Fecundity and spawning of the Atlantic horseshoe crab,Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, USA

Abstract

This study provided the first comprehensive analysis of Atlantic horseshoe crab (Limulus polyphemus) fecundity. Limulus appear to be a determinate spawner, maturing all eggs for the breeding season before spawning begins. On average, larger females held a larger number of eggs (63,500) than smaller females (14,500). By the end of the breeding season there was an average of 11,600 mature eggs per female left undeposited, regardless of female size. Larger females laid a higher percentage of the eggs they contained. Thus they not only contain more eggs, but are more effective at laying them as well. Size of spawning females ranged from about 185–300 mm prosomal width, with by far the highest concentration in the mid‐size ranges. Although on an individual basis large females carry and lay the greatest number of eggs, mid‐size crabs as a group contributed more to the horseshoe crab population in Pleasant Bay because they were more plentiful (net fecundity was highest for mid‐size crabs). These results have implications for the management of this important species, which is harvested for bait, scientific, and biomedical uses. Incorporation of these results into models and other management tools can help predict growth rates, effects of size‐selective harvest, reproductive value, and stable stage distribution of populations.

Conservation status of the American horseshoe crab, (Limulus polyphemus): a regional assessment

“…Some observations suggest that horseshoe crabs prefer to spawn around the time of the new and full moon high tides, which are the highest tides of the month (Rudloe 1980;Brockmann 2003b;Barlow et al 1986;Brockmann and Johnson 2011;Smith et al 2002b, Chabot et al 2008Watson and Chabot 2010). However, other studies have reported that the association between spawning activity and the lunar period is not strong or only slightly higher than expected by chance alone Cheng et al 2016) and that spawning occurs at a similar intensity during all daytime high tides regardless of lunar phase (James-Pirri et al 2005;Leschen et al 2006). In some areas horseshoe crabs seem to prefer the higher of the two daily tides regardless of light:dark cycle (Barlow et al 1986;Rudloe 1980;Chabot and Watson 2010;Brockmann and Johnson 2011).…”

“…Shuster (1982) reported 88,000 eggs per female for the Delaware Bay. Average fecundity was correlated with female size in Pleasant, Bay Massachusetts with fecundity ranging from 14,500 eggs for a 201 mm prosomal width (PW) female to 63,500 eggs for females [261 mm PW (Leschen et al 2006). Males externally fertilize the eggs as the female deposits them.…”

“…In Florida, cluster size was reported to be 1644 ± 103 for singly mated females and 1739 ± 93 for females with satellites (Johnson and Brockmann 2010) rising to 2365-5836 eggs/cluster in Delaware Bay (Shuster and Botton 1985;Weber and Carter 2009). In Long Island Sound, cluster size averages 3741 eggs (Beekey et al 2013) compared to 640-1280 in Cape Cod (Leschen et al 2006). Cluster size is not correlated with female size (Brockmann 1996;Leschen et al 2006), but larger females lay more clusters per spawning season than smaller females.…”

“…In Long Island Sound, cluster size averages 3741 eggs (Beekey et al 2013) compared to 640-1280 in Cape Cod (Leschen et al 2006). Cluster size is not correlated with female size (Brockmann 1996;Leschen et al 2006), but larger females lay more clusters per spawning season than smaller females. Females typically lay multiple nests during one tidal cycle (5 days of extra-high tides around the new or full moon) (Brockmann and Penn 1992;Brousseau et al 2004;Smith et al 2010;Beekey and Mattei 2015).…”

“…On spawning beaches, females excavate a pit below their body and deposit two to five separate clusters of eggs at depths from 5 to 20 cm (Rudloe 1979;Brockmann 1990;Leschen et al 2006;Brockmann 2003b). Horseshoe crab fecundity varies with latitude and with female size (Botton et al 2010).…”