Michael A. Kendall

Latitudinal gradients in the structure of macrobenthic communities: a comparison of Arctic, temperate and tropical sites

Abstract As part of a programme to re-assess the existence of latitudinal gradients in the diversity of the macrobenthic infauna of soft sediments, samples were taken from Sassenfjord, Spitzbergen. Abundancebiomass curves showed the shallowest sites to be moderately disturbed, possibly as a result of glacial run-off from the Gipselva. These clearly differed from a site at 123 m which appeared to be in an undisturbed state. A comparison of the diversity profile of the latter site (78 °N) with those of physically similar sites in the North Sea (55 °N) and off the coast of Java (7 °S), sampled by identical methods, shows no real difference in diversity.

Long-term changes in the geographic distribution and population structures of Osilinus lineatus (Gastropoda: Trochidae) in Britain and Ireland

Since the rate of global climate change began to accelerate in the 1980s, the coastal seas of Britain have warmed by up to 1°C. Locations close to the northern range edges of a southern trochid gastropod Osilinus lineatus in Britain previously surveyed in the 1950s and 1980s were resurveyed during 2002–2004 to determine whether changes in the success of near-limit populations had occurred during the period of climate warming. Between the 1980s and the 2000s, the range limits had extended by up to 55 km. Populations sampled over a latitudinal extent of 4 degrees from northern limits towards the centre of the range showed synchronous increases in abundance throughout the years sampled, suggesting a large-scale factor such as climate was driving the observed changes. These increases in abundance and changes in range limits are likely to have occurred via increased recruitment success in recent years.

Climate change effects on Arctic fjord and coastal macrobenthic diversity—observations and predictions

The pattern of occurrence and recent changes in the distribution of macrobenthic organisms in fjordic and coastal (nearshore) Arctic waters are reviewed and future changes are hypothesized. The biodiversity patterns observed are demonstrated to be contextual, depending on the specific region of the Arctic or habitat type. Two major areas of biotic advection are indicated (the North Atlantic Current along Scandinavia to Svalbard and the Bering Strait area) where larvae and adult animals are transported from the species-rich sub-Arctic areas to species-poor Arctic areas. In those Arctic areas, increased temperature associated with increased advection in recent decades brings more boreal-subarctic species, increasing the local biodiversity when local cold-water species may be suppressed. Two other large coastal areas are little influenced by advected waters; the Siberian shores and the coasts of the Canadian Archipelago. There, local Arctic fauna are exposed to increasing ocean temperature, decreasing salinity and a reduction in ice cover with unpredictable effect for biodiversity. One the one hand, benthic species in Arctic fjords are exposed to increased siltation (from glacial meltwater) and salinity decreases, which together may lead to habitat homogenization and a subsequent decrease in biodiversity. On the other hand, the innermost basins of Arctic fjords are able to maintain pockets of very cold, dense, saline water and thus may act as refugia for cold-water species.

Comparing the impact of high CO2 on calcium carbonate structures in different marine organisms

Abstract Coastal seas are critical components of the global carbon cycle, yet little research has been conducted on the impact of ocean acidification on coastal benthic organisms. Calcifying marine organisms are predicted to be most vulnerable to a decline in oceanic pH (ocean acidification) based on the assumption that calcification will decrease as a result of changes in seawater carbonate chemistry, particularly reduced carbonate ion concentration (and associated saturation states). Net calcium carbonate production is dependent on an organisms ability to increase calcification sufficiently to counteract an increase in dissolution. Here, a critical appraisal of calcification in five benthic species showed, contrary to popular predictions, the deposition of calcium carbonate can be maintained or even increased in acidified seawater. This study measured changes in the concentration of calcium ions seen in shells taken from living animals exposed to acidified seawater. These data were compared with data from isolated shells that were not associated with living material to determine a species’ ability to maintain the physiological process of calcification under high carbon dioxide (CO2) conditions and characterize the importance of dissolution and abiotic influences associated with decreasing pH. Comparison with palaeoecological studies of past high CO2 events presents a similar picture. This conclusion implies that calcification may not be the physiological process that suffers most from ocean acidification; particularly as all species investigated displayed physiological trade-offs including increased metabolism, reduced health, and changes in behavioural responses in association with this calcification upregulation, which poses as great a threat to survival as an inability to calcify.

Can ocean acidification affect population dynamics of the barnacle Semibalanus balanoides at its southern range edge

