Open Journal of Ecology, 2021, 11, 645-663 https://www.scirp.org/journal/oje ISSN Online: 2162-1993 ISSN Print: 2162-1985 DOI: 10.4236/oje.2021.1110041 Sep. 30, 2021 645 Open Journal of Ecology Spatial Zonation and Diversity of Bivalves and Gastropods in Mangrove Forests of Casiguran, Aurora, Philippines Maria Cristina B. Cañada, Eutiquio L. Rotaquio, Jr., RB J. Gallego Department of Graduate Studies, Aurora State College of Technology, Baler, Aurora, Philippines Abstract This study generally aimed to determine the spatial zonation and diversity of bivalves and gastropods in mangrove forest of Cozo, Esteves and Tinib in Ca- siguran, Aurora. Specifically, this aimed to determine the species composition and distribution, and determine the relationship between spatial zonation and diversity of bivalves and gastropods as influenced by ecological factors such as vegetation, soil texture, organic matter, soil salinity, and soil pH. A total of 22 taxa comprising eight species of bivalves and 14 species of gastro- pods were identified. The high tidal zone of Esteves had high diversity (0.66) of bivalve species compared to other tidal zones and areas. On the other hand, the diversity of gastropods was almost equal in the middle tidal zones of Cozo (0.60), Esteves (0.57), and Tinib (0.42). In terms of bivalve species’ density and abundance, Dendostrea folium was the most dense and abundant in the low tidal zone of Cozo (253,333 ind∙ha −1 or 25 ind.m 2-1 , 97.44%) while Gafrarium tumidum in the low tidal zones of Esteves (46,666 ind∙ha −1 or 4 ind.m 2-1 , 73.68%) and Tinib (126,666 ind∙ha −1 or 12 ind.m 2-1 , 50%). In terms of gastropod species’ density and abundance, Cerithidea cingulata was the most dense and abundant in the low tidal zone (666,666 ind∙ha −1 or 66 ind.m 2-1 , 65.79%) of Cozo and the middle tidal zone (5,280,000 ind∙ha −1 or 528 ind.m 2-1 , 61.40%) of Tinib. It was Terebralia palustris in the low tidal zone (1,263,333 ind∙ha −1 or 126 ind.m 2-1 , 63.06%) of Esteves. All tidal zones within each study area had greater dissimilarities in terms of bivalves but had greater similarities in terms of gastropod species’ compositions. On the other hand, all tidal zones between study areas had greater dissimilarities in terms of bivalve and gastropod species present. Most tidal zones had Gafrarium tu- midum as common bivalve species while Neritidae sp. and Cerithidea cingu- lata were common gastropod species. All these species were found thriving in a wide range of vegetation, soil texture, organic matter, soil salinity and pH. How to cite this paper: Cañada, M.C.B., Rotaquio Jr., E.L. and Gallego, RB.J. (2021) Spatial Zonation and Diversity of Bivalves and Gastropods in Mangrove Forests of Casiguran, Aurora, Philippines. Open Jour- nal of Ecology, 11, 645-663. https://doi.org/10.4236/oje.2021.1110041 Received: March 3, 2021 Accepted: September 27, 2021 Published: September 30, 2021 Copyright © 2021 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access