Size and age are important factors for marine sanctuaries: evidence from a decade of systematic sampling in a subtropical marine park

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Migration,homing and spatial ecology of common carp in interconnected lakes

The common carp, Cyprinus carpio, is a large, long-lived, fecund and mobile cyprinid, which evolved in complex inter-braided Ponto-Caspian rivers that experience both springtime flooding and freezing winters. Studies suggest adults often move to productive, shallow lakes and floodplains to spawn because they often lack egg predators and then return to deeper normoxic waters to overwinter. Whether these movements involve individuals consistently selecting, or homing to, the same spawning and refuge lakes as part of a strategy benefiting their reproductive success is unknown. To address this question, we examined the movements of 67 radio-tagged adult carp for 3 years in a watershed with 11 interconnected lakes. Carp were tagged and released into a centrally located, normoxic deep lake in spring and fall. Each spring over 95% of its adults left via a single stream and swam into one of 5 shallow lakes, with most individuals (84%) selecting the same lake(s) in which to spawn each year (median Bhattacharyya affinity coefficient of similarity of 0.82). Young were later found in those lakes without egg predators, which cannot survive winter anoxia. After spawning, carp spent summers moving between productive lakes in an individualistic fashion, presumably foraging, with most (89%) eventually returning to the same deep lake to overwinter (median Bhattacharyya affinity of 1.0). These movements appear to reveal a life-history tactic involving seasonal homing migration, first to a spawning location and later to winter refuges, that is well adapted to productive but highly heterogeneous and interconnected freshwater environments.     

Effects of long-term phosphorus fertilizer inputs and seasonal conditions on organic soil phosphorus cycling under grazed pasture

Soil microbes and phosphatase enzymes play a critical role in organic soil phosphorus (P) cycling. However, how long-term P inputs influence microbial P transformations and phosphatase enzyme activity under grazed pastures remains unclear. We collected top-soil (0–75 mm) from a grazed pasture receiving contrasting P inputs (control, 188 kg ha⁻¹ year⁻¹ of single super phosphate [SSP], and 376 kg ha⁻¹ year⁻¹ of SSP) for more than 65 years. Olsen P, microbial biomass P, and acid and alkaline phosphatase enzyme activities were measured regularly over a 2-year period. Pasture dry matter and soil chemical properties were also investigated. Results showed that long-term P inputs significantly increased pasture dry matter, total N, and the concentrations of ${\mathrm{NO}}_3^{–}$–N but significantly decreased soil pH and the concentrations of ${\mathrm{NH}}_4^{+}$–N. Total C was not affected by P fertilization. Although Olsen P significantly increased with increasing long-term P inputs, microbial biomass P was similar under P fertilized treatments. Long-term P inputs decreased acid phosphatase activity but increased alkaline phosphatase activity. Microbial biomass P was similar across seasons in the control but decreased in spring and autumn while increased in summer and winter under P fertilized treatments. Acid and alkaline phosphatase activities were significantly affected by season and followed similar seasonal trends being maximum in summer and minimum in winter regardless of P treatment. Correlation and principal component analysis revealed that acid and alkaline phosphatase activities were significantly positively correlated with soil temperature and significantly negatively correlated with soil moisture. In contrast, Olsen P and microbial biomass P were weakly correlated with environmental conditions. The findings of this study highlight the intertwined relationship between organic P cycling and the availability of C and N in soil systems and the need to integrate both soil moisture and temperature in models predicting organic P mineralization, especially in the context of global climate change.