The intermingling of benthic macroinvertebrate communities during a period of shifting range: The “East of Nantucket” Atlantic Surfclam Survey and the existence of transient multiple stable states

Abstract

A survey of the region eastward of Nantucket provided an opportunity to examine the cold temperate–boreal boundary along the high‐energy Great South Channel. Here described are the benthic macroinvertebrate community types encountered, with a focus on the influence of climate change on the range boundaries of the benthic biomass dominants and the potential existence of transient multiple stable states. The survey identified three primary community types. The shallowest sites were occupied by a surfclam‐dominated community, comprising an abundance of large (≥150 mm) surfclams, and a few common attached epibiota primarily attached to exposed surfclam shell. Two communities exist at intermediate depths, one dominated by submarket and small market‐size surfclams (<150 mm) and the other, created by mussel mats and their attendant epibiota, crabs, sea urchins, and other mobile epifauna. Mussels are a foundational species, establishing a hard‐bottom terrain conducive to these other denizens in soft‐bottom habitat. Cobbles were nearly ubiquitous, rocks were routinely recovered, and boulders were encountered occasionally. Slow growing attached epibionts were exceedingly rare and mobile epifauna were not obviously associated with these large sedimentary particles; nor were the surfclam or mussel communities. The frequency of barnacle scars suggests sediment scour under the high‐flow regime characteristic of the surveyed region, which voids the habitat potential of these sedimentary particles. The abundance of surfclam shell indicates that surfclams have inhabited the shoaler depths for an extended time; limited shell at deeper sites supports the inference from the absence of large animals that these sites are relatively newly colonized and represent further evidence of an offshore shift in range brought on by increasing bottom water temperatures. The dichotomous nature of the two primary community types at mid‐depths suggests that these two communities represent multiple stable states brought on by the interaction of an invading cold temperate species with the receding boreal fauna resulting in a transient intermingling of species, which, however, structure the habitat into exclusionary stable states rather than overlapping in a co‐occurrence ecotone.

The Middle Atlantic Bight Cold Pool is warming and shrinking: Indices from in situ autumn seafloor temperatures

“…This overlap coupled with the ability of ocean quahogs to estivate for long periods to avoid lethal temperatures results in the competitive overlap of these two species, the effects of which on their population dynamics remain undetermined. Farther north, Powell et al (2019)…”

Interactive Effects of Climate Change‐Induced Range Shifts and Wind Energy Development on Future Economic Conditions of the Atlantic Surfclam Fishery

“…Furthermore, the potential exists for the continuing range shift of Atlantic surfclams to alter the impact of offshore wind energy development if farm siting occurs in the anticipated direction of the species' range shift. The well-documented trend in the Atlantic surfclam's range shift (Narváez et al 2015;Hennen et al 2018;Hofmann et al 2018;Powell et al 2019Powell et al , 2020a suggests continued movement of the range of the clam offshore and northward relative to many of the proposed wind farm leases.…”

“…Warming bottom water temperatures have produced a shift in the Atlantic surfclam's range offshore into deeper water-a trend that is well documented throughout the species' range (Weinberg et al 2005;Hennen et al 2018;Hofmann et al 2018;Hornstein et al 2018;Powell et al 2019Powell et al , 2020bTimbs et al 2019). A northward and offshore transgression of the inshore southern range boundary likely began in the 1970s (Hofmann et al 2018), but it was not until 2000 that a historically important mass-mortality event inshore off the Delmarva Peninsula occurred (Kim and Powell 2004).…”

Sclerobiosis: A Term for Colonization of Marine Hard Substrates

“…Both neontologists and paleontologists have used the terms epibiont and epibiosis to describe the colonization of dead organic and inorganic substrates (see Taylor & Wilson, 2003 and references cited therein;Freeman et al, 2013;Schneider, 2013), as well as to refer to vagile organisms associated with a living organism (e.g., Ayres-Peres & Mantelatto, 2010;Fuller, et al 2010;Smyth & Roberts, 2010;Gordillo & Archuby, 2014). Some authors use the term epibiont to indicate invertebrates that live on rocks, pebbles or boulders (Plint et al, 2006;Chumakov et al, 2013;Powell et al, 2019).…”