Download BIO1100 AN INTRODUCTION TO MARINE BIOLOGY Lecturer: Prof

BIO1100 AN INTRODUCTION TO MARINE BIOLOGY
NOTES ON SHORES AND SHORE LIFE.
Lecturer: Prof Patrick J. Schembri
THE SHORE
The shore is the transitional area between land and sea. The shore takes the form of a
band, the width of which varies from place to place and is determined by the interaction of
marine and terrestrial coastal processes, both natural and those due to human activities.
There is a great diversity of views as to what constitutes the shore, both between and within
disciplines. Thus ecologists, geomorphologists and economists all have different ideas of the
limits of the shore. Ecologically, the shore can be regarded as that zone in which the marine
environment grades into the terrestrial environment. Natural processes that affect the shore
may be physical, chemical or biological in nature and include: coastal currents and sediment
flows, which lead to coastal erosion or accretion; storm and wave conditions, which alter
coastal profiles; sedimentation processes, which affect water and sediment quality;
ecological succession, which leads to changes in habitat types and biodiversity; and energy
and material cycles, which affect biological production.
Ecologically, there are two basic types of shore: rocky and sedimentary; however,
intermediate types between the two exist (e.g. boulder shores). The Maltese Islands have a
coastline of ~263 km. Of this only ~2.4% consists of sedimentary shores, the rest being
rocky (~90.6%) or built up (~7%).
ABIOTIC AND BIOTIC FACTORS
Several physico-chemical and biological factors influence the occurrence and composition of
biotic assemblages on rocky shores. These include exposure to wave action, the nature of
the substratum and its topography, the influence of sunlight and shade, climatic conditions,
biological interactions, salinity and the concentration of nutrient salts, and tidal cycles. On
rocky shores, water movement associated with tides, waves and spray results in
environmental conditions that are neither fully terrestrial, nor fully marine. As a result, the
biotic assemblages found on rocky shores do not survive full immersion or full emersion, but
conditions of wetness between these two extremes. The pattern of zonation on rocky shores
results from the gradient of environmental factors that characterizes this habitat. However,
two factors in particular play an important role: (i) competition for resources, and (ii) the
restricted potential of a given species to perform optimally under different environmental
conditions. Other factors may also be important in particular circumstances, for example,
predation by terrestrial and marine consumers.
Overall, rocky shores constitute a very harsh environment in which the biota is exposed to
extremes of conditions. As a result, the flora and fauna associated with this habitat type have
evolved morphological, physiological and behavioural adaptations, which enable them to
survive there.
Muddy, sandy and shingle shores are equally harsh since the substratum consists of
particles of various sizes that can move under the action of tides, waves, currents, storms,
runoff and other agents. As a consequence very few species live on the surface of such
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mobile sediments and the majority either burrow in it (= infauna) or live in the fine spaces
between the particles (= interstitial).
ECOLOGICAL ZONES ON ROCKY SHORES
Ecologically, Mediterranean shores may be divided into several zones depending on the
relative contributions of two key physical factors: light and wetness. The first region of the
shore is the Adlittoral – that part of the terrestrial environment that is under some maritime
influence from wind-blown salt and spray. The next region is the Supralittoral – that zone on
the shore which is permanently exposed to the air except for occasional wetting by sea
spray and the highest waves. Next comes the Mediolittoral – that zone which is regularly
exposed and submerged, mainly due to wave action. This zone corresponds to the intertidal
zone of tidal shores, however, in most of the Mediterranean, the tidal range is very small (in
the Maltese Islands, this is not more than 20cm at the extreme) and changes in sea level
brought about by wave action and atmospheric conditions are far more important.
What follows is a brief description of the typical biotic communities that are found on the
rocky shores of the Maltese Islands.
THE SUPRALITTORAL ZONE
This zone is characterised by organisms that require some wetting with seawater but not
immersion. On Maltese rocky shores the main species are various maritime lichens, mainly
species of Verrucaria (HAZIZ TAX-XATT) which are adapted to live in this extreme
environment, microscopic algae which live on or in the calcareous rock and give it a
characteristic blackish-brown colour, two species of periwinkle, of which the commonest on
Maltese shores is Melarhaphe (= Littorina) neritoides, [ZIBGET IL-BLAT] and the isopod Ligia
italica [DUD TAS-SAJD).
THE MEDIOLITTORAL ZONE
In this zone live organisms that tolerate more or less regular immersion in seawater but not
continuous submersion. On rocky shores, the upper reaches of this zone are characterised
by barnacles [KOCCLI] of which there are three species: Euraphia depressa [KOCCLA CATTA]
occurs in the highest levels and Chthamalus stellatus [KOCCLA KOMUNI] further down; the
third species Chthamalus montagui occurs at intermediate levels on some shores. At the
lower limit of the barnacle zone occurs the limpet Patella ulyssiponensis [MHARA TAL-FURAN],
and further down another limpet (Patella caerulea [MHARA KAHLA] and the chiton
Lepidochitona corrugata [HANZIR IL-BAHAR TAX-XATT]. On some shores, a third species of
limpet occurs: Patella rustica [MHARA TAS-SAMMA]. Close to sea-level the shore is
dominated by the attached snail Dendropoma petraeum [FARRETT TAX-XATT] in exposed
parts while another attached snail, Vermetus triquetrus occurs in sheltered microhabitats. On
most shores, the shells of Dendropoma are embedded in encrustations of the calcareous
alga Neogoniolithon brassica-florida (previously referred to as Neogoniolithon notarisii) to
form characteristic platforms known as ‘trottoirs’. The vagile top-shells Osilinus
(=Monodonta) turbinatus and Osilinus (=Monodonta) articulatus [BEBBUX TAL-MAZZA] occur
throughout the mediolittoral during calm weather but seek the shelter of pits and holes in the
lower reaches of the shore during rough seas. On many shores, the small shore mussel
Mytilaster minimus [MASKLU TX-XATT] occurs as individuals attached to the rock by means of
byssus threads. A second mussel, Brachidontes pharaonis also occurs; this is an alien
species that entered the Mediterranean from the Red Sea via the Suez Canal and which
has expanded its range in the Mediterranean; on some shores it may form small clumps of
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individuals or even beds. In the mid-mediolittoral, macroalgae (large algae) become evident.
On most shores there is a fringe of` red algae (mainly Polysiphonia setulariodes) followed by
fringes of Polysiphonia opaca, Ceramium ciliatum and Palisada tenerrima (previously
identified as Laurencia papillosa = Chondrophycus papillosus), with encrusting coralline
algae becoming dominant in the lowermost reaches of the mediolittoral.
© Department of Biology, University of Malta & P.J. Schembri 2013.
These notes are for the personal use of participants in BIO1100 An introduction to
marine biology study-unit organised by the Department of Biology of the University of
Malta and may not be duplicated, disseminated or reproduced by any means
whatsoever, electronic, mechanical or xerographic, without the written permission of
the author and of the Department of Biology, University of Malta.
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