Kimberly Heiman

Ph.D. student in Biological Sciences at Stanford University

2000 B. A. in Biology from New College of the University of South Florida (now New College of Florida)

Research interests

My interests are in facilitation, positive interactions, and community change due to human disturbances. Specifically I am working in estuarine invasions. My research explores the impacts of habitat altering invasive species on the community composition and ecosystem functions of the environments they invade. I am focusing on the effects of a reef building serpulid polychaete, Ficopomatus enigmaticus, on Elkhorn Slough, California. Ficopomatus enigmaticus forms large reefs that can be a meter tall and cover more than 500 square meters. In many areas around the world, including Elkhorn Slough, it provides one of the only biogenic (created by living organisms) hard complex substrate in the local environment. Through extensive surveys, recruitment monitoring, benthic sampling, and removal experiments, I will quantify the community level changes, spread potential, and role of human disturbance in the current distribution of this invasive species.

Specific research questions

1. Where are invasive species found in Elkhorn Slough and why?
2. What can recruitment patterns tell us about the potential for invasives species to spread?
3. Do F. enigmaticus reefs alter the composition of the animals that live in nearby mudflats?
4. Do F. enigmaticus reefs harbor disproportionately more invasive species than the only other biogenic habitat in the system, the native oyster?

Ficopomatus enigmaticus

Ficopomatus enigmaticus is a reef building serpulid polychaete, believed to be native to Australia. It has been introduced throughout the world through ship fouling or in ballast water. The serpulid is gregarious, meaning that larvae cue on the presence of adults during settlement, resulting in large congregations of individuals. The mass of intertwined calcium carbonate tubes can result in large complex tube reefs. Reefs in Elkhorn Slough, California, can be 1m high and over 5m in diameter. Although they require a piece of hard substrate to start colony formation, adult tubes can act as hard substrate for subsequent generations, making the potential spread and impacts of this species within a system dramatic.

Elkhorn Slough

Elkhorn Slough is a central California estuary 150km south of San Francisco Bay. A flooded river valley, Elkhorn Slough is primarily a soft-sediment environment with the mid and low intertidal zones comprised of mudflats and the high intertidal zone occupied by Salicornia virginica beds. The only major biogenic habitat in the system is Ficopomatus enigmaticus, which was initially identified in Elkhorn Slough in 1994. There are a few native oysters, Ostreola conchaphila, in Elkhorn Slough, but they are only observed in low densities. F. enigmaticus is limited to the northern half of Elkhorn Slough, with reefs only observed in the most northern locations. There are 58 known marine invasive species in Elkhorn Slough. Most were introduced into the slough either by small boats moving between Elkhorn Slough and nearby San Francisco Bay or with the culturing of non-native oysters. The pacific oyster, Crassostrea gigas, and the eastern oyster, C. virginica, were both cultured to varying degrees in Elkhorn Slough from the 1920s to the 1970s. Oyster culture is believed to have contributed to the introduction of 38 of the 58 invasive species in Elkhorn Slough.

1. Where are invasive species found in Elkhorn Slough and why?

The role of human-added hard structures in the distributions and within-system spread of marine invasive species.

Increasing numbers of invasive species are reported in estuaries worldwide. Once invasives establish, they can spread within their new environments. But how do they spread throughout these new systems and why? I set out to address this question through extensive surveys of Elkhorn Slough’s intertidal habitats. I surveyed the location and abundance of 6 invasive species, quantified aspects of each survey site such as abundance and type of hard structures, and photographed each site during 2002 and 2003. By mapping the locations of all sites electronically in the software package ArcGIS, I found that there are two areas in Elkhorn Slough with large numbers of invasive species. Both areas are characterized by the presence of a variety of human-added hard structures, including bridges, riprap, and docks. Multivariate statistical analyses show that all of the invasive species’ distributions are influenced, in part, by the presence of human-added hard structures. Additionally, the distribution of 5 of the 6 species was constant over the two years of the survey. However, Watersipora subtorquata, a colonial bryozoan, was found in significantly more sites in 2003 than in 2002. This result indicates that W. subtorquata may be spreading, but further experimentation and observation is needed to see if this is actually the case.

2. What can recruitment patterns tell us about the potential for invasive species to spread?

From the experiment described above, hard structures are important in determining where invasive species are found in Elkhorn Slough. Following up on this idea, would invasive species spread into new areas if hard structures were provided for them? To address this question I deployed 10 sets of recruitment plates throughout Elkhorn Slough. Most of the sites did not have substantial amounts of hard structures to begin with. I monitored the settlement and development of animals and plants on the plates each month for 30 months. All species settling on the plates were identified and their abundance was quantified. In addition to monitoring recruitment I measured a variety of physical environmental factors at each site, including flow speed, temperature, and salinity. I recorded the abundance of all local fouling animals and plants at each site. In addition to providing information about whether or not invasive species can spread beyond adult distributions observed in the surveys, this study provides a data set which will be used to understand the physical properties that might control the development of communities, as well as the spatial and temporal variability in community development through time.

3. Do F. enigmaticus reefs alter the composition of the animals that live in nearby mudflats?

Since 1994, F. enigmaticus has spread to several sites within Elkhorn Slough. At one site it occupies nearly 100% of the available hard structures, forming reefs that grow out from dock pilings and spread over the surrounding mudflats. The reefs greatly increase the amount of complex hard structure and create a new unique habitat. I explored the role of the F. enigmaticus reefs, on the animals living in surrounding mudflats. Replicate reefs were removed in an experiment designed to identify their impacts on mudflat animal communities under and near the reefs. Communities associated with reefs had low diversity and were dominated by invasive species. Mudflat communities showed a significant but highly localized response to the removal of reefs, with changes in the abundance of invasives, such as the amphipod Monocorophium insidiosum and the oligochaete Tubificoides brownae, driving the community responses

4. Do F. enigmaticus reefs harbor disproportionately more invasive species than the only other biogenic habitat in the system, the native oyster?

Invasive reefs as a structural habitat for introduced species

To determine whether a unique set of animals is associated with F. enigmaticus reefs, I compared animals living in the reef matrix to animals living in native oyster (Ostreola conchaphila) clumps, the only other biogenic reef habitat in the system. Analysis of similarity (ANOSIM) indicated that the distribution of native and invasive species varied significantly among locations and between tubeworm and oyster habitats. However, location within Elkhorn Slough explained much more of the observed native species distribution patterns than biogenic habitat type, where as habitat type explained more of the invasive species distributions than location. The presence of F. enigmaticus reefs appears to enhance the local abundance of invasive species, indicating possible facilitation by this habitat-forming invasive. Managers could target control efforts on habitat-forming invasives as a means of reducing abundances of a wide range of non-native animals.

Photos of all the fun you too can have in Elkhorn Slough