George M. Branch

ECOLOGICAL CRITERIA FOR EVALUATING CANDIDATE SITES FOR MARINE RESERVES

Several schemes have been developed to help select the locations of marine reserves. All of them combine social, economic, and biological criteria, and few offer any guidance as to how to prioritize among the criteria identified. This can imply that the relative weights given to different criteria are unimportant. Where two sites are of equal value ecologically; then socioeconomic criteria should dominate the choice of which should be protected. However, in many cases, socioeconomic criteria are given equal or greater weight than ecological considerations in the choice of sites. This can lead to selection of reserves with little biological value that fail to meet many of the desired objectives. To avoid such a possibility, we develop a series of criteria that allow preliminary evaluation of candidate sites according to their relative biological values in advance of the application of socioeconomic criteria. We include criteria that,. while not strictly biological, have a strong influence on the species present or ecological processes. Out scheme enables sites to be assessed according to their biodiversity, the processes which underpin that diversity, and the processes that support fisheries and provide a spectrum of other services important to people. Criteria that capture biodiversity values include biogeographic representation, habitat representation and heterogeneity, and presence of species or populations of special interest (e.g., threatened species). Criteria that capture sustainability of biodiversity and fishery values include the size of reserves necessary to protect viable habitats, presence of exploitable species, vulnerable life stages, connectivity among reserves, links among ecosystems, and provision of ecosystem services to people. Criteria measuring human and natural threats enable candidate sites to be eliminated from consideration if risks are too great, but also help prioritize among sites where threats can be mitigated by protection. While our criteria can be applied to the design of reserve networks, they also enable choice of single reserves to be made in the context of the attributes of existing protected areas. The overall goal of our scheme is to promote the development of reserve networks that will maintain biodiversity and ecosystem functioning at large scales. The values of eco-system goods and services for people ultimately depend on meeting this objective.

Application of ecological criteria in selecting marine reserves and developing reserve networks

Marine reserves are being established worldwide in response to a growing recognition of the conservation crisis that is building in the oceans. However, designation of reserves has been largely opportunistic, or protective measures have been implemented (often overlapping and sometimes in conflict) by different entities seeking to achieve dif- ferent ends. This has created confusion among both users and enforcers, and the proliferation of different measures provides a false sense of protection where little is offered. This paper sets out a procedure grounded in current understanding of ecological processes, that allows the evaluation and selection of reserve sites in order to develop functional, interconnected networks of fully protected reserves that will fulfill multiple objectives. By fully protected we mean permanently closed to fishing and other resource extraction. We provide a frame- work that unifies the central aims of conservation and fishery management, while also meeting other human needs such as the provision of ecosystem services (e.g., maintenance of coastal water quality, shoreline protection, and recreational opportunities). In our scheme, candidate sites for reserves are evaluated against 12 criteria focused toward sustaining the biological integrity and productivity of marine systems at both local and regional scales. While a limited number of sites will be indispensable in a network, many will be of similar value as reserves, allowing the design of numerous alternative, biologically adequate net- works. Devising multiple network designs will help ensure that ecological functionality is preserved throughout the socioeconomic evaluation process. Too often, socioeconomic cri- teria have dominated the process of reserve selection, potentially undermining their efficacy. We argue that application of biological criteria must precede and inform socioeconomic evaluation, since maintenance of ecosystem functioning is essential for meeting all of the goals for reserves. It is critical that stakeholders are fully involved throughout this process. Application of the proposed criteria will lead to networks whose multifunctionality will help unite the objectives of different management entities, so accelerating progress toward improved stewardship of the oceans.

