Case Studies

Northern Channel Islands: Connectivity across a network of marine protected areas contributes to positive population and ecosystem consequences

By Jennifer Caselle, Marine Sciences Institute, University of California Santa Barbara; Mark Carr, Department of Ecology and Evolutionary Biology, University of California Santa Cruz; and J. Wilson White, Coastal Oregon Marine Experiment Station, Oregon State University

Key lesson

The creation of an ecological network of marine protected areas has helped to restore species, increased connectivity and made the network more robust to invasive species.

Context and challenge

Temperate coastal marine ecosystems produce a diversity of ecosystem services, including the support of recreationally and commercially important fisheries, economically important ecotourism and other cultural values. One temperate marine ecosystem of particular importance is kelp forests, which support some of the most species-rich and productive ecosystems on Earth. They are subjected to a host of human impacts, particularly from fisheries, invasive species, and various manifestations of global climate change.

Approach

In 1998, a group of fishers, managers and other citizens in southern California, USA, was concerned about declining resources such as abalone, lobsters and rockfishes in nearshore ecosystems, including kelp forests. This group approached the California Fish and Game Commission with a proposal to set aside areas for protection in the northern Channel Islands, a chain of four islands north-west of Los Angeles and separated from the mainland by the Santa Barbara Channel. In 2003, following a multi-year public process, the state of California, in collaboration with Channel Islands National Park (CINP), created 13 marine protected areas (MPAs) within state and national park waters. In 2007, the National Oceanic and Atmospheric Administration extended eight of these MPAs into Channel Islands National Marine Sanctuary (CINMS) waters (Figure 1). Thus, the MPAs encompass both state and federally managed waters. The objectives of the MPAs were to help restore biodiversity, ecosystem health and fisheries species by protecting marine life and habitats. Extending from the intertidal zone to depths of 1,400 m, the MPAs encompass a diversity of ecosystems, distinguished by seafloor type (rock versus sand) and depth.

Today’s Channel Islands MPA network has a large number of overlapping agency jurisdictions. Eleven federal, state and local agencies have some jurisdiction in the planning region. While both CINMS and CINP overlap around the northern Channel Islands, neither agency regulates commercial or recreational fishing. The California Department of Fish and Wildlife manages all fisheries in state waters (within 5.6 km of the shore), while the California Fish and Game Commission (an appointed body) has authority to set all state fishery regulations, including the creation of MPAs.

Figure 1. Map of the distribution of marine protected areas across the Northern Channel Islands archipelago off the coast of southern California, USA (see inset). Map indicates the jurisdictional ranges of state and federal institutions and the two types of protected areas (marine reserves and marine conservation areas) © The Partnership for Interdisciplinary Studies of Coastal Oceans

Examples of ecological corridors

Though not originally designed as a network of MPAs connected to one another by the dispersal of young (i.e., fish and invertebrate larvae), subsequent analyses of oceanographic currents and larval dispersal patterns indicated that young generated in the MPAs very likely are transported to and contribute to the replenishment of populations and communities in other MPAs, thus forming a de facto network. The primary way ecological corridors have been analysed is by simulating the movement of larvae using numerical ocean circulation models that describe currents in the region. For example, Watson et al. (2010) simulated the movement of larvae of two important fishery species – kelp bass (Paralabrax clathratus) and kelp rockfish (Sebastes atrovirens) – to and from sites throughout southern California, including the Channel Islands MPAs. The simulations calculated the probability of larvae travelling from one location to another; the authors then multiplied those probabilities by estimates of the spawning biomass at each location to predict how many larvae travelled along each potential ecological corridor. The analysis showed that kelp bass larvae produced inside MPAs on Santa Cruz and Anacapa islands likely disperse to other MPAs in the network and to fished areas; the same was true of kelp rockfish larvae produced in MPAs on San Miguel Island (Figure 2). Thus, the MPAs are linked by ecological corridors, but different corridors are used by different species, depending on habitat. In this case, kelp bass prefer the warmer water of the eastern islands while kelp rockfish prefer the cooler western waters.

Figure 2. Predicted dispersal of larval kelp bass using an ocean circulation model of the Southern California Bight (Watson et al., 2010). Each coloured circle corresponds to a spatial node (site) in the model from which simulated larvae could be released and to which they can settle. In this example, the connectivity from Site 83 (which overlaps with the Scorpion State Marine Reserve on Santa Cruz Island) is shown. The colour of each dot represents the relative number of larvae that travel along the ocean corridor from Scorpion to the other sites (the numerical values are expressed as a proportion of the total number of larvae released from all sites in the simulation). Thus, there are strong connections to the other MPAs in the Channel Islands, as well as to non-MPA sites.

Results

The ecological network of MPAs implemented in the Channel Islands region contains 21% of the CINMS waters in 11 state marine reserves (no commercial or recreational fishing allowed) and two conservation areas (where some types of fishing are allowed). Following a decade of protection, monitoring of nearshore kelp forests in the Channel Islands MPAs showed increases in the biomass of targeted fish species inside the MPAs relative to fished areas. While the biomass did not increase spectacularly, the dramatic declines that were predicted by some models as a result of potential displacement and compaction of fishing effort did not take place either. More recently, protection of higher-level predators within older, fully protected areas has been shown to prevent invasion of a non-native macroalgae.

References

Watson, J.R., Mitarai, S., Siegel, D.A., Caselle, J.E., Dong, C., and McWilliams, J.C. (2010). ‘Realized and potential larval connectivity in the Southern California Bight’. Marine Ecology Progress Series 401:31–48. https://doi.org/10.3354/meps08376.