Long-term declines and collapse of an intertidal food webLong-term Temporal Trends

Peter Petraitis¹, Steve Dudgeon²

¹University of Pennsylvania, USA - ²California State University, USA

The Gulf of Maine, USA, is warming at alarming rates, and based on data from 1997 to 2018, Petraitis and Dudgeon (2020) reported from 1997 to 2018 declines in abundances of three common gastropods averaged 3.1% per year (Testudinalia testudinalis, Littorina littorea, and Nucella lapillus), and declines in recruitment of 15.7% per year for mussels and 5.0% per year for barnacles. Inspection of the trends seemed to show no changes in abundances and recruitment until sometime between 2004 and 2006, but because of the small sample sizes, Petraitis and Dudgeon did not have sufficient power to detect breakpoints in the trends. Here using a larger and more detailed dataset and segmented quasipoisson regressions, we show initial small increases prior to dramatic breaks after which there were very rapid declines. Breakpoints in trends in abundances of intertidal gastropods (not only T. testudinalis, L. littorea, and N. lapillus but now also L. obtusata) occur sometime between 2006 and 2010, and in recruitment of mussels and barnacles occur sometime between 2000 and 2006. After the breakpoints, declines in abundances averaged 8.7% per year and in recruitment averaged a staggering 16.9% per year. In 2020, we suggested these iconic intertial species would be rare within two decades. We now think the declines will be much more rapid and possibly lead not only to local extinctions but also loss of an alternative community state within the Gulf of Maine.