Gradients of intertidal primary productivity around the coast of South Africa and their relationships with consumer biomass

The structure of rocky intertidal communities may be influenced by large-scale patterns of productivity. In this study we examine the in situ rates of production by intertidal epilithic microalgae (chlorophyll a production per unit area per month), intertidal nutrient concentrations (nitrates, nitrites, phosphates and silicates), and standing stocks of different functional-form groups of macroalgae around the South African coast, and their relationships to consumer biomass. Clear gradients of in situ intertidal primary production and nutrient concentrations were recorded around the South African coast, values being highest on the west coast, intermediate on the south and lowest on the east coast. Primary production by intertidal epilithic microalgae was correlated with nutrient availability and could also be related to nearshore phytoplankton production. The dominance patterns of different functional forms of macroalgae changed around the coast, with foliose algae prevalent on the west coast and coralline algae on the east coast. However, overall macroalgal standing stocks did not reflect the productivity gradient, being equally high on the east and west coasts, and low in the south. Positive relationships existed between the average biomass of intertidal intertebrate consumers (grazers and filter-feeders) and intertidal productivity, although only the grazers were directly “connected” to in situ production by epilithic intertidal microalgae. The maximum body size of a widely distributed limpet, Patella granularis, was also positively correlated with level of in situ primary production. The maximal values of biomass attained by intertidal filter-feeders were not related to intertidal primary production, and were relatively constant around the coast. At a local scale, filter-feeder biomass is known to be strongly influenced by wave action. This implies that the local-scale water movements over-ride any effects that large-scale gradients of primary production may have on filter-feeders. The large-scale gradient in intertidal productivity around the coast is thus strongly linked with grazer biomass and individual body size, but any effect it has on filter-feeder biomass seems subsidiary to the local effects of wave action.

The dependence of intertidal consumers on kelp-derived organic matter on the west coast of South Africa

Abstract In this study we explored the trophic relationships between intertidal and subtidal ecosystems of a rocky-shore community. We selected the most abundant intertidal primary consumers, principally invertebrate grazers and filter-feeders, and investigated their trophic connections with in situ intertidal production (internal) and/or subtidal kelp production (external). Using two stable isotopes (nitrogen and carbon), we examined the degree to which filter-feeders depend trophically on kelp detritus or pelagic phytoplankton, and to which intertidal grazers depend on subtidal kelps or intertidal micro- and macroalgae. The filter-feeders used kelp-derived detritus as their main source of organic carbon and nitrogen. Similarly, two abundant and highly specialized grazers also used subtidal kelps as their main source of carbon and nitrogen, although other more generalized intertidal grazers relied mainly on the in situ epilithic algal production. We determined the extent to which kelp detritus contributes to the total particulate organic matter (POM) on exposed and sheltered habitats during different tidal phases. Kelp-derived detritus represented more than 65% of POM, being consistently high all year round and during both high and low tides, but was particularly high on exposed shores. Phytoplankton was seldom found and contributed no more than 6% of total intertidal POM. We conclude that kelp-derived detritus represents a steady source of food for filter-feeders, upon which they can rely all year round. A short-term experiment revealed that the water turnover on exposed shores was about seven times greater than on sheltered shores; the consequent increase in the supply of food may explain why filter-feeder biomass is high on wave exposed shores. Finally, a simple steady-state model was built to simulate mussel standing stock (biomass per unit area) as a function of food supply and water turnover. The model predicts significantly lower mussel standing stock on sheltered than exposed shores. We conclude that replenishment of food by wave action is sufficient to explain the observed differences of filter-feeder biomass between exposed and sheltered shores. It is also concluded that subtidal macrophyte production greatly influences the structure of intertidal rocky-shore communities on the west coast of South Africa.

