An example of drastic natural changes in the intertidal biota and the implications for monitoring programmes

Estuarine,

Coastal

and Shelf

Science

(1983)

17, 479-481

An Example the Intertidal Monitoring

of Drastic Natural Changes Biota and the Implications Programmes

J. P. Cullinane

and P. M. Whelan

of Botany,

Department Received

14 August

Keywords:

in for

University College, Cork, Ireland 1981

and in revised

form

17January

I983

pollution; barnacles

During a period of about two years at Parkmore Point, Co. Kerry, Ireland, fucoids drastically decreasedin the mid and upper shore,meanwhilebarnacle abundanceincreasedon the upper shoreand musselsincreasedon the lower shore.Causescould not be determinedbut humaninterference wasexcluded due to remoteness,and changeswere solocalizedasto excludeclimaticfactors. These drastic natural changesemphasizethe need for guardedinterpretation of monitoring datafrom areassuspectedof pollution. As part of a shore surveillance programme at the exposed headland of Parkmore Point at the extreme southwestern tip of Ventry Bay, Co. Kerry, some major changes in the inter-tidal community were qualitatively observed. These changes were noticed in 1979 over a 600 m wide area and they were quantified by transect surveys in 1980. The changesare illustrated in Figure 1 and may be summarized as follows. Both Fucus vesiculosusand F. v.f. linearis (other fucoids were not affected) declined from 55% maximum cover to 1% maximum cover in the transect. Barnacle cover increased, especially on the upper shore from a 50% maximum cover to 90% cover. Abundance of Myths edulis increased on the lower shore and decreasedon the upper shore so that the Mytilus showed a distinct shift to the lower shore. The shore on which these changes occurred is totally free of any source of pollution and so isolated as to be virtually unfrequented by humans so that the changes observed can only be attributed to natural causes. The localized nature of the changes suggest that they were not directly due to either meteorological or climatic factors. The changes were not considered attributable to a decline of an old fucoid population since some fucoid sporelings were also wiped out. Concurrent manipulative experiments showed that fucoids have a sweeping effect which inhibits barnacle settlement (see also Grant, 1977; Menge, 1976; Southward & Southward, 1978) but do not prevent colonization by mussels. Fucoids also provide shelter for Nucella and hence promote significant barnacle mortality due to predation. Waves acting on large fucoid plants growing on barnacles often dislodge them from the rock surface (Burrows & Lodge, 1950). Therefore, the decreasein the fucoid population probably either led to or facilitated the increased barnacle cover on the upper shore. The decrease in Myths on the upper shore could be attributed to the decrease in the overlying fucoid canopy since the manipulation experiments had shown that the presence of fucoids, while inhibiting barnacle settlement, indirectly favoured settlement by 479 0272-7714/83/100479+03

$03.00/O

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1983

Academx

Press

Inc. (London

1 I.~m:ted

480

J P. Cullinane

alogsladdn

& P. M. Whelan

Changes

in the intertidal __~__-

biota

and

implications

for

monitoring

programes

481

The increases in both barnacles and mussels on the lower shore could not be attributed to Fucus vesiculosus since it showed no change on the lower shore. This implies that higher levels of recruitment of barnacles and mussels could be involved in the changes. In view of the very localized nature of the changes it is likely that some local factors were involved. Of these, the most plausible suggestion for fucoid decline is that of increased grazing pressure by limpets and/or littorinids, possibly combined with other factors such as waves (Southward, 1956) or storm damage to cause the final disappearance of the fucoids. It is well known that limpets graze on small and large fucoids [see Southward & Southward, (1978) for a review]. It is extremely unlikely that the barnacles were responsible for the fucoid decrease since Hawkins (1981) has shown that a barnacle cover actually facilitates fucoid recruitment. The changes noted were drastic and would overshadow many of the small scale changes recqded in continuous monitoring programmes. In view of these large scale changes, attributable to natural causes, it is clearly important to stress the need for guarded interpretation of data recorded in monitoring programmes of polluted areas. Mytilus.

References Burrows, E. M. & Lodge, S. M. 1950 A note on the inter-relationships Pa&u, Balanus and Fucus on a semi-exposed coast. Report of the Marine Biology Station, Port Erin no. 62, 30-34. Grant, W. S. 1977 High intertidal community organisation on a rocky headland in Maine, U.S.A. Marine Biology 44, 15-25. Hawkins, S. J. 1981 The influence of season and barnacles on the algal colonization of Pate&r vulgara exclusion areas. Journal of the Marine Biological Association of the United Kingdom 61, 1-15. Menge, B. A. 1976 Organisation of the New England rocky intertidal community: role of predation competition and environmental heterogeneity. Ecological Monographs 46, 355-393. Southward, A. J. 1956 The population balance between limpets and seaweeds on wave-beaten rocky shores. Report of the Marine Biology Station, Port Erin no. 68, 20-29. Southward, A. J. & Southward, E. C. 1978 Recolonisation of rocky shores in Cornwall after use of toxic dispersants to clean up the Torrey Canyon spill. Journal of the Fish Research Board of Canada 3.5, 682-706.