Larval euphausiids collected using a 1 x 1 m square frame net with 333-μm mesh aboard Palmer LTER annual cruises off the coast of the Western Antarctic Peninsula, 1993-2013

Euphausiids (krill) are abundant along the Western Antarctic Peninsula where they have important impacts on the marine ecosystem and biogeochemical cycling. Euphausiids develop through a series of morphologically distinct larval stages within the first year of their life cycle. The calyptopis stages are followed by the furcilia stages before individuals recruit to the post-larval population. Larvae collected during Janury were most likely spawned during the preceding weeks or months of Antarctic spring/summer. Euphausia superba and Thysanoessa macrura are the most abundant euphausiid species along the Western Antarctic Peninsula. Euphausia crystallorophias, Euphausia frigida, and Euphausia triacantha are present but less abundant in the region. Samples were collected with a 1 x 1 m square frame net with 333-μm mesh towed obliquely to a depth of typically 300 m. Density of total calyptopis and furcilia larvae (all species combined) was determined for a subset of samples collected on the annual Palmer LTER cruises to cover the latitudinal and cross-shelf gradients of the study region. Larval euphausiid abundance varies spatially as spawning output is not homogeneous across the region. Larval euphausiid abundance also varies year-to-year due to changes in population demographics and environmental conditions.