Nutrient Fluxes and Ecological Functions of Coral Reef Sponges in a Changing Ocean

Abstract

Coral reefs are iconic examples of biological hotspots, highly appreciated because of their ecosystem services. Yet, they are threatened by human impact and climate change, highlighting the need to develop tools and strategies to curtail changes in these ecosystems. Remarkably, ever since Darwin's descriptions of coral reefs, it has been a mystery how one of Earth's most productive and diverse ecosystems thrives in oligotrophic seas, as an oasis in a marine desert. Sponges are now increasingly recognized as key ecosystem engineers, efficiently retaining and transferring energy and nutrients on the reef. As a result, current reef food web models, lacking sponge-driven resource cycling, are incomplete and need to be redeveloped. However, mechanisms that determine the capacity of sponge "engines," how they are fueled, and drive communities are unknown. Here we will discuss how sponges integrate within the novel reef food web framework. To this end, sponges will be evaluated on functional traits (morphology, associated microbes, pumping rate) in the processing of dissolved and particulate food. At the community level, we discuss to what extent these different traits are a driving force in structuring shallow-to deep-sea reef ecosystems, from fuel input (primary producers) to engine output (driving and modulating the consumer food web). Finally, as climate change causes the onset of alterations in the community structure and food web of reef ecosystems, there is evidence accumulating that certain biological pathways are triggered, such as the sponge loop and the microbial loop, that may shift reef ecosystems faster than their original stressors (e.g., warming oceans and ocean acidification). Unfortunately,

Global community breaks at 60 m on mesophotic coral reefs

“…In addition to picoplankton, sponges also feed on dissolved organic matter (de Goeij, Lesser, & Pawlik, ). Although picoplankton increases with increasing depth (Lesser, ), both dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) decrease from shallow to mesophotic depths (de Goeij et al, ; Figure ). For both picoplankton and DOC/DON abundance, there are significant differences occurring at ~ 60 m, coincident with the most dramatic changes in sponge diversity and biomass (Lesser & Slattery, ) and changes in underwater irradiance (Lesser, ; Lesser et al, , ; Slattery & Lesser, ).…”

“…For both picoplankton and DOC/DON abundance, there are significant differences occurring at ~ 60 m, coincident with the most dramatic changes in sponge diversity and biomass (Lesser & Slattery, ) and changes in underwater irradiance (Lesser, ; Lesser et al, , ; Slattery & Lesser, ). In particular, both DOC and POC sources do not appear to be limiting over the shallow to mesophotic depth range, whereas PON, in the form of picoplankton, increases and might close the C : N ratio sufficiently to promote increased sponge growth at mesophotic depths (de Goeij et al, ).…”

“…In addition to picoplankton, sponges also feed on dissolved organic matter (de Goeij, Lesser, & Pawlik, 2017). Although picoplankton increases with increasing depth (Lesser, 2006), both dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) decrease from shallow to mesophotic depths (de Goeij et al, 2017;Figure 4).…”

Sponge density increases with depth throughout the Caribbean

“…In addition to POM resources, the trophic biology of sponges includes the consumption of DOM, specifically DOC (de Goeij et al. , , ), and recent observations have suggested that different species and/or communities of sponges consume different proportions of POM and DOM (Maldonado et al. , Hoer et al.…”

Bioeroding sponges in a time of change: insights into the physiology and cellbiology of a photosymbiotic coral-eroding sponge

“…Rützler, 2002;López-Victoria and Zea, 2005;Ward-Paige et al, 2005;Schönberg and Ortiz, 2008;Carballo et al, 2013;Kelmo et al, 2013;Wisshak et al, 2014;Ramsby et al, 2017a) and of their potential role in phase shifts towards alternate steady or temporarily reversible states (Norström et al, 2009;González-Rivero et al, 2011a;Bozec et al, 2015;Chaves-Fonnegra et al, 2017). The prediction of increased abundance of bioeroding sponges is in accordance with a more general hypothesis of shifts towards sponge (and algae) dominated reef systems in the Caribbean and elsewhere, with important implications for nutrient cycling on coral reefs (Diaz and Rützler, 2001;Norström et al, 2009;McMurray et al, 2010;Colvard and Edmunds, 2011;Bell et al, 2013;Ruzicka et al, 2013;Villamizar et al, 2014;De Bakker et al, 2017;De Goeij et al, 2017). Recent studies have elucidated that both bottom-up (e.g.…”