Background Info on Grace's Research

Reading Update

Spent most of the last few weeks diving into the reading, thought I’d document some of the main questions that’ve arisen! Since there’s plenty of lit I haven’t had the chance to cover, there’s a good chance that these questions have been answered. Just putting them down here to document and highlight for further investigation!

Questions to Research

miRNA in Infected Crab M. Li et al. (2018) looked at differential expression of microRNAs in hematodinium-infected Portunus trituberculatus (Chinese swimming crab). They found that miRNAs were involved in several important pathways. Could repeat this experiment with infected Tanner crab.

  • Upside: Since we have lots of samples in -80, might be easy to investigate
  • Downside: Knowledge gain would be quite specific

Accuracy of Visual Inspections Analysis of accuracy for visual inspections of Hematodinium infection in Bering Sea snow crab. Could get samples from snow crab that visually have BCD and don’t, compare true infection rates.

  • Upside: Methodology already established, could be important for management
  • Downside: Has already been examined in SE Alaska Tanner crab (albeit 10-15 years ago)

Do We See Parasite Exclusion? Covariance of Bitter Crab Disease with torch/miscellaneous other diseases. Since some studies have found that Hematodinium infection can exclude other diseases, it’d be interesting to see if this has been observed in the Bering Sea survey data

  • Upside: Tons and tons of data already available, could be quick analysis
  • Downside: Data may not be too accurate, partially due to how surveys work, partially due to inherent inaccuracy in visual examinations for BCD

Hematodinium in Southcentral Alaska Hematodinium is extremely common in SE Alaska, and growing in prevalence in the Bering Sea. However, to my knowledge, it’s either not present or at extremely low levels in Kodiak. When working as a dockside sampler for the Kodiak Island commercial Tanner crab fishery, I looked at thousands and thousands of harvested Tanner crab, and don’t recall ever seeing one with BCD. This could be due to the fishermen throwing out infected crab, but papers indicate that in SE AK, infected crabs are sorted out at the dock (which makes sense - light levels are much better, and time is less precious than it is for fishermen, plus fishermen have an incentive to include as many crabs as possible in the catch).

  • I found a 1996 report that described a hematodinium prevalence of 3.5% in Kodiak Tanner crab, indicating they’ve historically been present
  • However, I also found a ADF&G news release from 2011 warning that Hematodinium had been detected in Deadman Bay (an inlet on the south end of Kodiak), with an infection rate of 0.25%. If such an extremely low level is worthy of a warning, this indicates that Hematodinium is much less common in the waters of Kodiak Island.
  • Investigating this presumed anomaly in distribution w*ould be quite interesting!

Miscellaneous Thoughts

  • Different fjords in SE Alaska have reliably different infection rates, which makes me think that hematodinium likely infects locally. Maybe through a short planktonic stage or a patchily-distributed intermediate host?

  • Butler et al (2014) found that Hematodinium infection increases predation rates in blue crab, even before any changes in energy (i.e. no lethargy) were seen. To me, this raises the question of behavior modification.
  • If Tanner crabs are actually the intermediate host, then Hematodinium could be modifying their behavior to increase the predation rate and get them to the next host
  • Alternatively, behavior modification could be targeted at increasing pathogen output, like we see in rhizocephalan-infected crabs, and that behavior modification just happens to make them more prone to predation (for instance, “don’t burrow, stay out in the open so spores get caught in the current”)
  • Alternatively, Hematodinium infection might just mess with their response, and any behavior modification is just a side effect
Written on October 11, 2020