Herbivory effects on the morphology of the brown alga Padina boergesenii (Phaeophyta)

254

181

The use of standardised classifications, or operational definitions, is essential if different researchers are to measure and compare similar entities. In the marine realm, algal 'turfs' are increasingly reported to be globally expanding at the expense of kelps and canopy-forming algae. However, ecological research about the underlying drivers of this shift is limited by a vague and inconsistent definition of what exactly a turf is. In order to stimulate more effective descriptions of 'turfs' and facilitate communication of research outcomes and comparisons across studies, we reviewed the use of the term turf in ecological studies of temperate coasts and coral reefs and (1) identified the main types and distribution of algal assemblages known as 'turfs', (2) examined the descriptions of turfs so that we may recognise some general characteristics, including those contingent on environmental conditions; and (3) offered character descriptions that could improve communication and comparisons. These descriptors centre on reporting information on the morphology, height, density of thalli, the amount of sediment trapped in turfs and a description of the area covered by turfs, including their patchiness and persistence. Our review recognised these as common attributes that could be usefully described across a wide range of circumstances and provide insights into the ecology of turfs and their interactions with other assemblages in a community. The use of common descriptors would provide the term 'turf' with greater scientific value.

Section: Morphologymentioning

confidence: 99%

What are algal turfs? Towards a better description of turfs

Connell¹,

Föster²,

Airoldi³

2014

254

181

“…However, herbivore communities are increasingly being affected by overfishing, potentially undermining the ability of reefs to resist a phase shift to dominance by macroalgae (Hughes 1994, McClanahan et al 2011a) and recover from disturbances (Nugues & Bak 2006, Hughes et al 2007. Here, transitions to macroalgae generally progress from filamentous turf algae and crustose coralline algae (CCA) to corticated and fleshy macroalgae, then to leathery and coarsely branched macroalgae or calcified algae that are un palatable to most herbivores (Hixon & Brostoff 1996, McClanahan 2000, Diaz-Pulido et al 2007). Thus, it is important to identify how different herbivores influence algal composition and succession on coral reefs, and what this means in the context of preventing shifts to macroalgal dominance (Hughes 1994, Hoey & Bellwood 2009).…”

Section: Introductionmentioning

confidence: 99%

Differential impacts of coral reef herbivores on algal succession in Kenya

Humphries¹,

McClanahan²,

McQuaid³

2014

In shallow-water systems, fisheries management influences herbivory, which mediates ecosystem processes by regulating algal biomass, primary production, and competition between benthic organisms, such as algae and corals. Sea urchins and herbivorous fishes (scrapers, grazers, browsers) are the dominant herbivores in Kenya's fringing coral reef and their grazing influences coral−macroalgal dynamics and dominance. Using experimental substrata and grazer exclusions, we tested the hypothesis that herbivores differentially affect algal composition and succession using 3 levels of fisheries management: fished reefs, community-managed closures (<10 yr old, < 0.5 km 2 ), and government-managed closures (20 to 40 yr old, 5 to 10 km 2 ). In fished reefs and government closures, herbivores facilitated maintenance of early successional algal species, such as turfs, associated with sea urchins in the former and scraping fishes in the latter. Crustose coralline algae were only abundant in government closures, and video recordings showed that fish grazing was greatest at these sites, most notably for parrotfishes (scrapers). A combination of sea urchins and small grazing and detritivorous fishes was present in community closures, which allowed macroalgae to quickly develop from turf into early then late successional stages. These reefs may represent an intermediate or transitional system of herbivore dominance characterized by macroalgae. Consequently, reefs in heavily fished seascapes initially protected from fishing may require additional management efforts to facilitate the recovery of larger-bodied scraping fishes, including bans on capturing parrotfishes and restricting gear (e.g. spearguns) that target these species.

“…Since Lewis et al (1987) showed that Padina jamaicensis induced morphological changes in response to fish grazing (growing as creeping filaments in the presence of fishes, but shifting to broad, upright blades in the absence of fishes), there seem to have been only a few published studies documenting a correlation between morphology or metabolite concentration and fish grazing intensity (Paul & Van Alstyne 1988, Coen & Tanner 1989) and, to our knowledge, only one experimental test (Diaz-Pulido et al 2007). Likewise, reviews (Harvell 1990, Hay 1996) and meta-analyses (Koricheva et al 2004, Toth & Pavia 2007, Jormalainen & Honkanen 2008) have not covered due to fish grazing, apparently because too few studies exist.…”

Section: Introductionmentioning

confidence: 99%

“…Firstly, fish grazing is not spatially or temporally uniform (Hay et al 1983, Diaz-Pulido et al 2007). Palatable algae in areas continually accessible to grazers may be rapidly consumed (even to local extinction), but those in areas of spatial or temporal escape experience periodic and non-fatal bouts of feeding, allowing time to induce defences before another feeding bout commences (Hay 1981, Hay et al 1983).…”

Section: Introductionmentioning

confidence: 99%

Induced defence to grazing by vertebrate herbivores: uncommon or under-investigated?

Dell

Hay

2016

There are many examples of macroalgae inducing defence in response to small invertebrate herbivores like amphipods, isopods, and gastropods but few cases of induction in response to vertebrate macrograzers like herbivorous fishes. This may be because larger grazers rapidly consume large quantities of seaweed before induction can occur, thus selecting for constitutive rather than induced defences. Alternatively, the pattern could occur because induction due to feeding by macrograzers is less commonly investigated. In Fiji, field assays with the brown macroalga Sargassum polycystum demonstrated that thalli growing in marine protected areas (MPAs) with abundant herbivorous fishes were significantly less palatable than those growing in adjacent fished areas (non-MPAs) with few herbivorous fishes. This significant preference occurred in 11 of 13 trials over 5 time periods and across 3 pairs of MPAs and spatially associated non-MPAs. This preference was not positively associated with algal nitrogen content or with the toughness of algal fronds. When S. polycystum ramets were taken from the non-MPA and half were partially grazed by fishes while the other half were protected from grazing, new growth from the controls was strongly preferred to new growth from the previously grazed ramets although these fronds originated from the same holdfast. This suggests that S. polycystum upregulates defences (probably chemical) in response to grazing by herbivorous fishes. This is one of the few published examples of induction of macroalgal defence in response to feeding by large, mobile grazers. It is unclear whether induced defences against fishes are rare or just under-investigated.