1. Reflections on Five Decades of Horseshoe Crab Science in Delaware Bay:
What We Have Learned, and Suggestions for Further Research
Mark L. Botton & Robert E. Loveland Delaware Estuary Science & Environmental Summit, 2011

2. The economic importance of HSC’s in the Delaware Bay area began in the 19th century

3. Economic Importance of Horseshoe Crabs Today
Biomedical Bait Ecotourism

4. HSC research had a modest start…
Hemocyanin
Monographs on anatomy
Source: Google Scholar

5. Dr. Carl N. Shuster, Jr.
First “modern” ecological study of HSC’s in Delaware Bay (late 1940’s to early 1950’s)

6. Development of Limulus amoebocyte lysate test
Levin and Bang – 1964
Licensing of LAL testing by FDA as alternative to rabbit testing for the detection of bacterial endotoxin – 1977

7. Exponential growth? Source: Google Scholar LAL Vision, agglutination
Hartline
Source: Google Scholar

8. We began our studies of horseshoe crabs before the recent increase in the horseshoe crab bait fishery

9. Bob Loveland - summer 1957
Mark Botton – summer 1977

10. Landings (Thousands)
Feeding ecology

11. Landings (Thousands) Feeding ecology
Mating, stranding, habitat quality

12. Landings (Thousands) Feeding ecology Egg abundance, shorebirds
Mating, stranding, habitat quality

13. Changing landscape in 1980’s and 1990’s
Dramatic increase in fishing intensity
Recognition of the importance of Delaware Bay HSC’s for migratory shorebirds

14. Principal accomplishments since the 1970’s
Implementation of the Atlantic States Marine Fisheries Commission (ASMFC) coast-wide management plan
Initiation of more rigorous population estimates in Delaware Bay and adjacent coastal waters through the use of improved beach spawning surveys, offshore trawls, and mark-recapture studies (D. R. Smith, J. Berkson, etc.)
Establishment of Carl N. Shuster Horseshoe Crab Reserve off the mouth of Delaware Bay (2000)

15. HSC landings have stabilized in the past decade (source: ASMFC)

16. Confirmation of the importance of HSC eggs to shorebirds and development of models linking bird populations to egg density

17. Better understanding of the reproductive biology of Limulus, esp
Better understanding of the reproductive biology of Limulus, esp. roles of body size and condition in mating success
Note rare “size reversal” (M>F)

18. Understanding effects of pollutants and environmental factors (e. g
Understanding effects of pollutants and environmental factors (e.g. temperature, salinity, DO) on the survival of the embryos and larvae
Botton, Tankersley & Loveland (2010) Curr. Zool. 56:

19. Among horseshoe crab and shorebird researchers, there is now worldwide recognition of the global importance of Delaware Bay
International Symposium on the Science & Conservation of Horseshoe Crabs – June, 2007
Hong Kong Workshop on Asian Horseshoe Crabs – June, 2011

20. Horseshoe crabs finally have some respect!

21. Moving forward, what are the big gaps in our knowledge?

22. We lack essential information about HSC’s between the early juveniles and sexual maturity – a gap of ~ 10 yr

23. What are the ecological factors that affect the survivorship of particular year-classes?

24. close to 90% survival of fertilized eggs to trilobites in beach

25. close to 90% survival of fertilized eggs to trilobites in beach
~ 98% mortality in plankton/early post-settlement phases

26. close to 90% survival of fertilized eggs to trilobites in beach
~ 98% mortality in plankton/early post-settlement phases
~ 90% mortality with each molt in 1st year
Botton, Loveland & Tiwari (2003) MEPS 265:

27. ? Where are the juveniles?
Basic ecological questions (feeding, predation)?

28. Within the mosaic of intertidal and subtidal benthic habitats in the estuary, which (if any) are critical for juvenile HSC’s?

29. Small juveniles have been assumed to use intertidal sand flats
Suction dredge sampling by Burton has found much higher densities of subtidal juvenile crabs in Delaware Bay than previously recognized
Photo credit: W. Burton

30. Horseshoe Crabs and Sea Level Rise
Initial studies concentrated on pristine sandy beaches
With concerns about rising sea level and coastal development, more attention needs to be devoted to marginal, disturbed and restored beaches

31. http://tidesandcurrents. noaa. gov/sltrends/sltrends_station. shtml

32. http://tidesandcurrents. noaa. gov/sltrends/sltrends_station. shtml

33. East Point, NJ Overwash Study Area 1930s

34. East Point, NJ Overwash Beach Site 2010

35. Overwash beaches and tidal creeks

36. Summary: Major Accomplishments
Fishery management and standardized survey methodologies

37. Summary: Major Accomplishments
Fishery management and standardized survey methodologies
Better understanding of the shorebird – horseshoe crab relationship

38. Summary: Major Accomplishments
Fishery management and standardized survey methodologies
Better understanding of the shorebird – horseshoe crab relationship
Influences of habitat and water quality on horseshoe crab spawning and development

39. Summary: Major Accomplishments
Fishery management and standardized survey methodologies
Better understanding of the shorebird – horseshoe crab relationship
Influences of habitat and water quality on horseshoe crab spawning and development
Some aspects of basic horseshoe crab biology are much better known (e.g. mating behavior, larval and early juveniles)

40. Recommendations – Future Research
Life history of juvenile horseshoe crabs
What happens during the 10-year interval between eggs and adults remains poorly understood

41. Recommendations – Future Research
Life history of juvenile horseshoe crabs
What happens during the 10-year interval between eggs and adults remains poorly understood
Are recruits to the adult population (fishery) some constant proportion of the number of eggs (spawners), or is the adult population sustained by occasional strong year-classes?

42. Recommendations – Future Research
Horseshoe crabs and sea level rise
Given the ongoing erosion of the Delaware Bay shoreline (linked in part to global sea level rise), we see further studies of the ecological importance of eroding and artificially stabilized beaches on the NJ and DE side of the bay as an essential research priority

43. Resilient animals!
Photo credit: Rudkin & Young (2009)

44. Thanks for your attention!