Abstract
The San Ignacio Lagoon is one of the largest in the northwest area of Baja California Sur; it is characterized by high levels of commercial fish catch; however the number of investigations related to taxonomic diversity is low. The variation in taxonomic diversity was determined for the assemblage of fish associated with soft bottoms, at 11 locations in a period from spring of 1998 to winter of 1999. Variation in diversity of the soft bottom fish were evaluated considering the taxonomic distance between species, using the indices of alpha, average alpha, beta and gamma diversity, also the indices of taxonomic distinctness (Δ*) and average taxonomic distinctness (Δ+). Bottom trawls were performed using an experimental net to an average depth of 5 meters, between 9:00 to 17:00 hours. 1361 organisms were observed, belonging to 44 species on 35 genera. According to the average alpha, beta and gamma diversity indices, the season with higher value on average alpha diversity was summer, with 6.68 species followed by spring with 5.73 species. In beta´s case the highest value was observed during spring (21.27%) followed by summer (20.18%). Taking gamma in account, the highest values were observed during spring and summer, both seasons with 27 species each. The lowest values observed according to the average alpha beta and gamma indices, was observed during winter season (5.27, 20.18% and 20 species, respectively). In the spatial analysis, the average taxonomic distinctness index (Δ+) show a significant difference (p ≤ 0.05), while taxonomic distinctness index (Δ*) showed no significant difference (p ≥ 0.05). In the temporal analysis both indices showed no difference (p ≥ 0.05).
Highlights
Coastal lagoons and estuaries are physically unstable areas, characterized by spatial and temporal variations in temperature, salinity, oxygen concentration, turbidity and other factors [1,2]
The coastal lagoons, estuaries and bays on the west coast of northwestern Mexico, are considered areas of particular interest within the Eastern Tropical Pacific Ocean (ETPO), due to its complex geological history and the confluence of the California current and the north equatorial current, which have produced a series of environmental and climatic conditions that result in a wide variety of habitats for marine organisms [3]
Fieldwork Four campaigns were conducted during the seasons of spring, summer and fall of 1998 and winter of 1999. 44 trawls were conducted at 11 locations (Figure 1); trawls were conducted for 30 minutes, performing three replicates of 10 minutes each
Summary
Coastal lagoons and estuaries are physically unstable areas, characterized by spatial and temporal variations in temperature, salinity, oxygen concentration, turbidity and other factors [1,2]. The coastal lagoons, estuaries and bays on the west coast of northwestern Mexico, are considered areas of particular interest within the Eastern Tropical Pacific Ocean (ETPO), due to its complex geological history and the confluence of the California current and the north equatorial current, which have produced a series of environmental and climatic conditions that result in a wide variety of habitats for marine organisms [3]. Laguna San Ignacio (SIL) is the second most important in the Pacific Ocean side of Baja California Sur (BCS). From the zoogeographical point of view, SIL is found in the Californian province [4], so it is geographically located in the temperate region. This lagoon is used during winter as breeding, rearing and refuge of the gray whale Eschrichtius robustus [5], as well as some species of migratory birds such as Branta bernicla, Limosa fedoa y Numenius americanus [6]; few ecological studies include fish fauna in this lagoon [2,7,8,9]
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