Modeling Potential Impacts of Beach Replenishment on Horseshoe Crab Nesting Habitat Suitability

Abstract

Beach replenishment has been proposed to increase nesting habitat for horseshoe crabs, but its environmental consequences may compromise the egg development and viability of this declining species. Horseshoe crab habitat requirements were used to build a habitat suitability model in STELLA to predict the potential impacts of beach replenishment on horseshoe crab eggs. A habitat suitability index (H.S.I.) comprised of six variables (dissolved oxygen, sediment grain size, sand temperature, sand moisture, wave energy, and salinity) was developed and compared between replenished and natural beaches. Sediment grain size and dissolved oxygen were higher in the natural beach, whereas sand temperature and moisture were higher in the replenished beach, resulting in significantly higher suitability of the natural beach (p = 5.39 × 10 −15 , df = 30). The model was most sensitive to air temperature, rainfall, tide, and sediment grain size. This model is useful for understanding the processes affecting horseshoe crabs and predicting impacts of coastal management activities on habitat suitability. Based on the results of this model, beach replenishment is not recommended for increasing or improving horseshoe crab habitat, unless care is taken to match fill sediment to natural grain size and color.

Spatial and temporal overlap between foraging shorebirds and spawning horseshoe crabs (Limulus polyphemus) in the Cape Romain-Santee Delta Region of the U.S. Atlantic coast

“…Sand grain size affects both the drainage and oxygen content of sand and subsequently has been found to affect where HSC lay their eggs (Anderson andShuster 2003, Smith et al 2011). Previous studies have found that the optimal sand grain size for development of HSC eggs is 350-500 lm (Smith et al 2002a, Avissar 2006), which are larger particle sizes than we observed in our study. We did not find that the difference in sand grain size among our plots affected the distribution of eggs among our plots, which may be partly attributed to sampling surface sediment instead of including sediment of deeper depths where eggs are originally deposited.…”

The first investigation record of threatened horseshoe crabs in the Banyuasin estuarine, South Sumatra, Indonesia

“…High salinity habitat was preferred by T. gigas on the contrary, C. rotundicauda prefers low salinity habitat (Jawahir et al, 2017). The sediment with medium grain size (sandy substratum) was preferred by T. gigas (Tan et al, 2012) due to suitable for their larvae survival (Jackson et al, 2005) while C. rotundicauda prefers muddy sediment (Avissar, 2006).…”

Mangrove horseshoe crab (Carcinoscorpius rotundicaudaLatreille, 1802) populations reveal genetic break in Strait of Malacca, with connectivity along southern coasts of Peninsular Malaysia

“…This could be explained by the fact that C. rotundicauda lays eggs in the sediment with a high clay–sand composition (Fairuz‐Fozi et al, 2018; Zauki et al, 2019a; Zauki et al, 2019b). The abundance of sand could help the substratum not only to retain moisture and supply oxygen for the development of the eggs (Avissar, 2006), but also make it easier for C. rotundicauda to dig holes and place their eggs at suitable depths. As Kuala Sepetang falls under the riverine mangrove category (Goessens et al, 2014), more than 80% of the sediment is dominated by silt and clay (Ariffin & Mustafa, 2013) that is unfavourable for the nesting activity of C. rotundicauda .…”