Alan J. Southward

Seventy years' observations of changes in distribution and abundance of zooplankton and intertidal organisms in the western English Channel in relation to rising sea temperature

Abstract 1. 1. Extensive changes in marine communities in southwest Britain and the western English Channel have been recorded during the past 70 years. 2. 2. Over the same period there was a climatic warming from the early 1920s, then a cooling to the early 1980s, with recent resumption of warming; the change in annual mean temperature was approximately ±0.5°C. 3. 3. Marked changes occurred in plankton community structure; the distribution of both plankton and intertidal organisms was affected, with latitudinal shifts of up to 120 miles; there were increases or decreases of 2–3 orders of magnitude in abundance. 4. 4. Warm water species increased in abundance and extended their range during periods of warming, while cold-water species declined or retreated; the reverse occurred during the period of cooling. 5. 5. Climate change can influence marine communities by a combination of: direct effect on the organisms; effects mediated by biotic interactions; and indirectly through ocean currents. 6. 6. From climate models that indicate rises of mean temperature of 2°C in the next 50 years, and from the observed changes, we can expect future latitudinal shifts of 200–400 miles in distribution of plankton, fish and benthos, with extensive restructuring of planktonic, pelagic and benthic communities. 7. 7. Species common now in the Bay of Biscay will become common in the English Channel; those presently restricted to the western English Channel could colonise the central Irish Sea; changes in community structure could lead to lower abundances of infaunal benthos and fish. 8. 8. To fully prove the effects of global warming, future changes in the marine biota must exceed those recorded in the 1950s and 1960s.

Note on the temperature tolerances of some intertidal animals in relation to environmental temperatures and geographical distribution

In experiments on four species of barnacles and four species of top-shells, the barnacles were found to be more resistant to high or low temperatures than the top-shells. Among each group of animals the degree of tolerance was related to the geographical distribution of the species and their zonation on the shore. Thus most tolerance of high temperature was shown by species of southern distribution, especially by those occurring at the upper limit of the midlittoral zone, and most tolerance of low temperature by species of northern distribution. Least tolerance of high and low temperatures was shown by species found only in the infralittoral fringe or below low water. Field measurements of the body temperatures of barnacles and limpets while exposed to the air were made with thermocouples. Under many weather conditions the body temperatures were higher than would be expected from local meteorological values of air temperature. This difference was due to retention of sea temperature by the animals and the rocks and to the heating effects of sunlight. The results of the laboratory experiments and of the field measurements are discussed together in relation to weather and geographical distribution. It is clear that the temperatures experienced on the shore are well within the tolerance limits of most of the animals, and even exceptional extremes of temperature may have little direct influence on the distribution of adult intertidal animals. Evidence for a causal relation between temperature and distribution must be sought in non-lethal terms such as debilitating effects, or indirectly through competition between species, or in combination with other factors.

Changes in the Range of Some Common Rocky Shore Species in Britain – A Response to Climate Change?

Since the 1990s there has been a period of rapid climate warming in Europe. Long-term broad scale datasets coupled with time series at specific locations for rocky intertidal species dating back to the 1950s have been collected in Britain and Ireland. Resurveys of the original locations in 2001–2003 have been undertaken to identify changes in the biogeographical range and abundance of these species. The results show that some ‘southern’ species including Osilinus lineatus da Costa and Gibbula umbilicalis da Costa have undergone north and north-eastern range extensions. Populations have increased in abundance and adult size has decreased since the previous surveys were conducted. These changes have been synchronous throughout Britain, strongly suggesting that climate is responsible. The use of intertidal species as indicators of climate change is proposed.

Detection of environmental change in a marine ecosystem--evidence from the western English Channel.

To separate human-induced changes from natural fluctuations in marine life requires long-term research. The western English Channel has been investigated from Plymouth for over 100 years. The abundance of marine life has been recorded and related to physical changes in the environment. By comparing different parts of the ecosystem we can demonstrate historic natural fluctuations, allowing prediction of effects of future global change. From the 1920s to the 1950s there was a period of warming of the sea, with increases in abundance of species of fish, plankton and intertidal organisms that are typically common in warmer waters to the south of Britain. After 1962 the sea cooled down and northern cold-water species became more abundant. Since the 1980s regional sea surface temperature has increased again and warm-water species are once more becoming abundant.

Timing of squid migration reflects North Atlantic climate variability

The environmental and biotic conditions affecting fisheries for cephalopods are only partially understood. A problem central to this is how climate change may influence population movements by altering the availability of thermal resources. In this study we investigate the links between climate and sea–temperature changes and squid arrival time off southwestern England over a 20–year period. We show that veined squid (Loligo forbesi) migrate eastwards in the English Channel earlier when water in the preceding months is warmer, and that higher temperatures and early arrival correspond with warm (positive) phases of the North Atlantic oscillation (NAO). The timing of squid peak abundance advanced by 120–150 days in the warmest years (‘early’ years) compared with the coldest (‘late’ years). Furthermore, sea–bottom temperature was closely linked to the extent of squid movement. Temperature increases over the five months prior to and during the month of peak squid abundance did not differ between early and late years, indicating squid responded to temperature changes independently of time of year. We conclude that the temporal variation in peak abundance of squid seen off Plymouth represents temperature–dependent movement, which is in turn mediated by climatic changes associated with the NAO. Such climate–mediated movement may be a widespread characteristic of cephalopod populations worldwide, and may have implications for future fisheries management because global warming may alter both the timing and location of peak population abundance.

