Carrying Capacity on a Small Island
A 0.4 km² car-free island nature reserve receives up to 4,200 day visitors on August days, but only about 600 in winter. Around 70% arrive between 10:00 and 14:00 on 40 daily boat trips. The island has 12 permanent residents, one seasonal snack bar, two composting toilets and no sewage connection. A survey found that 35% of the Posidonia seagrass bed within the main bay is scarred by anchors, and litter counts peak at 180 items per 100 m of beach. The management plan proposes a daily cap of 1,500 visitors, an online booking system, a €6 landing fee, 60 eco-moorings, and a seasonal no-anchor zone. Ferry operators warn that the cap will cut revenue by 40%; residents want quieter summers; the environment ministry wants the seagrass to recover within five years. The island is also a Natura 2000 site. The plan must be approved before the next summer season.
1. Explain why visitor numbers alone are an insufficient measure of carrying capacity here.
Read the worked answer
A total of 4,200 visitors sounds high, but the timing matters more. About 70% arrive between 10:00 and 14:00, so roughly 2,940 people may be present at once on a 0.4 km² island - a much greater concentration than the daily total suggests. The main bay has limited space, the toilets are only two composting units, and anchoring directly damages Posidonia. Carrying capacity therefore has ecological, social, infrastructure and perceptual dimensions: seagrass scarring, crowding, litter, resident disturbance and visitor experience. Winter numbers of 600 are not a problem. A daily cap of 1,500 reduces the total, but if all 1,500 arrive in the same four-hour window the peak pressure may still be too high. Time slots, mooring controls and closed areas are needed alongside a number cap.
2. Evaluate the proposed cap and pricing package. Recommend one modification and justify it.
Read the worked answer
The cap of 1,500 cuts the August maximum by 64% from 4,200 and is a strong response to ecological pressure. The €6 landing fee would raise €9,000/day at the cap, which could fund enforcement, toilets and monitoring, but it may not deter visitors who have already paid for a boat trip. Ferry operators’ claim of a 40% revenue loss is plausible if they depend on day trippers. The cap protects seagrass only if anchoring is controlled; eco-moorings and the no-anchor zone address the direct damage. Modification: use timed booking with, for example, 500 visitors per two-hour slot and a higher peak fee, such as €10 before 14:00 and €3 after. This spreads the peak, protects the bay and shares revenue across the day. Conditions: independent visitor counts, seagrass cover triggers and litter triggers, with the cap reviewed after one season.
3. Suggest three indicators and trigger thresholds for adaptive management of the island.
Read the worked answer
First, seagrass condition: measure Posidonia cover and anchor scars in permanent quadrats; if scarring rises above an agreed baseline, close the affected zone and reduce moorings. Second, visitor pressure: count arrivals per hour and boat numbers in the bay; if the two-hour slot exceeds its booking limit or more than 60 boats are present, stop further landings that day. Third, environmental quality: litter per 100 m and toilet/facility performance; if litter exceeds, say, 50 items per 100 m or toilets fail, increase collection and cleaning and review the daily cap. These indicators are measurable, linked to the plan’s objectives and can trigger a management response before irreversible damage occurs. They also give the regulator evidence for the Natura 2000 review.