No evidence for food limitation of Caribbean reef sponges: Reply to Slattery & Lesser (2015)

Abstract

Slattery & Lesser (2015; Mar Ecol Prog Ser 527:275-279) offer a Comment on our review of the literature for evidence of bottom-up control of sponge communities on Caribbean reefs. We briefly address the criticisms presented in the Comment and reiterate the lack of evidence for food limitation, including inter-oceanic comparisons of Caribbean reefs with IndoPacific oligotrophic reefs, where sponge communities show strong evidence of food limitation, and past and recent evidence for the importance of dissolved organic carbon (DOC) in sponge nutrition. We did not claim that 'predation is the primary process that determines the growth, biomass and biodiversity of sponges on Caribbean coral reefs,' but we identified 3 depth-related factors that influence sponge community structure on Caribbean reefs: turbulence, spatial competition and predation. We agree that multifactorial manipulative experiments are the best way to address the interaction between top-down and bottom-up processes in this system; indeed, one such experiment has been performed, with an outcome that does not support bottom-up effects.

Consumption of dissolved organic carbon by Caribbean reef sponges

“…This could provide a competitive advantage to seaweeds and sponges over corals, further reinforce coral depletion, and lead to reduced reef resilience (Pawlik et al ). The Indo‐Pacific, by contrast, is dominated by phototrophic species (e.g., Wilkinson ; Powell et al ) that are net primary producers whose nutrients are likely retained and cycled internally as opposed to expelled in the excurrent jet (Pawlik et al ). These reefs would be less susceptible to the feedback between sponges and seaweeds, and thus could exhibit higher overall resilience than those where sponge assemblages are dominated by heterotrophic species possessing the capacity to feed on dissolved organics (Pawlik et al ).…”

Sponge density increases with depth throughout the Caribbean

“…Nonetheless, the important role of trophic resource availability, both POM and DOM, for sponges from shallow to mesophotic depths as a primary factor controlling the patterns of sponge abundance and distribution, is still contested (Pawlik et al. , , b). This despite evidence supporting a strong role for bottom‐up control of sponge populations through food limitation (Lesser , Trussell et al.…”

Assessing the Potential of Sponges (Porifera) as Indicators of Ocean Dissolved Si Concentrations

“…At least at regional scales, water depth acts as a surrogate variable for light penetration, temperature, and nutrient concentrations; these all are inter-correlated and could be influencing sponge distributions (Vacelet, 1988). Other depth-related factors such as food resources (i.e., particulate and dissolved matter), turbulence, spatial competition, and predation have been suggested as drivers of sponge community structure and distribution (Pawlik et al, 2015;Slattery and Lesser, 2015).…”

“…De Laubenfels (1936) recognized that the spatial distribution of shallow water sponges is limited by strong environmental barriers (e.g., depth, light or temperature). More recently, the spatial distribution of marine sponges at local scales (e.g., 10 s of km; coral reefs, straits or gulfs) has been correlated to geomorphological features (Przeslawski et al, 2014), sediment properties, depth, distance to the coast, nutrient availability (including dSi), light penetration, hydrodynamics (Huang et al, 2011), deep sea currents (Cárdenas and Rapp, 2015), and biotic factors such as predation or competition for space (Huang et al, 2011;Pawlik et al, 2015;Slattery and Lesser, 2015). In general, these observations are replicated at regional or broader scales (e.g., >>100 km; seas or oceans).…”