Forty Years of Changes in Species Composition and Population Density of Barnacles on a Rocky Shore Near Plymouth

The abundance of the common intertidal barnacles, Chthamalus montagui, Chthamalus stellatus, Semibalanus balanoides and Elminius modestus has been monitored since 1951 at a site near Cellar Beach, River Yealm, south Devon. Counts are made at 12 levels on a transect between high tide and low tide. The two chthamalids are of warm-water distribution while S. balanoides is a boreo-arctic species; changes in the abundance of these species are linked to environmental temperature. Maximum fluctuations occur in the lowermost third of the intertidal zone. The proportion of Chthamalus adults is correlated with annual mean inshore sea temperature two years earlier, while the proportion of S. balanoides adults is negatively so correlated. This relationship accounts for over 40% of the variance. A smaller part of the variance ( E. modestus , is an Australasian immigrant that arrived in England during World War II and reached south Devon in 1948. It increased during the 1950s on the transect but has since stabilized at a low level of abundance that shows large interannual variations not directly related to temperature. Between 1951 and 1975, coinciding with a secular decline in sea temperature, there was a long-term trend towards reduction of Chthamalus and increase in S. balanoides ; this trend has reversed since. Removal of the long-term trend reveals a short-term fluctuation of approximately 10-y frequency that correlates with a cycle in sea temperature two years earlier. These cycles are close to the 10–11 y solar (sunspot) cycle between 1951 and 1975.

Fluctuations in the distribution and abundance of intertidal barnacles

It is well known that towards the limits of an animals geographical range both its abundance and exact boundaries may fluctuate from time to time. These fluctuations can sometimes be correlated with environmental changes, and thus may help to assess the relative importance of the factors that control distribution. For example the distribution of the common intertidal barnacles Chthamalus stellatus (Poli) and Balanus balanoides (Linnaeus) underwent changes which were attributed to a general rise in temperature over several years (Southward & Crisp, 1954a). The abundance of these barnacles has fluctuated further since 1951–52, and we are now able to analyse more closely the relation between the population changes and environmental variations.

Recovery of polluted ecosystems: the case for long-term studies

Recovery of marine ecosystems from pollution has tended to receive less attention than the study of new or continuing impacts, but such studies are important in charting recovery from acute incidents and following legislation to deal with chronic contamination. Recovery is inevitably a long-term process, and where such studies have been made they are often too short-lived. Interest quickly wanes following an acute incident and governmental bodies rapidly switch to new legislative priorities for chronic inputs. We review three case studies: recovery of dogwhelk populations after local extinction by tributyl tin leachates from anti-fouling paints; recovery of rocky shore communities from oil spills; and recovery of estuarine ecosystems from industrial and urban development. We then make some generalisations about recovery processes before making a plea for long-term studies of polluted areas.

Chemoautotrophic Symbionts in the Gills of the Bivalve Mollusc Lucinoma borealis and the Sediment Chemistry of its Habitat

Lucinoma borealis has enlarged gills, which contain numerous prokaryotes in specialized cells (bacteriocytes) in the subfilamentar region. The gills also contain high concentrations of elemental sulphur and of a c-type cytochrome. Homogenates of gill tissue show ribulosebisphosphate carboxylase and phosphoribulokinase activity; they also show activity for adenylylsulphate reductase, an enzyme concerned in the oxidation of sulphur, and will phosphorylate ADP on the addition of sulphite or sulphide. Fixation of bicarbonate by gill tissue from starved animals is enhanced in the presence of 100 μm sulphide. The sediment in which the animals live contains 1–6 μg atoms per litre of dissolved iron and hence there is very little dissolved sulphide, 200 nM, or less (80 nmol dm-3 sediment). Thiosulphate concentrations are also low, 300 nM, or less (120 nmol dm-3 sediment). In contrast, there are acid-labile sulphide concentrations up to 14 mmol dm-3 and elemental sulphur concentrations up to 4 mg atom per cubic decimetre of sediment. The mean sulphate reduction rate in the sediment varied seasonally with temperature over the range 1640–4920 nmol sulphate reduced per hour per cubic decimetre. L. borealis was usually found below the region of maximum sulphate reduction. Hydrogen, methane and carbon monoxide concentrations were all 160 nmol dm-3, or less. Despite the low levels of dissolved sulphide the association between prokaryote and host appears to be able to exploit this habitat by the oxidation of reduced sulphur species; ways in which the bivalve may be able to extract these from the sediment are discussed. The bivalves may obtain half their carbon from the autotrophic prokaryotes.

Food sources, behaviour, and distribution of hydrothermal vent shrimps at the Mid-Atlantic Ridge

Five species of bresilioid shrimp were investigated at seven hydrothermal sites on the Mid-Atlantic Ridge: Menez Gwen, Lucky Strike, Rainbow, Broken Spur, TAG, Snake Pit and Logatchev. Samples were prepared for analysis of stable isotopes, elemental composition and lipids. Shrimp behaviour was observed from the submersible ‘Alvin’ and in the laboratory aboard RV ‘Atlantis’. The distribution and zonation of the shrimp species was recorded. Juvenile shrimp of all species arrive at the vents carrying reserves of photosynthetic origin, built-up in the pelagic larval stages. These reserves are used while the shrimp metamorphose to the adult form and, in Rimicaris exoculata and Chorocaris chacei , while they develop epibiotic bacteria supporting structures, the modified mouthparts and the inside of the carapace. The main food of adult R. exoculata is filamentous bacteria that grow on these structures. The intermediate sizes of C. chacei also feed on such bacteria, but the final stage gets some food by scavenging or predation. Mirocaris species scavenge diverse sources; they are not trophically dependent on either R. exoculata or mussels. Adults of Alvinocaris markensis are predators of other vent animals, including R. exoculata . The dense swarms of R. exoculata , with their exosymbionts, can be compared to endosymbiont-containing animals such as Bathymodiolus and the vestimentiferan tube-worms of the Pacific vents. Such associations, whether endo- or ectosymbiotic, may be necessary for the development of flourishing communities at hydrothermal vents.