The global ocean and atmosphere are warming. There is increasing evidence suggesting that, in addition to other environmental factors, climate change is affecting species distributions and local population dynamics. Additionally, as a consequence of the growing levels of atmospheric carbon dioxide (CO2), the oceans are taking up increasing amounts of this CO2, causing ocean pH to decrease (ocean acidification). The relative impacts of ocean acidification on population dynamics have yet to be investigated, despite many studies indicating that there will be at least a sublethal impact on many marine organisms, particularly key calcifying organisms. Using empirical data, we forced a barnacle (Semibalanus balanoides) population model to investigate the relative influence of sea surface temperature (SST) and ocean acidification on a population nearing the southern limit of its geographic distribution. Hindcast models were compared to observational data from Cellar Beach (southwestern United Kingdom). Results indicate that a declining pH trend (-0.0017 unit/yr), indicative of ocean acidification over the past 50 years, does not cause an observable impact on the population abundance relative to changes caused by fluctuations in temperature. Below the critical temperature (here T(crit) = 13.1 degrees C), pH has a more significant affect on population dynamics at this southern range edge. However, above this value, SST has the overriding influence. At lower SST, a decrease in pH (according to the National Bureau of Standards, pHNBs) from 8.2 to 7.8 can significantly decrease the population abundance. The lethal impacts of ocean acidification observed in experiments on early life stages reduce cumulative survival by approximately 25%, which again will significantly alter the population level at this southern limit. Furthermore, forecast predictions from this model suggest that combined acidification and warming cause this local population to die out 10 years earlier than would occur if there was only global warming and no concomitant decrease in pH.

Species body size distribution patterns of marine benthic macrofauna assemblages from contrasting sediment types

Species body size spectra have been constructed for macrofauna assemblages from four sites with contrasting sediment granulometry and heterogeneity in and around Plymouth Sound. The number of species and species turnover (β diversity) were higher on coarse sediment. While the fauna were distinct between sites, the median geometric size-class was conservative (class 14; 0.153–0.305 mg dry blotted weight). Only one site had significantly lower heterogeneity within the species size spectrum, yet this was the most heterogeneous sediment. As such, we were unable to reject the null hypothesis that species body size distribution patterns are conservative despite differences in sediment granulometry and heterogeneity.

Annual variation in recruitment and population structure of Monodonta lineata and Gibbula umbilicalis populations at Aberaeron, mid-Wales

The recruitment of the trochid gastropods Gibbula umbilicalis and Monodonta lineata was studied between 1978 and 1984 at Aberaeron in mid-Wales. In the former species the post winter density of ‘O’ class animals varied greatly (<1–21 m−2) and this was reflected in changes in the adult population which fell sharply following the failure of the 1978 year class but recovered after the addition of the 1980 cohort. Subsequent heavy recruitment in 1982 and 1983 had little effect on population density. The 1978 year class of M. lineata also failed, compounding an over-winter loss of adults and leading to a substantial decline in density. In the years that followed, variation in the level of recruitment had little impact on adult abundance. Although Aberaeron is close to the northern geographic limit of both species, neither population exhibits the normal near-limit characteristics of infrequent recruitment, large individual body size or missing year classes; this is possibly the result of the stable cobble shore providing an abundance of nursery areas for newly settled juveniles.

Species size distributions in Arctic benthic communities

Abstract In most subtidal soft-sediment faunal assemblages there is a trough in the species size distribution separating the macrofauna and meiofauna. To examine the hypothesis that this may be maintained by the avoidance of competition between macrofaunal adults and settling larvae, samples were taken from around Svalbard, an area where most macrofaunal species have either lecithotrophic or direct development. At three contrasting sites, bimodality of the species size spectrum was conserved. However, it is proposed that the adult-larval interaction hypothesis should not be rejected as low endemism in the fauna of the study area suggests its species size spectrum probably reflects evolutionary processes outside rather than within the Arctic.

The accumulation of fluorescent age pigments in the trochid gastropod Monodonta lineata

Abstract Several recent studies have shown the potential value of chloroform-soluble fluorescent age pigments (FAPs) in determining the age of marine invertebrates with no permanent hard parts. The primary assumption in estimating age from FAPs is that there is a linear (or at least monotonie) increase in FAP content with time. We have tested this assumption with the trochid gastropod Monodonta lineata , a species whose age can be established unequivocally from shell growth checks. Samples of 10 age classes (1.5–10.5 yr) were obtained and FAPs extracted from lyophilised cerebral ganglia and digestive gland. The fluorescence emission spectra were similar to those reported for other organisms, though the wavelength of maximum intensity varied with tissue, sex and age. Cerebral ganglia often showed two major emission peaks, digestive gland only one. Thin-layer chromatography indicated that at least three fluorescent compounds were present in the extracts. Digestive gland total FAP content did not vary for the first 5 yr of growth, but then trebled during the next 5 yr. The tissue concentration of FAP showed no statistically significant trend. Cerebral ganglia total FAP content increased during the first 5 yr then remained constant for the next 3 yr before declining. There was a steady decline in the concentration of cerebral ganglion FAP throughout life. These patterns indicate a complex relationship between FAP content and calendar age, and indicate that (at least in Monodonta ) FAPs have little practical value for determining age.

The sublittoral macroflora of Hornsund

Combined hydroacoustic, video and direct examination by scuba-diving of the underwater meadows of Hornsund, a flagship biodiversity site in Svalbard, revealed 17 species of macroalgae with a biomass, dominated by Laminariales, of as much as 3 kg m−2. The biomass dominants were Laminaria digitata and Saccharina latissima, which were most abundant at depths of between 5 and 10 m. The species data presented are the first records for the fjord and provide a starting point for new research and a baseline for future assessments of climate-induced changes.