student listing

A Photo of  Leah Sloan

Contact Information

Grad student office 1, Rae Building
University of Alaska Fairbanks
Seward Marine Center
P.O. Box 730
201 Railway Ave.
Seward, AK 99664-0730
Phone: (907) 224-4321

Leah SloanPh.D. Student

Marine Biology

Thesis Title

King crab biology and sustainability: From inter-annual distribution patterns to a parasitic castrator


  • The Crustacean Society
  • American Fisheries Society AK chapter
  • American Society of Parasitologists


  • invertebrate zoology, larval biology, crustacean biology, crustacean fisheries, marine ecology, parasitology, herpetology


  • B.S. 2009 California State University - Long Beach (Biology)
  • M.S. 2012 Humboldt State University (Biology)

Research Overview

As large bodied crustaceans, king crabs play an integral role in both the marine ecosystem and Alaskan fisheries. They influence benthic community structure through predation effects, help regulate trophic cascades, and are an important food source for large mammals, including humans. King crabs support one of the most valuable shellfish fisheries in Alaska. Thus, sustainable management of Alaskan king crabs benefits large commercial operations, but also smaller coastal Alaskan communities. I am interested in multiple factors that influence sustainability of the Alaskan king crab fisheries. I primarily focus on a king crab parasite that has the potential to reduce king crab biomass. I also look at the value of skippers’ logbooks for understanding inter-annual changes in crab distributions with temperature.

Current Research Projects

  • Environmental effects on Briarosaccus regalis larvae ( NSF-IGERT: MESAS (no. DGE- 0801720))
    Parasites can represent a significant stressor in crustacean populations, and render previously healthy stocks unable to recover from fishing pressures. Rhizocephalan barnacles in the genus Briarosaccus parasitize and castrate king crab hosts, thereby preventing host reproduction and potentially altering host abundance. Once infected the crabs are transformed into “zombie crabs”. In other words, the parasite does not kill its crab host, but reduces it to no more than a body that is controlled by the parasite. Infected crabs can no longer reproduce; instead they raise and care for the eggs and larvae of the parasite. Rhizocephalan barnacles do not look anything like their relatives that live on rocks and sides of ships. Instead these parasites live inside crabs and their bodies consist of branching green strings (interna)(see photo below). The parasite’s egg sac (externa) is located under the abdomen (see photo) of the host and takes the place of the host’s own egg mass. Prevalence and distribution of Briarosaccus regalis is poorly understood. Most records indicate a low level prevalence (< 1% of crabs infected) throughout Alaskan king crab populations. However, outbreaks have occurred where over 75% of king crabs were infected. Outbreaks at this level will greatly reduce reproductive output in king crab populations and likely lead to population declines. Causes of variability in B. regalis prevalence have not been identified. To better understand how environmental factors in Alaska may influence Briarosaccus prevalence, we studied the effects of temperature and salinity on the larvae of B. regalis. Nauplius larvae were reared at 7 temperatures (2 to 16 C) and 8 salinities (19 to 40) to determine larval survival and development rates. Maximum survival occurred from 4 to 12 C and at salinities between 25 and 34. In the Gulf of Alaska and Bering Sea, ocean temperatures and salinities are often within these ranges; thus current conditions appear favorable for high B. regalis larval survival. In addition, temperature was negatively correlated with larval development time; thus warmer waters can reduce the time larvae are exposed to the dangers of the planktonic environment.
  • Changes in metabolites with a parasitic infection (NPRB Graduate Student Research Award)
    Parasitic barnacles can influence the behavior and morphology of host crabs to favor the production of their own larvae. For example, infected crabs will groom the parasite’s externa as if it was their own egg sac, and pump their abdomens to assist with parasite larval release. In addition, many rhizocephalan species cause feminization of male crabs. Despite the physiological, morphological, and behavioral changes these parasites cause in the host, no one has ever determined how the parasite “takes control” of its host and manipulates its behavior. To manage the detrimental effects of B. regalis on king crab fisheries and the people who depend on them, we need to understand how these parasites are gaining control of their hosts and the susceptibility of host populations. Metabolomics is a newly emerging technique that allows for the simultaneous measurement of hundreds of metabolites. Metabolites are low molecular weight molecules (e.g., hormones), which respond quickly to changes within the body. As a result of this rapid response, metabolomics is a useful technique to identify how a body reacts to foreign substances, such as toxins, pharmaceuticals, or disease. I am comparing the metabolite profiles of infected and non-infected king crabs to determine how B. regalis changes the physiology of its host. Hormones that differ will help elucidate how the parasite controls, castrates, and feminizes its host. Metabolomics will also help identify if there is an immune response from the host crabs.
  • King crab distributions from fishery log books (Bering Sea Fisheries Research Foundation)
    Spatial distribution of fisheries species must be well characterized to avoid local depletions, identify critical habitat, and predict interactions with other fisheries. The Bristol Bay red king crab fishery is one of the largest crab fisheries in the state of Alaska. Its summer distribution has been well documented over decades of trawl surveys. However, king crab are a highly mobile species, with both seasonal and inter-annual changes in distribution. Crab movement and distribution are poorly understood outside the summer survey period, which creates many management challenges. One important component of Bristol Bay red king crab management is the existence of no-trawl zones, which protect crab from trawl fisheries. However, it is difficult to evaluate the placement of no-trawl zones, since most crab bycatch occurs in winter trawl fisheries when crab distributions are not known. Daily fishing logs, kept by skippers in the king crab fleet since 2005, contain detailed information on the spatial distribution of catch and effort of legal sized male king crab during the autumn crab fishery. However, the data within these hand-written logbooks has not been readily accessible. We digitized daily fishing logs from 2005 - 2016 and used spatial information on catch and effort to infer distributions of legal sized male king crab. Changes in distribution were tracked across this twelve year period and comparisons were made between warm and cold temperature regimes. In warm years, crab aggregated in the center of Bristol Bay, while in cold years they were closer to the Alaska Peninsula. The majority of crab were caught within no-trawl areas, but variations occurred among years and with temperature regime. As temperatures continue to shift in the Bering Sea, it will be important to continue monitoring crab distributions outside the summer survey period.


Sloan, L.M. and S.M. Hardy. 2017. Larval biology and environmental tolerances of the king crab parasite Briarosaccus regalis. Journal of Parasitology 103(1): 22-31.

Sloan, L.M. 2012. Population structure, life history and terrestrial movements of Western Pond Turtles (Actinemys marmorata) in lentic habitats along the Trinity River, California. Thesis, Humboldt State University, California, USA.

Sloan, L.M, S.V. Anderson, and B. Pernet. 2010. Kilometer-scale spatial variation in prevalence of the rhizocephalan, Lernaeodiscus porcellanae on the porcelain crab Petrolisthes cabrilloi. Journal of Crustacean Biology 30(2): 159-166.