The effects of short space and time scale current variability on the predictability of passive ichthyoplankton distributions: an analysis based on HF radar observations

Abstract

The importance of small scale variations in currents on the predictability of spatial distributions of fish eggs is investigated using dense observations of surface currents. The currents were measured with HF radar and used to drive an advection–diffusion model of ichthyoplankton concentration. We first demonstrate that the model produces acceptable agreement with observed egg fields. We then use the predicted egg fields as a basis for comparison with model runs made with currents subsampled in space and filtered in time. Significant error was found for spatial sampling intervals as small as 3 km, even though most of the variance in the currents occurred at much longer length scales. This was primarily due to the loss of the rich small scale variability in horizontal divergence. Nevertheless, most of the error is due to the misfit in the egg fields at larger length scales; that is, small scale forcing is necessary in this system for the larger scale features to be reproduced. This study thus suggests that considerable caution should be exercised before assuming that circulation models, even very sophisticated and detailed ones, capture enough of the variability of marine systems to make accurate forecasts of plankton distributions.

Linking sardine recruitment in coastal areas to ocean currents using surface drifters and HF radar: a case study in the Gulf of Manfredonia, Adriatic Sea

“…They have reached quite a wide distribution over the ocean coastlines (Rubio et al, 2017); their high temporal and spatial resolution and their synoptic view allow for a continuous and detailed monitoring of coastal dynamics and of transport processes occurring in coastal areas (Bellomo et al, 2015). The regularity of their data coverage in space and time, and the possibility of processing and disseminating such data in near-real time, makes them extremely valuable in the framework of coastal oceanography both for operational (Falco et al, 2016;Iermano et al, 2016) and for ecological (Helbig and Pepin, 2002;Bassin et al, 2005;Morgan et al, 2012;Cianelli et al, 2017) studies.…”

Dynamics and sea state in the Gulf of Naples: potential use of high-frequency radar data in an operational oceanographic context

“…HFR synoptic and repeated surface current fields are well suited to the reconstruction of particle paths that can be statistically analysed to characterise several processes, such as pollutant-retention area formation (Kaplan & Largier 2006), oil spill evolution (Klemas 2010), discharged ballast ship water fate (Larson et al 2005), larval transport from spawning areas to other regions (Bjorkstedt and Roughgarden, 1997) and residence time calculation at basin and sub-basin scales (Uttieri et al 2011). Backward trajectories reconstructed using HFR current fields have helped to reconstruct larval paths from source to settlement regions in a number of studies (Helbig & Pepin 2002;Nishimoto & Washburn 2002;Mantovanelli & Heron 2012). Backward trajectories reconstructed using HFR current fields have helped to reconstruct larval paths from source to settlement regions in a number of studies (Helbig & Pepin 2002;Nishimoto & Washburn 2002;Mantovanelli & Heron 2012).…”

High-Frequency Radar Observations of Ocean Surface Currents

“…Time series of surface current maps from HF radar have proven useful in a range of Lagrangian studies of particle dispersion, larval transport, and the connectivity between larval source and settlement regions (Emery et al 2006, Helbig & Pepin 2002, Ullman et al 2006, Zelenke et al 2009. To assess the connectivity among marine protected areas (MPAs) along the south-central California coast, Zelenke et al (2009) computed reverse trajectories, each lasting 40 days, over 1 year between potential larval source regions and destinations within established MPAs.…”

“…By reconstructing larval trajectories, they concluded that larvae settling on the platforms likely would have been advected far from shore in the absence of the platforms, and therefore it is unlikely that the platforms reduced settlement on natural reefs. Helbig & Pepin (2002) investigated evolving spatial patterns of fish eggs in Conception Bay, Canada, based on HF radar surface current observations and concurrent shipboard ADCP and egg surveys. An ocean circulation model was used to simulate egg transport over 4 days separating the egg surveys.…”