Influence of food, body size, and fragmentation on metabolic rate in a sessile marine invertebrate

Abstract

Metabolic rates vary among individuals according to food availability and phenotype, most notably body size. Disentangling size from other factors (e.g., age, reproductive status) can be difficult in some groups, but modular organisms may provide an opportunity for manipulating size experimentally. While modular organisms are increasingly used to understand metabolic scaling, the potential of feeding to alter metabolic scaling has not been explored in this group. Here, we perform a series of experiments to examine the drivers of metabolic rate in a modular marine invertebrate, the bryozoan Bugula neritina. We manipulated size and examined metabolic rate in either fed or starved individuals to test for interactions between size manipulation and food availability. Field collected colonies of unknown age showed isometric metabolic scaling, but those colonies in which size was manipulated showed allometric scaling. To further disentangle age effects from size effects, we measured metabolic rate of individuals of known age and again found allometric scaling. Metabolic rate strongly depended on access to food: starvation decreased metabolic rate by 20% and feeding increased metabolic rate by 43%. In comparison to other marine invertebrates, however, the increase in metabolic rate, as well as the duration of the increase (known as specific dynamic action, SDA), were both low. Importantly, neither starvation nor feeding altered the metabolic scaling of our colonies. Overall, we found that field‐collected individuals showed isometric metabolic scaling, whereas metabolic rate of size‐manipulated colonies scaled allometrically with body size. Thus, metabolic scaling is affected by size manipulation but not feeding in this colonial marine invertebrate.

Size Is the Major Determinant of Pumping Rates in Marine Sponges

“…Food availability has been demonstrated to affect the pumping rate of sponges and other suspension filter feeders such as polychaetes, bivalves, ascidians, and bryozoans (Winter, 1973;Frost, 1980;Navarro and Winter, 1982;Robbins, 1983;Stuart and Klumpp, 1984;Riisgård and Ivarsson, 1990;Riisgård, 1991;Petersen and Riisgård, 1992;Petersen et al, 1999;Schuster et al, 2019). These studies observed a pattern characterized by a decrease in pumping rate with the increase in food concentration that was attributed to a regulation of food uptake, in such a way that the number of filtered particles remained constant as a protection against overloading of the feeding system (Winter, 1973;Navarro and Winter, 1982;Robbins, 1983;Riisgård and Ivarsson, 1990;Riisgård, 1991;Petersen and Riisgård, 1992;Petersen et al, 1999).…”

Plastic but not adaptive: habitat‐driven differences in metabolic rate despite no differences in selection between habitats

“…We collected ~80 sexually mature B. neritina colonies from the Royal Melbourne Yacht Squadron in Port Phillip Bay, Victoria, Australia (37°51''43.1''S, 144°57'51.2''E) in March and April 2018. To obtain individuals for our experiments, we spawned colonies according to standard procedures (Schuster et al 2019). Briefly, we kept colonies in the laboratory in field-collected seawater in aerated tanks in the dark.…”

Energetic mechanisms for coping with changes in resource availability

“…Phenotypic plasticity of standard and basal metabolic rate in response to changing food availability is found across a wide variety of taxa including invertebrates [20,46] and all major vertebrate classes such as fish [12,21,47,48], amphibians [49], reptiles [22,50], birds [51][52][53][54] and mammals [55,56]. Changes in energy metabolism occur over timescales ranging from days to weeks [47,57] and differ considerably among individuals [12,21,48,57].…”