Objective:
Determine the critical areas of seagrasses and seaweeds distribution in Laguna San Ignacio and in Gilmore’s Lagoon (Estero La Pitahaya) to the south as habitats for conservation of protected and endangered species, and the conservation of other marine species and their associated biodiversity.
Project Overview
San Ignacio Lagoon is part of the Vizcaino Marine Biosphere; a wetland considered as part of the Convention on Wetlands of International Importance or RAMSAR convention and is consider a critical area for bird and marine species conservation in North America. In this lagoon several economic activities are present (e.g. eco-tourism, fisheries and aquaculture), and other activities (i.e., mineral mining or seaweed aquaculture) could potentially occur in the lagoon. San Ignacio is well known for the extensive seagrasses and seaweeds beds that provide habitat and food for marine fish, invertebrates, gray whales (Eschrichtius robustus), brant (Branta bernicla) geese, and green sea turtles (Chelonia mydas) (Mexican NOM 059). However, little is known about the importance of the role these critical habitats provide for conservation (such as seagrasses and seaweeds), and there is an urgent need to develop an understanding of their historical distribution to evaluate which areas would be critical for conservation and supporting the species diversity in the lagoon. Another need is to understand the role of these plant habitats in relation to associated biodiversity and recruitment of fisheries species.
Seasonal visits (summer, fall 2008, spring 2009) were made to the Laguna San Ignacio to observe and to evaluate the density, cover and area of seagrass meadows to establish baseline information for comparison with satellite imagines. To document associated biodiversity, cores of the bottom sediments were taken in representative sites around the lagoon and density and richness of macrofauna were evaluated. Seagrasses beds are dominated by Gracilaria vermicullophyla (an introduce species) and were evaluated similar to the seagrasses from observations made during visits from 2006 to 2008. Evaluations of the volume and richness of feeding items of the green turtle were undertaken at least for one season and samples for isotope analysis were gathered for comparative analysis between the main four coastal lagoons of Baja California (i.e., Guerrero Negro, Ojo de Liebre, Bahia Magdalena, and San Ignacio).
The results of this study in Laguna San Ignacio indicate that seagrass distribution is highly variable around the lagoon based on size and density of the beds, also the size of the seagrass beds were different between the December 2008 and the April 2009 samples. The observed seagrass densities were similar to the values obtained in our previous study (1999) and other recent publications (Cabello Pasini et al. 2002). However, there was a noticeable presence of Ruppia marina populations along the western side of the lagoon and very low seed numbers in the cores. The associated fauna was found to exhibit spatial heterogeneity related to the sediment type and the presence of seagrass or seaweeds. Small rhodolith beds were detected south of the islands at the middle of the lagoon. The Gracilaria beds were highly variable among years and sites. This variability may be dependent on the water temperature and also might be relative to consumption by herbivores (such as turtles and nudibranchs). This is evident when stomach contents of the green turtle were analyzed and found to contain a high proportion of red seaweed in their diet and the noticeable amount of Ruppia marina.
We will continue to investigate the feeding ecology of green turtle around Pacific Baja California Sur by monitoring the invertebrate diversity by species (to the lowest possible level), and by evaluating the temporal and spatial trends of the invertebrates in relation to the substrate composition. We will continue sampling the diet of the sea turtles by analyzing the esophagic contents of dead turtles, and by conducting isotopic analyses of blood and skin tissue samples in relation to prey items.