Dr. Catherine deRivera - Research Overview
I study the ecology and behavior of intertidal and nearshore marine and estuarine animals. My main research interests include the limits to and consequences of biological invasions and how ecological factors affect mating behaviors and reproductive success. I also am interested in the intersection between behavior and invasions. For example, I plan to test whether successful non-native species are more behaviorally plastic than their less successful counterparts or native species. My research projects, discussed below, can be further developed in multiple ways , and aspects of each are ideal for local research with students.
Ecology of marine invasive species
Biotic resistance - range limits and habitat use
Non-native species that have invaded multiple regions provide a natural experiment for studying which factors affect local and geographic distributions. Taking advantage of this natural experiment, I am investigating the role of biotic resistance in determining the range and habitat use of an invasive species. On the east coast I found that predation by blue crabs, Callinectes sapidus , reduced the abundance of the invasive green crab, Carcinus maenas , in the southern part of its range where blue crabs are common. These crabs had reciprocal abundances across latitudes and within a bay; Carcinus used higher intertidal zones when blue crabs were locally abundant; the few Carcinus that lived among blue crabs had a much higher incidence of injury; and tethered Carcinus and ones in aquaria and enclosures were eaten by blue crabs (deRivera et al, in review). I am now examining biotic resistance to Carcinus on the west coast.
To understand the relative importance of biotic factors, I am identifying the extent to which environmental factors limit Carcinus's distribution. Laboratory experiments suggest Carcinus larvae could develop in short warm seasons and so, without biotic resistance, could spread further north (deRivera et al, in prep). I am comparing multiple environmental factors in Carcinus's native and recipient areas, using GARP, to obtain a second estimate of Carcinus's potential range. Finally, an enclosure experiment at several latitudes will examine survivorship of adults free from predation.
Long-term impacts of invasive species
Another important question for invasions biology is whether an invasive species can have long-term repercussions to native species or communities. My recent analysis of Ted Grosholz's long-term data in Bodega Harbor starts to answer this key question (Grosholz, deRivera, & Ruiz, in review). Carcinus preys on the native intertidal crab Hemigrapsus oregonensis and decreases its abundance. Carcinus abundance has declined since 1998, and Hemigrapsus abundance has rebounded to pre-invasion levels. However, three other measures are lagging behind this numerical recovery, showing potential long-term consequences of the Carcinus invasion. Hemigrapsus median size decreased by one third; female abundance decreased eightfold; and a much higher proportion of Hemigrapsus (18.5 times more) have shifted to our highest intertidal transect, and this shift is not solely an artifact of small crabs using higher areas. I will build upon this analysis by experimentally examining the consequences and direct causes of these shifts. I will investigate whether Hemigrapsus reproductive output is significantly lower in Bodega Harbor than in populations to the north and south that have not been impacted by Carcinus . I will also determine whether Carcinus preferentially prey upon females and cause behavioral or habitat shifts.
Diversity and invasion patterns of fouling and nearshore crab communities
Identifying broad patterns of marine invasions remains a priority for researchers of non-indigenous species. I am coordinating a joint effort among the National Estuarine Research Reserves, the National Marine Sanctuaries, and the Smithsonian, testing hypotheses about spatial and temporal patterns of marine invasions along the west coast of North America. We are investigating whether non-native species are more common in bays than in more exposed habitats, whether the number of introduced species decreases with increasing latitude, and whether the percentage of introduced species increases with decreasing salinity from marine to estuarine waters. I have submitted grant proposals for future funding, and I will be writing several manuscripts on our findings. Greg Ruiz and I have developed additional research hypotheses that would expand on this body of research. For example, we will examine the relative importance of vector activity and disturbance on invasion processes. We will also use these data to characterize the structure and composition of sessile invertebrate communities at various spatial scales and to identify how these communities vary in space and time due to forcing functions such as climate change and invasions.
Ecology and reproductive strategies
Discussions of mating systems and sexual selection have largely overlooked questions about the role of ecological factors in determining which sex searches for mates, how long courtship persists, and variability of mate choice. I have started to tackle these original questions by investigating how and why density affects which sex searches, search length, and benefits from searching. I have conducted this work on fiddler crabs but will further investigate some of the central questions using other marine taxa.
My fiddler crab studies demonstrate that density and habitat influence many aspects of mating. Across species, males only searched for mates when they lived at low density on silt substrates and when females incubated eggs in their own burrows or on the surface (deRivera & Vehrencamp 2001, deRivera 2003a,b). Field experiments on a Panamanian crab supported these findings: females often searched for mates at high density while males searched more at low density (deRivera et al. 2003). Similarly, female California fiddler crabs selectively chose mates in high-density sandy sites where burrows were variable, but males searched in low-density silt areas (deRivera 2003a). At high-densities, females sampled many males, then selected mates near to their size that maintained long burrows with narrow openings (deRivera in press). I also found that search patterns and preferences varied with female size (deRivera in press). Large females sampled burrows at a faster rate and entered fewer burrows than smaller females. Large females selected large mates with long burrows.
My research also has identified an under-investigated direct benefit of resource selection. Searching female crabs incubated eggs in their mates' burrows, and burrow structure affected incubation time. Control pairs and pairs transferred to similar-sized burrows released larvae synchronously at maximum amplitude tides. In contrast, mated pairs that were transferred to wider burrows released larvae days before these optimal tides (deRivera in press). Release at maximum amplitude nocturnal tides increases larval survival in many fiddler crab species.
This research has inspired several future projects. I will examine whether density and risk affect the basic mating system --courtship persistence, number of mates, and average mate quality. In addition, I will investigate ecological causes and evolutionary consequences of variability in female mate choice, including how the degree of variability in selecting a mate changes with ecological conditions. I also have become interested in the reproductive physiology of burrowing organisms. I will study which cues initiate mate searching in fiddler crabs and how burrow structure affects incubation duration.
When 'in a pinch' won't do
Bay Science - Biologists on the hunt for invaders
Blue crabs in the bay find green invaders delicious
Green Crabs Coming To Maryland