Spatial and temporal variations of coastal fish larvae, ectoparasites and oceanographic conditions off central Chile

The objective of this study is to determine the temporal variation of oceanographic conditions, ichthyoplankton and their ectoparasites in nearshore marine waters. From October 11^th 2012 to June 5^th 2014, 30 ichthyoplankton surveys were carried out along a cross-shelf transect from 0.25 km of the coastline to 4.50 km offshore off Montemar, Bahía Valparaíso, central Chile. We identified a total of 5,553 fish larvae, belonging to 37 taxa. The most abundant fish larvae with pelagic spawning were the common sardine Strangomera bentincki (relative abundance= 26.39%), the anchoveta Engraulis ringens (8.94%), and the lanternfish Hygophum bruuni (7.72%); whereas the most abundant species with benthic brooding were the blennies Scartichthys viridis (15.77%), Hypsoblennius sordidus (8.27%) and the clingfish Gobiesox marmoratus (7.06%). The most parasitized fish larvae were from benthic brooding origin, namely the clingfishes G. marmoratus (prevalence= 9.63%) and Sicyases sanguineus (0.54%), the kelpfish Auchenionchus variolosus (1.72%), and triplefin blenny Helcogrammoides cunninghami (3.28%). Only one species from pelagic spawning origin, the sandperch Prolatilus jugularis (0.57%), had ectoparasites. The abundance of some larval fish species with ectoparasite decreased with distance to the shore; S. bentincki, H. bruuni (pelagic spawning) or S. viridis (benthic brooding) were found to be more abundant at 2.0 km offshore. The ectoparasites were identified as Trifur spp. (Copepoda: Pennellidae) and Caligus spp. (Copepoda: Caligidae), with pennellids being the most frequent (1 to 3 parasites per larva). Ninety-four and 88% of pennellids and caligids, respectively, were collected in the nearshore station. During periods of high ectoparasite prevalence on fish larvae, seawater was vertically stratified with a cross-shelf deepening (late autumn) or shoaling (summer) of the pycnocline from offshore to nearshore. The results suggest that fish larvae with BB were more frequently parasitized and that physical conditions of the water column may contribute both to coastal retention of fish larvae as well as ectoparasite infestation in nearshore waters.