Journal
MARINE ECOLOGY PROGRESS SERIES
Volume 561, Issue -, Pages 123-136Publisher
INTER-RESEARCH
DOI: 10.3354/meps11913
Keywords
Caulerpa prolifera; Cymodocea nodosa; Hydrodynamics; Microtopography; Rhizophytes; Seagrasses
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Funding
- Spanish National Research Project EVAMARIA [CTM2005-00395/MAR]
- Spanish National Research Project IMACHYDRO [CTM2008-0012/MAR]
- Andalusian Excellence Research Project [FUNDIV P07-RNM-02516]
- FPI grant of the Spanish Ministry of Science and Technology
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Rhizophytic green algae of the genus Caulerpa are potential competitors with sea-grass-dominated habitats. At Cadiz Bay Natural Park, Caulerpa prolifera and the seagrass Cymodocea nodosa co-occur in overlapping patches, which may be considered as transition zones. In these zones, changes in microtopography are stepped because patches of C. prolifera normally occur at 5 to 10 cm above the adjacent C. nodosa patches. We hypothesized that hydrodynamics influenced by this microtopography may foster sedimentation on the C. nodosa side, which in turn would facilitate the spreading of C. prolifera. To test this hypothesis, an experiment simulating the flow between both species was conducted in a race-track flume tank, allowing us to study the influence of unidirectional free stream velocity (low velocity, LV = 0.065 m s(-1), vs. high velocity, HV = 0.14 m s(-1)) and microtopography (flat bottom, FB, vs. stepped bottom, SB) on shear stress (tau), turbulent kinetic energy above the canopy (TKEabove) and volumetric flow rate through the canopy (Q(c)). Under our experimental conditions, comparison of tau-values with theoretical thresholds revealed sedimentation scenarios. However, at HV, the probability of sedimentation was higher in C. nodosa than in C. prolifera patches. Moreover, Qc was higher within C. nodosa canopies than within C. prolifera, ensuring a higher source of sediment with potential to be trapped within the canopy. Although we found no species-specific differences in TKEabove values, they increased with HV increasing the vertical mixing. Overall, conditions for sedimentation seemed more facilitated in C. nodosa than in C. prolifera in SB only under HV conditions.
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