Immanent conditions determine imminent collapses: nutrient regimes define the resilience of macroalgal communities.
Predicting where state-changing thresholds lie can be inherently complex in ecosystems characterized by nonlinear dynamics. Unpacking the mechanisms underlying these transitions can help considerably reduce this unpredictability. We used empirical observations, field and laboratory experiments, and mathematical models to examine how differences in nutrient regimes mediate the capacity of macrophyte communities to sustain sea urchin grazing. In relatively nutrient-rich conditions, macrophyte systems were more resilient to grazing, shifting to barrens beyond 1 800 g m-2(urchin biomass), more than twice the threshold of nutrient-poor conditions. The mechanisms driving these differences are linked to how nutrients mediate urchin foraging and algal growth: controlled experiments showed that low-nutrient regimes trigger compensatory feeding and reduce plant growth, mechanisms supported by our consumer-resource model. These mechanisms act together to halve macrophyte community resilience. Our study demonstrates that by mediating the underlying drivers, inherent conditions can strongly influence the buffer capacity of nonlinear systems.
Centre d'Estudis Avançats de Blanes (CEAB-CSIC), Carrer d'Accés a la cala Sant Francesc 14, 17300 Blanes, Spain jboada@ceab.csic.es.
Jordi
http://orcid.org/0000-0002-3815-625X
J
Boada
Centre d'Estudis Avançats de Blanes (CEAB-CSIC), Carrer d'Accés a la cala Sant Francesc 14, 17300 Blanes, Spain.|Nature Conservation Foundation, 3076/5, 4th Cross, Gokulam Park, 570002 Mysore, Karnataka, India.
Rohan
R
Arthur
Centre d'Estudis Avançats de Blanes (CEAB-CSIC), Carrer d'Accés a la cala Sant Francesc 14, 17300 Blanes, Spain.
David
D
Alonso
School of Ocean Sciences, Bangor University, Menai Bridge, Wales LL59 5AB, UK.
Jordi F
JF
Pagès
Centre d'Estudis Avançats de Blanes (CEAB-CSIC), Carrer d'Accés a la cala Sant Francesc 14, 17300 Blanes, Spain.
Albert
A
Pessarrodona
Dipartimento di Scienze della Natura e del Territorio (DIPNET), Università di Sassari, Via Piandanna 4, Sassari, Italy.
Silvia
S
Oliva
Dipartimento di Scienze della Natura e del Territorio (DIPNET), Università di Sassari, Via Piandanna 4, Sassari, Italy.
Giulia
G
Ceccherelli
Dipartimento di Scienze della Natura e del Territorio (DIPNET), Università di Sassari, Via Piandanna 4, Sassari, Italy.
Luigi
L
Piazzi
Departament d'Ecologia, Facultat de Biologia, Universitat de Barcelona, Avenue Diagonal 643, 08028 Barcelona, Spain.
Javier
J
Romero
Centre d'Estudis Avançats de Blanes (CEAB-CSIC), Carrer d'Accés a la cala Sant Francesc 14, 17300 Blanes, Spain.|Nature Conservation Foundation, 3076/5, 4th Cross, Gokulam Park, 570002 Mysore, Karnataka, India.
Teresa
T
Alcoverro
D000818:Animals; D018533:Biomass; D020387:Food Chain; D044423:Kelp; D008962:Models, Theoretical; D012617:Sea Urchins
alternative stable states; buffer capacity; catastrophic shifts; compensatory feeding; sea urchin barrens; tipping points