intertidal invertebrate and algal communities on the rocky shores of the bay of morbihan, kerguelen...
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P.S.Z.N. I: Marine Ecology, 8 (3): 207-220 (1987) 0 1987 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0173-9565
Accepted: March 26,1987
Intertidal Invertebrate and Algal Com- munities on the Rocky Shores of the Bay of Morbihan, Kerguelen (South Indian Ocean) JOHN M. LAWRENCE & JAMES B. MCCLXNTOCK'
Department of Biology, University of South Florida, Tampa, Florida 33620, U. S. A.
I Present address: Department of Biology, University of Alabama at Birmingham; Birmingham, Alabama 35294, USA.
With 5 figures and 4 tables
Key words: Intertidal, communities, Kerguelen, South Indian Ocean.
Abstract. Both the emergent surfaces and tide pools of the rocky intertidal shores of the Bay of Morbihan, Kerguelen are depauperate in number of macroinvertebrate and macroalgal species. Diversity (H') was high and similar for macroinvertebrates in tide pools from the high to low intertidal and on the emergent surface exposed at extreme low-tide when calculated in terms of numbers of individuals. H' was lower when calculated in terms of energy and twice as high for the tide pool in the high intertidal than the lower tide-pools and the emergent surface. H' for macroalgae was 0 in the highest tide-pool and highest in the lower tide-pools. The densitykpecies- rank curves for the macroinvertebrates and the macroalgae are logarithmic but vary in linearity. Algal biomass was 37 % of the macroinvertebrate biomass on the emergent surface at the extreme low-tide, but 106% in the highest tide-pool. Twenty-three months after denudation of the tide pools, the ratios of total densities of the macroinvertebrates (ind . m-l) to the original densities were 48 % for the pool in the high intertidal, 25 ?6 for the middle tide-pool, and 4 % for the pool in the low intertidal. The diversity indexes for the macroinvertebrates were similar to the original ones. Recolonization at Kerguelen is slow and shows an intertidal gradient. The composition of the rocky intertidal community at Kerguelen results from the rigorous physical environment and the small number and functional types of species. In the absence of major predators on macroinvertebrates and of herbivores on macroalgae, interaction among the species present seems to be competitive in nature.
PAINE (1966) pointed out that although longitudinal and latitudinal gradients are ' well known geographically, they are poorly known ecologically. Most of the studies of the communities of the rocky intertidal have been done on north- temperate (CONNELL, 1972; DAYTON, 1971,1975; LUBCHENCO, 1978; LUBCHENCO & MENGE. 1975; MENGE, 1976; PAINE, 1966,1974) and south-temperate (BERRY,
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208 LAWRENCE & MCCLINTOCK
1982; JAM & MORENO, 1984; MAY er al., 1970; MCQUAID & BRANCH, 1984; MORENO & JARAMILLO, 1983; PAINE, 1971; UNDERWOOD, 1981; UNDERWOOD & JERNAKOFF, 1984) continental coasts. These regions are productive, with an abundance of species and individuals, and with many functional types (plants and animals) in common.
In addition to the preponderance of information about communities of temperate regions, almost all information pertains to emergent surfaces. The tide pools that frequently occur in the rocky intertidal are rarely studied. It is known that tide pools extend the distribution of species upwards, but that there is still an increased stress associated with increased height of the pools so that intertidal zonation occurs with tide pools as with the emergent surfaces (DOTY, 1957; LEWIS, 1964; NEWELL, 1979; STEPHENSON & STEPHENSON, 1972). These stresses can be qualitatively different from those associated with emergent surfaces (e. g., pH, oxygen concentration, salinity) and can have interactive effects with each other and with temperature (NEWELL, 1979). These physical factors have been considered to control primarily the abundance and distribu- tion of algal species in tide pools, but both biological and physical controls exist (LUBCHENCO, 1978; PAINE & VADAS, 1969; SZE, 1980; UNDERWOOD & JERNAKOFF, 1984).
The island of Kerguelen is isolated in the South Indian Ocean and subject to rigorous oceanic conditions. Its marine flora and fauna are known ~(ARNAUD, 1971) and the general zonation of the emergent surfaces and tide pools of the rocky intertidal has been described qualitatively (ARNAUD, 1974; BELLIDO, 1981; DELEPINE, 1963). Basic functional types of invertebrates which can control community structure (e. g. asteroid carnivores such as Pisaster and echinoid herbivores such as Srrongylocenfrorus) are missing from the rocky intertidal zone. Many of the algae found in the rocky intertidal of Chile and Southern Australia (JARA & MORENO, 1984; UNDERWOOD, 1981) are also absent at Kerguelen.