Effects of sediment on the energy budgets of four scleractinian (Bourne 1900) and five alcyonacean (Lamouroux 1816) corals

The physiological reactions to sediment of four scleractinia and five alcyonacea from South Africa were observed in the laboratory. Species tested were Favia favus Forskal, Favites pentagona Esper, Platygyra daedalea Ellis & Solander, Gyrosmilia interrupta Ehrenberg, Lobophytum depressum Tixier-Durivault, Lobophytum venustum Tixier-Durivault, Sinularia dura (Pratt), Sinularia leptoclados (Ehrenberg) and Sarcophyton glaucum (Quoy & Gaimard). Natural sedimentation levels and light conditions were simulated. Photosynthetic carbon production and respiration were measured by respirometry. Loss of fixed carbon through mucus production was measured directly by filtration. The results were used to model daily energy budgets for these species. One set of models allowed for 50% PARs (photosynthetically active radiation at the surface), another set of models allowed for 25% PARs. The models showed severely diminished productivity and decreased respiration under sedimented conditions. Production/respiration (PR) ratios of all species were above 1 in the absence of sediment and dropped below unity when the corals were subjected to sedimentation. Although overall respiration dropped, its demand upon the also diminished amount of photosynthetically produced carbon rose dramatically. Without sediment, mucus output averaged 35% of daily respiration; this rose to 65% when sediment was applied. Sediment affects coral metabolism by decreasing photosynthetic production, increasing relative respiration and increasing carbon-loss through greater mucus output.

A zoogeographic and functional approach to the selection of marine reserves on the west coast of South Africa

Three objective criteria for assessing sites being considered as marine nature reserves are developed and applied to a region of the west coast of South Africa, between the Groen and the Spoeg rivers, that has been mooted as a possible nature reserve. On a national and regional macroscale, zoogeographic analyses of 2 000 species of invertebrates were used to reappraise accepted marine biogeographic provinces. On a mesoscale and local scale, the intertidal community composition of rocky shores was examined and related to the physiographic habitat diversity. Five major zoogeographic regions are identified around the southern African coast, including a distinct Namaqua province. The Groen-Spoeg area, which receives no adequate conservation, is representative of both the major zoogeographic province that it falls in and the Northern Namaqua sub-province. A long period of limited human access as a result of diamond-mining has kept the shore near-pristine. On a global scale, the region is unique in the extent t...

The impact of the sand prawn Callianassa kraussi Stebbing on sediment turnover and on bacteria, meiofauna, and benthic microflora

Field cages were used to manipulate the density of the thalassinidean Callianassa kraussi Stebbing to test its effects on the turnover of sediment and on the abundance of benthic microflora, bacteria, and meiofauna. By introducing layers of stained sediment into the cages the rate of bioturbation could be quantified, and over a month averaged 59% turnover down to a depth of 30 cm (equivalent to a deposit of 12.14 kg · m −2 · day−1 on the surface). Virtually no bioturbation occurred in cages lacking Callianassa, even although all other infaunal species had been left undisturbed in the cages. Benthic microalgae accumulated on the surface in the absence of Callianassa, but were relatively more abundant at depths of 15 to 25 cm in their presence. Even at this depth they were fully viable, presumably because the turnover of sediment brought them to the surface often enough to maintain them. Bacterial numbers increased between 30 and 100% in the presence of Callianassa, and were concentrated around the linings of their burrows. Meiofaunal numbers declined in proportion to the density of Callianassa, although the reason for this decline is unknown. Taken in conjunction with published work on the detrimental effects Callianassa spp. have on corals, suspension-feeders and seagrasses, these results emphasize the powerful role Callianassa plays in structuring the communities of soft sediments.

