Benthic input rates predict seagrass (Posidonia oceanica) fish farm-induced decline.
Fish farms represent a growing source of anthropogenic disturbance to benthic communities, and efficient predictors of such impacts are urgently needed. We explored the effects of fish farm benthic organic and nutrient inputs on the population dynamics of a key seagrass species (Posidonia oceanica) in four Mediterranean deep meadows adjacent to sea bream and sea bass farms. We performed two annual plant censuses on permanent plots at increasing distance from farms and measured benthic sedimentation rates around plots. High shoot mortality rates were recorded near the cages, up to 20 times greater than at control sites. Recruitment rates increased in variability but could not compensate mortality, leading to rapid seagrass decline within the first 100 m from cages. Seagrass mortality increased with total sedimentation rates (K=0.55, p<0.0002), and with organic matter (K=0.50, p=0.001), total nitrogen (K=0.46, p=0.002) and total phosphorus (K=0.56, p<3.10(-5)) inputs. P. oceanica decline accelerated above a phosphorus loading threshold of 50mg m(-2)day(-1). Phosphorus benthic sedimentation rate seems a powerful predictor of seagrass mortality from fish farming. Coupling direct measurements of benthic sedimentation rates with dynamics of key benthic species is proposed as an efficient strategy to predict fish farm impacts to benthic communities.
Interdisciplinary Oceanography Group (GOI), IMEDEA (CSIC-UIB), C/Miquel Marqués No. 21, 07190 Esporles, Spain. elena.diaz-almela@uib.es
Elena
E
Díaz-Almela
Núria
N
Marbà
Elvira
E
Alvarez
Rocío
R
Santiago
Marianne
M
Holmer
Antoni
A
Grau
Simone
S
Mirto
Roberto
R
Danovaro
Anthony
A
Petrou
Marina
M
Argyrou
Ioannis
I
Karakassis
Carlos Manuel
CM
Duarte
D035961:Alismatales / Q000502:physiology*; D000818:Animals; D005398:Fisheries; D005843:Geography; D019015:Geologic Sediments; D008522:Mediterranean Sea; D008954:Models, Biological; D011156:Population Density; D011157:Population Dynamics; D013030:Spain