The purpose of the present paper is to quantitatively describe the macroin- vertebrate and algal components of the communities of the tide pools and emergent surfaces that occur at different levels of the rocky intertidal zone at Kerguelen. The basic question was whether the rigorous physical environment and the suite of species which exists at Kerguelen affects density, species richness, and species diversity.
Material and Methods
1. Study site
The Kerguelen archipelago (495 , 70"E) is situated in the South Indian Ocean just within the antarctic convergence, approximately 4000 km southeast of Africa and 2000 km north of the Antarctic continent (Fig. 1). Grande Terre is the largest of over 300 islands which comprise the archipelago, and is ca. 140 km in width and length. The island is of volcanic origin., composed primarily of basalt which has been extensively modified by glaciation. The extreme isolation of the island contributes to its oceanic climate. Winds have a mean annual speed of 10m . sec-I and may reach speeds as great as 62 m . sec-' (ARNAUD, 1974). The number of d . a-' with winds exceeding 16m . sec-' can be as high as 333 (ARNAUD, 1974). The weather is typically cloudy with light rain 13 to 25 days each month and monthly precipitation of 27 to 117mm (HUREAU, 1970; ARNAUD, 1974).
Fig. 1. Map of Kerguelen. The ar- row points to Port-aux-Frangais in the Bay of Morbihan.
I ,$ KERGUELEN
I I Snow and hail fall at sea level, more frequently in winter but even in the austral summer. The air temperature is moderate at sea level, but may be as high as 20C during the summer and, although rarely below O'C, as low as -8C during the winter (HUREAU, 1970; ARNAUD. 1974).
The present study was conducted in the Bay of Morbihan, an extensive (ca. 100 km') semi- protected bay at the eastern end of the island. The shoreline of the bay has a variety of habitats including sand and cobble beaches, fjords, and extensive rocky-intertidal areas. Tidal cycles occur twlcr a day with an amplitude ranging from 30 to 210cm (HUREAU, 1970). Surface seawater temperatures range from 5 . 5 T in the summer to 2.1"C in the winter; surface salinities range from 31.9 to 33.6%0 (HUREAU, 1970). Although the bay is protected from open ocean swetls, high winds frequently generate surf conditions, particularly on the northern side which faces the prevailing winds.
The site of the transect was at the west end of the Promenade des Amerlocks, west of the Pte. de la Baignade (Fig. 1) on the northern coast of the bay, west of Port-aux-Frangais. The transect has the general features described for similar intertidal areas by DELdPrNE (1963), ARNAUD (1974), and BELLIDO (1981). Prevailing winds and waves strike this coast so that extremely high-energy wave action can occur. Occasional periods of dead calm result in the absence of wave activity. The transect (Figs. 2-4) was a broad, gently sloping rock shelf of ca. 45 m between extreme high-tide (EHT) and extreme low tide (ELT) (ca. 2M)cm vertical height). There were five stations on the transect including three tide-pools and two emergent surfaces.
In her study on the algae of tide pools, LUECHENCO (1978) selected three pools because they subjectively appeared to represent two extremes of the continuum in types of algae present. We selected three representative tide-pools at different levels because they were similar in size but showed distinct differences in-plant and animal composition. Pool 1 was closest to the edge of the shelf, 125 x 150cm (18,750cm') in area and 37cm in depth. Pool 2 was the middle tide-pool, 200 x 225cm (45,000cmZ) in area and 16cm in depth. Pool 3 was the highest tide-pool, 200 X 125cm (25,000 cm') in area and 6 cm in depth. At an ELT during moderate wave activity Pools 1 and 2 were isolated from the sea for ca. 3 h 30 min while Pool 3, because of orientation and neighboring relief, was isolated from the sea for only ca. 1 h. Maximal temperatures reached during these periods were 12.5"C, 17"C, and 17.5"C for Pools 1 , 2 , and 3, respectively. Minimal temperature during isolation at low tide in the austral winter 1983 were 1.5"C and 2C for Pools 1 and 2, respectively (F. GUILBERT, pers. comm.). No ice forms in the pools during the winter.
One emergent-surface station was on the shelf below the lowest tide-pool and was exposed only at ELT. The second emergent-surface station was adjacent to the middle tide-pool and was exposed at moderate low tides.
2. Sampling and analyses
As UNDERWOOD (1981) pointed out, his and other similar studies on intertidal community structure restricted sampling to those species that were common, reliably identified, and quantified. The
210 LAWRENCE & MCCLINTOCK EHT E LT
. P O O L 3 POOL 2 POOL 1
BOULDERS (depth 6 cm) (depth 1 6 c m ) ( d e p t h 3 7 c m ) SHELF
I , I I -t---b (m) o 10 za 30 40 5 0
Fig. 2. Diagram of the tra