Infaunal community responses to ancient clam gardens

Abstract

Aquatic ecosystems have been managed for millennia. Indigenous communities in North America pioneered numerous marine resource management strategies to ensure food security and support thriving economies, which have been active throughout the Northwest Coast of North America for over 14 000 years. Developed to increase shellfish productivity, clam gardens have been active for millennia. The diverse infaunal communities within these ecosystems can act as indicators of habitat alterations and provide an opportunity to study ecological community responses to seascapes shaped by millennia-old resource management structures. To determine how community structure differs between clam gardens and unmodified areas, we assessed infaunal diversity and density between intertidal mudflats, sandflats, and clam gardens. Differences in community composition were found among site types, with certain taxa, including culturally important species increasing within clam gardens. Per cent similarity analyses indicated that infaunal communities were more dissimilar among, than within site types. Furthermore, regression trees indicated that increases in diversity and density were closely correlated with the amount of shell and gravel within each habitat, which are associated with clam garden function and management practices. Species-specific and environmental responses to clam gardens indicate that human modifications in nearshore habitats created novel and distinct types of soft sediment communities.

11,500 y of human–clam relationships provide long-term context for intertidal management in the Salish Sea, British Columbia

“…We suggest that creation of this new clam habitat combined with other cultivation methods (e.g., tilling, removal of nonhuman predators, altering substrate, rock removal) (14, 16) and spatially explicit designated access rights (35, 36) ensured an ongoing, sustainable harvest of clams. Furthermore, the creation of the coarse sediment garden terrace and associated rock wall had the added benefit of increasing the abundance and availability of other edible marine foods (e.g., red rock crabs, sea cucumbers, snails, a variety of seaweeds) (37, 38).…”

Similarity analyses in restoration ecology and how to improve their utility

“…First, all biological communities vary through space and time, and no two communities will ever be identical in species composition or density. For instance, undisturbed (as much as that is possible in the Anthropocene) intertidal invertebrate communities in similar habitats naturally vary from each other in similarity from 35 to 65% (Gerwing et al 2015 a ; Gerwing et al 2015 b ; Gerwing et al 2017 a ; Gerwing et al 2017 b ; Gerwing et al 2018 a ; Cox et al 2019). However, such natural variability is seldom discussed or incorporated into restoration targets, with regards to community similarity between reference and restored habitats.…”

“…The appeal of measuring community similarity in restoration studies is obvious, as by simply measuring community composition and density/abundance, contrasts can be made between restored/impacted and reference sites. However, restoration studies that use community similarity measures often only assess community similarity, and do not go on to examine ecosystem function (Gerwing et al 2017 b ; Campbell et al 2019; Cox et al 2019; Gerwing et al 2020 b ). Habitat functionality is difficult to define, and we will not summarize this debate here (Schwartz et al 2000; Jax 2005).…”

Habitation Sites Influence Tree Community Assemblages in the Great Bear Rainforest, British Columbia, Canada

“…Similarly, anthropogenically mediated nutrient inputs, such as the accumulation of charcoal and shell middens, can alter soil chemistry through increases in nutrients such as calcium (Ca), phosphorus (P), and pH (Cook-Patton et al, 2014;Vanderplank et al, 2014;Hoffman et al, 2016a;Trant et al, 2016;Fisher et al, 2019). Within the Pacific Northwest, shell midden deposits, often found along the shorelines, can be used alongside other unique landscape features, such as clam gardens or estuarine root gardens, to locate previously occupied habitation sites -places of repeated, longterm, or high occupancy human settlement (McLaren et al, 2014;Jackley et al, 2016;Cox et al, 2019). Within the context of this study, shell middens are considered to be the accumulated remains of intertidal and subtidal taxa that were purposely deposited to alter soil characters or discarded after consumption.…”