DOI: 10.5061/dryad.rv15dv47v
title: Data from: Effects of a trophic cascade on a multi-level facilitation cascade

description: 1. The role of cascades in natural communities has been extensively
 studied, but interactions between trophic and facilitation cascades are
 unexplored. In the White Sea (65° N) shallow subtidal bivalve primary
 facilitators provide hard substrate for secondary facilitator barnacles,
 that in turn provide substrate for conspecifics, ascidians, red algae, and
 multiple associated organisms, composing a multi-level facilitation
 cascade. Previous research revealed that predation by the whelk
 (Boreotrophon clathratus) accounts for ~7% of adult barnacle mortality.
 Low whelk abundance limits their effect, with barnacles living on
 conspecifics several times more vulnerable to predation than those living
 on primary substrate. 2. Trophic cascades can selectively shield
 foundation species from consumers, and hence may affect the structure and
 length of facilitation cascades. We tested the hypothesis that low
 abundance of the whelks results from mesopredator predation on their
 juveniles. Depending on the magnitude of the effect, this would mean that
 a trophic cascade controls the abundance of barnacles on all substrates or
 only barnacles living on conspecifics. We also suggested that barnacles on
 primary substrates and conspecifics facilitate different dependent
 assemblages. 3. We manipulated the presence of crab and shrimp
 mesopredators in field caging experiments to assess their effect on whelk
 recruitment. In a field survey we compared the assemblages of sessile
 macrobenthic organisms associated with barnacles living on different
 substrates. 4. Caging experiments evidenced that crab and shrimp
 mesopredators reduce whelk recruitment by 4.6 times. Field data showed
 that barnacles on primary substrate and on conspecifics promote different
 dependent assemblages including secondary facilitator ascidians. 5.
 Although mesopredators do not shield barnacles from elimination, their
 absence would restrict them from living on conspecifics. Barnacles on
 conspecifics are functially different from barnacles on primary substrate,
 and can be concidered a separate level of the facilitation cascade.
 Trophic cascades thus can generate community-wide effects on facilitation
 cascades by affecting their structure and possibly length.
description: <strong>Field experiments</strong>. We tested
 mesopredator effects on <em>Boreotrophon
 clathratus</em> (hereafter 'whelk') recruitment to
 barnacle clusters in a series of year-long field experiments conducted at
 a 12 m deep subtidal site in the Solovetsky Islands (65°01.180’N,
 35°39.721’E, see Yakovis & Artemieva, 2015). In July 2009-2012 and
 2015 we collected empty shells with live <em>Balanus
 crenatus</em> and similar shells with empty barnacle tests (the
 latter are almost equally abundant in the field). We defaunated these
 shells except of adult barnacles (4 or more annual growth rings) and their
 empty tests and attached them in alternating order to the bottom of
 300×375×70 mm plastic cages covered with 2.5 mm nylon mesh (2-3 shells
 with live barnacles and 2-3 shells with empty tests per cage).
 <em>Boreotrophon</em> is a direct-developer with crawl-away
 recruits, attaching egg masses to hard substrates, with a lifespan of
 several years. The mesh is permeable for juvenile whelks with shell height
 within 7 mm (Yakovis & Artemieva, 2015).<br> Each year we
 deployed a new set of cages (which were collected next year) randomly
 distributed between 2-5 treatments: (i) full cages (predator exclusions)
 and (ii) open cages (unmanipulated controls, no mesh, subject to normal
 predation) in all years; (iii) partial cages to control for caging
 effects, similar to full cages but with two side windows 175×50 mm each,
 in all years except 2012; (iv) cages with predatory spider crabs
 <em>Hyas araneus</em> (crab enclosures) in 2015 only, and (v)
 cages with predatory shrimp <em>Spirontocaris phippsi</em>
 (shrimp enclosures) in 2015 only. The set of cages deployed in 2015 was
 also used to assess the effect of crustacean predators on other mobile
 fauna associated with barnacles (Yakovis & Artemieva, 2019). There
 were 2 cages/treatment/year in 2009-2010, 2010-2011, 2011-2012, and
 2012-2013. In 2015-2016 there were 6 cages/treatment, except for predator
 exclusions, which were 8, and open cages, which were 5. We exposed all the
 cages anchored to the bottom in a haphazard pattern (≥0.5 m apart) for one
 year, collected them, counted, weighed and individually measured (since
 2011) crabs and shrimp with carapace length ≥2.5 mm and whelks with shell
 height ≥0.5 mm found inside (except for crustaceans in open cages, which
 were too mobile to be sampled in absence of mesh). For details of the
 2015-2016 predator enclosures experiment see Yakovis & Artemieva
 (2019).<br> In the field whelks, crabs and shrimps concentrate in
 patches formed by barnacles and their empty tests rather than on
 unstructured sediment. Thus, the abundance of predators is more related to
 that of adult barnacles rather than bottom area. To account for that,
 barnacle weight in each cage was estimated in the end of the experiments
 from aperture length measurements using allometric relationships (Yakovis
 & Artemieva, 2015). Empty barnacle tests were also measured and
 their equivalent weight was calculated using the same allometric
 relationships. The sum of calculated weights of live and dead barnacles is
 hereafter called equivalent barnacle weight, EBW, 151±6 g per cage
 (n=53). <strong>Field survey</strong>. To
 compare associated assemblages of sessile organisms between barnacles
 attached to primary and secondary hard substrates (which are differently
 affected by predators) we used eight samples obtained by SCUBA divers at
 the experimental site (65°01.180’N, 35°39.721’E) in July 2012-2014. Each
 sample contained all the hard substrates visible on the sediment surface
 collected from a 0.25 m2 square frame haphazardly placed on the bottom
 (10-26 such primary substrates per frame). We counted and identified all
 the sessile macrobenthic organisms larger than 0.3 mm by substrate type;
 the individuals attached to first- and second-layer barnacles were
 recorded separately.<br> <br>
 <strong>References.</strong><br> Yakovis E., &
 Artemieva, A. (2015). Bored to death: community-wide effect of predation
 on a foundation species in a low-disturbance arctic subtidal system. PLoS
 ONE 10:e0132973. http://dx.doi.org/10.1371/journal.pone.0132973<br>
 Yakovis, E., & Artemieva, A. (2019). Epibenthic predators control
 mobile macrofauna associated with a foundation species in a subarctic
 subtidal community. Ecology and Evolution, 9, 10499– 10512.
 https://doi.org/10.1002/ece3.5570
description: Tabs 'Experiments 2009-2012' and 'Experiments
 2015-2016' contain raw data from the field experiments. The tab
 'Field Survey' contains raw data from the field
 survey.