Context and challenge 

Figure 1. Major habitats represented in the Gulf of California (Munguia-Vega et al. 2018).

The Gulf of California stretches 1126 km (700 miles) south from the mostly dried Colorado River Delta, down along Mexico to the Pacific Ocean. It supports an extraordinary diversity of marine life and habitat types (figure 1), including a host of endangered species such as sea turtles, whales, sharks, nesting and migratory seabirds, and the vaquita (the world’s smallest porpoise). One third of all marine mammal species found on earth are represented in the Gulf. Habitat types vary throughout and include rocky reefs, sargassum (seaweed) forests, mangroves, some seagrass beds, and seamounts, since it is situated along a rift (Munguia-Vega et al. 2018; WWF). Notably, the northern Gulf has a unique oceanographic characteristic: strong asymmetric ocean circulation patterns. This means that currents flow one direction eddying around the northern shores one part of the year, then switch and turn the opposite direction in the other (figure 2). This creates a strong northward current along the eastern coast in the spring-summer and a predominantly southward current along the eastern coast in the fall-winter (Álvarez-Romero et al. 2017; Beier & Ripa 1999).

The Gulf of California is an important economic powerhouse for the region, hosting commercial fisheries of shrimp, sardine, and squid, and sport fisheries of billfishes and tuna. About 75 percent of Mexico’s total annual fish catch is sourced from The Gulf, with a majority sent to the United States. The beaches, marine life, and colorful coral reefs also attract large numbers of tourists.

Overfishing, unsustainable fishing practices, habitat destruction, coastal development, and climate change threaten gulf marine ecosystems. The economically-important fisheries in The Gulf have little regulation, and are believed to have caused dramatic declines in cetaceans, sharks, rays, and other fish stocks from disrupted food chains. Additionally, the predominance of fisheries such as shrimp, which use bottom trawlers, causes not only seafloor destruction, but also high levels of bycatch. This practice is the most predominant threat to the endemic and threatened vaquita porpoise. As a tourism hot spot, the region is also subject to rapid coastal development and destruction of habitats like wetlands and mangroves, which serve as nursery habitat for fish. Climate change-driven warming threatens biodiversity and fisheries production by suppressing upwelling and reducing primary productivity, changing the distribution and abundance of species and habitats, and reduced larval connectivity via decreased dispersal ranges (Álvarez-Romero et al. 2017; WWF).

Approach

Using an amalgamation of best available data drawn from existing and synthesized information produced by local modeling studies and confirmed by empirical data, scientists modeled species, larval, and habitat connectivity with and without climate change effects to inform conservation design and practice. Several models were made; a model to describe larval dispersal and implications for the location and spacing of reserves, a model to predict species richness patterns and a niche model of the interaction of species under climate change, a model to estimate recovery times to inform reserve duration, and a model of recommended marine reserve sizes. (Munguia-Vega et al. 2018).

These models highlighted important implications of connectivity considerations inclusion in reserve planning. Larvae, especially those that spawn in a single season, exhibited movement that was highly constrained by the direction of currents. For example, eastern coast larvae spawning in summer are more likely to move in a northerly direction, while those in the same location spawning in fall are more likely to move south. Therefore, identifying a target species and preserving both nursery habitat downstream from spawning locations and the spawning locations themselves are important considerations requiring an understanding of currents and life cycles (Munguia-Vega et al. 2018). Larval dispersal distance is also an important consideration, as the scientists found that often, dispersal ranged between 50-200 km (31-124 miles), informing reserve distance appropriateness. Adult species migration distances can also indicate protection (figure 3) (Álvarez-Romero et al. 2017; Munguia-Vega et al. 2018).

Figure 3. Recommended minimum marine reserve length (km) for 63 fish species from the Gulf of California, based on modeled maximum distance traveled (Munguia-Vega et al. 2018).

Ecosystem modeling of climate change effects also informed important implications for reserve design. Scenarios simulating the effects of future ocean warming and ocean acidification were modeled for 13 trophic or taxonomic groups and their environments. Employing the Atlantis ecosystem model for the Northern GOC  allowed scientists to predict spatial range shifts for species and habitats, based on climate-driven stressors (figure 4). Using these overlapping predictions between target species and habitats fulfilling life cycle needs, reserve design can incorporate future species range shifts to maintain connectivity (Munguia-Vega et al. 2018).

Results

Despite some protections, namely designated in the north and central regions of the Gulf, fishing restrictions remain lax and the compounded pressures on marine environments persists. This research, which makes use of available data to predict species and habitat range shifts due to climate change and seasonal variations, can be instrumental in future designations and area expansions. The Gulf of California is listed as a Mission Blue ‘Hope Spot’, characterized by an area that needs new protection, despite existing protections. In collaboration with government, communities, and NGOs, the effort is actively aiming for increased protections, taking into consideration research such as species migration patterns and future climate change impacts (Mission Blue).

Research that models future scenarios based on the most currently available data is essential for impactful protection in marine environments, yet more research is needed in order to obtain highest accuracy. Scientists have identified that the most important research priority is understanding more about the potential effects of climate change on the distribution and abundance of major habitats and focal species, life history traits within species, and associated changes in communities, trophic and connectivity networks in the Gulf of California (Munguia-Vega et al. 2018).

Figure 4. Projected changes in species distribution, 2015 – 2015, using estimated sea surface temperature increases for a; leopard grouper, b; leopard grouper nursery habitat (sargassum), and c; areas where both ranges are predicted to overlap (Munguia-Vega et al. 2018).

References

Álvarez-Romero, J.G., et al. 2017. Designing connected marine reserves in the face of global warming. Global Change Biology 24: e671-e691.

Beier, E., and Ripa, P. 1999. Seasonal gyres in the Northern Gulf of California. Journal of Physical Oceanography, 29(2), 305-311.

Mission Blue. Hope Spots.

Munguia-Vega, A., et al. 2018. Ecological guidelines for designing networks of marine reserves in the unique biophysical environment of the Gulf of California. Reviews in Fish Biology and Fisheries 28: 749–776.