Floristics, phenology, and ecology of the sublittoral marine algae in an unstable cobble habitat (Plum Cove, Cape Ann, Massachusetts, USA)

The macrobenthic community of a shallow subtidal cobble bed at Eagle Head on the Atlantic coast of Nova Scotia was monitored from ca 4 mo before to 41 mo after mass mortalities of sea urchins Strongylocentrotus droebachiensis in September 1983. Biomass of erect algae on cobbles increased from 0 to between 50 and 75 g (dry weight) m-' after the sea urchin die-off, and consisted mainly of small and sparsely distributed plants of Fucus evanescens and Chondrus crispus. In contrast, algal biomass increased from 0 to ca 2.8 kg m-2 on an adjacent boulder ridge where large kelps (Laminaria longicruris, L. digitata, Saccorhiza dermatodea) formed a dense canopy. The macroflora of cobble beds at 2 other sites was similar in biomass and con~position to the cobble bed at Eagle Head. At a third site, the sea urch~n population had recovered and precluded the establishment of non-calcareous algae on the cobbles. In the absence of sea urchins, herbivorous molluscs, mainly perwinkles Littorina littorea, limpets Notoacmaea testudinalis and chitons Tonicella rubra, dominated the cobble macrofauna, reaching densities of up to ca 150, 400, and 1300 ind. m-2 respectively at Eagle head. However, these grazers (and other organisms) suffered mass mortalities in summer 1986, when thick mats of drift algae inundated the bottom creating anoxic conditions. Suspension feeders consisted mainly of small bivalves of which juvenile mussels (Modiolis modiolis, Myllis edulis) were most abundant. Predators/ scavengers included crabs, lobsters, whelks, sea stars, and polychaetes, many of which were small and seasonally active. With the exception of juvenile mussels, which increased in abundance (but rarely reached adult size), there was no evidence of a numerical response among macrofaunal populations to the elimination of sea urchins.

Section: Introductionsupporting

confidence: 67%

Section: Introductionmentioning

confidence: 98%

Community dynamics on a subtidal cobble bed following mass mortalities of sea urchins

Scheibling¹,

Raymond²

1990

“…Contrary to other species that are not reproductive during the winter, crusts were reproductive throughout the year, as also observed in other studies (Adey & Vassar 1975, Dethier 1981, Davis & Wilce 1987, Kaehler & Williams 1997. Early rates of recruitment of crusts, however, were significantly lower during winter and were spatially very variable.…”

Section: Discussionsupporting

confidence: 77%

“…wave action, sediment stress, bottom instability, herbivory, competition) than are sexual propagules (Hansen 1977, Sousa 1980, Sousa et al 1981, D'Antonio 1986, Davis & Wilce 1987, McCook & Chapman 1992, Airoldi 1998). Thus vegetative propagation should be an important mechanism of recovery after most common disturbances (Davis & Wilce 1987, Airoldi 1998, especially when damage to algae is patchy (Sousa 1980, McCook & Chapman 1997 .…”

Section: Discussionmentioning

confidence: 99%

Responses of algae with different life histories to temporal and spatial variability of disturbance in subtidal reefs

Airoldi¹

2000

Colonisation of patches disturbed at different times of the year and at d~fferent locations was investigated from November 1995 to August 1997 in subtidal, rocky-shore, algal assemblages (Mediterranean Sea. Italy). A field experiment tested specifically: (1) whether and how the success of turf-forming, encrusting and erect algae are influenced by the timing of disturbance and (2) whether recovery of these species is cons~stent across space (from about 1 m to 100s of metres). Clearings were made at 8 different times within 1 year, in order to identify possible temporal trends in responses of algae to disturbance. Reproductive traits of the most abundant algae were also investigated. Encrusting, turf-forming and erect algae responded differently to spatial and temporal variation in disturbance, depending on their varylng abilities to colonise available space and on spatlal and temporal differences in rates of recruitment and growth. Turf-forming algae colonised space by vegetative propagation and quickly regained spatial dominance in patches cleared at all times of the year and at all locations. Conversely, encrusting and erect species occupied space mostly by colonisation of propagules; their recruitment was influenced by the timing and location of disturbance, probably depending on the concomitant availabil~ty of bare rock, viable propagules and favourable environmental conditions. A regime of d~sturbance adverse to recruitment of erect algae was identified as the probable cause of their low abundance in the study area. Overall, results suggested that while recruitment by sexual propagules can be highly variable through space and time, recovery by vegetative propagation can be constant and highly predictable over a range of environmental conditions, and that vegetative reproduction is likely to be fundamental to spatial dominance in a variety of habitats.

“…The main ecological mechanism responsible for the control of the community structure in those habitats was recognized as a physical disturbance (Davis & Wilce 1987b). Disturbance is defined by Grime (1977) as a n 'event, biotic or abiotic in origin, that destroys biomass, affecting from one organism to entire communities'.…”

Section: Introductionmentioning

confidence: 99%

Structure of subtidal algal assemblages on soft-bottom sediments: fauna/flora interactions and role of disturbances in the Bay of Brest, France

Hily¹,

Potin²,

Floc′h³

1992

: Algal and fauna1 assemblages living on soft bottom sediments were studied in the Bay of Brest, France, using quantitative descriptions of the distribution, diversity and biomass of epibenthic species. Similar classification and ordination analyses were used on floral and animal data. Dense assemblages of macrophytes, mainly Rhodophyceae, were found to grow on sandy mud sediments. Sediments were essentially covered by maerl beds of the calcareous red alga Lithothamnion corallioides and various shell substrates. Five maln algal assemblages extended along a west-east decreasing gradient of hydrodynamic activity (i.e. tidal currents, waves and turbidity). The high frequency of storms during the year is the main feature which disturbs both flora and epifauna. Interactions between flora and fauna were either direct, e.g. grazing and spatial competition, or indirect, most of the substrata occupied by macrophytes being shells of dead bivalves and gastropods. Moreover attachment of algae was largely dependent on population dynamics of shell species living in the area. As a consequence, in the most disturbed area, the macrophytes found were opportunistic species (Polysiphonia fibrillosa and Polysiphonia urceolata). In areas where the assemblage was unstructured, a fact which prevented the development of the herbivorous species, the animal assemblage was then dominated by suspension feeders (FicuLina ficus and Phallusia marnmillata) which competed for space with the macrophytes. In the least disturbed area, the herbivorous species dominated the fauna assemblage while flora assemblage had a high level of organization. However, in those places eutrophication and high turbidity prevented the establishment of many algal species, causing the ubiquitous ones to domInate (Ulva sp., Ceramium rubrum). Between these extreme areas, the living Lithotharnnion beds were more developed and were defined as a characteristic assemblage of diversified Rhodophyceae species such as Chyloclad~a verticillata, Halarachnion ligulaturn, Crytopleura ramosa. Finally, the role of wave disturbance as the main factor controlling algal assemblages of shallow soft-bottom sedlments is discussed.