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Rocky intertidal community structure in oceanic islands : scales of spatial variability

Publication . Martins, Gustavo M.; Thompson, Richard C.; Hawkins, Stephen J.; Neto, Ana I.; Jenkins, Stuart R.

There is a clear bias in the literature on island ecology towards terrestrial rather than marine systems, which have remained comparatively poorly studied. Marine populations are typically open, and local production may have little impact on local recruitment, such that long-distance dispersal is an important determinant of population ecology. Since oceanic islands form discrete patches of habitat surrounded by a structurally different environment, we tested the general hypothesis that processes operating at the scale of islands have a greater influence on these populations than the processes operating at smaller, intra-island scales. A hierarchical design examined the patterns of abundance and distribution of conspicuous taxa at 3 tidal heights at a range of spatial scales, ranging from a few meters to hundreds of kilometres apart in the rocky intertidal of the Azores. Both uni- and multivariate analyses showed that at the largest scale (islands), significant variation was detected in the lower and mid-shore communities, but not on the upper shore. Along the vertical gradient of immersion there was a trend for increasing small-scale patchiness towards the top of the shore. The potential role of local environmental stress gradients and broad-scale oceanographic patterns of recruitment in structuring these assemblages is discussed. This study corroborates the suitability of the analytical tools used here to examine patterns of distribution over a range of spatial scales and its applicability in the field of island marine ecology.

2008-03Journal article

Open access

Illegal harvesting affects the success of fishing closure areas

Publication . Martins, Gustavo M.; Jenkins, Stuart R.; Hawkins, Stephen J.; Neto, Ana I.; Medeiros, André; Thompson, Richard C.

There is clear evidence that marine reserves can be used as effective tools to foster the recovery of disturbed ecosystems. In the Azores, intense exploitation of the patellid limpets Patella candei and P. aspera has led to a rapid decline in their populations and subsequent collapse of the fishery in 1985. In 1993, legislation was passed to protect limpets, including the establishment of limpet protected zones (LPZs) where harvesting was completely prohibited. Outside LPZs, a seasonal fishing closure prohibited the harvesting of limpets from October to May. Here we examine the effect of such measures 16 years after they were put into practice. In each of the 3 years examined, limpet density, biomass and size were generally similar both inside and outside the LPZs. In addition, there were clear signs of exploitation as most individual limpets inside the LPZ were smaller than the legal catch size suggesting that illegal harvesting was taking place. Observations confirmed that illegal harvesting of limpets was common both inside and outside LPZs. Lack of enforcement of regulations is therefore a likely reason for the failure of legislation to protect limpet populations and facilitate stock recovery.

2011-06Journal article

Open access

Exploitation of rocky intertidal grazers : population status and potential impacts on community structure and functioning

Publication . Martins, Gustavo M.; Jenkins, Stuart R.; Hawkins, Stephen J.; Neto, Ana I.; Thompson, Richard C.

A wide range of anthropogenic activities are impacting the ecology of coastal areas. Exploitation of marine resources is one such activity, which, through cascading trophic effects, can have influences well beyond that of the target species. We investigated the mid-rocky-shore community structure of the Azores archipelago, a seldom-studied habitat, where there is a local tradition of exploiting limpets, the main intertidal grazers. The limpet population structure differed among islands, and there was an inverse relationship between the abundance of larger limpets and the human population per coastal perimeter, but not the associated catch data. At small scales of resolution (quadrats), there was a negative relationship between the cover of algae and limpets and a positive relationship between barnacles and limpets. These relationships were also apparent at the larger scale of islands as a function of the gradient of exploitation. Our results show how natural habitat fragmentation may be useful where the experimental testing of a hypothesis is not possible, and provide evidence for the trophic cascading effects of limpet exploitation at landscape scales.

2008-07Journal article

Open access