Variation of the Structure of the Intertidal Fish Community of the Pacific Coast of Baja California Sur, Mexico

Abstract

The intertidal zone is a transition zone between terrestrial and coastal systems. During low tide, rocky pools are exposed to air for several hours throughout the day, and environmental conditions such as temperature and salinity are highly variable. There are not many studies of fish communities inhabiting the intertidal zone in Mexico. Therefore, the aim of the present study was to analyze the variation of the community structure of intertidal fish considering temperature, salinity and dissolved oxygen of the water that remains trapped in the tide pools during low tide. Visual censuses were carried out monthly during spring tides on full moon days, when fluctuations of environmental variables are significant. From January to December 2015 visual census were performed in the intertidal zone of El Faro, a locality belonging to the common land of Conquista Agraria in the City of La Paz, west coast of Baja California Sur, Mexico. Extension of censuses was 156*5 m, 145 tide pools were divided in three groups (small, medium and large) according to size and depths that ranged from 20 to 45 cm. Temperature, salinity and dissolved oxygen fluctuate throughout the year of study. Thermal difference between open ocean and tide pools ranged from 3.5 to 4.5°C. A total of 3,754 organisms from 22 species, 12 families, four orders and one class were recorded. To analyze community structure, the following ecological indices were used: species richness (SRI); evenness (J’); Shannon-Wiener’s diversity (H’) and Fisher’s alpha (α-Fisher) with overall values of 2.80, 0.91, 3.20 and 5.15, respectively. According to BVI, 12 species were dominant. All species recorded were grouped as abundant (2), frequent (11), common (5) and rare (4), according to their relative abundance and frequency.