By-catch in no-fed aquaculture: exploiting mussel seed persistently and extensively disturbs the accompanying assemblage

Although aquaculture sometimes lessens the negative effects of fishing by lowering the need to capture wild animals and plants, some aquaculture practices still require the exploitation of wild populations. A largely overlooked case is the use of wild populations to provide seed to sea farms. Mussel farming in Northwest Spain involve the capture of thousands of tons of young mussels (0.5–2 cm long) from the nearby rocky intertidal every year to supply floating rafts. Despite its volume, the impact of this activity on other sessile organisms remains unassessed. To fill this gap in our knowledge, we monthly monitored the sessile intertidal assemblage of five protected and six exploited sites during the closed season in 2016 following a nested sampling plan. Like the by-catch typical of other fisheries, harvesting young mussels for aquaculture was detrimental to the abundance and diversity of the associated sessile assemblage not directly targeted by this activity. Coverage and richness were also significantly lowered by the exploitation of mussel seed, and the community structure of protected and exploited sites was significantly different. These differences continued until the next open season, suggesting that the closed season was too short for the recovery of the associated non-target sessile assemblage. Given the size of the local mussel industry, the incomplete recovery along the closed season implies that mussel aquaculture must be putting a sustained pressure on a sizeable portion of the rocky intertidal of Northwest Spain.

Middle to Upper Jurassic Saudi Arabian carbonate petroleum reservoirs: biostratigraphy, micropalaeontology and palaeoenvironments

ABSTRACT Recent work has improved understanding of the benthic foraminiferal stratigraphic and palaeoenvironmental ranges of the Middle to Upper Jurassic reservoir-containing carbonates of Saudi Arabia. The entire Jurassic succession includes the Marrat, Dhruma, Tuwaiq Mountain, Hanifa, Jubaila and Arab formations that terminate with a succession of evaporites, the final, thickest unit of which is termed the Hith Formation. This study focuses on selected carbonate members studied from the Dhruma Formation and above, and includes the Lower Fadhili, Upper Fadhili, Hanifa and Arab-D reservoirs. The Hadriya and Manifa reservoirs are not considered. An ascending order of tiered deep-to shallow-marine foraminiferal assemblages has been determined for each formation and applied to distinguish both long- and short-term palaeobathymetric variations. The Lenticulina-Nodosaria-spicule dominated assemblage characterises the deepest mud-dominated successions in all formations. The consistent presence of Kurnubia and Nautiloculina species suggests only moderately deep conditions, considered to be below fair-weather wave base and shelfal. A foraminiferally-depleted succession then follows that is characterised by encrusting and domed sclerosponges, including Burgundia species, in the Tuwaiq Mountain, Hanifa and Jubaila formations. This assemblage is followed, in the Hanifa and upper Jubaila formations, by a biofacies dominated by fragments of the branched sclerosponge Cladocoropsis mirabilis, together with Kurnubia and Nautiloculina species and a variety of indeterminate simple miliolids. Pseudocyclammina lituus, Alveosepta powersi/jacardi and Redmondoides lugeoni are present within this assemblage. A slightly shallower, possibly lagoon-influenced assemblage is developed in the Hanifa and Arab formations that include Cladocoropsis mirabilis, Kurnubia and Nautiloculina species and the dasyclad algae Clypeina sulcata and Heteroporella jaffrezoi. A further shallower assemblage, found only in the upper Arab-D Member, is characterised by the presence of Mangashtia viennoti, Clypeina sulcata and Cladocoropsis mirabilis. This assemblage is gradually supplemented by “Pfenderina salernitana” and is interpreted as slightly shallower conditions in the upper Arab-D. A very shallow assemblage in the uppermost Arab-D is characterised by the presence of Trocholina alpina, which is then followed by an intertidal assemblage of cerithid gastropods and felted calcareous algae in which foraminifera are typically absent. These various microbiofacies have provided depositional and potential reservoir stratification. A phenomenon termed “palaeobathymetric compression” has been observed in which depositional cycles are enhanced by rapidly shallowing upwards tiered biofacies that encompass less than 3m of sediment thickness but represent in excess of 20m of water depth reduction. This is attributed to short-term rapid lowering of sea level, and may be considered as the microfaunal signals of high frequency forced regressions.