By Ricardo Domínguez, Christian Alfonso Martínez, Carlos Lozano García, and Aldo Franco Díaz

The intertidal zone is a place of transition where abrupt changes occur due to the movement of tides. Delimited by low tide and high tide, this area is classified depending on the type of soft or rocky soil.

The intertidal region is usually divided into parallel to the coastline zones:

• Splash zone (permanently discovered).
• High tide zone (zone exposed to the longest drying time).
• Mid tide zone (covered and uncovered twice a day by daily tidal cycle).
• Low tide zone (less time of exposure and presence of tide pools) and the subtidal zone (almost always wet).

The presence of different kind of sessile organisms (without movement) and / or with little displacement is characteristic of the intertidal zone. Some of the organisms that stand out are mussels, starfish, crabs, macroalgae, to name a few.

Due to its proximity to human settlements, the communities of the intertidal rocky area are subject to constant anthropogenic pressures, such as the destruction and/or modification of habitat, collection and overexploitation of species, contamination of the ecosystem, among others. All this generates disturbances in the structure of the community of the intertidal rocky zone. Therefore, its study is of great importance because it allows us to know the way the community is being affected.

In San Quintín, for example, there are plans to install a desalination plant close to the intertidal rocky zone. Although it represents a benefit for the population, once it starts operations, it will discharge wastewater into the ocean, which represents a concentration of 1.3 to 1.7 times higher than the average seawater. This could impact the benthic communities of the rocky intertidal zone because of the physicochemical variations in the ecosystem. It could cause disturbances that would lead to the loss of richness and abundance of species, which are used by the local population of San Quintín.

Three intern students from the National Autonomous University of Mexico (UNAM) collaborated to carry out a characterization of the macroinvertebrate community using transects parallel to the coast and quadrants (for the determination of abundance and diversity of macroinvertebrates and algal extension, respectively).

The sampling was carried out in the northern and central intertidal zones of San Quintín. Three and eight beaches were considered per zone, in which two of the three intertidal rocky areas (high and medium intertidal) were sampled, for a total of 0.8 miles approximately, along the coast. For the algal extension, 124 quadrants were placed along the transects, adding a total of 333 square foot recorded.

As a result, 137,800 organisms belonging to 37 identified species of macroinvertebrates were counted. Among them, Tegula sp., Pollicipes polymeros¸ Chthamalus sp., and Mytilus californianus. In addition, a total of 32 species of macroalgae divided into four functional groups were identified. The Ochrophyta group presented the highest number of species (17), followed by Rodophyta (11), Chlorophyta (3) and Tracheophyta ( 1).

This study is considered the baseline in the characterization of the intertidal rocky zone in San Quintín. Therefore, in order to determine if an impact is generated or not on the diversity of marine organisms in the intertidal zone, it is necessary to conduct a greater sampling effort, evaluation, and monitoring of natural and anthropogenic disturbances. The information obtained will contribute to future decisions considering the before and after operations of the desalination plant.

It should be noted that the landscapes and organisms were photographed to expose the particular beauty of what exists in the San Quintín Valley.

About the authors

• Aldo Franco Díaz is a Biology intern of Iztacala School of Higher Studies, with special interest in conservation biology in large cetaceans and taxonomy. He has ventured into various fields, both scientific and artistic. Literature has been one of his greatest strengths. He has partcipated and has been recognized in several literary contests in Latin America. He is currently developing his thesis project on invertebrate taxonomy and ecology of inland waters, as well as an investigation on the traffic of endangered species in Mexico City.
• Christian Alfonso Martínez Ávila, a Biology major at the National Autonomous University of Mexico, completed his studies in Iztacala School of Higher Studies. He specialized in ​​biogeochemistry and marine ecology and based his thesis on trace element analysis in tissues of pelecypods and surface sediment of the Jamapa-Atoyac fluvial system, Veracruz. He participated in several dissemination workshops focused on climate change and coral reefs. In the future, he aspires to be a teacher and researcher following the steps of his mentor and thesis director, Dr. Rafael A. Cabral-Tena.
• At first, Carlos Uriel Lozano García, intern of Biology at the National Autonomous University of Mexico (UNAM), wanted to study engineering. Nonetheless, his passion for biological sciences led him to pursue a degree in Biology. As a result, since high school, he studied at UNAM to later join Iztacala School of Higher Studies, where he is currently doing his thesis on copper pollution in sediments of the Jamapa-Atoyac River System in Veracruz. He belongs to the project PAPIIT IN114616 headed by Dr. Guillermo Horta-Puga and Dr. Rafael A. Cabral-Tena.
• Ricardo H. Domínguez-Reza, oceanologist graduated from the Autonomous University of Baja California (UABC), is currently completing his postgraduate studies at the Center for Scientific Research and Higher Education of Ensenada (CICESE) in the Marine Ecology program.

References

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• Einav, R., Harussi, K. and Perry, D., (2003). The footprint of the desalination processes on the environment. Desalination, 152 (1-3), 141-154.

• Murray, S.N., Ambrose, RF. and Megan N.D., (2002). Methods for Performing Monitoring, Impact, and Ecological Studies on Rocky Shores. MMS OCS Study. Coastal Research Center, Marine Science Institute, University of California, Santa Barbara, California. MMS Cooperative Agreement Number 14-35-0001-30761. 217 pp.

• Prado L., Castilla J.C., (2006). The bioengineer Perumytilus purpuratus (Mollusca:Bivalvia) in central Chile: Biodiversity, habitat structural complexity and environmental heterogeneity. Journal of the Marine Biological Association of the United Kingdom, 86: 5227/1-5.
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