Recovering a lost baseline: missing kelp forests from a metropolitan coast

Abstract

There is concern about historical and continuing loss of canopy-forming algae across the world's temperate coastline. In South Australia, the sparse cover of canopy-forming algae on the Adelaide metropolitan coast has been of public concern with continuous years of anecdotal evidence culminating in 2 competing views. One view considers that current patterns existed before the onset of urbanisation, whereas the alternate view is that they developed after urbanisation. We tested hypotheses to distinguish between these 2 models, each centred on the reconstruction of historical covers of canopies on the metropolitan coast. Historically, the metropolitan sites were indistinguishable from contemporary populations of reference sites across 70 km (i.e. Gulf St. Vincent), and could also represent a random subset of exposed coastal sites across 2100 km of the greater biogeographic province. Thus there was nothing 'special' about the metropolitan sites historically, but today they stand out because they have sparser covers of canopies compared to equivalent locations and times in the gulf and the greater province. This is evidence of wholesale loss of canopy-forming algae (up to 70%) on parts of the Adelaide metropolitan coast since major urbanisation. These findings not only set a research agenda based on the magnitude of loss, but they also bring into question the logic that smaller metropolitan populations of humans create impacts that are trivial relative to that of larger metropolitan centres. Instead, we highlight a need to recognise the ecological context that makes some coastal systems more vulnerable or resistant to increasing human-domination of the world's coastlines. We discuss challenges to this kind of research that receive little ecological discussion, particularly better leadership and administration, recognising that the systems we study out-live the life spans of individual research groups and operate on spatial scales that exceed the capacity of single research providers.

The other ocean acidification problem: CO 2 as a resource among competitors for ecosystem dominance

“…only nutrients and not CO 2 ), whereas their alternate state (characterized by turf algae) was co-limited by both nutrients and CO 2 . This difference in carbon limitation demonstrates the potential for elevated CO 2 to influence turf expansion [32], especially when amplified by human activities that also increase nutrient loads [33]. This response is characteristic of co-limitation by multiple resources [34].…”

Global patterns of kelp forest change over the past half-century

“…Kelp forest declines have now been documented in many regions in response to a variety of stressors (18,(31)(32)(33)(34)(35), but kelp abundances have been stable or increasing in other areas (17,36,37). Here, we amass a global database of kelp abundances to provide a comprehensive picture of kelp forest change.…”

Can strong consumer and producer effects be reconciled to better forecast ‘catastrophic’ phase-shifts in marine ecosystems?

“…Alternately, loss of coral or kelp often involves rapid colonisation of new space by ephemeral and fast growing algae, which can persist for decades in both coral reefs (Hughes, 1994) and kelp forests (Connell et al, 2008). Identification of the conditions that cause these algae to change function from early successional stages to more permanent occupiers of space is often key to understanding why corals and kelps fail to regenerate after natural or human impacts.…”

“…coral reefs, kelp forests and seagrass meadows) that transition to a contrasting state under altered environmental conditions (e.g. shifts to primary producers of simpler architectural complexity; Bellwood et al, 2004;Connell et al, 2008).…”