Small spatial scale effects of wave action exposure on morphological traits of the limpet Lottia subrugosa

Many studies have already assessed how wave action may affect morphology of intertidal species among sites that vary in wave exposure, but few attempted to look to this issue in smaller scales. Using the most common limpet of the Brazilian coast, Lottia subrugosa, and assuming position on rocky boulders as a proxy for wave action at small scale, we tested the hypothesis that waves may also influence limpet morphology at a smaller spatial scale by investigating how individual size, foot area and shell shape vary between sheltered and exposed boulder sides on three shores in the coast of Ubatuba, Brazil. Limpets consistently showed a proportionally larger foot on exposed boulder sides for all shores, indicating that stronger attachment is an important mechanism to deal with wave action dislodgement at a smaller scale. Shell shape also varied in the scale investigated here, with more conical (dissipative) shells occurring in exposed boulder sides in one exposed shore across time and in the other exposed shore in one year. Shell shape did not vary regarding boulder sides across time in the most sheltered shore. Although we did not assess large spatial scale effects of wave action in this study, variations of the effect of waves at small spatial scale observed for shell shape suggest that it may be modulated by the local wave exposure regime. Our work highlights the importance of wave action at small spatial scales, and may help to understand the ecological variability of limpets inhabiting rocky shores.

Isoetes ×gopalkrishnae (Isoetaceae), a new interspecific sterile hybrid from central India

Isoetes ×gopalkrishnae hybr. nov., is described, illustrated and compared with possible parent species. Based on morphological characteristics and habitat conditions, this taxon is considered to represent a sterile hybrid between I. coromandelina and I. panchananii. The new hybrid is amphibious and grows on the exposed shore of an artificial pond. It is known only from a single locality on the Vindhya plateau in Uttar Pradesh, India. It can be distinguished from other taxa by a combination of characters including the lack of a scale, the leaf which is terete in transverse section, velum absent to rudimentary, a sporangial wall with internal pigmentation, rugulate megaspores with a smooth equatorial girdle and microspores with densely echinate to short-cristate ornamentation. It is the first Isoetes hybrid reported from the Indian subcontinent.

Spatial distribution of the invasive bivalve Isognomon bicolor on rocky shores of Arvoredo Island (Santa Catarina, Brazil)

The invasion of marine species is a threat to local and global biodiversity and can have many ecological, economic and social impacts. The bivalve Isognomon bicolor has invaded the rocky shores of Brazil and spread along the coast, occurring from Rio Grande do Norte to the Santa Catarina State. The present study evaluated the distribution of I. bicolor on different rocky shores of Arvoredo Island (Santa Catarina State) and its relationship with other taxa. A high density of I. bicolor was found on the exposed shore, which was associated with the occurrence of articulated calcareous macroalgae. In addition, I. bicolor was also found in empty shells of the barnacles Tetraclita stalactifera and Megabalanus spp. The physical structure of these habitats probably plays an important role in the success of I. bicolor invasion. For these reasons, I. bicolor evidences an alteration on the benthic community of the rocky shores and its potential consequences become a threat to local species.

Spatial variation in the community structure of intertidal habitats at Macquarie Island (sub-Antarctic)

The shore environments of most sub-Antarctic islands have been described in a number of previous studies. However, there have been few attempts to quantify the variation in population and community patterns over different spatial scales. The objectives of this study were to provide an analysis of differences in the community structure of the biota of three exposed shore zones and of the macrofauna inhabiting holdfasts of the kelp Durvillaea antarctica across spatial scales of hundreds of metres, kilometres, and between a sheltered and exposed coast. Data were collected using a combination of quadrat, transect and direct sampling methods over the 1994–95 summer season. The results indicated that there were significant differences between coasts for some of the biotic variables in most of the habitats examined but that differences at the smaller spatial scales were more often significant. Thus, although wave exposure exerts an obvious effect on the shore biota of Macquarie Island, these effects are modified by other factors operating at smaller spatial scales. For the holdfast macrofauna, the overall patterns of community structure are likely to be due to the differential response of the component taxa to variation in holdfast volume and holdfast sediment content as well as other, currently undetermined factors.