Tenacity and shell shape in six Patella species: Adaptive features

Abstract Measurements were made of te forces necessary to detach various South African Patella spp. These ranged from 5.18 to 1.95 kg/cm 2 , with significant differences between the species. P. cochlear Born. had the highest value, followed in sequence by P. argenvillei Kr., longicosta Lam., P. granularis L., P. granatina L., and P. oculus Born. Adhesion is the only mechanism capable of providing forces of this magnitude. Differences between the species are related to differences in their morphology, high tenacity being associated with low mucus secretion, small number of mucocytes, and inflexibility of the foot. This is associated with a large area of muscle attachment on the shell and the size of basal haemocoelic spaces. Features favouring high tenacity conflict with those favouring mobility, and the limpets fall into two groups. P. granularis, P. oculus , and P. granatina occur on the upper shore and the last two usually occur in areas which are sheltered from strong wave action. They a rapid growth and high gonadal output, demanding extensive foraging and hence mobility at the cost of tenacity. P. cochlear and P. longicosta are territorial and together with P. argenvillei , remain low on the shore, grow slowly, and have a low reproductive output. Feeding is localized and mobility sacrificed for high tenacity which is essential in P. cochlear and P. argenvillei as they occur in areas of strong wave action. Shell height is not correlated with tenacity nor with the intensity of wave action normally experienced by each species, but P. cochlear, P. argenvillei and to a lesser extent P. granularis , are subjected to strong wave action and have proportionally narrower shells (increasing streamlining) and low coefficients of drag. The latter are low due to the rough but regular texture of the shells creating a turbulent boundary layer and hence reducing drag.

Disturbance associated with bait-collection for sandprawns (Callianassa kraussi) and mudprawns (Upogebia africana): Long-term effects on the biota of intertidal sandflats

The sandprawn Callianassa kraussi and the mudprawn Upogebia africana are used extensively as fish bait in southern Africa. A holistic analysis of disturbance associated with experimental prawn-collecting was undertaken to determine its repercussions upon the sediment and associated macrofaunal, meiofaunal, microbial and microalgal communities. Patterns of recovery were examined for 18 months following the disturbance. The recovery of both C. kraussi and U. africana was far more protracted than predicted, taking 18 months for completion. Sedimentary compaction, associated with the removal of prawns, could account for these prolonged recoveries. Both C. kraussi and U. africana suffered greater depressions of population densities (ca. 70%) than would have been expected from the proportions removed (ca. 10% and 46% respectively). This suggests that disturbance and sedimentary compaction have greater effects than the removal of sand- and mudprawnsper se. One month after the disturbance of C. kraussi, chlorophyll levels increased above control levels and remained elevated for a further 2-3 months. In contrast, the removal of U. africana resulted in nett decreases in chlorophyll levels for approximately one month following the disturbance. A short-lived decline in bacterial numbers was apparent following the removal of C. kraussi but not U. afiicana. Meiofaunal numbers declined immediately after disturbance of both C. kraussi and U. aficana, but this depression was followed by explosive increases and then a return to control levels. The macrofauna was slower to recover and, after initial reductions of numbers, biomass and species richness, still showed signs of depression 18 months after the disturbance. Three response patterns were apparent: species which were immediately reduced by the treatments and were also slow to recover; species which appeared to have their recruitment suppressed relative to the control; and species which were unaffected by the treatment. Only a single macrofaunal species, the hermit crab Diogenes brevirostris, benefited from the disturbance. Similar trends were observed following the harvesting of both C. kraussi and U. africana.

Differential polyphenolic distribution among tissues in the kelps Ecklonia maxima, Laminaria pallida and Macrocystis angustifolia in relation to plant-defence theory

Abstract The intraplant distribution of total polyphenols in the three kelps Ecklonia maxima, Laminaria pallida and Macrocystis angustifolia and the maturation and residence time of their sporogenous tissue were investigated. Polyphenols were found to be almost entirely restricted to the thin outer meristoderm of these plants as predicted if they serve as a defence against grazers. The inner cortex and medullary tissue, forming most of the bulk of the plants, contained very low levels of polyphenols. Comparing different meristoderm tissues, high levels were recorded in the holdfasts, stipes and meristems of all plants, values ranging from 5 to 39% of dry mass whereas infertile vegetative tissues contained the lowest levels. Again, these patterns are concordant with defence theory. Sporogenous tissue in E. Maxima and M. angustifolia contained high polyphenol levels (23 and 6%, respectively) but in L. pallida levels approximated only 0.01%. Since spores remain resident on L. pallida for a significantly longer period than on the other two species, their relative availability to herbivores cannot be invoked as an explanation for these low levels.