Acute toxicity and sub-lethal effects of common pesticides in post-larval and juvenile blue crabs, Callinectes sapidus

Abstract

The coastal plains of the southeastern United States support extensive agricultural operations that apply pesticides and herbicides. The shallow tidal creeks and ditches that directly drain agricultural fields are home to the young of the ecologically and economically important blue crab, Callinectes sapidus (Rathbun, 1896). Massive mortality observed by peeler crab fishers led us to investigate the acute toxicity of several commercial pesticide formulations and their active ingredients to blue crab megalopae and J1–J4 stage juveniles. Twenty-four hour acute toxicity assays were conducted with the organophosphate acephate (Orthene®), the carbamate aldicarb, the chloro-nicotinyl imidacloprid (Trimax™), the pyrethroid lambda-cyhalothrin (Karate® with Zeon Technology), and the glyphosate-based herbicide Roundup® Pro. LC50 values ranged from 0.22μg/L for megalopae exposed to lambda-cyhalothrin to 316,000μg/L for juveniles exposed to Roundup. The acute toxicities of active ingredient insecticides to blue crabs followed the order: lambda-cyhalothrin>imidacloprid≈aldicarb>acephate. Megalopae were almost always more sensitive than juveniles and there was little difference between the LC50s of each commercial formulation and its active ingredient. Treatment of intermolt megalopae with LC20 levels of Roundup resulted in significantly reduced time to metamorphosis (TTM) compared to estuarine water controls, while no differences resulted from treatment with the four active ingredient insecticides. Treatment with acephate, aldicarb, imidacloprid, and Roundup significantly increased the frequency of juveniles that died within 6h of molting. The sensitivity of molting blue crabs to these pesticides makes frequently molting juveniles particularly vulnerable to pesticides in estuaries.