Plant Part Age and Size Affect Sessile Macrobenthic Assemblages Associated with a Foliose Red Algae Phycodrys rubens in the White Sea

Abstract

Facilitation by foundation species commonly structures terrestrial and marine communities. Intraspecific variation in individual properties of these strong facilitators can affect the whole suite of the dependent taxa. Marine macroalgae often act as ecosystem engineers, providing shelter and substrate for numerous associated organisms. Epibiosis of foliose red algae, however, remains underexplored, especially in the high latitudes. Here we studied sessile macrobenthic assemblages associated with a foliose red algae Phycodrys rubens in the White Sea (66° N) shallow subtidal, and the effect of individual plant properties on their structure. The blades of P. rubens develop annually, and it is possible to tell the young (usually larger) plant parts from the old ones. We hypothesized that epibenthic community structure depends on plant part age and size. We examined epibiosis on 110 plants at two sites, and the results generally supported our hypotheses. Old plant parts were several times smaller, and had higher total cover than young parts. Sponges strongly dominated the epibiosis on old parts, and young parts were dominated by polychaetes and bryozoans. Plant part surface area negatively correlated with total cover on young parts, while on old parts the relatioship was location-specific. On young parts the relative abundance of a polychaete Circeis armoricana increased with surface area, and the proportion of sponges decreased. The patterns indicate that epibenthic community structure is linked to the demography of an ecosystem engineer.

Effect of a generalist mesopredator on modular and unitary sessile prey associated with a foundation species

“…Celleporella showed relatively high survival rates in the trials, with a mean colony size of at least 25–30 zooids (2 mm 2 ), while most of the Juxtacribrilina and Electra colonies were within 1 mm 2 before treatments. On less ephemeral substrates, both Electra and Juxtacribrilina commonly sustain colony sizes reaching hundreds or thousands of zooids (Chava et al., 2019 ; Nekliudova, Shunkina, et al., 2019 ; Shevchenko et al., 2020 ), possibly having higher predation survival rates. Also, the brief starvation imposed on shrimp before the trials could potentially reduce their feeding selectivity (Perry, 1987 ).…”

“…Young blades of a red foliose algae Phycodrys rubens in the White Sea host an epibiosis codominated by unitary serpulid tubeworms Circeis armoricana and modular encrusting bryozoans Celleporella hyalina , Juxtacribrilina annulata , and Electra pilosa (Chava et al., 2019 ). Punctate blade shrimp Spirontocaris phippsii (Figure 1a ) is a common generalist mesopredator previously known to prey on small polychaetes, amphipods, bivalves, and gastropods (Yakovis & Artemieva, 2019 , 2021 ).…”

“…All sessile macrobenthic organisms on a blade were counted, and individually measured (zooids number in bryozoans and hydrozoans, aperture diameter in tubeworms) in the beginning and at the end of each trial. Substrate area covered was estimated using previously established relationships (Chava et al., 2019 ). We performed 24‐h experimental trials with a single Spirontocaris individual added to a tank (Figure 1b ).…”

“…Frequently, immobile unitary and modular organisms share common habitats and codominate the same communities. Numerous examples include co‐dwelling giant clams and corals (Hamner & Jones, 1976 ; Hardy & Hardy, 1969 ; Lucas, 1988 ; Soo & Todd, 2014 ), and bivalves, tubeworms, ascidians, sponges, hydroids, and bryozoans in various combinations (Barnes & Clarke, 1995 ; Chava et al., 2019 ; Davis & White, 1994 ; Hiebert et al., 2019 ; Nandakumar et al., 1993 ; Velimirov et al., 1977 ). Coexisting immobile unitary and modular organisms commonly compete for substrate space (Jackson, 1977 ).…”

“…We expected the ability of unitary species to outgrow predation pressure and the ability of modular ones to be consumed partially would change with predator size, providing the link between the demography of the predator and community response to predation. Importantly, the focal system is shaped by the demography of a foundation species (Chava et al., 2019 ), which provides the background to examine the complex interplay of predation, facilitation, and competition driving community structure and functioning.…”