Zooplanktonic Crustacea and Ichthyoplankton of the Patagonian Shelf-Break Front

This chapter reviews information from the 1970s to the present day about zooplankton and ichthyoplankton occurring at the Patagonian shelf-break front (PSBF), aiming to establish a baseline of knowledge for both groups. Zooplankton information focuses on copepods, hyperiid amphipods, and euphausiids because of their abundance and relevance to the food web. General patterns of species diversity and biogeographic zonation of these zooplanktonic groups are described. Copepod diversity roughly increases northward, and the shelf-break front does not represent a sharp boundary between shelf and oceanic zooplankton species. Key species are defined, and data about their seasonal distribution, abundance, and life-history traits indicate that the same few species dominate the composition of these taxa all year round. The presence of larvae of some demersal and mesopelagic fish typical of cold sub-Antarctic waters denotes reproductive activity in the PSBF surroundings. Ichthyoplankton can be classified, according to bottom depths, as pertaining to the shelf-edge (80–200 m); slope (200–800 m); or oceanic regions (800–3100 m). Larvae show higher abundances immediately offshore of the front, especially above the thermocline. Copepods, especially their larval stages, constitute the main feeding source for fish larvae inhabiting along the shelf-break. Zooplankton and ichthyoplankton composition and abundance along the shelf-break are compared with those of the adjacent shelf. We finally go over open questions and prospects for future work on zooplankton and ichthyoplankton along the shelf-break.