Seasonal variability in the juvenile growth rate of an infaunal polychaete is related to major rain events

Abstract

We measured juvenile growth rates of the spionid polychaete Polydora cornuta in situ by transplanting and recovering small vials containing labeled individuals and measuring each worm's body volume before and after week‐long transplantations into field sediments. To measure seasonal variation of in situ growth rates, we performed 15 intertidal transplantations between November 2008 and January 2010 in Oneonta Slough within the Tijuana River National Estuarine Research Reserve. Our study period included four major rain events with precipitation greater than 2 cm d‐1 that reduced salinity in the tidal channel below 20‰. On average, we recovered one third of the 72 juveniles that were deployed during each transplantation. Mean relative growth rates ranged from 0% to 15% d‐1 among the 15 transplantations and were positively correlated with the mean salinity during each transplantation period. Mean relative growth rates during or a few days after major rain events averaged 2% d‐1, whereas relative growth rates during all other weeks exceeded 7% d‐1. During the November–March rainy season, mean relative growth rates exceeded 8% d‐1 when rain did not occur during a transplantation or during the preceding 7 d, indicating that environmental conditions favoring rapid growth of P. cornuta juveniles returned approximately 1 week after a major rain event. Although the small size of P. cornuta juveniles imposes methodological challenges, their rapid growth and our transplantation methods provide a way to assess environmental quality from the perspective of infaunal performance on small temporal and spatial scales.