The Gulf of California: Biodiversity and Conservation

4. Invertebrate Biodiversity and Conservation in the Gulf of California

CHAPTER 4 Invertebrate Biodiversity and Conservation in the Gulf of California richard c. brusca and michel e. hendrickx Summary An analysis of the Macrofauna Golfo invertebrate database indicates that the Gulf is home to over 4,900 species of named and described invertebrates. This is estimated to be about 70 percent of the actual invertebrate fauna of the Gulf of California. The most poorly known regions for invertebrates are the open sea and the deeper (below the continental shelf ) benthic environment. In the intertidal region of the Gulf 2,158 species occur, although only 45 of these are strictly intertidal in distribution. Thirty-six hundred species occur at or above the 30 m isobath, and 4,078 species occur on or over the continental shelf (200 m and above). Most invertebrates recorded from the Gulf, 4,350 species, inhabit benthic habitats. There have been 329 species recorded from coastal lagoons in the Gulf, 260 of these from mangrove lagoons. In general, invertebrate diversity increases from north to south in the Gulf. The unique oceanographic attributes and broad seasonal water temperature range of the Northern Gulf create tropical marine conditions in the summer but warm-temperate conditions in the winter. This provides a refuge for many disjunct warm-temperate (i.e., Californian) species in the upper Gulf that are not found in the Central or Southern Gulf. It perhaps also explains the high invertebrate endemicity seen in the Northern Gulf (128 species). Most of the Gulf’s invertebrate fauna, however, is tropical and derived from the Tropical Eastern Pacific, and dozens of these species have a transisthmian distribution with populations in the Caribbean. Relative species diversity of invertebrates can be predicted based on substrate and habitat type, although (aside from a few dozen very common species) Invertebrate Biodiversity and Conservation / 73 the actual presence or absence of a species is difficult to predict and largely stochastic in nature. Overall, the most diverse phyla in the Gulf are Mollusca (2,198 species), Arthropoda (1,062 species), Annelida (722 species), Echinodermata (263 species), and Cnidaria (262 species). The greatest threats to invertebrates in the Gulf are bottom trawling , hand-collecting by humans during low tides, coastal development, and pollution. In addition, artisanal harvesting of molluscs and swimming crabs (Callinectes) is a growing threat. On mainland shores, most large-bodied species at most localities are now gone from the intertidal region. Diversity on islands and on some largely inaccessible stretches of shore (especially on the eastern coast of the Baja California peninsula) are critically important refuges for littoral species now largely extirpated from mainland coasts. Industrial shrimp trawling is probably the most destructive form of fishery in the Gulf to invertebrates and also to the ecological integrity of the seafloor. Estero-based aquaculture is also harmful to invertebrate habitats, and the relocation of shrimp farms inland may ultimately be the only way to protect the fragile coastal lagoons of the Gulf and at the same time find a use for old agricultural land that had been ruined by salinization. Introduction Much of the information presented in this chapter was mined from the Macrofauna Golfo Project database, the product of a 10-year effort by many scientists in Mexico and the United States. The database catalogs every macrofaunal species (i.e., animals larger than 5 mm; thus ostracods and copepods are excluded) known to occur in the Gulf of California (Mar de Cortés, Sea of Cortez). The project was funded by grants from several organizations , including Conservation International, CONABIO (Comisión Nacional para el Uso y Conocimiento de la Biodiversidad), CIAD (Centro de Investigación en Alimentación y Desarrollo), Pronatura-México, and the Arizona-Sonora Desert Museum. Lead investigators for the Macrofauna Golfo Project were: Richard C. Brusca, Lloyd T. Findley, Philip A. Hastings , Michel E. Hendrickx, Jorge Torre, and Albert van der Heiden. The database provides information on taxonomy/classification, geographic distribution (in the Gulf and worldwide), depth, and habitat for about 6,000 species (4,916 invertebrates). An abridged version of the invertebrate data 74 / brusca and hendrickx was published by Hendrickx et al. (2005). The complete invertebrate database is available at www.desertmuseum.org/center/seaofcortez/database .php. See Hastings et al. (chapter 5 in this volume) for more information on the Macrofauna Golfo Project, including descriptions of the four recognized biogeographic regions (Northern Gulf, Central Gulf, Southern Gulf, and Southwestern Baja California...