Influence of the structural complexity of phytal substrates on intertidal meiofaunal community structure in a tropical system (NE Brazil)

Abstract Phytal environments harbor meiofaunal communities due to the variety of available niches and resources. Meiofauna play essential roles in aquatic ecosystems, contributing to energy transfer in food webs, recycling organic matter, and serving as bioindicators of environmental changes. Despite their ecological importance, studies on phytal meiofauna remain scarce in tropical systems, especially along the Amazonian coast of Brazil. In this context, the present study analyzed the effects of the structural complexity of Spartina alterniflora and Ulva lactuca from the Maranhão Gulf (Maranhão, Brazil) on meiofaunal community structure. Ten specimens from each species were collected over a period of five months, totaling 100 samples. Eighteen taxa were recorded, with 16 associated with S. alterniflora and 13 with U. lactuca . Mean densities were 3.22 ± 1.17 ind. 10 cm⁻² in S. alterniflora and 2.8 ± 2 ind. 10 cm⁻² in U. lactuca . Nematoda, Copepoda, and Amphipoda dominated, with nematodes more abundant in S. alterniflora and amphipods in U. lactuca . Structural complexity did not significantly affect meiofauna density; however, it strongly influenced taxonomic richness and community composition. These findings highlight the relevance of substrate complexity in shaping tropical meiofaunal communities and provide a baseline for future ecological and monitoring studies in Amazonian coastal ecosystems.