Critical Horseshoe Crab Habitats in the Great Bay Estuary

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Winsor Watson UNH - Department of Biological Sciences Principal Investigator

Students Involved:

Kyle Harris UNH - Department of Biological Sciences
Alicia Franklin UNH - Department of Biological Sciences
Helen Cheng UNH - Department of Biological Sciences
Goals and Objectives
The main objective of this proposal is to identify the critical habitats used by horseshoe crabs in the Great Bay estuary, throughout all their life history stages. We will achieve this objective by: 1) Conducting visual surveys of spawning horseshoe crabs during the height of their spawning season; 2) Performing tag/ recapture studies at these spawning beaches to estimate the size of the adult horseshoe crab population in the estuary; 3) Identifying areas where juveniles horseshoe crabs reside, to test the hypothesis that the areas near mating beaches serve as important nursery habitats for juveniles and; 4) Conducting laboratory studies to determine if horseshoe crabs use olfactory cues to locate mating beaches. The research we are proposing to conduct will be the first step towards completing a comprehensive study of essential habitats for multiple stages of a horseshoe crab’s life history in the Great Bay estuary.  
A secondary goal of this project is to integrate the Great Bay estuary into the larger New England and Atlantic Coast Annual Limulus Survey. We plan to use existing information from UNH scientists and N.H. Fish and Game, along with the new survey we will conduct, to identify the locations within the Great Bay estuary where the majority of horseshoe crabs spawn. We will use this information to organize and develop a monitoring program that is consistent in scope and methods with the surveys currently being conducted in other states.
The third major goal of this proposal is to develop the tools necessary for a more comprehensive study on this subject and to demonstrate that these approaches are suitable for addressing these questions. This will help us write more effective full proposals to Sea Grant and NSF in the future. In particular, based on the feedback we received from a previous Sea Grant full proposal, we aim to demonstrate that: 1) In N.H. horseshoe crabs spawn as often during the day as at night, and therefore aerial surveys, using radio-controlled planes equipped with video cameras, could be an effective technique for identifying spawning beaches and quantifying spawning activity; 2) Custom designed suction sampling devices are an effective tool for quantifying the abundance of juvenile Limulus; 3) Tag-recapture methods can be used to estimate the size of the Limulus population in the Great Bay estuary and; 4) Behavioral assays are effective for determining some of the cues that horseshoe crabs use to identify suitable spawning beaches. We believe that if we are able to demonstrate the feasibility of our methods, reviewers will be much more inclined to recommend funding of future proposals.
The final goal of this project is to provide support for a portion of Helen Cheng’s MS research. We expect that during the first year of the project she will both prove the feasibility of some approaches and obtain some useful data. This will also help her obtain additional funding to support her second year of study. In fact, Helen has already submitted a proposal for a NEERS Fellowship and the goals of this proposal and that submission overlap.

Resulting Publications
Watson, W., S. Johnson, C. Whitworth and C. Chabot (2016). Rhythms of locomotion and seasonal changes in activity expressed by horseshoe crabs in their natural habitat. Marine Ecology Progress Series 542:109-121, January 2016.

Cheng, H., C. Chabot and W. Watson. 2015. Influence of environmental factors on spawning of the American horseshoe crab (Limulus polyphemus) in the Great Bay Estuary, New Hamsphire USA. Estuaries and Coasts. Online November 2015.

Cheng, H., C. Chabot and W. Watson. 2015. The life history cycle of Limulus polyphemus in the Great Bay Estuary, New Hampshire, U.S.A. In R.H. Carmichael, M.L. Botton, P.K.S. Shin and S.G. Cheung (Eds.), Changing global perspectives on horseshoe crab biology, conservation and management (pp. 237-253). New York, N.Y.: Springer. NHU-BR-15-001

Horseshoe crabs in Great Bay (2014). Helen Cheng. NHU-G-14-010

2014 Accomplishment

N.H. Sea Grant publications provide overview of horseshoe crab biology and research in Great Bay
N.H. Sea Grant produced a pamphlet and information sheet in 2014 that provide an overview of horseshoe crab biology in Great Bay and research, some of which was funded by NHSG, that has been conducted on the species in the region. Horseshoe crabs are a charismatic species that generates a lot of public interest in the Great Bay ecosystem. The publications offer the same information in two different formats: the pamphlet for hardcopy distribution in science centers around the Seacoast and the information sheet for people who access the publication digitally and want to print it out themselves. These publications help to educate the public about horseshoe crabs and the importance of conducting research relating to their populations and biology.

2012 Accomplishments

Horseshoe Crab Spawning Surveys Offer More Comprehensive Estimate for Great Bay Populations
The horseshoe crabs of Great Bay have the potential to be a good sentinel species in the estuary, providing an index of impacts such as climate change and oil spills. While intermittent efforts have been made to monitor the horseshoe crab populations in the estuary, little is known about the size of the resident population, their spatial distribution, spawning areas and characteristics of the habitats where juveniles reside. Using NHSG development funds, researchers initiated horseshoe crab spawning surveys in the estuary and counted more than 2,000 crabs in three major spawning areas during the summer of 2012. These surveys involved coordinated volunteer efforts that far surpassed previous monitoring by local natural resource agencies. Results from these studies provide a better understanding of horseshoe crab populations in Great Bay, which will improve the ability of scientists to detect the impacts of perturbations caused by natural events and human interventions in the estuary.

Scuba Surveys Confirm First Sightings of Juvenile Horseshoe Crabs in Great Bay
Although intermittent efforts have been made to monitor horseshoe crab populations in Great Bay, relatively little is known about them and their use of specific habitats at various life stages in the estuary. Using Scuba dive surveys in 2012, NHSG-funded researchers found juvenile horseshoe crabs throughout Great Bay. They captured, measured and released 63 juveniles ranging in size from 30 mm – 100 mm. These are the first confirmed sightings of juvenile horseshoe crabs in the estuary. This information will augment a comprehensive study of the essential habitats for multiple life stages of horseshoe crabs in Great Bay, allowing resource managers and scientists to more accurately monitor this species in the estuary.

Tag-recapture Program Provides More Accurate Population Estimates for Horseshoe Crabs in Great Bay
Horseshoe crab populations have been in decline in areas along the Atlantic Coast in recent years. Effective management of horseshoe crabs depends in part on accurate information about their local populations. NHSG-funded researchers initiated a tag-recapture program for horseshoe crabs in Great Bay during 2012, a first-of-its-kind effort for this species in the estuary. In its first year, over 200 horseshoe crabs were caught and tagged, with 30 recaptured in the same season (~14% recapture rate). These results, combined with data from future recapture efforts, will allow scientists and resource managers to more accurately estimate the size of the horseshoe crab population in Great Bay.

Researchers Use Remote Controlled Planes to Conduct Aerial Spawning Surveys
Using NHSG development funds, researchers equipped remote controlled planes with video cameras in order to conduct aerial horseshoe crab spawning surveys over the Great Bay Estuary. This technique allowed researchers to conduct surveys quickly and more extensively than in person, providing scientists and resource managers with detailed information for improved monitoring of their populations.