configuration incorporates latitudinal variation in species distribution, habitat characteristics, and oceanographic processes. Fish and bird assemblages, for example, tend to vary biogeographically according to latitude. Geology and submarine canyon type also vary north and south of the Monterey Canyon in the MBNMS.
5. Consider continuity of offshore MPAs with existing nearshore MPAs to capture age-related and seasonal migratory patterns of species. MPAs can be networked through two processes: continuity and connectivity. Networking through continuity is based on active movement of juveniles and adults from one MPA to another, while connectivity is based on dispersal of larvae. Maximum continuity for juvenile rockfish (Sebastes spp.), for example, could be achieved using nearshore and offshore MPAs that are contiguous (sharing a common boundary), thus providing uninterrupted protection as the fish migrate to deeper water as adults. For an offshore network of fewer, larger MPAs, effective networking via larval dispersal will likely be achieved given the following criteria: the size of the managed area is not disproportionately large relative to MPA sizes within the network; offshore species have larvae with large dispersal distances; and MPAs in the network contain representative habitats.
6. When appropriate, protect unique or rare habitats (such as seamounts and canyons with endemic species) regardless of the feasibility of networking such potentially remote areas. Not all MPAs are easily connected within a network.

For more information

Lisa Wooninck, National MPA Center, Science Institute, 110 Shaffer Rd, Santa Cruz, CA 95060, U.S. Tel: +1 831 420 3965; E-mail: Lisa.Wooninck@noaa.gov