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- Particle retention efficiency of a coastal ecosystem in the Northeastern Atlantic OceanPublication . Mendonca, Vanda; Sprung, Martin; Castro, Margarida; Canario, Adelino V. M.Based on filtration rates obtained in situ at several habitats (mud flats, sand flats, and seagrass beds of Cymodocea nodosa), particle retention efficiency of benthic communities was estimated at Ria Formosa, a coastal lagoon in southern Portugal. The distinct physical characteristics of the water flow (water depth, current speed) at different tidal regimes (spring tide and neap tide) were also considered. Median filtration rates ranged 5.0−45.0 lm−2 h−1, despite the lack of dense bivalve beds or reefs. Based on median filtration rates of benthic communities on the studied substrate types, a model we developed showed that seagrass bed areas retained 15% of suspended particles during spring tide and 47% during neap tide. These retention efficiencies were much higher than those observed on mud flats (2.8% during spring tide, and 8% during neap tide), sand flats of finer grain size (8.8% during spring tide, and 50% during neap tide), and sand flats of coarser grain size (7% during spring tide, and 31% during neap tide). Removal of particles from water column was higher during the ebb tide than during flow tide, with particles of <5 μm diameter (especially diatoms, flagellates, and small-sized particulate matter) being the most commonly removed.
- Interactions between Green Turtles (Chelonia mydas) and Foxes (Vulpes vulpes arabica, V. rueppellii sabaea, and V. cana) on Turtle Nesting Grounds in the Northwestern Indian Ocean: Impacts of the Fox Community on the Behavior of Nesting Sea Turtles at the Ras Al Hadd Turtle Reserve, OmanPublication . Mendonca, Vanda; Al Saady, Salim; Al Kiyumi, Ali; Erzini, KarimVanda Mariyam Mendonca, Salim Al Saady, Ali Al Kiyumi, and Karim Erzini (2010) Interactions between green turtles (Chelonia mydas) and foxes (Vulpes vulpes arabica, V. rueppellii sabaea, and V cana) on turtle nesting grounds in the northwestern Indian Ocean: impacts of the fox community on the behavior of nesting sea turtles at the Ras Al Hadd Turtle Reserve, Oman. Zoological Studies 49(4): 437-452. Green turtles Chelonia mydas nest year round at the Ras Al Hadd Nature Reserve, Oman, with a distinct lower-density nesting season from Oct. to May, and a higher-density nesting season from June to Sept. On these beaches, the main predators of turtle eggs and hatchlings are foxes Vulpes spp., wolves Canis lupus arabs, and wild cats Felis spp. and Caracal caracal schmitzi. During 1999-2001, both the nesting behavior of these turtles and the diets of foxes (the main predator on the beaches) were investigated, and we tested whether female turtles were able to avoid/reduce predation pressure on their eggs and hatchlings on the nesting grounds. Elsewhere in the region and globally, foxes are known to feed on rodents, lizards, birds, and insects, but at Ras Al Hadd, their diet is basically composed of sea turtle eggs and hatchlings (comprising about 95% in volume), with smaller contributions from other marine invertebrates (mostly ghost crabs Ocypode spp. and large gastropods), although they also sporadically ingested birds and lizards. The ability to adapt to a diet of sea turtle eggs and hatchlings, on these beaches, is certainly a factor behind the success of this carnivore community in the arid lands of the Arabian Peninsula. Field experiments indicated that nesting sea turtles recognized both natural predators and humans as threats to their offspring, and this was reflected in modifications to their nesting behavior. In relatively undisturbed areas (by both natural predators and humans), sea turtle nest density was significantly higher, and nests were placed further away from the surf's edge, in contrast to results from relatively disturbed areas, where turtle nests were closer to the surf's edge, thus reducing the distance hatchlings had to travel when they emerge and begin their journey to the sea. Nesting turtles interrupted their nesting cycle if they sensed the presence of people or foxes, returning to the sea without laying a clutch. However, if they had already initiated oviposition when they sensed the presence of people and/or predators, they continued, although they significantly increased efforts to camouflage their nests. Other reasons behind nest site abandonment included sand collapsing events (critical during preparation of the egg chamber) and intraspecific competition for nest sites. These behavioral patterns of sea turtles result from their evolutionary adaptation to nesting on beaches, which surely played a role in their survival, but also highlight the importance of minimizing human disturbance and activities on turtle nesting beaches. http://zoolstud.sinica.edu.tw/Journals/49.4/437.pdf
- The ecological role of overwintering fish in the food web of the Culbin Sands lagoon ecosystem, NE Scotland: identifying major trophic links and testing effects of the fish Pomatoschistus microps (Pallas) on benthic invertebratesPublication . Mendonca, Vanda; Raffaelli, David; Boyle, Peter; Emes, ChasThe Culbin Sands lagoon ecosystem in NE Scotland was studied during a three-year period (1994-1996) to identify the major trophic links from benthic invertebrates to epibenthic predators, and to assess impacts of overwintering fish on their prey communities. Every 2-4 weeks, samples of mobile fauna were collected to study their diets. The major trophic links identified between benthic invertebrates and epibenthic predators were from benthic invertebrates to the shrimp Crangon crangon, and to the common goby Pomatoschistus microps and the plaice Pleuronectes platessa. The energy flow from benthic invertebrates to overwintering fish was estimated at 133 kJ m(-2)yr(-1). A flow of 10 kJ m(-2)yr(-1) was also observed from eggs and larval stages of the overwintering shrimp Crangon crangon to the overwintering fish. Nevertheless, manipulative field experiments showed no significant impacts of the most abundant overwintering fish Pomatoschistus microps on prey community densities, despite an overall individual ingestion rate of 89 J day(-1).