Marine fungi of U.S. Gulf of Mexico barrier island beaches: Biodiversity and sampling strategy

Allison Kathleen Walker

Abstract

Marine fungi are an important but often overlooked component of marine ecosystems. Primarily saprotrophic, they are vital to coastal nutrient cycling processes and food webs. However, basic marine fungal distribution data are lacking in many parts of the world, as is knowledge of the sampling intensity required to characterize the biodiversity of these communities. The roles of substrate, season and latitude in shaping intertidal ascomycete community structure were examined for the U.S. Gulf of Mexico, and the role of sampling frequency on species richness estimates was also addressed. Best sampling practices were developed and 750 collections of beach detritus, sand and seafoam were made from the Florida Keys north to St. Vincent Island, Florida, from South Padre Island north to Galveston Island, Texas and from West Ship Island, Mississippi. Intertidal beach substrates were collected in winter and summer 2008-2009 from three Texas and four Florida barrier islands and incubated in the laboratory for six to twelve months to study fungal succession. Sampling was conducted every other month at West Ship Island, Mississippi from April 2009 through February 2010 and weekly at East Beach, MS during May 2010 to investigate changes in marine fungal communities over shorter timescales. Morphological and molecular techniques (ITS T-RFLP community fingerprinting, ITS gene sequencing) were employed to characterize and compare intertidal ascomycete communities. Species occurrence and abundance data were used to determine biogeographical patterns of marine fungal distribution on abundant intertidal substrates. Diversity indices and results from MDS and ANOSIM analysis of T-RFLP data indicate marine ascomycete diversity may increase with decreasing latitude. Substrate type strongly influenced fungal community structure. Most ascomycete species were substrate-specific, but several were found U.S. Gulf-wide on a variety of intertidal substrates. Substrates rich in lignocellulose (wood, saltmarsh plant detritus) housed the greatest ascomycete diversity, and seafoam provided a conservative snapshot of the intertidal fungal community as a whole. Sand was species-poor and dominated by Corollospora maritima , the most frequently-occurring marine fungus encountered in this study, indicating most marine fungi may arrive with their substrates and not become resident in sand. A seasonal trend was noted U.S. Gulf-wide for marine plant detritus only, which showed higher ascomycete diversity in winter. This study has increased the number of fungal species reported from the Gulf of Mexico by over 60%. Texas and Florida sampling was completed prior to the Deepwater Horizon oil spill (20 April 2010), providing valuable baseline data for the U.S. Gulf of Mexico. The diversity of species and substrates encountered over four weeks of sampling on East Beach, MS and ten months of sampling on West Ship Island, MS indicates more intensive sampling is required to fully characterize marine fungal communities of the highly dynamic intertidal zone of the GOM.