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

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

Economic Importance of Horseshoe Crabs Today Biomedical Bait Ecotourism

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

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

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

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

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

Bob Loveland - summer 1957 Mark Botton – summer 1977

Landings (Thousands) Feeding ecology

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

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

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

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)

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

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

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)

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: 550-562

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

Horseshoe crabs finally have some respect!

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

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

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

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

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

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: 175-184

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

Within the mosaic of intertidal and subtidal benthic habitats in the estuary, which (if any) are critical for juvenile HSC’s? http://www.swc.dnrec.delaware.gov/coastal/DNERR/Documents/Benthic4pLet.pdf

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

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

http://tidesandcurrents. noaa. gov/sltrends/sltrends_station. shtml http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8557380

http://tidesandcurrents. noaa. gov/sltrends/sltrends_station. shtml http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8534720

East Point, NJ Overwash Study Area 1930s

East Point, NJ Overwash Beach Site 2010

Overwash beaches and tidal creeks

Summary: Major Accomplishments Fishery management and standardized survey methodologies

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

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

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)

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

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?

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

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

Thanks for your attention!