Bridging the spawner-recruit disconnect: trends in American lobster recruitment linked to the pelagic food web

In the Gulf of Maine, landings of American lobster, Homarus americanus H. Milne-Edwards, 1837, have doubled since the early 2000s, and are currently at record-breaking levels. Estimates of spawning stock biomass (SSB) are correspondingly high, but benthic recruitment of young-of-year (YoY) lobsters has been declining precipitously since 2012 and is currently at time-series lows. We analyzed a long-term time series of larval abundance collected off the coast of New Hampshire, USA, via neuston tows to explore linkages between trends in lobster SSB, larval abundance, and YoY recruitment. There was a significant increasing trend in stage I larvae in coastal New Hampshire, consistent with the increasing levels of SSB in the Gulf of Maine over the same period. However, the planktonic postlarvae from the same survey have been declining in recent years, which correlate well with diminishing benthic YoY recruitment at monitoring sites in the western Gulf of Maine, from mid-coast Maine to Cape Cod Bay, Massachusetts. Furthermore, we found that both postlarval and YoY lobster time series were significantly correlated with the abundance of the copepod, Calanus finmarchicus (Gunnerus, 1770), but not other potential zooplankton prey, gelatinous predators, or environmental indicators, such as temperature or wind advection. To our knowledge, these results are the first to (1) narrow the likely timing of the decoupling of spawner abundance and settlement to the few weeks of lobster planktonic larval development, and (2) suggest that variability in YoY recruitment, including recent widespread declines, may be linked to changes in the zooplankton assemblage at the base of the pelagic food web.