Revisiting cross-shelf transport of Dungeness crab (Metacarcinus magister) megalopae by the internal tide using 16 years of daily abundance data

Abstract

Listen

Translate article

Many marine organisms have a biphasic life beginning with a planktonic larva that undergoes development on the continental shelf. These larvae ultimately need to return to the nearshore environment to settle. One proposed mechanism of transport to the nearshore is the internal tide. The Dungeness crab, Metacarcinus (Cancer) magister, is one species that is hypothesized to be transported by the internal tide. In addition to daily cycles in catch of megalopae being correlated with the internal tide, the annual catch of megalopae is correlated with the Pacific Decadal Oscillation. However, intial studies occurred during a positive phase Pacific Decadal Oscillation. In this study, we analyze an additional 12 years of data (16 years total) to determine if the internal tide continues to be correlated with the transport of Dungeness crab megalopae. We used wavelet analyses and cross-Fourier analysis to relate the catch of megalopae to the daily maximum tidal range, wind speed, and sea surface temperature. We found that over 16 years, the correlation with the daily maximum tidal range continues to be the strongest correlate with the daily catch of megalopae. These results continue to suggest megalopae are transported across the continental shelf by the internal tide. Our use of wavelets allowed us to examine the annual trends in periodicity of returning megalopae. We found that the periodicities at tidal frequencies did not persist throughout the settlement season. We hypothesize this indicates cross-shelf transport is primarily regulated by the internal tide but additional, unknown factors, interact with the internal tide affecting the number of returning larvae. We conclude by discussing why high-frequency sampling is an important component of ecological time series.