Position affects gastropod predation of sessile colonizers on a tropical rocky shore

A long-term experiment was carried out to determine the relative abilities of five sessile animals to colonize cleared plots in the presence or absence of predators. The experiment was done on two adjacent rocky shores, one sheltered and one exposed, on a small tropical island. The effect of predation in maintaining bare space was greatest on the exposed shore/upper mid-intertidal, less on the sheltered shore and absent on the exposed shore/lower mid-intertidal. The barnacle, Tesseropora rosea, recruited heavily at the exposed shore/lower mid-intertidal and was dominant, but was unable to colonize the exposed shore/upper mid-intertidal or the sheltered shore. The barnacle, Tetraclita squamosa, successfully colonized only the exposed shore/upper mid-intertidal and did not appear to be affected by predation. The oyster, Saccostrea amasa, had low colonization levels only on the sheltered shore and exposed shore/upper mid-intertidal, small individuals were susceptible to predation. The barnacle, Chthamalus maylayensis, heavily colonized only the exposed shore/upper mid-intertidal but was removed from this shore height by gastropod predators. The oyster, Saccostrea echinata, colonized only the sheltered shore and was very susceptible to predation. Given the variability found on this small spatial scale, it is suggested that consistent differences in ecological processes between regions (tropical versus temperate) are unlikely but, rather, that differences between localities will be found at the level of species interactions and abiotic effects in particular habits.

Distribution, abundance and recruitment of Chthamalus (Crustacea: Cirripedia) populations along the central coast of Portugal

The distribution, abundance and recruitment of Chthamalus species were studied for one year at two rocky shores on the central coast of Portugal. Chthamalus montagui is the most abundant intertidal barnacle on the Portuguese mainland. Higher abundance of C. montagui was found on the lower levels of the more sheltered shore, which is closer to the influence of the Tagus estuary. Chthamalus stellatus was also present, in very low densities, and always confined to the lower level of the barnacle zone. Chthamalus stellatus was more common at the shore farther away from the estuary, in which exposure to wave action is higher. The metamorphs of C. stellatus settled at the studied shores are considered to be immigrants from other populations, where the density of adults is sufficient for cross-fertilization to occur. Chthamalus spp. recruited almost continuously throughout the year, with a peak between July and September and a gap during February and March. Variations in phytoplanktonic assemblages and temperature may be the main factors controlling the reproductive season of Chthamalus spp. Recruitment was usually stronger on the lower shore levels but extended for a longer period higher on the shore. Seasonalvariations of C. montagui abundance were greater on the lower levels of the more exposed shore. This is probably due to faster growth and higher mortality of barnacle populations occupying the lower shore levels at the more exposed habitats.

A mass stranding of the asteroid Asterias rubens on the Isle of Man

Over the period 1—4 April 1999 a large number of dead asteroids were washed ashore at the northern end of the Isle of Man. The area is commonly used for public recreation and the stranding prompted numerous alarmed telephone calls to various bodies. Initially, disease or pollution were suspected, but a more detailed examination of the circumstances indicated that the mass stranding was probably a result of tides and weather conditions. The stranding occurred on the east coast of the Isle of Man from about 100 m to the south of the Point of Ayre, which is the northernmost point of the Isle of Man, and extended southwards for ≈600 m. This is a highly exposed shore with a strong tidal flow, subtidally it is shallow, with coarse gravel and exposed bedrock, and extensive mussel (Mytilus edulis) beds, which may be expected to attract large numbers of predatory starfish.

The meiofauna asssociated whith Sargassum cymosum at Lázaro Beach, Ubatuba, São Paulo

In this study, the meiofauna associated with Sargassum cymosum was qualitatively and quantitatively analyzed between December 1990 and July 1991. Sampling was carried out on a moderately exposed shore at Lázaro Beach, Ubatuba (32°S - 45°W). Each alga was washed in a formaldehyde solution and the fauna in suspension was washed through a series of 500, 250, 120 and 60 µm mesh sieves. The biomass of each taxonomic group was estimated as ash-free dry weight (AFDW) according to size categories. Algae volume and dry weight were determined, incIuding epiphytes. Densities of epifauna ranged from 502.9 to 2706.6 ind.20 ml-1 as algae volume. The biomass values (326.6 to 1214.4 µg.20 ml-1 AFDW) represented a low standing stock. Harpacticoid copepods and their nauplii were the dominant group and also showed the highest biomass values, being represented by larger individuaIs (250 to 120 µm). Higher values were observed between the end of the summer and the beginning of the fali (March and April), decreasing until winter (July). This variation may be explained by habitat complexity changes, or reproduction of some taxa, as higher meiofaunal densities were found on the 60 µm mesh sieve, incIuding high percentages of nauplii.