How strange to call this planet 'Earth' when quite clearly it is ocean. Arthur C. Clarke

Research Interests


I am interested in eco-evolutionary dynamics in marine ecosystems. This includes:
  • how organisms evolve at the same pace as ecological processes
  • environmental effects of intraspecific phenotypic variation
  • coevolutionary dynamics 

Questions I like to ask:

How does intraspecific trait variation affect communities?
How are plasticity and local adaptation dependent on ecological context (biotic or abiotic)?
How broad and large are the effects of plasticity or genetic adaptation in a community? 
How does trait change due to phenotypic plasticity compare with trait change due to genetic adaptation?
How do anthropogenic influences such as harvest affect traits, evolution, and ecosystems?

Current research:

In my doctoral research, I am exploring population-level trait variation and community dynamics in rocky intertidal communities. I am focusing on the interaction between dogwhelks (Nucella) and California mussel (Mytilus).

Nucella dogwhelks are drilling predators that use acid to make tiny round holes into hard-shelled sessile animals like barnacles and mussels. Since it is very easy to track mussel drilling, I chose to study their relationship with their prey species Mytilus californianus, the California mussel. California mussels are especially important because they form habitat for many intertidal organisms like crabs, other snails, and a variety of algae. For this reason they are considered a foundation species.

This dogwhelk drilled through the shell of this mussel to  begin consuming it. Then, after the mussel relaxed (probably  because it died), the dogwhelk went around to the gaping edge  where it is easier to access the mussel's viscera and inserted  its proboscis to continue feeding, shown here.

Dogwhelks have small ranges and do not disperse gametes or larvae at sea, making them an ideal species to study local adaptation. After copulation, the female glues egg capsules to the substrate, in which her eggs develop (Fig 2). When the eggs hatch, the juveniles crawl away and make their home in the same habitat (Figs 3 & 4). This life history means there is low gene flow between populations, and many generations are exposed to the same selective pressures. Therefore, populations are extremely likely to evolve differentially.

A dogwhelk (the snail in the middle) with its egg capsules (the yellowish 
ovals around the snail) at Fogarty Creek, Oregon, 17 June 2014. The egg 
capsule contains dozens of eggs, which will develop into baby dogwhelks
that will crawl away and live out their lives in the same rocky area.

A juvenile dogwhelk emerging from 
its egg capsule. The capsule is about
1 mm in diameter.

Ocean acidification ties into my project because seawater pH along the west coast is highly variable. Intertidal pH sensors placed by the Ocean Margin Ecosystems Group for Acidification Studies (OMEGAS) in Oregon and California show how varied and dynamic seawater pH is along the west coast. This variation could be the source of differential selection pressures in intertidal habitats.

Chapter 1: Dogwhelk prey selectivity and pH in the field
I went to eight sites along the west coast of the US and recorded what mussels the dogwhelks were eating by looking for the mussels with a characteristic borehole. Among the populations, I found differences in dogwhelks' preferences for California mussels, which seemed to be roughly linked to seawater acidity.

Chapter 2: Dogwhelk drilling may depend on pH and origin
I also tested how well dogwhelks from different populations drill in acidic seawater. I thought that greater acidity could either impede drilling ability by negatively affecting their neurology such as chemoreception, or enhance drilling by creating a more favorable environment for the dissolution of the shells of their prey. I also hypothesized that dogwhelks from sites with lower average pH would drill larger mussels than other populations. My results showed that seawater acidity had no effect on what the dogwhelks drilled, and while there were differences among populations, it didn't correspond well with seawater acidity at their home site. These little dogwhelks seem to be very resistant to changes in seawater chemistry!

Chapter 3: Drilling variation and the mussel bed community
Finally, I am interested in how trait differences among populations can act broadly and affect the whole mussel bed community. In this system, I'm studying how dogwhelks drilling different sizes of mussels affect the mussel bed structure. I'm currently conducting a field experiment in the mussel beds outside the UCSC Coastal Science Campus with different populations of dogwhelks on replicate mussel beds. In nine months I will record how much dogwhelks from each population ate, what sizes of mussels they ate, and what remains living in the mussel bed. Since dogwhelks also use mussels as habitat, I am excited to see how their predation affects the place they live.

Research about intraspecific variation in intertidal predators is important because it will tell us about the potential of marine species to evolve to environmental changes, such as climate change, and the effects this rapid evolution can have on communities.

Nucella radula under ~100x magnification. The upper left end is the posterior end, 
which is cut. Not bad for a cell phone camera-through-compound microscope shot!


Former research system and ideas

If you are interested, this is what I was originally proposing to study.

Here is a conglomeration of keywords where larger words are more important in my research (it's called a wordle).

I am developing a project to examine contemporary trait change in an important harvested fish species, the California sheephead (Semicossyphus pulcher). This long-lived fish lives in kelp forests along the southern California coast south to Baja California, Mexico. Size-selective fisheries have decreased the average size of the sheephead, and smaller sheephead are less effective at eating sea urchins (Strongylocentrotus spp). Since sea urchins are a major kelp herbivore, decreasing sheephead sizes could lead to greater urchin abundance which could lead to lower giant kelp (Macrocystis pyrifera) biomass. Giant kelp is extremely important for habitat since many organisms rely on it for growth and development. My research will examine how fisheries have changed the traits of sheephead across its range and how these trait changes affect urchin and kelp abundances.

Fig 5. A california sheephead (Semicossyphus pulcher) approaching a 
sea urchin. Perhaps the fish will devour the urchin. Perhaps 
the fish will pass up the urchin and continue on its merry way.
Photo credit: Mark Conlin

There are two major types of sheephead fisheries in southern California, and they have different effects on sheephead populations. The commercial fishery targets intermediate-sized sheephead and can take them in very large quantities, while the recreational fishery strongly targets only the largest sheephead, and potentially fewer of them. The result is that populations of sheephead have had different treatments: (a) significant size reduction while density remains relatively normal and (b) significant density reduction while size structure remains relatively normal. My goal is to identify populations with each "treatment" and survey those populations and the associated habitat. I would then determine what effects reducing sheephead sizes and reducing density have separately on sheephead, urchins, and giant kelp. And, thanks to the excellent MPA system in California, there are plenty of populations that are not directly affected by fishing which can serve as control groups (Fig 1).

Eventually, I want to create a model to help policy makers understand the ecosystem effects of the sheephead fishery. In the model you could input values for fishing selectivity and intensity and find out what the ecosystem effect might be. For example, with the model you could answer a question like: If there are only really selective fishers taking all the biggest fish (say, over 2 feet long), how many fish could they take before we start seeing an increase in urchin populations? or How many fish could they take before we start seeing a decrease in giant kelp?

Fig 6. Hypotheses of effects of fishing on the sheephead-urchin-kelp trophic cascade. Sport fishing selectively removes largest fish but leaves many small that feed on very few urchins, greatly reducing kelp biomass (left column). Commercial fishing is highly intense but leaves largest fish that eat urchins, so urchin grazing only somewhat reduces kelp biomass (middle column).  Where both fisheries are present, sheephead body size and density are reduced, resulting in many urchins and no kelp (right column). 

No comments: