High Grazing Rates on Cryptophyte Algae in Chesapeake Bay

Matthew D Johnson,Emily F Brownlee,David J Beaudoin,Diane K Stoecker,Miguel J Frada

doi:10.3389/fmars.2018.00241

Abstract

Cryptophyte algae are globally distributed photosynthetic flagellates found in freshwater, estuarine, and neritic ecosystems. While cryptophytes can be highly abundant and are consumed by a wide variety of protistan predators, few studies have sought to quantify in situ grazing rates on their populations. Here we show that autumnal grazing rates on in situ communities of cryptophyte algae in Chesapeake Bay are high throughout the system, while growth rates, particularly in the lower bay, were low. Analysis of the genetic diversity of cryptophyte populations within dilution experiments suggests that microzooplankton may be selectively grazing the fastest-growing members of the population, which were generally Teleaulax spp. We also demonstrate that potential grazing rates of ciliates and dinoflagellates on fluorescently labeled (FL) Rhodomonas salina, Storeatula major, and Teleaulax amphioxeia can be high (up to 149 prey predator-1 d-1), and that a Gyrodinium sp. and Mesodinium rubrum could be selective grazers. Potential grazing was highest for heterotrophic dinoflagellates, but due to its abundance, M. rubrum also had a high overall impact. This study reveals that cryptophyte algae in Chesapeake Bay can experience extremely high grazing pressure from phagotrophic protists, and that this grazing likely shapes their community diversity.

Highlights

Cryptophyte algae are predominantly a photosynthetic lineage of flagellated protists in aquatic ecosystems (Mallin et al, 1991; Gervais, 1997; Marshall et al, 2005), capable of thriving in turbid and low light environments due to their highly efficient green light harvesting phycobiliproteins (Spear-Bernstein and Miller, 1989)
Our findings demonstrate that cryptophyte populations in Chesapeake Bay are heterogeneous in their species composition, cell size, and growth rates, and experience high in situ grazing pressure
During October 2011 in Chesapeake Bay, cryptophyte populations had high grazing pressure due to protistan predators throughout the system, but the impact was severe in the southern regions where growth rates were very low

Summary

Introduction

Cryptophyte algae are predominantly a photosynthetic lineage of flagellated protists in aquatic ecosystems (Mallin et al, 1991; Gervais, 1997; Marshall et al, 2005), capable of thriving in turbid and low light environments due to their highly efficient green light harvesting phycobiliproteins (Spear-Bernstein and Miller, 1989). Several species have been shown to use dissolved organic carbon (DOC) to supplement their growth requirements (Lewitus et al, 1991; Lewitus and Kana, 1995; Gervais, 1997), while others, in freshwater and polar habitats, ingest bacterial prey (Marshall and Laybourn-Parry, 2002; Yoo et al, 2017). These traits allow cryptophytes to thrive in diverse environmental conditions.

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Conclusion