Diversity and distribution of ascidians

Abstract

My research focuses on the biodiversity and biogeography of ascidians, the mechanisms controlling the distribution of species and communities, and how human activities, such as shipping, coastal hardening, and climate changes can alter those distributions. Working with my masters and undergraduate student researchers, I use morphological and molecular taxonomy (Nydam et al., 2022; Reinhardt et al., 2010; Stefaniak et al., 2009), molecular ecology (Stefaniak et al., 2012), and observational and manipulative field and lab studies (Stefaniak, 2017; Stefaniak & Heupel, 2016; Stefaniak & Whitlatch, 2014) to explore these questions.

While I always knew I wanted to be a marine biologist, my entry into the world of ascidian biology is best described as a series of serendipitous events. It started in 2005 when I joined Dr. Robert Whitlatch's lab at the University of Connecticut as a PhD student. Bob was working on introduced species in fouling communities, which means lots of ascidians. The newest ascidian was Didemnum vexillum, though that name was still uncertain at the time. Then, the following summer, I was fortunate enough to attend the first ascidian taxonomy workshop at the Smithsonian Tropical Research Institute in Bocas del Toro, Panama, taught by Gretchen Lambert, Dr. Rosana Rocha, and Dr. Charles Lambert, where I learned that I enjoy the puzzle of identifying ascidians I have never seen before. Attending the course led to Gretchen offering me her D. vexillum samples from around the world if I would do the molecular taxonomy, and to Gretchen and Charlie giving me an introduction to Dr. Hitoshi Sawada. Dr. Sawada would become my host at the Sugashima Marine Biological Laboratory (Nagoya University) for a summer of collecting D. vexillum around Japan and several summers teaching in an advanced marine biology course at Sugashima MBL. Combined with my training as a field marine biologist during my undergraduate research at Cornell University (advisor: Dr. Myra Shulman) and my time working in and managing a molecular evolution lab at the University of Iowa (Dr. John M. Logsdon, Jr.) after college, I was now very well positioned to tackle both the biology and molecular ecology of D. vexillum. In my PhD I was able to help determine that all these “new” didemnids were D. vexillum (Stefaniak et al., 2009), to identify the northeast Pacific Ocean as the likely native range (Figure 1, Stefaniak et al., 2012), and to characterize the life history of the species (Stefaniak, 2017; Stefaniak & Whitlatch, 2014).

Joining Dr. Daniel Gleason (Georgia Southern University) in his work monitoring the benthic habitat community in the Gray's Reef National Marine Sanctuary (GRNMS) brought me to the southeast US Atlantic coast where I am now based, an area particularly conducive to studying the effects of human activities on ascidian distribution with its overlapping biogeographic faunas. Through my research and participation in bioblitzes and rapid assessment surveys, I have had the opportunity over the past 17 years to get to know the ascidian fauna of much of the US Atlantic coast as well as parts of the Pacific Northwest and Caribbean coasts. Currently, I am focused on three geographic areas: the coasts, reefs, and mangrove cays of Belize (with Drs. Susanna López-Legentil, Marie Nydam, and Patrick Erwin); GRNMS and other continental shelf areas in the southeast US (with Dr. D. Gleason); and natural and artificial habitats along the southeast US Atlantic coast (Figure 2).