Declines in spider abundance and diversity at inland and coastal sites

Many taxa show alarming declines in diversity and abundance. Although charismatic megafauna and plants are the primary focus of such studies, a growing body of research documents drastic changes among terrestrial arthropods. These latter studies emphasize insects. We examined changes in spider abundance and diversity at two sites in New Jersey, USA, for which historic data were available: Hutcheson Memorial Forest (HMF - inland area of mixed field and forest) and Great Bay Boulevard Wildlife Management Area (GBB - coastal salt marsh). Survey methods used in 2019 mirrored those of the original 1985 (GGB) and 1993 (HMF) studies.

At both sites, spider abundance had declined significantly by 2019: spider densities at GBB were 3-to-7-fold lower in 2019; at HMF, total spider abundance was 4-fold lower in 2019. Family-level diversity also declined at the two sites. Only 9 of the 12 families present at GBB in 1985 were found in 2019 (25% loss). HMF experienced a 26% decrease, dropping from 19 to 14 families. Due to the protected nature of the two sites, the observed declines in spider abundance and diversity are likely to be direct or indirect results of regional climate change, rather than consequences of land use changes. An absence of female lycosids carrying egg sacs and spiderlings in the 2019 HMF samples suggests a possible phenological shift in the timing of reproduction in some members of this group, with eggs now being produced in June (or earlier), rather than in July as in the past.